![]() I have used a wide variety of equipment during my 15 years of Electronically Assisted Astronomy (EAA). This includes refractors, SCTs and even a Newtonian along with all sorts of analog video cameras and CMOS digital cameras. I have also tried many different live stacking software packages including ASI Live, TSX Live Stack and, mostly, Sharpcap. In every case, like so many others doing EAA, I had to pull together all of the necessary components including mount, OTA, camera, laptop and mini-pc, USB and power hubs, cables and SW and integrate all of these to make sure that everything worked seamlessly, which was often not the case. So, I watched with interest over the past 4-5 years as all-in-one Smart Telescopes began to hit the market. With a price point of $499 ($450 on sale) I finally decided to give one a try and purchased the ZWO Seestar S50 Smart Telescope. I have used it extensively in my light polluted back yard over many nights and even tried it out at our club's local dark site to see what it can do. In this Blog I will provide the basic run down of the Seestar's equipment, explain what you need to know to get it working, share some of my images and list what I think are its Pros and Cons. ![]() Seestar's Design The Seestar S50 uses a 50mm f/5, 250mm focal length triplet objective with one element of ED (extra low dispersion) glass. The combination of 3 elements in the objective enables it to focus the red, green and blue light at the same focal plane. Therefore it does not show any hint of chromatic aberration, a purple color fringe around any bright object, which is typical with an objective using only one or two glass elements. In addition, because all three colors focus at the same focal plane the resulting images are sharp with good detail limited by the local seeing conditions. Light from the objective is directed off a pair of mirrors to an internal CMOS camera using the Sony IMX462 color sensor. This sensor has just over 2MPixels arranged in an 1080 x 1920 array of 2.9microns size pixels. As such the overall sensor is is very small with a diameter of just 6.46mm, quite similar the the IMX224 color sensor which first came out around 2014. The small size of the sensor combined with the 250mm focal length of the optics produces a small field of view of 76.5 x 43 arc minutes. While this is large enough to fit the entire image of the sun or moon, it is too small to fit the entirety of large deeps sky objects (DSOs) like the Andromeda galaxy. I normally do not recommend a small sensor like this as it also can make it difficult to find dim DSOs because of the small field of view. However, the Seestar has solved both of these problems for us. First, it has the option to capture images as mosaics up to 2X in width and height of the imaging sensor. With a 2X mosaic the Seestar can now fit the entirety of the Andromeda galaxy and many other large DSOs into one image. Second, the Seestar using Plate Solving to find and locate objects in the night sky. This means that when it goes to a point in the sky where it thinks the object you want is located, it takes an image, calculates the relative positions of the stars in the image, compares the result to a data base, determines accurately where it is actually pointing and commands the mount to move to the right location to center the desired object. So with both of these clever features you are not overly limited by the small size of its imaging sensor. Focusing is accomplished with an internal focus motor which moves the sensor in and out to achieve focus automatically by measuring and minimizing the size of the stars measured in pixels. There is an option to perform focus manually but in my experience the Seestar's automatic focus routine does a very good job of achieving sharp focus. The Seestar has 3 filters and a shutter. The shutter blocks all incoming light so that the Seestar can take dark frames. It automatically creates a master dark frame from 5 individual dark sub-frames which are subtracted from each light frame to minimize the impact of sensor fixed pattern noise such as hot and warm pixels, as well as, sensor dark current. The first filter is an internal UV-IR cut filter which is designed to eliminate star bloat so that images have sharp stars. Seestar automatically deploys this filter on all objects other than emission nebulae. The second internal filter is a Dual Band filter designed to block all light except for that around a 30nm band at the wavelength of OIII and a 20nm band at the wavelength of Ha. This filter will block a large amount of ambient light pollution should be used for emission nebula, not reflection nebula, which have lots of light at these two wavelengths. Th Seestar will automatically place the correct filter in front of the sensor depending upon the object type. The Seestar comes with an external white light filter which must always be placed in front of the lens when there is a chance that sunlight might be directed into the Seestar. If sunlight reaches the imaging sensor without this filter it is highly possible that the sensor will be irreparably damaged. The Seestar is an Alt-Az mount which means that it has two rotation axes, one in the plane of the horizon and one perpendicular in altitude. Alt-Az mounts are commonly used for EAA and do not track the earth's rotation like an Equatorial mount does. While an Alt-Az mount will keep a point object like a star centered in the field of view, stars away from the center and any portion of a deep sky object like a galaxy or nebula not in the center of the field of view will slowly rotate about the center as the earth rotates on its axis. For this reason, the basic rule of thumb is to limit exposures to no more than 30sec to avoid having the stars appear to rotate about the center at longer exposures, looking elongated or trailed instead of point like. For this reason, the Seestar has a maximum exposure of 30sec. The Seestar has an internal computer with 64GB of internal storage which automatically controls all of the hardware and software functions necessary for imaging. It can be accessed through its own WiFi via the Seestar App on your phone or tablet. The Seestar can be connected to a PC with the include Type C USB cable to download images stored in the Seestar's internal memory and recharge the internal battery. However, the Seestar cannot be controlled by a pc. All of the Seestar's function must be accessed through a smart phone or tablet using the Seestar app. The Seestar also has BT which is required for initial setup. The Seestar has an internal 6Ah internal battery which can be re-charged through a USB-C port on the side of the Seestar. You can also connect an external 12V power supply through this USB-C port to power the Seestar longer than the internal battery alone can do. All of these components are sealed inside a 5.5lb (2.5kg) plastic enclosure measuring 5.6" x 5.1" x 10.1" making it a truly light weight and compact Smart Telescope. The Seestar comes with a short but very sturdy tripod with a minimum height of 10.8" and a maximum height of 14.3" which screws onto the bottom of the Seestar with a 3/8" screw. Everything fits neatly inside a sturdy foam carrying case making this truly an all-in-one astronomy solution. As such, the Seestar is by far the most compact and travel friendly of any of the EAA setups I have ever used. It certainly would be very easy to bring as a carry on when traveling by airplane. Initial Setup Connecting to the Seestar for the first time requires a few steps than are needed one time only and the process is well documented in the included instruction sheet. The basic steps include downloading the Seestar App to your phone or tablet, turning on the Seestar's power button (push once, wait, push a second time until you hear the beep) and connecting to it with the Seestar's WiFi. The first time also requires access to the internet but that is not needed for subsequent connections. For all future startups just turn on the Seestar (hold down the power button until you hear the beep), open the App and click on the red Connect button and follow the prompts to complete the connection. When connected you will see the screen below which is the main Seestar App screen, or Home Page, from which you can Open the Seestar arm, enter one of 3 observing modes, view images stored on you phone/tablet or the Seestar's internal drive, view a wealth of video tutorials to get you going, view local weather information and more. You can also see the serial number for you Seestar unit and the current battery state of charge at the top. I encourage you to start by viewing each of the well done tutorials so that you thoroughly understand what how everything works. ![]() Compass & Level Calibration The next step with a new Seestar is to calibrate the internal compass and the level sensor. The Compass Calibration and Level Sensor Calibration procedures will ensure that the Seestar will be able to easily and accurately find and center targets in its field of view. In fact, the Compass Calibration is essential for finding the Sun or the moon during the day as the Seestar will not be able to use its Plate Solve procedure to find either without any visible stars. If you have ever used a Celestron Nexstar or Skywatcher Alt-Az mount you know that the initial setup calls for leveling the optical tube and pointing it north. This is called "Level North" and allows the mount to make a good estimate of the location of objects in the sky using that information along with the local time, latitude and longitude. With this the mount can put the first alignment star close to, if not in, the field of view. Similarly the Seestar compass calibration enables the Seestar to determine the direction for north and the level sensor calibration will allow it to provide feedback to the user when performing the Level Sensor procedure each time the Seestar is set up for an observing session. Hence, Seestar will be able to GoTo the first object and place it in or very near the field of view as well. The difference between the calibration procedures and Level North is that the former only needs to be done once while the later must be done any time the telescope is moved to a new location. To do the calibration and leveling tap the image of the Seestar in the upper left corner of the Home Page to get the next page. Here you have more information about your Seestar along with options to adjust the Sound, the ability to manually adjust the focus, On/Off switches for the dew heater and a Watermark which writes the name of the object imaged along with the exposure time and your location at the bottom of the jpeg images produced after stacking. At the very bottom is a slider to turn off the Seestar power. Just above this is the "Advanced Feature" bar. Tap this to get to the Advanced Feature page where the calibration options can be found. Clicking on the Compass Calibration will display a short video which will guide you through the process. The procedure involves rotating the Seestar about its vertical axis while watching feedback of a white circular ring which slowly turns to green as the calibration is complete. Next, watch the Level Sensor Calibration video which you can find on the App's main page and then then press and perform the level calibration. This involves placing the Seestar on a level surface with a small bubble level on the base of the Seestar, then using thin sheets of paper or similar underneath the edges of the Seestar until the bubble is centered indicating it is level. Once leveled press Calibrate in the App to confirm calibration. This tells the Seestar internal level sensor what true level is so that it can provide feedback to the user when performing the Adjust Level procedure before each session. Again, this sensor calibration procedure only needs to be done once and is not to be confused with the Adjust Level procedure which should be done every time you set up the Seestar. If, at some point while imaging you are having great difficulty getting the Seestar to find and center objects, or it is dropping too many images instead of stacking them you may want to go back and repeat these two calibrations as any degradation in either can impact performance. ![]() On this same page of the App as the Compass and Level Calibration procedures you will find several other important features. At the top you can set the exposure to one of the three possible times. Below that you can tell Seestar to save all of the individual frames as FITS files along with the stacked JPEG image which you may want if you plan to do your own post processing to enhance the final image. The Initialization button takes you to another page where you can turn off the Horizontal Calibration and/or the Auto Focus routine. I suggest you leave these turned on. The Horizontal Calibration routine is on by default and is designed to improve the pointing and guiding accuracy of the Seestar. When the Seestar goes to the first object it will take a short exposure image and perform a Plate Solve operation to use the star positions to get an accurate measurement of the RA and Dec at the center of the current field of view. It will then slew 15 deg in Azimuth to the east and repeat the Plate Solve operation and slew 15 degrees in Azimuth to the west to repeat the process. With 3 Plate Solve solutions the Seestar will update its pointing model and then center the desired object. With the Horizontal Calibration routine turned off, the Seestar has to rely on its compass and level only to find the desired object. With Auto Focus turned on (default setting), the Seestar will automatically perform a focus routine when it goes to the first object after being turned on. The focus routine works very well and I have not found the need to do a manual focus. But, if you want to you can enter the manual focus routine on the previous page and set the focus position manually to try and improve the focus. It should also be noted that it is a good idea to force the Seestar to do an auto focus as the temperature cools down during the night. Some people like to focus for each new deep sky object. To do that use the focus button on the right of the screen during a Live View (see later). Take note of the Adjust Level button on this page as we will need to use this each time we set up the Seestar for a viewing session. Nightly Setup Procedure A typical viewing session begins by placing the Seestar outside on its tripod on a relatively level surface free from vibrations and wind, both of which can be a cause for poor star images resulting in failures in the stacking process. Keep the Seestar as low to the ground as possible for better stability, but if you must elevate it to see over obstacles use a sturdy tripod. The tripod from a telescope you already own is a very good option, although it will not be as light weight and compact as a camera tripod you can purchase on Amazon. An extremely helpful optional accessory is a 3 point tripod leveling base which fits between the Seestar and the tripod. It is much easier to level the Seestar using the three leveling knobs on this than trying to adjust the height of the three tripod legs. But either method will work. Next, power on the Seestar, open the App and Open the Seestar arm. Go to the page shown below to perform the Adjust Level operation which can be reached from the Advanced Feature page by clicking on the Calibrate button. The Adjust Level operation should be performed each time the Seestar is moved to ensure that it set up in a level position which helps improve the accuracy of the initial GoTo procedure. Pressing on the Adjust Level button brings up the following screen which provides feedback to help achieve the optimum level. As you adjust the level two Green Circles will either overlap more or less depending upon whether you are improving the level or not. Adjust the leveling knobs until you have the best overlap you can get, typically a number less than or equal to 0.3 should not be difficult to get and should provide satisfactory results. Once leveled you can set the exposure time and indicate whether you want to save each individual frame as a FITS file for subsequent post process or not and then go back to the Apps main page to select your target for live stacking. Be aware that longer sub-exposure times will likely result in more dropped frames due to star trailing, especially when pointed at Altitudes greater than or equal to 75 degrees, as well as, to Azimuth angles close to 0 and 180 degrees as these are the locations where field rotation is maximum. ![]() Routine Operation Once the setup procedure has been completed it is time to pick a target. For best results, try to stick with objects which will be between 30 and 70 degrees altitude for the duration of imaging. Objects higher than 70 degrees will begin to exhibit greater field rotation which will result in more rejected frames. Objects below 30 degrees are viewed through a great deal of atmosphere which can make for more distortions and also rejected frames. All-in-all the Seestar requires overhead to analyze each sub-frame and decide to accept or reject it, stack the image and dither the mount discussed later) which amounts to as much as 25% of the total imaging time. So, expect to be able to stack no more than 15 min of exposures in 20 min if the Seestar tracks perfectly, the skies are perfectly clear and steady, there is not wind, etc. More often than not we do not have these ideal conditions so expect stacking efficiencies as low as 40% with 75% as a maximum when measured as total stack time divided by actual time elapsed. The Stargazing and Solar System pages provide lots of helpful information to guide you in selecting deep sky or solar system targets, respectively. If you tap on Stargazing it will bring you to another page which displays some of Tonight's Best deep sky and solar system objects which are visible that night. You will also find Tabs for specific Deep Sky Objects such as