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Autofocusing from a Remote Site

PrimaLuceLab SESTO SENSO 2 Acquisition Auto-Focusing Deep Sky Troubleshooting
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Jerry Gerber avatar
Jerry Gerber avatar
Hello,

Does NINA have a log of error messages?  I ran autofocus, stars look fine,  but at the very end I got the message saying autofocus couldn't complete.  It seems to have completed.  What should I do when I get this message?  I'm using the Sesto Senso 2 focus motor. 

One more question:  Is  there a way to speed up the focusing routine?  I can focus manually with a Bahtinov mask in about 60 seconds.   Electronic focusing is taking much longer, at least at the start of the sequence.  I run autofocus every 30 minutes and it seems to go quicker after the initial focus routine.  I am imaging from a remote site and can't just walk up to the scope and re-focus, I'm nearly 1000 miles away..   Thanks, Jerry
Philippe Barraud avatar
Philippe Barraud avatar
Hi,

I am using remotely Asiair EAF and it works rather quickly, i.e. around one minute to make its V-curve, after every filter change.

Philippe
jeffreycymmer avatar
jeffreycymmer avatar
NINA reverts to the last best focus on error.  You can set up retries.  The autofocus speed depends on the number of samples and the exposure times which you can control.
Peter Graf avatar
Peter Graf avatar
Hi,
Unfortunately, I cannot help with the error message you get. There are log files in this directory: %LOCALAPPDATA%\NINA\Logs\, see also here.

For speeding up the autofocus procedures in general, there is a setting in the advanced sequencer that I am currently using: "AF after HFR increase", instead of "AF after time". This helped me at least to get little bit more imaging time during the night, whereas with my portable setup (ZWO EAF, 150PDS), focusing feels really quick.
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Jeffery Richards avatar
Jeffery Richards avatar
Peter Graf:
Hi,
Unfortunately, I cannot help with the error message you get. There are log files in this directory: %LOCALAPPDATA%\NINA\Logs\, see also here.

For speeding up the autofocus procedures in general, there is a setting in the advanced sequencer that I am currently using: "AF after HFR increase", instead of "AF after time". This helped me at least to get little bit more imaging time during the night, whereas with my portable setup (ZWO EAF, 150PDS), focusing feels really quick.

And setting up filter offsets will help speed things up as well if doing more than one filter per night.
Bill McLaughlin avatar
Bill McLaughlin avatar
1) I would not focus by time. Time has little to do with whether you are staying focused. It basically depends on the depth of focus for your scope combined with the shift of your focal plane. The shift is about 95% due to temperature and varies with your scope materials and construction. Of course focus also can be seeing but that is not within your control. That is why I do not like focus triggered by increased star size - if seeing gets worse, it will be constantly doing focus runs that will not do any good.

2) Since focus shift  is mostly temperature, you need to figure out how much your system changes focus with temp. Typically you use the temp provided by the focuser and it is best in that case to have a focuser with a temp probe that can be attached to the part of the OTA that  causes the most temp shift (typically the metal parts).

NINA has a routine where it will keep track of focus position vs temp and plot that and after a few nights you can get a good idea of how many focuser steps per temp degree your system shifts.  Then you need to calculate the depth of focus in focuser steps for your system (not to be confused with depth of field). There are several formulas for this and I think an online calculator. You can also do this empirically if need be. Now you know how much away from the ideal focus position you can be w/o being out of focus so you combine that with your temp vs focus shit to figure how much temp shift you can handle w/o a new focus. Be conservative. Typically for amateur system this ranges from .5 degrees C to maybe 2 degrees C.

I would also use offsets and focus with the most reliable filter (often green gives the best results). This is especially true for narrowband filters which can be tough. You can use NINAs focus offset calculator but DO NOT just do one run and think it is accurate. IT IS NOT, despite claims to the contrary. If you do multiple runs you will find that they vary and they often do so by amounts greater than your depth of focus. Use that and you guaranteed out of focus images. You need to do many runs until you can eliminate the outliers and converge on a reliable offset number for each filter. It typically takes 2-4 nights to get to a set of solid offsets.
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Jeffery Richards avatar
Jeffery Richards avatar
Bill McLaughlin:
1) I would not focus by time. Time has little to do with whether you are staying focused. It basically depends on the depth of focus for your scope combined with the shift of your focal plane. The shift is about 95% due to temperature and varies with your scope materials and construction. Of course focus also can be seeing but that is not within your control. That is why I do not like focus triggered by increased star size - if seeing gets worse, it will be constantly doing focus runs that will not do any good.

