How to Drift Align Using ASIAir

 

V1.5.3

While ASIAir has a great polar alignment (PA) routine, some people do not have a clear view of the north or south pole even within 30 degrees of it, the limit of the PA routine.   So how does one get polar alignment?  An alternative is a manual method called drift alignment.  This is how we did polar alignment in prehistoric days but today remains the method used by permanent observatories around the world.  With a lot of patience you can obtain perfect alignment and require only minimal guide corrections in RA or if you can use PEC mode in your mount maybe not even need to guide anymore. For the rest of us who want to get set up an imaging quickly this can be just as good as a polar scope or using the ASIAir PA routine. 

There is some preliminary set up that can help speed things up.  First you must have a clear view to the south along the meridian within 10-20 degrees of the celestial equator (if you use the south pole then you will want a northern view and use the ecliptic there.  The process is the same.).  The closer the better but use what you have.   Next you need to have a clear view of the east or west horizon within 30 degrees of the horizon is ok but again along the celestial equator line.  These two areas will be used to adjust the mount altitude and azimuth. 

Now using your main scope with imaging camera attached, turn on the asiair crosshairs under the tool icon. Then go into focus mode which gives you more magnification and faster refresh rates.  Choose a star near the meridian along the celestial equator and center it on the cross hairs.   Now you can use the slew controls to move the star near the edge of the field.   Now rotate the camera in the scope so one of the cross hairs align on the star.   This should get your cross hairs lined up with RA and Dec to make the declination drift easier to see.   You can slew a bit in RA to see which crosshair is associated with ra drift and which is dec. You can also do this with your guide scope as it may be easier to rotate that to get the axis aligned. Just make it your primary camera for the duration of this exercise.

Now we are ready to begin.  Since we started the setup using a star near the meridian lets start with that.  Using the slow motion slew controls (less than 4x on the speed slider).  Adjust the the star position so its centered on the cross hairs.  If you want you can also move the green focus box to a star and center the tiny green crosshair on it.  It doesn't matter as long as you can determine star movement along the declination axis line.  Tracking should be on but guiding should be stopped.  Watch over a period of minutes to determine which way the star drifts. The further you are from the pole, the faster it will drift so likewise the closer you get the longer you have to wait.  Now that it has drifted, you will want to use the azimuth controls on the mount to move the star back to the RA line.  You will repeat this until the star stops drifting or starts drifting the other way in which case you have over corrected and need adjust it the other direction.  Continue the process until you can run about 10 minutes without any drift.  This should be good enough to allow guiding to make corrections over the long term.

Now with the azimuth alignment complete, lets move to the altitude adjustment.  Select a star in the east or west within 30 degrees of the horizon along the celestial equator.  Now center the star on your crosshairs and repeat the procedure as before.  This time adjust your altitude setting to bring the star back to the RA line.  It is always best when lowering the altitude to overshoot a little and end with the adjustment pushing the mount upward.  This takes out any slack in the mechanics and ensures it stays in place.  Repeat this process until the star doesn't drift for a period of 10 minutes.

For those with permanent piers you should strive for as perfect alignment as you can.  Spend one night doing just one axis and target for no drift over the course of hours.  Do the next axis the following night.  You may be able to get away without guiding at all and using just the mounts PPEC routine for RA.  For those that set up and take down nightly the 10 minute rule is sufficient.  With practice this can be done in  about 30 minutes or less but plan for an hour or more the first time.

To summarize:

Choose a star within 10-20 degrees of the equator lying near the meridian.  Use the azimuth controls to move the star back to the RA line.  Repeat until you see no drift long the declination line over 10 minutes.

Next choose a star less than 30 degrees above the east or west horizon near the celestial equator.  Use the altitude control to bring the star back to the RA line.  Repeat until you see no drift along the declination line over 10 minutes.

Drift align is not very complicated but it does take a while to complete.  Using a higher magnification or adding a barlow into the optical path can speed up the process as the drift will be more apparent in a shorter time period.

How to Autofocus with ASIAir

 

V2.1 - 2/21/2023

Just an update that EAF firmware version 3.3.7 now adds support for a maximum step count of 600000.  This should help hyperstar users who switch back and forth between native mode and require 120k+ steps to reach focus.

