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SGP Autofocus issue

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#1 thekubiaks

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Posted 06 June 2020 - 10:57 PM

I am running into a new problem with SGP autofocus and I am not sure how to fix it.

 

I am imaging ic1396 tonight with narrowband filters.   In the image there are a couple of bright stars.   When SGP starts the autofocus run, it defocuses as always but only takes its HFR from the two bright stars.  On the next step,  the weaker stars start coming into focus but so does the bright stars and HFR goes the wrong way and SGP aborts the focus run.

 

How do I fix this??

 

Any ideas would be appreciated.



#2 Phil Sherman

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Posted 06 June 2020 - 11:34 PM

I believe that if you have entered focus displacements for all of your filters, you can use a luminance filter for focusing and SGP will just use the filter displacements for your narrow band filters. An alternative could be to not use autofocus at all and pre-focus on a bright star before slewing to your target. You would have to do this for each filter though. A final option to try is to deliberately defocus to the opposite side that SGP chooses when doing autofocus before starting the autofocus routine. This wouldn't help very much for an imaging run that changes filters.



#3 AstroBrett

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Posted 06 June 2020 - 11:48 PM

Assuming you are using a 7 step autofocus, decrease your step size by 35% and it should solve your problem. Then your starting point will be the same as it is now on your second AF frame.

 

Brett  


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#4 premk19

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Posted 06 June 2020 - 11:51 PM

Use subframe for autofocus (crop a region excluding the bright stars)

#5 Stelios

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Posted 07 June 2020 - 03:02 AM

Use subframe for autofocus (crop a region excluding the bright stars)

How do you do that for SGP? I know it works for frame & focus, but how does it work for autofocus?



#6 Tapio

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Posted 07 June 2020 - 03:17 AM

You can crop focus image (but can't set center coordinates for it).

 

"Auto Focus Crop:  This is designed to help those who image with severe field curvature at the edges of the image and will prevent the auto focus algorithm from using "bad" edge stars to determine focus.  This feature is specified as a percentage of the CCD's dimensions.  For instance, if you specify a crop value of 5% and your CCD dimensions are 800x600, auto focus frames will not consider any stars within 20 pixels of the left and right edges (40 pixels total) and within 15 pixels of the top and bottom edges (30 total pixels)."

 

https://www.mainsequ.../AutoFocus.html



#7 ChrisWhite

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Posted 07 June 2020 - 04:08 AM

This is a simple fix. You can use filter offsets as mentioned above and focus with lum... or you can use longer exposures and bin if you are not. I use 10 to 20 second exposures for narrowband depending on the scope and bin 2x2.

You need more stars for the algorithm to evaluate.

#8 thekubiaks

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Posted 07 June 2020 - 04:13 AM

Thanks for the tips.   The autofocus crop trick worked.   The two stars that were causing me issues were near the edge of the image.   I used crop 30% and SGP draws a box on the screen where it is looking.  This cropped out my offending stars and autofocus worked.



#9 ChrisWhite

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Posted 07 June 2020 - 04:18 AM

Thanks for the tips. The autofocus crop trick worked. The two stars that were causing me issues were near the edge of the image. I used crop 30% and SGP draws a box on the screen where it is looking. This cropped out my offending stars and autofocus worked.


That's only a bandaid fix and may not work on other targets. You need more stars than two for the routine to produce reliable results.
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#10 thekubiaks

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Posted 07 June 2020 - 10:41 PM

That's only a bandaid fix and may not work on other targets. You need more stars than two for the routine to produce reliable results.

This is true.....

 

Tonights issue is the moon is blaring again and I am having trouble getting autofocus with my narrowband filters.   I have SGP set to 2x2 binning and 30 sec exposures and focus is still inconsistent with Ha, Oiii, and Sii.

 

I'm afraid if I dont babysit it, I'll wake up and the whole sequence will fail due to autofocus issues.

 

Any recommendations??   thx


Edited by thekubiaks, 07 June 2020 - 10:44 PM.


#11 Tapio

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Posted 07 June 2020 - 11:15 PM

Like others have said - use lum focus and use offsets.
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#12 ChrisWhite

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Posted 08 June 2020 - 05:25 AM

The offset solution is the simplest.  However that does ignore that you have some settings you could tweak.

 

How large does your HFR value get during an AF routine when using broadband filters?  What is the HFR when you are in focus?  Whats your focuser?  Whats your step size?  How many steps are you using? 



#13 thekubiaks

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Posted 08 June 2020 - 06:22 AM

So you guys are saying that I should use Lum focus and then an offset to focus Ha?   I guess that as I am imaging in Ha and it is time to focus, SGP will switch to the Lum filter, do the autofocus, and then switch back to the Ha filter, apply the offset and resume the sequence???   Is that correct??   I see the setting in SGP to use Lum for Autofocus.

 

ChrisWhite, When in focus, my HFR are in the 2's.  PegasusFocusCube2, step size 200, 9 steps.   This has been working well in LRGB, I am somewhat new to narrowband issues.

 

Thanks for the replies!



#14 ChrisWhite

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Posted 08 June 2020 - 06:36 AM

So you guys are saying that I should use Lum focus and then an offset to focus Ha?   I guess that as I am imaging in Ha and it is time to focus, SGP will switch to the Lum filter, do the autofocus, and then switch back to the Ha filter, apply the offset and resume the sequence???   Is that correct??   I see the setting in SGP to use Lum for Autofocus.

