LiFePO4 batteries are becoming more and more common for use in powering astronomy equipment either in the field at a dark site where no power is available or in a remote observatory with only solar power.  There are many very good LiFePO4 batteries on the market and I have reviewed two of them on this Blog page previously:  Battleborn's 100Ah and Bioenno Power's 50Ah batteries.  While both of these are very good options, they are on the expensive side, costing ~$8.7 and ~$10.8 per Ah, respectively.  So I
searched for another option with a much better price point and found Ampere Time's 100Ah LiFePO4 battery which sells for ~$4 to $4.7 per Ah.  Ampere Time also makes 200Ah, 300Ah batteries for even less per Ah and a smaller 50Ah for ~$5.8 per Ah.  With a cost of half the other two batteries and many excellent on line reviews the Ampere Time battery caught my attention.  So I contacted them and they agreed to send one of their 100Ah batteries to me to test.

Basic Features
The Ampere Time 100Ah battery weighs only 22.25lbs which is nearly 1/3 the total weight of a 100Ah lead acid battery making it much easier to carry back and forth out into the field or even just the back yard, especially with the included strap.  The 100Ah battery is 13" long x 6.82" deep x 8.48" tall which is similar in size to any other 100Ah battery.  The battery is expected to have a 10 year life and provide 4000 or more full discharge cycles.  It also comes with a 5 year warranty and Ampere Time claims they will respond to questions and service requests within 24hrs although I have not verified this myself.  The battery includes the best documentation for operation and care of any of the three batteries I have tested.

Since this is a Li battery it comes with a Battery Management System (BMS) which is internal to the battery case itself.  The BMS works in the background to monitor the individual lithium cells and make sure that the battery is operated in a safe mode at all times.  It provides protection from short circuits, over current, over charging and over discharging.  The later means that one can safely fully discharge the battery at which point the BMS will shut down the output.  While considered "fully discharged" there is still sufficient voltage on the internal cells to avoid damage and maintain the projected useable life of 4000 or more such full discharges.  Operating temperatures are -4 deg F to 140 deg F (-20C to 60C ) for discharging and 32 deg F to 122 deg F (0C to 50C) for charging, which is typical of most LiFePO4 batteries on the market. It should be noted that unlike the other LiFePO4 batteries I reviewed, this Ampere Time battery does not have a low temperature sensor to automatically prevent charging or discharging below the lower temperature limit.  This means that the BMS cannot protect the internal cells from damage if one attempts to charge the battery below 32 deg F or discharge it below -4 deg F.  However, for astronomy applications I think it is very doubtful that we would be in a situation where we would attempt to recharge the battery when the temperature is below 32 deg F and most do not work in temperatures below -4 deg either.  While an unlikely scenario, if one has the need to recharge below freezing Ampere Time makes a battery with an internal self heater that allows charging down to -4deg F.

Inside the Battery
Besides the low cost of this battery the other reason I decided to review it was the tear down video on Ampere Time's 50Ah battery by Will Prowse which shows the internal components (Li cells, BMS, Wire Gauge, etc.) and build quality to be quite good.  I recommend anyone interested in an Ampere Time battery to take a look at that video.  The tear down also shows that Ampere Time uses prismatic cells instead of the cylindrical cells used by Battleborn and Bioenno Power.  Because prismatic cells are larger and have greater capacity than cylindrical cells only 4 cells are needed to achieve the 100Ah capacity compared to the 120 cylindrical cells found in the 100Ah Battleborn battery.  The four prismatic cells are arranged in series with each cell having a nominal voltage of 3.2V and a capacity of 100Ah.  In this configuration a nominal voltage of 12.8V is obtained.  While less cells has its obvious advantages, damage to a single cell will result in a drop in the voltage making the battery no longer useable.  In contrast, damage to a few cylindrical cells in the Battleborn battery may hardly be noticed by the user.

Capacity and Discharge Voltage Tests
The first test of any battery that I review is a full discharge capacity test.  Since these types of batteries are shipped with less than a full charge the battery must first be charged to full capacity.  I used a 10A AC charger from Bioenno Power designed for lithium batteries to fully charge the battery.  Next, I used a battery capacity tester from MakerHawk to measure the actual full discharge capacity of the battery to compare to its manufacturer's spec.  I used a discharge current of 5A which is equivalent to ~65W since most typical astronomy setups will use less than this and the ones which use more will not be much more.  Once fully discharged I repeated the process to check for consistency.  The results were 102.8Ah for the first discharge and 103.1Ah for the second discharge.  These are equivalent to 1307Wh and 1314Wh, respectively.  So the results from both tests are consistent and show that the battery exceeds its specification of 100Ah by ~3%.

Now, while the full capacity is important, the voltage drop off versus capacity is even more important since some equipment will not work properly if the voltage drops too much below 12V.   So I captured the voltage versus capacity data during the discharge tests and this data is shown in the graph above.  The average of both tests showed that the battery maintained its voltage above 12.0V for 98.5Ah or 1262Wh which is excellent compared to other batteries I tested or am aware of.  By comparison the voltage of a typical lead acid battery drops below 12.0V at ~44% SOC.  This means that you will get twice the capacity of a typical lead acid battery with this Ampere Time battery without risking damage to the battery.

Re-Charge Tests
There are multiple ways to recharge a battery and I tested the two most common.  First, using the above mentioned 10A AC charger I was able to fully recharge a depleted battery in 10.5 hours.  This matches very well the measured capacity of 103Ah and the fact that the charger is supplying 10A.   Now there are higher capacity AC chargers like the 20A charger from Ampere Time or the much cheaper 20A charger from Expert Power which will charge the battery in half that time if desired.

Out in the field we usually do not have access to AC power so we cannot use the AC charger to recharge the battery.  In that case, the battery can easily be recharged with one or more solar panels and a solar charge controller.  I used a pair of 100W solar panels from Jackery connected to the battery through a 20A solar charge controller from Bioenno Power.  It is important to make sure that the solar charge controller is programed for a Li battery with the correct charge profile and voltages.  With this setup, I was able to fully recharge the fully discharged battery in less than 11 hours on a sunny day.  The two 100W panels supplied 11A during the bulk of that time while the sun was high in the sky.  The charging current obviously falls off quickly as the sun gets lower in the sky.  Now, one will not always have 11 hours of sunlight available but the battery reached 84% of full charge in just 8 hours.  Also, It is likely not necessary to fully recharge a 100Ah battery during the day since typical astronomy power draws are 60W or less which would only use half the battery capacity over a 10 hour long night.  So using a strategy of topping off the battery during the day one could run indefinitely so long as the days are sunny.

Typical Astronomy Use Tests
Before taking the battery out to a dark site I first set it up to power my astrophotography/EAA setup at my home observatory over a period of a month.  My home setup includes a Celestron 11" Edge SCT, a Software Bisque MX mount, an ASI1600MC uncooled imaging camera, an ASI224MC guide camera, a Celestron Motorized focuser, a Pegasus Pocket PowerBox Advanced Power/USB Hub, a Beelink Mini-PC, a GL-iNET GL-AR750S-EXT wireless router and a Dell 15.4" laptop.  Power was supplied directly to the Pegasus which then powered the MX and the Beelink.  The cameras and focuser drew power from the MX while the router drew power from the Beelink.  I connect from the laptop to the mini-pc through the wireless router from inside my house where I was able to power the laptop separately with house AC.  

​Since the Ampere Time battery does not come with cables I needed to make my own to connect from the battery terminals to the Pegasus.   I made a pair of 12 gauge cables with lug nuts on one end to connect to the battery and Anderson Power Pole connectors on the other end.  Since the Pegasus uses the standard 5.5mm x 2.1mm connectors I made a cable with 5.5mm x 2.1mm connectors on one end to Anderson Power Pole connectors on the other end to connect the battery to the Pegasus.  I prefer the Anderson Power Pole connectors wherever I can use them as they make a solid connection which is not easily dislodged in the dark.  I prefer the genuine Anderson Power Poles compared the slightly less expensive imitations made in China.  If you make your own you will need a crimping tool and the proper gauge wire for your current.  This silicone wire will remain flexible in cold weather.  If you do not want to make your own cables you can always buy one like this.