V1.5.3

One recent feature that is still being improved is autofocus.  Using the ZWO EAF you can electronically focus your telescope and now it can be done automatically.  The EAF is attached to your telescope focuser either with the included bracket or with a custom bracket.  If you are handy you can even make one on your own.  Before AF can work efficiently you must ensure that the shafts are locked really good.  Most shafts including that on the EAF have a flat side that must have a set screw torqed properly against the flat to reduce backlash. As of this writing, ZWO has released a new EAF that runs off USB power.  The original version required 12V and a USB connection.  I have been told that the mechanics and gearing are the same so should be interchangeable.

Everyone is familiar with autofocus on their cameras or phones.  These work great with bright daytime scenes but don't work well or at all under low light levels.  With telescopes the current method utilizes multiple exposures while advancing the EAF motor in fixed steps to plot a vcurve similar to the one shown at the top of this page and is based on the size of stars in the field.  You first must start with an image that is in eyeball focus.  Then, a dozen or more shots are taken and are run through a formula to determine the curve.  The curve is an approximation, but the apex should represent the position with the best focus.  Lastly the routine will do a short validation test taking 3 or 4 shots near the apex to select the best possible position of the motor.  The curve will never be precise due to atmospheric seeing.  However, we are not shooting for precise.  We really want to know where the bottom of the vcurve is.  This point represents the EAF position that should result in the lowest HFD or smallest star size.  This is the red dot shown in the first image here.

So this explains how it functions.  So how do we use it?  In principle it is very easy.  The autofocus settings are located under Focuser Settings.  There are two main settings that affect how well AF works, AF Exposure and Step Size.  The AF Exposure setting here is the default AF exposure. The exposure used depends largely on what filter if any you are using.  Shorter exposures generally work best. However with narrowband or broadband filters exp of 1-3 seconds wont work very well.  In those cases you want to use 3-4X what you would use with a luminance or no filter.   Because each scope is different you have to try different exposures to see whats best.   If you use an EFW filter wheel, you will notice now that each filter has its own AF exposure time.  This is set under the filter wheel configuration screen.  This allows you to set custom exposures based on the current filter used. 

The next setting is Step Size.  This is the number of EAF motor steps that will advance between AF exposure tests.  This can be useful to tune the AF sequence when you have custom setups where the default of 30 steps is not correct.  Examples for changing this are when you have connected the EAF to your 10 to 1 fine focus shaft.  You could multiply the default by 10 to make it 500 steps.   Another example would be if you use a homegrown belt system to focus your Redcat or camera lenses.  Or maybe you just want to speed up the AF sequence and are ok with a little loss of precision.   Whatever the reason this setting can help you tune the AF for your particular setup.  My C11 Edge with a Feathertouch focuser uses 60 steps.

The other settings dictate when asiair should start an AF sequence.  These are pretty self explanatory so I wont detail them here.  Just note that these can be used in combinations so that any activated trigger will kick off an AF.  If a trigger is met, asiair will wait until the end of the current image before initiating the AF sequence.  

I will add a note here about temperature changes.  The EAF contains an internal temp sensor which can be used to monitor for environmental changes.  A remote temp sensor can be added for focusers that have a slot for such a sensor.  I have also been inclined to add a remote temp sensor into the rear cell of my SCT to monitor the change internally to the OTA.  In most cases you can just use the internal EAF sensor.  Also its important to note that these sensors are NOT calibrated.   They will not accurately measure the outside air temperature. All we are concerned about is the change in temp not the absolute value. 

You can initiate an AF routine manually by clicking the focuser icon on the left side of the screen and then clicking AF.  Clicking the play icon starts the routine. The process can be stopped by pressing the stop icon.  The settings described previously are only used when an Autorun sequence is running.  Otherwise you must conduct the AF sequence manually. 

The other EAF settings such as fine and course have no effect on autofocus. Currently the backlash setting is only used when manually focusing using the on screen controls or EAF hand paddle.  Exposure and step size are the only settings that control how AF works.  Its important to get them right.  This may change in future releases but ZWO currently wants to keep it simple. 

