Disassembly – Voigtlander 75mm F1.5 Nokton VM

In this article I’m disasembling one of the latest portrait lens for Leica M mount – Voigtlander 75mm F1.5 Nokton Vintage Line. This lens sample is provided by Dale Tu (thank you Dale!) for inspecting slightly stiff focus ring rotation, and I’m using this opportunity for sharing lens construction details in case you’ll have a need to perfrom DIY repair.

Voigtlander 75mm F1.5 portrait lens is already well known for it’s beautiful image rendering and great level of details wide open. Optical formula consists of partial dispersion and aspherical elements, and you can read more detials on official Voigtlander site. What makes me curious about this lens – is its relatively lightweight and slim lens frame comparing to lots of large glass inside.

Cosina engineers designed this lens to fit recent Vintage Line models that have body style closer to 1950 production. It makes Voigtlander 75mm F1.5 look very unique. From the other side that uniqueness leads to increased complexity of components assembly, and harder to understand how to put it apart safely. It took me few days to discover required steps.

Disassembly

Traditionally I’m starting from unscrewing four bolts and removing Leica M mount ring.

And then the “magic” begins – I don’t see securing ring which is holding optical lens core inside of foucusing frame. My best guess was that securing ring is located inside of the rear optical tunnel. If you focus lens and look how the rear area moves it unveils some information about build mechanics. So I assumed that following ring is the one I need. Cosina engineers like to add some glue to securing rings, so I’m applying few drops of acetone to the inner wall of that ring and spreading it to its bottom by tilting lens body.

That ring is hard to access with spanning wrench, and even if you do so – there is very high chance to strip the ring edges because thay are very thin. There are multiple safer ways to unscrew securing rings by catching surface area, and today I’m using one of exotic approaches – unscrewing ring using a … plastic water bottle.

Well, I’m using that bottle simply because its opening diameter is just slightly smaller than the securing ring diameter. For effective grip I’m adding layer of thick rubber strap between the bottle and ring surfaces and accurately press bottle inside for good grip. It looks scary, but is actually safe since bottle plastic is soft and gentle securing ring paint is protected by rubber layer.

Firm press and few rapid CCW high torque moves making securing ring loose, then I’m unscrewing it until it moves very loose. It’s not a surprise that ring can not be extracted from the rear, because rangefinder coupling ring inner diameter is slightly more narrow than it. So I’m just removing bottle and rubber, and accurately elevating focusing frame up.

Note – there are focus precision calibration radial shims. They should be positioned right on top of rear optical frame during assembly. The securing ring remains inside of the focusing frame, looks like it can not be extracted from bottom.

At this point you have full access to focusing mechanics. Next step here is to memorize position of each bolt, unscrew four of them holding focusing ring brass guiders, and take them out.

Then I’m unscrewing four black bolts in the mount area, and extracting focusing core.

Note the bright silver bolt at the edge of inner focusing core – it should fit corresponding socket of optical lens core during assembly, and it’s position fits the infinity point of focusing ring (when it’s rotated to infinity).

If you rotate focusing mechanics it will expand up and allow to check the grease conditions.

Next step is to unscrew silver bolt of the focusing ring.

Then unscrew the focusing ring from the base by making two full turns CCW.

At this point you have access to the focusing ring thread, which in case of this lens sample required grease change. For this fine thread I’m using HELIMAX-XP grease purchased on eBay from this seller. I also performed slight geometry correction of the focusing ring, it had some moderate hit to the side which caused slight elliptical shape and making focus ring thread to wearing out more actively. Now ring rotates smooth like new and I’m assembling everyhing back in a reverse order.

Few important notes on reverse assembly:

  • Collapse focusing core before inserting it into focusing ring frame
  • Screw in focusing ring brass guiders but keep bolts loose, then move brass guider close to focusing core center and secure bolts. Check that focus ring rotates without reverse direction play
  • Fit the silver bolt with socket of optical core frame when assembling it with focusing frame
  • Use rubber/bottle again to secure ring that holds optical core inside focusing frame, I’d still avoid using spanning wrench
  • Check that rangefinder couple ring slightly cut surface area is located near M mount ring area cut for rangefinder roller

Brief conclusions

Voigtlander 75mm F1.5 lens mechanics is robust and very well designed for easy maintenance, though unscrewing first securing ring is quite challenging. It’s great to see brass guiders in focusing ring and helicoid construction that have option to readjust their position for higher movement precision. Optical frame is beautifully crafted and it looks like access to the aperture ring is available from the rear side.

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