Disassembly - Voigtlander 23mm F1.2 Nokton Fuji X lens

Cosina made smart move decade ago by producing dedicated Micro Four Thirds mount Voigtlander lens with ultra fast F0.95 aperture, extremely high quality optics and buttery smooth manual focusing with great precision. I can tell lots of good word about years of shooting with Voigtlander lens on Panasonic and Olympus MFT cameras. It was a dream to see one day similar high class manual focus Voigtlander lens dedicated for APS-C. Cosina made that dream true with their Voigtlander 23mm F1.2 Nokton lens. In this article I'm going to take a closer look at lens internal mechanics and electronics to get better understanding how it can me maintained in case repair is needed.

Compatibility with Fujifilm X-Pro3 camera

Voigtlander 23mm F1.2 lens has real manual focus with well dampened focus ring. High benefit of having electronics in this particular lens - is transferring information about focusing distance to camera.

It allows Fujifilm X-Pro3 to show correct bright frame line size in optical viewfinder when focusing. Even more, by knowing selected aperture value X-Pro3 camera can show estimated DOF range on manual focus scale in optical viewfinder too. I'm very curious to see how Cosina solved this question mechanically and electronically.

NOTE: Looks like previous X-Pro2 and X-Pro1 cameras do not interact with Voigtlander 23mm F1.2 electronics and can't apply frime line corrections (thanks Spock66 for these useful details).

Native Fujinon XF lens do not have real manual focus and information about focusing distance is rather discrete, provided by focus-by-wire sensors reading position of multiple focusing ring pins. That system requires self-calibration each time lens is booting up with camera. Due to that Fujinon lens often annoyingly taking extra seconds of precious shooting time to retract focusing core when you decide to preview picture. In some situations it is fine to wait for few seconds, but I personally prefer to avoid unnecessary distractions while shooting.

Voigtlander lens for Fuji X do not have that re-focusing lag when previewing pictures, no matter which focus is selected because focus is real manual and lens core simply remains in same position until refocused. There should be something inside Voigtlander 23mm F1.2 lens that is able to quickly read focus core position and transfer that to camera to show correct size of frame lines.

Lens disassembly

Typically there is nothing challenging with accurate disassembly of Voigtlander lens made for Leica M mount, though new generation of Voigtlander Vintage Line and Fuji X series have something new there making it more difficult. I've noticed that almost every recently made Voigtlander lens has some glue added here and there on bolts securing mount ring or internals. Perhaps there is new standard of lens quality demanding that on Cosina factory, but that decision is making it harder to unscrew lens bolt and increasing risk of stripping the bolt head.

The Voigtlander 23mm F1.2 lens copy I'm disassembling today is no exception - multiple bolts didn't want to unscrew with regular turning effort due to securing glue. One option would be to melt that glue by warming up bolts with precise soldering iron, though I don't know if there is any plastic or electronics inside which could be melted too, so using another option. I'm holding precise JIS screwdriver firmly pressing on bolt head, and catching screwdriver with pliers making few degrees rapid turn by moving pliers radially. It helps to safely break the glue without stripping bolt head - worst case would be light bending of bolt head but not stripping it. For this lens I had to do it for at least 4 stubborn bolts out of more than dozen unscrewed.

Four silver bolts and three black need to be unscrewed first. 

Next accurately extract metal circle surrounding rear of optical core and unscrew two bolts holding lens contacts group. Gently elevate mount ring and release contacts group, move very slow and do not stress ribbon cable holding contacts group. Mount ring is light and looks like made of aluminum, which is reasonable to keep lens light enough for typically lighter Fuji X system (compared to more premium brass mount rings of Leica M Voigtlander lens).

Under mount ring you will find precise focus calibration shims. In my Voigtlander 23mm F1.2 copy I counted five plates if different thickness. It's a very good design allowing to recalibrate focusing precision in case of using Fujifilm camera that has offset of mount ring precision. 

NOTE: It's better to use rubber gloves of tweezers to remove calibrating shims. During years of disassembling different lens I found so many copies with someone's fingerprints on shims, they collect fingerprints easy and in case shim is made of brass - post-oxidization are making prints impossible to wipe easy.