Running in my home observatory I encountered no issues with the Ampere Time battery.  All told, the load on the Ampere Time battery was ~30W so I was able to run many nights before I needed to recharge the battery.   
 
The final test was a field test at a dark site over multiple nights of astrophotography.  For this setup I had all of the equipment mentioned above ( Celestron 11" Edge, ASI1600MC uncooled camera, Celestron motorized focuser, Pegasus Power Box Advanced, Beelink Mini-PC, GL-iNET GL-AR750S-EXT wireless router) but this time mounted on my travel mount, a Software Bisque MyT mount.  Also, because I was using Hyperstar no guide camera was needed.  But, because of significant dew I has to turn on the dew heater.  In this configuration the power load was 52 watts over each of 3 nights.    I did not recharge during the day and used a  total of 60Ah (784Wh) in 15 hours over the 3 nights leaving me with 40Ah capacity remaining in the battery.  That means that I could have run for another 10 hours for a total of 25 hours at my consumption rate before needing to recharge the battery.

Now everyone has a different setup and a different power consumption.  For instance, a cooled camera can add another 10 to 20W of power required depending upon the depth of cooling bringing the total power needed to 62W to 72W.  That would still have allowed over 17 hours of run time before a recharge would be necessary.  Also, if using a laptop directly connected to the setup instead of a mini-pc the power load could be as high as 100W.  Even then, the Ampere Time 100Ah battery could supply all the power needed for a full 10 hours which would likely necessitate recharging during the day to enable multiple nights in the field.  Regardless of your power requirements, the Ampere Time battery seems to be up to the challenge.

Final Impressions
Overall I found that the Ampere Time 100Ah battery delivered the full capacity promised, is very light weight especially compared to a 100Ah lead acid battery and was straight forward to use and re-charge.  Obviously I cannot comment on the long term reliability of this battery or any other manufacturer's battery  through the simple tests I have available and testing only one battery.  But I have no reason after having used it and checking out other reviews to expect it to be problematic.  After my tests I even recommended this battery to my friend to replace the AGM batteries in his RV who purchased 3 of these and already installed them and tested them out when he joined me on my field tests.

What I like about the Ampere Time 100Ah battery:
1.  It is one of lowest cost LiFePO4 batteries on the market with an excellent reputation.
2.  At 103Ah capacity it exceeded its 100Ah specification.
3.  It comes with the best care, use and charging instructions of any battery I have tested.
4.  They claim 24hr response from their technical support team.
5.  It comes with a convenient carry strap.

What I do not like:
1. No US based support hot line.  Support is obtained either on line or by calling their number in Hong Kong.

So, if you are looking for one of the least expensive of the LiFePO4 batteries on the market, you should seriously consider Ampere Time.  I was not paid by Ampere Time for this review nor did they have any input to it but they did send the battery at my request and at no charge to me.

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I was looking for something to consolidate and manage the power to all of my different pieces of equipment when I came across the Pegasus brand of power distribution hubs.  Pegasus Astro makes a number of different astronomy tools including three different power distribution hubs, the Pocket Powerbox Micro ($228), Pocket Powerbox Advanced ($329) and the Ultimate Powerbox Ver2 ($620).  I quickly zeroed in on the Pegasus Power Box Advanced (PPBA) which also serves as a USB hub as well and made my purchase.  After using it both at my home observatory and on numerous trips to the field I can provide a comprehensive review for anyone interested in one of these.

Basic Hardware Features of the PPBA
The electronics for the PPBA are contained in a sturdy but light Al enclosure measuring just under 4" x 3" x 1" weighing just under 11 ounces.  My version (Gen 1) of the PPBA can support up to 10A of current at 12V for all outputs combined while the latest version (Gen 2) has increased the maximum to 12A.  The PPBA has 4 dc power ports utilizing 5.5 x 2.1mm connectors which are typical for astro equipment.  The 4 dc channels can be switched on/off in software but not, unfortunately, independently.  For astro equipment which need voltages other than 12V, there is a 3A dc output with adjustable voltages of 3, 5, 8, 9 or 12V.  No single dc output can supply more than 10A for Gen 1 and 12A for Gen 2.  Output voltage is unregulated between 12.0 and 13.8V.

The PPBA include two pulse width modulation (PWM) channels to power a pair of DEW heaters using RCA jack.  The output level can be set independently for each channel in software manually or controlled automatically with the external temperature and humidity sensor.  Maximum current is 5A per channel.  Again, please note that the total current capability of all outputs combined is no more than 10A (12A for Gen 2).  I should also note that the length of the cable on the sensor is only 1ft but it seems possible to add an RJ12 extension cable to set up the sensor at the telescope if desired.

Software Features of the PPBA
One very nice feature of the PPBA is that it can be used as a standalone power and USB hub without the need to be connected to a computer.  Just plug power into the power input jack, connect the dc outputs to your astro devices along with up to two dew heaters and any USB devices and it will supply power to everything.  You have the option to set which ports are powered at startup: 1) All On; 2) Only 4 x 12V On; 3) Only Adj Voltage port On; 4) All ports Off. 

I prefer to use the included software to manage and control the PPBA from my laptop.  A separate USB3.0 port is used to connect the PPBA to a pc.  The software app is very simple to use and has multiple tabs at the top to switch pages including Control, Env, Power, Focus, Config and Info.  The software is fully upgradeable as well.  Above the page tabs is a Connect switch which connects the software to the hardware module.  There is a button to make sure that the PPBA application is always on top of the other software open, one for a Ghost window, another to export data collected from the onboard meters and sensors, one for a 2nd version of the app and another to check for software updates.

The main Control page on the application provides the ability to turn on/off power to the 4 12V dc outputs (again, not independently), turn on/off power and set the voltage to the variable voltage output and turn on/off the dew heaters and set their power level manually or set them to auto control using the temperature/humidity sensor.  A feature I really like about the PPBA is the internal power, current and voltage meters along with the external temperature and humidity sensor.  The input voltage and the output current along with the temperature, humidity and dew point are shown on the control page.  You can even export these data to be saved and reviewed later.  Export is both to a CSV file and a png file for each metric.

​The Env page page logs the temperature, humidity and dew point versus time while the Power page logs the input voltage and output current versus time.  Real time plots are shown for each measurement.  Unfortunately the graphs are very small and there is no apparent way to enlarge them. 

​A Focus page to connect and control your Pegasus or Ascom compatible focuser if you should want to.  The Config page provides some setup options, a place to set the Auto-Dew control aggressiveness and the ability to set the startup power settings mentioned previously.

I have come to appreciate the data in the Info page which shows the average current used, total Ah and total Wh consumed as well as the total run time.  I have used these to measure the total power consumption of my astro setup, as well as, the individual power consumption of each separate device.  This information has allowed me to determine what size power supply I need and how long I can run everything when I go out into the field.

Summary and Overall Conclusions
Having used the PPBA for nearly two years both at home and out in the field the best summary I can give is that it just works.  The build quality is excellent with the enclosure strong enough to stand up to normal wear and tear without any damage.  Its compact size makes it easy to pack for trips to dark sites and easy to mount in any number of locations either on the OTA or the tripod as desired.  I have not noticed any looseness in the connection ports and the cables fit tightly into their connections preventing an inadvertent loss of power to a device.

My one minor complaint is that the software application window is rather small and I have not found any way to enlarge it.  It is just barely big enough for me to be able to read all of the numbers displayed on the various pages.  But it would be nice to be able to stretch the app.

I think the $329 for both a power and USB hub is reasonable.  If one only needs the power hub they can save $100 with the micro version and if one needs more total power up to 20A, another dew port which can also be used to power a focus motor or flat box and/or more USB ports the Ultimate is the way to go.

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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 on an Alt-Az mount for $936, while the Celestron Nexstar 6SE is only slightly ore expensive at $1099 and the Nexstar 8SE is $1600 as of this writing.  Celestron also offers a better mount in its Nexstar Evolution series 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 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 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 for their standard OTAs and a 0.7X reducer for the Edge OTAs to reduce the focal ratio down to f/6.3 and f/7 respectively.  Starizona sells their Night Owl reducer for 0.4X reduction and Optec offers a 0.33X focal reducer 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 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 from Starizona 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.