If you are getting error messages that the EAF moved less than 900 steps then you need to increase your step count by 5 or 10 at a time until you have success.   Smaller step sizes will generate a more precise curve but will take much longer to complete.  Conversely, using a step size too large will generate a curve quickly but will not be very accurate.  Use a step size that will take at least 12 sample points then compare a number of preview images. If your precision is still off then decrease the step size by 5 or 10 and try again.  Try to use as large of a step size as you can and still get consistent results.  Dont go overboard on the step size.  Increase it by 10 each time and see how it performs.   Every system will be different. 

The ASIAir autofocus is evolving and expect to see improvements in the function with each new release. 

ASIAir Power Ports

 V1.5.3

With the introduction of the ASIAir Pro, four 12V power ports have been added and made possible by a custom power board that piggy backs onto the main cpu board.  Each port accepts a standard 2.1x5.5mm plug and the product includes 4 power cables to use with your various astrophotography equipment.  The ASIAir supports a total of 6A or 6 amps total across all four ports plus the ASIAir itself.  Each port can only support 3A of power as long as the total power consumed doesn't exceed the 6A.  Most devices will have an amp rating in their specifications that represents the maximum power the device will consume with all features in use cranked up to the max.  Amp ratings are additive so take all of your devices and add up the amp ratings to get the maximum power that can be consumed.

There are many uses for these power ports but ZWO does not recommend plugging your mount into a power port.  Most mounts consume too much power especially when slewing and can cause the ASIAir to go into fault mode and shut down or cause other operational issues.  Please purchase a splitter cable to use to split power from your source, one to the mount and one to ASIAir.  Suitable mounts to use with a power port would be those low power devices that only track in RA.  Check the power specs on the mount to make sure it does not exceed 3A maximum.

TIP: Choose a power source that is twice the capacity of what you need.  If all of your equipment totals up to a maximum draw of 5A to include the mount you just split off, then use a power pack that is rated at 10A.  The reason for this is that most of these power supplies are switching power supplies and when they start to reach their maximum rating they get really hot and they also can produce noise on the power wire.  This can often cause electronics to do strange things or crash or can cause noise in your images to appear. The best power sources are batteries, battery packs, or what are called linear power supplies.  Fortunately switching power supplies are now cheap even at twice the capacity needed so no need to skimp on the rating.

Now with the disclaimers out of the way, lets take a look at the options now available.  To access the power configuration, click on the wifi symbol at the top of the screen and select “Power Output”. Each power output can be given a name and some of these enable PWM or Pulse Width Modulation.  The available options at this time are:

Telescope - Full time 12v off/on

Camera - Full time 12v off/on

Dew Heater - 12v PWM 0% to 100%

Focuser - Full time 12v off/on

Flat Panel - 12v PWM 0% to 100%

Others - Full time 12v off/on

On some devices the list does not completely display and you will have to scroll to see the other options.  You would be surprised how many people miss this.

The PWM outputs are useful for controlling things like dew heaters to control the temperature at the scope, lens, or mirror or for a flat panel or other LED lighting used at the mount for setup or safety.  You should not use the PWM options for devices designed to require full time power.  Nor should you use PWM to reduce the output to power your DSLR.  Doing so will almost certainly damage your camera.  Use an appropriate 12V power adapter for this.  Remember 12V PWM is still 12v its just turned off and on at a very fast rate and made faster or slower by using the slider.  It does not vary the voltage.

The settings you choose are sticky and will reset to the on/off or PWM setting that were set previously upon boot up.  While its not a huge deal its important to know that when ASIAir boots up, all power ports get turned on briefly at full power until the configuration is loaded and settings applied.  This is usually only a few seconds but important because dew heaters will run at maximum and cause maximum start up current until PWM kicks in and cuts the power draw or some ports are turned off.  Its important to know the power requirements of your devices so you do not exceed the maximum that ASIAir can handle.

The case on the ASIAir is made of aluminum much to the dismay of wifi users.  The reason for this is because the case also acts as a heatsink or heat dissipator for the power board.  The more power that is needed, the hotter the case will get.  Be mindful if you decide to use sticky velcro to hold it to something that likely it will come unstuck when it gets hot.  Use the supplied finder foot or other screwed on attachment to fix it firmly to your scope or mount.

