15th Feb 2024: Astro Pixel Processor 2.0.0-beta29 released - macOS native File Chooser, macOS CMD-Q fixed, read-only Fits on network fixed and other bug fixes
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Hello Mabula,
maybe you can help me on this topic.
I made an astrophotography from Helix-Nebula and afterwards I did flatfields as usual.
I have an ASI 071 and exposure for flatfield is 0,2 sek, which gives me 49.000 ADU peakvalue.
In the histogram (Fitswork) I see clearly 3 peaks for red, green and blue. No clipping.
After stretching the processed files in photosphop I have the impression as the flatfield was't applied:
I see clearly the light-dropoff / colorshift in the corners and the dustspots.
Pity that I can't upload a picture. With 30B there is not much room for that...
Besides Helix I have this same problem with M83 or in other words: With every Picture with much dark background and a tiny/medium object in the middle of the picture.
It seems I don't have this problem if I have much nebula in my pics (Eta Carina-Nebula, Sadr-region, Orion Nebula, ...). Or maybe it's just not apparend then.
So I want to know, why APP isnt able to uniform the background with my flats?
Maybe something is wrong with my flats?
If there is something wrong with my flats, maybe APP can tell me that. There is a quality grade for the lights, maybe there is a quality grade for flats, too (in the future)?
Would love to give you access to my dropbox so you might have a look. I'm happy to provide one light as well as one flat and the dark-files.
Thanks in advance,
Andreas
Hi Andreas,
Maybe i can give you a bit of assistance.
I also do own a asi 071mc-pro, so I've got a bit experience with this cam ;).
As I'm reading you're post there are a few things I notice, you said that the ad has a peak value of 49.000e. I do think there is a misconception. The max say for this cam is 46.000e-adu.
If the number of 49k is right can't it be the white colour cast, that will go to 65500? (Histogram from 0 = black till 65500 = white)
What kind of capture program do you use? If you're making flats with this cam you need to try to aim for 23.000adu at 14bit.
I use APT you've got a nice tool to make auto exposures where you can define the target adu. ( see screen shot APT and a fat of my ).
You can check you're flats in APP, make an shot, open this in APP and set the strecht parameters to NO STRETCH DATA AS IS.
(screen shot APP same flat)
Now have a look to the histogram in APP, if you're histogram has 3 spikes but there are between 30% till 50% you're good. Don't go much over the 50% because you're data isn't linear any more.
How do you make you're flats? You say that the exposure is 0,2 sec, that is extreme fast. Mostly I make my flats with a led panel then I need to shoot 2 sec exposures.
Hope this helps a bit.
Clear skies Jan-Willem
Great points Jan-Willem! And indeed, usually it's the case that something is wrong with the flats. Unfortunately flats aren't the easiest frames to get right. If the above doesn't help, let us know and we can maybe help by looking at some of your flats directly.
