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Fed 5b rangefinder adjustment

I’ve written about picking up a battered but working Fed 5b body. When I put a lens on it I found that the focus was off at closer distances. The point of actual focus was further away than the rangefinder focus point, meaning that the lens was not as far out on its helical thread as it should be. So the rangefinder mechanism needs to be adjusted so that it thinks the lens is closer,  so that I then have to wind it out a bit further, which brings the point of focus closer. That’s a lot to digest. A diagram might help.

The lens is moved further out to focus closer.
The rangefider mechanism has a little lever that feels how far out the lens has moved.
The rangefider thinks the lens is further out than it is, so thinks the point of focus is closer.
So the solution is to move the lens further out to focus closer, and fill the gap so that the rangefinder agrees with the lens.

What I need to do is compare the actual point of focus of the lens with what the rangefinder mechanism thinks it is. (Now you see why SLRs are such a good idea.) The ideal way to do this is to put a ground glass plate over the film gate to be able to see the actual focusing point of the lens. The back of the Fed comes off, so access to the film gate is easy. Only, I don’t have any ground glass. What I do have is a thread magnifier. Basically a small magnifier with a clear plastic plate at the point of focus. The plate is engraved with 1/10mm lines to allow small flat objects to be counted or measured. I had it from when I worked in a paper mill. So perhaps a bit of translucent tape or tracing paper fixed over the plate might give me both a focusing screen and a focus magnifier? I do also have a small sheet of clear 2mm plastic that is an off-cut from another job. I will try cutting a piece of the right size and matting it with some emery paper. And the winner is … the thread magnifier with some tape on it.

For my next challenge I had to get access to the rangefinder adjusters. They are under the faceplate around the viewfinder. Online sources say to slide the metal plate to the left. So I gave the protruding nameplate a push to the left but it wouldn’t budge, even with harsh language. So I took a closer look at what I might be missing, and found that there is a metal decorative plate on the front of the eyepiece that can be slid sideways. And there were the adjusters.

The method for adjusting the focus of the Fed is two-stage. Infinity focus and vertical alignment are adjusted with the main rangefinder controls (see my initial tweaks here). As the lens is screwed out away from the camera body to focus closer, a spring-loaded metal finger bears on the rear of the lens and moves out with it. The tip of the metal finger has a small cam, which is a tight press-fit onto the end of the finger. Twisting this cam makes the contact point with the lens move further in or out on the end of the metal finger.

So the method is to get infinity focus right, then focus closer and adjust the cam so that the image in the rangefinder concedes with what you can see in focus at the film gate, then check and adjust infinity focus again. You repeat these to hone-in on the best settings that work both far and near. I picked 2m as my close distance test as it’s easily achieved indoors and also suits the sort of distance you might shoot pictures of people.

And did it work? Well, it’s a faff juggling the camera with the shutter held open on B and holding the thread magnifier I’m using to check focus. Until I remembered I have a locking cable release. That held the shutter open and gave me back a free hand to focus the lens. I was wary of how much force to use to twist the cam on the end of the rangefinder arm. And the screw for the rangefinder adjustment was locked with dab of paint which needed some initial force to break its seal. But then, I used to maintain my own motorbikes. When the manual says to drift out the spindle, you might think it’s a gentle nudge. What it means is to put a piece of metal rod against the end of the spindle and belt it with a hammer. You know you’ve drifted it when you hear the spindle hit the far wall of the garage. So it was ‘just’ a case of offering a suitable level of violence to the camera. Once I thought it was adjusted, I took some test shots.

Right on the spot. Previously it was focussing behind the target.

The other thing I thought about was whether the focus worked with different lenses. The lens I’m using on the Fed is (I think) a Tessar design. I have another lens on my other rangefinder that has a Sonnar design. I’d heard that Sonnar lenses can shift their focus point depending on aperture. But the only way to do this would be to put the camera on a tripod, focus it and then take a series of shots at differing apertures. One day perhaps, when I have nothing better to do. Until then, the Fed 5b is back in business.


Author: fupduckphoto

Still wishing I knew what was going on.

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