Yesterday I disassembled ZongYi Mitakon Speedmaster 35mm F0.95 Mark II lens to lubricate helicoid threads. This time it’s silver model that is mechanically same as black one. In the article I’m showing more details about focusing mechanics.
First step is to remove three screws from lens mount ring.
Then take off ring with DOF scale.
Unscrew small black bolt limiting focus ring rotation.
Focus lens to minimal focusing distance of 1ft.
Now unscrew four black bolts on the helicoid guiders, and remove them.
Lift the lens up and slowly unscrew the lens core out until it detaches. Remember that position (better take few pictures as well).
I also removed rear lens glass module, at this point you can just unscrew it CCW for cleaning of aperture chamber if needed. This module is one of the heaviest part of Speedmaster 35mm F0.95 MK II – it weights 91g.
Here is the look at fully closed aperture blades.
Next step is to disassemble helicoid. Take it and rotate focus ring CW until it is disconnected, count number of turns you made (during assembly you need to screw it in CCW to exact same number of turns. NOTE: the thread is reversed – that is why you need to unscrew it in CW direction.
Here is closer look to the focus ring rotation reversed thread with single start point marked on picture. Inner core thread has 10 start points. So when you are rotating focus ring of assembled lens the rear ring and lens core do not rotate, and focus ring is moving to about 0.5mm in its thread while lens core is moving to about 1cm in inner helicoid thread.
Now mark focus ring position and partially unscrew three small black bolts on focus ring and remove it. At this point all surfaces of helicoid are accessible to cleaning. Just make sure you mark exact positions before cleaning with some small scratches on aluminum edges (if you mark with pencil or marker that may be wiped during cleaning and lubrication). Focus ring bolts are going to inner ring groove area, so when attaching it back just position bolts right above marks in that groove.
Thread machining is quite accurate, however if you assemble lens back without the grease – inner core can be tilted up to few degrees causing optical decentering and IQ degradation. Comparing to Voigtlander or Zeiss lens where part of thread is made of brass, this Speedmaster thread is fully aluminum, so it can wear faster and requires to be properly relubricated. The amount of grease should be quite large, it is compensating lens core tilting in the inner helicoid thread, and optical axis remains centered. I personally didn’t greased enough thi first time, so had do disassemble lens again to add more grease and stop core to tilt. Well, it’s quite heavy core, so such behavior is expected, however I wish ZhongYi make helicoid threads with higher precision for eliminating tilt.