Galaxies, Nebulae, Star Clusters, etc along with a Solar System tab. Selecting one of Tonight's Best or one of the Solar System objects opens another page which gives detailed background astronomical information about the object. Selecting Galaxy, Nebula, etc under Deep Sky takes you to a list of those objects. If you click on the "GoTo" icon to the right the Seestar will immediately go to that object. If, instead you click on the name of one of the objects you will go to a page with details about that particular object, including a plot of its Altitude over time which is helpful for deciding when it is best to view the object. At the bottom of this page is the red Go Gazing button which will direct Seestar to GoTo the object. If you do not see the object you want you can type the name or astronomical designation in the search at the top of the page. Or, tap the red Skip bar at the bottom of the page to go directly to the imaging page. The Seestar App also has a nice Sky Atlas which can be entered by pressing on the "SkyAtlas" icon on the bottom of the Home Page. This works like a typical Sky Atlas program with buttons on the right column to find "Objects", turn on the "Compass" to allow the view of the sky to rotate as you phone/tablet does, a "Grid" button to turn On/Off the sky grid, a "Ground" button to show where the horizon is, and a "Framing" button to set up the Mosaic feature which we will discuss later. Now here is where the Seestar takes makes EAA really easy. Once you tell Seestar to go the object you selected, it slews to the point in the sky it thinks the object should be located. It is able to get close to the object because the compass calibration lets it know where true north is positioned and because it has been leveled. Most likely it will not have the object centered in the field of view, but in most cases it should be visible unless the object is very dim. Now, the Seestar will automatically go through its Horizontal Calibration process where it takes an image at the GoTo location, rotates the mount 15 degrees in one Azimuth direction to take another image and 15 degrees in the other Azimuth direction to take another image. Seestar then plate solves all three images refining its model of the sky so that it can next move the mount to the correct location to center the desired object in the field of view. In my experience, Seestar does an outstanding job in this regards. If you have trouble with this operation, check your level. If you still have trouble you many want to redo your compass calibration and your level training. After it centers the object it will perform the "image enhancement" which means that it takes 5 ten second dark frames and combines them into a single Dark Master which it will seamlessly subtract from all individual light frames to remove the fixed pattern background noise. Next the Seestar performs an automatic focus and then it begins the image capture and stacking. The Horizontal Calibration and Focus routines are only performed on the first object viewed. You can force a focus any time you want by using the focus button on the right column of the live view screen. Prior to beginning the image sequence, Seestar will place either the internal Dual Narrow Band or UV-IR filter in front of the sensor depending whether the object is an emission nebula or not. The former is only useful for emission nebula, while the later is useful to minimize star bloat. The user has the option to tap the filter Icon in the upper right side of the screen to move the Dual NB filter in or out. If it moves the NB filter out the UV-IR filter will replace it. The image above shows the imaging page which appears after selecting GoTo for any target. A preview of the image will appear in the center. On the right are buttons to turn On/Off the Filter, Adjust screen brightness, Mark, force an Auto Focus and go to the Sky Chart. The red button at the bottom turns On/Off the exposure. Pressing it will begin an exposure and the live stacking process. Tapping the small white circle in the center of the screen will bring up the Joy Stick button shown in the image above which provides the ability to move the mount left/right or up/down to change the position of the object in the field of view. The Sky Chart button takes you to the a celestial chart which shows the field of view overlaid on the chart along with identification of key objects on the chart. You can use the Sky Chart to move the mount around to different locations in the sky as an alternative way to move to different objects in the sky or to fine tune the image in the field of view. Live Stacking
Once the live stacking process has begun, the Seestar will take successive exposures according to the time set (10s, 20s, 30s) and continue to stack them until you hit the red imaging button at the bottom of the screen. Once you tap that button Seestar will save a jpeg file to you phone or tablet of the stacked image and save a Fits image of the same to the Seestar memory. If you tap the red imaging button again you can continue to build up the image or stop and start of new image of the same target or go back in the App and find a new target. A countdown timer appears at the bottom of the screen during the imaging process counting down the individual exposure time. As successive images are added to the stack the timer in the upper right will add to the total stacked time. When an image is deemed not acceptable to stack by the internal software either because of star trailing or other poor quality the stack timer will not be advanced for that frame. Typical stacking acceptance rates vary from roughly 40% on up and are impacted by the object's altitude, azimuth, the seeing conditions, high thin clouds, wind or any other sources of vibration. The higher the altitude the more likely to loose frames due to the effect of field rotation so most users stay between 30 and 75 degrees in altitude to get the best stacking efficiency. The Seestar also has an automatic feature called dithering which is used to minimize the impact of fixed pattern noise. After every 5th frame the Seestar will move so that the image is shifted by ~30 pixels in the frame to shift the fixed pattern noise around so that it is averaged out in the final stacked image. This dithering takes time along with the internal stacking of the frames so that there is an overhead of ~20 to 25% of the total time. Hence, even if you were to achieve 100% stacking success, you will still only get 45min of stacked image in a total time of 1 hour. Seestar Pros and Cons Based upon my experience with the Seestar and many other scopes over the years, I would call the Seestar the simplest scope to begin obtaining dramatic images of deep sky objects in your first night with it with no prior experience required. It is truly as simple as setting down, leveling, connecting the App and telling the Seestar to go to whatever object you want to image. It is light weight and compact making it amazingly portable and quote practical to take on an air plane. And the cost, at $499, is at least 1/3 of what it would cost to put a similar setup together on your own. The other nice thing about the Seestar is that ZWO continues to update the software to add new features and improve upon the existing ones. Recently they introduced the Plan Mode which allows us to set up an imaging plan ahead of time and then allow Seestar to start the plan on its own at the preset time and finish own its own. You can set it up and go to bed and look at the captured images the next morning. They are also planning to add an Equatorial Mode in another month or two which will add much more capability at the cost of having to do a Polar Alignment. As far as the Cons with the Seestar, it would be nice if it had a better imaging chip which could provide sub 2 arc-sec per pixel resolution and a larger field of view. But of course, this would add cost so it is only a relative Con. All-in-all I can highly recommend the Seestar S50 to anyone wanting an almost fool proof tool to capture dramatic images of what the universe has to offer. You can watch my Seestar Tutorial video with step by step instructions on how to set up the Seestar and begin taking images you first note. You will find it here www.youtube.com/watch?v=x3TXn5GT8SQ If you are interested in a Seestar, either the S50 or the smaller S30 please consider using my affiliate links below for your purchase. It will not cost you anything and will provide a small commission which helps to support my web site. High Point Scientific Seestar S50 bit.ly/3YL9aoY Seestar S30 bit.ly/3WR9sJg Agena Astro Seestar S50 bit.ly/4fISCUP Seestar S30 bit.ly/4gB2xLn
0 Comments
In my July Blog I came up with a list of the 10 Challenges, one or more of which, anyone getting started in EAA is likely to face at some point. I explained covered the first 3 of these providing a troubleshooting guide for each one. If you haven't read that Blog yet, I suggest you start there. In any case here again are the Top 10 Challenges: 1. Cannot Get the Camera to Connect to the Imaging SW 2. Cannot See Anything in the Image 3. Can See Stars, but Not DSOs 4. Live Stacking Not Working 5. Poor Focus 6. Elongated stars 7. Comet Shaped Stars 8. Noisy background 9. Significant Vignetting 10. Plate Solve Fails In this Blog I will address the 4th and 5th of these challenges. ![]() #4. Live Stacking Not Working Live stacking is the key ingredient to EAA. The ability to take many short exposure sub frames and stack them in real time, averaging out the background noise so as to improve the SNR is why we can see so much detail in Deep Sky Objects (DSOs) as we allow the stacking process to proceed. It is not uncommon for the Live Stacking software (SharpCap, ASILive, etc.) to reject some frames from the stacking process for a number of different reasons. This is no reason for alarm and can be a good thing as it may be eliminating bad frames from messing up the stacked image. Moments of poor seeing, a light wind gust, errant mount behavior, etc. can cause a frame here or there to be rejected. However, sometimes one finds that after the first frame is captured, no subsequent frames are successfully stacked no matter how long we wait. There are several reasons why this may happen. In this Blog we will use Sharpcap as our example Live Stacking software. Other such software will behave generally the same, but may not have all of the stacking settings available to the user in Sharpcap. Generally they don't. Live Stacking is one aspect of EAA that you will not be able to check out during the daytime. However, if you run into trouble at night, follow the guidelines below to, hopefully, quickly pinpoint and solve your problem. 4A. Check the "Align Frames" Box in the Live Stacking Feature To begin stacking you must start the Live Stacking function and under "Controls" click "Align Frames". This is likely only a novice oversight, but it doesn't hurt to check. ![]() 4B. Not Enough Stars Detected For live stacking to work, the software needs to detect at least 3 stars in each image to be able to shift and rotate frames to align to the first image frame. That is not to say that alignment will always work or even that it will do a good job with just 3 stars as that is the bare minimum required to compute the necessary adjustments that need to be made. Sharpcap specifies that 10 - 20 stars with good distribution across the frame are required for the best possible stacking to proceed. The user can set the number of alignment stars under the "Alignment" tab. Defaut is 15 stars. You may not be able to see the stars yourself even though Sharpcap can. But, you can check the number of stars detected in the "Alignment" tab under "Star Detection Status". If not enough stars are being detected there are several quick things to try. 1. First, increase the exposure and/or gain. If the exposure is too short the camera might not capture enough stars in parts of the sky where the number of visible stars is small, such as pointing away from the galactic center. 2. Check the focus. A poor focus will make stars dimmer and harder to detect, as well as, broader and less star like. 3. If both of those fail you can try adjusting the Star Detection parameters. While Sharpcap automatically adjusts the Sensitivity (up if less than 25 stars are detected; down if more than 200 stars are detected) you can still try to see if this helps. Increasing the Noise Reduction setting helps with star detection when the overall image is noisy and when hot pixels may be causing a problem. Lowering the Maximum Star Size measured in pixels can help prevent small deep sky objects from being misidentified as stars. Suppress Hot Pixels is a default setting which will help to prevent hot pixels from being identified as stars. It's default setting is to be checked. If there are obviously faint stars not being detected you can try checking Optimize for Faint Stars. On the other hand, this can also cause non-star objects to be falsely identified as stars so if it is turned on and you are having trouble stacking and nothing else seems to work, try turning it off. Highlight Detected Stars is a good trouble shooting tool to see what and where stars are detected. A yellow highlight indicates a star used for stacking while a red highlight indicates stars not used for stacking. 4C. Elongated Stars Elongated or egg shaped stars may be one of the most common reasons for live stacking to not work on some or all frames. Live stacking software is looking for stars to be point like and may not identify a star shaped like an elipse as a star. Stars become elongated when the exposure time is too long for the mount to keep the stars from moving within the frame. If you are using an Equatorial Mount, either go back and re-do the polar alignment or shorten the exposure time. You should also make sure that your mount is up to the task for the given exposure time. This includes keeping within the mount's rated capacity, obtaining a good balance of the optical tube and shielding the mount from gusts of wind. If you are using an Alt-Az mount, it is important to keep the exposure short enough to avoid star elongation due to field rotation. A maximum of 30sec is the general rule of thumb for Alt-Az mounts, but the fact is that longer exposures are possible in some areas of the sky such as due east and due west. For a more in depth discussion on this check my page on Field Rotation. 4D. Poor Frame Quality Besides elongated stars there are other reasons that a frame can be rejected by the stacking algorithm. Poor focus, poor seeing, bad collimation can all cause the overall frame quality to be rejected by the stacking algorithm. Check the Full Width Half Maximum (FWHM) tab to see if frames are being rejected (highlighted red) from the stacking process because of star size. You should use the focus tools under Focus Assistant under the Tools Tab at the top of the screen to make sure that you have good focus first. You can also use a Bahtinov mask to check and optimize the focus if you prefer. You can check for poor seeing with the Seeing Monitor under the Tools Tab at the top of the screen but make sure that you have a good focus first or the Seeing Monitor can be fooled. 4E. Forgot to Remove the Bahtinov Mask Sometimes we so distracted that we forget to remove the Bahtinov mask if we used one to focus. The distorted stars will give the imaging software agita and the stacking process will have problems. 4F. Camera Issues It is possible that frames get dropped because of problems with the connection between the camera and the software. These can be due to cable timing issues between the SW asking for an image frame and the camera sending it over. Try connecting the camera directly to the computer if it is not already. You can also try a different USB cable. 4G. Check the Forums When all else fails you may want to check the appropriate software forum where you can find additional help, especially for uncommon problems. Here is the link to the Sharpcap forum forums.sharpcap.co.uk/index.php and here is the link to the ASIStudio forum bbs.zwoastro.com/t/asistudio If live stacking is working well, very, very few frames should be dropped. In fact, I find that if live stacking is working, I rarely see dropped frames. ![]() #5. Poor Focus Poor focus at best will result in soft images with important detail obscured, and at worst produce undiscernible images. It can also adversely impact live stacking and the plate solving process. During the daytime checkout of your setup, checking focus should be foremost on your list. Focus on a distant object like a building, tree, power pole, etc. The further away the better but even once you have achieved focus in daylight you will still have to fine tune it at night on the stars. At night, you should focus right after everything is connected and the optical axis is pointed at a clear region in the night sky. Start you viewing session by focusing on a region of the sky just after dusk with lots of stars. There are a number of different tools available for focusing depending upon the software used and whether a motorized focuser is available. Also, if you change focal length you may be far from focus at the new focal length. With my SCT I find that I have to move the mirror with the focus knob almost all the way to the other side of focus when I change from f/10 to f/7 on my Edge C11. 5A. Manual Focus If you do not have a motorized focuser it will be necessary to focus manually. While one might think that they can tell when the optics is focused by looking at the image of a star field by eye it is unlikely that they would achieve the best possible focus without some feedback mechanism. One of the simplest of these is an inexpensive Bahtinov mask to focus on a single bright star. Placed over the front of the optical tube, the cutouts in this plastic mask cause the light passing through to create a diffraction pattern with two lines forming an "X" and a third passing through the "X" vertically. When the third vertical line bisects the "X" the optics is well focused. If necessary, increase the exposure to help make the pattern easy to discern. A Bahtinov mask is capable of achieving a very good focus on par with other automated methods. Sharpcap has a focus assistance tool for the Bahtinov mask that analyzes the diffraction pattern and gives a score to help determine the best focus point. An alternative to the Bahtinov mask is to focus directly on a single star or a field of stars. Sharpcap measures the pixel width of the star or stars and displays a value for the Full Width Half Maximum (FWHM). A well focused star will cover the minimum number of pixel widths, hence will have the smallest possible FWHM number. Use the FWHM method for a single star or the Multi-Star FWHM method for a field of stars. Adjust focus while watching the FWHM feedback number until you have minimized it. 5B. Auto Focus
