Mix and Match: Processing Diverse Data [TAIC Short]

[@glen2880]

Thank Alex! I'll be watching this a few times.

[@TAIC]

That's great! So glad you found it helpful!

[@cosmoscarl4332]

My question is, can I create usable calibration frames after the fact. I live near Houston but I image with a large rig in west Texas two or three times a year. I'm usually pressed for time because I have only three or four nights each trip out west to image and up till now I've not taken calibration frames. I usually get beautiful multiple light frames of deep sky targets such as galaxies and nebulae. Next new moon I will be doing one target per night and I will be shooting calibration frames for each target. Darks, flats and bias frames. Yet I do have sets of 25 to 30 light frames from before of targets like the Snake Nebula, The Leo Triplett, M 31, The Cats Paw Nebula, and many more. They're all dithered light frames, especially useful since I use DSLR, for eliminating Bayer noise. I have also recorded most temperatures each frame was shot under. Would it be possible to generate at least some calibration frames at home?

[@TAIC]

You cannot do as well as if you had done it at the time. But faking it may be better than not trying. (or it may be worse!----but give it a try). To start with, you can certainly take darks and if you like bias. Try to match the ambient temperature as well as you can, and just take bias/darks as if you were there that night. YOu may need a refrigerator to do it, or whatever to match the ambient. (This is advice for a DSLR. Anybody with a temperature regulated camera, of course has no problem because they can control the temp.) But, do your best. The problem is flats. They will work as far as the major optics go (usually) because the light path is most often circularly symmetrical. So, as far as vignetting, and hotspots in the optics, etc, no matter which way you rotate your camera, it will be somewhat the same. However, if you were using an Off Axis guider, and there is intrusion of the pickoff mirror, or, if there is something weird about the DSLR viewfinder mirror (which does some vignetting in some DSLR's), then you may have a problem. Sometimes it can be cures with cropping. Where you most likely will have a problem is if you have dust bunnies. The dust may have shifted. But, it might not have. Just try it and see. If it has, a little cloning and touch up may get you over the hump. So, put the rig back together and go for it. See what you get.

[@cosmoscarl4332]

@@TAIC Thanks for that. I know what the ambient temperature was for most of my light frames. I figured that it would be difficult to match dust spots though. I did not mark the orientation of my camera to coma corrector, to telescope though. If the weather is good next new moon I will be heading to west Texas again and I will be shooting all calibration frames and using the T- shirt method for flats, as I do not have a flat panel. The only thing is that by Sun up I'm pretty exhausted. Luckily flats are shot quickly. I just hope I understand my histogram well enough to get usable flats. Thanks and clear skies to you.