Super zoom options (1 Viewer)

I have a Nikon P100 (26x optical). The barrel travels about 4.5" out from the body at 26x so it's obviously not an ideal candidate for digiscoping. It does well even with the 4x digital zoom on top of the 26 optical. The P100 focal length is 26-678mm. Nikon says normal focus range is 60cm and in macro mode it's 1cm. Does focal length determine the level of vignetting, or is it more related to the scope eyeglass diameter? I tried putting this up to a 12x50 binocular and it was about 85% black, like a door peep hole heh.

Spotting scopes have a larger eyeglass than my binoculars so will this reduce the vignetting for all cameras? I know people with SLRs do plenty of astrophotography with telescopes with small eyeholes and still get amazing shots. I don't have a screw on adapter option so I may make my own. So my question is, can the super zoom body camera even come close to working or am I always going to get massive vignetting no matter what I build? I can use my old Canon A720 but with those tiny lenses and small sensors lighting will be an issue looking through a scope. Do super zooms

The smaller sensors do a good job of grabbing light.
With a long zoom lens you'll need a high eye relief eyepiece to have any chance of vignette-free images. I haven't tried the P100 , but I have the P500 and just bought the Canon SX40IS (24 - 840 mm ) . With the 25x LER ( 32 mm of eye relief ) you can get some unvignetted views at the short end of the zoom lens but you might have better results using the digital zoom. Certainly the Canon will zoom out to 1680 mm with good Image Stabilising.
Neil.

Thanks for your input. My Canon A720 was very good in its day but suffered on low light shots. So anything astrophoto related would be full of noise. But it would probably perform admirably birding.

I bit the bullet and got a Celestron C90 Mak. It should suit my needs for astro and bird photography. It comes with a T-mount and SLR adapter. The stock eyepiece is 32mm, so maybe I'll have decent luck on this combo. I bought the Celestron because they have so many different eyepieces available. So I should be able to find a focal length that works. I don't mind a little vignetting, so long as I have enough picture to crop. I'll report back for folks if I have success.