New from William Optics - 1.25" Eyepiece Holder with Helical Focuser for Wiliiam Optics Right Angle Correct Image Finder.
For use only with William Optics' 50mm right angle correct image finderscope to convert finder into a CCD guidescope. Eyepiece holder features a helical focusing mechanism with approximately 15mm of focus travel (Be careful while unthreading the eyepiece holder from the main barrel as it will separate and come apart if you unscrew it too far) . Also features a brass compression ring and three large thumbscrews for a secure grip.
The male thread on the finder side is M52x1.0 which is not a common astronomy thread, so the use of this item with other finders is highly unlikely.