I'd seen earlier posts questioning whether you could convert a straight through finder (e.g., Orion 9x50) into a RACI finder. Here is the result of my little project, and how I did it.
1. Started with a straight-through 9x50 finder, and unscrewed the reticle / eyepiece assembly and threw them away; then unscrewed the rear plate
2. Disassembled an old Celestron prism diagonal, and glued the diagonal and finderscope plates together (Gorilla Glue, but I should have used epoxy as GG expands and is messy)
3. Unscrewed the lens and locking ring from the finderscope tube, and took it to a muffler shop to chop off all but 70mm on the front.
4. Filed and leveled the cut end of the tube; filed the threads off of the rear plate, and joined the two with epoxy
5. Cleaned and reassembled the diagonal and front lens.
6. Inserted a 12.5mm Svbony illuminated reticle eyepiece ($36) in the top of the diagonal, and adjusted optical path on the Moon
All told, about two hours worth of work over a couple of days.
I've attached before and after pictures. The SVbony eyepiece has a separate adjustment for the reticle. Fine focus by screwing the front lens in and out, and firming up the locking ring.
In terms of optical quality, it's the best RA finder that I've yet used.
Edited by Chris Westland, 19 February 2021 - 11:26 AM.