If you have a motorized focuser you can use the software to focus automatically. For this to work, the software must be able to connect to the focuser which will require that you download the appropriate ASCOM driver for the focuser from the focuser manufacturer's web site. In addition, you will also need to download the ASCOM platform which you can find on the ASCOM web site ascom-standards.org/Downloads/Index.htm. You can use the same focusing aids (Bahtinov Mask, FWHM, Multi-Star FWHM) in the auto focus mode as in the manual focus mode. The difference is that the software will control the focuser based upon the focus score it calculates. 5C. Re-Focus Occasionally As the temperature drops throughout the night the optical tube will contract changing the optimal focus position. For this reason it is a good idea to check the focus from time to time. It will also be necessary to refocus if you remove or change a filter as the optical path length can change due to differences in filter glass thickness and/or indices of refraction. 5D. Elongated Stars Elongated stars due to poor tracking, for instance, will make it difficult to achieve a good focus. In that case, the reason for the elongated stars needs to be resolve before trying to refine the focus. A good focus is key to a sharp image showing the best detail. And, a good focus is important for the other ingredients of a successful EAA session including automatic stacking and plate solving. ![]() EAA has been a rewarding endeavor for me over the past 15 years. I have been able to see hundreds of interesting celestial objects from distant galaxies, nebulae, star clusters and more. I started with a 9.25" SCT, moved up to a 14" model and then back down to a more portable 11" one. I have done EAA with multiple refractors and even a 6" Newtonian. Over the years I graduated from analog video cameras to CMOS digital cameras and from sensors with 6.5mm diameters to one with a 28.3mm diagonal. I went from single shot long frame captures to short sub-frame live stacking as well. Needless to say, all of these transitions have not been without their challenges which have caused many frustrating nights along the way. So that I have not suffered these trials in vain I decided to pen a series of Blogs to help others avoid or, at least, minimize their frustration when they encounter these same challenges. Based upon my experience and what I know from what others have encountered, I have come up with what I think are the Top 10 common challenges in EAA. Here is my list of these: 1. Cannot Get the Camera to Connect to the Imaging SW 2. Cannot See Anything in the Image 3. Can See Stars, but Not DSOs 4. Live Stacking Not Working 5. Poor Focus 6. Elongated stars 7. Comet Shaped Stars 8. Noisy background 9. Significant Vignetting 10. Plate Solve Fails I will cover each of these in detail through a series of Blogs offering possible root causes and solutions to each. These may not prevent everyone from suffering from the same, but should help to minimize the possibility of encountering one of these and possibly reducing the frustration level when dealing with one that raises its ugly head. In this Blog I will discuss the first three of these which are pretty common for beginners to suffer through when first getting started. Before jumping into these specific issues I would encourage any beginner to test out as much of their equipment as they can during the day. It is better to discover problems and troubleshoot in the daylight rather than try to track down bad cables, etc. in the dark and loose valuable viewing time. Obviously some issues cannot be discovered until darkness, but many can. So, let's start with the first one on the list, which is likely the first problem one would encounter, failure to get the imaging software to see the camera. #1. Cannot Get the Camera to Connect to the Imaging SW You are all set to start you EAA session and go to connect your favorite live stacking SW to your camera and then, nothing. You close the SW and re-start it but still no connection. You re-boot your computer and try again. Still nothing. You unplug and re-plug the USB cable to the camera and no joy. What is the problem? Below is a trouble shooting list starting with the simplest things to try. Most likely the problem is with one of these, but there are no guarantees that the problem still doesn't persist after trying all of the trouble shooting tips below. 1A. Check the SW Compatibility & Camera Drivers The first thing to check is to make sure that the SW you are using is designed to work with your particular model of camera. Some SW like ASILive from ZWO, or Starlight Live will only work with cameras from ZWO and Starlight Xpress, respectively. So cameras from QHY, Player One, etc. will not connect to their SW. Other SW like Sharpcap and The Sky X Live Stack will work with a host of cameras. The tables below show which cameras Sharpcap and TSX work with natively. Note that for TSX there is a dependence upon which operating system is used on the computer. Native support means that the SW has access to the most controls that the camera manufacturer offers and is the best way to connect to a camera when available. To successfully connect the camera the latest version of the camera driver must installed prior to connecting to the camera. The driver will be found on the camera manufacturer's web site. This is true for all Live Stacking software including Sharpcap, ASILive, Starlight Live SW, etc. Make sure that you have the latest driver as older drivers may not work with updated versions of the stacking software. After loading the driver restart your computer. Cameras not on the above lists may still work with Sharpcap, TSX or other live stacking SW (but not ASILive or Starlight Xpress Live) but only through an ASCOM connection. In that case, the camera's ASCOM driver must be loaded from the camera manufacturer's web site along with the ASCOM platform before attempting to connect to the camera. The ASCOM platform can be downloaded from the ASCOM web site here ascom-standards.org/Downloads/Index.htm Another thing to try is to see if there is an updated version of the software. If so, download and try it. This is especially true if you just got the latest version of a new camera. 1B. You Must Have 12V DC Power Connected for a Cooled Camera If you are using a cooled camera, you must connect 12V power to the 12V DC power input for the cooler. This is the case regardless of whether or not you intend to turn on the cooler. Both Sharpcap and ASILive will automatically detect your camera if 12V is applied. You can turn off the cooling function within the software but if you turn off the input power to the camera the software will drop the camera. 1C. Check the Cable If you have loaded the necessary drivers and restarted your computer and SW but your camera still will not connect, the next thing to check is the connection between the camera and the computer. If the camera is directly connected to the computer without a USB hub between the two and does not work, try another cable. It is preferable to use the cable which came with the camera but if that does not work or you do not have one, make sure that the USB cable you are using is the proper USB type cable (USB3, USB2, etc). The camera manufacturer should specify this, but note that most recent cameras that I know of now use USB3 cables. Also, use the shortest USB cable that you can, as the most common problem with cables is due to signal loss from poor quality cables. 1D. Eliminate any Middlemen between the Camera and the Computer If you are using a USB hub you will first have to check both cables with a direct connection between the camera and the computer. Again, it is best to use the cable that came from the manufacturer or at least make sure it is the correct USB type and keep the cable length short. If the direct connection between the camera and the computer works with both cables the problem is in the hub. 1E. Check The USB Hub If the problem is with the hub, check other ports on the hub to see if one of them works. On many hubs some ports are USB3 and some are USB2 while others work with both types. If you cannot get any port on the hub to work, replace or eliminate the hub. The ideal connection is to avoid a hub if at all possible and connect the camera directly to the computer. But this is not always possible. 1.F Check the Computer If the camera still does not connect try another USB port on your computer. If it still does not connect try rebooting. You can also try a different computer if you have one. 1G. Check the Software One day I found that I could not get The Sky X software to connect to my camera. It had connected without issue previously, but for some reason it stopped. I could get the camera to connect using SharpCap and ASILive but not The Sky X. I tried the above troubleshooting tips but in the end found that the solution was to completely uninstall The Sky X and reinstall it. That solved the problem. So, whether this was a problem with an updated version of The Sky X or a Windows update I will likely never know, but at least I am back on track. Once your solve your connection problem make sure to mark the cables and USB ports so that you can connect everything the same way every time. ![]() 2. Cannot See Anything in the Image Here we have the camera successfully connected and recognized by our Live Stacking SW, but, after we slew the telescope to the object we are interested to see and take an image the screen is blank. There are several possible causes for this. Once again, it is a good idea to shake down your setup during the daytime as much as possible. This would include focusing on a distant object such as a building, tree, power line or hill side to not only make certain that the camera can provide an image, but also to make certain it is in focus. 2A. Check the Optical Path We have to start with the easiest and obvious root cause, a blocked optical path. Don't laugh, but I once did forget to remove the dew cap on my scope and it took me a minute to realize that it was what was keeping me from seeing anything. It is also possible that an object like a tree or a house is blocking light from reaching the scope. This seems to happen most often when working remotely when one cannot see where the scope is pointing. The other possibility is a bank of clouds which may have suddenly rolled in. 2B Check the Exposure Another easy thing to check is the exposure. If you are observing from a location with significant light pollution with a short exposure and low gain setting on the camera, stars may not stand out against the bright background. Raise the gain to maximum and check again. If the exposure is too short the high gain will make the stars stand out against the bright background. Once you verify that you can now see stars, lower the gain back down and raise the exposure so that you can still see stars in your image. 2C. Check the Focus If neither of those are the cause of a blank image the camera may be so far out of focus so that the light from the stars is so spread out they become impossible to see. It is possible to be centered on a very bright star but not see anything if the scope is badly out of focus. This is a more common problem than one might think as many scopes, especially Schmidt Cassegrain telescopes (SCTs), can be used at very different focal lengths. For instance, the focus points on my 11" SCT when used at f/2 and f/7.5 are nearly at opposite ends of the focus travel. So, when I switch from one to the other I have to make a very large change in the focuser position to achieve focus. It can be a challenge to find the proper focus position when the telescope is so far out of focus. If the mount is not accurately aligned, you won't be sure when you are pointing at a bright star or planet. The easiest way to solve this problem is to focus on a very distant terrestrial object such as a power pole, tree or hill side during daylight. Then, at night you will be much closer to focus and should be able to see stars appearing as donuts which you can then bring to focus as sharp points. If, like me, you cannot see a distant object to focus on from your observing location you will have to wait to focus on the moon at night. I find that it is easier to get the telescope pointed at the moon than a bright star, not just because of its size, but also because of its brightness, even when the scope is badly out of focus. Even if the moon is slightly out of the field of view you will still see a bright glow on the side where the moon located. Moving the mount in the direction where this bright glow gets bigger and/or brighter will center the moon allowing you to adjust the focus in either direction to see it come into sharp focus. This is one reason why I find it useful to have a unity finder aligned to the optical path of the scope. That way, if you are badly out of focus and cannot find a bright star or even the moon in the camera, you can still find and center it with the unity finder and then proceed with focusing the scope. ![]() 3. Can See Stars, but Not DSOs You take a short exposure and you can clearly see a field of stars, but you cannot see that pesky Deep Sky Object you are looking for. Where is it? Well there are several possible reasons for its ability to hide from you. 3A. Exposure and/or Gain Settings are Too Low All but a few very bright DSOs can be very hard to see due to their low surface brightness and inability to stand out against a bright light polluted background. After all, this is why we do EAA rather than visual observing. The first thing to try is to raise the exposure and gain to see if that makes the object magically appear. 3B. Check the Histogram The object may actually be there but still difficult to see because the black level on the histogram is set too high. This is unlikely but is something simple to check. Below is how a typical Histogram should look. If the black level slider on the bottom left is set too far to the right the image will disappear. 3C. Check the Focus If the focus is off you may have a hard time detecting the DSO. Focusing methods are not the subject of this blog, but Sharpcap has several focusing aids to choose including both automatic if you have a motorized focuser connected and manual if you do not. And, there is the tried and true Bahtinov mask focusing technique which is very simple to use. 3D. Check the Mount Alignment If you do not have a good GoTo alignment you may not be centered on the DSO you have commanded the mount to slew to. You can check this easily by telling the scope to GoTo a bright star in the night sky that you are familiar with. If after slewing to where the mount thinks the star is you cannot see it in the field of view then you need to do one of several things. First, you can re-do the GoTo alignment making sure to use at least three stars and carefully center each star in the field of view. Most Live Stacking SW has a reticle overlay that can be applied which you should use to center the star as accurately as possible. Also, it is good practice to center the stars using the UP and RIGHT controls on the mount (either with the hand control or in the SW) to take out any backlash in the mount. Also, make very certain that you are actually pointing to the stars the mount believes it is centered upon. If you are not absolutely certain, use a star map or use a different star. One mis-identified star will mess up the alignment. With the Celestron Nexstar mounts you don't even need to know the names of the alignment stars, you just have to point the scope at 3 of them and center each and the Nexstar will even tell you the names of the stars. Another important point when doing a GoTo alignment is to use stars widely separated across the night sky to get the best accuracy in the alignment. Second, an easy method for letting the mount fine tune its position in the sky is to use the Sync command. To do this, move the mount to a known star nearby the DSO you are trying to find, center that star and then press the Sync command. This will let the mount know exactly where it is pointed so that it can have a better chance of putting the DSO in the field of view after the Sync procedure. For this to work, you must know the name of the star, it must be relatively close to the DSO and you must properly center it before Syncing. Note, however, that Syncing on a star in one section of the sky may not guarantee that the mount will accurately center DSOs in another section of the sky far away. You may have to do a second Snyc. This is where a good GoTo alignment can make finding multiple DSOs in different parts of the sky go much faster. A third method, which has become very popular these days and may, in fact, be the preferred method for most folks is to use Plate Solving to accurately place DSOs in the field of view. In simplest terms, the SW commands the mount to slew to the position in the sky where it thinks the DSO should be, takes an image, identifies the positions of the stars in the image and compares these to a database to accurately