Leica LTM Noobie Question No. 5 - this is a real dumb one: What is the infinity lock for?

Leica M39 screw mount bodies/lenses
David.Boettcher said:
No, I'm not convinced by any of these theories.

It seems to me there was some optical/photographic purpose Barnack had in mind when he created the hockey stick infinity lock on those early cameras.

When interchangeable lenses were introduced the infinity lock moved to the lens mount, because it had to. And then it gained the other purposes which have been mentioned - but that didn't change its *prime* purpose, the reason it was created - which we don't seem to know!

Regards - David
Click to expand...

Dear David,

Ever owned or used a fixed-lens Leica? The infinity lock really does make it a LOT easier to pull out/collapse the lens, even when the focusing mount is old and sticky. With a clean, new, well-lubricated lens, it must have been even more compelling.

Why do you reject this argument? To repeat, I'm not saying it's right. I'm just asking if anyone can do better (apart from the other, additional purposes it 'grew' later).

Cheers,

R.
 
Soooo, looks like the answer has been lost in antiquity and no best guesses will do. Good question to ask if playing Leica trivia. Sometimes you just have to settle for it is there just like an appendix on a human, no real reason.

Bob
 
many moons ago my guru told me return the lens to infinity to keep presure off rangefinder spring it keeps the camera at rest, I never thought about it until now and that was fifty years go
 
dave lackey said:
For my use, I find that keeping the Summarit on infinity lock, I always have a reference point from which I turn the lens in only one direction to the desired position...which is a very short distance, btw.;) Just one less thing to think about and it becomes second nature very quickly. At my age, I like to keep it simple.
Click to expand...

This is the answer that accords best with my own experience; it flows from the phenomenology of Leica photography, rather than from objective fact.
 
The theory of not forcing during screwing-unscrewing the lens makes the most sense to me. Do we see an infinity lock in any M-mount lens? (except the collapsible ones) I agree with Roger on this
 
Last edited:
Quote:
Originally Posted by t6un
Additionally, infinity may be the safest setting to avoid burning pinholes into the shutter.
Um, I think we'll give you the Friday afternoon bonus for this one ;-)
Click to expand...

My reasoning is based on the fact that the first shutter curtain of my Leica is ca 2,8 mm closer to the lens mount than film. Accordingly, the sun will be focussed at the curtain when the lens is extended 2,8 mm from infinity position? With 50mm lens this happens around 1,2 m focussing distance, this is the best setting to fry the shutter. with the wider lens the focussing distance will be less, with the longer lens more.
 
Last edited:
I've always thought it had something to do with the RF cam in the body of those old bodies, but that's just a guess. I do hate the ∞ lock too.

Roger, your notion sounds the most believable thus far to these ears.
 
Technically there's only one plane of focus regardless of aperture. Hyperfocal only works because you run out of resolution.

:)

Thanks for checking your books, Mr. Hughes, cool stuff!
 
I don't buy the suggestion that the infinity catch is there to take pressure off the rangefinder spring, or to avoid burning pinholes into the shutter, because Leitz could have just written in the user manual "When not in use, turn the lens to infinity to take pressure off the rangefinder spring and avoid burning pinholes into the shutter." But they didn't write this, they provided the infinity catch, which cost money to make, seemingly without any explanation as to its purpose.

But I don't *have* to turn my lens to infinity and engage the infinity catch when I am not using the camera, I can just as easily leave it focussed on the last distance I set, in fact I would usually leave it set at a hyperfocal setting just in case I need to get off a quick shot. The infinity catch has no means of *forcing* you to use it - it doesn't have a spring return so that the lens snaps to it when you let go.

Roger Hicks said:
Ever owned or used a fixed-lens Leica? The infinity lock really does make it a LOT easier to pull out/collapse the lens.
Click to expand...

Hi Roger, yes I have a IIIa with an Elmar and a Summar, and I agree that the locked focussing lever enables you to stop the screw mount rotating when locking/unlocking the lens (if this is indeed what you meant) but it does not have the appearance of being designed to do this job - why lock the focussing ring to the mount to stop the mount rotating? As an engineer, if I were designing something to help me grip the mount to stop it rotating, I would have put two fixed projections, one on either side, on the fixed base of the mount which the lens moves against, there is no need to lock the focussing ring, just the base part. This would have been cheaper, simpler and easier to use.

