I'm more of an SLR person than a rangefinder person, so I don't use my FED 2 or FED 5 that much, but I do own both, along with Jupiter-12 35mm and Jupiter-11 135mm lenses, and a handy multi-focal-length viewfinder that mounts on the accessory/hot shoe. The Jupiter-12 is a nice 35mm lens, and I can certainly recommend it. I have less of an opinion of the Jupiter-11; I've just not used it that much. Both will work on the Zorki 4. The accessory viewfinder is a practical necessity when using accessory lenses with the FEDs, which show only a 50mm view in their viewfinders. I don't know offhand if the Zorki is the same way or if it has frame lines for extra focal lengths in its viewfinder.

Quote Originally Posted by David H. Bebbington
As with any focal-plane shutter camera, if you hold the body with lens and back removed against a light (like a window) and fire the shutter at all speeds, you should see a complete rectangle with sharp corners if the shutter is opening OK. This doesn't of course test the accuracy of the speeds, although you can guess whether they sound right
Actually, it's possible to use an (old-style CRT) television as a shutter speed tester. I used to have a URL to a site that gave specifics, but I lost the bookmark in a disk crash. The idea is to look through the shutter at the TV as you trip the shutter. At 1/60s and slower (in the US and other NTSC countries; 1/50s in PAL countries) you'll see a complete frame. As the speed increases, you should see partial TV frames. With a horizontal-travel shutter, such as in Zorkis, the partial frames will appear as diagonal bands. This is of course a crude test, but it can help you to verify that the shutter speed isn't grossly off. I used this method to help adjust the shutter speed on a Kiev 6C medium format camera that I bought a few months ago. It arrived with shutter speeds that were way off, and I managed to adjust them to the point that my exposures are reasonably accurate, at least when using print film. (I've not yet shot slide film in my 6C.)