determine the RA and Dec of the center of the field of view. If the resulting RA and Dec are not the same as the coordinates of the DSO, the mount moves to the correct coordinates and takes another image. It solves (Plate Solves) the new image to determine the new RA and Dec and compares these again to the position of the DSO. It will continue to make small adjustments until the solved RA and Dec are within a pre-determined distance from the desired RA and Dec. For Plate Solving to work one must have the Plate Solving SW and database(s) installed on the computer along with the correct focal length of the scope and pixel size of the camera. We will not go into Plate Solving details in this Blog. The nice thing about Plate Solving is that it doesn't even require a GoTo alignment and it is extremely accurate in centering objects. Hopefully if you ever encounter one of these three problems you will remember this troubleshooting guide and work through to a solution quickly and painlessly. In my next Blog installment I will tackle some of the next challenges on my list. ![]() Celestron's 6.3X focal reducer/field flattener is a very popular accessory for non-Edge SCTs because it reduces the focal ratio of the SCT from its native f/10 to f/6.3. This increases the field of view (FOV) and increases the optical speed of the SCT as well. Both effects are helpful for astrophotography and Electronically Assisted Astronomy as they make shorter exposures possible and allow larger Deep Sky Objects (DSOs) to fit in the camera's sensor. And because it is also a field flattener it will improve the sharpness of the image at the edge of the FOV. The same benefits of a wider field and more intense image apply to visual observers as well Reducing the focal ratio with this reducer speeds up the optics by a factor of (10/6.3)^2 = 2.5. It concomitantly increases the FOV by the same amount. For instance, an 8" SCT with the ZWO ASI533MC camera has a FOV of 19.4 x 19.4 arcminutes at f/10 which increases to 30.8 x 30.8 arcminutes at f/6.3. That is 376 arcminutes-squared vs 949 arcminutes-squared with the later 2.5X the former. For the 8" SCT the focal length reduces from 2000mm to 1260mm with the reducer. Determining the Correct Back Spacing Target For any focal reducer to work as designed It is important to place the sensor of the camera at the correct back spacing, or distance, from the focal reducer. This will ensure that the focal reduction will match the design target, in this case 6.3X. It also ensures that the field flattener works optimally to provide sharp, round stars to the edge of the FOV. If the camera's sensor is placed closer to the focal ratio will be larger, say 6.5X or 7X, and the focal reduction will be less. If it is placed further from the reducer the focal ratio will be smaller, say 6X or 5X, and the reduction will be more. In addition, the field flattener will not perform optimally so stars near the edge of the FOV may be distorted. For astrophotography we want to get the best possible images so we want to be as close to the ideal back spacing as possible. For Electronically Assisted Astronomy (EAA) we may be less fussy about the edge of the FOV and more interested in speeding up the optical system and/or fitting more of the larger DSOs in the FOV. In that case a slightly larger back spacing is sometimes used. Regardless, it is important to know how to get the correct back spacing to begin with. ![]() So, how do we achieve the correct back spacing when using the Celestron 6.3X focal reducer? We need to know the correct back spacing and how it is measured. If you search the internet you will find answers ranging from approximately 100mm to 110mm with the most common answer being 105mm. Surprisingly Celestron has not published a spec for the back spacing for this reducer. If you also look to find out where on the focal reducer the back spacing measurement is made, this is where you will find the most disagreement. Some suggest the measurement should be made from the center of the lens' inside the focal reducer (1 in the image above), others from the flat surface on the inside of the threads (2), or the back edge of the threads (3) as shown in the photo. The correct answer to both of these questions is 105mm from the extreme back surface of the focal reducer as shown in the photo identified as location 4 in red. So how do we know that these are correct? ![]() First, we know that the industry standard back spacing for focal reducers used on refractors is 55mm (there are some exceptions). Second, because the optics of an SCT is very different from a refractor it is not possible to make a focal reducer for an SCT with a back spacing of 55mm. So, Celestron did the next best thing. They made an adapter which attaches to the back of the focal reducer and is exactly 50mm long. This leaves the industry standard 55mm left to obtain the correct back spacing of 105mm. Also note that the 50mm length of this adapter is measured from the the flat surface of the flange which mates with the surface "4" in the image above to the flat surface on the other end of the adapter not including the threads where the next spacer will bottom out when screwed all the way on. Similarly, Celestron makes a 7X focal reducer for their Edge SCTs and in this case they do specify the back spacing as 146.05mm. And likewise, they make a T-Adapter to attach directly to this focal reducer which is 91mm long leaving 55.05mm of additional spacing to meet the back spacing spec. So, I think it is clear that the design back spacing for the 6.3X reducer is 105mm and not 100mm, 110mm or something else, and that it is measured from surface 4 on the focal reducer. Imaging Train Options for the 105mm Back Spacing Now that we have established that we need 105mm of spacing for the Celestron 6.3X reducer we need to figure out what options are readily available. But first, we need to take into account the back spacing of the camera sensor itself. This can be found from the manufacturer and we will use ZWO's ASI cameras as an example. Below is ZWO's mechanical drawing for their ASI2600MC camera. This shows the position of the CMOS image sensor relative to the front surface of the camera to be 17.5mm. Likewise the ASI585MC has a back spacing of 17.5mm for the sensor even though it uses a different coupler on the front face. If you look at most cameras these days from ZWO and other manufacturers you will find that 17.5mm is the most common back spacing for the sensor. However, be careful to check as the ASI224MC shown below only has a 12.5mm back spacing. Like plumbing or garden irrigation systems there are many different spacers and adapters available such that one can find many combinations of such to make up the additional back spacing needed. After searching through multiple astronomy supplier's sites I have come up with what I believe to the be the least complicated solutions using the simplest set of adapters available to achieve the 105mm back spacing. I list the parts needed below along with links to either Agena Astro or HighPoint Scientific, two of my goto astronomy suppliers. Links are affiliate links which will earn a small commission at no cost to you. Please use these if you can to support my web site. From Agena Astro Celestron 6.3X focal reducer Celestron 50mm SCT-T Adapter Blue Fireball 37.5mm Extension ZWO 11mm Female to Female Adapter If you want to fine tune the spacing you can use Baader T2 Delrin spacers to adjust the spacing in small increments from 0.6 to 1.4mm. If you want to make larger spacing changes you can search for the desired M42/T2 spacer from Blue Fireball, or substitute the Baader Varilock 46 T2 Variable Extension in place the 37.5mm Extension listed above for greater versatility. Here is an almost identical solution from HighPoint Scientific. Since they do not list a 37.5mm spacer it uses a 30mm and 7.5mm spacer which are sold together as a kit from Celestron. From HighPoint Scientific Celestron 6.3X focal reducer Celestron 50mm SCT-T Adapter Celestron M42 Spacer Kit (30mm + 7.5mm) ZWO M42 Female to Female 11mm Adapter Alternatively to the Celestron M42 spacer kit one could substitute the Baader Varilock 46 T2 Variable Extension which, while almost twice as expensive, allows for variability in the spacing. Also the Baader T2 Delrin Spacer Ring Set is an option for fine tuning the spacing on the order of a mm or less. Back Spacing Solutions With a Filter Drawer Now if we want to use filters with our camera we can put a filter drawer in line so that it is easy to change filters in real time. In this case we will need some different spacers and adapters. Also, we need to take into account the fact that the glass of the filter has a different index of refraction compared to air. Filter glass is typically 2-3mm thick so we need to add ~1/3 of that thickness to our optical path for an additional ~1mm. Below is the same setup as above showing the parts needed along with links to either Agena Astro or HighPoint Scientific. Agena Astro Celestron 6.3X focal reducer Celestron SCT-T Adapter Blue Fireball 10mm Extension Blue Fireball 7.5mm Spacer Ring ZWO M42 11mm Female to Female Adapter ZWO Filter Drawer M42 Male to M48 Female ZWO M48 Male to M42 Female Adapter HighPoint Scientific Celestron 6.3X focal reducer Celestron SCT-T Adapter Apertura10mm Extension Baader 7.5mm T-2 Extension ZWO M42 11mm Female to Female Adapter ZWO Filter Drawer M42 Male to M48 Female ZWO M48 Male to M42 Female Adapter Back Spacing Solutions for SE/Evo/CPC Mounts at 90deg Altitude The solutions above work with cooled and uncooled cameras on any Equatorial mount. In the case of a single arm Alt-Az mount like the Celestron SE or Evolution mounts, or a dual arm mount like the CPC mount, the solutions above will only work as long as the OTA is not pointed higher than ~75 degrees in altitude. Higher altitudes will cause the camera to crash into the base of the mount. A simple solution to reach an altitude of 90degrees without hitting the mount is to add a rail extension along with the imaging trains shown above so that the OTA can be pushed forward to provide enough additional clearance. An inexpensive rail extension is available from SVBony which will work on the 6" SCT. The longer Celestron Universal Mounting Plate is probably a better option for the 8" and 9.25" SCTs and is available from both Agena Astro and HighPoint Scientific. If using a cooled camera there will not be enough room to push the OTA forward and a different approach is needed. This approach uses a diagonal to place the camera at a right angle to the optical axis to gain additional clearance. The details of this configuration can be found in the equipment recommendations section of this web site here. If you would like to see all of these configurations in action, please take a look at the video I put together on this subject where I demonstrate each solution in detail. The video is on my YouTube channel here where you can also find other helpful videos for the amateur astronomer. All links are affiliate links which can earn a commission without any additional cost to you. Please consider using them to help support this channel. ![]() If you own a Celestron SCT and do not already have a hyperstar adapter you should. What is hyperstar? It is a multi-element optical adapter which converts the focal ratio of an SCT from its native f/10 to f/2. Since the optical speed of a telescope is proportional to the square of its f-ratio, adding a hyperstar will increase the speed of an SCT by a factor of 25: speed ~ (10/2)^2 = 5^2 = 25. My first experience with hyperstar was back in 2015 when I first tried it on my 14" SCT to capture a breathtaking view of NGC253 the Sculptor Galaxy in just 22seconds. I was just blown away by what the hyperstar was able to capture in such a short time. Of course, smaller aperture telescopes will not produce such an image in the same time, but they will still have 25X faster optics resulting in amazing images in short times of their own right. Hyperstar is available for the 6", 8", 11" and 14" Celestron Edge and non-Edge SCTs and the 9.25" Edge version. It has been available for these models for some time. Just check the front of the Secondary mirror for the phrase "Fastar", where Fastar is the original Celestron name for this, to see if your older model is compatible. For those that do not say "Fastar" a conversion kit is available for all 6" through 14" models except the 9.25" model. ![]() How does hyperstar work? An SCT consists of three optical elements, a corrector plate at the front, the primary mirror in the back and the secondary mirror in the center of the corrector. SCT primaries are spherical mirrors configured to a focal ratio of f/2. Actually the focal ratio of a Celestron SCT primary varies between f/1.9 and f/2.3 depending upon the model as shown in the accompanying table. For the sake of simplicity, lets stick with f/2 as our example. The secondary mirror is figured to a focal ratio of f/5 so the combined effect is a focal ratio of f/10, f/2 x f/5 = f/10. ![]() Hyperstar is installed by removing the secondary mirror and replacing it with the hyperstar compound lens. With no secondary the focal ratio is that of the primary mirror, or f/2. Obviously the hyperstar element can only be used with a camera for imaging, either for traditional astrophotography or electronically assisted astronomy, and not for visual observations. A camera is attached to the hyperstar via an adapter which is specific to the camera and hyperstar size. The light enters the SCT through the front corrector plate and reflects off the primary mirror just as it always does. But now, instead of reflecting off the secondary mirror back through the center of the primary and out the back of the SCT, it travels through the optical elements of the hyperstar and into the camera. The hyperstar is a multi-element lens/corrector which not only focuses the light onto the sensor in the camera, but also corrects for the spherical aberrations and field curvature which would be present without the corrective capability of the hyperstar. Images taken with the hyperstar should be sharp and flat across the field of view. Hyperstar can be used for both traditional astrophotography and electronically assisted astronomy. In both cases, the faster focal ratio enables more light to be collected in a given time compared to the SCT's native focal ratio of f/10. The results can be stunning as in the traditional astro photo of M31 shown below taken on a C11 with hyperstar for a total exposure time of 213 minutes using Pixinsight to combine and process hundreds of sub-frames. Similarly, amazing results can be obtained during live stacking and viewing during an EAA session as seen in the image of the Rosette Nebula taken with TSX's Live Stack feature stacking and stretching 120 x 5 sec sub-frames for a total of 10 minutes also using a C11 with hyperstar. ![]() Installing Hyperstar Removing the secondary mirror from your SCT may sound scary but it really is a simple matter. I like to set the OTA at a slightly elevated angle so it is easy to reach the secondary and gravity will still help to keep it in place when its retaining ring is removed. The secondary slides out and can be placed into the protective holder which comes with the hyperstar. The hyperstar is threaded onto the secondary holder. But be careful not to over tighten the hyperstar. Finger tight is sufficient. I once got the hyperstar so tight that I had to remove the corrector plate to get it back off. You should not have this problem if you do not over tighten the hyperstar like I once did. After installing the hyperstar several times you will even feel comfortable doing this in the dark. The procedure should take only 5min or less. While hyperstar can weight as much as 3lbs for the 14" SCT it is not going to damage your corrector plate when handled carefully. An SCT corrector plate is much stronger than one may realize. Still, I would never transport an SCT with a hyperstar installed as the possibility of banging into the hyperstar is always present. Also, when covering the telescope using a hyperstar with an all weather cover just be careful that the cover does not snag on the hyperstar which protrudes from the OTA. I leave my hyperstar on for multiple days while in the field using a dew shield and cover over the hyperstar and correct which keeps dirt and dust off the corrector. At home I leave my hyperstar mounted on my SCT in the backyard observatory as long as I plan to work at f/2. There is really no need to remove and re-install hyperstar every day. ![]() Hyperstar Collimation Just like the secondary mirror on an SCT, hyperstar will need to be collimated from time to time. Fortunately, hyperstar seems to hold collimation just as well as a secondary mirror so you should not expect to need to collimate any more frequently than you do without it. Also, you most likely will not need to re-collimate your scope when you put the secondary back since it is indexed to the optical axis with a pin which fits into a notch in the flange which holds the secondary. Hyperstar has 3 sets of push/pull pins located at 120 deg increments around the outside for the purpose of collimation. There are two strategies for initial collimation. The simplest takes advantage of the high precession machining of the two hyperstar mechanical bodies. Just adjust the push/pull pins so that both flanges of the hyperstar bodies are in contact all the way around and then tighten the pins. So long as these two flanges are parallel to one another and the corrector plate is aligned with the primary mirror you should have good collimation. Several folks have reported that this has worked for them so it is worth trying first. If you are not satisfied with the collimation with that approach you can use the second method. With this approach you will need 3 shims 30 to 40 mil thick. Metal stock of this type can be found at your local Ace hardware or online. I use Cu stock which I cut