The introduction by ZWO of their camera, the ASI1600, in early 2016 has been a game changer for Camera Assisted Viewing (CAV), also known as Electronically Assisted Astronomy (EAA) or Near Real Time Viewing. This camera was the first astronomy camera to use Panasonic's latest CMOS sensor, the MN34230. The 4/3 format sensor has 16.3 Megapixels (4644 x 3506), each 3.8 microns square with a total chip size of 17.6 x 13.3mm. The larger chip size has a diagonal of 22mm which provides a much larger field of view compared to the cameras commonly used for CAV . Compare this to the analog cameras from Mallincam which have less than 0.5 Megapixels and diagonals of only 6 and 8mm depending upon the camera model. Even the recent CMOS cameras like the ASI224 only has 1.2 Megapixels and a diagonal of 6mm, much smaller than the ASI1600.
And with 3.8 x 3.8 micron pixels it provides high resolution images for excellent image detail. Additionally, this sensor supports extremely low read-out noise on the order of 1 electron which made stacking many very short exposures much more practical. This reduces the demand on the quality of the polar alignment and the mount tracking for a successful CAV session. With such a large sensor and 16 million pixels, this chip supports binning 1x1, 2x2, 3x3 and 4x4 which trades resolution for sensitivity by making the "effective" pixel size larger. This is also useful in tailoring the image scale (arc-sec/pixel) to different optical setups.
Panasonic's new sensor was quickly incorporated into new cameras from ZWO, QHY, Mallincam and others and soon took the CAV community by storm making these the new hot cameras to have. ZWO was the first to incorporate this sensor into its ASI1600 camera which came in both uncooled Color ($699) and Monochrome ($899) versions. The uncooled color camera is now discontinued, but still can be obtained on the used market. They later came out with a cooled Monochrome version ($1280) called the Pro with 2 stage cooling down to -40deg, a 256MB DDR3 memory buffer to help avoid lost frames during high rate data transfers, a USB3.0 port and a USB2.0 Hub to connect accessories such as a filter wheel, guider and a focuser. The camera also has an autoguider port in case you want to use it as a guide camera.
QHY and Mallincam soon followed with similar cameras of their own incorporating this new Panasonic sensor. The QHY163 comes in color ($899) and monochrome ($1199) versions and also includes 128MB of DDR memory, a USB 3.0 interface, guide port, two stage cooling to -40C cooling and a sealed chamber with a heated window to prevent dew from building up. Mallincam's SkyRaider DS16 comes in 3 versions, color ($999), monochrome ($1299), both with a fan for passive cooling and TEC version ($1700 color, $1900 monochrome) with active cooling. They all have a USB 3 interface, a sealed chamber, DDR memory and a full featured software, Mallincamsky, for camera control, capture, live stacking and dark frame subtraction. The TEC version includes a USB Hub and a heated window for dew prevention. Both the ZWO and QHY cameras use the free software Sharpcap which performs all of the same functions as Mallincamsky and much more if you pay for the Pro version, but that is a topic for another blog.
There are still more versions of cameras incorporating the Panasonic 4/3 chip, but I will not list all of them here.
These new cameras appear to have had two major impacts on the way we do real time viewing.
First, if you read the threads on the Cloudy Nights forum, you will see that many amateur astronomers have moved away from the long exposures of 30 sec to minutes common with the security type astronomy cameras like the Mallincam Xtreme and Xterminator or the Revolution Imagers 1 and 2. With such low read-noise it is now practical to use programs like Sharpcap to stack many very short exposures of a few seconds on the fly to get as good or better image after 30sec to minutes but with less demand on the quality of the mount and the polar alignment. In fact, Alt-Az mounts become even more practical for CAV with such short exposures and the use of an on-the-fly stacking program. This can both minimize the cost of the setup and reduce the overall hassle in getting a good polar alignment. Obviously, a better mount and more time spent on a good polar alignment will improve the experience, but less so with exposures of 2 to 5 sec which is now practical with this new sensor.
Second, since the pixels are square not rectangular stars are round unlike their appearance with CCD analog cameras and they do not have the black halo common to stars in images taken with analog cameras. Also, with pixels about 1/3 the size of the pixels in analog cameras much more detail can be seen in galaxies and nebular with the new sensor. Images obtained are of much higher quality than ever before. The net result appears to be a move by many CAV folks more and more in the direction of traditional astrophotography. It has become increasingly the case that dark frame subtraction and even flat frames are both employed with on-the-fly stacking to get the best possible image. The ideal case is to be able to view the image in real time to get the immediate enjoyment of observing deep sky objects, while saving individual frames for later post processing to obtain an astrophotography quality image. In fact this can be done with Sharpcap using the Live Stacking feature while selecting the option to save individual frames in FITs or PNG format for later post processing.
As is always the case, time marches on and even newer products come to market. It appears that the successor to the ASI1600 is the ASI294 with the Sony IMX294 CMOS chip. It too is a 4/3 sensor with extremely low read noise. Even thought it has less pixels at 11.7 Megapixels, the major new advantage of the ASI294 is it's much deeper well which provides a significant advantage for dynamic range. Perhaps a topic for a later blog.
Until recently the only way to view deep sky objects in real time with the assistance of a camera was with one of the many analog cameras like those from Stellacam, Mallincam, Altair Astro, Samsung and a few others. These security cameras re-purposed for astronomy have very sensitive CCDs which can collect enough light in a few seconds to a few tens of seconds to provide stunning views of a wealth of deep sky objects. Some of these cameras have been modified to provide improved astronomical performance. These may include extended exposure, reduced amp glow, sensor cooling, remote control and more, while other cameras like the Samsungs have no astronomy modifications at all. In either case, they provide the user with many important advantages over the traditional view through an eye piece such as:
Since these are analog cameras, they provide a video signal which can be viewed directly on any video monitor, LCD or television with a video (RCA) input. All that is needed is the appropriate cable and connector. Images can also viewed on a computer if the video signal is connected to the computer through a video capture device like the Pinnacle Dazzle or EzCap. Using a computer has the added advantage of allowing the user to capture images, as well as, utilize fancy software programs to stack frames on the fly, remove hot/warm pixels with dark frame subtraction and perform other miraculous feats to greatly improve the detail in the image being viewed live.
Somewhere around 2009, people discovered that the Starlight Xpress Lodestar guide camera was actually a very good camera for viewing deep sky objects in real time. This camera uses the PAL version of the same very sensitive CCD sensor as the Mallincam Xterminator, the Sony ICX829. While the Xterminator is another analog camera, the Lodestar is a digital camera with a USB output which can be connected directly to a computer without a video capture device. And, unlike the analog cameras which need separate cables for power, signal and control, this digital camera uses the single USB cable for all three functions. On the other hand, since the output is digital it cannot be connected directly to an LCD or other analog display device and needs a computer to control the camera and view its output. The Lodestar is controlled with Paul Shears software, Lodestar Live (now called Starlight Live) which also provides the ability to view, capture, stack and stretch images live while watching them improve in depth and detail. Despite these capabilities, most real time viewers seemed happy to continue to embrace their analog cameras including several newer and better cameras like the aforementioned Mallincam Xterminator, the LnTech300 ( also sold as the Revolution Imager 1) and the Revolution Imager 2.
