Recently I had the idea of trying to photograph the Andromeda galaxy by stacking several exhibitions of it with a normal telephoto lens (I saw a video on YouTube about that).
Now, I do not have a tracking setup, so I'll have to take short exposures of about 1 s, according to the NPF rule (taking into account the megapixels of my camera and the focal length).
Which of the following scenarios will give the best results?
- I take 300 photos, each of 1 s (300 s of total exposure), with ISO 100 (the minimum in my camera)
Reasoning: Each frame will be absolutely dark, but when stacking the images the noise will be eliminated, so that I can increase the exposure in the post and obtain my image.
- I take 300 photos, each of 1s (300s of total exposure), with ISO 6400.
Reasoning: Although ISO 6400 will introduce noise, stacking should cancel this noise and I will get my image.
- I take 150 photographs, each of 2 s (300 s of total exposure), with ISO 6400 (suppose I DO NOT have any stars).
Reasoning: Each shot performed singularly has better SNR than the corresponding 1s exposure, and stacking them will further reduce the noise.
What option should I choose? What's wrong with the options that would not work?