into 3 pieces long enough to fit between the two hyperstar flanges. With the shims spaced 120 degrees apart between the two hyperstar flanges, tighten the push/pull pins just enough so that you can barely pull the shims out. Make sure that you tighten pins are engaged so that the flanges do not come loose. Then, under the stars perform a collimation as you normally would using the push/pull pins in the same way as you would the 3 screws on the back of the secondary mirror. You will find that it is a lot easier to adjust the push/pull pins with your fingers. Just make sure they are all tight when you are satisfied with collimation. A very large variety of cameras are compatible with hyperstar including those from ZWO, QHY, ATIK, SBIG, etc. When ordering the hyperstar element you will need to specify the camera that you will use with it since a camera adapter is required to attach the camera to the hyperstar lens at the optimum distance from the camera sensor. ![]() Using Hyperstar The hyperstar adapter has 3 thumbscrews which are designed to allow 360 degree rotation of the hyperstar so that you can adjust the orientation of your camera. Just loosen all three thumbscrews 1/4 turn, rotate the the outer body of the hyperstar to the desired orientation of the camera. Then tighten the thumbscrews to lock the camera orientation. Since these thumbscrews hold the two halves of the hyperstar together, you should never completely remove them. USB and power (if needed) cables are attached to the camera as usual. If you are using a dew shield you can either bring the cables out the front of the shield or, out the back of the shield if it has a notch in it. In either case tie off the cables so they do not drag. In some cases, the cables may produce diffraction spikes on bright stars just like the spider vanes on a Newtonian secondary. This can be minimized by avoiding running the cables in a straight line across the front of the OTA. The hyperstar camera adapter is threaded inside so that a filter can be attached. This works well if you intend to use only a single filter, such as a light pollution filter, a UV-IR filter or a multi-band filter during you imaging session. Just unscrew the front piece on the adapter, screw in the filter and screw the adapter/filter combination back on. Then attach the camera. If you want to change filters during a session you will need a filter drawer for the hyperstar. The filter drawer screws onto a separate hyperstar adapter such that the combination provides the correct backspacing for your camera. Everything else in an imaging or EAA session will be the same as if you did not have the hyperstar except it will require much less time to be able to see DSOs compared to operating at f/10. Wide Field Since the hyperstar reduces the focal ratio to f/2 but does not reduce the aperture of the telescope, the field of view will be much wider. In fact, the field of view will also be 25X larger compared to f/10, 5X in each axis of the camera sensor. This is precisely how the hyperstar speeds up imaging. To understand this let's take a look at the difference in image scales at f/10 and f/2. Image scale depends upon the size of the pixels in the camera and the focal length of the telescope. It is defined by the following equation: Image Scale (arc-sec/pixel) = 205 x pixel size (microns) / focal length (mm) So, for the same camera, the image scale varies inversely with the focal length. In other words, the image scale increases as the focal length gets smaller. Adding the hyperstar reduces the focal length proportional to the reduction in focal ratio. For the C11 discussed above the focal length is reduced from its native 2794mm to 559mm with hyperstar. The image scale is then reduced by the same factor of 5 across the x and y axis of the camera chip. This means that each pixel is collecting light from an area of the sky 25X larger with the hyperstar than without the hyperstar which is why the exposure time is reduced. Keep in mind that with the wider field of view the resolution is now reduced by the same amount. But since seeing conditions usually dominate image resolution stars and most CMOS cameras used for astronomy have sensors with pixels smaller than 4microns on a side the image quality will still be excellent, even if you zoom in on the image. Summary
Hyperstar is certainly expensive costing just under $1000 for an 8" SCT and more for larger apertures. However it should be viewed as turning your f/10 SCT into a completely new telescope with a focal ratio at least 4X faster than the fastest refractors available while maintaining an aperture many times larger than a refractor. Think of it as investing in an entirely new scope but without having to purchase a new set of accessories (finder, dew heater, focuser, etc.). As the few images shared here show, hyperstar can produce incredible images in real time and is well suited to capturing more of the larger DSOs. If you want to see more about the amazing hyperstar check out my hyperstar YouTube video Links are affiliate links which can earn a commission without any cost to you. Please consider using them to help support this web site. Hyperstar is available from HighPoint Scientific bit.ly/3RO8vgv ![]() Mini-pcs are becoming increasingly popular for both Electronically Assisted Astronomy (EAA) and astrophotography. This is because a mini-pc allows one to connect remotely to the telescope, mount, camera, and other equipment with a laptop, tablet or phone without being tethered by a USB cable. Remote may mean inside one's house while the telescope is out in the back yard or inside a small tent or EzUp where you can stay comfortably warm and away from annoying bugs when observing away from home. It may even mean sitting in your own house with your telescope set up at a distant remote observatory. In my case, it means being inside my house when observing at home with my equipment setup in the backyard observatory or inside my RV when at a star party or other remote site. Being untethered allows me to move freely from inside (house or RV) to the side of the telescope whenever I need to be close but then being able to return to the inside for most of the night. Utilizing a mini-pc at the telescope will also reduce the power required to keep everything running through the night. A mini-pc uses much less power than a typical laptop. If you connect remotely to the mini-pc with a laptop you can still save power since you do not have to have the laptop on all the time since it is only being used as a monitor to check in on the mini-pc from time to time. In fact, you can simply turn off the laptop once the mini-pc is up and running and leave it off until you are ready to shut down the session. A tablet or phone can be used instead of the laptop to remote into the mini-pc which gives more options in terms of saving power since these use much less power than a laptop. What is a Mini-PC? A mini-pc is a headless computer which comes in a small form factor typically 5" - 6" on a side by about 2" - 3" thick or even smaller. Headless means that it comes without a monitor, keyboard or mouse. This cuts down on the size, cost and power consumption, all important for astronomy applications. Since a mini-pc is a computer it will have a CPU, RAM, non-volatile memory, a GPU, USB and HDMI ports, a LAN port, WiFi, and Bluetooth capability. It will also come with an installed operating system such as Windows 10 or 11. The mini-pc can do anything a laptop can while running the applications needed for complete control of mounts, cameras, focusers, dew heaters, etc. This includes running image capture software, guiding software, planetary software, plate solvers, planning software and imaging session automation and control software like NINA or SGP. For instance, on my mini-pc I have The Sky X for mount/camera/focuser control and image capture, Sharpcap for EAA, Ph.D2 for guiding, All Sky Plate Solver and ASTAP for plate solving, Cartes du Ciel as my planetary software, and Sky Tools 3 Pro for planning. I recently added NINA which will take responsibility for overall control and sequencing of my astro-imaging sessions which still uses TSX, Ph.D and ASTAP. In general, a mini-pc is not expected to do the heavy lifting of post processing the photos captured during an astrophotography session, although it is expected to handle the live image stacking, dark frame subtraction and stretching typical in an EAA session. Usually, the burden of post processing astro images is tasked to a separate, more powerful and more expensive laptop or desktop computer. But, there is no reason it cannot be done on the mini-pc if configured to do so which requires a keyboard, mouse and monitor. Even when post processing is left to a separate computer, it is imperative to have a keyboard, mouse and monitor to attach to the mini-pc for initial setup and for analysis in case something goes wrong. In two years I have only had to pull out these once in the field and it turned out that the problem was operator error, not something wrong with the mini-pc or my WiFi router. Still, having these as backup is essential in the rare case that something goes wrong. ![]() Choosing a Mini-PC When it comes to mini-pcs there are a seemingly endless number of options available which constantly change as new hardware components become available. New mini-PCs can be found for under $200 on models with Celeron and Core i3 processers to over $1000 for models with high end processers, GPUs and lots of memory. Keep in mind that even with the same models, prices fluctuate frequently both up and down. The correct choice depends upon one's particular application, future plans and pocketbook. Typically, the trade off in performance and price leads to mini-pcs used for astronomy costing somewhere between $200 to $500. Beelink is probably one of the most popular mini-pc manufacturers in this price range. Recently, inexpensive models from Mele Quieter have gotten a lot of notice on the Cloudy Nights forum as well. Intel NUCs (Next Unit of Computing), designed and built by Intel, are also quite popular and include some of the high end mini-pcs as these NUCs come in many configurations including kits which can be customized to the users requirements. ![]() When choosing a mini-pc the first feature to consider is the CPU. At this point in time mini-pcs used for astronomy usually include a Celeron or Core i3 processer for the less expensive models or an i5 processer for the slightly more expensive models. Many people report success in astrophotography and even EAA with mini-pcs using Celeron processors. However, for high data rate applications as is the case with larger format cameras (20Mpixels or larger) or live stacking of very short exposures (less than 5 sec subs) with dark frame subtraction and flat frame calibration for EAA, the Celeron class of processor may not be up to the more challenging tasks. In these situations an i5 processor would be a safer choice while the added cost of an i7 processer might be better applied to more RAM or a larger and faster SSD. For planetary imaging requiring extremely high image capture rates one should consider at least an i5 and possibly an i7 processor with fast SSD storage. Celeron processors found in these mini-pcs include the Gemini Lake J4125 and the Jasper Lake N5095. For Core i5 processers the Tiger Lake 113567 and Coffee Lake 8279U are typical. In addition to processing speed and cost another attribute of CPUs to be considered is the Thermal Design Power (TDP) which is indicative of the maximum power that the CPU can generate. The higher the TDP the more power one needs in the field to keep the mini-pc running all night long. One of the desirable features of the mini-pc is its lower total power consumption compared to a laptop. The accompanying table shows the tradeoff in CPU capability and TDP. After the CPU the amount and type of RAM and mass storage is probably the next most important consideration. 8GB of RAM is sufficient for most situations and is fairly common in pre-configured mini-pcs, while 16GB can help when many applications are open at the same time. As far as mass storage one should consider 128GB to be the minimum choice in which case you may have to constantly download image files to another storage device after an imaging session. I opted for 256GB which allows much more margin, but even then I sometimes wish that I had paid the extra for 512GB. The choice will depend on your imaging/EAA habit and how often you are willing to transfer images from your mini-pc to your processing pc. Mass storage on the mini-pcs often used for astronomy typically have one of three types of mass storage including M.2 SATA SSDs, M.2 NVE SSDs or eMMC. The first two can be replaced while eMMC is soldered onto the motherboard and cannot be replaced. NVE SSDs use the PCIe interface which is much faster than the SATA interface used by SATA or eMMC devices. All will work but the M.2 NVE SSD is the better choice for high data rate applications. Probably the next most important consideration in choosing a mini-pc is the number and type of USB ports because of the need to connect our many astro devices to the mini-pc. Most mini-pcs in the price range being discussed usually provide at least 4 USB ports in some combination of USB2.0 and USB3.0. Some also provide a USB Type C port with even faster data transfer rates. Don't forget to reserve one USB port for a WiFi dongle when using a wireless keypad and mouse. On other hand, if like me, you have a USB hub like the Pegasus Power Box which you use to connect your astro devices, you will only need to connect the hub to the mini-pc, preferably over a USB 3.2 port for fastest transfer rates. Another choice is whether or not to choose a mini-pc with a fan or not. Fans consume additional power. And they can, in principle, cause vibrations although I have never witnessed any such problem with my mini-pc attached to the leg of my tripod. On the other hand, fans will keep the CPU cool so that it can operate at its highest speed whereas air cooled mini-pcs can get hot causing the CPU to throttle back. Beelink tends to incorporate fans into their models while MeLE Quieter does not. Many folks agonize unnecessarily over the fact that some mini-pcs require 19V power input instead of 12V. This is easily rectified with an inexpensive DC-DC boost converter which takes a 12V input and provides a steady state 19V output. The boost converters are ~95% efficient while the AC transformer typically supplied with any mini-pc is likely ~80% efficient. I find the easiest way to incorporate these into my setup is to attach Anderson Power Poles to the leads and use Anderson Power Pole to 5.5 x 2.1mm adapter cables to connect to my equipment. All mini-pcs include an ethernet port for wired connection, WiFi and BT capability, along with one or more HDMI ports. You will need one HDMI port to connect a monitor initially to set up the mini-pc and any time something goes wrong with your connection to the mini-pc and you need to trouble shoot the situation. Mini-pcs come with Window 10 or Windows 11 software already installed. Look for the Pro version which is required for some remote connection software like Team Viewer and Remote Desktop. ![]() Mini-PC Models to Consider Below are a number of different mini-pc models currently available. Prices will vary and over time models will change, but this can be a good starting point. Beelink has a large following in the astronomy community judging from posts on CN and is the brand I have used and been happy with for the past 2 years. You can search through all their models on the Beelink Amazon store. A few examples are worth considering. The Beelink U59 Pro comes with a Celeron N5105 processor, 8GB of RAM, a 500GB M.2 SATA SSD, 4 x USB 3.0 and 1 x USB C ports, 2 LAN ports, 2 x HDMI ports, WiFi, BT, and Windows 11 Pro. It has a cooling fan and operates on 12V and is currently on sale for $219. You can add 8GB more RAM for another $25. The Beelink SEi8 has an i5-8279U processor, 16GB of RAM, a 500GB M.2 NVME SSD, 4 x USB 3.0 and 1 x USB C ports, 1 LAN port, 2 x HDMI ports, WiFi, BT and Windows 11 Pro. It also has a cooling fan and operates on 19V and also has an auto startup feature so that you can set it to automatically turn on at a set time each day. This model is currently on sale for $397. Compared to the model above you get a faster processor, twice the RAM and a faster SSD. ![]() If you are looking for a fanless mini-pcs, the models from MeLE Quieter are becoming popular among amateur astronomers lately. Here are two worth considering. The MeLE Quieter 2Q uses the Celeron J4125 processor, 8GB of RAM, 128GB of eMMC storage, a Micro SD card slot of storage expansion, 4 x USB 3.0 ports, 1 LAN port, 2 x HDMI ports, WiFi, BT and Windows 11 Pro. It does not have a cooling fan and can also be configured for auto startup. This model is currently on sale now for $210. Like most mini-pcs there are upgraded versions of this model with up to 512GB of eMMC storage for an additional $90. The MeLE PCG35 has a Celeron N5105 CPU, 8GB of RAM, a 256GB NVMe M.2 SSD, a Micro SD card slot of storage expansion, 2 x USB 2.0 and 2 x USB 3.0 ports, 1 LAN port, 2 x HDMI ports, WiFi, BT and Windows 11 Pro. It does not have a cooling fan and can also be configured for auto startup. This model is currently available for $310. Both of these MeLE models require 12V input power. Intel NUCs can be found at the Intel Store for as little as $200 to well over $1000. An example is the Intel NUC 10i3FNHN which currently lists for $499 and includes an i3-10110U processor, 8GB of RAM, an 512GB of PCIe SSD, 3 x USB 3.2 ports, 1 Thunderbolt (Type C) port, 1 HDMI port, 1 LAN port, BT, WiFi, an SD card slot and Windows 10Pro. It requires 19V for power. ![]() Mini-PC Operation Being small and light, a mini-pc can be mounted on top of the telescope which minimizes the length of cable runs between cameras, focusers, dew heaters, filter wheels, the mount and