Then, in 2015 a company in China called ZWO introduced an astronomy camera with a CMOS sensor, the Sony IMX224. Their ASI224, like the Lodestar, is a digital camera but with much higher resolution than the Lodestar and all of the analog cameras while maintaining very good sensitivity. The ASI224 is controlled with a software program called Sharpcap, which has all the same features as Starlight Live and more. Even though the ASI224 has a small sensor, 1/3", it has 1.27 Mega pixels, more than double the Lodestar and all astronomical analog cameras. And, its square 3.75 micron pixels are less than half the size of the typical analog camera pixels which provides more detail and more realistic looking stars, i.e. round instead of square. In addition, the read out noise of the ASI224 is so low as to make it much more practical to perform live stacking of many very short exposures (2 to 5 sec) with a program like Sharpcap. This minimizes the demands on mount alignment and makes it more practical to use Alt-Az mounts for real time deep sky viewing. The relatively inexpensive ASI224 (originally $350) fast became a favorite of many who had been using the analog camera and soon other manufacturers like Mallincam, QHY, Rising Tech, Orange County Telescopes, Altair Astro came up with their own versions of cameras with the Sony IMX224 CMOS sensor.
Within just a few months, two other digital astronomy cameras for real time viewing became available. One is the well regarded camera from Atik named the Infinity. This camera uses the Sony ICX825 CCD sensor with 1.4 Mega pixels which are slightly larger at 6.45 microns than the IMX224. This is also a 2/3" sensor which provides a much larger FOV at 11mm diagonal compared to the ASI224 at 6mm. It comes with the highly acclaimed Infinity software with all of the same great features for live viewing as the Lodestar software. In fact, the Infinity was the first ATIK camera marketed as a "video camera". Even with a substantial price tag of $1000, the Infinity became very popular particularly as it is noted for its ease of use, especially for beginners.
Around the same time StarLight Xpress came out with their own camera using the ICX825 sensor called the Ultrastar which uses the Starlight Live software just like the Lodestar. And it was not long till Mallincam came out with their version of an ICX825 camera called the StarVision. While the Infinity, Ultrastar and StarVision use CCD sensors as opposed to a CMOS sensor like the ASI224, they all are digital cameras with a single USB output. With these cameras widely available in late 2015 or early 2016, one could say that the floodgates were suddenly opened to digital cameras for real time astronomy.
Not to be outdone, ZWO came out with another digital camera in the spring of 2016, the ASI1600 camera utilizing the Panasonic 4/3" CMOS sensor with 16 Mega pixels. This was a quantum leap in field of view compared to the 1/3" IMX224. The ASI1600 came in color, B&W, cooled and uncooled versions. Atik followed with their own version of this sensor called the Horizon. Both cameras have extremely low read noise, making them ideal for stacking of very short exposures. It was not long before Mallincam also came out with a camera, the DSC16, which uses the Panasonic 16Mega pixel sensor. Camera manufacturers try to differentiate themselves from the pack using identical sensors by providing unique mechanical form factors, added internal memory, different methods of cooling and different software. More recently, ZWO (ASI294) and Mallincam (DS10c) have come out with digital cameras for camera assisted viewing using the latest Sony 4/3" format IMX294 sensor. The IMX294 is a CMOS sensor with 11.7 Mega pixels and very good light sensitivity.
Judging from the posts on the Cloudy Nights "EAA Observation and Equipment" forum, digital cameras are now the new norm for camera assisted viewing. This is not to say that analog cameras are long gone, but do not expect new models to be introduced as all of the manufacturers appear to have shifted to digital cameras. Analog cameras will still have their place so long as they are available new or used, but it is clear that the digital wave has taken the forefront.
Just what is live stacking? Live stacking is the process of averaging successive frames of an object such as a galaxy, nebula, star cluster, etc. to improve the signal to noise ratio (SNR) while watching the stacked image quality improve right before your eyes in real time. Live stacking has become a common technique employed by amateur astronomers engaged in deep sky video astronomy (also called Electronically Assisted Astronomy, Near Real Time Viewing, Camera Assisted Viewing, etc.). The SNR is improved because noise is random and signal is fixed. So, for a given pixel within the sensor, noise varies from frame to frame randomly while the signal remains fairly constant. Therefore, when multiple frames are averaged together, the noise mostly cancels out while the signal remains relatively constant. Thus, the SNR goes up and the image shows more detail and the background sky has a smoother, more uniform appearance rather than the grainy appearance usual in a single frame. In other words, the image looks a lot better. The more frames averaged the better the image appears, up to a point.
There are two kinds of live stacking used: 1) in-camera stacking; 2) stacking with a computer and specialized software program. Let's discuss these one at at time.
In-camera stacking is available on some of the more recent analog video cameras but not on any of the digital cameras like the many CMOS cameras that have become available in the last few years. Analog cameras like the Revolution Imagers 1 & 2 (RI1 and RI2), Mallincam Micro and the LnTech 300 can do live stacking internally without the need for a computer. All of these cameras are security cameras which are used for astronomy, but are not purpose built for astronomy. In low light conditions the camera images can have a very grainy appearance making it hard to distinguish features such as license plates and people, which also means less ability to make out details in faint nebulae and galaxies. Security camera manufacturers combat this problem with Digital Noise Reduction (DNR). There are two types of noise reduction, 2D-DNR and 3D-DNR. With 2D-DNR the camera has an algorithm to compare the signal at each pixel relative to the signal at the same pixel in successive frames to identify and reduce noise by averaging the signals for each pixel frame to frame. 2D-DNR is a temporal noise reduction method since it looks at the time averaged variations. The drawback to 2D-DNR is the potential to blur images for moving objects. Such would not be a problem for astronomical use cases, but, once again, these cameras were created for video surveillance applications and are only being adapted to astronomy applications. To eliminate blur another DNR algorithm called 3D-DNR was developed. 3D-DNR combines the temporal noise reduction from frame to frame of 2D-DNR with spatial noise reduction within a frame by examining and comparing the signal at neighboring pixels to further reduce the overall noise within an image. 3D-DNR is more effective in reducing noise and improving image clarity and detail than 2D-DNR.
The DNR feature within the camera menu allows one to turn this type of noise reduction on or off. The RI1, Micro and LnTech 300 cameras use 3D-DNR while the RI2 does not specify either 2D or 3D. I would assume that it is also 3D since it is the newest of the cameras. When turned on, the user specifies the number of frames to average from 1 to 5 (RI1, Micro, LnTech 300) or 6 (RI2). When DNR is off, the camera does no averaging and what you see on your monitor is just a single frame exposure.
So, as an example, let's assume that DNR is turned on with frame averaging set to 4 frames. And, let's assume that the exposure is set to 5 sec. After 5 seconds, the camera has captured its first frame which it sends to a buffer and outputs this same frame to an attached video monitor at a rate of 60 (NTSC) or 50 (PAL) frames per second. We see the same image until the next 5 sec exposure is finished. At that point, the camera performs the DNR algorithm on the 1st and 2nd frames and stores the result, an average of both frames, in the camera buffer and simultaneously outputs this to the monitor. When this happens, we will see an improvement in the image quality. This processes is repeated for the 3rd frame, this time the image we see is an average of 3 frames and once again with the 4th frame. The image quality continues to improve after each frame until we reach the end of the 4th frame. If the camera is allowed to continue to run with no changes in exposure or DNR settings, the 1st exposure will be discarded and the 5th exposure will be averaged with the 2nd, 3rd and 4th exposure and placed in the camera buffer as well as out put to the monitor. This image averaged over 4, 5 sec frames has taken 20 sec to complete. In general, once the maximum number of frames has been reached, 4 in this example, the image will not get any better. However, if for instance a satellite trail passes through the field of view during one of the frames, it will be eliminated once 4 new frames have been taken after the passing of the satellite. This averaging process will continue with each new frame replacing the oldest frame in the sequence until the exposure is stopped.
