A mini-digiscoping system
A typical spotting scope used for birding has a focal length of 500mm and an 80mm dia. lens. With such a unit a person can expect to use an equivalent focal length or 2,000 to 2,500. Anyone attempting to go over that is fooling themselves and getting mush because of the Rayleigh resolution limit of the lens, regardless of pedigree.
So, a system half as powerful could use a 300mm lens with a dia. of about 45mm. Of course all you need is the lens properly mounted in a tube with an inexpensive focuser and eyepiece on the other end. Found a great lens at Surplus Shed. SKU B1013 A Mil. Spec. coated, air spaced achromat objective. Perfect. 57mm x 360 F.L. Separate this air spaced objective with three small tabs of aluminum foil tape. Was used in the M49 Military telescope.
If you don't like the image to be upside down, a 45 degree first surface viewing mirror on the back of camera will flip it right side up and shade the screen. You would look down like in the old dual lens reflex cameras. For a digiscoping eyepiece for this small scope I would use an Orion 20mm Expanse, at about $50. USD.
I suggest the $120. USD. Lumix FS-10 or FH1 (same) camera ONLY 140 grams. Am testing a new one and it equals my new EPL1 with Pany 20mm lens in image sharpness and quality. Darn, what wasted money, Oly! It BEATS it by 2 stops in actual digiscoping light processing power because of the brightness advantage of a small optical system. I will post the pictures in a couple of days with a new thread. Good Luck Gene