Recently made Voigtlander lenses having brand new and quite unique mechanical and optical design. In this article I'm taking closer look at ultra-fast aperture Voigtlander Nokton 50mm F1 lens in Leica M mount by performing partial disassembly. I purchased this lens copy used and it's previous use history is unknown, but I had to open optics for cleaning out large dust particles, so disassembly was necessary anyway.
WARNING: I've performed successful cleaning of this lens optics by opening it from the front, though unlike with many other older Voigtlander lenses models - Nokton 50mm F1 opening process is extremely difficult. I would NOT RECOMMEND to open your lens from the front. It will be better to send it to professional service instead. Reason for that is - opening front area optics will make your lens optically decentered and rendering quality will dramatically degrade. This Voigtlander lens assembly requires very precise calibration of optical modules centering paired with use of optical testing bench. It is very hard to achieve without lots of try/fail attempts of DIY process I'm currently involving.
UPDATE (2024-02-18) I've discovered that rear optical area can be safely opened though without a risk of optical decentering, so article is now updated with extra steps and pictures.
Front area disassembly
The only safe area to DIY open from the front in Voigtlander Nokton 50mm F1 lens is the aperture control ring.
Front nameplate has outer thread and can be unscrewed CCW from filter thread. Ring is glued so first apply few drops of acetone to the filter thread. Then use e.g. plastic cylinder with some adhesive putty to grab and unscrew front nameplate.
After unscrewing nameplate ring you will see 12 bolts - that's a lot. Do NOT touch silver bolts - they are secured with red factory glue and are holding set of front optical frames and axial calibration shims.
To remove only mechanical aperture control ring unscrew three black bolts marked below.
Take off the aperture control ring. It has groove on the inner side connecting to the brass slider of aperture transmission. Please point attention to its position during assembly.
After removing aperture control ring it can be disassembled further into two rings by unscrewing another set of three black bolts. I've checked it during first explorative disassembly, but not opening again. When unscrewing bolts you will notice inner ring elevation in the area of spring loaded aperture click-stop ball. Click-stop grooves are also anodized for extra durability.
Now few words about opening front optical modules, which you better NOT without serious reason (e.g. need to clean mold or seriously polluted surface). Red arrow marked silver bolts (three of them) are holding whole composite front optical frame. Unscrewing them is providing access to aperture chamber. There is set of axial shims that need to be accurately centered as well during assembly. I'm not going to open lens second time, since it's already centering-calibrated on my DIY bench (which took lots of time) and partially opening lens again just for this article.
If there is a need to access surface between front glass, another green arrow marked silver bolts (three of them) need to be unscrewed. It will also require further re-centering of front frame. There is another set of axial shims between front optical frames.
Rear area disassembly
Rear DIY disassembly is much more safe and may help you to calibrate rangefinder precision of lens with properly RF calibrated camera.
UPDATE (2024-02-18) - rear optical module can be also detached without risk of optical decentering to get access to aperture chamber, where dust is usually appearing over time of normal use.
First unscrew four mount ring bolts. They are secured with factory glue, so pre-heating may be required. There is set of infinity distance calibration rings under mount.
Next step is to unscrew set of four black bolts. Surprise, they are also factory glued and easy to strip so be careful. Remove the rear shell ring.
There is long radial groove on the mount shell ring, it is limiting focus ring rotation at infinity and 0.9m focus distances. You will need to accurately fit the shell ring during assembly by pre-focusing lens to medium range first.
Set of four silver bolts marked below with green arrow are holding the Rangefinder couple cylinder. There is also set of metal shims under it used to calibrate RF distance precision after lens infinity distance is calibrated (by shims under mount ring).
My lens copy was showing minor back-focus (actual focus slightly behind the target in focus of RF viewfinder). Adding 0.02mm shims under each bolt solved problem and now lens is precisely focusing using rangefinder.
It's intimidating to find so many bolts - 20 of them! Voigtlander Nokton 50mm F1 lens mechanics is built with extremely high precision and involvement of FIVE thick brass helicoid guiders to support buttery smooth focusing, FLE movement and RF cylinder movement. I don't remember so large number of guiders in any other opened lens, though not surprising to see in this high quality engineered lens.