2) Since focus shift  is mostly temperature, you need to figure out how much your system changes focus with temp. Typically you use the temp provided by the focuser and it is best in that case to have a focuser with a temp probe that can be attached to the part of the OTA that  causes the most temp shift (typically the metal parts).

NINA has a routine where it will keep track of focus position vs temp and plot that and after a few nights you can get a good idea of how many focuser steps per temp degree your system shifts.  Then you need to calculate the depth of focus in focuser steps for your system (not to be confused with depth of field). There are several formulas for this and I think an online calculator. You can also do this empirically if need be. Now you know how much away from the ideal focus position you can be w/o being out of focus so you combine that with your temp vs focus shit to figure how much temp shift you can handle w/o a new focus. Be conservative. Typically for amateur system this ranges from .5 degrees C to maybe 2 degrees C.

I would also use offsets and focus with the most reliable filter (often green gives the best results). This is especially true for narrowband filters which can be tough. You can use NINAs focus offset calculator but DO NOT just do one run and think it is accurate. IT IS NOT, despite claims to the contrary. If you do multiple runs you will find that they vary and they often do so by amounts greater than your depth of focus. Use that and you guaranteed out of focus images. You need to do many runs until you can eliminate the outliers and converge on a reliable offset number for each filter. It typically takes 2-4 nights to get to a set of solid offsets.

Bill,

Is there an advantage to using the temperature driven focus adjustment over the HFR delta method? Like Peter above, I have been using the HFR delta method and have been satisfied.
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Bill McLaughlin avatar
Bill McLaughlin avatar
Jeffery Richards:
Bill McLaughlin:
1) I would not focus by time. Time has little to do with whether you are staying focused. It basically depends on the depth of focus for your scope combined with the shift of your focal plane. The shift is about 95% due to temperature and varies with your scope materials and construction. Of course focus also can be seeing but that is not within your control. That is why I do not like focus triggered by increased star size - if seeing gets worse, it will be constantly doing focus runs that will not do any good.

2) Since focus shift  is mostly temperature, you need to figure out how much your system changes focus with temp. Typically you use the temp provided by the focuser and it is best in that case to have a focuser with a temp probe that can be attached to the part of the OTA that  causes the most temp shift (typically the metal parts).

NINA has a routine where it will keep track of focus position vs temp and plot that and after a few nights you can get a good idea of how many focuser steps per temp degree your system shifts.  Then you need to calculate the depth of focus in focuser steps for your system (not to be confused with depth of field). There are several formulas for this and I think an online calculator. You can also do this empirically if need be. Now you know how much away from the ideal focus position you can be w/o being out of focus so you combine that with your temp vs focus shit to figure how much temp shift you can handle w/o a new focus. Be conservative. Typically for amateur system this ranges from .5 degrees C to maybe 2 degrees C.

I would also use offsets and focus with the most reliable filter (often green gives the best results). This is especially true for narrowband filters which can be tough. You can use NINAs focus offset calculator but DO NOT just do one run and think it is accurate. IT IS NOT, despite claims to the contrary. If you do multiple runs you will find that they vary and they often do so by amounts greater than your depth of focus. Use that and you guaranteed out of focus images. You need to do many runs until you can eliminate the outliers and converge on a reliable offset number for each filter. It typically takes 2-4 nights to get to a set of solid offsets.

Bill,

Is there an advantage to using the temperature driven focus adjustment over the HFR delta method? Like Peter above, I have been using the HFR delta method and have been satisfied.

