Quote:
Originally Posted by robatman
Just trying to get my head around why stack multiple images.
Assuming you have perfect tracking and same exposure per image theoretically each image made should be exactly the same. Why not just stack the same image?
I have also read a little about thermal noise and it would seem the last image can tend to be noisier than the first so the latter images will be of a lesser quality.
I get the need for darks (to map noise reduction) and i think flats (to aid in alignment and reduce distortion?)
What am i not getting?
Robert
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Hi Robert, loads of questions in there
. In a nut shell stacking will increase your SNR (signal to noise ratio) and also allow you to reject bad pixels.
Darks are for minimising thermal noise (random). Flats are for getting rid of uneven illumination (vignetting) and all sort of dust motes, stains on your optics, etc... that stay in the exact same spots within your imaging run provided the camera and the focus haven't moved.
Stacking pictures minimise sky noise and other nuisance like satellite trails, asteroids, bad seeing. This is achieved in many softwares by running rejection algorithm so you keep the good data and reject the bad data. It is also achieved by slightly dithering (offsetting) your picture so when you realign them the "bad pixels" don't fall on top of each others and therefore become rejected over the number of sub frames you stack.