I'm always trying to improve my astro-pics. Here are several shots of the galaxy Andromeda that I took last night, using a Nikon D5100 DSLR and a Celestron C6R refractor/Atlas EQ-G Mount/FeatherTouch focuser as a prime-focus lens. Shot info is underneath each picture. As always, click to embignify.
30-second exposure at 1600 ISO.
30-second exposure at 3200 ISO.
30-second exposure at 6400 ISO.
152-second exposure at 1600 ISO. I like this one the best, so time beats ISO. ISO just means the sensitivity--the higher the number the more sensitive. Notice that the more light that gets gathered, the bigger the galaxy seems. That's especially true with nebulas; a longer exposure picks up colors and size that the eye would miss otherwise. A longer exposure or higher ISO also picks up more "noise", which is pixels showing light that isn't really there. In Nikon Capture NX2 I can deal with some noise, but not all. There's also a bag of tricks with exposure compensation, contrast, levels, and saturation, that can greatly improve the pictures.
I didn't edit any of the above photos because I wanted to see a realistic comparison. All I did was convert the .NEF format to .JPG.
Posted by Dave