Do you have a rangefinder with a double-image that's almost too faint to see? Take a look at Rick Oleson's quick fix: http://rick_oleson.tripod.com/index-165.html He posted a link to this on the rangefinder forum, and acknowledges there that for all he knows someone else probably came up with it before he did. Whatever. It is simple and really works. I just resurrected a Zorki with a nearly too dim to use patch, in 2 minutes, with a tiny piece of black tape!