In-camera stacking is a simple and convenient way to greatly improve the image you see on your monitor without a computer and additional software. And since the camera is continuously outputting frames you get to watch the image improve live. However, in-camera stacking has two limitations. First, it will only support 5 or 6 frame averaging depending upon which camera is used. This greatly limits the amount of improvement to be had since there are many very faint objects that would benefit from averaging over many additional frames. Second, the camera does not make any allowance for the object to drift within the field of view from frame to frame. In other words, there is no alignment of the frames being stacked as the camera algorithm assumes the image does not move. This is fine for surveillance applications, but for astronomical use cases objects can drift within the field of view if the telescope is not perfectly aligned with the polar axis, or one is using an Alt-Az mount. In this case, stars can tend to become elongated as the successive frames are averaged. It all depends upon the exposure time, number of frames selected for DNR and the mount type and setup. For instance, the maximum exposure of the Revolution Imager 1 is 20.48sec and the maximum DNR setting is 5, so this would mean the object would have to remain fixed in the field of view for 102.4sec. If one was using an Alt-Az mount it is virtually certain that the stars will appear elongated and not round. For the Revolution Imager 2, the maximum exposure is 5.12sec and the maximum DNR setting is 6, so the maximum total exposure would be about 31sec which would probably not show appreciable star trailing even with an Alt-Az mount.
Stacking with a Computer
Now, lets suppose you want to use a computer and software to do live stacking. One advantage of this method is the fact that you can stack as many frames as you like to bring even more detail and sharpness to the image. Another advantage is that the software aligns each successive frame to the first which can avoid star trailing for stacks of 10min or more without guiding when using a polar aligned EQ mount. The maximum time without star trailing depends on the quality of the polar alignment and the mount capability. In addition to stacking frames, most software also allows one or more of the following: dark frame subtraction: flat frames; and a histogram to stretch the stacked image. Computer stacking is a necessity for all of the digital cameras since none of them has the capability to do in-camera stacking. Examples of these are the USB cameras from ATIK (Infinity), ZWO (ASI224/1600/294, etc.), QHY (Horizon), Mallincam (SkyRaider) and Starlight Xpress (Lodestar, Ultrastar). Computer stacking can also be used with analog cameras even if they have their own internal stacking function. In the later case, it is best to turn off in camera stacking if you are using computer stacking.
Computer stacking is a little different with a digital camera compared to an analog camera since a digital camera only outputs an image when an exposure is complete, whereas, an analog camera outputs an image at 60 or 50 frames/sec. Lets discuss stacking with a digital camera first.
With a digital camera the output USB cable is connected to the USB port on the computer. This allows the software to control the camera functions like exposure, gain, cooling etc., preview an image, capture an image and perform live stacking. Some software works natively with certain cameras which means that the software will simply recognize the camera and provide control for all of it's functions. This is true for Sharpcap and the ZWO, Altair Astro, QHY, Starlight Xpress and a few other cameras. The Starlight Xpress Lodestar and Ultrastar cameras also work natively with Lodestar Live, while the Atik Infinity camera works natively with the Infinity software, and the Mallincam SkyRaider cameras with the MallincamSky software. If the software does not natively support one of the cameras, it likely will support the camera through an ASCOM driver but may not support every camera function.
Now, as an example of live computer stacking with a USB camera, consider an exposure setting of 5 sec. The camera outputs a new image every 5 sec to the computer. The software aligns each successive image to the first by translating and rotating the images to match. This continues until the user stops the stacking process. So, if stacking is allowed to run for 20 frames, the total stacking time is 5sec/frame x 20 frames = 100 sec. If dark frame subtraction is turned on, the appropriate dark frame from a dark frame library is subtracted from each frame prior to stacking. Similarly, if the software supports flat frames, flat frame scaling takes place on each captured frame prior to stacking. Also, the user has access to a histogram during the stacking process where adjustments to the black and white levels can be made on the fly to improve the detail captured. At the end of the stacking process, the user has the option to save the stacked frame.
Computer stacking with an analog camera is identical to what has just been described except for two things. First, the camera's output must be connected to an video capture device which digitizes the image and outputs that on a USB cable to the computer via its USB input. Second, the analog camera sends out frames at 60 or 50 frames per second regardless of the length of the exposure. So, if the exposure is set to 5sec as before, the camera will output 60 (or 50) frames x 5 sec = 300 frames from the first 5sec exposure before it starts to output a new exposure. All 300 frames will be stacked regardless of the fact that these are essentially identical frames. The computer software has no idea whether the individual frames are identical or not since it does not see the camera but only sees the video capture device and has no idea what the camera exposure time is set to. Thus, for the same 100sec stack, there will be 60 (or 50) frames/sec x 100sec = 6000 frames in the stack. The computer just sees each frame as it arrives and diligently stacks them all. The fact that the analog camera is outputting 60 (or 50) identical frames for each 5sec exposure is not really a problem. In fact, because the signal is analog, it is prone to pick up noise in the interconnecting cable between it and the image capture device which digitizes the frames. This noise will be random so, in fact, the 60 frames/sec are not completely identical and the fact that they are all stacked together further helps to improve the image SNR. An exception to this is the MiloSlick Mallincam Control software which can do all of the live stacking functions described above, but can also be synchronized to the actual exposure time of the analog camera so that it will stack only new frames output at the end of each complete exposure time. This software was designed to work with a variety of Mallincam analog cameras such as the Xtreme, the Xterminator and others.
So, that is how live stacking works for both analog and digital cameras using either in-camera stacking (if available) or stacking with a computer. No matter what method used, live stacking is a powerful tool to greatly improve the quality of the deep sky objects we view in real time.
I must first explain that I have only attended 2 different star parties in my lifetime, Golden State Star Party (GSSP) and CalStar. I have attended both many times over the last 10 years. You can read my August 2016 review of GSSP in the blog archives. Today, I will discuss CalStar since I just returned from another successful and enjoyable event just two weeks ago.
Calstar is a very informal star party which is held at the Lake San Antonio campgrounds in southern Monterey County. What does that mean? It means that there is no registration, no scheduled star party events, no speakers, no vendors, no hospitality tent, no on-site food, etc. But, there are dark skies and great people to share them with. CalStar is sponsored by the San Jose Astronomical Association and the Left Coast Observers (the people who put on GSSP). They decide on a date, post it on the CalStar web site (calstar.observers.org/ ) and people just show up. It's not free, you do have to pay the park camping fee which is around ~ $32/day for dry camping ($27/day for seniors). The star party is held during the new moon, of course, in Sept or early Oct. When the park was closed due to drought recently, the star party was moved to a nearby religious retreat but it is now back at Lake San Antonio. And, starting this year, a spring CalStar was added in April.
