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Does this donut mean I've messed up my flats?


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Hello all

I'm very green when it comes to astrophotography and could do with some advice please. I've been trying to image the Auriga clusters and came up with this problem:


I assume the donut like pale area is because I've had problems with my flats?

I made the flats at the end of the nights imaging session by taking the scope and DSLR indoors and pointing it at a blank laptop screen. I took about 10 shots with the brightness histogram around the middle of the spread and stacked them in DSS.

The orientation of the scope and camera may have changed - could that have caused this?

Do you normally make flats after each imaging target or can they be generic for each combination of scope and camera?

Thanks for any advice.


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That does look like a flats problem - you're right that the flats are setup specific rather than for each target so you don't need to take new ones each time. As they can deal with dust bunnies as well though, it's best to refresh your flats from time to time.

I'm no expert on taking flats but I'm not keen on the laptop method as you can't be sure you're getting even illumination. I use a piece of white paper over the scope and point it at the sky in daylight - then I adjust the exposure on the camera until I see the histogram peak at about 1/3 of the way across from the left - it seems to work for me.



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I can't see the image but the flats must be done withthe imaging train unaltered. No change of focus, no camera rotation.

I can never get sky flats to work because of light leaks and think a good lightbox or EL panel is the way to do them, in the dark.


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