50mm Summicron f/2 focus throw and patch off

[Chris Draughon]

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I recently purchased this lens, and I think it is defective. I am new to the Leica ecosystem, so I may be wrong. The focus throw rolls to the left of the 0.7m min. distance mark and the focus patch in the VF stops moving below 1.5m. I can use Live View to focus at 0.7m, but the patch is not showing the image in focus. See pics for example of the focus throw. This is my first Leica M lens. I bout it used from a very large online retailer located in NYC and it came with all of the original packaging. The label from Leica on the outer box is stamped 2024/04/25 and it matches the S/N.

My 35mm Voitlander works as expected. The focus patch, etc. function as intended.

Is this lens defective? Is my understanding of how the lens should operate incorrect?

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[adan]

The focus throw rolls to the left of the 0.7m min.distance mark - NORMAL

The focus patch in the VF stops moving below 1.5m. - NOT NORMAL

It is possible for a Leica-M lens (or camera) to be out of adjustment somewhere within the focus chain (multiple connected mechanical parts) between turning the focus ring with its visible markings - and the final output of the lens focusing cam pressing on the camera's roller that transmits the lens's movement to the rangefinder movement.

One possibility:

Take the lens off the camera, and study the back edge of the lens mounting flange (silver ring on the lens(es)that twists/bayonets into the camera when mounting the lens). Study your functioning Voigtlander lens alongside the Leica 50.

You will see that there is a crescent-shaped cut-out designed and machined into the flange top-dead-center - to allow the camera's spring-loaded rangefinder roller to "follow" the lens cam as it retreats into the lens when focusing to minimum distance.

It has been known for the camera's roller to be positioned in such a way (usually vertically) that - with a specific lens sample - it jams against the mounting flange before completing that movement.

This is all a matter of tiny physical tolerances being slightly mismatched - either camera or lens or both.

While the lens is removed, try pressing the cameras RF roller in and out with a fingertip - it should move freely throughout its range. This will check whether the roller is jamming somehow on the camera body itself (unlikely, since it apparently does move correctly with the C/V lens - although, what is the focal length of the C/V lens?).

Another test you can make to begin diagnosing this problem is:

- set the new 50mm lens to the infinity hard stop.
- look through the finder to see if the RF images are aligned for far-distant objects when the lens is set that way.
- take a picture of something at least a mile/1.6km away - at f/2.0
- check the focus of that picture on the camera screen
- if THAT picture is sharp, then the "basic" infinity calibration of the lens is correct (eliminates one variable in the equation)
- if THAT picture is blurry, then there is a overall mis-positioning between the lens's mechanical parts and the glass inside

 

Edited September 22, 2024 by adan

[Chris Draughon]

Thank you adan. I will follow these recommendations.

[lct]

5 hours ago, adan said:

[...] While the lens is removed, try pressing the cameras RF roller in and out with a fingertip - it should move freely throughout its range [...]

+1