I did something similar last July. Here's a shot of my set up. I have a Bushnell Spotting Scope - Discoverer Zoom Telescope. It is 60X and it included a F mount - bonus. I attached it to my D70. According to the adapter, it can provide an equivalent 4000mm lens.(!) My tripod carrier was slung from the tripod and had a ten pound lifting weight in it for stability - I had to. And, I was able to achieve a good shot or two. I hope you will keep trying - I will.
"The Nikon did the work; I just happened to be behind it at the time." TP
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.