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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.

I attended my first Nightfall Star Party this month which was held from Nov 4 - 7 at the Palm Canyon Hotel and RV Resort in Borrego Springs, CA.  This star party is hosted by the Riverside Astronomical Society (RAS) in conjunction with Woodland Hills Camera and Telescopes.  Nightfall has a long history as their first star party was held in 1993.  Nightfall is unique as it is held at a desert resort with full hookup RV sites and hotel rooms on site.  The official star party web site can be found here.


Location
Borrego Springs is small city in the southern CA desert which is easily accessible to all of San Diego, Los Angeles, Riverside and surrounding counties.  It is just 90 miles northeast of San Diego,  106 miles southeast of Riverside, CA, and 150 miles southeast of LA.   As expected, most attendees come from locations within a few hours drive but I did run into friends from Santa Cruz and came with a friend from the San Francisco Bay area which is 8.5 hours away. 

One attraction of Borrego Springs in November is the weather.  While other areas of the country are experiencing cold, cloudy nights with the possibility of rain and even snow, the weather there is warm and dry.   Daytime highs are typically in the low 80s but can reach into the low 90s.  Nighttime lows are expected in the low 50s.  For my visit, the daily highs were right around 90 which was hot if you were in direct sun, but with a slight breeze it was very pleasant in the shade.  Nights were generally warm and did not become cool until late allowing for a light jacket even into the early morning hours.  Past events had similar temperatures with only a few cloudy nights reported.

Another advantage of this star party location is the lower latitude compared to much of the country and the rest of the state of CA.  At 33.25deg latitude a few objects which are typically too low in the sky to be viewed or photographed may be just high enough here.

​Venue
The Palm Canyon Hotel and RV Resort has over 140 RV sites with full hookups on level ground and paved driveways. There are 60 hotel rooms spread across 5 buildings for those who prefer to stay in a nice hotel room with air conditioning, a TV and a refrigerator.  Some rooms even have balconies to enjoy in the evening.   Those without RVs can tent camp in the RV sites or can choose to rent one of the handful of vintage RVs on site.  A pair of bathhouses with showers and bathrooms along with a laundry and fitness center are all on site.  Telescopes are typically set up at the RV sites or in the designated blocked off parking lots.  

The hotel design is a western theme with conference rooms for talks and two pools each with a jacuzzi.  The Big Horn Grill is open from 11AM until 8PM and has a modest menu with mostly burgers, fries, shakes, and a few salads.  One can tire quickly of the menu but there are other restaurants not far off in town.  There is also a bar in the main building along with a small store in case you need nice or forgot your hat, like I did.

You can get a birds eye view of the site and the surrounding desert in this drone video on the star party Archives page.

Local Area
The center of town is 1.5 miles to the east of the resort.  It is an easy walk from the resort to a number of different shops.  There you can find banks, a hardware store, gas stations, food and various other stores.  Just a mile down the road is "The Mall" which hosts Carmelita's Mexican Grill (had a nice dinner there one night), Kendall's Cafe (ate breakfast there twice), a pizza place, Borrego Outfitters which has all sorts of camping equipment and a small grocery store.  Across the street is the larger Center Market where you can find most of the typical grocery items although neither grocery is a "super" market.  A bit further down is the center of town where the hardware store is located along with an art gallery and some additional restaurants.

There are a number of things to do in the area, most notably hiking at Anza Borrego State Park which is only a mile away.   There are a number of golf courses in the area to occupy your afternoon if you are so inclined, along with a few spas.   For unusual art work there is Galleta Meadows which has over 130 large scale free standing metal sculptures spread over 1500 acres of desert.  

For those who want to venture a little further away to a cooler climate, the town of Julian is just over 30 miles away at an altitude of 4200 feet in the Cuyamaca mountains.  Julian is an historic gold rush town and has a bunch of interesting shops and places to eat.

Summary
Overall this was a successful star party as my friend and I were both able to get lots of imaging data over all 4 nights that we were there.  Having the full hookup capability for my RV was a real treat.  My friend and his wife enjoyed their nicely equipped hotel room.  The ability to walk into town for breakfast and/or dinner, as well as, stopping by a few of the shops and the Central Market was a welcome opportunity to explore and get away during the day.

There were a few things that were disappointing.  As I mentioned before, the downright disregard for the white light rules by a few people was surprising and I hope not typical of this event.  It would be nice if the Big Horn Grill could add of few more items to their menu which would have led us to eat there more often.  The biggest disappointment, however, was the steaks at the Coyote Steakhouse down the road, especially given how pricey the place is.

If the event were closer to home I would surely attend every year just because it is so nice to have all the amenities in a place with reasonably dark skies.

​This past summer I had the opportunity to stop at the Battleborn factory in Reno, NV on my way back from 3 nights of astrophotography at a northern CA dark site.  The folks at Battleborn were nice enough to give me a factory tour and answer many of my questions about their batteries.  I decided to visit because I became impressed with the company and their lithium batteries from my prior research.  At my request, they sent one of their 100Ah batteries to me to try out as a power source for my astronomy equipment on my next trips out into the field. 

Battery Basics
Battleborn makes a line of different capacity LiFePO4 batteries which they sell under the parent company name Dragonfly Energy to OEMS like RV manufacturers.  They sell the same batteries to the public with a different color casing under the brand name Battleborn.  They are a US company which designs, assembles and tests their batteries here in the US.  While many of the components are sourced from outside the US, including the lithium cells inside which are only made in Asia at this point, the components are built to their own particular specifications.  Unlike most of the Chinese batteries found on line, the folks at Battleborn can be easily reached on the telephone for technical support and service.  And, you can even stop by the factory I did if you are passing through the Reno area, but call ahead first.

The 100Ah battery I received weights 31lbs and is sized similarly to any 100Ah lead acid battery weighing more than twice as much.  Because this is a lithium battery with a battery management system (BMS) inside it is capable of supply the full 100Ah capacity for 3000 - 5000 full discharge cycles.  This compares to the typical 100Ah lead acid battery which is only capable of suppling 50Ah without damage to the internal cells for up to 450 cycles.   The Battleborn battery is designed and warranted for a 10 year service life.

As discussed in previous blogs, the BMS is an internal controller whose function is to protect the cells inside from unsafe operating conditions which includes:

1.  High/Low Voltage Protection
2.  Short Circuit Protection
3.  High/Low Temperature Protection
4.  Cold Charging Protection
5.  Automatic Cell Balancing 

This battery can be used to supply power at low and high temperatures given its discharge temperature range of -4°F (-20°C) to 135°F (57.2°C)   Like all lithium batteries, it cannot be recharged at a temperature much below freezing given its charge temperature range of 25°F (-3°C) to 135°F (57.2°C).  The battery has internal temperature sensors so that the BMS will prevent charge or discharging outside of the allowable range.

Inside a Battleborn Battery
It is worth looking inside any battery that you would consider buying to understand both the quality of components and build process.  Unfortunately, this is not something we can typically do but there are YouTube videos showing the teardown of the Battleborn battery and some of the others as well.   Here is one from Will Prowse from which I was able to grab a few images for this blog.  In this video you can see the excellent build quality and components which can be contrasted with another vendor which is not of very high quality.

Looking inside the Battleborn one can see that it uses cyclindrical cells which are the most common cell type found in lithium batteries at this point since they are more amenable to automated manufacturing processes.  This makes them less expensive and provides for consistent build quality from cell to cell.  You can also see that the cells are arranged in 4 groups in series of 30 cells each in parallel for a total of 120 individual cells.  The cells in parallel provide the voltage ( 4 x 3.2 to 3.3V = 12.8 to 13.2 V).  The 30 cells in series provides the overall capacity (30 x ~3.4 to 3.5Ah = 102 to 105Ah ). 

