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

[batterytypehah!]

Allows moving your aperture ring with one finger, and places the dang aperture scale where you can see it in the first place. Focussing down from inf. comes afterwards.

That's right, I don't do "F.A.S.T." Never did like it. Light changes less often than distance.

 

[David Hughes]

Well, I've been using them since the 70's, have a dozen or more and have read this thread through twice but I'm still none the wiser.

Attempts to stop the "big bang" seems the nearest we'll get to the truth. But probably not as we know it...

Regards, David

 

[David.Boettcher]

Well, I've been using them since the 70's, have a dozen or more and have read this thread through twice but I'm still none the wiser.

Attempts to stop the "big bang" seems the nearest we'll get to the truth. But probably not as we know it...

Regards, David

Hi David,

Yes; I was convinced that I was just missing something obvious, but it seems no one knows why the infinity lock is there - at least no one in this thread so far. Maybe it was not such a dumb question after all . . .

Regards - David

 

[1ScrewLoose]

OK, I'm not that dumb, I know that it is used to lock the lens focus on infinity.

But why? Locking a lens on infinity "loses" half of the depth of field for whatever f-stop is selected at the time.

I always thought that it is far more useful to keep a lens set to a median aperture and shutter combination for the current conditions, and the lens set to the hyperfocal distance for that aperture, then if an opportunity suddenly arises you can get off a quick shot and it is likely to turn out when you may have missed it messing about with the light meter.

No doubt there is some blindingly obvious reason for an infinity lock which I just can't think of.

Regards - David

I think there might be something to the hyperfocal business, but in the other direction. I only have one lens with an infinity lock (rigid 50mm cron) but the infinity lock is positioned so that one "bumps against it" exactly at the hyperfocal distance for f8... is that the situation for other lenses so endowed?

 

[David.Boettcher]

I think there might be something to the hyperfocal business, but in the other direction. I only have one lens with an infinity lock (rigid 50mm cron) but the infinity lock is positioned so that one "bumps against it" exactly at the hyperfocal distance for f8... is that the situation for other lenses so endowed?

I don't think so. I just checked a 5cm Elmar and a 5cm Summar and the focussing lever bumps into the start of the infinity stop at the f4.5 hyperfocal distance on the Summar, and just over f4.5 on the Elmar. Not really an ideal setting for hyperfocal, unless I suppose you were working with very slow film.

Regards - David

 

[David Hughes]

Hi,

I've a reasonable collection of Leica literature from the 1930's and the infinity lock is often mentioned but never explained.

F'instance: in "Handle the Leica" (August 1938, London) it says "This lever ensures rapid and steady focusing of the lens" but nothing else.

In "Leica the camera of modern times" (April 1937, Wetzlar & London) it says nothing about it at all.

And in "The interchangeable Leica lenses" (October 1937, Wetzlar) it says "When the focusing mount reaches the 'infinity' mark, it locks in position ...". It adds that only the 2.8, 3.5 and 5cm lenses have them.

And that seems to be it; I've the "Summar" and "Summitar" leaflets and they say nothing (from memory, as I can't find the "Summar" one). There's nothing in the little lens tables book and the 3 part "Directions" is also vague.

I'd high hopes when I opened the "Supplementary Directions for the Standard Leica Camera" (January 1934, Wetzlar) as there is a page headed "Focusing the infinity near point" but it's about the hyper-focal distance and refers you to the little lens tables book.

Sometime this evening I'll try and plough my way through the unofficial "The Leica Data Book" by Karl Barledon (Ohio 1934) and, of course, Morgan & Lester's, Kisselbach's and Matheson's books but I have my doubts even now.

Regards, David

 

[dave lackey]

Well, actually, in my M3 Instruction Book, it plainly states that the infinity lock should be on when installing, removing the lens. Pretty simple language for a simple feature on the lens.:angel:

 

[Roger Hicks]

Try removing a collapsible lens, or simply erecting it and collapsing it, without using the infinity lock. Sure, you can do it. But it's a LOT easier with!

Cheers,

R.

 

[David.Boettcher]

Well, actually, in my M3 Instruction Book, it plainly states that the infinity lock should be on when installing, removing the lens. Pretty simple language for a simple feature on the lens.:angel:

Yes it is. But as David Hughes has pointed out, literature from the 1930s doesn't say this. "Directions Leica Camera Model II" of January 1933 doesn't mention it - it says "The lenses are simply screwed moderately tight into the changing flange." No mention of the infinity lock at all. On the subject of the infinity catch (later on) they just describe how it works, not what its purpose is. The writer of your M3 book has described *a* use for the infinity lock, but not its original purpose.

