|
No, but it is a good idea to do more than one. I typically average 3 "good" dark frames if doing things manually, or more if it's running automated so I don't have to sit around waiting for them.
By good I mean excluding some that have out of the ordinary hot pixels/cosmic rays? through them. I don't find it such a problwm with the 350D but the SBIG will sometimes pick up abnormalities in some dark frames. I think the difference purely comes down to sensitivity of the camera.
Same for flat and bias frames, I'd usually do 10 of each of those and average them.
Oh, and you can re-use dark frames. I sometimes keep using the same dark frames for the next month or so. But that's only with the SBIG where it's cooled accurately so the conditions are repeatable.
Roger.
|