Capacity and Discharge Voltage Tests
I performed extensive testing of the Battleborn 100Ah battery both at home and in the field on two different dark site trips.  The results of these tests are summarized here.  The first test was a capacity test to see if the battery delivers its rated Ah.  Three full discharge cycles were performed using a 90W, 60W and 60W load.  A typical astronomy setup might use between 30W and 60W with 90W being a very high power case.  Regardless, these loads are very small compared to the battery's 100A maximum current capacity so, not surprisingly, the measured capacity remained constant within 1Ah across all three tests with an average capacity of 110.5Ah.  Considering that the voltage drops, especially during the last 10% of capacity, a more relevant number is the capacity at 12.0V which was 105.5Ah.  This is in line with the fact that Battleborn overbuilds their batteries using cells packs measured during test and assembly to be between 104 and 108Ah.  I was actually able to see the capacity markings on the sides of the cell packs before final assembly which are used to balance the final capacity within their manufacturing tolerance of 104 to 108Ah.

Next, is the voltage drop off with the state of charge (SOC).  Since LiFePO4 cells have a voltage of 3.2 to 3.3V and are combined with 4 packs in series, the initial voltage of a fully charged battery will be between 12.8V and 13.2V.    The discharge curve which I measured below shows that the initial voltage under load was 12.9V and that the voltage remained above 12.0V until 96% of the total capacity was consumed which is the 105.5Ah number stated above.  The voltage curve was the same for a 60W load as it was for a 90W load.  In contrast, a typical lead acid voltage curve also shown indicates that the voltage drops below 12.06V at 50% SOC which is the minimum SOC to avoid damage to the cells.  For comparison only, a lead acid battery drops below 12.0V at ~44% SOC.
​

Field Tests
I was able to take the battery with me to the Calstar star party in California for 4 nights under the stars.  It was nice to only have to carry a single 31lb battery rather than my usual 63lb lead acid battery, or even 2 of those if I could not recharge during the day.  My setup included a Software Bisque MyT mount, an ASI1600MC uncooled imaging camera, an ASI224MC guide camera, a Celestron Motorized focuser, a Pegasus Pocket PowerBox Advanced Power/USB Hub, a Beelink Mini-PC, a GL-iNET GL-AR750S-EXT wireless router and a Dell 15.4" laptop.  Power was supplied directly to the Pegasus which then powered the MyT and the Beelink.  The cameras and focuser drew power from the MyT while the router drew power from the Beelink.  Because my Dell laptop can only use AC power from its AC adapter, I used a 300W Inverter attached to the Battleborn to provide the AC power to the laptop.

  The Pegasus Powerbox Advanced has an internal power meter which allowed me to monitor the power to everything except the laptop.  I used an in-line power meter to keep track of the power consumed by the inverter/laptop.  The net power for everything was 63.2W with 41.6W going to the Pegasus and 21.6W going to the inverter.  ​The Beelink ran The Sky X which controlled everything (cameras, focuser, imaging) while the laptop was used as a remote control by connecting to the Beelink through the router using Team Viewer.  This explains the low power consumption by the laptop.

The first night I did my TPoint model, Polar Alignment and imaged, running for a total of 7 hours using 32.85Ah (432Wh), or 31% of the Battleborn's 105.5Ah measured 12.0V or higher capacity.  On the second night I imaged for 5hrs and 20min before turning in and used an additional 25.9Ah for a net of 56% of the total capacity.  The third night was a bust due to high winds, but I was able to image for 6 hrs and 20min on the fourth night using another 31.48Ah.  Adding these up, I ran for a total of 18.5hrs and consumed 86% of the battery capacity which indicates that the maximum run time is 21.5hrs for a 63W load without a need for a recharge.

Everyone's power consumption will be different from mine so I put together a table with three different power ranges to provide estimates of run times with the Battleborn 100Ah battery.  Because one can use the full capacity of this battery, it provides seriously long run times without a re-charge and obviously longer with a re-charge in the field.

Re-Charge Tests
While I was able to run my setup for three nights without a re-charge, there will be times when I am imaging for longer periods each night, running a heavier load or spending more nights under the stars.  In those cases I will want to re-charge the battery during the day.  

If one has access to AC power during the day, an AC charger designed for lithium batteries can be used to top off the battery.  I used this 10A charger from Bioenno Power to recharge from a complete discharge to fully charged in 11 hours.  The nice thing about lithium batteries is that they can take a higher charge current than a lead acid battery.  The Battleborn spec indicates 0.5C or 50A maximum.  Even a 20A lithium charger like this one would recharge the battery fully in 5hrs.  Also, it is unlikely that one could fully discharge the battery in one night anyway so a 20A charger is probably more than sufficient to top off the energy used during the previous night.

In most cases, we do not have access to AC power during the day which is why we carry a battery with us in the first place.  For this situation solar panels along with a solar charge controller are required.  You will have to add a pair of wires to connect from the solar panel to the charge controller and from the charge controller to the battery.  Always connect the battery first and the solar panel last.  In my case, I used these pre-made Power Pole Adapters from Bioenno, but you can make your own cables with Power Pole connectors, a crimper and zip cord from West Mountain Radio.  You can get all of the components needed from any number of suppliers on Amazon for less, but I have found that the genuine Anderson Power Poles work best.

​In the first solar recharge test I used a 100W Bioenno solar panel along with a Bioenno charge controller with full sun.  This setup recharged the battery from fully discharged to fully charged in 20hrs as the average current supplied to the battery was a little over 5A.  The math works as it should (5A x 20hrs = 100 Ah).  Obviously, we do not get 20hrs of sunshine during the day but since it is unlikely that one would have to fully recharge the battery after a single night's use a 100W solar panel should provide at least 6hrs of re-charge time or roughly 30Ah which would have topped off the battery after one of my typical nights usage. 

Clearly more solar panels will re-charge the battery faster, so in the second test I used two 100W Jackery Solar Panels in parallel along with the same Bioenno charge controller to recharge the battery.  With two panels supplying 11.3A of charging current, I was able to fully recharge the Battleborn in 9.75hrs.  So, if you want to be certain to have sufficient charging power to fully recharge the battery if you are using more than ~30Ah a night, a second 100W panel will be necessary.

Summary
The Battleborn 100Ah LiFePO4 battery met all of my expectations and even exceeded its capacity spec by 5%.  This battery packs a lot of energy into a small light weight design and can easily supply power for most astronomy setups for multiple nights on a single charge.  For larger power requirements you will need to invest in solar charging equipment to re-charge during the day or have access to AC power to use one of the lithium based AC chargers.

What I like about the Battleborn 100Ah Battery:
1.  Designed and manufactured in the US 
2.  US sales and technical support
3.  Delivers 105% of its rated capacity at 12.0V or higher
4.  Uses cyclindrical cells
4.  Unheard of 10 year warranty

What I do not like:
1.  At $799 from the factory the Battleborn battery is still one of the most expensive LiFePO4 batteries compared to some of the Chinese brands like Ampertime, Chins and Zooms who all use prismatic cells instead of  cyclindrical cells. And, all three of those based upon tear down videos look like they are built in the same Chinese factory although they are sold under different brand names.www.youtube.com/watch?v=4yu4Ei1-2jA&t=1s

​So it comes down to whether or not you are looking for the cheapest option, or a good battery with US support that is easy to reach if you need it.

​Amazon links are Associate links from which I can earn commissions at not cost to you.

​Edit:  I have created a video version of this review which you can find here on YouTube

​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.

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.


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Having previously tested and reviewed lithium powered solar generators from Jackery and Bluetti I wanted to test a simple lithium battery as an alternative power solution when in the field.  Solar generators are convenient as they come with all of the power ports, a display, power meter, AC inverters, etc.  But not everyone needs all of that in which case a stand alone lithium battery may be the better solution.  Fortunately, the folks at Bioenno Power were kind enough to send one of their 50Ah LiFePO4 batteries to me to test along with one of their 100W solar panels, a solar charge controller and a 10A lithium AC charger.

Battery Basics
The first thing to note about Bioenno Power is that they are located in Santa Ana, California and can be easily reached on the telephone for sales and technical support.  That is how I reached the owner, Kevin, who advised me on the equipment that I would need.  Like most other lithium power suppliers, Bioenno Power products are manufactured in China, but tested at and distributed from their facility in California.