I would estimate that Calstar attracts 100 people tops, sometimes less. Set up is in the "Overflow" campground which is a nice name for what once used to be a ball field but is now a dry, dusty open area. This is where most people set up. This is the strict light enforcement area with most visual observers setting up here. The open area provides a clear view of the skies in all directions with nearby hills and trees limiting views only at very low altitudes. The ground is dirt which is typically dust in the fall given the fact that no rain will have fallen for 5 months. There is a band of trees off to the west which provide shade during the day but do not interfere much with sky views.
There is an section just to the east of the ball field which is about twice as large interspersed with open areas, trees and bushes. This is the late arrival, early departure section with less strict light enforcement so the people set up here are fewer and further in between.
There are porta potties and some old beat up but serviceable picnic tables in the overflow campground. There are also spigots with water which must be boiled before use. No open fires are permitted due to the fire danger, but camping on propane stoves set off the ground is ok. The nearby Redondo Vista campground has bathrooms and shower houses. There are also RV pads with power hookups. This time of year the park is not too densely populated so one can use the power outlet at an empty RV site to recharge their batteries during the day. The park also has some cabins for rent down by the lake. Most people dry camp in tents, cars, trucks or RVs in the overflow campground.
There is a gas station and a small store down by the lake. The store has water, ice, propane and a very limited selection of groceries due to the star party being held at the end of the camping season. There is a full service grocery store just 20 minutes west of the park at a shopping plaza called Heritage Park. It also has a gas station, pizza parlor and coffee shop. The pizza parlor is a great place to visit in the afternoon to cool off when it gets hot, have a salad, burger, sandwich or pizza and watch some sports on the TV, sit and talk with friends, work on your image processing or surf the internet. Paso Robles is 34 miles to the southwest of the park which takes about 40 to 45 minutes to get to. It has a Walmart, Target, several supermarkets, gas stations, restaurants and a nice library, a park and a movie theater.
The weather is typically very hot during the day, in the 90s and even reaching 100 degrees. Night time temperatures are usually in the low 50s or 40s, but I have been there when the temperature dropped into the 30s. It has never rained while I have been at CalStar.
You will see jack rabbits, deer and the occasional rattle snake or wild pig in the park. The park has lots of hiking trails and, when the lake is full there is a beach where you can swim in the lake.
The skies are very dark, I measured 19.74 to 20.11 with my SQM over many different trips. There are some small light domes in the direction of Paso Robles and King City, but these are very low in the sky and not much of a problem. The seeing is usually very good with steady skies being that the park is not far from the ocean as the crow flies.
Now that there are two Calstars every year I look forward to the opportunity to have dark skies and good seeing conditions for the different deep sky objects visible in the spring and early fall.
Many people who do video astronomy like the option of keeping things as simple as possible. This is one reason to choose an analog video camera at a time when many are moving to digital video cameras like those from ZWO. The analog cameras do not require a computer unlike the digital cameras. An analog camera only needs a video display device which will accept an analog input. A light weight 7" or 9" LCD will suffice for viewing by 2-3 people. Simply connect a video cable between the camera and the display to view images. The camera can be controlled with the 5 control buttons on its back, or with a hand control if the camera is configured for one.
But what if you want to ditch the video cable and LCD monitor to further simplify the setup? That is quite easily done with a WiFi Emitter and your phone or tablet making the gear requirements including power all that much simpler.
The WiFi Emitter connects to the camera analog video output and is compact and lightweight enough to be attached to the telescope with the accompanying double sided adhesive. It can be powered with the same 12VDC battery used to power the camera further minimizing the number of required cables. If both the WiFi Emitter and battery are attached to the telescope there will be no need for long cables nor any concern about cord wrap or snags on the mount, etc. The WiFi Emitter works with Android and Apple devices, both phones and tablets and is very simple to setup and connect. With this you can view your video images on your cell phone or tablet completely untethered by cables over distances of 150ft or more depending upon intervening obstacles. I was able to connect to my camera in the back yard from inside my house. If you also have WiFi control for the telescope mount, say through Sky Safari or similar, this setup makes for a very comfortable viewing from inside your home.
You can get a WiFi Emitter from Orange County Telescopes (OCT), the home of the Revolution Imager 1 and 2, for $90. If you are more of a DIY person you can obtain one on Amazon for less than $40 if you search for"AV WiFi Emitter". The WiFi emitter comes with 3 short cables hard wired to the unit, a screw on antenna and an instruction book. The one I bought from Amazon also came with double sided tape which I used to attach the emitter to my camera but you could also attach the emitter to your scope instead. It also included plastic cable ties and another power connector in case I wanted to hard wire the power input to a power source. The emitter sold by OCT does not have the tape, cable ties nor the extra power connector but does include an RCA to BNC adapter which is needed to connect the emitter to the camera. If the emitter you purchase does not have this adapter, you can purchase one on Amazon for a couple of dollars.
The emitter has three short cables. The yellow cable connects to the video output of your camera. This cable has a male RCA jack so you will need an RCA to BNC adapter to make this connection. The other two cables are red and are for the power connections from the battery and to the video camera. Connect the power from your battery to the red input connector which has a female DC plug and connect the other red cable with a male DC plug to the power input of your camera. The WiFi unit runs on 9 -30V DC so a simple 12V battery used to power your analog camera will suffice to power it as well.
A one time setup of the required software is necessary to get started. Using you phone or tablet connect to your APP store, simply search "WIFIAV" software and install it. For iPhones and tablets this would be the Apple Store and for Android phones and tablets this would be the Google Play Store. You will see an icon on your phone that looks like the emitter broadcasting a signal from the antenna. This is the app you will need to launch whenever you want to connect wirelessly to the camera.
When you are ready to connect to your camera, turn on the power to your emitter and camera and you should see the Red LED on the emitter light up. Next, push the button on the emitter and you should see the green "Link" LED on your emitter light up. Now go into your phone or tablet settings and connect its WiFi to "WIFIAV". You may need to type in a password the first time you connect which is probably "12345678", and will be included with the instructions which came with the emitter. Launch the WIFIAV app on your phone or tablet and you will see a screen with 6 blue icons at the bottom and an image from your camera if you are already pointed to an object and focused. Or, you may see the camera menu screen if you have enabled that. Shown here is the camera menu for the Revolution Imager 2. At the bottom of the screen are 6 WiFi controls to capture a video, record to a DVD, save an image, check the emitter signal, go to a file folder which contains the saved images and videos, and change settings. If you plan to only view images live you need not use any of these. If you would like to save images to your phone or tablet just click on the camera icon. You can retrieve these using the file folder icon.
You are now ready to view images from your camera remotely. Just move your telescope to the object of interest and adjust the camera settings as you normally would and you are ready to view objects from planets to DSOs wirelessly on your phone or tablet. While this device makes wireless viewing a simple reality, I have to say that the image quality is definitely not as good as what I can see with the video hard wired to an LCD. I believe there is some video compression which occurs in the wifi transmitter which causes this. Nonetheless, this device enables one to step away from the telescope, view effortlessly from inside or walk around at a public outreach event and share images live without having to crowd around the telescope.
