[tims]

I asked this question on another forum but didn't get many replies and still am not sure what, if any, are benefits of using large fast mirrors. So...

I'm interested in astro-photography and the benefits (if any) of using large Dobsonian telescopes with fast mirrors.
In conventional photography, if I understand correctly a very fast or short f/ratio camera lens will enable shorter exposure times so does the same apply to very "fast" or short f/ratio mirrors?
Will a large fast mirror (say > 25 inch/ F4) in a Dobsonian allow shorter exposure times as opposed to a smaller mirror with a longer f/ratio?

cheers


Tim