Mainly that HFR driven can respond to seeing and thin clouds and wind/mount issues that have nothing to do with actual focus shift and are beyond one's control.
Jerry Gerber avatar
Jerry Gerber avatar
Thanks for sharing your experience regarding focusing at a remote site everyone. Really helps. 

I'm shooting OSC so filter changes not an issue. 

I too figured out late last night that autofocus by time isn't working well. 

Still wondering about this error message:


Thanks, 
Jerry
Jeffery Richards avatar
Jeffery Richards avatar
Bill McLaughlin:

Mainly that HFR driven can respond to seeing and thin clouds and wind/mount issues that have nothing to do with actual focus shift and are beyond one's control.

Well wouldn't the only drawback here be possibly some "extra" autofocus runs? I understand from an efficiency standpoint doing "extra" runs will decrease imaging gathering time overall.
Jeffery Richards avatar
Jeffery Richards avatar
Jerry Gerber:
Thanks for sharing your experience regarding focusing at a remote site everyone. Really helps. 

I'm shooting OSC so filter changes not an issue. 

I too figured out late last night that autofocus by time isn't working well. 

Still wondering about this error message:


Thanks, 
Jerry

Jerry,
You don't mention what type of autofocus you are using (straight NINA v-curve or HocusFocus) and such. Do your step sizes normally create a good v-curve shape? Since you are autofocusing purely on time, it's possible something was going on (clouds, wind gusts, etc.) that impacted that particular run resulting in no "v-shape".
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jeffreycymmer avatar
jeffreycymmer avatar
The error message is stating that the actual result deviated from the expected result(coefficient of determination).  0.7 is pretty forgiving.  I usually use 0.9.  Could be caused by bad seeing.  What's your focal length?
Jerry Gerber avatar
Jerry Gerber avatar
I'm using the NINA V-Curves. It usually finds focus after around 20 points or so. 

I realized that using AF based on time is a waste of time and won't use that method again. 

I'm using the Askar 130PHQ refractor (1000mm focal length) and the Sesto Senso 2 focuser, NINA, and a 10Micron GM1000 mount. 

Where do you change the focuser coefficient, in NINA?
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jeffreycymmer avatar
jeffreycymmer avatar
Find it under Options/Autofocus - R^2 Threshold
Jerry Gerber avatar
Jerry Gerber avatar
Find it under Options/Autofocus - R^2 Threshold

Thanks Jeffrey!
Jerry Gerber avatar
Jerry Gerber avatar
Any suggestions as to a good Autofocus Step Size and Autofocus Exposure Time for a 1000mm focal length refractor with a Sesto Senso 2 focus motor?

Jerry
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jeffreycymmer avatar
jeffreycymmer avatar
Lots of YouTube videos on this topic
Alan Brunelle avatar
Alan Brunelle avatar
Jerry Gerber:
Any suggestions as to a good Autofocus Step Size and Autofocus Exposure Time for a 1000mm focal length refractor with a Sesto Senso 2 focus motor?

Jerry

Patriot Astro has a good YouTube video on how to set up autofocus properly on NINA.  It is basic, but a bit more than that, and he goes through the logic pretty well.  You should be the one to determine the exposure times based on your fl, camera settings, such as gain, etc.  I know that I start my sessions by taking short exposures with my 91mm refractor and just seeing what the stars look like depending on my camera's read mode and gain, etc.  But it is you to figure that out.  You don't need to be able to see huge numbers of stars.  And during that early time of the night, before astronomical darkness, I do not expect to see all the stars.  But I can get my autofocus to work when I need to, and that is prior to starting my sessions.  

Other factors require telling NINA properly your setup and setting the step size of your routine, so that there is enough focusser travel to make significant differences in hfr for each reading.  If you set things too small (or numerically tight between points), then the expected differences in read values will be too small to exceed the error generated in the numbers.  That will make your stats look bad and NINA will fail the run.  For this, you will need to know the ratio of focuser travel-to-tick numbers for your Sesto Senso motor.  Again, Patriot Astro deals with all of this.  But the motor is specific to you, so read your motor manual.  And once the understanding of the autofocus process works, then you doing trial and error is a great way to learn all the ins and outs of your system.

