v5 Summicron - infinity stop or misaligned helicoid or what?

[qqphot]

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I have one of the odd "v5" Summicron 50s that were made in LTM mount. I use it both on a IIIg and an M2. On neither body does it perfectly reach infinity at the hard stop, which leads me to the unexpected suspicion that the lens itself is somehow misadjusted.  Is this even a thing that can happen? 

Other lenses reach infinity ok on the same bodies.  But the distance scale isn't offset- at the hard stop the pointer is right at the middle of the infinity symbol.

Usually if I'm focused at infinity it's stopped down enough that it doesn't matter much, but even at f/4 it's noticeably front-focusing. Doesn't seem to make much difference which adapter ring I use, but even if the (leica branded) one I use were off, I'd need a thinner than normal one to correct this. 

I'm just wondering if there is a capacity for adjusting this lens, or if it's just luck of the draw. I assume there are some shims or something inside but I'm not about to disassemble it.

 

[spydrxx]

I'd bet DAG could make a good tweak on it.

[qqphot]

yeah i know i could just send it to someone but I’m trying to understand the internals a little first, just for my own education.

[hdmesa]

19 minutes ago, qqphot said:

yeah i know i could just send it to someone but I’m trying to understand the internals a little first, just for my own education.

That's what DAG can tell you after Don figures out what's going on.

But please tell us – are you saying:

1. The rangefinder patch shows infinity focus when the lens is at the hard stop, but the lens is not optically focused at infinity (results are out of focus);
2. or, the lens is actually in optical focus at the infinity hard stop (results are in focus) but the rangefinder patch is aligning to infinity before the hard stop or never reaches infinity alignment before the lens hits the hard stop.

Since other M lenses work on these two cameras correctly, one or more of these can be at play:

• Lens needs a focus overhaul (realigning the elements to achieve infinity focus at the hard stop)
• Lens cam/helicoid needs adjusting (so that it correctly tells the rangefinder focus patch where to be)
• LTM adapter is not the correct thickness (too thick won't allow the lens to reach optical infinity focus, too thin will let the lens focus past infinity at the hard stop)

[qqphot]

The lens is not optically focused when the focus ring is at the hard stop. (it is focused somewhat closer than infinity)

I'm not considering the rangefinder at all in this; of course it can be adjusted to have the split images coincide wherever, but this would be pointless because it still wouldn't be in focus on the film.)

I've kept the rangefinder adjusted so it's correct with my other lenses, where it matches optical focus on film very well.   Even then, it's not far off with the summicron either, except for not reaching infinity.

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Lens needs a focus overhaul (realigning the elements to achieve infinity focus at the hard stop)

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Lens cam/helicoid needs adjusting (so that it correctly tells the rangefinder focus patch where to be)

Yes, these are the things I'm curious about.  Is there in fact a mechanism by which the relationship between helicoid position and rangefinder cam can be changed? I was under the impression that with 50mm lenses at least, they were one and the same contiguous piece of metal.

The only part I can successfully visualise it is if there are shims internally that change the spacing between the lens mount flange and the focusing body itself. 

[hdmesa]

3 hours ago, qqphot said:

The lens is not optically focused when the focus ring is at the hard stop. (it is focused somewhat closer than infinity)

I'm not considering the rangefinder at all in this; of course it can be adjusted to have the split images coincide wherever, but this would be pointless because it still wouldn't be in focus on the film.)

I've kept the rangefinder adjusted so it's correct with my other lenses, where it matches optical focus on film very well.   Even then, it's not far off with the summicron either, except for not reaching infinity.

Yes, these are the things I'm curious about.  Is there in fact a mechanism by which the relationship between helicoid position and rangefinder cam can be changed? I was under the impression that with 50mm lenses at least, they were one and the same contiguous piece of metal.

The only part I can successfully visualise it is if there are shims internally that change the spacing between the lens mount flange and the focusing body itself. 

If the lens is not in optical focus at the hard stop, then it needs what DAG calls a focus overhaul, which is cheaper than a CLA. IIRC, that includes making sure the lens is properly calibrated to the standard for rangefinder alignment. I have no idea what that involves. And don’t bother Don with chit chat about how M lenses work, he doesn’t have time. He’ll tell you what he did to fix the lens, but he doesn’t have time to teach/explain how they work.

[qqphot]

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Yeah, I'm really more interested in learning about the mechanics.  I'm sure Don's a very busy man, and I'll leave him to his backlog.