Bioenno Power sells a wide range of lithium battery capacities from 3Ah to 300Ah.  The 50Ah battery I got comes with integrated Anderson Power Pole connectors which made it easy to connect to my Power Distribution Hub with a simple adapter cable which converts from Power Pole to 5.5mm x 2.1mm connectors.  If you do not like the Power Pole cable you can simply add your own cable like you would on any other battery.  If you prefer, you can even use a Power Pole to Cigarette socket cable.  The battery is compact with dimensions of 8.4" (L) x 4.3" (w) x 5.8" (H).   It weighs only 13.3lbs. and has an integrated plastic carrying strap which makes it a breeze to transport back and forth into the field.  It is rated for >2000 charge cycles which is typical of LiFePO4 batteries. 

Like all lithium batteries, this one has an internal module, which they call the Protection Circuit Module (PCM) to provide overall protection from unsafe operating conditions such as low and high temperature charging, short circuits, overvoltage, etc.   It also has the responsibility to balance the individual cells inside so that no cell gets discharged before the others.  It sounds like their PCM is just what the industry typically calls a Battery Management System or BMS.  One of the great this about a BMS is it allows the battery to supply the full capacity (100%) without damaging the individual cells inside in contrast with a lead acid battery which should be re-charged once it has depleted 50% of its capacity.  The PCM (BMS) will shut the battery down to prevent the individual cells inside from being damaged when they reach a minimum voltage.

​Capacity & Discharge Voltage Tests
​Like most LiFePO4 batteries, the Bioenno battery uses cylindrical LiFePO4 cells which have a nominal voltage of 3.6 to 3.7V.  Multiple cells are connected in parallel banks to supply the rated Ah or Wh capacity and then 4 of the banks are connected in series to give the nominal full charge voltage of 12.8 to 13.2V.  Thus, the number of cells in the battery is determined by the Ah rating of the individual cells which indicates that this battery has 4 stacks in series of 16 cells in parallel for 64 cells total.

My first test was full discharge capacity test to see how the battery compared against its manufacturer's spec of 50Ah, or 640Wh.  I used a constant 65w load which is representative of a typical astroimaging setup with a dew heater and cooled camera.  This is a little over 5A, or 1/10 C which means it is not stressing the battery which is designed to deliver 1C, or 50A in 1 hour.  The test was performed 3 times and the results were very consistent providing 47.6Ah (606Wh) which is 95% of the rated capacity of 50Ah.  That is well within their specs and typical for lithium batteries where the BMS (PCM) shuts the battery down to reserve power to keep the BMS functioning for the battery re-charge cycle.

​The discharge curve voltage shows that the battery voltage stays above 12.0V through 91% of its rated capacity of 50Ah (96% of my measured capacity of 47.6Ah).  This slow voltage roll-off is one of the advantages of Li batteries compared to lead acid which drops below 12.0V just below 50% capacity.

Field Tests
After initial testing of the battery on my setup at home, I took it with me to a dark site for three nights under the stars.  I used the Anderson Power Pole leads from the battery to connect to an in-line power meter which kept track of the number of Ah and Wh used so that I could match that against the capacity I had measured to keep track of the remaining capacity after a night's use. The output of the power meter feeds into my Pegasus Power Box Advanced (PPBA) which then feeds power to the rest of my equipment.  The PPBA has its own internal power meter so, in my case, I did not actually need the external power meter but chose to use it to show those who do not have the Pegasus how to measure the power used with an inexpensive (~$15) meter.

The Bioenno Power battery supplied power to the entire setup which included:

1.  Pegasus Power Box Advanced Power/USB Hub
2.  12V to 48V DC-DC converter for power to the MyT mount
3.  ASI1600 guide uncooled camera - powered through the mount
4.  ASI224MC guide camera - powered through the mount
5.  Celestron Motorized focuser - powered through the mount
6.  Cooling fans for the Celestron C11 SCT - powered through the mount
7. Beelink U57 Mini-PC
8.  GL.iNET AR750 portable wireless router

The Beelink controlled everything using The Sky X including guiding and imaging.   I connected wirelessly over the GL.iNET WiFi to the Beelink with my Dell 15.4" laptop to monitor activity, but the laptop was powered by a separate power supply for this set of tests.   The average power draw with this setup was only 30W, which is representative of many typical setups with uncooled cameras and no dew heater.  We will discuss more power hungry setups below.  I was able to image for 2 nights (3rd night was a bust for other reasons) for a total of just under 12 hours.  Based upon my initial capacity measurement and the in-line watt meter, 57% of the capacity was used over that period.  That means that the Bioenno battery could last for just over 20hrs at 30W without a re-charge.

Now my setup did not include a cooled camera nor a dew heater which are very common and can draw between 10 and 20W each, on average.  Also, if I had used my Dell laptop to run everything, the total power consumed would be much higher.  To address these situations, I performed measurements of the power draw for these additional equipment and put together a table with 3 increasingly power hungry setups to estimate the run time for this Bioenno 50Ah battery for each setup.  From that, you can estimate the run time for your particular setup as well.  As you can see from the table, adding a dew heater and camera cooling can drive the power consumption up to 60W or slightly more.  In that case, this battery would last for one long night or two shorter nights without the need to re-charge.  If one needs to use the power hungry laptop instead of a Raspberry Pi or mini-pc, 50Ah may not be sufficient capacity.   This leads us to the question of re-charging the Bioenno battery.

Re-Charging
There are two basic ways to re-charge a lithium battery;  1) with an AC charger designed for lithium batteries; 2) with a solar panel(s) and a solar charge controller.  You can get a 10A, 15A or 20A charger from Bioenno which has Anderson Power Pole connectors to conveniently connect to the battery.   They sent their 10A charger to me which is very simple to use.  Just connect the Power Pole connectors to the battery and plug in the charger.  Since it is already set for lithium batteries it will use the correct charging cycle and shut itself off when completed.  In my case, I was able to re-charge from 0% SOC to 100% SOC in 4.7hrs.  The higher amperage chargers will charge in correspondingly shorter times.

Since we do not always have access to AC power in the field, we usually need to use a solar panel to recharge a battery.  I recharged the Bioenno battery with 2 different 100W solar panels, one each from Jackery and Bioenno.  When charging a stand alone battery with a solar panel, a solar charge controller is required such as this 30A MPPT controller that Bioenno sent to me.  To use it, you will have to add a pair of wires to connect from the solar panel to the charge controller and from the charge controller to the battery.  Always connect the battery first and the solar panel last.  In my case, I used these pre-made Power Pole Adapters from Bioenno, but you can make your own cableswith Power Pole connectors, a crimper and zip cord from West Mountain Radio.  You can get all of the components needed from any number of suppliers on Amazon for less, but I have found that the genuine Anderson Power Poles work best.  

​Both panels were able to re-charge the battery in 8hrs with full sun.  The Jackery is an extremely well designed bi-fold panel which I previously reviewed here.  But at $300 it is more expensive than the Bioenno panel at $210 and requires an 8mm to Anderson Power Pole Adapter which are difficult to find.  The Bioenno panel is also well designed, folds out into 4 segments for a smaller footprint, and comes with a 50A Power Pole connector.   The later means that you will need a 50A to 45A Power Pole adapter cable to connect the solar panel to the charge controller.

Summary
The Bioenno Power 50Ah LiFePO4 battery performed well both at home and out in the field as expected.  Because of it's small form factor and light weight, the Bioenno battery works well for someone needing 30W or less for 2 or 3 nights in the field without the need to recharge.  For larger power requirements you will need to invest in solar charging equipment to re-charge during the day if you want to run for multiple nights in the field.

What I like about the Bioenno Power 50Ah Battery:
1.  US sales and technical support
2.  Delivers 91% of its rated capacity at 12.0V or higher
3.  Small, lightweight form factor
4.  Comes with Anderson Power Pole cables
5.  2 year warranty and 30 day return policy

What I do not like:
1.  $470 for 50Ah is expensive compared to some of the Chinese brands like Ampertime, but not compared to other US based retailers like Battleborn and  Dakota lithium.

​So it comes down to whether or not you are looking for the cheapest option, or a good battery with US support that is easy to reach if you need it.

