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Possible amp glow issue on ASI1600MC-cool?

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#1 Lead_Weight

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Posted 13 August 2017 - 10:52 AM

Twice now I've experienced this white glow coming from the right hand side of my frames. In the image below, you can see I've used Automatic Background Extraction, and applied a quick stretch. I'm able to process it out using DBE, but I'm sure I'm losing some data in those areas.

 

amp_glow.jpg

 

I've had this camera for a year, and never experienced this issue, so I don't know how to explain it.  For the most part, I've not imaged for longer than 120s previously due to the amount of light pollution I have in my area (red zone). But I got an IDAS LPS P2 filter which has allowed me to image for longer (3 min subs). 

 

I normally image at -20 degC but the last two imaging sessions I did at -15 degC because it seemed like the cooler was having trouble getting down to -20 and holding it there. It's pretty warm here right now with high 80 degF in the evenings. So that would be the only commonality between imaging sessions, however, I've made proper darks, which didn't seem to remove the glow. It's possible this glow is from the Moon, but I don't know how that translates into the images. The moon was quite bright towards the later part of my imaging session.

 

I'm hoping someone here can provide some insight into the issue I'm facing.

 

Here's a link to my data which includes one bias, one dark, one flat, and one light image, plus the calibrated registered combined result of the night (3 hours total).

 

Also, if you see anything else I could do differently based on my light pollution, I'd love some suggestions. If anything, I think 3 min subs might be pushing it.



#2 rmollise

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Posted 13 August 2017 - 10:59 AM

Longer exposures and higher ambient temps will tend to bring this sort of thing out. With calibration it's pretty much a non issue.



#3 Lead_Weight

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Posted 13 August 2017 - 11:14 AM

Would making my darks in the same ambient temp have helped this? I made the darks inside the house, but at the same cooling temp.

#4 rockstarbill

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Posted 13 August 2017 - 11:22 AM

Yes, you need a dark master that is the exact temperature and duration as the light files were. 

 

If you are using PixInsight to calibrate your data, be sure the Optimize checkbox in Image Calibration is unchecked.


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#5 Lead_Weight

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Posted 13 August 2017 - 11:25 AM

Just to be clear, I did lights at 180s -15 degC, and darks for 180s at -15 degC. And the above image is calibrated with those darks.

#6 rockstarbill

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Posted 13 August 2017 - 11:26 AM

Was the data calibrated in PixInsight? If so, was the Optimize checkbox disabled?



#7 Lead_Weight

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Posted 13 August 2017 - 11:36 AM

It was calibrated in PixInsight, but not sure about that option. I used the batch preprocessing script. I don’t know how it’s set in the script.


Edited by Lead_Weight, 13 August 2017 - 11:38 AM.


#8 rockstarbill

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Posted 13 August 2017 - 11:38 AM

It will use optimize, IIRC.

 

Manually run image calibration and specifically disable it and see if that helps. FWIW, I find that BPP is suboptimal over manually processing your images. 



#9 ChrisWhite

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Posted 13 August 2017 - 11:59 AM

To be honest, that does not look like ampglow to me.  I've worked with three of these cameras and they all exhibit two glows on the right edge of the frame near the top and bottom and one slightly lesser glow at the left side near the top of the frame.  The glows to not push into the corners of the frame like the image you have presented.   Honestly, you should be able to take much longer exposures and with proper calibration not have a problem with ampglow. 

 

Check your individual subs to see if the glow presents itself in this exact place or if it is more how I describe.  (See screengrab below of master dark with 3 minute subs).

 

How did you calibrate and process this image?  It looks like you might have used BPP script?  If so, I recommend that you don't do this as it sometimes ends up with strange results particularly with flat calibration.  My second thought is that this looks more like a mismatched master flat or an overcorrected flat. 

 

MasterDarkCapture.JPG

 

I looked at the files you included:  Notice how your dark frame when stretched looks more like my master dark?  I think you have a flat frame issue, or a calibration issue.  



#10 rockstarbill

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Posted 13 August 2017 - 12:05 PM

To be honest, that does not look like ampglow to me.  I've worked with three of these cameras and they all exhibit two glows on the right edge of the frame near the top and bottom and one slightly lesser glow at the left side near the top of the frame.  The glows to not push into the corners of the frame like the image you have presented.   Honestly, you should be able to take much longer exposures and with proper calibration not have a problem with ampglow. 

 

Check your individual subs to see if the glow presents itself in this exact place or if it is more how I describe.  (See screengrab below of master dark with 3 minute subs).

 

How did you calibrate and process this image?  It looks like you might have used BPP script?  If so, I recommend that you don't do this as it sometimes ends up with strange results particularly with flat calibration.  My second thought is that this looks more like a mismatched master flat or an overcorrected flat. 

 

I looked at the files you included:  Notice how your dark frame when stretched looks more like my master dark?  I think you have a flat frame issue, or a calibration issue.  

+1 on what Chris mentions about BPP and Flat Calibration. Manual processing is the way to go, and does not take that much more time.