the pc. Often the mini-pc can be found mounted to the leg of the tripod or at the base of the mount. If the mini-pc has a cooling fan, this may be the best place to mount it to minimize the chance of vibrations in the optical system. This is my typical configuration since I have a Software Bisque Mount with through the mount cabling. In addition to the mini-pc some method to connect between a laptop/tablet/phone and the mini-pc is required. This involves a remote desktop application like Team Viewer, VNC Connect, Remote Desktop or one of the many others which are free and easy to use. These generally require that the mini-pc has the Pro version of Windows to work. The second requirement for remote connection is the ability to make a WiFi connection. At home this could simply be your home internet network assuming that you have a LAN line to connect to the mini-pc in the back yard. I use a Cat5 cable I strung out to my backyard observatory 10 years ago to connect from my laptop anywhere inside the house to my mini-pc outside on my home network. In the field or at home if you don't have a wired connection in the back yard, you will need to create your own WiFi network. This is simple to do with an inexpensive portable router. I have reviewed 2 such inexpensive routers from GL.iNet in an earlier blog which you can find here. A video version of my review can also be found here. I have been using the GL.iNet 750S Ext (Slate) for 2 years and could not be happier. I can stay connected from inside my RV to my telescope up to 100 feet away. At home I can use the Slate as a repeater and connect to my home internet without the need for a LAN cable connection. GL.iNet has another model capable of higher data rates called the Beryl for just a few dollars more which is worth considering. If you need help setting one of these up, I created a video showing how to do this step by step. Summary Having used my mini-pc for two years both at home and at many star parties I have been extremely happy that I finally made the move to untether myself. With one exception (operator error) I have not lost any time due to problems connecting or using the mini-pc. And, I have not noticed any problems when using it for astrophotography or EAA. Hopefully I have given you a helpful overview of the considerations required to set up your own remote connection so that you can make the right choice for your situation. The one possible downside of using a mini-pc is that it tends to keep me inside, even at star parties, instead of out under the night sky. I have had to remind myself that one of the great things about being at a star party is to be able to look up and appreciate the wonder of the Milky Way with my naked eyes. So, I make it a point to spend some time outside both viewing the night sky and talking with my fellow amateur astronomers instead of spending the entire night away from the action inside the RV. You can find a complementary video tutorial on this subject on my YouTube channel which you can find here www.youtube.com/watch?v=TRk2wsrOnNM Beelink Mini PCs amzn.to/48Vp3Lm
MeLe Quieter Mini PCs amzn.to/47KLXUK Intel NUCs amzn.to/47KM1ns GLi.Net Portable Routers amzn.to/4b1oamt Links are Amazon Affiliate links from which I can earn commissions at no cost to you. If you would like to support my web site and its content please consider using my links when ordering products. ![]() Two years ago I decided that I was no longer willing to have my laptop tethered to my telescope with a long USB cable. When I am in the field I normally site inside my EZUp tent with my laptop to stay warm and to limit the light infringement on my neighbors. While this has worked well for many years, the cable presents a tripping hazard especially at star parties where other folks tend to stop by. And now that I have an RV I want to sit inside and not worry about running a USB cable through an open window or door. So, I looked into what is needed to go wireless and found that it was not at all difficult. First, we need computing power at the mount to run all of the software used to control the mount, camera, focuser, guider, dew heaters, etc. Second, some sort of WiFi either built into the computer or through a small travel router is required to link the computer at the mount to the device inside. Third, software designed to allow a laptop, tablet or phone to be connected to and control the computer at the mount is also needed. Let's look at each of these in detail. Off the Shelf Solutions There are a number of different ready made solutions available from the astronomy industry. On the high end there is TheSky Fusion (available from High Point Scientific) from Software Bisque. At the heart of the Fusion is a 64bit Hex-Core CPU with 4GB of RAM which drives TheSky imaging addition software which is included with the Fusion. A total of 190GB of on board memory is available to store images. It has an integrated WiFi with an external antenna to provide wireless connection to a pc, laptop, tablet or phone. It also comes with an ethernet port in case of the need for a hard wire connection and it has internal GPS. TheSky Fusion integrates USB hub capability with 4 USB3.0 ports and can operate as a power distribution hub with 8 configurable power ports capable of supplying up to 40A using Anderson Power Pole connectors for reliable connections. At 4.2lbs the Fusion is designed to be mounted on top of the telescope to allow for simpler cable management. With a price of $1895 TheSky Fusion is on the high end of off the shelf WiFi solutions but it is certainly packed with useful features combining the functions of a computer, WiFi, USB hub and power distribution all in one. Another high end solution comes from Prima Luce Labs in their line of four different telescope control units ranging in price from $795 to $2195. The least expensive model is the Eagle LE (available from High Point Scientific) while the most expensive model is the Eagle 4 Pro (available from High Point Scientific) The LE has an Intel Celeron Dual Core CPU with 4GB of RAM and 120GB SS memory while the Pro has a Quad Core I5 CPU with 16GB of RAM and 480GB of SS memory. Both provide connectivity via WiFi with an external antenna and through an ethernet port. Both models have ample USB ports and 7 power ports, 3 of which allow voltages to be configured from 0V up to 12V. The Pro model includes a GPS. Any software can be installed onto these units just like a normal pc and, like the Fusion, these units are designed to be installed on top of a telescope. The Eagles use proprietary connectors on the 4 12V non-configurable power ports so one has to add the cost of these cables to the total cost of the unit. Like TheSky Fusion Prima Luce Labs' models combine multiple capabilities into one device. ZWO's ASIAIR Plus (available from High Point Scientific)is a much less expensive WiFi solution but with less computing power and fewer bells and whistles. At the heart of the Plus is a Raspberry PI 4 processor with 32GB of internal storage and a slot for a MicroSD card. It has an external WiFi antenna and an ethernet port. Unlike the models from SB and Prima Luce Labs, the ASIAIR will only work with ZWO cameras, focusers and filter wheels but it will work with a large variety of mounts. Like the SB and PL units it also acts as a USB hub with 4 USB ports and a power distribution hub with 4 12V power ports capable of a total of 5A. The ASIAIR is also designed to be mounted on top of a telescope but has a much smaller footprint than the SB and PL units and weighs less than 0.5lbs. At a price tag of $299 the ASIR Plus is a slimmed down version both in size and capability of the more expensive SB and PL models. The Stellarmate Plus is the least expensive ready made WiFi solution at $229. Like the ASIAIR it uses a Raspberry PI 4 processor, has 2GB of RAM and includes a 32GB MicroSD card for storage. In addition to the WiFi the Stellarmate also has an ethernet port but no external WiFi antenna. It has 4 USB ports but no external power ports. Like the ASIAIR the Stellarmate is compact and light weight. Unlike the ASIAIR, Stellarmate works with a wide variety of astronomy equipment. It includes a copy of EKOS Astrophotography software and is compatible with a variety of other software applications. ![]() Build Your Own Solution While the above ready made wireless solutions will work, each has its cons. The high end models are expensive and better CPUs, and more RAM and memory can be found for less money. The lower cost models only come with a Raspberry PI processor, which works, but is limited in ultimate capability and they have very little RAM and memory. With just a little bit of effort, and not much more cost, if at all, compared to the ASIAIR and Stellarmate options, one can put together a better custom tailored solution on their own. I chose to build my own solution with the features and capabilities that I wanted. A custom WiFi solution requires three components. The first is a CPU at the mount to run all of the software used to control the mount, camera, focuser, guider, dew heaters, etc. This could be an inexpensive laptop, a headless Intel NUC or mini-pc, or a home brew Raspberry PI. I decided that the best solution for me was a headless mini-pc because it offered the best price to feature ratio. I bought a Beelink U57 mini pc with an Intel Core I5 processer, 8GB RAM and a 256GB solid state drive for under $360. And considering that I use a Pegasus Power Box Advanced which cost $330 I have all of the features that TheSky Fusion offers that I need for less than half the price. The mini pc comes with Windows 10 Pro installed so that I can run any of the typical software that I use such as The SkyX for mount/camera/focuser/guider control and image capture. I can also use SharpCap if I want to do electronically assisted astronomy (EAA), PhD for guiding, Nina or Sequence Generator Pro for image sequencing, etc. I am also not constrained to work with any one manufacturer's equipment as a mini pc works with any mount, camera and accessory that is ASCOM compatible. While my model is no longer available, you can find something similar for just $249 or choose from a wide variety of mini-pcs from Beelink with different processors, RAM, memory, USB ports, etc. While my mini-pc uses 12V, most mini-pcs or Intel NUCs require 19V which can easily be supplied using a 12V battery and a 12V to 19V DC-DC voltage converter like this one. The second component is WiFi. I found two inexpensive portable wireless routers from GL.iNet that I bought and tested, the GL-MT300N (Mango) and the GL-AR750S (Slate) models. The 750S provided greater range due to its pair of fold up antennas and also offered 5GHz capability which helps to mitigate potential interference on the 2.4GHz band from nearby equipment. I am able to set up inside my RV up to 100 feet away from the mini-pc and maintain a good connection all night long with the Slate. I can also set up just inside my house and stay connected to the mini-pc inside my backyard observatory when at home. You can read my review of the Slate and its smaller Mango alternative in my Feb '21 Blog or view my video review of these two on YouTube. There is a newer model with fold up antennas, the GL-MT1300 (Beryl), which offers twice the data rate of the Slate. The last component to make this all work is a way to make the remote connection from the laptop (or tablet or phone) to the mini-pc to use the laptop as a terminal to view and control the software on the mini-pc. There are many free remote connection options and I tried two of them, Remote Desktop and Team Viewer. I chose Team Viewer but any of the many options will work fine. The choice seems to come down to personal preference. Also, you will most likely need to have the Pro Version of Windows software installed in order to use the remote connection software, but most of the mini-pcs seem to come with that. ![]() Set Up & Operation I choose to have my mini-pc attached to the leg of my telescope tripod since my SB MyT mount can supply all the power I need to the cameras and focuser through the mount itself. I also have through the mount wiring for the dew heater. For some people this will work, but others may choose to set up the mini-pc or Intel NUC on the telescope itself. These are small enough and light weight enough as to add little inertia to the telescope. The Slate router gets its power from the mini-pc. Power to everything comes from a LiFePO4 battery or Jackery solar generator which is fed through the Pegasus Power Box Advanced. I just power up the PPBA, turn on the mini-pc and the mount and step away to my laptop. It takes a few minutes for the router to set up its WiFi signal which I connect to with my laptop. Once connected to the router I run Team Viewer to connect to the mini-pc and begin my session with The SkyX and any other software that I need which resides on the mini-pc. Images are captured difrectly to the mini-pc and retrieved later for post processing on my laptop. When my session is over, I simply park the mount, turn off the cameras and close The SkyX and any other software (ShapCap, PhD) that I have running on my mini-pc. Then I turn off the mini-pc remotely. I can leave everything like this or I can go over to the telescope and disconnect the battery or turn off the Jackery. Additional Considerations If you go the route of a headless mini-pc or NUC I suggest that you carry with you a mouse, keypad and small LCD display. This way, if something goes wrong you can connect to the mini-pc and see what is going on. You can use a wired mouse and keypad you may already have lying around or you can purchase a wireless set similar to the one I did. You will also need a small LCD display and there are many to choose from. It is also worth knowing that the wireless routers I discussed above can also work as WiFi repeaters at home which is how I use mine. The router can be set up to connect to the home WiFi and then I can use my laptop from anywhere inside my house to connect to the mini-pc out in the observatory. Of course, how well this works depends upon the strength and coverage of your home WiFi signal, but it is a nice additional advantage of the wireless router if you do not already have either WiFi or cable at your backyard observing location. Summary For those who prefer ready made solutions there are several very good options which we discussed to choose from across a broad range of prices and features. However, if you are inclined to set up your own system you can customize it to your specific needs, including only those elements that you need and avoid paying for features you do not want. And, a custom solution will give you the greatest flexibility in terms of equipment and software compatibility. You can find a companion video I made on this topic here www.youtube.com/watch?v=quoWbvN5VWc&t=1220s Some links are Affiliate links where I can earn with purchases at no cost to the buyer which help to support this web site. If you would like to support my web site and its content please consider using my links when ordering products. ![]() Why SCTs In this installment of my "EAA for Beginners series" we will discuss the use of a Schmidt Cassegrain Telescope (SCT) for EAA on an Alt-Az mount. SCTs seem to be a popular choices for EAA for good reasons. First, large apertures up to 14" are possible with an SCT because the cost per inch of aperture is so much less than that of a refractor. Second, because the SCT design uses folded optics, SCTs are more compact than the same size aperture Newtonian. With its smaller moment of inertia for the same weight Newtonian, an SCT places less demands on the mount for smooth tracking and is guides better in the wind. But the versatility in focal ratio (or focal length) may be the biggest reason SCTs are popular for EAA. An SCT is natively f/10 but can easily be reduced to f/6.3 for an non-Edge model or f/7 for an Edge model with the addition of a focal reducer. And, with hyperstar capable models, focal ratios of f/1.9 to f/2.2 are achievable depending upon the model SCT. As I discussed in detail in an earlier installment of this series, the lower focal ratio results in a faster optical system so that much shorter exposures are needed providing spectacular images in real time and less demands on telescope tracking. This versatility is like having 3 different telescopes in one with just the added cost of the focal reducer and hyperstar. Any size SCT which can be found in sizes from 5" to 16" primarily from Celestron and Meade will work for EAA . I have used 6", 9.25", 11" and 14" SCTs myself for EAA with great success and you can find some real time images in the "My Images" section of this web site. The tradeoffs with a larger size scope is cost and the need for a larger and more expensive mount. That is why some consider an 8" SCT as a ideal size scope in terms of aperture vs size and weight. ![]() Alt-Az Mounts Just as SCTs are very popular for EAA, Alt-Az mounts are also popular. Alt-Az (Altitude-Azimuth) mounts do not track the rotation of the earth like Equatorial (EQ) mounts do. EQ mounts have two axes of rotation called Right Ascension (RA) and Declination (Dec). EQ mounts must be polar aligned so that the RA axis, also called the Polar Axis, follows the earth's axis of rotation. This is done with a procedure called Polar Alignment (PA) in which the elevation of the mount is set to the local latitude while the Polar Axis is carefully aligned with the north celestial pole. By doing this the mount rotates about its RA axis so that it matches the earth rotation to keep objects centered in the field of view (FOV). This allows for long exposures of up to many minutes determined by the quality of the mount and the precision of the PA. While an Alt-Az mount also has two axes of rotation and motors on each axis to find and track objects in the night sky, it cannot exactly match the earths rotation. The Azimuth axis is defined by the local horizon and the Altitude simply