I was not paid by Bioenno for this review nor did they have any input to it but they did send the equipment at my request and at no charge to me.

 Amazon links are associate links from which I can earn a commission.

Edit:  You can find a video version of my Bioenno Power battery review on my YouTube Channel

In this edition of my "EAA for Beginners" series we will discuss the different software available today for camera control and live image enhancement.  The most commonly used ones are SharpCap, ASILive, Starlight Live, Infinity, ToupSky, MallincamSky, RisingSky and Miloslick.  It is impossible to go through each of these in detail in a short artical like this.  Complete details for each package can be found in its respective user manual.  Instead, this will be an overview of the main features which are necessary or very useful for EAA followed by a brief discussion of some unique features of each specific software package without going into great detail on any of them.  The objective is to give you the big picture so that you can zero in on one or two of the applications and do more detailed homework to decide which one is best for you.  In a later edition, I will do an in depth review of SharpCap since that is one of the most used applications, the one with the most features, and the one I use most of the time.  While I have also used Starlight Live and Miloslick I prefer SharpCap.

Today's EAA Software
Today's EAA software consists of similar camera control capability like that in Stephane's and Steve's earlier software, but it also includes a wealth of live image enhancement features.  There are many different software available today for use in EAA with most developed to work only with a specific brand of camera.  These include software from ZWO (ASILive), Starlight Xpress (Starlight Live), Atik (Infinity), Mallincam Video Cameras (Miloslick), Touptek (ToupSky), Mallincam Digital Cameras (MallincamSky), and Risingcam (RisingSky).  The most widely used software for EAA (also works well for traditional astrophotography) is SharpCap which is designed to work with most cameras on the market today.

​Today's software consists of two basic elements.  First, there is the camera control element which enables adjustment of camera settings which, like Stephane's and Steve's earlier software, makes changing camera setting so much more user friendly, simple and quick.  The second element which was missing from the earlier software includes live image stacking, dark frame subtraction, histograms, FWHM measurements, and much, much more.  It was this second element which provided a revolution in EAA capabilities early last decade.  We will go through the basic EAA software features below starting with camera setting controls.

Camera Controls
As mentioned above, for EAA the camera settings need to be adjusted depending upon the target object and the sky conditions so all of the applications mentioned above provide the ability to set and adjust all of the typical settings in cameras available today.  First and foremost is the image exposure which, depending upon the camera, can be set from sub milli-seconds to infinity.  The exposure progress is displayed showing the remaining time left before the image is displayed.  Single images or a sequence of images can be viewed on a screen and/or captured to local storage.  Images can be saved in a number of different file formats such as FITS, TIFF, JPEG, PNG, etc.  Also, a video sequence can also be captured which is useful for lucky imaging of the planets.  These are saved as AVI, SER etc. files.

All cameras have a gain setting which can be increased to boost the sensitivity of the camera for a given exposure to bring out more detail, or reduced to minimize background noise.  Typical cameras today have the ability to combine adjacent pixels into an effectively larger single pixel called binning.  Binning increases sensitivity at the cost of resolution.  Binning choices are 1 x 1 (native camera resolution), 2 x 2 (4 pixels), 3 x 3 (9 pixels) and 4 x 4 (16 pixels).  Also, most cameras today come with the option of cooling the sensor with an internal Peltier cooler attached to or nearby the image sensor. ​

Live Image Enhancement​
​As we said above, the second element of software used for EAA is the ability to manipulate the image in real time which has led to a revolution in the quality and sophistication of EAA images which can now rival long exposure astrophotos.  Each of the software packages used for EAA include the basic elements of live image enhancement.  Let's go through each of these in a little detail

Image Preview
A preview of the latest image is shown on the monitor.  As each exposure is taken, the latest image replaces the previous one.  If stacking is turned on, the image refreshes with each new frame in the stack.  The previewed image can be enhanced on the fly by using the white balance, brightness, contrast, saturation, hue adjustments, depending upon which are present.  In addition, further image enhancements are possible through histogram controls discussed below.

Image Stacking
Among all of the technical advances in cameras and software, many would agree that live stacking has done more to enhance the ability of EAA than any of the others.  Live stacking adds or averages any number of successive frames together, aligning them to the first frame by translating and rotating subsequent frames in software to align the stars in the image.  Live stacking greatly improves the image viewed by reducing the noise and increasing the signal, since random noise from frame to frame is overwhelmed with the fixed signal content in each frame.  This makes it possible to see spiral arms and dust lanes in galaxies and brings out faint nebulosity in planetary nebulae.  Instead of having to capture many images for post processing the next day as in traditional astrophotography, one can watch the image improve before their eyes as each subsequent frame is added to the stack.

Live stacking has made it possible to take and stack many very short exposures of a few seconds instead of taking a single long exposure of several minutes to bring out detail.  Using short exposures means that one does not need a mount with high tracking accuracy.  No does one need to do a very precise polar alignment as needed for astrophotography.  Instead much less expensive mounts and even Alt-Az mounts are highly capable for EAA when live stacking is employed.  Of course, there is a limit to the ability to adjust successive images to overlay the original frame if the polar alignment is way off or an exposure much longer than 30sec is used with an Alt-Az mount.  Live stacking can only do so much.

While all of the applications provide live stacking, they differ in stacking options which they may provide.  These include stacking by Summing frames,  Averaging frames,  Sigma Clipping which discards frames with satellite or airplane trails, and FWHM filtering of frames which discards frames with bloated stars.

Histogram
The histogram is a graphical representation of the amount of light reaching each pixel.  It shows the number of pixels on the vertical axis and the grey scale on the horizontal axis with completely black (no signal) on the far left and completely white (saturated pixels) on the far right.  So each point on the histogram curve represents the number of pixels at each level of brightness.  One can quickly see if the image is over-exposed as the curve will be shifted too far to the right.  This means that stars will look bloated and detail is lost.  On the other hand, one can also quickly determine if the image is under-exposed as the curve will be shifted too far to the left so that the background will appear grainy and faint detail will be lost.  The ideal histogram will show space between the lower edge of the curve and the left axis and a long tail decreasing to the right.

The histogram is a valuable tool which can be used to tease out an improved image live on the display screen.  There will be 3 sliders shown at the bottom of the histogram for the black, mid and white level settings.  The black slider at the lower left controls the position of the black point (pure black - zero signal) for the image.  Moving to the right closer to the peak of the histogram darkens the background.  Moving it too far to the right will clip data at the low end causing detail to be lost.  The slider to the right controls the position of the white point (pure white - saturated signal).   Moving it to the left brightens the image.  Moving it too far overexposes the image.   The mid point slide is used to stretch the grey scale linearly which helps to bring out faint detail.  Some software, like ToupSky and Miloslick provide a feature called Curves, which allows the histogram to be stretched in a non-linear fashion.  Curves provides more control over which parts of the image are darkened while others are lightened.  Histogram sliders can be adjusted on the fly to improve the appearance of the image on the display in real time, but do not change the settings on the images being captured.

Color Balance
If a color camera is used the histogram will have one curve each for red, green and blue, whereas for a mono camera there will be a single luminance curve. The color can be balanced by manually adjusting the three histograms so that their peaks coincide.  This can also be done in most applications automatically.

Dark Frame Subtraction
Image quality can be degraded due to noise coming from the camera itself in the form of hot pixels (defective pixels which are always on) and warm pixels (thermal noise).  Noise can also come from the electronics in the form of amp glow  which is thermal noise from camera amplifier circuits next to the image sensor. Dark frame subtraction is used to counteract these noise sources.  A dark frame is taken with the telescope optics covered so that no light gets into the camera.  It is important to take the dark frame with the exact same settings (exposure, gain, binning, cooling) as the image (light) frames.  Although a single dark frame can be used, it is best to take multiple dark frames and average them together into a single master dark frame.  16 frames is considered a good compromise number of frames.  Many who have a camera with cooling build a master dark library with different camera settings during times when they cannot observe (cloudy nights, daytime) so that they preserve precious time on good nights for observing.

