The Stellarvue R50C is a one piece clamshell ring that is made expressly for Stellarvue 50 mm finders and guidescopes. It will not fit any other finderscope. The R50C clamshell has velvet lining and a compression ring that allows the user to rotate or position the finder/guide scope as needed and then lock it in place. A separate mounting base is included with 1/4-20 threaded holes.
To attach the R50C clamshell, remove the entire back end of the finder or guide scope. Slide on the clamshell, being careful not to pull up the adhesive backed velvet as you install it. Replace the parts you so carefully removed and you are ready to go. Do not remove the dew shield to attach the clamshell as the lens will fall out onto the floor!