 

ChrisWhite, When in focus, my HFR are in the 2's.  PegasusFocusCube2, step size 200, 9 steps.   This has been working well in LRGB, I am somewhat new to narrowband issues.

 

Thanks for the replies!

 

Correct on your assumption of the offsets. 

 

What is your out of focus HFR at your extreme in the routine?

 

It's worth figuring out even though the offset method works well with SGP.  If you decide to switch to another capture software, it may not support offsets. 



#15 thekubiaks

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Posted 08 June 2020 - 06:47 AM

Chris, when my autofocus is running normally on broadband, my first HFR is about 9, which is about 4 times my in focus value.   With narrowband, it is all over the place because it can't get a solid HFR value



#16 ChrisWhite

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Posted 08 June 2020 - 07:03 AM

Chris, when my autofocus is running normally on broadband, my first HFR is about 9, which is about 4 times my in focus value.   With narrowband, it is all over the place because it can't get a solid HFR value

OK.  All that seems reasonable.  Try bin 4x4.  I'm kind of guessing as I go based on the idea that you are not gathering enough "signal" for stars to become present enough for the algorithm to evaluate.  Try bin 4x4 and see if that helps. 



#17 Dereksc

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Posted 08 June 2020 - 08:01 AM

You can also try using increased gain during AF:

 

In SGP set Control Panel -> Camera -> Bin 2x2 = 200 for example
Then in Control Panel -> Focus -> Use Auto Focus -> Set Options -> Bin 2x2
For imaging sequence just set the Gain the way you normally do. This assumes that you choose different binning options for imaging and autofocus (I do). Using this technique you may be able to reduce your AF exposure time for NB and thus speed up your NB AF routines and at the same time making them more reliable. 

 

Regards

 

Derek


Edited by Dereksc, 08 June 2020 - 08:10 AM.


#18 f430

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Posted 12 June 2020 - 11:11 AM

I find this interesting as I'm also having problems with SGP auto focus.

It seems that my issue is that the auto focus exposure time is set at about 6 seconds, Bin 1x1, and I can't change it.

I have entered 12 seconds, Bin 2x2 in the Equipment Profile Manager/focus, and also in the View, Control manager/focus, but the auto focus continues to use Bin1x1 and 6 sec exposure.

Any help would be greatly appreciated!

John 



#19 Tapio

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Posted 12 June 2020 - 11:30 AM

Strange. And you make new sequence with profile (or apply it at some point) ?



#20 kathyastro

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Posted 12 June 2020 - 11:41 AM

I find this interesting as I'm also having problems with SGP auto focus.

It seems that my issue is that the auto focus exposure time is set at about 6 seconds, Bin 1x1, and I can't change it.

I have entered 12 seconds, Bin 2x2 in the Equipment Profile Manager/focus, and also in the View, Control manager/focus, but the auto focus continues to use Bin1x1 and 6 sec exposure.

Any help would be greatly appreciated!

John 

Settings in SGP can get confusing, because the same settings occur in two different places.  If you changed the autofocus settings in the Equipment Profile, make sure you propagate the changes to any existing sequences you have.  Also make sure that you use the modified Equipment Profile to create new sequences.

 

If you made the change in the Control Panel of a sequence, make sure you save the changes to the appropriate Equipment Profile.

 

If you don't make the changes in two places (Equipment Profile and Control Panel), one of them will be unmodified and will give you the old settings.


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#21 thekubiaks

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Posted 12 June 2020 - 11:51 AM

Settings in SGP can get confusing, because the same settings occur in two different places. If you changed the autofocus settings in the Equipment Profile, make sure you propagate the changes to any existing sequences you have. Also make sure that you use the modified Equipment Profile to create new sequences.

If you made the change in the Control Panel of a sequence, make sure you save the changes to the appropriate Equipment Profile.

If you don't make the changes in two places (Equipment Profile and Control Panel), one of them will be unmodified and will give you the old settings.


Agreed, this took me a while to realize.

#22 FlankerOneTwo

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Posted 12 June 2020 - 12:09 PM

If I remember correctly, SGP also has "per filter" focus exposure settings that you have to change. Once I found those, autofocus does actually seem to work quite well for me with Chroma 3nm narrowbands using an ASI1600 at gain 200 (0.5 e-/ADU), and 10 second exposures, on a WO FLT132.

 

I did notice that SGP did not pause autoguiding when autofocus is triggered from a running sequence. This didn't bother the FLT132 much as there's not really any focus shift with the big FeatherTouch, but on my SCT when focusing with the stock focuser this results in PHD moving the guide star while the autofocus exposure is running, which of course screws up the HFR. On the FLT132 this only happened if seeing was choppy during the autofocus exposure, but did result in outlier HFRs. Telling SGP to pause guiding during autofocus fixed that, but the checkbox is on the Autoguider setup tab, not the Autofocus tab - so it took me a while to find it.



#23 f430

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Posted 12 June 2020 - 02:45 PM

Thanks you all for your help and suggestions. I've made those changes, plus clicked "add profile to sequence", so will look forward to tonight to see if it worked out okay.



#24 f430

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Posted 13 June 2020 - 10:19 AM

Thanks again. Everything worked great last night.

With the changes to the auto-focus settings, it worked flawlessly without a single failure!


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