Flat Frames
Some of the software applications allow for flat frames to be captured and used to scale subsequent image frames.  Flat frames are commonly used in astrophotography to correct for differences in light intensity across the image plane.  Without such correction images typically will appear brighter in the center and darker toward the outer edge of the frame, an effect called vignetting.  Vignetting will be exacerbated when strong focal reduction is used.  Flat frames are also valuable in eliminating the doughnut appearance from out of focus dust on the optical elements in the light path.

Defective or Hot Pixel Removal
Many of the software provide the capability to automatically detect defective and/or hot pixels.  These are pixels that always appear black or pixels which always appear bright detracting from the overall view of the image.  The application detects these pixels and averages the signal from the surrounding pixels so the pixel blends in.

FWHM (Image Quality, Focus Tool)
Several software provide information about the Full Width at Half Maximum (FWHM) of the stars.  This is a mathematical measure of how many pixels a star covers.  The less pixels the sharper the star appears.  If a star covers too many pixels the stars appear bloated.  This may simply be an indicator of too long of an exposure or of poor seeing due to momentary turbulence.

The FWHM can be set to trigger an image to be captured only when the FWHM is below a set level.  This is useful during live stacking so that only the images meeting the FWHM setting are stacked, improving the overall image quality.

The FWHM measurement can also be used as a tool to focus the image.  This is done by moving the focuser in and out while capturing the FWHM at several different focus points.  Data for FWHM versus focuser position is collected and a curve its fit to the data.  The best focus is defined at the point where the curve is at a minimum, i.e. the smallest FWHM and the tightest stars.

Misc Controls
A number of different features may or may not be available depending upon which software application is used.  These include the ability to zoom into a region of the image to get a more detailed view.  Image orientation is a feature to rotate or flip the image upside down or left to right which allows the viewer to correct the image orientation which may be reversed due to the type of telescope used.  Several of the applications provide a selection of screen overlays such as a cross hairs or grids which can be viewed on top of the image.  These can be quite useful for centering an image, performing a polar alignment and measuring separation of objects in the field of view.   Overlays may also include text to help label the image and exposure details.  Second Screen allows one to place a duplicate view of the image on another screen to be more easily viewed by additional people.

SharpCap
In 2010, Robin Glover created a software program called Sharpcap to improve upon AmCap and similar Webcam viewing software.  By 2012 he had modified SharpCap to work with video cameras commonly used for EAA.  Not long after, he was among the first to add live stacking capability which immediately made SharpCap a hit with most everyone doing EAA.  Today, SharpCap is probably the most used software for EAA, and also one that many astrophotographers use as well.  Over the years Robin has added many helpful features to SharpCap which has led to the only complaint that I have heard raised about it.  Because it is so feature rich, it presents a steep learning curve.  But once mastered, useful features abound.

SharpCap comes in two versions.  There is a free version which contains all of the essential features for EAA and several extremely powerful additional features.  The second version costs a mere ~$19 a year but includes quite a few unique features not available in other common EAA software.  An extensive manual is available on Robin's website.  SharpCap works natively with many cameras including those from ZWO, Atik, QHY, Starlight Xpress, Basler, Celestron and many more.  Also, it works with other cameras which have an ASCOM driver.  SharpCap provides support for Ascom focusers, filter wheels and mounts allowing them to be controlled directly from SharpCap rather than through additional SW applications.

​Before looking at the added features of the Pro version, lets look at some unique features of the free version.   Many would agree that the capability to Plate Solve is key among these.  With this, an image of the sky is taken and using one of four free Plate Solving tools in the background, SharpCap determines the actual coordinates at the center of the frame and moves the mount to center the telescope at the desired location.  Plate Solving is a powerful tool to help located dim objects in the sky or to accurately return to a specific location.  The free version of SharpCap also has a Sensor Analysis Tool which can automatically measure the read noise of your camera's sensor versus gain. Another useful unique feature is the ability to utilize one of 6 different Focus Aides including one for analyzing the diffraction image from a Bahtinov mask, another with single or multi-star FWHM analysis, and so on.

The pay version of SharpCap adds some useful tools not available in the free version and also not available at this point in any other EAA software.  First, it has a Polar Alignment tool which eliminates the need for another SW package or additional hardware to make an accurate polar alignment.  Not only that, but the polar alignment routine is simple to use and fast.  A Smart Histogram is also available with the pay version which, working with the Sensor Analysis tool, can determine the best exposure and gain to use for the specific sky conditions.  The Sequence Planner is another powerful tool in the pay version  which automates the process of collecting images allowing the user to set the Planner up and let SharpCap run in an automatic mode.  This feature is more of an astro-imaging tool than an EAA tool, but is good to have if there is an interest to do some traditional astrophotography as well.  

ASILive
ASILive is free software from ZWO which only works with ZWO cameras.  It is a sub-set of ASIStudio which includes applications for Planetary and Deep Sky imaging, along with a Deep Sky stacking application and a FITS viewer.  ASILive is one of the few EAA software that work with Windows, MAC and Linux and iOS.  A very limited ASILive manual is embedded in the Help section of the program.

Due to the popularity of ZWOs cameras for EAA, ASILive is probably the 2nd most used application for EAA.  It has almost all of the features described above and a few additional ones described here including the capability to remove the last frame from a stack using the "Undo Last Sub" command.  This is useful if a satellite, plane or cloud passes through an image while live stacking.  ASILive also adds Bias Frames to its ability to take Darks and Flats.  And, since ASILive is fully integrated with ZWO hardware, it includes the Focuser and Filter Wheel Control for ZWOs own focuser and EFW filter wheel.  Most ASILive users fully integrate with ZWO's platform including their ASIAIR hardware for complete camera and equipment control and power.

Infinity
Atik's Infinity software is free to download from Atik's web site but only works with Atik cameras such as the Infinity and Horizon cameras.  The manual can be downloaded from the Atik web site.  The Infinity software is also works with Windows, MAC and Linux and iOS.  It has most of the features discussed above but is noticeably lacking dark frame subtraction and flat frame scaling

Infinity does have a few features which are unique. There is a Finder Mode designed to facilitate finding deep sky objects by using high gain and short exposures.  Images will be noisy but once found, the user can switch to better settings.  The Record and Replay Mode allows one to record every FITs image during a session which can be played back later for review or sharing.  There is also a Live Broadcast mode which allows for broadcasting a session live view on YouTube  or the Video Astronomy Live website.

Starlight Live
Starlight Live started out as Lodestar Live, a program created by Paul Shears to allow enhanced live viewing with Starlight Xpress' Lodestar camera.  It eventually became part of Starlight Xpress and was renamed Starlight Live.  It is free software which only works with SX cameras.  At present there is a Lodestar Live manual which is the same as Starlight Live.

In addition to most of the features outlined above, Starlight Live includes Non-Linear Stretching of the histogram that changes the contrast of the image, reducing the brighter regions like cores and enhancing the dimmer regions like the spiral arms of a galaxy.  It lacks the ability to take Flat Frames.

MiloSlick Mallincam Control
Bill Koperwhats has developed software designed to work with Mallincam and some generic analog video cameras.  Along with Robin's Sharpcap and Paul's Lodestar Live, Bill's software was one of the earliest providing camera stacking and histogram adjustments.  It has evolved over the years and now has most of the features discussed above.  MioslSlick works with Windows and MacOS.  A manual is available on the Mallincam web site.

MiloSlick also has a Curves adjustment feature with four adjustments points instead of just three.  It also has the ability to Autodetect and Remove Hot Pixels.  Frame stacking, however, is limited to no more than 10 frames.  But frame stacking also allows for Rolling Frame Stacking which stacks the most recent frames and replaces the oldest frame with the newest in the stack.

One of the more unique features of MiloSlick is its High Dynamic Range (HDR) Averaging.  HDR allows the user to take images of different exposure times and stack them together into a single image which helps to retain detail in dark regions of an image while bringing out more detail in bright regions of the image.   Without HDR viewers have to choose between "blowing out" the bright regions like the cores of galaxies in order to bring out detail in the spiral arms and dust lanes, or, the reverse.  MiloSlick also has Sharpening and Smoothing algorithms to further enhance images.