In summary, the total power draw of the ASIAir cannot exceed 6A or 3A on any one port!  Power requirements are additive so look up the specs and add up the maximum amp ratings.  The introduction of power ports opens up a lot of possibilities for controlling devices from the tablet or phone.  I use one power port for cooling fans to help cool down the primary mirror on my C11.  After 30 minutes I can turn off the fan power and start imaging.  Another port is used to control 12V LED lighting on the tripod legs.  With PWM I can safely control the brightness of the LEDs.  I use these for safety so I or others do not trip on the tripod legs or wires nearby in the dark.  I’m sure you will find other unique uses for these ports that will help in areas I haven't thought about yet.

Finding A Planet or the Moon with ASIAir

 

V1.5.3

I get a lot of reports from folks that ASIAir will not plate solve on planets or the moon.  The reality is that any object that moves against the stars cannot be plate solved.

Plate solving compares the field of view with recorded plates of known star positions to determine the exact position of the telescope.  An interloping planet or moon can mess up the ability to solve the location.  So what can we do?

The trick is to goto a nearby star or object that is in the asiair database.  This object should be within the same quadrant of the sky and as close as possible to your target.  For planets this is fairly easy.  Choose a star nearby and then do a platesolve and then sync the location.  If you have autocenter enabled then this will be done for you.  I recommend that for planets and the moon you disable goto autocenter and do the platesolve and sync manually.  Once the star goto has completed and has been solved and synced, goto the star again and make sure it it is in fact centered.  Then goto the planet thats nearby and the planet should be reasonably centered.

The process for the moon is the same but the brighter the moon is the more difficult it will be to get that nearby star platesolve completed.  As long as you can achieve a platesolve and sync on a star somewhere in the same quadrant as the moon or worst case same hemisphere as the moon you should get reasonably close.  Try different exposures or filters if the moon interferes with the platesolve.  

The idea here is that you really dont want to do your platesolve on the other side of the meridian from the target.

ASIAir Pro Live Stacking

 

V1.5.3

Live Stacking is a feature only available to the ASIAir Pro.  This is due to the faster processors and IO buss currently used in the device.  Live Stacking is an incredible feature that grows on you the more you use it.  In this age of instant gratification, it is incredibly rewarding to watch your image build one exposure at a time as it happens all in real time.

One can just start a live stack and get instant success.  However, with a little prep ahead of time one can prepare calibration frames and have them applied in real time as the image is stacked. 

To get started we need to prepare our calibration frames bias, dark, and flat frames.  ASIAir will automatically stack each once we get things rolling.  The resulting stack will be added to the light frame setup and then enabled. Make sure that your calibration frames are all made using the same gain, BIN, and temperature setting.

Bias frames are really important if you are using a dslr camera.  Dslrs are not really designed for astrophotography and so no attempt is made to improve the sensor read noise because usually pictures of Fido are so bright that it just swamps all of the read noise and its not a problem.  But for astro work this read noise can be devastating.  To get rid of the bias read noise and banding, we take a series of very short exposures, as short as the camera will allow, with the scope covered.  The resulting data is JUST the read noise.  For astro cameras like the ASI series, the noise is so very low already and with cooling its virtually non existent that bias frames are not necessary and in fact could add noise to the image. If you are using an ASI  astro cam then just skip the bias frames.  To set up for a bias stack, cover the scope or lens and then edit the live configuration.  The configuration window will appear with 4 tabs at the top.  Select Bias.

For the exposure this will be very short, the fastest exposure your camera will support.  For BIN you should use the BIN setting you plan to use to shoot your target.  If you are not sure then just use BIN1 for everything.  ZWO has a white paper on BIN settings if you want to learn more.  For the number of frames just use the maximum of 40.  When done, click OK and then star the live exposure.  The bias stack will build and when 40 have been stacked it will automatically save the master bias into the Live folder.

Next we will do the same with dark frames.  In the live configuration screen select the dark tab.  The set up is similar to bias but we now want to use the same exposure time that we will use for the light frame. In the example image this shows as 300s but it should be 120s to match the light exposure we will be using.  You can figure out the best exposure to use by trying some preview frames of your target to get your desired exposure.  If time permits you may want to make several dark stacks at different exposures to have for future use.  Select the maximum number of frames and begin the live stack.  When its complete it will save the master dark to the live folder.

