Hi all,
Bored due to weather - thought I might try comparing data processed with and without darks and flats applied/subtracted.
Processed in PS4 - all the same processing steps performed on both images.
Which do you prefer? Please forgive the compression artefacts.
Doug
What are you on about Doug?.Are you implying they are comparable?, you are bored.
Yep - b-o-r-e-d!!
Data is from new cooled DSLR - images all taken at around -13ºC, just wondered if using darks from a temp matched library would yield much better results.
The 'Darks+Flats' image was much easier to stretch and control. And the flats certainly clean up the vignetting big style.
I always take darks, darkflatts, flats and biases each ttime I image. Ive found that theyy ccan vary from night to night sso that somtimes they dont work well enough.
Fred should be ashamed of himself for abusing anybody prepared to experiment and learn!
I think there are several common assumptions that you could prove wrong with this experiment (I've done it myself).
Clearly the flats win in terms of reducing vignetting. Absolute must have with just about any imaging system (you might get away without it for awhile with some tele lenses but not when you start pushing it).
Unless you had a camera with serious amp glow or other large scale artefact, dark subtraction will not show at all at the resolution of the images you've presented.
Can you give us a 100% crop from one part of the image with and without darks. I believe that there will be less difference than most people expect. The darks can only reduce hot pixels (things that are constant from one image to next). They can't reduce the random noise which is all that will be affecting 99.9% of the pixels in the image (from a high quality CMOS sensor).
Depending on what software you are using (eg ImagesPlus), you can tell it to use the dark frames to only subtract the hot pixels from the light frames, which prevents it adding further noise to other parts of the image (by subtracting one lot of random noise from another). It also means that a slight temperature mismatch between lights and darks becomes less of an issue.
Thanks all for commenting - my photobucket pro account lapsed and I didn't renew so high res images may be a wee while coming!
Might look elsewhere for a hosting site - any suggestions?
Phil I'll investigate the dark subtraction options in IP.
Next experiment looks like trying the flats alone - will post soon.
Doug
Second looks the best for sure. As for darks and flats subtration with a DSLR camera cooled; I used a darks and flats library. Using IP I just used the standard darks subtraction and this produced good results on many occasions. I don't agree with H that you need to take them on the night. I found variations of up to 5 degrees or so did not really matter much. Especially in wide field mode.
Second looks the best for sure. As for darks and flats subtration with a DSLR camera cooled; I used a darks and flats library. Using IP I just used the standard darks subtraction and this produced good results on many occasions. I don't agree with H that you need to take them on the night. I found variations of up to 5 degrees or so did not really matter much. Especially in wide field mode.
Cheers Paul - you're past experience with the Astro 40D is helpful.
I'm trying to match darks temperatures as closely as I can.
Thanks
Doug