Set of silver bolts marked with green and red arrows below is repeating every 90 degrees. Green marked one is holding together rear optical frames. I didn't need to access that area and red glue on green marked bolts is making me assume that opening that may also cause optical decentering. I don't have proper equipment to calibrate optical centering of multiple optical groups, so opening that area is beyond my technical skills and I can only speculate here on how internals are built further without closer look.
There is set of axial calibration shims visible between rear optical frames. It is indicating high complexity of precisely putting together optics of Nokton 50mm F1, and another reason to avoid DIY servicing and sending it to qualified professionals.
UPDATE (2024-02-18). Four bolts marked with red arrows below are holding whole rear optical module, which is well centered inside metal cylinder when re-attached, so it's safe to unscrew them to access aperture area. I'm adding pictures of that process in separate section of this article.
One of brass guiders is connecting external focus ring with internal helicoid ring supporting RF cylinder rotation. Two other guiders (one visible below) are transmitting rotation to another inner focusing cylinder. It's a very complex helicoid system allowing to move front and rear optics to different distance (Floating Lens Element) together with another range of distance for RF couple. Opening and re-lubricating this system is also a high labor effort which I'd personally also not DIY perform.
Accessing Aperture chamber for cleaning
If you need to clean dust in aperture chamber there is relatively easy access from the rear area.
First unscrew four silver bolts holding RF cylinder and detach it. There is set of RF calibration shims under cylinder (I have set of 0.2mm + 0.1mm + 0.05mm).
Next step is to unscrew four silver bolts marked with RED arrow. Do NOT unscrew bolts marked with green arrow - it will most likely cause optical decentering of rear optical module which will be hard to correct.
Lens need to be focused to infinity for easy extraction of rear optical module. Before extracting it - use pencil to mark module radial orientation, it is important to assemble it to exact position to keep optimal performance of tuned optics.
Conclusions
Voigtlander 50mm F1 Nokton lens is one more sophisticatedly engineering Cosina gem with impressively complex and durable mechanical build. Optically it's excellent lens with unique though more modern Nokton rendering with great sharpness wide open and beautiful OOF blur. I personally like how it's performing comparing to Voigltander 50mm F1.2 Nokton (M mount) and that extra power of blur is useful and worth the extra weight (not sure about price though).
Any optical DIY maintenance of the front area is highly NOT RECOMMENDED because it's not possible to open front optics without completely ruining proper optical centering. Minor mechanical DIY maintenance of the aperture control ring is possible though.
UPDATE (2024-02-18) Fortunately it is also possible to DIY open lens from the rear area and perform fine tuning of RF precision or cleaning of the aperture chamber from any accumulated dust.
I'll keep shooting with both Noktons 50mm F1 and F1.2 on M camera (and adapted on Fuji X) to better understand their strong sides, however they both perform excellent as first impression and it's hard to choose which I like more from perspective of rendering. Speaking of maintenance and ease of optical cleaning F1.2 Nokton version is definitely a winner : )
Picture samples
Speaking of Voigtlander 50mm F1 Nokton rendering on M sensor - lens is delivering great amount of details wide open and it's designed to be used that way most of the time (otherwise you could just shoot with much lighter F1.1 or F1.2 models). The calm and gentle way resulting picture is forming is quite easy to adopt for personal taste of shooting, and of course the OOF look is very different depending on the frame area and distance to background object. Some people may like is and some may not - it's very subjective area, but Nokton 50mm F1 has it's unique character for sure.
Here is one image sample taken with M10 at wide open F1. The day was cloudy and shy signs of Spring just started to show up on the nearby trees.
Center 100% crop
Top right corner 100% crop
What I like personally - level of details is very decent at F1 even in the corners (if your lens is properly optically centered). It just takes some practice to use benefits of so narrow DOF. Thanks to very large diameter of the focus ring of Nokton 50mm F1 it is very easy to focus quick and precise, however I'd highly recommend to involve 1.4x viewfinder magnifier for more confident results.
More pictures below taken at F1 with M10P
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