The last calibration frame needed is a flat frame.  I strongly suggest you read my other blog on using the new AutoFlat option.  There is a lot of information there that is helpful for successful flat creation.  Once you have mastered the creation of flats, you will set up the flat options in the live configuration panel under the flat tab. As with the others, select the exposure or Auto if using AutoFlat, the BIN setting used and the maximum number of frames.  Once complete, start the live stack and the master flat will be stored in the live folder when done.

Now we are ready to set up our light frame.  Once in the live configuration panel, select the light tab.  Here you will select the exposure time, BIN setting, and stack duration.  Here you can select the number of frames to stack, or no limit.  With no limit, live will keep stacking until you pause it.  The image will only be saved once you select the image save option on the lower right of the screen.

Below these settings are the options for selecting and enabling the calibration frames to use.  Tap the > symbol for each calibration type and select the saved master calibration stack you created earlier.  Complete this for each type bias, dark, and flat.  These will not be enabled by default.  You must select each one by clicking the box to the left of the file name.  If you want to run a stack without a calibration file, just deselect it here.  The last option is save every frame when stacking.  This will save each frame as its taken so you can stack it with other software later.

Once these have been set its show time.  Go back to the preview screen and go to your desired target and get it framed as desired, focused, and then start guiding.  Go back to live mode and start the exposure.

If you set a fixed number of frames to stack, the asiair will continue until all frames have been stacked and the image will be saved in the live folder.  If you selected no limit, the stack will continue until you stop it.  It will not be saved until you select the download icon at the bottom right.

If you stop a stack, you can resume it again.  This is helpful if you need to dodge clouds, aircraft, or starlink satellites.

Currently there is no way to combine mono images taken with different filters.  You can stack them individually with live but they will need to be registered and combined with other software. If you plan to livestack using filters, don’t forget to make flat frames for each filter.  Then select and enable them before shooting your light frames.

Live stacking is a rewarding experience that gives instant gratification.  The more i use it the more I prefer it for short term projects.  I’m sure you will find it just as enjoyable  

ASIAir - AutoFlat Frame Exposures

 

V1.5.3

This version of ASIAir introduces a new feature I call AutoFlat. Before i go into how to use this let me explain a little about flats and how we used to calculate the proper flat exposure. 

Flats are used to map out vignette, gradients, dust, and other filter variants.  This data is then applied to your target light frames to balance the gradients and remove dust and other optical imperfections so that the resulting image is flat and evenly exposed without the defects of the optical system.

Typically folks use layers of tshirts against the sky, led flat panels, EL or electroluminescent panels, or light boxes.  Some have even used their ipads.  The idea is to use a known even illumination source so gradients and dust can be recorded.  The trick is obtaining the proper exposure.  Previously it was common knowledge to use what is called 1/2 full well.  Some have suggested to use 1/3 full well but like anything we do there are plenty of folks to challenge every step.  The process of calculating this exposure is to slowly ramp up your exposure until your average ADU value shown on the preview screen just reaches 65534 or the maximum value for your camera.  Basically its the exposure where this value doesnt increase anymore.  For 1/2 full well we would take exactly one half of this exposure time.  The 65534 value represents the point where the pixels on average have been fully saturated and will record no more photons; a full well.  Half of the exposure time will record one half full well.  If you are in the 1/3 full well family then you would take 1/3 of the exposure time.  This would then be your ideal flat exposure time.  It is not 1/2 ADU or the middle of the histogram.

So in reality, this is really only important for the purists.  ASIAir makes this legacy model easier since we can immediately see the ADU value on the preview screen.

With 1.5.3, ZWO introduced Autoflat.  When you set up the autorun tile for flat exposure you will find there is now an Auto option for the exposure.  There are some limits however.  ZWO has introduced a 10 second exposure limit. If your exposure time hits 10s them you need to increase the brightness of your light source.  There can be a lower limit with some cameras.  There have been reports that some cameras show banding with exposures shorter than 2s.  This is something to watch out for.  So for this to work reliably, your exposure should be between 2 and 10 seconds when using auto.  

