MOD - closer focus of 0.75m - Leica Summicron 50mm F2 Rigid

 Many vintage Leica mount lenses have minimal focusing distance of 1m (about 3ft). Modern Leica lenses are able to focus much closer with rangefinder couple support is extended down to about 0.65m on latest line of digital Leica M cameras. Many photographers are building habit to focus closer for some shooting scenarios with newer lenses and looking for custom modifications of vintage lenses they like to use.

Extending focusing range of some lenses is relatively simple and reversible DIY process, e.g. for Leica Summilux-M 35mm F1.4 . For other lenses it may require significant grinding effort and RF calibration, and some lenses are not possible to modify due to limited movement of focusing mechanics.

In this article I'm exploring quite challenging lens - Leica Summicron 50mm F2 Rigid. The lens copy is provided by Fred Miranda (thank you!). 

Please note that this modification is experimental and intended for knowledge sharing only. I don't have plans to perform it again per request since it's time consuming and I prefer to dedicate hobby time for new explorations. In case you have interest in modifying your Leica 50mm F2 lens - please consult with nearest available lens repair specialist and check if they would accept such request. Thank you for understanding.





Primary goal to explore lens mechanics was to find if front-focus rangefinder calibration is possible. My first attempt to open this lens was extremely hard because retention ring holding optical core was tightened very strong. It required making custom metal plate to mount into bench vise and then secure lens retention ring sockets on top of plate, which allowed to safely unscrew lens frame in a way I later also used for MS Optics Apollon 36mm F1.3 lens disassembly. After reassembly I happened to unintentionally tighten lens optical core a bit further into its mount thread which led to slight compensation of front-focus, but it didn't solve issue completely.

Additionally Fred was interested to learn if it's possible to extend close focusing range so I analyzed lens mechanics for that purpose.


Unfortunately, the 1m focusing distance is physically limited by the radial socket range of focusing frame. Helicoid guider bar has range of about 170 degrees of radial movement. It sits quite close to inner brass cylinder even at middle focusing distance.


When lens is focused down to 1m, helicoid guider bar is almost touching edge of inner brass cylinder. Additionally its movement is hard stopping by edge of radial socket.


Rangefinder couple cylinder edge is also merging with mount edge cut area for M camera rangefinder couple roller. Focusing past 1m would move RF cylinder down but camera RF roller will be blocked by mount edge.



With that details my answer to Fred was something like "It's technically possible but with significant amount of grinding, that will slightly reduce durability of focusing frame, and perhaps extending range by only 10-15cm". Structuraly the frame of Leica 50mm F2 is very durable thanks to very thick brass parts. If radial cut is increased from 170 degrees to about 215 degrees, the outer frame would still connect strong to inner cylinder.

I've got approval though to move forward and perform this experimental modification, that requires in total:

  1. Completely disassemble focusing frame
  2. Cut the arc for extended radial movement of helicoid guiding bar
  3. Cut the helicoid guiding bar in its bottom to allow further axial movement
  4. Cut the mount area to allow M camera rangefinder roller move further into mount
  5. Precisely grind rangefinder couple cylinder edge for new extended close focus range
I planned to cut up to 40 extra degrees of radial movement arc.



It required full disassembly of focusing frame. I may list more details of the process if requested, though it's quite old lens and there is lots of info online already how to open it.

Here's picture with all focus frame parts. Inner brass helicoid frame shows area of initial very rough grind. I've protected helicoid thread and focus shell thread with few layers of masking tape during manual grinding with thin rounded metal file.


Accurate grinding requires patience, sturdy hand and high accuracy. Don't forget to wear protective glasses and mask - brass dust is not healthy. Precise manual grinding may take at least few hours, though it also gives you more control and helps to avoid accidental side cuts in case of using e.g. electric rotary tool.


Here's the final grinding and minor polishing result in reassembled focusing ring module - extra 45 degrees of radial movement is available.


I had to cut the helicoid guider bar - about 1.5mm of it's bottom edge area, but didn't take the picture of process.

Next area to accurately manually grind is the mount edge. Then I separately extended cut curve on rangefinder cylinder edge by performing repetitive iterations of minor grindings, polishing of RF edge, then assembling lens and checking camera RF focusing at new range.



Cleaned, greased and assembled focusing frame is now able to rotate 45 degrees further.



The helicoid guider bar remains tall enough to properly move inner cylinder by sliding in the range of its rectangular socket when assembled.



Assembling lens now.



At new minimal focusing distance focus shell is slightly elevating above mount frame, so extra caution required if focusing in dusty or sandy air conditions.


Here's the comparison of default 1m, and new 0.75m distance of focusing rotations.



Focusing knob is not blocking viewfinder, though it's better to grab the focus ring for closer focusing.

As a result this modified Leica Summicron 50mm F2 Rigid lens is able to precisely focus down to 0.75m while using rangefinder which may be quite useful for closer objects or portraits shots. I took it for short walk taking pictures in local Botanical Garden.











Conclusions

Modifying Leica Summicron 50mm F2 Rigid lens for closer 0.75m focusing is quite challenging. It's definitely not something I'd recommend as a regular DIY activity. This mod requires accuracy, proper skills and tools and should be performed by experienced lens repair person. It was very interesting exploration though, and it's great to see that this Leica 50mm lens model has durability capacity for such modification without loosing high precision of its its mechanical and optical performance. Having extra 25cm of closer focusing is quite convenient and focusing frame performing smooth at new range thanks to all durable brass mechanics.




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