What makes a great star party is a broad question that varies from person to person. However, there are some features which most everyone would agree are essential for a great star party. These would include dark skies and good observing weather. Fortunately, the major star party sites are chosen specifically for their dark skies. Some, like the Okie-Tex, Texas and Nebraska star parties are noted for their extremely dark skies. Weather is another factor which weighs heavily in the minds of star party organizers. That is why you will find the majority of major star parties occur during the months of June-September when the weather is warm and snow is a forgotten memory. A key exception is the Winter Star Party held every February in the sunny and warm Florida keys. There are a lot of other things which distinguish one star party from another which I will divide into 6 areas:
1. Observing Conditions
2. Observing Field
3. Typical Weather
4. On Site Facilities
5. Local Area Amenities
6. On Site Activities
Observing conditions include sky darkness, seeing, light domes, 360 degree clear views, altitude, total hours of astronomical twilight, and number of days the star party is held. Star party sites are typically located away from major cities in in order to provide the darkest skies possible. Sometimes, light domes from nearby small towns can limit visibility in certain directions, but this is usually not a major problem. Clear views in all directions will depend upon the star party proximity to nearby mountains/hills and the presence or lack of shade trees onsite. Since most star parties take place in the summer months, there are significantly less hours of darkness compared to the winter months so it is helpful to have many nights over which to take advantage of the dark skies. Aside from weekend star parties, the major star parties are usually held for 5 days or as long as a week which gives plenty of time to enjoy the dark night skies and daytime activities.
Observing Field features include the size of the observing field and camping area, type of field surface (grass, dirt, hard/soft), availability of shade, and grade of the field. Large observing fields are necessary for plenty of room between individuals for tents, shelters, and cars/trucks/RVs. It is also important to have a fairly level surface for both the telescope and for sleeping. While I have never attended the Nebraska Star Party (I do hope some day to attend) the video on their web site shows that they offer a lot of fairly flat open space for observers to spread out and great unobstructed 360 degree views. The two star parties I regularly attend, Golden State Star Party (GSSP) and CalStar, are held on large, flat fields which provide plenty of space. But both are dirt fields which tend to generate lots of dust. When I get home I have to wipe down all my equipment before I bring it back into my house. I look forward some day to attending a star party on grass. GSSP has no trees to obstruct views, but that also means no shade other than what we bring with us. On the other hand, CalStar has trees scattered throughout which help a lot during the day but can limit sky views. It is a good idea to bring a pop up shelter like an EzUp to provide shade during the day. Many people also use a shade cloth like aluminet which they put over the EzUp, a tent, car, etc. to further cut down on the sun's heating. Aluminet can be found on line, for example www.shadeclothstore.com/depts/aluminetshadecloth.html. This allows you to sleep longer in the morning or stay more comfortable in the afternoon sun. Most star parties provide for sleeping and parking next to one's equipment which is a definite advantage, but some do not allow driving on-off the observing field during the day. This limits the ability to drive to surrounding points of interest and stores during the day, or forces one to park their car away from their setup.
It is no accident that most star parties take place over the warm spring and summer months. Still, weather can turn nasty at any time of the year and one needs to be prepared for rain, cold, and wind. The first night I brought my 11 year old son to a star party a thunderstorm rolled in shortly after sunset on our first night. Nevertheless, we had a great time watching a movie on our portable DVD player while staying dry and warm inside our tent. Sometimes a big rain storm will bring exceptional seeing the next night making the wait worthwhile. Wind can be another troublesome visitor especially in the afternoons at some star parties so be sure to tie down tents and shelters well and be careful with big Dob telescopes. Scopes and anything important should always be covered to keep them cool in the hot sun and to protect them from rain and dust. I use a Telegizmos 365 scope cover which works very well to keep the sun and elements off my scopes, but there are other brands which I assume work equally well and many people use a much cheaper option of a tarp with bungee cords. Dew can be a concern at some star parties as well so be prepared with some sort of dew control for your scope.
Star party site facilities may include bathrooms, showers, sleeping facilities, food, water, ice, power and RV hookups. Since many star parties are held at a secluded open field, standard bathroom facilities are not always available. Bathrooms vary from porta potties to camp style brick buildings with sinks and toilets. Showers may or may not be available on site. GSSP rents a shower truck which provides both showers and a place to shave and brush teeth. Some star parties are held at sites which are campgrounds or some other permanent site which may have cabins, bunkhouses, or Yurts for rent. Food can run the range from a dining hall, a food truck, barbecues or nothing at all. If you are preparing your own food at a star party, it is most likely that open campfires are not permitted so propane stoves will be needed for cooking. Water and ice are sometimes available at the star party site but many do not provide one or both of these. There are some very good, but expensive coolers like the Yeti cooler that will keep things cold for many days. The other option is to drive to a nearby town for additional water, ice and other supplies which can be as much as an hour away. Fortunately, a small town general store is only 10 min away from GSSP and they have water, ice, groceries, and a deli counter which is sufficient to resupply for the duration of the star party. When I retire, I hope to purchase an RV which will make camping at star parties much simpler allowing me to concentrate on observing and meeting with fellow astronomers.
Local area amenities include nearby grocery, hardware and electronics stores, restaurants, gas stations, small town libraries, national and state parks, astronomical observatories, historical sites, quaint towns and so on. Because of the need for dark skies, star parties are found in sparsely populated areas with very small towns nearby. Some are so small you would miss them if you blinked while passing through. But this can add to the enjoyment of getting to see things off the beaten path. I have made it a habit to venture out during the day to the nearby towns for the two star parties I regularly attend so that I am aware of what is available in case the need arrives. Some of these are 5-10min away and others are 1 hr away. Nearby grocery stores are great to provide additional water, ice and food as required. If there is a hardware store or Walmart close by they can be helpful for picking up an essential camping item that you forgot to pack or broke. If there are parks nearby, these can provide a nice opportunity to take a hike through forests, near waterfalls, swim in a lake, etc. while cooling off in less hot conditions. When my son was little, we would drive to the closest town, take in a matinee move and have a nice dinner at a local restaurant. It was a good way to get out of the heat, but I admit I almost fell asleep a couple of times during the movie. If a nearby town has a local library, it can be a place to go and cool off while checking in on the internet.
The overall experience of a star party is further shaped by the on site activities at the star party. These can include guest speakers, equipment vendors, swap meets, workshops, contests, raffles, barbecues, public nights, equipment walk abouts, organized tours, etc. Most star parties will have several of these activities available. The Stellafane Star Party in Vermont is famous for it's fantastic telescope making competition. And it may be the only one to host a lobster dinner. On the other side of the country, the Riverside Telescope Makers Conference (RTMC) held in southern California also provides a great opportunity for telescope makers to show off their handiwork and is noted for the many equipment vendors attending. Some star parties have organized day trips to nearby attractions, especially to a local observatory or historic site. The Almost Heaven Star Party in West Virginia hosts a tour of the Green Bank Radio Telescope Observatory. For many of us, the overall star party experience is also a social one. This is where we meet old friends who we met long ago and may only see once or twice a year the same star party. And this is where we can make new friends as well.
I invite you to make your preferences known by taking a Star Party Survey that I have put together on this web site. It will only take a few minutes and no personal information is required. When enough people fill out the survey, I will post another blog with a summary of the results. The survey can be found under the "More" tab on this web site, or a direct link to the survey is available here: www.californiaskys.com/star-party-survey.html
Nearly two years ago I obtained my first USB camera, an ASI224MC sold by ZWO. ZWO had introduced this camera in July 2015 for $350 and it was an immediate hit with the EAA crowd for good reason. The ASI224MC uses a 1/3" format Sony IMX224 color CMOS sensor with 1.27 Million 3.75 micron square pixels. This provides round, pin-point stars with high resolution unlike typical analog video cameras which have rectangular and much larger pixels. With a high sensitivity rated at 2350mV this Exmor sensor combined with an extremely low read noise of 0.55e to 3e means (depending upon the gain) the camera is well suited to live stacking of many short exposure images. This is very helpful for Alt-Az mounts where single frame exposure lengths are limited by field rotation to around 30sec. When combined with the powerful and free Sharpcap software this camera shows great detail in a wide range of deep sky objects.