After removing shims you have access to electronic mainboard of Voigtlander 23mm F1.2 lens. Unlike common light-green board color of Fujinon this board looks more premium with darker base material. For some reasons there is a bright red paint dot on main chip.

There are two ribbon cable connector in bottom area of mainboard. Left one is serving for focusing distance sensor, and the right one is transferring information about aperture value. Right cable is also attached to frame with quite strong double-side adhesive tape. Connecting sockets have elevating black plate locks, that need to be flipped up from the outer edge.

Cables are very thin and extreme caution is required while disconnecting them. Once connector sockets are unlocked you will see how far ribbon cables are fitting inside connector socket. Make sure they are positioned far enough when assembling lens back.

Disconnect both ribbon cables - they should slide out with minimal effort. Then accurately disconnect adhesive tape from frame which holds right ribbon cable of aperture sensor. 

Then unscrew three black bolts holding mainboard and accurately remove mainboard.

Next step is to unscrew three black bolts closer to lens core, they are holding ring with DOF scale.

Remove DOF ring carefully, watching the aperture cable and preventing adhesive tape to stick to it. Ring comes out easy together with focus distance sensor. 

And here's opposite side of DOF ring, that shows simple and elegant solution Cosina used for detecting focusing distance. Inner arc is connected to outer dark arc with sliding contacts pair mounted to focusing ring when assembled. Dark arc is covered with electro-resisting layer which leads to different level of signal which is capable to read analog electronic signal precisely indicating position of focusing ring. That is how Fujifilm X-Pro3 camera always knows precisely exact focusing position immediately after booting up, unlike numerous Fujinon AF lenses that need to run time consuming position recalibration first.

Bottom area has large white cylinder which is serving as focus ting rotation limiter and also dampening end of focus stop point. 

Here's top view to Voigtlander 35mm F1.2 focus ring. At 9 o'clock there is focusing ring contacts pair for focusing distance. Over long time of intense use there is a possibility these contacts may require cleaning.

NOTE: Make sure to NOT rotate focusing ring out of its normal focusing range, because limiting white cylinder is not preventing ring to rotate to distance closer and potentially dismount helicoid cylinder.

Next step is to unscrew three black bolts holding focusing ring. Take focusing ring out.

Now it is possible to unscrew two silver bolts and remove plate holding focus distance merging contacts.

Closer look at Voigtlander 23mm F1.2 main board, for reference how healthy operating board should look.

I see three cylinders around rear optical core have slots for unscrewing different areas, there is also visible layers of securing glue. If there is a critical need to access inner glass surface I think it's the place to start by attempting unscrewing bottom one cylinder that should potentially allow whole rear optical module to be removed. I don't have reason to open perfectly working optics so will leave it alone.

Another area to mention - pair of helicoid guiders secured with pair of silver bolts each with red securing glue. Guiders can be released and extracted for fine width calibration in case focus ring has rotation lag. There is also side access to focusing ring thread edge to add helicoid lubricant if it dries over time.

I suppose that Nikon mount Voigtlander 35mm F1.2 may have similar inner frame construction, though the aperture ring position is different on that lens and ribbon cable could lead from upper area.

At this stage I'm assembling lens back by looking at each guide picture, and taking extra caution when mounting ribbon cables to mainboard, ensuring they are completely inserted like shown on earlier pictures and accurately locking connector cages. Finally I'm checking that lens operates corrects on Fujifilm X-Pro3 camera, and now Voigtlander 23mm F1.2 is ready to continue taking more pictures.

Conclusions

I'm very impressed by the mechanics and reliable design of electronics in this Voigtlander 23mm F1.2 Nokton lens. The precise way focusing distance information is collected is one of huge benefits of true manual focusing Voigtlander lens comparing to focus-by-wire most Fujinon lens. All parts are made from metal and precisely machined up to highest Cosina quality standards similar to Leica M mount lenses. For sure this lens can outlast any Fujinon lens with intense use, because it can be effectively operating fully mechanically even if its electronics breaks, while Fujinons are completely dead lens if electronics fails there.

Regarding the optical rendering of Voigtlander 23mm F1.2 - it's a area of discussion for another articles, and there are tons of them already. I can only add that personally it's a great experience shooting with this lens and the IQ is high enough to often grabbing this lens for shooting with X-Pro3 instead of using X100V camera.