by the height of an object in the sky. There is no latitude adjustment knob to account for the tilt of the earth's axis. Only at the north and south poles will the Azimuth axis of an Alt-Az mount be pointed at the celestial pole and the mount be able to track the earth's rotation. Everywhere else on the surface of the earth, an Alt-Az mount can keep a star centered in the field of view, but it cannot prevent the surrounding stars in the FOV from appearing to rotate around the central star. This field rotation can cause objectionable elongation in the appearance of stars in images depending upon how long of an image exposure and where in the sky the object is located. The typical rule of thumb is that exposures must be limited to less than 30seconds unless the object being viewed is nearly due east or due west to avoid star trailing or elongation. The actual details are much more complicated and can be found on this web site here. Despite this, Alt-Az mounts work very well for EAA since the trend in recent years has been to take short exposures, much less than 30seconds, and use software like SharpCap to stack successive image frames in real time to give images with an effective exposure of minutes of longer without star trailing. Despite its limitation in following the earths rotation, Alt-Az mounts have several advantages for EAA compared to EQ mounts. First, Alt-Az mounts are less expensive than their EQ counterparts. Also, Alt-Az mounts are typically lighter than EQ mounts for the same load capacity which makes them easier to transport, whether from inside the house to the back yard or to a distant dark site. Finally, since an Alt-Az mount cannot be Polar Aligned, it is much easier and faster to set up a telescope on an Alt-Az mount and get started viewing objects in the night sky. Alt-Az SCTs The combination of SCTs on Alt-Az mounts are now very popular for EAA and come in a number of different sizes and configurations. These are some of the least expensive telescope setups for SCTs. You can get a Celestron Nexstar 5SE SCT (available from High Point Scientific, Agena Astro or Amazon) on an Alt-Az mount for $936, while the Celestron Nexstar 6SE (High Point Scientific or Agena Astro or Amazon) is only slightly ore expensive at $1099 and the Nexstar 8SE (High Point Scientific or Agena Astro or Amazon) is $1600 as of this writing. Celestron also offers a better mount in its Nexstar Evolution series (High Point Scientific, Agena Astro) which is available with a 6" SCT for $1679, an 8" SCT for $2199 and a 9.25" SCT for $2849. The Evolution mount offers integrated WiFi so that the scope can be controlled wirelessly from a phone or tablet, it includes an internal rechargeable Li battery which should last all night long, has improved gears for better tracking and other improvements like manual clutches, etc. The larger the aperture the greater the magnification of the image, but also the more the telescope weighs. The field of view (FOV) of a 6" SCT is 2.46X larger than the FOV of a 9.25" SCT at the same f-ratio so more of very large objects like M33 can be viewed in the smaller SCT, but more detail will be seen in smaller objects like M82 with the 9.25" SCT. The weight difference between an 6" SCT and an 8" SCT is small with the former weighing just 10lbs and the later 12.5lbs. But, at 20lbs the 9.25" SCT weighs twice that of the 6". On the other hand the Evolution mount/tripod weights only 33% more at 28lbs compared to the SE mount/tripod at 21lbs. The SCTs discussed above are Celestron's standard optical tubes. They also make their Edge series of optical tubes (High Point Scientific, Agena Astro) which have additional optical elements in the baffle tube which is designed to give a flatter FOV so that stars are more pin point from center to edge. These are offered in 8" and larger OTAs and come at a premium price with the 8" Edge OTA costing ~$300 more than the non-Edge version and the 9.25" version costing ~$1500 more. If you objective is to also do traditional astrophotography you should seriously consider an Edge version OTA. On the other hand, if you only plan to do EAA the added expense of an Edge OTA is not so clearly justified. Celestron does not offer an SE or Evolution mount with an optical tube larger than 9.25" because the weight of the larger OTAs is too great for these single arm mounts. If you want a larger OTA on an Alt-Az mount you must choose a dual arm fork mount like Celestron's CPC series (High Point Scientific, Agena Astro) with 8" to 11" OTAs. With dual arms these telescopes come with built in GPS, improved drive gears, a heavy duty mount, an auto-guider port, clutches and Periodic Error Correction (PEC) capability. The dual fork telescopes come at much higher cost with the CPC8 at $2600 compared to $2199 for the 8" Evolution. But an even bigger difference is found in the weights, exacerbated by the fact that the OTA is permanently attached to the mount in this design. The CPC8 mount/OTA is 42lbs while the tripod is 19lbs. This compares to 12.5lbs for the 8" OTA and 28lbs for the Evolution mount which makes the SE and Evolution designs much easier to transport and set up compared to the CPC design. Meade does not offer single fork SCTs but they do offer dual fork versions. They only offer these in their ACF (Advanced Coma Free) version of optical tube similar to the Celestron Edge. The 8" ACF sells for $3000 and comes with built in GPS, and over-sized mirror, PEC, and more. Meade offers versions all the way up to OTAs of 16". ![]() Focal Reduction with SCTs As I mentioned in the beginning, the ability to use SCTs at multiple focal ratios is what makes them so versatile and ideal for EAA. Natively SCTs are f/10 which results in very high magnification, especially with cameras using a small chip. For instance, an 8" SCT at f/10 has a focal length of 2000mm. When used with the low cost ASI224MC camera which has a chip diagonal of 6.1mm the magnification is approximately 2000/6.1 = 328. Such high magnification not only means that only the smallest DSOs will fit in the field of view, but that it can be very hard and frustrating to locate the object to begin with. In addition, the exposure times needed to see detail may need to be very long. For these reasons, EAA is most commonly performed at focal ratios of f/2 to f/7 to obtain a combination of wide field and fast optics. Focal reduction is fairly straightforward requiring that a focal reducer be placed between the telescope and the camera. To obtain the specified focal reduction ratio the camera must be placed at the correct distance from the back of the focal reducer according to the manufacturer's specification, usually within a couple of millimeters. If the camera is too close, the focal reduction will be less and if it is too far, the focal reduction will be more. Also, if the spacing is off by too much it may result in vignetting and other types of image distortions. Adapters are available to achieve the correct spacing and spacers in various sizes can be used to fine tune the spacing. For instance, Celestron has a series of T Adapters designed for each of their different OTAs including Edge and non-Edge designs. ![]() There are many focal reducers on the market but not all are designed to work with SCTs. Celestron offers a 0.63X focal reducer (High Point Scientific, Agena Astro or Amazon) for their standard OTAs and a 0.7X reducer for the Edge OTAs (High Point Scientific , Agena Astro) to reduce the focal ratio down to f/6.3 and f/7 respectively. You can also get the Starizona Night Owl reducer for 0.4X reduction ) or the Optec 0.33X focal reducer (High Point Scientific) to produce an even lower focal ratio of f/3.3. All of these are both focal reducers and field flatteners which improves the sharpness of the stars from the center to the edge of the FOV. Since EAA is not meant to produce the high quality images sought by astrophotographers, one can even use a generic 0.5X focal reducer (High Point Scientific, Agena Astro, or Amazon) to get down to a focal ratio of f/5. These come in both 1.25" and 2" versions and are much cheaper than the focal reducers from Celestron, Starizona and Optec. If one is not terribly concerned about vignetting it is also possible to stack focal reducers to achieve an additional focal reduction such as stacking two 0.63X reducers to get a focal ratio of ~f/4. HyperStar While the HyperStar adapter(High Point Scientific) is a field flattener and not actually a focal reducer, it does enable the Celestron SCT focal ratio to be reduced from f/10 to ~f/2. The Hyperstar is a compound set of lenses which replaces the secondary mirror on the front of the OTA. Just unscrew and remove the secondary mirror and screw the HyperStar in its place. The camera is then screwed into the back of the HyperStar adapter so it is looking directly at the primary mirror which has a focal ratio of between f/1.9 to f/2.2 depending upon the aperture of the OTA. Camera cables such as the USB cable for camera control and image capture along with a power cable if camera cooling is used are routed from the front of the OTA to the back. They typically do not cause much interference in the image. Many older model OTAs are not compatible with the HyperStar attachment so check before you buy. Also, be careful not to overtighten the HyperStar onto the corrector plate as it can become frozen in place as it did on my C14 requiring removal of the corrector plate to get the HyperStar adapter off. Hyperstar speeds up the optical system dramatically with required exposures reduced by the square of the ratio of the native and HyperStar focal ratios, or (10/2)^2 = 25 times. The effect is dramatic. In addition the reduction in focal ratio greatly increases the FOV by a factor of 10/2 = 5 which makes HyperStar great for viewing very large DSOs like M33, the North American Nebula, etc. Summary
EAA with an SCT on an Alt-Az mount is becoming increasingly more popular. The relative low cost of such a setup puts it in the reach of many more people interested in astronomy. Also, these setups tend to be fairly light in weight making them easy to move around without disassembling everything each time you want to have an observing session. And, perhaps, most importantly, the versatility of an SCT on an Alt-Az mount is the biggest attraction. Links are Affiliate links from which I can earn commissions at not cost to you. If you would like to support my web site and its content please consider using my links when ordering products. A good focus is critical to achieving the sharpest details in an image viewed through a telescope whether using an eyepiece for visual observation or a camera for EAA or astrophotography. Because the human eye is capable of focusing over a wide range of distances it is not difficult to achieve a satisfactory focus for visual work simply by adjusting the focuser until the image looks sharpest through an eyepiece. Our eyes can adjust to slight focus offsets or changes in focus with temperature without much difficulty. But for astrophotography or EAA the Critical Focus Zone (CFZ), or distance over which focus is limited by seeing, tube currents, diffraction, can be a fraction of a mm and a camera cannot adjust for deviations from this like the human eye. The CFZ is defined by equation below and depends upon the focal ratio of the telescope and the wavelength of light observed: CFZ = 4.88 x (f-Ratio) ^2 x L where the CFZ is given in microns and L is the wavelength of light in microns. Since L doesn't change much over the range of wavelengths we observe (~0.4 to 0.6 microns) we can use the wavelength for green light, 0.5 microns. For a telescope at f/10 we have: CFZ = 4.88 x (10)^2 x 0.5 = 244 microns while for f/2 (for example using Hyperstar on a SCT) we have: CFZ = 4.88 x (2)^2 x 0.5 ~ 10 microns As you can see, the CFZ is not only very small (244 microns = 0.244mm), it reduces dramatically with focal length because the light cone becomes much steeper at shorter focal lengths thereby compressing the distance over which focus can be achieved. You can see how challenging achieving a sharp focus can be at very short focal lengths. This is why focusing aids are critically important for EAA and astrophotography. Rough Focus While focusing by eye is not sufficient for EAA it is at least good enough for an initial rough focus. To make life easier in the dark it is a good idea to focus during the day time using a distant object like a power pole or tree. This can save a lot of frustration later since one can be centered on a star but not even know it because the light from a badly out of focus star is spread out so much as to be nearly invisible. If like me you do not have sufficient line of sight from your backyard to a distant object for focusing you can use the craters on the moon to obtain the sharpest possible image. If the moon is not visible but Jupiter or Saturn are, another good method is to adjust the focuser until the planet's moons become visible. But this method will have to wait until the sky is dark. Likewise, rough focusing at night can be achieved by observing a star cluster and adjusting the focuser until the number of stars in is maximized. To simplify the process for future nights, make a note of the number of turns from full clockwise or full counter clockwise rotation of the focuser needed to achieve focus. Do this for each optical configuration such as at each focal ratio for your telescope. This way, you will only need to do this once and will be able to quickly achieve rough focus with your telescope in any optical configuration at night without wasting time or getting frustrated. ![]() Mechanical Focus Aids To achieve the best possible focus, one or more focusing aids are necessary. The most common and simplest is a focus mask. Focus masks of one form or another have been around for quite some time. In 2005 Pavel Bahtinov invented what has become the premier and most widely used focusing mask. This mask consists of a set of three grids etched into a thin plastic sheet which, when placed in front of the entrance to the optical tube, creates a diffraction pattern from the light passing through it. The diffraction pattern consists of an "X" with a vertical line passing through the "X". Precise focus is achieved by adjusting the focuser until the vertical line bisects the "X". The vertical line will move left or right of the center of the "X" as the focuser is moved in and out of focus. A point source such as a star is required to create the diffraction pattern. Use a bright star and/or an exposure of 1-2 seconds to obtain a bright and large diffraction pattern for greater sensitivity. Also, use the camera's zoom feature to magnify the diffraction pattern to achieve the best sensitivity. Bahtinov masks are readily available in sizes to fit most telescope apertures and even come with a center cut-out to accommodate the secondary mirror on an SCT. Many make their own Bahtinov masks as I did meticulously cutting out the pattern in a piece of cardboard for my 14" SCT when I could not find a ready made one at that size. A thin but rigid plastic sheet is a better choice, but my cardboard Bahtinov mask lasted many years until I sold the 14" SCT. Most telescope focusers have a rough and fine focus knob to help achieve a sharp focus. If the focuser that comes with your telescope does not have a fine focus it may not have sufficient sensitivity to achieve the desired sharp images and may need to be replaced with an after market focuser. This is especially true for SCTs which do not have a fine focusing control. There are a number of manual fine focus replacements from companies like Starlight Instruments which are made specifically for SCTs. Also, JMI sells motorized focusers for SCTs which can be controlled by a hand control or via a computer. Both Celestron and Meade provide motorized focusers with fine adjustment control which can help to achieve sharp focus. ![]() Automated Focusing Since EAA entails the use of a camera and, most likely, software to operate the camera, automated focusing is an excellent way to go. There are many different software available for automated focusing either as a stand along function or as a utility in a larger software suite. FocusMax is a stand alone software which automatically adjusts the focuser on both sides of focus to obtain a V-Curve from two intersecting lines which define a precise focus where the lines intersect. FocusMax uses the Half-Flux Diameter (HFD) to determine the best focus position. The HFD is defined as the diameter of the circle containing half of the star light (flux), which is spread out due to the Gaussian nature of starlight caused by seeing. The smaller the HFD the better the focus and the better the seeing. Since FocusMax connects to and automatically adjusts the focuser, an electronic focuser which can be recognized and controlled by the software is required. A manual focuser will not work in this case. @Focus3 is an excellent focusing utility in The Sky X software. Like FocusMax it requires an electronic focuser which is connected to The Sky X software and @Focus3. It uses the Full Width at Half-Maximum to determine the best focus position. Much like FocusMax, @Focus3 adjusts the focuser on both sides of focus to generate a curve of light intensity versus focuser position. But instead of a V-Curve it produces a bell-shaped curve. Measurement of the width of the curve at half the maximum height defines the FWHM which is then used to find the peak of the curve for the best focus point. Many EAA'ers use SharpCap for real time viewing, live stacking and on the fly processing. SharpCap offers 6 different focus utilities. There are 3 different utilities for deep sky objects, two of which use the FWHM metric to define the best focus. One uses measures the FWHM on a single star and the second obtains an average FWHM on multiple stars in the field of view. The third deep sky focus utility requires a Bahtinov mask and determines the best focus at the point