Screw mount lens with no threads?

I came across a very nice Canon 50mm f/1.8 lens advertised as M39 Leica Screw Mount. Everything looks right except the brass collar shaft that is normally threaded is smooth -- there are no threads. I'm new to Leica's, but all the LSM/M39 lenses I've seen have an outer steel collar ~39mm in diameter and then an inner brass collar that is threaded on the outside. The measurements are correct, but the brass collar is missing the threads.

 

I will try to add a photo.

 

If anybody can tell me what this is, if it could work in a Leica II or IIIb, or if it could be made to work (e.g., could I replace the brass collar with a threaded collar). I am also curious about the history surrounding this unusual mount.

 

Cheers,

Brian

The answer is, you may never know. No telling who owned it before you and possibly had it modified at some point for another use, which no one would now know. People sometimes do weird things with cameras and lenses.

Hi. This link may shed some light on your variation: Confused about a Canon 50mm f/1.4 LTM

 

The brass cylinder acts to move the cam in the rangefinder. Depending on the internal focussing mechanism, the brass cylinder will be threaded or not. Canon was apparently notorious in the mechanical changes to their focussing mechanisms during production cycles. I note that the brass cylinder is fully extended, as it should be with the lens focussed on infinity.

 

Enjoy it.

Regards, Arthur (apiarist1)

Agree with Arthur. There should be no problem.

Well, that is good news. I appreciate the link. I can see now the brass barrel retracts and extends with the focusing ring. I looked at several other LSM Canon lenses for sale and all of them had the same barrel without the threads.

 

The focus ring is smooth throughout the range. The glass is so clear and bright, perhaps the lens is newer than I thought.

 

Thanks again for the responses,

Brian

Canon lenses seem to hold their age well, glass and chrome. It will have to be made before 1968 I assume. Someone will have lens production and serial number dates.

As well as I know, for 50mm lenses, the rangefinder ring moves at the same rate as the lens moves, when focusing.

 

For other focal lengths, it has to move faster or slower than the lens elements, and so many need threads.

Though none that I know of have such threads.

Canon was apparently notorious in the mechanical changes to their focussing mechanisms during production cycles. I note that the brass cylinder is fully extended, as it should be with the lens focussed on infinity.....

 

Absolutely not true. Once a design was locked in, it wasn’t changed until the next major redesign (if then). See Peter Kitchingman’s Canon rangefinder lens book (page 11) for more info.

Good find of a nice lens, my guess its from the late 60's. It'll work well on any of the LTM/Leica or Canon bodies. There are also adapters that can be threaded on the LTm moun for use on the M body Leicas. I use my 50 1.4 Canon on both a Leica IIIg and an M3.

Absolutely not true. Once a design was locked in, it wasn’t changed until the next major redesign (if then). See Peter Kitchingman’s Canon rangefinder lens book (page 11) for more info.

I would say that this is absolutely not true! I have two black/chrome 135/3.5 lenses that are externally identical in every visual way, including looking in the back. The first was messed up, so I bought another with a scratched back element, to build one good one. Nope, though they're identical outside they're not the same--the way the two optical components fit in is different, as is the back element. mounting. I guess you could argue that this is a "major" redesign, but it doesn't look like one to me. I have found the same type of minor changes in identical Nikon camera models, too, and my conclusion was that when a manufacturer finds a tiny thing to change that he perceives as an improvement, he will make it, no excuses needed.

 

One warning on this particular lens, the aluminum mount 50/1.8s: they are prone to internal fogging, and it's often of a type that can't be cleaned out--a sort of etching of the internal elements rather than just the fog of evaporating oil that is more common. Check it by shining a flashlight in from one end while looking in (indirectly, at the elements, not through them) from the other. If you see fogging, stay away!

 

As others have noted, the lack of threading is not an issue.

Edited October 27, 2017 by michael_darnton|2

The lens shown is a late version 50/1.8. The later Canon 50/1.8 lens does not have threads on the RF cam.

 

Peter Kitchingman's Canon Rangefinder Site

Looks very much like mine, other than that the focusing scale is in meters. Maybe the threaded part is a tiny bit shorter than mine, but only a fraction of a millimeter.

 

The brass focusing coupling cam should protrude from the "mating" surface of the mount by 7.5mm when the lens is focused at infinity.