#11 Lead_Weight

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Posted 13 August 2017 - 12:17 PM

 

To be honest, that does not look like ampglow to me.  I've worked with three of these cameras and they all exhibit two glows on the right edge of the frame near the top and bottom and one slightly lesser glow at the left side near the top of the frame.  The glows to not push into the corners of the frame like the image you have presented.   Honestly, you should be able to take much longer exposures and with proper calibration not have a problem with ampglow. 

 

Check your individual subs to see if the glow presents itself in this exact place or if it is more how I describe.  (See screengrab below of master dark with 3 minute subs).

 

How did you calibrate and process this image?  It looks like you might have used BPP script?  If so, I recommend that you don't do this as it sometimes ends up with strange results particularly with flat calibration.  My second thought is that this looks more like a mismatched master flat or an overcorrected flat. 

 

I looked at the files you included:  Notice how your dark frame when stretched looks more like my master dark?  I think you have a flat frame issue, or a calibration issue.  

+1 on what Chris mentions about BPP and Flat Calibration. Manual processing is the way to go, and does not take that much more time.

 

Just curious though, if this were a flat frame issue (which it might still be), would it show up as a white glow? Don't most flat frame issues exhibit a brighter spot in the middle? Or do you think I'm overcompensating with the flat frame? I did my flats at around 7900 median ADU which I thought was correct for this camera (7-9k range). I could take another set of flats, but should I do them with less or more ADU?

 

Incidentally, I found an option to turn off optimize darks in the batch process. Still have not tried manually processing. But here's the result from the batch with optimize blacks off. It looks slightly better but still probematic.

 

ampglow_2.jpg



#12 rockstarbill

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Posted 13 August 2017 - 12:20 PM

It could be that BPP is not processing your flats correctly. Interestingly enough I am processing data I took for this same target now. :) Anyhow, I would do a manual run of the data in PI and compare the results. 



#13 ChrisWhite

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Posted 13 August 2017 - 12:50 PM

Flats are very tricky, and if you don't nail them you can definitely end up with the result you just posted.  I have seen this happen quite a few times, and once I get a perfectly matched flat... problem resolves. 

 

I assume that the ADU numbers you are referring to are in 16bit? Regardless, 7,000 is a bit low and you might not be exposing enough above read noise in some areas.  Try for a stronger number like 18,000 or 20,000. 

 

Another thing you could do is run your data without flats at all.  I think you will see your problem go away, but of course you will have the problem of dust motes (if there are any) and vignetting (dark corners). 



#14 Lead_Weight

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Posted 13 August 2017 - 01:27 PM

These are some great suggestions. It seems like you’re on the right track with what the issue probably is. I’m going to experiment some with the flats. All the equipment is still rigged up and I can do some tests to sort it out. 



#15 My 2 Stars

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Posted 13 August 2017 - 02:16 PM

As Chris mentioned, try to get your FLATS at around 17K. Makes a big difference.



#16 Lead_Weight

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Posted 13 August 2017 - 02:48 PM

Here's a reprocess with 18.4k ADU flats. Showing some improvement here, the glow is now gone from the bottom, but at the top it seems to be worse if I overlay them.

 

Of course this is still using ABE, but using DBE I can remove it completely.

 

Think I should try flats with 25k ADU?

 

ampglow_3.jpg



#17 Lead_Weight

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Posted 13 August 2017 - 04:36 PM

After some further tests, I pushed the flats all the way to 32k ADU. 24k ADU looks best. At 25K ADU I start to see some black areas show up, With 32k there's huge black swaths. So it looks like 24 is the best I can get. Overall I see more nebula, less glow, but some still exists in the upper left corner. Any other speculation on what might be causing the glow?

 

Here's 24k ADU:

24k ADU.jpg

 

 



#18 Lead_Weight

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Posted 13 August 2017 - 04:38 PM

Here's what 24k ADU flats look like using DBE to remove any remaining gradient.  Looks pretty decent, but I can't help feeling like there must be something else contributing to the issues. Thoughts?

 

24k DBE.jpg



#19 Lead_Weight

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Posted 13 August 2017 - 04:54 PM

Here's the final with a little processing. Needs about 10 more hours of lights. smile.gif

 

Elephant Trunk Processed.jpg



#20 CharlesW

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Posted 13 August 2017 - 07:39 PM

On an 80f degree night your camera is still maxed out at -15c. You might still be using 100% power just to stay there. You might try something a little easier on the camera like -5. 



#21 Lead_Weight

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Posted 13 August 2017 - 08:33 PM

On an 80f degree night your camera is still maxed out at -15c. You might still be using 100% power just to stay there. You might try something a little easier on the camera like -5. 

Good to know. Thanks!

 

I'm wondering if the remaining gradient is just over exposure in a light polluted area. I'm thinking of dropping down to 120s exposures instead of 180s to see if that lowers the amount of remaining gradient I couldn't get out with flats and DBE.



#22 ChrisWhite

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Posted 13 August 2017 - 09:27 PM

Have you tried manual integration?  BPP can do strange things with flats... and maybe other stuff too. 

 

http://trappedphotons.com/blog/?p=693



#23 GeneralT001

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Posted 13 August 2017 - 11:43 PM

Are you subtracting a master bias frame from the darks?

 

If you are - don't - just use the darks only to make a master dark. Only add the master bias to the Flat master. May not help your problem, but still worth a try.




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