In any case, understanding the logic of how these devices work and how the software deals with it is the best approach.  It is easy to ask someone for just the specific numbers to plug into the dialog boxes, but then you are left with going back to the forum "well" each time you run into trouble again.  I think the old saying goes along the way of "you can give someone an ear of corn each time they are hungry, or you can teach them how to plant corn seeds and grow their own...".  With that philosophy, Patriot Astro videos are good that way.  My only gripe with them is that his presentations move along very fast!   So be prepared to pause and rewind a number of times.
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Jared Willson avatar
Jared Willson avatar
Looks like NINA couldn't match the parabola (or hyperbola--whatever you have chosen) with enough accuracy to feel it had a good focus run. I have had that happen lots and lots of times over the years.  Usually, it's tube currents or poor correction from lack of equilibration that causes a bad fitting of the curve. Poor seeing can contribute as well since my HFR numbers do not grow symmetrically on both sides of focus with really bad seeing. Poor SNR (passing clouds) can produce the same error. All of this is totally normal, and NINA will just return to the last point of best focus. Nothing to worry about.

I have a temperature sensor in my focuser, so one would think that having the point of focus adjust automatically as temps drop would make sense. I tried that--measured how much the focus shifted over the night and what my delta T was and assumed a nice straight line. For me, that didn't produce very good results. First, the focus would change in the middle of the exposure. This was an older version of NINA, and I'm not sure whether this is still the case, or whether NINA limits itself to making adjustments just between exposures.  In any event, my focuser transmitted just enough vibration and just enough flexure that I really didn't want the focuser to move during an image. Second, once I added insulation to my telescope I found that the delta T for the primary had very little to do with the delta T at the focuser, so I wasn't getting accurate results. People using different telescopes may not have this issue, but for me I just couldn't use delta T to automatically adjust focus.

So, I settled on using two additional approaches. First, I adjust focus with changes in HFR. If my HFR grows by a certain percentage, I probably need to refocus.  Second, I use time. Just counting on HFR growth will not optimize things since HFR may change from subject altitude, changing seeing conditions, etc., not just from poor focus, so I setup my system to re-focus whenever HFR has increased by a certain threshold amount or when a certain amount of time has elapsed. The time component is required since my subject may actually get sharper as it rises to its maximum altitude, even though the focus is actually deteriorating due to falling temps. Different scopes and different observing conditions will require different thresholds.  Some scopes are super stable with falling temps, while others are not. For my scope, which includes both refractive and reflective optics and a primary mirror that is made of optical glass rather than something more stable like fused silica, I need to refocus pretty frequently. That means every 45m to 60m (depending on the season) as well as whenever HFR has increased by more than 7%. 

I have my focusing routine setup to check four points on either side of focus.  That's enough to get me a pretty obvious curve to fit against. It seems to be quite a bit more reliable than just 3 points on either side of focus. I usually avoid the "v curve" fit (trend lines) since my relatively short curve sections that are close to linear. My best results seem to be with a "hyperbola" fit.  Filter offsets are a must for any telescope that includes refractive elements. Also, supposedly parfocal filters may not quite be as parfocal as one would hope, even with a simple reflector. Use of filter offsets will almost certainly let you get better results than focusing with filters since you can use a shorter exposure time with just a luminance filter and still have accurate HFR calculations (short error bars). 

I use the HocusFocus plugin to speed things along. It lets the system shift to the new focus point and stabilize while it's still doing the math on the last focus point--improves the speed of the routine.

My system will perform a focusing run in about 90s. That's fast enough that in an eight hour imaging session (typical time that I have full dark with my target well placed), I will lose about 10 minutes total to focusing runs. That's about a 2% loss in efficiency vs. a system that remains perfectly focused throughout the night--not too bad.

Take my experiences as general guidance on an approach and things to consider when setting up your AF routine. Each system and each location will need its own parameters, but my experiences may give you some things to think about and experiment with. Don't assume that because someone else has done rigorous testing and found a certain set of parameters to be "the best" that they will work well--or even at all--for your system and conditions. 

- Jared
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