where all three lines created by the diffraction pattern intersect. SharpCap generates a focus score for each focusing utility with the best score giving the best focus. There are also 3 different focusing utilities optimized specifically for planetary viewing which derive scores using measurements of contrast or detail in the image to generate a focus score. SharpCap's focusing utilities can be used with a manual focuser or with an electronic focuser controlled by SharpCap. In either case, the observer adjusts the focuser either by hand or through the SharpCap software. Unlike FocusMax and @Focus3, the process is not completely automated but still works quite well. Thermal Effects As the night air cools, the telescope tube will shrink causing the telescope to go out of focus over time. This is especially true for an Al tube compared to a graphite tube. For this reason it is important to refocus throughout the night. One technique is just to refocus at a fixed time interval such as every 30 minutes which can be done manually or automatically if the right software is used. A more sophisticated method is to use a temperature sensor connected to software to automatically refocus for every half a degree change. Summary Achieving the best possible focus need not be difficult nor expensive. For those wanting simplicity a Bahtinov mask is the way to go. For those wanting automation there are many electronic focusers with compatible software which can make the process practically invisible to the user. Obtaining and maintaining a sharp focus throughout a viewing session will insure the best possible images and the most detail limited primarily by the seeing conditions. ![]() Whether you are doing astrophotography, Electronically Assisted Astronomy or traditional visual observations it is important to understand the difference between a Polar Alignment (PA) and a GoTo Alignment and how to correctly perform each. PA requires aligning the right ascension (RA) axis of the mount to the north celestial pole. This keeps a star or other target centered in the field of view as the earth rotates on its axis. Since Alt-Az mounts have Altitude and Azimuth axes instead of RA and declination (Dec) axes, a PA is not possible with an Alt-Az mount. On the other hand, both EQ and Alt-Az mounts can be GoTo aligned. The GoTo alignment creates a model of the sky so that the mount can slew to, i.e. "GoTo", objects on command and put them within the field of view every time. This makes it much easier and faster to find objects, especially at high magnification. GoTo Alignment A GoTo Alignment requires providing the mount with enough information to build a model of the night sky. Every motorized GoTo mount will have its own alignment routine but the basic principle and inputs are the same. Inputs include accurate information on the date, time and geographic latitude and longitude to start. Next, the telescope will need to be roughly Polar Aligned by leveling the mount and pointing it's RA axis as accurately as possible toward the north celestial pole using a compass or Polaris as described in the PA section below. Using the hand control (or software emulation) you will need to slew to 1 or more stars or solar system objects, center them in the field of view of an eyepiece or camera with the hand control and then confirm that when each is centered. The mount uses the RA and Dec data for these objects, along with the date, time and location to generate a sky model. The concept is simple and the process is straight forward and only varies slightly from mount vendor to vendor For example, Celestron's GoTo mounts offer several different alignment options. The Solar System Align option simply requires that the mount be slewed to a visible solar system object like the Sun, Moon or a planet. Once the slew has been completed, the hand control is used to center the object in the field of view and then confirmed with the hand control. A Solar System Align is useful when one wants to do the alignment during daylight, but is not as accurate as a multi-object alignment. A One Star Alignment is similar except a star instead of a solar system object is used which is more accurate than aligning on the Sun or the Moon since a star is a pinpoint object which provides a higher a degree of accuracy when centering it in the field of view. A still more accurate alignment is obtained by using the Two Star procedure which is identical to the One Star alignment except that two stars are used instead of one. At the end of the Two Star alignment, the hand control will ask if you want to add one to four calibration stars. The calibration stars compensate for any offset of the telescope's axis to the mounts declination axis. The Two Star + Four Calibration Stars will provide the best GoTo model and has the greatest chance of putting objects in the center of the field of view at higher powers than the other methods. It simply adds 4 more stars on the other side of the meridian to center in the field of view. Other mount manufacturer's like Meade and Synta (Sirius, Atlas) use an identical procedure with One, Two, or more stars for alignment but do not add the Calibration Star correction. Since the GoTo alignment will be disturbed if you need to adjust the mechanical axes of the mount for the PA procedure discussed below, the GoTo alignment will most likely need to be repeated after the PA. So why not do the PA first and then the GoTo alignment. Because having a basic GoTo alignment prior to the PA is helpful so that the mount will slew to the star being used during the PA process. Unless you have a good handle on the names of the stars, you might not be able to locate the PA star easily, especially at a dark site, if the mount does not put it close to the field of view. Therefore, do the simplest possible GoTo alignment before the PA and then come back with the 2 + 4 star alignment after if using a Celestron EQ mount. ![]() The GoTo alignment procedure for an Alt-Az mount is pretty much the same using as few as 1 star and as many as 3 stars for a more accurate alignment. Some Alt-Az alignment routines do not even require that you know the names of the stars. For instance, Celestron's Sky Align routine only requires that you slew to 3 bright objects (stars and or planets) in the sky one at a time and center them in the field of view. The 3 objects should be chosen to be as far apart as possible to provide greater precision. Once completed, the mount build the sky model and let you know the names of the 3 objects you chose. This is very convenient if you are not yet familiar with the stars in the sky. There are other routines where the mount provides a list of stars for you to pick the ones to slew to, allowing alignment with only 1 or 2 stars. Meade's AudioStar alignment procedure requires that the telescope be set to the "home" position first with it pointed north with the optical tube level. Some higher end Meade telescopes can automatically find north and the home position. AudioStar then slews to two of the brightest stars in each location so that it is easy for you to find them and center them in the field of view. There are also hardware solutions like Celestron's Star Sense AutoAlign, which can both automate and speed up the GoTo alignment process. Star Sense works only with Celestron mounts and contains a small camera and software. First time setup requires attaching it to the mount and aligning its axis to the telescope's optical axis. Star Sense then connects to the mount and slews to different parts of the sky taking images which it plate solves to determine the RA and Dec of each image. From this information it is able to build a GoTo model of the sky. ![]() If you use The Sky X (TSX) from Software Bisque you will have access to a separate software algorithm called T-Point which generates one of the most accurate GoTo models and uses a process that is easily automated. T-Point requires a minimum of 6 points and can handle a maximum of 500 points. T-Point can be run manually by using the hand control to slew to and center each star one by one and confirming such to the software. If using a camera it is better to use the automatic mode. In this case, a map is first generated of the points to be used which should be distributed across the night sky While T-Point requires a minimum of 6 points, most will use 30 or more points for greater accuracy. Once the points have been generated, TSX will automatically slew to one point after another, take an image, and plate solve the image to determine the exact RA and Dec at the center of the image. Once all the points have been collected, regardless of whether this is done manually or automatically, a multi-parameter model of the night sky is generated and the mount is ready to put objects close to the center of the field of view every time. Obviously this process will take longer than doing an alignment with 1 to 6 points, but the automated process can do as many as 60+ points in 20 to 30min and the resulting model will be a much more precise GoTo model. Unlike the other GoTo procedures, the T-Point alignment does not need to be repeated after using T-Points PA procedure. Polar Alignment During a PA the right ascension (RA) axis of a telescope mount is aligned with the rotation axis of the earth so that a celestial object in the field of view will stay centered over time. Without a PA, the object will drift across the field of view. This is not generally a problem for a visual observer but for those doing astrophotography it will cause stars to become elongated in an exposure of only a few tens of seconds. The better the PA achieved, the longer the unguided exposure possible to maintain pin point stars in the image. This of course, also depends upon the quality of the mechanics in the mount being used which is why it is often said that the mount is the most critical component in the astrophotography setup. For EAA with live stacking, things are more relaxed, but it is still true that the better the PA the longer the exposure possible and the longer one can stack images before field rotation becomes an issue. There are many different ways to achieve a PA, some software based and others hardware based. Let's review some of these. Rough Polar Alignment A rough PA is good enough for visual work but not for EAA and astrophotography. However, it is a necessary starting point for both an accurate GoTo and PA. First, point the mount in the direction of north and level it. Do this without the telescope attached so that it is much easier to make the necessary mechanical adjustments especially if using a heavy telescope. It is not necessary to have the mount perfectly level, but the more accurately you level it the easier the rest of the procedure will be. Use a compass to find north but be careful to stand back away from the mount since the metal in the mount will affect the accuracy of the compass. Also, be aware that magnetic north (where the compass needle points) is not the same as true north (Earth's north pole). You will need to offset the position of the mount by the local magnetic declination of your location which you can look up here. For example, the magnetic declination of Adin, CA, where the Golden State Star Party is held, is 13deg 43min East (positive), which means that true north is 13deg and 43min East of where the compass needle points. It is helpful to make certain that the Azimuth adjustment is centered leaving you plenty of room to make an adjustment to the east or west as needed during the fine tuning of the Azimuth during the accurate PA step later. Next use the Altitude adjustment bolts to raise or lower the mount's altitude to match your latitude. Now mount your telescope. If your telescope has the option of using a Polar Scope you can get a more accurate rough PA by sighting through the Polar Scope and adjusting the Alt. and Az. mechanical bolts until Polaris is positioned in the field of view according to a mobile application like this one which will show where Polaris should appear in the reticle depending upon the time and your location. However, a Polar Scope will not give a good enough PA to avoid the accurate PA process so many just skip this complication and move from the rough mechanical alignment to the accurate PA. Accurate Polar Alignment The rough PA needs to be followed by one of the following procedures to obtain an accurate PA. Drift Alignment The drift alignment method is considered the gold standard for PA because it measures the actual drift of a star over time. This allows one to make continual adjustments until the drift has been reduced to a level which will not cause noticeable drift during an exposure. First locate a star close to the celestial equator and the meridian and center it in the cross hair of an illuminated reticle or the center of a camera image. The closer the star is to this location the greater the sensitivity but it is ok if a convenient star is off in RA by a bit. Next, observe the star for a length of time approximately 5X as long as your longest expected exposure and watch to see which direction the star drifts. If it drifts north, adjust the Azimuth axis so that it points more to the east. If it drifts south, adjust the Azimuth axis so that it points more to the west. You tell determine which way is north or south ahead of time by moving the telescope to the south and watch the stars move which will be to the north. Ignore any drift of the star to the east or west for now. Repeat this process until you have reduced the drift to a negligible amount. Now locate a star near the celestial equator and on the eastern or western horizon about 20 to 30 degrees of altitude. Center it in the field of view and watch for drift over the same 5X time period. If it drifts north, lower the mount's altitude. If it drifts south, raise the mounts altitude. Repeat the process until the drift is negligible. The drift alignment method is tedious and time consuming when first mastering the process but it gives direct visual feedback on the PA achieved. There are many tutorials on line which explain the drift alignment method in detail. There are also many software applications which are designed to simplify the drift alignment method, such as PHD2 's drift alignment tool. T-Point If you use The Sky X (TSX) you will have access to a separate software algorithm called T-Point which simultaneously performs a PA and a GoTo alignment. The first part of the procedure which generates a GoTo model has been described above. Once this has been completed, the next step is to begin the accurate PA routine. TSX provides a list of stars for you to choose one. Once chosen the mount slews to the star and you center it in the FOV with the hand control. Then TSX moves the mount to where the star should be if accurately PA. Next you re-center the star using only the manual controls for Azimuth and Altitude. Once completed, TSX takes into account the adjustments made and adjusts the GoTo model so that it does not have to be repeated. Celestron's All Star Polar Align Celestron has a PA routine called All Star Polar Align which does not require the ability to see Polaris. In fact, like the drift alignment method, greater PA sensitivity is achieved by picking a star near the intersection of the celestial equator and the meridian. The process will be easier if a GoTo alignment has been performed first so that the mount is more likely to put the star in the field of view. It is a good idea to have a finder, either unity of 50X, to help locate and center the star if it is not in the field of view. After the slew the star should be centered at high power and then verified with the hand control. The mount will then slew to the position where the star should be if accurately polar aligned. Next, using only the mechanical adjustments for Azimuth and Altitude, re-center the star in the field of view and confirm with the hand control. The mount will now be PA. It will be necessary to re-do the GoTo alignment since the mount has been adjusted from its position during the original GoTo alignment. ![]() SharpCap Many people find the Polar Alignment routine in SharpCap software to be easy, fast and accurate. It works by taking two pictures, one around the pole and the other with the RA axis rotated 90 degrees. SharpCap then plate solves both images and determines the position of the celestial pole and the center of rotation of the RA axis. SharpCap will show how far off the PA is in degrees/minutes/seconds and give directions for which way to adjust the RA and Altitude axes. The process is repetitive until the user has decided that the offset from the celestial pole is at a minimum. You will need the pay version of SharpCap for the PA routine but the cost is rather minimal. QHY's Pole Master QHY has a hardware solution for accurate PA which, like Celestron's Star Sense, attaches to your mount and has a camera and software. QHY's Pole Master connects to you computer and takes an image of the sky around Polaris. It plate solves and then requires that the mount be rotated by ~15 degrees with the hand control and takes another image from which it determines the axis of rotation. Fromm this it will determine the adjustments you need to make in the Az and Atl mechanical knobs. So the methodology is the same as with Sharpcap except it uses a separate hardware device. Summary
So it should be clear by now that a GoTo and a Polar Alignment are not the same. You can have one but not the other such as with an Alt-Az mount. If you are using an EQ mount you will want to make sure that you perform both alignments so that you can quickly locate objects and then track them over the length of you chosen exposure without objectionable star trailing. For the beginner, these may sound daunting, but with a little practice over a couple of nights under the stars, both methods will become second nature. OPT links are Affiliate links from which I can earn commissions on purchases. |
Categories
All
Archives
October 2024
|