MOD - Click-stop aperture – Mitakon Zhong Yi 35mm F0.95 II Speedmaster Fuji X (part II)

This time I’ve got contacted by one of the blog readers Dawn Kim asking if I’m commissioning click-stop aperture mods. In fact I do not, but decided to make this mod again just in purpose of writing more extended guide, and it will be done for free.

Today I found some time for initial steps. Will continue this guide closer to weekend.

Here’s the lens. SN: 004287 , silver version. I noticed some manufacturer difference of lens body comparing to my old one – engravings are more accurate and less deep on newer version.

It’s great sharp sample with very smooth focusing ring and even rotation effort on all focusing distance. Glass is in perfect shape, and aperture blades are closing to same positions forming good shape.

As usual I’m unscrewing CCW front black naming lens plate. It’s not a surprise to see “calibrating mark” – a thin scratch on the metal that is indicating best radial position of front lens group. It is important to fit that marks during assembly.

Then I’m unscrewing three bolts, taking out front filter thread ring, and finally pulling out front lens group.

The Speedmaster’s 10-blades aperture is fully accessible at this step, however I don’t need to touch it.

It’s time to unscrew long bolt of aperture control ring, it is moving inner aperture transmission ring, so locate it in same position when assembling (and we need to do that many times during this mod for click-stop position checks).

That bolt is usually sliding inside side groove.

Focus lens to 0.35m distance to fully extend the front area. After that accurately wipe out all grease from the inner area of aperture ring, and outer area of front black frame.

It should be completely clean.

The most important part of the mod – is selecting bearing ball of proper size. I have bearing part from old disassembled Vivitar zoom lens. There are balls for dozens mods : ) I only need one for now.

Measurements show that ball size is 1.6mm, that is very good size which is quite close to what I saw in many Fujinon / Nikon / Zeiss / Voigtlander click-stop apertures.

Ok, it’s going to be a little scary, but at this time the lens need to be drilled. Yes you read right I’m going to drill the lens frame.

It’s important to cover all surfaces with easy removable adhesive tape. First I’m covering all outer area. It’s needed to prevent drilled pieces going to helicoid thread.

Then I’m protecting aperture and all inner surface. Note – you need to close aperture blades first by rotating inner controlling ring. Just gently apply small pieces of tape. Finally air pocket should be created in the drilling area (on the top of picture below).

I’m using Li-ion hand drill with 60rpm speed (one rotation per second). First I’m using 1.2mm drill bit.

After hole is drilled, I’m switching to 1.6mm drill bit and drilling again with slower speed. Finally it’s done and tape can be accurately removed.

Then I’m carefully removing small metal pieces and using rocket blower to clean the surfaces. Done!

Now inserting the 1.6mm metal ball. It should move freely because actual hole diameter is slightly larger than 1.6mm.

Then I’m using copper plate to create radial spring from metal strip. It’s 6mm x 100mm.

Strip should be slightly shaped first.

Then I’m inserting 4mm long pin.

And finally the spring.

Before moving spring to not of the pin – put on aperture control ring to hold the ball on place. After that screw in long bolt which controls aperture, and move aperture ring from F0.95 to F16 and back at least 20 times. Then disassemble ring again. You will notice trace on surface created by ball pressure.

I’m marking end of the trace and using precise file to make a thin groove. After that I’m using 1.2mm drill bit to make deeper groove.

After cleaning surface I’m assembling aperture ring back – now it clicks at F0.95 position – great!

The most complex part is done. Next steps will be detecting proper position of other stops and making grooves there. Dawn asked me to make half-stops, which will be also easy – I’ll just make more thin grooves there. It was not possible with my first Speedmaster click-stop mod because ball diameter there is too large for adding half-stops on the ring.

2019-09-25 – second day

Now I’m focusing lens to infinity and securing focus ring with tape.

Then I’m marking position of aperture indicator – on the focus ring (using pencil).

It’s time to disassemble aperture ring again (unlosd spring, removing pin, then unscrewing long bolt, pulling out aperture ring). After that I’m making special tool for marking aperture stop positions. One side has arrow for aperture value.

I’ve added that arrow after locating tool opposite edge right on the first groove made yesterday.

So the gove is corresponding the F0.95 value.

Now I’m sliding tool over the ring to each value and marking the future groove position using pencil.

Again I’m using metal file to accurately grind the tiny grooves on each marking.

At this time it’s important just to make very thin grooves.

Now I’m assembling aperture ring back, loading the spring and rotating aperture ring. Each new groove should interact with bearing ball and gently stop at them.

I’m checking if every aperture value stops near the mark on the focus ring. If not – I will be able to shift groove position a little when making it wider.

Disassembling the ring again and making grooves larger.

After that I’m marking few extra stops requested: F1.2, F5.6, F6.7, F11, F13. You can see how tight is the space between F8 and F16 – I can only make more narrow grooves due to space constraint.

Now I’m grinding new stops.

And finally I’m using flat side thin file to make grooves deeper to catch the ball better.

After cleaning all the metal dust and greasing surface I’m assembling lens back. Aperture ring now rotates with snappy clicks at each required stop. Final step is to add red dot at F1.2 aperture value.

And lens is now ready to be shipped : ) MOD is completed successfully.


  1. Hi. This looks fun and useful. I’ll have to try!
    Which kind of copper do you use? Plain 1mm plate?
    Thanks, H.

    1. I used 0.2mm copper for both modifications, brass should also work.


Post a Comment