[morls (Stephen)]

Hi,

Oh boy, another question...hope I'm not bombarding the forums too much....

I'm wondering if different f-ratios have an effect on field of view or contrast or something similar? The example I'm thinking of is a 12" f/6 vs a 12" f/4.5

I'm aware of how coma increases as the f-ratio gets faster. I'm mainly interested to know if the different f-ratios are for convenience, keeping the overall scope length down, or if there are other reasons as well, beyond avoiding optical aberrations.

Cheers

Stephen