I kind of agree with Nikon Bob, that it looks like the answer may have been lost in antiquity. But to Nikon Bob, and to Sparrow, I would say that if you aren't interested in the question, then why are you reading this thread and posting sarcastic replies? It started out with a simple question which I thought would have a simple answer. The fact that the answer is not known is interesting in itself to some people. If it is not interesting to others, than no one is forcing them to read this thread.

Regards - David
 
Last edited:
David, are you talking about mounting the lens or extending and collapsing it? Roger's idea that the focus ring had to be locked somewhere to comfortably extend the lens seems like a good enough primary reason to me. The designers then took into account the other factors and put the lock at infinity position... No, it doesn't force you to use it, but it builds a habit of it, especially if it is on the lens you use most.
The rangefinder spring was obviously not the reason, since it's at it's highest tension at infinity position.
 
On my old ones focussing on infinity moves the lens and therefore the RF cam back into the body. Take the lens off and you'll see that that means compressing the spring that pushes the cam forward.

So, as I see it, on infinity the RF cam is pushed back and therefore under more tension and under less when focused on 1m.

And as I should have said the early ones didn't have range-finders and didn't have removable lenses. Early means 1925 and the coupled RF appeared on the model 2 in 1930 and then modified in 1932 (from memory).

Anyway, when locked it does give you something to grab when unscrewing the things. But I'm still going to screw the lenses in when set to 1m as that way the RF cam isn't being hit and knocked about before the 39mm threads engage.

I've spoken to people who've worked on very early pre-production(or even prototypes) and their descriptions suggest a lot of trial and error went into the camera. Evidence being things drilled out and then plugged, etc. So why the infinity lock with no obvious use at first?

So I'm baffled and this is one of those annoying loose ends you come across, hence the thread running on. Anyway, I'm not going to lose sleep over it but I'd love to understand the thinking behind it. FWIW, I'd love to get my hands on a lot of their 1920's microscopes and work out what off the shelf bits from them were used in the Leica. And then there's the Mikro-Summar lens of microscope fame...

Regards, David
 
My 35mm summilux pre asph is m mount non collapsable and has an infinity lock. So yes I think the keeping pressure off the RF coupling mechanism seems like the most logical. I might even start leaving my other lenses at infinity when not in use on camera.
 
David Hughes said:
But I'm still going to screw the lenses in when set to 1m as that way the RF cam isn't being hit and knocked about before the 39mm threads engage.
Click to expand...

I agree with you, but Leitz does not. From the IIIf manual (red dial era):

Lenses in collapsible mounts must be pulled out and locked in the bayonet catch, their focusing lever in the infinity position, before being screwed into the changing flange.
Click to expand...

(The manual is frustratingly quiet about the actual purpose of the lock, however.)
 
t6un said:
My reasoning is based on the fact that the first shutter curtain of my Leica is ca 2,8 mm closer to the lens mount than film. Accordingly, the sun will be focussed at the curtain when the lens is extended 2,8 mm from infinity position? With 50mm lens this happens around 1,2 m focussing distance, this is the best setting to fry the shutter. with the wider lens the focussing distance will be less, with the longer lens more.
Click to expand...

You are right. I hadn't given it that much thought.

2.8 mm sounds like a lot for a Barnack body, but that aside, it is certainly a good chunk of the total travel of a 50 lens.
 
I kind of agree with Nikon Bob, that it looks like the answer may have been lost in antiquity. But to Nikon Bob, and to Sparrow, I would say that if you aren't interested in the question, then why are you reading this thread and posting sarcastic replies? It started out with a simple question which I thought would have a simple answer. The fact that the answer is not known is interesting in itself to some people. If it is not interesting to others, than no one is forcing them to read this thread.

Regards - David

After replies to a question by some extremely knowledgeable people yield no conclusive or acceptable answer then it may be time to let it go. It is an interesting question but how important is to know the real answer?

Bob
 
batterytypehah! said:
I agree with you, but Leitz does not.
Click to expand...

Hi,

Well, FWIW, I don't agree with them about a lot of things. Why such a tiny little view-finder, f'instance?

And why not 1, ½, ¼ second and so on to 1/500th? (OK I know that should have been 1/512th second to be a rational sequence.)

I'm the first to say that they are lovely cameras and use all my outfits (Standard to CL via IIc etc) for the pleasure of it but when you think that they spent 5 years mulling over the RF I wonder why they didn't increase the size of the view-finder. It really is poor and not something that should have been miniaturised.

Ditto the spool chamber not taking proprietary cassettes, (Agfa, Kodak etc). Ditto the filter to go over the RF window when it could have been built in etc.

Regards, David
 
You must log in or register to reply here.
Back
Top Bottom