When I got into Rangefinder Photography I got a camera that needed focus checked. The rangefinder, sadly enough, lined up perfectly, meaning that the lens was NOT in the correct location for infinity focus.
What to do? How the devil did the factory set up the camera when it rolled off the assembly line?
The answer is easy and obvious after a bit of thought, but I certainly didn’t have the wherewithal to figure it out for myself. Sadly, all rangefinders seem to come to me way off in one way or another, so I end up running this procedure more often than I’d like for “mint” cameras.
I include the procedure in advance of another article or two about other cameras I’ve had to align.
Collimating, in this procedure, is the simple act of using a known good lens on another camera to see if the focus plane is right where the film is supposed to go. Once a camera is set, adjusting the rangefinder to infinity will set the camera to something close (and perhaps better) than what left the factory.
To do it, you need a tripod, translucent tape, cat fur (dog fur might work but I can’t vouch for the results
) a camera to be tested, and an SLR with a long-ish lens (135mm works fine for me, I’ve heard that the longer the better). For the last bit I use my mother’s award winning Canon FTBN and a cheap 135mm lens. Make sure that the lens on the SLR brings things at “infinity” in focus at the lens infinity position.
Put the camera to be tested on the tripod and open the back door and shutter. Set the lens for “infinity,” and as wide open as it will go. Touch the tape to the floor to pick up a strand or 10000000 of cat fur (depending on if you are shacking up or not). The fur presents a good point on which to focus. Stick the tape to the inner film rails so that the edge with the cat fir is about ½ way across the film gate. The object is going to be for you to look through the SLR, through the lens of the camera to be tested, to see if what’s in the film plane is in focus.
Do that. Aim the butt of the camera to be tested at a light source and find the edge of the tape looking through the SLR perpendicular to the film plane of the camera to be tested.
Do whatever it takes to the test camera's lens (move it fore and aft) to make that furry tape focus as perfectly as you possibly can and set your rangefinder for infinity.
That’s it! It’s not a tough thing, complicated only how hard it is to lock the shutter open (and the rangefinder adjustment itself)
The theory behind it is that lenses at infinity see the rays coming into them at a perfectly perpendicular (in theory, unless you are using REALLY CHEAP FSU gear) angle. When both lenses are set perfectly to infinity, the film plane of the camera to be tested should be exactly where it needs to be to focus light at infinity.
(Edit: Spelling collimation and collimating...)