Since this is a USB camera and not an analog camera, a computer is required to operate the ASI224. A single USB cable from the camera to the computer is all that is required for both camera power and control. One less cable to deal with and to potentially snag on the mount compared to analog cameras is a pleasant advantage. Sharpcap is probably the most commonly used software for the ASI224 and it provides control over all of the camera menu settings. It provides for image display, capture, histogram stretching, dark frame subtraction and on-the fly alignment and stacking among other nice features. Sharpcap can be downloaded from the ZWO web site along with the native driver necessary to connect the camera to the computer. To use other software you will have to load the ASCOM driver also available on the ZWO website.
Camera settings include an exposure range of 32micro-sec to 1,000sec which makes the camera highly capable for both planetary and deep sky viewing. The camera has a gain setting range of 0 - 450. Lower gain provides higher dynamic range while higher gain provides the lowest read noise. Typically, people report working with gains in the range of 300 - 350. This camera also has the capability for 2x2 binning which makes the pixels effectively 7.5 x 7.5 microns, increasing the sensitivity and speed of the camera at the cost of resolution.
With a sensor diagonal of 6.09mm, the ASI224 has a field of view and magnification factor similar to a 6mm eyepiece. This can make it challenging to place a faint object in the field of view unless the mount's GoTo alignment is very good.
The ASI224 comes with a 2m USB cable to connect the camera to a computer along with a 1 1/4" nose piece adapter to connect the camera to the telescope like any eyepiece. It also comes with an f/2 all sky lens with a 151 degree field of view for detecting meteor showers. This must be removed before attaching the 1 1/4" nose piece. The ASI224 is also designed to work as an autoguider when used with a program like PhD. As such, it has an ST4 guide port and comes with a 2m cable to connect to the mount. While the camera comes equipped with a 1 1/4" nose piece to fit inside a standard 1 1/4" focuser like any eyepiece, the camera can also be inserted into a 2" focuser since the camera body has a 2" diameter collar in the front. This is helpful to achieve additional in-focus when using Newtonians and Dobsonians which are not designed for astrophotography. In addition, the front of the ASI224 has an M42 x 0.75 thread making it ready to be used with T-adapters.
The ASI224C was upgraded in April 2016 with anti-amp glow circuitry. Amp glow is caused by the heat produced in the read out circuit of the sensor during long exposures and is common in analog video cameras. It produces a bright glow at the edge of the image making that part of the object appear over-exposed. Short exposures and/or dark frame subtraction are commonly used to eliminate or minimize the impact of amp glow. With the ASI upgrade this is no longer necessary. The USB connection was also upgraded from USB2.0 to USB3.0 to support better download rates. In addition, the price of the ASI224 has been reduced to $249.99 as other cameras with the IMX224 sensor have become available. A cooled version of this camera, the ASI224MC-C was available for a while and sold for $599, but has since been discontinued.
As can be seen from the images here, the ASI224MC camera performs very well for all sorts of deep sky objects. It produces nice round, pin point stars and has very good color saturation. All images were captured using Sharpcap and have had no post capture image processing. What you see here is what you would have seen on my computer screen live.
With the popularity of the ASI224MC, many other camera suppliers have introduced versions of their own with the IMX224 sensor in the last couple of years. QHY makes and sells a cooled camera with the Sony IMX224 sensor for $669. It's 2-stage regulated TEC cooler can cool to 40deg. C below ambient. It also has the anti-amp glow circuit, a USB 3.0 computer interface and a 128MB image buffer to prevent lost frames when capturing images with a high frame rate. This camera has exposure settings of 7micro-sec to 400sec and the same read noise as the ZWO camera. With the active cooling, the QHY camera body is significantly larger than the ZWO but it also has an M42 x 0.75 thread making it ready to be used with T-adapters.
While ZWO and QHY make their own cameras with the Sony IMX224 sensor, there are many other retailers who appear to re-brand cameras from a Chinese company called Touptek and sell them under their own label. These include three cameras from Rising Tech in China, and one each from Mallincam in Canada and the U.S., Orange County Telescopes in the U.S. and Altair Astro in the U.K.
Rising Tech sells three versions of the IMX224 based camera. The USB 2.0 version, Model GPCMOS, comes without the amp glow reduction and sells for $162 making it the cheapest IMX224 based camera currently on the market. This camera also has a lanyard which can be used as a safety strap to attach the camera to the scope. Model G3M224C has the USB 3.0 connection and the amp glow reduction circuit for $245 and has a slightly larger body than the GPCMOS camera. However, both models are small bullet shaped cameras which can fit well inside a focuser making it easier to achieve focus with Newtonian telescopes which are not designed for astrophotography.
Model G3-1200KPA also has both the USB 3.0 and the amp glow reduction, but comes with a cooling fan for $295. The G3 also has a much larger camera body and has M42 X 0.75 threads making it straightforward to attach a t-adapter to the camera. All cameras come with camera control software called Rising Sky, which appears to be a re-branded version of Toupsky camera control software. Toupsky has many of the same features found in Sharpcap such as image display and capture, on the fly stacking, dark frame subtraction, histogram stretching, etc.
Mallincam's IMX224 camera is called the Skyraider AG1.2c, and comes with a USB 2.0 computer connection, MallincamSky software which looks like re-branded Toupsky software for $250. The Skyraider camera body has built in cooling fins to facilitate passive camera cooling and also has a lanyard which can be used as a safety strap to attach the camera to the scope. The web site makes no mention of amp glow reduction so I assume it does not have it. The bullet shaped front also enables this camera to fit further into a focuser making it possible to achieve focus where some of the larger cameras cannot.
Altair Astro's GPCAM3 224C has a USB 3.0 computer interface and comes with a UV-IR filter and AltairCapture software. The camera body has cooling fins and the same bullet shaped front as some of its competitor. The GPCAM3 sells in the U.K. for £249. It also comes with a 1 year license for the Pro Version of Sharpcap.
Orange County Telescopes sells the Revolution Imager 224 (R224) but does not hide the fact that this USB 2.0 camera is manufactured by Touptek. The R224 makes no mention of the amp glow circuitry, comes with the ToupSky software and sells for $250. The R224 is another of the bullet style cameras. It comes with a UV-IR filter, a 0.5X focal reducer and a soft carrying case for the camera, cables and accessories.
Maximum exposures are 1,000sec for all of these cameras, but the stated minimum exposures vary. While several of the camera suppliers do not specifically mention the read noise, I believe these all have the same read noise specs which are determined by the CMOS sensor itself. All of these cameras come with a 1 1/4" adapter to connect the camera to a 1 1/4" telescope focuser and a USB cable to connect to a computer. They also all have the standard ST4 guide port to use as an autoguider and guide cable. Some come with additional adapters and some also have T-threads to attach T-thread adapters. All should work with the Sharpcap software but may need the ASCOM driver to do so. Any of these cameras should function well as a low cost camera for real time viewing of the deep sky with the added advantage as an autoguider if and when you move on to a more expensive camera.