Try removing a collapsible lens, or simply erecting it and collapsing it, without using the infinity lock. Sure, you can do it. But it's a LOT easier with!

Cheers,

R.

Again, while this is undoubtedly true, it surely is not the primary purpose of the infinity lock.

Regards - David

 

[peter_n]

It was expressly designed to tick me off when I least expect it. 😡

Exactly! I traded my rigid Summicron for a DR because of the damn thing. However I've found out that there are infinity locks and infinity locks. The one on the rigid Summicron is seriously awkward, but the one on the 35 Summicron v.1 is easier to use.

 

[Pherdinand]

... that and it stops infinity getting too close

LOL that is a good one. It always amused me how people call it.

 

[Roger Hicks]

Again, while this is undoubtedly true, it surely is not the primary purpose of the infinity lock.

Dear David,

Why not? Quite possibly this was the primary purpose, and it just carried on out of habit. I can't think off-hand of any lenses longer than 50mm with an infinity lock, possibly because longer lenses had enough barrel to grab to unscrew the lens.

I had the infinity lock on my Canon 50/1.2 'reversed', so it was normally unlocked, but I could squeeze it to lock it for removing the lens without rotating the focusing mount as I did do.

I'm not saying that I'm right. I'm just saying that I've yet to see any other mechanically convincing explanation.

Cheers,

R.

 

[Pherdinand]

Locking a lens on infinity "loses" half of the depth of field for whatever f-stop is selected at the time.

Your argumentation is flawed from its definition, "infinity" lock.
If you focus at infinity, the DoF will be infinitely large - it will extend from just in front of infinity to way behind infinity - so how much is "half" of that that you say you lose? 😀

 

[t6un]

Quote:
Originally Posted by David.Boettcher
Nice theory, but the early models without interchangeable lenses had infinity locks on the body. It was only when interchangeable lenses were introduced that it moved to the lens mount.

It may be a use for it, but it wasn't the original reason for it.

Regards - David
Dear David,

True, but with collapsible lenses, there's still the need to pull the lens barrel out and lock it/unlock it without rotating the focusing mount.

This and the aperture changing and the fact that leaving the focus at infinity also locks the rangefinder arm so it doesn't bounce around when camera gets knocked - there are plenty of reasons, the last one is also true for a rigid lens on an M camera. Additionally, infinity may be the safest setting to avoid burning pinholes into the shutter.

And, the greasy helicoid of the Elmar lens is exposed to the dust in every position except infinity.

 

[Dr Gaspar]

I think it was meant to be used for pick-up lines.
"Have you ever heard about the infinity lock? no? alright, follow me...".

 

[Sparrow]

Your argumentation is flawed from its definition, "infinity" lock.
If you focus at infinity, the DoF will be infinitely large - it will extend from just in front of infinity to way behind infinity - so how much is "half" of that that you say you lose? 😀

... sorry to be picky; but I'm not sure one can have anything beyond infinity, well except on those kiddies' movies perhaps

 

[David Hughes]

Well, actually, in my M3 Instruction Book, it plainly states that the infinity lock should be on when installing, removing the lens. Pretty simple language for a simple feature on the lens.:angel:

Hi,

Interesting that it took them from 1925 to 1955(?) to decide that; and shows that no one can accuse Leitz of jumping in without thinking about it first...

By the way, the early ones without interchangeability of the lenses had one, didn't they? Meaning the hockey stick.

BTW (2) I can't be bothered to read all the books again but I'm certain that they recommend unscrewing and vice versa with the thing far from infinity; something to do with not messing up the RF coupling. Anyway, it's what I always do.

Regards, David

 

[batterytypehah!]

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 ;-)

And, the greasy helicoid of the Elmar lens is exposed to the dust in every position except infinity.

Good point.

 

[David.Boettcher]

No, I'm not convinced by any of these theories.

The fact that the early models without interchangeable lenses had infinity locks on the body - the hockey stick - is the killer for me. 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

 

[Sparrow]

No, I'm not convinced by any of these theories.

The fact that the early models without interchangeable lenses had infinity locks on the body - the hockey stick - is the killer for me. 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

... or care? ...