Lens focussing errors

[wakarimasen]

Hello Folks,

Is it possible for one focal length of lens (i.e. 35mm) to focus correctly on a Leica M body, whereas another (50mm) will not? By this, I mean is it possible for the fault to lie with the camera rather than the lens?

Best regards
RoyM

[L David Tomei]

I would think it is conceivable but not likely. You would have to run some simple focus tests to get a better measurement at different f-stops at a set distance, for instance 10 feet from a defined target. It is more likely that one lens is good and the other a bit off. The body need only have a specific distance between the lens and film plane (registration) which is not likely to change. To begin diagnosis, I would first assume that the 50mm lens is good and the 35mm lens needs adjustment/repair.

[mdarnton]

Probably not. The camera has a standard; the lens has a standard. If you change something and get different results, what you change is to blame, not what you didn't change.

Which camera, what lenses, what issues?

For instance, I used to use a lot of Canon lenses on my Ms, and Canon's attitude about focus was notably sloppy relative to Leica's. The Canon teles, where it really mattered, I ended up adjusting the focus cams myself. Soviet lenses, made for Soviet "Leicas", if unadjusted to Leica standards, mis-focus at close distances, thanks to a different standard being used in the RF.

People like to blame LTM>M adapters, but that hasn't been my experience, and I tried some pretty shoddy-cheap adapters. An adapter isn't all that hard to machine correctly, as regards focus, anyway.

[wakarimasen]

I'm comparing a Voigtlander Ultron (35mm F/1.7) ltm with adapter to a rigid Summicron. The first focuses perfectly on an object that is over one mile fro our house. The Summicron does not however.

[zuiko85]

Do you mean the Summicron goes past infinity or short of infinity? What does the scale on the lens show at a measured distance? Do the lenses agree at shorter distances such as 1 meter, 2 meters, 5 meters?

There are several more questions to look at here.

[mdarnton]

Probably you need to throw a third lens into the mix. Also, if this is the older Summicron you mentioned in another post, look at the brass ring on the back that interfaces with the cam in the camera and see if it appears to have been messed with in any way--look for a difference in texture at the infinity position, for instance. Any abrasion there would cause the RF to not reach infinity.

As I mentioned before, I found my lenses were inconsistent. After all of the fixing I could do, I finally adjusted the camera's RF for the 85/1.5--the lens with the least depth of field, and let the others do what they wanted to do.

Depending on the amount of error, it may not even be important. I never felt that obsessing with my M cameras focus adjustments was very rewarding, and that's one of the reasons I switched to SLRs, since I'm pretty compulsive about focus (man, we don't even want to get into that--how many Leica owners have bothered to worry about how the plane of focus moves when you focus on something off center, then rotate the camera to your intended composition???) I'd encourage you to shoot some pix to see if there's a real problem. The lenses I chose to fix had real, serious focus problems.

[wolves3012]

It's possible for one lens to focus adequately when another doesn't and the body to be at fault. If the body has an incorrect flange-to-film distance then some lenses will show this up more than others (shorter focal length may cover up the error due to extra depth-of-field, for instance). That's assuming the two lenses are exactly set up correctly too.