Quote:
Originally Posted by Terry B
Very long exp darks will need more sub exposures compared to short exposures for a different reason. Assuming that cosmic ray hits appear at a reasonably constant but random rate, the longer the total exposure is, the more likelihood that they will affect your dark exposures. They are removed essentially when you combine your darks but are not part of the dark current and can leave residual noise. The more exposures you have, the better they are removed.
Shorter exposures will have less hits and as 10x 30 sec frames is less total exposure than 10x 20min exposures you can get away with less subframes for the same noise in the final master dark.
|
Interesting post, thanks Terry! You've actually inadvertently answered a question I had regarding these seemingly random squiggles that appeared in these long darks. After googling about cosmic rays and CCDs I now have the answer.
I think I'll be capturing some more darks in the near future for these long narrowband subs if nothing else.
Quote:
Originally Posted by Slawomir
Hi Lee,
For comparing noise in deferent images, selected area does not necessarily need to be just the background. Maybe pick a region that is fairly uniform and with low signal.
I still believe in the future of noise reduction being skilfully applied to Master Darks  |
Ah ok, fair enough. Interesting idea using NR in master darks... I've never actually thought of that.