Sat 13-Oct-12 08:56 AM | edited Sat 13-Oct-12 08:57 AM by elec164
>I'm sure f/8 in astronomy refers to something different to >the f/8 we refer to in photography. Don't ask me what
Actually it refers to the exact same thing, focal ratio.
Reflector telescopes are usually defined by the clear aperture and f-number, not focal length.
Although with eyepiece projection I believe the effective aperture and focal length will be affected by the eyepiece itself as well as the amount of extension of the slide tube adapter which attaches the t-ring to the eyepiece.
This would be a great question to ask over in our Astrophotography Forum where Neil (moderator and very knowledgable on this) will more likely see it and give you a more precise answer.