Disassembly – Mitakon ZhongYi 25mm F0.95 Speedmaster lens

I’m shooting with APS-C Mitakon 35mm F0.95 Speedmaster lens since it release in 2016, and already disassembled it numerous times. Today I’m going to disassemble another Speedmaster lens – Zhongyi Mitakon 25mm F0.95.

It’s smaller model from Zhong Yi Speedmaster series designed for Micro Four Thirds sensor size. And it has exactly same design of focusing area as its larger Speedmaster brothers: 35mm F0.95 (APS-C) and 50mm F0.95 (Full Frame). So you can use this disassembly guide as a reference while maintaining other Speedmasters.

The lens sample is generously provided by Greg Hall (thank you Greg!). I’ll probably also find time to make short comparison of this lens and Voiglander 25mm F0.95 prior to returning the lens sample to its owner.

Unlike my other disassembly guides I’m going to write this one in the reverse order to show the assembly process. It will be descriptive enough to run disassembly as well.

First step is to accurately clean all disassembled parts and glass surfaces. I’m starting with the lens core. Grease should only remain on the helicoid thread and two side sliders sockets.

Then I’m cleaning and lubricating two silver helicoid rings.

Helicoid outer ring (left one on picture below) is connecting to camera mount and keeps its position. There is small black bolt stopper on it, to limit black focus ring rotation. This outer ring has inside CCW small-step thread that looks like lens filter thread but has opposite rotation direction.

Helicoid middle ring (right one on picture below) is connecting to the lens black Focus Ring using three bolts accessible from Focus Ring surface. That bolts go into outer groove area on the helicoid middle ring. This ring also has outer CCW small-step thread to connect with helicoid outer ring. Also there is inner CW large-step thread to connect Lens Core. Please note – this inner CW large-step thread has 10 different entry points (so lens core can be connected inside helicoid middle ring in 10 different positions, but only 1 position is correct).

Apply small amount of grease to CCW small-step thread. Then screw in both helicoid rings together until the end. Please note that it has reverse thread and requires CCW rotation (unlike the CW rotation when you screw in lens filters). Don’t finish screwing too tight, apply low effort until it stops rotating.

Now both helicoid rings are allocated in minimal focusing distance position (that corresponds to “0.8” “0.25” mark of focus ring).

Clean the black Focus ring, and check that all three tiny bolts on focus ring sides are screwed out. Gently attach the focus ring on top of helicoid middle ring into position where “0.8” “0.25” mark is located right near the black stopper bolt on helicoid outer ring.

Accurately screw in all three tiny bolts, make same amount of turns on every bolt so they go inside to same depth. These three bolts should catch the groove area on helicoid middle ring. After you screw in all three bolts into groove area – they will catch the helicoid ring firm.

Now rotate the focus ring until black stopper bolt appears near the “infinity” mark (like it’s on the picture below). So helicoid is now tuned for infinity focus. Later you will be able to calibrate infinity focus precision, but now it’s time to continue the lens assembly.

Now is the most challenging assemply phase – you need to connect focusing helicoid to the lens core. Rotate aperture ring to the F0.95 position. Then put helicoid ring on top of lens core like on the picture – “0.3” m white mark should be above the black screw of the aperture ring. You need to catch the thread in this area, then it will be correct one from all 10 possible.

NOTE: you may catch incorrect position at “0.4” mark or “0.25” mark – in this case your lens will not focus to correct distance. If you see that your lens can’t focus properly after assembly – disassemble it back to this step and try to connect lens core in position closer to “0.3” white mark.

Once the tread is connected, slowly rotate it down until the infinity mark appears near the F0.95 aperture mark.

NOTE: when “infinity” mark is near F0.95 there should be about 2mm distance between focus ring and aperture ring edge like on the picture below.

Then you need to position helicoid slider slots near the slider screws sockets.

This lens sample had one brass slider little distorted. I’ve corrected it, each slider should nicely fit the width of the corresponding slot.

Secure brass sliders with black bolts. Try to center themas much closer to the lens core – it will reduce the focus direction lag.

BTW I’ve noticed that stopper black screw has too thin cap, so added small shim ring to it.

Last step is to clean the glass surfaces and attach the mount ring  with rear glass element. DOF scale center should match the black stopper bolt, aperture indicator dot position, and infinity mark on the focus ring.

Now the lens is assembled, and I only need to find someone with MFT camera to test the lens focus and calibrate the infinity focus position using related guide.

Few words about build quality

This particular lens sample with SN:01341 is built very well. Aperture and focus rings are rotating smooth without any lag, and with pleasant friction effort. Nine aperture blades are moving simultaneously creating correct shape. Nothing is wobbling or shaking. I like that all parts are metal and there are no weak connections – lens is quite solidly built. Another good point of this design – adjustable focus ring position, that allows to fine tune infinity focus position wihout lens disassembly.

Though there are few minor mechanical drawbacks I can also highlight.

Like the Speedmaster 35mm this one has aluminum helicoid. It will not last so long like Voigtlander or Zeiss helicoids that are mashined from brass. I’ve noticed some play in the thread – more than I’d like to see. However it should perform great for many years – typically out of the factory there is large amount of grease. I also like that helicoid sliders are thick, durable, made of brass, and have adjustable geometry.

Another weak design point is the way front area is constructed. I didn’t disassemble it completely but noticed that if you add some extra effort when removing lens filter – the front ring with filter thread may also rotate same direction. It may happen if you attach some low quality filter with stiff thread and try to remove it later. I’m using brass B+W filters and they are typically easy to unscrew. It’s not critical issue though, because ring requires numerous full 360 turns to be completely detached, which unveils access to the front glass assembly firmly secured on place. So if that happens you can simply screw it in back, aligning the aperture white dot to the focus indicator. Some manufacturers are using opposite thread direction or securing front ring with extra stopping screw.

Personally I think it’s quite good build quality. Prior to switching completely to Fuji X system I was shooting for about year with Voigtlander 25mm F0.95 on Panasonic GM1 as my primary set. It was great and pleasant experience especially when shooting in lower light conditions. Taking into account lens weight and size I’d prefer Mitakon Speedmaster 25mm F0.95 these days because it’s two times smaller and noticeably lighter.

It would be interesting to also evaluate and compare optical quality of this Mitakon 25mm F0.95 Speedmaster vs the Voigtlander 25mm F0.95.