How to Calibrate Focus on Viewfinder Camera?

[RJ Jacoby]

Greetings everyone. I'm very much new to this forum so apologies if this isn't the perfect place to post this question.

In any case, I have just acquired a new toy (and if I can get it working, something more perhaps). It's a SEM KIM, a French scale focus camera from the 1940s. Lovely little thing. Problem is, the guy I bought it from told me that the lens focus is out of whack. I was feeling cocky and assumed this is an easy fix, so I took it home in exchange for some loose change.

Only when I got home did I begin to realize how tricky this really is. I remember adjusting the focus of my Kodak Signet 35 - it was really easy since the camera came to me with the RF recently adjusted, so all I had to do was to calibrate the lens by adjusting the focus ring and helicoid to align with the RF patch at the correct distances. Finicky, sure, but since the camera displayed the correct focus in the viewfinder, it was at least doable.

With the SEM though, I'm at a bit of a loss. There's absolutely no way to tell where the lens is focusing, since there is no rangefinder. I'm sure there is some kind of method to this that I am just missing, but I guess my question has to go back to the very basics: How do you make sure the focus is accurate on a scale focus camera (or, I suppose, a rangefinder camera where the RF is not reliable/inaccurate/broken etc.)?

If anyone with experience with this would weigh in, I'd be super grateful. Thanks everyone! Cheers

 

[Andrew O'Neill]

I know nothing about this camera... I'm assuming it zone focuses with the helicoid, similar to the Holgas that I own? I had to calibrate focus with one of my Holgas, by removing the back, taping a piece of frosted mylar on the film plane. With a loup, and the camera focused on something far, far away, check the focus. Make a mark on the camera with tape and a marker. I did the same for closest focus, and distance in between. Seemed to correct the issue.

 

[nosmok]

What A O'N said. Will add 1) A lot of times there's an 'infinity stop' that is just what it sounds like-- if you can find it and remove it, then you can dial the lens a few turns to correct infinity focus, replace the stop, and maybe the existing lens scale will be accurate. 2) Scotch 'Magic' Transparent tape (the frosty looking stuff) taut across the film gate makes a cheap, quick, easy ground glass/ mylar replacement.

 

[RJ Jacoby]

Thanks so much for these responses, guys! Like I thought, it's a simple solution that only required a little bit of that classic outside-the-box thinking. I tried it with scotch tape and it worked surprisingly well - I am not sure if the focus is really pinpoint-accurate now, but it should certainly be fine enough for taking some pictures, and I am not the kind that obsesses about sharpness. (The lens is fairly slow anyway, so accuracy of focus won't matter a whole ton)

Anyway, again thanks a lot for the quick replies, they really helped!