Thanks!
Larry
Thanks Kathy! That makes senseKathyNS wrote: ↑Fri Aug 12, 2022 11:27 am If you don't need darks, then you shouldn't need dark-flats. But if you don't use dark-flats, you must include bias frames.
You can process lights without removing the read noise and you probably won't notice. But applying flats without removing read noise messes up the math. You can easily have your flats over-correct if you don't use bias frames. It is a common problem.
Note that read noise is not the same as thermal noise. Modern cameras, including yours it seems, produce so little thermal noise that you don't need darks to correct it. But all cameras produce read noise, and the bias frames are there to correct it.
I used to skip bias frames with myLarry 1969 wrote: ↑Fri Aug 12, 2022 1:48 am My camera (Altair 26C) produces very little noise. So little that I don't bother taking dark frames. My question is regarding dark flats (or flat darks). If the purpose of dark flats is to remove the noise from the flat frame and I'm not getting any noise in my light frames, should I even bother with them? I can turn off the calibration warnings in APP and just stack lights and flats right?
Thanks!
Larry
STEVE333 wrote: ↑Sat Aug 13, 2022 8:44 pm Just a little clarification:
1) None of the calibrations frames remove noise. In fact, they actually add a slight amount of noise. That is why it is important to average many calibration frames to reduce the noise in the "Masters" so that the noise they add is negligible.
2) All frames (Light, Dark, Bias, Flat and Dark Flat) contain offsets by design to ensure linearity and to prevent clipping any signal.
3) Flat frames require the offset to be removed to work properly. For CCD's subtracting a Master Bias frame is usually used for this purpose. For CMOS subtracting a Master Dark Flat is usually used for this purpose. Flat frames help remove any effects from vignetting or dust motes.
4) Master Dark frames are used to remove bad pixels and any Amp Glow for CCD's and CMOS.
With CCD cameras the Master Bias is often subtracted from the Light frames as well as from the Dark frames before the Master Dark is created. Then the Master Dark is subtracted from each Light frame.
With CMOS the Master Dark often still contains the offset, and, the Master Dark is subtracted from each Light frame (that still contains an offset).
Both approaches work and properly remove the unwanted offsets.
Hope this makes sense.
Steve
You need to be a member in order to post a reply
Not a member? register to join our community
Members can start their own topics & subscribe to topics
It’s free and only takes a minute