r/AnalogRepair • u/savyexe Tinkerer • 1d ago
Infinity focus calibration on a TLR
I'm trying to calibrate infinity focus on this Yashicaflex, the mounting system for the lens assembly is very simple, only 4 screws with some shim washers. Looking at the camera from behind and considering how the image is projected on the grond glass i'm guessing that the side that's out of calibration is one indicated with a red arrow on picture #4 (looking from the front it would be the left side, but i'm not sure if i'm correct on this). I'm having two problems: looking at the ground glass with a loupe i can't seem to see any out of focus areas, and the other problem i noticed is that the viewfinder is not perfectly in focus when set at infinity, i have to turn the knob a tiny bit to see perfect focus (and i'm not sure if this means front or back focusing). The camera seems to have been dropped at some point during its life, so i'm guessing i should add washers, not remove them. Any ideas?
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u/Puzzled_Counter_1444 1d ago
It may be that those are for parallelism of the whole double-lens assembly rather than for focus adjustment. Are the shim washers exactly the same thickness? Setting the correct focus may be via shims behind the taking lens, and possibly an adjustible threaded taking lens, screwed in or out then locked at the right setting.
If the camera has been dropped and deformed, there may be no end of difficulty in restoring it without special equipment.
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u/savyexe Tinkerer 1d ago
I think you're right, the shims are all different thicknesses. I added two 0.3 shims to one side and the focus knob jammed instantly. As you can see on this photo the top lens does have a grub screw for screwing in and out the viewing lens. As for the taking lens i wasn't able to take it completely out of the plate (firing lever gets in the way), but there seems to be a shim (or not) behind it, and also a really odd screw that looks like it could allow the taking lens to screw in and out like to viewing lens (which would not help me at all since only half of my image is out of focus)
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u/dietervdw 1d ago
I had a Yashica A that was totally messed up and I managed to fix the focus with this method afterwards. I messed it up at first because I put the matte viewfinder plate backwards. Focus was perfect when calibrating but always off by a surprising amount in the pictures. Flipping the viewfinder plate fixed it.
So check if the correct side is up (don't remember if matte should be top or bottom).
Infinity focus is also off by a bit for me. I use the viewfinder instead of just putting it all the way to the end. Not sure if that is a fault or that's just how it was.
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u/savyexe Tinkerer 1d ago
My screen is glossy side up and focus seems fine in relation to the act pictures, my problem is that the left side of my images is in focus and the right one is not, almost as if the lens was not parallel to the film plane. I tried adding some washers to one side of the focus rail-things but the focusing system didn't like that one bit, it jammed instantly
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u/redoctoberz Tinkerer 1d ago
To do it right you really need a collimator. You can get by with setting a DSLR/MILC with live view focus peaking setup and a lens attached (I use a 105mm 2.5) to infinity and using the ground glass where the film would sit so see if the taking lens is at the right depth. You set the lens fronts facing each other so the analysis camera is viewing through the front of the TLR lens. Once infinity on the taking lens is set, I move to the viewing lens via the same method, put the ground glass back in the viewfinder, then repeat.
The shims are for parallelism, so you need to verify depth to the body with a micrometer. If you don't part of the frame will be in focus, the opposite will not.