Summary
​There are many good software packages which can be used for EAA.  Several are also quite capable for traditional astrophotography as well.  The decision as to which to use may come down to whose camera you have as most are designed specifically for particular cameras.  Below is a table with a summary of most of the features found in EAA software.  As it shows, SharpCap, especially the Pro version is the most feature rich which is why it tends to be the most commonly used.  While the learning curve is steep, it has a good manual and there is lots of online support including on the SharpCap forum and from several YouTube tutorials.​

Last November I reviewed the Jackery Explorer 1000 solar generator on this web site: www.californiaskys.com/blog/archives/11-2020 (scroll down below the solar panel review) The Explorer 1000 packs almost 1000Wh of power into a compact and rugged design weighing only 22lbs making it well suited to multiple nights of astro-imaging without the need to recharge.  But not everyone needs that much power or cannot afford to pay $1000 ($880 on sale) for their power supply.  So, I got hold of Maxoak's Bluetti AC50s which is a 500Wh model costing only $400 ($380 on sale) to run through the same set of tests to evaluate its usefulness as an astronomy power supply in the field.  In short, the AC50s worked well over multiple nights in the field.

Let's first start with a run down of the AC50s' included accessories and then its features.  The generator comes with an AC charger, a car charging cable, an MC4 cable to use when charging with a solar panel, a USB Type C extension cable, a decent user manual and a 24 month warranty.  Unlike the Jackery, a carrying case for the accessories is not included.  The AC50s is well built with a rigid ABS plastic casing, very compact at 11.6 x 7.7 x 7.5 in. (L x W x D) and extremely light weight at 13.6lbs.   It has fold down handles which makes it easy to carry around and store.  Most everything one needs to access is conveniently located on the front of the generator including:

1)  a regulated 10A DC cigarette adapter socket with dust cap
2)  two unregulated 3A DC 5.5mm x 2.1mm ports
3)  a 45W PD type C charging port
3)  four USB A 5V/3A ports
4)  two 110V AC outputs from the internal 300w pure sine wave inverter
5) an LCD display showing DC/AC power output, charging input power and battery State of Charge (SOC) in 20% increments
6)  On/Off buttons for the power outputs and the display

This generator also has a 10W magnetic charging port for phones equipped with magnetic charging capability located on its flat top.  On the backside you will find an 8mm port for the internal MPPT charge controller used to re-charge the generator either with the included AC charger or an optional solar panel.  There you will also find a large white LED light.  This light is much more useful than the small LED spotlight on the Jackery for illuminating a large area.

As noted above, a major convenience of solar generators is the inclusion of a pure sine wave inverter to supply AC power for any devices being powered with an AC wall charger like a laptop.  At 300W the AC50s' inverter will easily power all of our astronomy equipment if we so choose.  Also, the internal MPPT charge controller eliminates the need for an external charge controller when recharging the generator.  Simply connect the solar panel output with the appropriate cables to the 8mm charging input of the solar generator.  Always keep any lithium battery shielded from the sun when charging with a solar panel.  I like to use the panel itself to shade the lithium power supply.​

Just like with the Jackery Explorer 1000, I ran a series of tests of the AC50s both at home and in the field powering my Software Bisque MyT mount, Celestron C11 OTA, Celestron focuser, ASI1600MC camera, ASI224MC guide camera, TEMP-est cooling fans, mini-PC and a Pegasus Power Box Advanced (PPBA).   I used a cigarette adapter to 5.5mm x 2.1mm cable to supply power from the AC50s to the PPBA which in turn distributed power to the MyT.  The cameras, focuser and fans drew their power from the MyT.  Since the MyT requires 48V I used  a DC-DC up converter on the output of the PPBA to transform 12V to  48V rather than using the less efficient AC adapter.  I use The Sky X (TSX) to control everything except the PPBA which is controlled by its own application. 

First, I measured the total energy capacity of the AC50s by running the generator from 100% to 0% SOC multiple times.  Yes, with lithium based power supplies you can safely run them down to 0% SOC quite unlike a lead acid battery which should never be drained below 50% SOC to avoid permanent damage.  In the case of lithium batteries, an internal battery management system (BMS) functions to protect the battery from all manner of unsafe operating conditions.  This includes over-voltage, shorts, charging below freezing, charging/discharging above 104 degrees F, over-charging and over-discharging the individual lithium cells inside.  All lithium batteries with an internal BMS, this includes solar generators, are designed to be discharged to the point where the BMS shuts the output down to avoid dropping the voltage of the internal lithium cells below the voltage where permanent damage may occur.  Thus, these solar generators can use 100% of their SOC without damage to the internal cells while maintaining the manufacturer's full discharge cycle spec.  In the case of the AC50s, it is spec'd to 1000+ full discharge cycles at which point it's capacity will be reduced to ~ 70 to 80% of the original capacity.  That will provide energy to run a setup more than 100 nights a year over the 10 year expected lifetime of the generator.  The results of my capacity measurements produced an average of 461Wh or 92% of the rated capacity, which is in agreement with another on line review I have seen, and is similar to what I found for the Jackery Exporer 1000.  Not surprisingly, some power is lost in the regulation circuit, etc.

After each full discharge test I was able to make measurements of the recharge times using both the supplied AC charger and a 100W solar panel.  I made repeated tests for each method.  It took between 7 and 7.5 hours to recharge the generator using the AC charger while it took only 6 to 6.5 hours to recharge using the 100W solar panel.  The faster charging rate with the solar panel occurs because the AC charger supplies ~ 82W while the solar panel supplied 95W of input power, hence the faster charge time with the solar panel. 

Now the most important question is "How long with the AC50s be able to power your astro rig?".  That, of course, depends upon what is included in your particular rig.  After verifying that the AC50s powered all of my equipment over many nights in my home observatory without any issues, I took it into the field for 3 nights under the stars with the setup described above:

1.  Software Bisque MyT mount
2.  ASI1600 MC uncooled camera
3.  ASI224MC guide camera
4.  Beelink Mini-PC
5.  Pegasus Astro PowerBox Advanced
6. TEMP-est cooling fans
7. Celestron Focuser

The cameras, cooler fans and focuser all drew power from the MyT Versa-Plate power connections.  The mount and mini-PC were connected directly to the PowerBox which was itself powered directly from the AC50s through the 10A regulated cigarette port.

The first night using the guider, my setup drew an average of 35W per hour over 6hrs for a total of 210Wh leaving the AC50s with 60% SOC at the end of the night.  During the next day, I used a 100W solar panel to re-charge the generator to 100% SOC in just a few hours.  Over the next 2 nights I ran without guiding, averaging 29W of power for 7 hours the first night and 5 more hours the second night without re-charging in between.  Thus, after 12 hours I had used 352Wh, or 76% of the measured total capacity, leaving me with 3.75 hrs more run time at 29W.  Overall, the Bluetti AC50s performed flawlessly as expected.  

Now, there are setups which require more than ~30W of power.  From my own measurements here www.californiaskys.com/blog/archives/11-2020, adding a dew heater for the C11 at full power requires 20W additional power and Peltier cooling for a camera will also add ~20W at maximum power.  That would push the power requirements of the above setup to ~70W.  At that consumption, expect the AC50s to last for 6.6hrs.  You can estimate your power consumption by scaling my numbers to your typical use conditions.  I believe typical power consumption falls into one of 3 ranges:  1) 20-30W;  2) 30 - 60W;  3) 60 - 90W.  Likely most fall into either range 1 or 2 and only those using a laptop to control their setup along with significant dew control and camera cooling will require as much power as indicated for range 3.  If we divide the measured maximum capacity of 461Wh by 30W, 60W and 90W we can estimate run times of 15.3hrs, 7.7hrs and 3.8hrs.  If your needs fall within category 1 the Bluetti AC50s will likely support 2 nights of imaging without a recharge, but if you fall within category 2 you will need some way to recharge during the day to obtain multiple nights in the field.  If your needs fall into category 3, you will need a solar generator rated with a much higher capacity like the Jackery Exporer 1000.

In summary, the Maxoak Bluetti AC50s 500Wh solar generator is well designed, simple to use and easy to carry about.  It sure beats lugging a 64lb 100Ah lead acid battery to provide the same amount of energy and comes with all of the power connections and additional features designed in. 

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