I requested a higher limit like 30s but was told 10s was enough.  Lets hope they bump this up in the future as its difficult to run flats for an entire wheel of filters if you have lum, rgb, and narrowband filters in the same wheel.  For now you just have to run them separately.

Now, folks have also abandoned bias frames with asi cameras in favor of using flat darks.  This is due to the banding issue mentioned earlier.  Flat darks are the same exposure as the flats but with the scope covered.  Fortunately ZWO added a way to do this. After running the flats, go into autorun and reset the autorun, go into the flat tile and click the exposure edit icon.  The previous auto exposure will populate the

exposure field.  Now you can select bias or dark as your image type.  Your choice.  Cover the scope and run the sequence again.  You now have your flat darks.  If you are using a DSLR please use true bias frames, not flat darks.

One will notice that the histogram does not show the hump at the manually calculated 1/2 full well.  I’ve been told that this is due to the exposure being calculated before white balance has been applied and before debayer for an OSC camera.  Honestly I have never seen an issue between a variance here in the fractional full well used except in cases where there are extreme gradients.  The important thing is that for all filters used that the fractional full well value is the same for all filters, somewhere between 1/3 and 1/2 full well is fine, to help with color balance when all are combined to produce a color image.

Previously getting the correct flat exposure was a painstaking effort that needed to be performed whenever you changed gain and filters.  With the introduction of Autoflat this has been made quite a bit easier to accomplish.  Currently this is limited to exposures between 2 and 10 seconds.  You can vary the light intensity to get you in that range.  One option is to use frosted lexan or plexiglass or for very bright led tracing panels you can use cling on window tint from the auto parts store.  Find some that have 20% transmission and are neutral grey in color.  It comes in rolls 2ft x 12ft for only 12.00US.  Just cut with scissors and tape to your led panel.  Stack layers if you need even more light reduction.

One last tip.  If you are using a LED flat panel or light box and normally orient the scope vertically to keep them in place, be sure to park the scope to the home position.  This will set the scope to a known position you can reset to after the flats are taken, disable tracking, and prevent an automatic meridian flip if that is enabled in autorun.  May be a good idea to just turn that off when shooting flats this way.  You dont want any movement to cause your equipment to slide off and get damaged.

I hope this has been helpful and simplifies your calibration workflow.

How To Set Up Automeridian Flip in ASIAir

 

V1.5.3

With the introduction of ASIAir version 1.4, a new feature is available called Automeridian Flip often referred to as AMF.  During an imaging sequence using autorun, the mount will now automatically flip the telescope to the other side of the mount once the target has crossed the meridian. In addition this function is available even when using SkySafari to goto and frame the target image.

Under mount settings there is a setting to control the Center Exposure TIme (1s-10s). For most setups the exposure time can be set from 1s-3s. However, if you are using narrow band filters you should set this to 10s to ensure enough stars are recorded to allow the system to plate solve the image before and after the flip.

Automeridian Flip is currently only available when imaging a sequence using Autorun. The autorun page now displays how long it will be before the meridian flip will take effect. When the target reaches the meridian, autorun will pause imaging and tracking will stop. The amount of time it waits for this to happen is based on a couple of settings and the programmed autorun exposure currently being executed.

The first setting is “Stop tracking x min before Meridian”.  This is useful to stop everything to prevent your scope or camera from hitting your pier or tripod.  The second option, “Do AMF x min after Meridian”, is similar but controls the time to do the AMF after the target crosses the meridian.  Again, this is to prevent the equipment from hitting the pier or tripod on the other side.

The last option, “Recalibrate Guiding after AMF”, will clear the guide calibration data and start the guide calibration sequence.  This is sometimes needed for mounts with backlash that differs after AMF.  The recalibration ensures backlash is measured and added to the correction pulses to improve guide response.

Once the flip has completed, the goto will be plate solved and adjusted to recenter the target precisely to where it was prior to the flip. The image will however be inverted. At this point guiding will autoselect a guide star, flip the guide calibration data or recalibrate if selected, and begin guiding. The imaging sequence will then resume.

Automeridian flip further enhances the ASIAir to minimize the interaction needed to complete an imaging sequence.