We found an awesome hack on Lomography magazine for those of you who are really into rangefinder photography (and we’re talking about actual rangefinder coupled cameras.) Basically, if you look through the viewfinder at the middle area (which corresponds to focusing) you’ll see the two images that line up. If you place a little bit of gaffers tape right over that focusing area, the rest of the rangefinder screen will brighten.
The staff here was talking about this and we didn’t totally believe it until I tried it. With my Polaroid 185, Voigtlander Bessa R and Yashica Electro 35 GSN, it worked flawlessly. The key is to not put it over the rangefinder itself, but instead the key area in the viewfinder.
Try it out for yourself. But before you do, take a look at this piece on how a rangefinder focuses.