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

Mitakon 35mm F0.95 Speedmaster version II lens has clickless aperture ring with same texture as its focus ring. I’m shooting with this lens since review on March 2016 and it’s one of my favorite glass on Fuji X cameras. But I often mistakenly turn aperture ring instead of focus while looking through camera viewfinder.

Manual lens with aperture-clicks are more convenient for shooting. You can blindly change aperture value by counting clicks, and that value remains selected.

In this article I’m showing how to modify Speedmaster 35mm F0.95 II to the click-stop aperture mode.

I’ve already posted Mitakon 35mm F0.95 Mark II disassembly guide for the front area, so will focus on the main modification required.

There is one very common way of implementing aperture clicks used by numerous lens brands including Fujinon lens. Small ball is loaded by spring and is catching aperture ring holes at click positions. I’ve implemented similar clicks for my 7artisans 35mm F1.2 lens. Mitakon has larger diameter so it requires stronger spring, it was quite challenging to find proper location for the spring. My first attempt failed, so I decided to use another design.

Mitakon’s aperture chamber has plenty of space, so I decided to use radial spring instead of classic way. For this mod I’ve involved:

  • 2.8mm metal ball
  • 3mm pin cut from 2.4mm brass pipe
  • 6x100mm plate of 0.2mm copper ribbon
  • 2.8mm and 2mm drill bits
  • masking tape
  • caliper, scissors for metal, mechanical pencil, masking tape, screwdrivers, tweezers

First step is to drill a hole in the aperture chamber wall right at the level of aperture ring center of thicker wall area. Metal ball has 2.8mm diameter so I’ve used 2.8mm drill bit. That part can be separated first, but I’ve simplified process by covering all lens with masking tape to isolate drilling area, including the inner aperture chamber. After drilling I’ve simply removed the tape.

Aperture chamber already has long slot on the side for aperture transmission. So I’ve measured inner circle length and subtracted distance of that slot. Then I’ve cut 6x100mm strip and bended it into the shape shown below. I’ve also cut 3mm pin from 2.4mm wide brass pipe.

Little grease is required for the copper strip, then I’ve inserted it into aperture chamber. After that brass pin and metal ball can be located in drilled hole. Aperture ring goes back to its place together with aperture transmission screw at this stage. I need that to precisely measure aperture click position.

Then I added masking tape on the aperture ring side and marked position of the ball center for each selected aperture value (except F16 which I’m never using).

Next step is to take out aperture ring, and mark positions of aperture stop holes. It’s very important step and measurements should be very precise. I’ve screwed up initially by starting drilling holes right after marking them. It’s more safe to make tiny hole at each mark first and try aperture ring rotation to make sure ball is catching proper location. It allows you to shift hole position up to 2mm for better precision (and I followed this approach during second attempt). I’ve used 2mm drill bit to make aperture stops holes.

Following two shots displaying copper spring movement range while changing aperture stops. There is plenty of space around the front lens case, so spring is moving free transmitting enough power to the ring.

Finally I’ve slightly reduced outer hole diameter by adding small dent on the edge, which keeps the ball inside while it’s loaded with spring.

As a result this Mitakon 35mm F0.95mm II sample holds aperture position firm and producing audible clicks while rotating. It’s a joy to shoot and quickly change aperture to desired value without looking at the ring.

UPDATE: I’ve found good source of smaller bearing balls, and here’s one more article on click-stop aperture mod for Mitakon Speedmaster 35mm F0.95 II