Leica IIIc and Industar 61 52/2.8 infinity focus

Hello everyone,

I recently picked up a Leica IIIc that while it shows its age, it appears to be fully functional. I'm running a test roll of film through it, but haven't yet shot every exposure.

At present time, the only M39 lens I have is an Industar 61 52/2.8 that came to me many years ago on a FED 4. This is the plain glass, non-radioactive Industar 61. I took it apart recently to clean and re-lube the helicoil, and I'm pretty sure I got it back together the way it's supposed to be. There's only one way to get the parts back where the fins and the screws seem to hit each other in the right places.

I took it outside focused to infinity and looked up at the moon through the rangefinder. It was not showing in focus. It was like if I could have turned it just a hair further, the two images of the moon would have fully united instead of being just slightly off.

Is this because the lens isn't exactly 50mm?

I'm not sure that I buy into the whole idea that M39 FSU lenses can't be used well with Leica bodies because their thread pitches don't match, or whatever the latest version of that idea is. There are too many stories where the lenses work just fine and produce good results with a Leica body, and the Industar 61 along with its L/D version seem to be very much on the list of lenses that are supposed to work well with Leica bodies.

What do I need to do to my lens where it will show up properly focused to infinity in my Leica's rangefinder?

Thank you,
-Bill

Have you checked infinity focus with another lens?

Usually in cases like this the problem is in the RF alignment, and not in the lens.

WilliamKT50 said:

Is this because the lens isn't exactly 50mm?

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A lot of Elmars aren't exactly 50mm, either.

The infinity position of the Industar is almost certainly correct. Like Nicholas said, the rangefinder needs adjustment. That's completely normal for a battered IIIC. Adjusting the rangefinder is easy but you have to be careful. You need a 1mm screwdriver and you probably only need to turn the adjustment screw a very tiny amount. You need to be careful that you don't push the screwdriver too hard into the adjustment hole.

As for the focus issue, the lens is very likely good enough.

Russian Leica clones, while LTM, have a different flange to film distance than Leicas. Some modification is required to achieve infinity when using a Russian lens on a Leica.

guangong said:

Russian Leica clones, while LTM, have a different flange to film distance than Leicas.

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That would not prevent the lens from registering infinity when set at the infinity lock. Every fsu lens I have registers infinity at the infinity lock, even if they don't actually focus on it.

I just checked it with two fsu lenses on a Leica III I know is set correctly. If his Leica IIIC is not registering infinity correctly, it needs to be adjusted.

Don_ih said:

That would not prevent the lens from registering infinity when set at the infinity lock. Every fsu lens I have registers infinity at the infinity lock, even if they don't actually focus on it.

I just checked it with two fsu lenses on a Leica III I know is set correctly. If his Leica IIIC is not registering infinity correctly, it needs to be adjusted.

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Somehow I misunderstood the problem. I understood the problem to be not able to achieve infinity focus, not if both lens and camera click infinity simultaneously. My only Russian clones are of Zeiss Contax cameras, which are exact copies down to flange film distance. My own LTM cameras are Leica and Canon with Leitz and Canon lenses, never bothered with Russian Leica copies of cameras or lenses.

Don_ih said:

A lot of Elmars aren't exactly 50mm, either.

The infinity position of the Industar is almost certainly correct. Like Nicholas said, the rangefinder needs adjustment. That's completely normal for a battered IIIC. Adjusting the rangefinder is easy but you have to be careful. You need a 1mm screwdriver and you probably only need to turn the adjustment screw a very tiny amount. You need to be careful that you don't push the screwdriver too hard into the adjustment hole.

As for the focus issue, the lens is very likely good enough.

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Looks like a little adjustment to the screw under the screw beside the viewfinder window has taken care of the problem. I went to an area in my city where I could see some communication towers in the very far distance. On a hazy day, they would have been hard to see. When I first looked at them through the rangefinder window, they were doubled. Some small adjustments brought them together when the lens was set to infinity. The distance scale now appears more accurate when focusing toward something closer as well.

Sounds like it's fixed. It is worth noting the issue mentioned by @guangong - even if the rangefinder is adjusted, the lens may not actually be focusing that well, due to differences in the design of the Industar lenses. I personally have not noticed it - but I haven't used non-Leica lenses on Leicas very many times.

If the lens does not focus to infinity, adjustment of the rangefiner won't help. You need to adjust the infinity stop of the lens.

Comments:

- Industar lenses do not to my knowledge come in a "radioactive" version. Some of them are marked LD which may refer to lanthanum used in elements or coatings. However, lanthanum oxides used in lenses are essentially non-radioactive, unlike thorium oxides. Naturally occurring lanthanum is almost entirely the stable isotope, unlike thorium.

- The difference between Russian/Soviet/Ukrainian screwmount lenses and Leica isn't in the flange-focal distance, it's in the fiducial lens focal length that the rangefinder is calibrated to (how much the rangefinder expects the cam to move as you turn the focus barrel). This means that even if you mix lenses and cameras they all ought to focus at infinity if properly adjusted, but the error should come in as you focus closer than infinity.

- The difference in RF calibration due to the fiducial focal length difference, roughly 51 vs 52mm, should cause a focus offset that goes up as focal length squared and down as f-number. It should be hard to notice it with a wide angle or a slow normal lens. It should be more obvious with a tele lens or a fast lens. Thus, people using a 52/2.8 may not see it, people using a 50/1.5 wide open, or 85/2 or 135/4 might see focus offsets. This may account for why some people report it and others don't.

reddesert said:

Thus, people using a 52/2.8 may not see it, people using a 50/1.5 wide open, or 85/2 or 135/4 might see focus offsets. This may account for why some people report it and others don't.

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That would be what I've used - all 50mm, 2.8 and slower. I think I have one Jupiter lens that's faster, but I don't think I've ever used it.

Thanks for the explanation of the difference.

Don_ih said:

That would be what I've used - all 50mm, 2.8 and slower. I think I have one Jupiter lens that's faster, but I don't think I've ever used it.

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The Jupiter-8 is an excellent optic if you get a clean example that has not been improperly rebuilt or hacked. I have a 1962 version that Brian Sweeney in USA adjusted to focus correctly on my Leica IIIC. It produces a different "look" than my other 50s. I do not know the exact focal length of my example.

https://worldofdecay.blogspot.com/2021/07/optical-treasure-1960s-jupiter-8-lens.html