Newtonian and Dobsonian telescopes are commonly used for astronomy because of their relatively low cost and fast focal ratios, typically f/5 or faster. Dobsonians are just Newtonian optical tubes on an Alt-Az mount after the style made popular by John Dobson. There is a critical consideration when choosing a Newtonian for deep sky video astronomy, Electronically Assisted Astronomy, or Near Real Time Viewing, whichever you call it. Newtonians and Dobs, unlike Schmidt Cassegrains and refractors, do not have a lot of in-focus travel which is required to focus analog cameras like the Revolution Imager, Mallincam Xtreme, Strellacam, Samsung, etc, or digital USB cameras like those from ZWO, Atik, Rising Tech,etc. This is especially the case if using a focal reducer to speed up the optical train and/or achieve a large field of view. When there is not enough focus travel, modification of the optical tube may be required to achieve focus with a camera. Fortunately, there are many Newtonians and Dobs which are able to achieve focus with a camera without the requirements for scope modification. These are often, but not always, sold as imaging Newts. The table below shows a list of Newts and Dobs that have been reported on Cloudy Nights as compatible for use with various cameras without modification to the scope. There are certainly many more than listed here, but these are the ones I am currently aware of. They span the range from 100mm aperture to 305mm and all are fairly fast even without a focal reducer. Several of these scopes have also been verified to work with a focal reducer without the need for any modifications. This is shown in the "Focal Reduction" column.
When a Newtonian scope does not have enough in-focus travel to work with a video camera, there are two options. First, modify the scope by moving the primary mirror closer to the secondary. Some truss tube collapsible scopes make this easy to do with a specific configuration for imaging which brings the primary mirror closer. But the solid tube Newtonians do not have this option and require mechanical modification to bring the mirror closer. Many have done this modification to make their existing Newts compatible for use with cameras. It will require re-doing the collimation, but Newts seem to require frequent collimation anyway.
If shifting the primary mirror position is not something that you are comfortable with, there is another option. There are many bullet style cameras with 1 1/4" diameters either their full length or enough of it that they can fit further down the focuser, bringing the camera's imaging sensor close enough to focus, even with the addition of a focal reducer. Examples include the Starlight Xpress X2C, Revolution Imager IMX224, and the Rising Tech IMX224. It has been reported that this works with the 8" f/6 and 12" f/5 GSO Dobsonians along with a 16" f/4.5 Meade Lightbridge Truss Dob. These can even achieve focus with a 0.5X focal reducer by using a 2" negative profile adapter like this one from ScopeStuff which allows the camera body to slide even further inside the focuser.
Even though cameras like the Mallincam Micro Ex, LnTech300, Revolution Imager 1 are not bullet shaped, they are small enough to fit down inside a 2" focuser allowing these cameras to achieve focus with many Newts. However, with both the bullet style cameras and these small rectangular cameras, be careful that they do not slip down and contact the secondary. The 1/4" x 20 mounting bracket found on the Micro, etc. is useful as positive stop to prevent this from happening.
It has been nearly 20 years since SBIG in Santa Barbara introduced the STV for the tidy sum of $1995. This video camera was marketed as both a deep sky video camera and a stand alone guider. At its heart is a Texas Instruments TC-237 1/3" format B&W CCD sensor with 656 x 480, 7.4micron square pixels. In retrospect, for its time, the STV was revolutionary. From my research it the first video camera to be capable of deep sky video without modification, years before the Stellacam, Mallincam, Samsung, Mintron or Watec cameras. Not only that, it came with an amazing list of features which we now take for granted in our CMOS based video cameras but which did not become widely available until the past few years. This includes, exposures up to 60 minutes, manual gain (1x or 2x), thermo-electric cooling, 1x1, 2x2 and 3x3 internal binning, internal stacking and alignment of successive frames called "Track & Accumulate" and an optional 5.3" LCD monitor. In addition, it had an internal filter wheel with a green filter to act as a "neutral" density filter when viewing the moon, and an opaque filter to support internal automatic dark frame subtraction. An optional color filter wheel was also available for color imaging. The unit came with 2MB of internal memory to save up to 14 images which could be downloaded to a computer later.
The camera came with a rather large control module with buttons and knobs to scroll through the camera menu and adjust camera settings. The settings were viewed on a small, two line LCD display. An optional 5" LCD monitor showed the live images. Accessories included a very thorough manual, a 110VAC to 12VDC transformer, RS232 cable to connect the control module to a computer, RJ11 auto-guide cable, red screen shield for the LCD monitor, 1.25" nose piece adapter, software for remote operation of the camera via a computer, and copies of CCDSoft and CCDSharp. Additional options included an eFinder tube assembly with a focal reducer to turn the camera into a stand alone guider, the previously mentioned color filter wheel, adapters for 35mm cameras and a hard carrying case with custom cut foam.
I have seen some surprisingly good images of galaxies and nebulae taken with this camera and posted on the internet. So, as a student of deep sky video history, I recently purchased one of these cameras on Cloudy Nights to see what it could do for myself. First of all, everything is big from the camera, to the control box to the power supply. I guess this is not a surprise given the state of the art of electronics 20 years ago. Second, a short read of the quick start guide in the manual enabled me to begin taking images in quickly. The controls are quite easy and mostly intuitive. When in the imaging mode, the two round knobs on the front panel are used to adjust the brightness and contrast of the image as viewed on the LCD. To capture images with this camera, I used the video out port on the control module and fed the signal through a video capture device to my computer which was running Sharpcap software. I used Sharpcap to view and capture the images shown below.
So far I have only tried the camera with an ES 127mm, f/7.5 Apo refractor, but have been pleasantly surprised with the results. I have used the camera both with and without a generic 0.5X focal reducer and without any filters. I will note, the images as they appear on the SBIG LCD monitor are noticeably better than the images on my computer screen. I use the same video cable and Pinnacle Dazzle 100 to send the signal to my computer as I do with all my other analog video cameras, so I am guessing the difference is due to the output on the SBIG control module.
Since it is the Christmas season, Orion is an obvious target. Below is a single frame, 10sec image of M42 taken with a gain of 1X. While the core is blown out, we can see significant detail in the nebulosity. Next is a 30sec single frame image of the Flame Nebula. The 5.6mag variable star NSV16638, which is just on the edge of the top of the image makes it difficult to avoid washing out the nebula but I was still able to see it clearly. The HorseHead nebula is difficult to see in a light polluted back yard, especially without filters, but this 60sec image shows it quite well.
One of my favorite galaxies this time of the year is M82, the Cigar Galaxy. The STV had not trouble bringing out the split in this galaxy even at a few tens of seconds. The image shown here used the Track & Accumulate feature, aligning and adding 5 x 30sec frames for a total of 150sec. Notice how nice and round the stars are and compare this to the elongated stars in the 60sec single frame of the HH Nebula. I would say that the T&A feature works quite well, and this was available almost 20 years ago. Next are two 60sec single frame images of M82, the first without the internal dark frame subtraction and the second with dark frame subtraction. Notice the dramatic difference. And, I did not even have to get up and cover and uncover the scope to do this. It was all automatic one I check yes in the camera menu for dark frame subtraction. Since this CCD sensor is nearly 20 years old, I have no way of knowing if this is typical of the number of hot/warm pixels when the sensor was new. Nevertheless, dark frame subtraction is able to take care of the objectionable noise.
