Disassembly - Voigtlander 35mm F1.5 Nokton type 1 lens in Leica M mount

 This article is showing how to open Voigtlander 35mm F1.5 Nokton for cleaning dust in aperture chamber, which is not a trivial path comparing to older Cosina lenses like Voigtlander 35mm F1.4 Nokton.

This Cosina lens model is very new and I was surprised to see the lightly used copy with very large white dust particles in aperture chamber. Disassembly helped to also unveil the mystery of dust origin, and most important - to understand that it's not a dust but something else.

Like with many other lenses opened in my articles, there were no online guides or materials on how the Voigtlander 35mm F1.5 lens is constructed mechanically and what are safe steps to open it. Discovering the right path takes time and patience, small mistakes may lead to disaster. It took me few days to accurately explore mechanics. This article is showing results, but also few short points where I accidentally failed and had to deal with consequences. Please read it carefully first if you choose to open your lens copy for a maintenance.

Rear area disassembly

I started disassembly by unscrewing four mount ring bolts and removing the ring. At this point it's quite obvious and trivial step, though all four bolts have minor amount of factory glue so extra caution is required.

Next - remove the DOF scale ring. There is a set of brass calibration shims (green arrow) for lens infinity focus tuning, use tweezers to remove shims.

Red arrow is indicating RF couple cylinder. It is made of two rings - main cylindrical frame with glossy anodized surface, and matte black ring slightly elevated above cylindrical frame. NOTE: there are two detents on the glossy black cylinder - they are not for unscrewing it, so put your spanner wrench aside.

The matte black ring though can be unscrewed CCW. I'm using 3D-printed hollow cylinder with matching edge area covered with blue Loctite putty. First apply few drops of acetone at the outer edge of matte black ring to dissolve factory glue, then unscrew it CCW.

After unscrewing matte black ring from RF cylinder you will see another set of brass/steel calibration shims. They are precisely setting elevation of RF cylinder edge for correct RF couple focusing.

Next step is to apply another drop of acetone to the inner wall of RF gloss blackcylinder to reach the thread connecting thread of rear optical module. Accurately unscrew optical module in CCW direction.

Well, to my big surprise, unscrewing that module is not providing access to the aperture chamber, there is another framed glass module inside. I can also see set of brass shims that are most likely calibrating precision of Nokton 35mm F1.5 optical formula. At this point I was not able to safely unscrew that module so had to assemble rear area back.

Front area disassembly

The most challenging portion of front area disassembly is - to dissolve factory glue (using acetone) holding the front nameplate and extract it directly using strong adhesive tape. The nameplate ring does not have outer thread like older lenses, there is also set of detents on the opposite ring side, so it can be only fit back by matching detents to the lens bolts.

After removing front nameplate unscrew three black bolts that sit most deep (right near the hood mount petals). Do NOT unscrew other bolts, otherwise it will distort the optical alignment of front lens area and lead to image quality degradation.

Remove the hood mount ring by simply pulling it out. Attach the rear cap, place the lens facing front up and do not turn over during next steps. Unscrew three bolts marked with red arrows. Accurately and slowly pull up the aperture control ring with front optical frame connected to it.

At this step you have access to the aperture chamber.

I was happy at this disassembly point, and as usual took the Rocket Air Blower to blow out the large white dust particle sitting at the inner lens surface. That was a BIG MISTAKE!

The light metal ring marked with red arrow is an aperture transmission. Green arrow is marking bolt that is transmitting external aperture ring movement to inner metal ring rotation. Unfortunately the inner aperture ring is not secured by anything else, so when I blower air at glass - deflected air lifted up inner aperture ring and all aperture blades happily followed it. That was a bit stressful moment, and it took me another 15min to accurately assemble aperture back, so I was not taking pictures of that process.

If you have a need to blow air to clean the glass - first secure the light metal inner ring so it can't elevate. I did it after re-assembly of aperture. Putting 12 blades to their original location is not very hard if you have experience but definitely requires high accuracy and patience.

It's also important to find the small aperture click-stop spring loaded ball (marked with green arrow), and put it there during assembly.

Image below is depicting the aperture transmission ring socket (red arrow) that is capturing aperture frame plate. That plate is also not secured, so if you allow it to lift - aperture blades will fall out of plate sockets. The green arrow is showing location of aperture transmission bolt.

Speaking of a dust origin - the white particle I cleaned out was a dried out factory grease. It migrated from the edge of aperture outer frame. To prevent similar cases in this lens copy I removed exceeding amounts of grease from the inner wall.

Brief Conclusions

Voigtlander 35mm F1.5 Nokton lens has advanced mechanics with more complex design comparing to older 35mm Nokton lens model. Maintenance and cleaning of optical area is more difficult process. From the other side it's great to see that both focusing infinity and RF precision calibration are implemented by classic set of brass shims with relatively easy access. That is allowing to precisely tune lens copy focusing to the RF camera.

I didn't have a need to explore the focusing frame mechanics, though that double-helicoid system looks familiar with two helicoid guiders for focusing and two for RF couple cylinder. My lens copy is focusing precisely and very smooth and it's good to see that durable brass guiders are involved (or perhaps it's sort of strong copper alloy).

It seems that removing front optics frames directly is not possible without compromising optical alignment. The safer way is to open the aperture mechanics frame, which allow to locate it back to exactly same axial position. Though extra caution is required due to aperture components become unsecured.

I'm wondering if new Voigtlander 28mm F1.5 has some internal design similarity. Both lenses are surprisingly very compact which means the optical assembly is most likely also quite complex.