I'm quite nearsighted, and have worn glasses or contacts for decades (since second grade). I gave up contact lenses about ten years ago.
Before giving up contacts, I bought a Zeiss Ikon 532/16 (Super Ikonta B), 6x6 with coupled rangefinder, but I stepped away from photography before going back to full time glasses. Now, on picking up the camera again, I find it's hard to use the very small viewfinder (I can see the RF patch pretty well, but can't see all the edges of the frame at once) because of the distance from eye to viewfinder enforced by my glasses.
I've just purchased a Kiev 4A, a Soviet copy/upgrade of a pre-War Contax 35 mm RF camera (intechangeable lenses, similar overall to an early Leica); I've wanted a camera in this class for a long time, but I see that the viewfinder window (based on a Zeiss-Ikon design, of course) is very similar in size to that on my Super Ikonta, and I suspect I'll have the same problem using the viewfinder.
I'm aware of diopter eyepieces that can be added to various cameras, but as far as I can see, these Zeiss-Ikon designed viewfinders don't have a provision for such a corrective lens (if they're even available in -6.75 diopter strength). I might be able to cut up a lens from an old pair of glasses and attach it, but I hate to make a permanent alteration that affects every subsequent user, to a camera that (in the case of the Super Ikonta) is a decade or so older than I am.
What else might I be able to do in order to see through these tiny viewfinder/rangefinder windows?