All in all, I am very impressed with what this camera can do. When I realize that this camera had all of the extra features in 1999 that most cameras/software did not have until recently I am even more impressed by SBIG. If not for the much older vintage (1996) and smaller format (1/3") CCD (TC-237), this system would still be a competitive analog video performer today. Not to mention, that many people still use this as a stand alone auto guider for their long exposure imaging. No wonder I had a tough time getting someone to part with this.
Next time I have clear dark skies, I will see if I can improve the images, especially the star bloat with filters. And, I would like to try the camera out on my 9.25" SCT which will pull in more light than the 127mm refractor.
The question of which type of video camera one should buy for deep sky astronomy, an analog camera like one of the Revolution Imagers or Mallincams, or a digital camera like a ZWO ASI224 or one of the other IMX224 based cameras often comes up. The simple answer is that it all depends upon personal preferences and objectives. Below I will outline the main differences between the two types of cameras. I own and use both types of cameras myself so I am trying here not to be biased one way or another, nor trying to conclude which one is best as this depends upon the individual. I am just stating the facts as best as I know them from my own personal experience.
For clarification I will note that all cameras are actually analog since the chips used, whether CCD or CMOS, accumulate electrical charge proportional to the number of photons of light that strike them. This charge is converted in the camera to a digital count in an analog to digital converter. Additional processing of that digital information takes place inside the camera circuitry. The "digital" cameras then output a digital signal, whereas the "analog" cameras convert that digital signal back to an analog signal which they output.
The least expensive digital cameras that one would likely use for near real time deep sky video are the IMX224 based cameras like the Mallincam AG1.2c ($250), Altair Astro GPCAM2 - ($279 Canadian), Generic GCMOS available from a number of non-Astronomy companies on AlieExpress (~$200) and the ASI224 from ZWO at $299. They come with everything needed to get started (camera, USB cable, nose piece) except a focal reducer which can be found on Ebay for $15 for a 0.5X version and a computer which is required to power, control and view images from the camera. If you already have a computer you are set. If not, you will need at least $150 more for a low cost laptop. Other digital cameras used for deep sky video from ASI, Starlight Xpress and Atik range up to $1000 and include larger and more sensitive sensors with more pixels for higher resolution and faster acquisition times. Some come with thermoelectric cooling to minimize background thermal noise. And the Starlight Xpress and Atik cameras come with their own control and imaging software.
The least expensive analog cameras are the Mallincam Micro and the Revolution Imager which can be obtained for $100. But then one must add a focal reducer for $15 on Ebay for a 0.5X version, a power/video combo cable and power adapter, both also available on Ebay for around $15 or from any camera which sells security cameras. If you have a television with an RCA video input, you can use it as your monitor or you can purchase a 9" LCD monitor on Amazon for around $60. Make sure it can display in a 4:3 format as the 16:9 format will cause round objects like the moon to appear oblong. The Revolution Imager comes as a kit for $300 which includes the camera, nose piece, all cables, a rechargeable Li-Ion battery, focal reducer, 7" LCD monitor, IR filter, hand remote and carrying case. The Mallincam kit includes the camera, nose piece, all cables, focal reducer with an additional spacer, 7" LCD monitor, hand remote. More expensive analog cameras like the Mallincam Xtreme or Xterminator are available for prices ranging up to $1800 and include larger and more sensitive sensors, thermoelectric cooling and computer control.
Analog cameras have a lower resolution than digital cameras since they typically use sensors with fewer than 600k pixels while most digital cameras have 1.3Mega pixels or more. Also, the pixels in digital cameras tend to be smaller (3.75 to 6.45 microns) than those in analog cameras ( 5 to 9.8 microns). In addition, the pixels in analog cameras are not square while those in digital cameras are square. Thus, by using smaller and square pixels, the stars in digital camera images will look round while those in analog cameras usually do not. Images from digital cameras can also handle more zoom because of the higher pixel count. That is not to say that images from analog cameras are objectionable, just that those from digital cameras generally have more of a picture quality to them.
In general, but not in all cases, the sensors used in analog cameras are more sensitive than those used in digital cameras. This, along with the larger pixels typical for analog cameras means that shorter exposures are required with most analog cameras for the same image brightness. This puts less strain on the requirements for the mount and the degree of polar alignment required. Thus, analog cameras are a good choice for those with expensive mounts, or with less interest in spending the time and effort to obtain a very good polar alignment.
Digital cameras need only 1 cable for power, camera control and video output. Analog cameras need at least two cables, one for power and one for video output. However, combo video/power cables are quite common and allow for a single cable running from the camera to the computer or monitor. Another option with video cameras is to use a rechargeable Li-Ion battery attached to the scope or mount with Velcro and a very short power cable from the camera to the battery. Then only a separate video cable needs to be run from the camera to the computer or monitor. The Revolution Imager kit ($300) comes with a rechargeable Li-Ion battery and short power cable. 6.8Ah Li-Ion batteries or larger can be found on Amazon( $20) along with short power cables (<$10).
Both analog and digital cameras draw very little current, less than 500mamps, unless they have active cooling. In that case, they will draw up to about 2amps. Digital cameras like the cooled versions of the ASI224 or ASI1600 require an extra power cable and a 12VDC 2amp power source for cooling while cooled analog cameras like the Mallincam Xtreme need no extra power cable or supply.
6. Camera Control
Digital cameras are controlled through the included USB cable with software on the computer. Digital cameras like the Mallincam AG1.2c, AltairAstro, Generic GMOS ICMX224 cameras, ATIK Infinity and Starlight Xpress Ultrastar or Lodestar come with proprietary software for complete control of the camera menu. Analog cameras and the ZWO digital cameras do not come with their own software. However, ZWO cameras can be controlled with freeware like Sharpcap.
Analog cameras have 5 buttons on the back of the camera for control of the camera menu, but these buttons are small and can be difficult to manipulate in the dark and cold and do not allow remote operation. Alternatively, analog cameras can also be controlled with a wired remote. The Mallincams use a separate cable attached to the back of the camera with a hand remote control (costs extra unless camera is purchased as a package). The Revolution Imager uses a UTC hand controller (costs extra unless camera is purchase as a kit) which is connected in line with the video cable so it does not require an additional cable to hang from the camera. Some analog cameras, like the Mallincams can also be controlled through a computer with an optional computer control cable and the free Mallincam Camera Control software. There are also DIY instructions on Cloudy Nights to add wired hand or computer control as well as wireless control of analog cameras.
7. On the Fly Image Processing
On the fly image processing including stacking (some with frame to frame rotation and translation for precise registration, histogram adjustments), dark frame subtraction and image capture is available with both analog and digital cameras depending upon the software used. The software included with the Mallincam AG1.2c, AltairAstro, Generic GMOS ICMX224 cameras, Atik and Starlight Xpress cameras will perform on the fly image processing. Sharpcap will perform all of the same functions for analog cameras and digital cameras. To use software like Sharpcap with an analog camera, a video capture device ($30) is required to connect the camera video output to a computer ($150), but no additional cable is needed.
So, if you defintely do not want to use a computer for EAA, your only choice is an analog video camera. If you want high resolution, you will have to choose one of the high end digital cameras like the Atik Infinity, ZWO 1600 or Starlight Xpress UltraStar. Entry level cameras can be obtained for under $300 including all necessary accessories for both the analog and the digital versions.