Mitake 135mm F1.8 Lens Repair – Disassembly Guide

September 30, 2014 by CPBurrows

A while back I was at the Bargain Camera Show in Pasadena, and I saw a bit of an odd lens somebody  had. With its huge front element and ability to diminish even larger full-frame bodies, it was quite a striking piece of glass. I don’t remember the make of that particular one, but I do remember it being a 135mm F1.8
I don’t do a lot of portraiture, but the oddity/uniqueness of the 135mm F1.8 drew me and I eventually purchased one. I was delighted when it arrived, appearing to be in great condition and in a generic, but original box. Unfortunately, it turned out to have a tremendous amount of oil seizing the aperture closed.
I scoured the internet for quite some time, hoping to find some information about disassembling/repairing the lens, but while I came across numerous mentions of hazy elements, nothing actually described its disassembly, or even referenced having an oily aperture.
One of the only things I did find was a Flickr thread which discussed the existence of 135mm F1.8 lenses. My interest was specifically in my lens, badged “Apollo Low Light TV Lens,” which appeared in the following list taken from the thread.

Spiratone Plura-Coat, Porst, Computar, Promura CP Hi-Lux, Kenlock, Formula 5, Eyemik, Apollo, Accura, Varo, Vivitar and Weltblick.

Striking out on finding an existing repair guide for any of the listed lenses, I ended up doing the repair by trial and error, and documented the process. They’re such interesting lenses that it would be a shame to let any be thrown away or destroyed as a result of defects that could be repaired.

Repair Guide

As far as lens repairs go, this one is very straightforward, but still requires patience and a little mechanical skill. Luckily, it requires very little in the way of tools.

  • Small Phillips screwdriver (I used a Husky 8-in-1)
  • Small flathead screwdriver (~1mm)
  • Gloves
  • Aperture-appropriate solvent such as Ronsonol, if you need to clean the aperture


Lens before disassembly

Lens viewed from the front, prior to beginning the disassembly process.

Lens after removing the rear mount and collar.

Just in front of the rear mount, containing the aperture control assembly, there are 3 flathead setscrews. Loosen them slightly, and hold the lens with the mount facing upward. The collar will slide down, revealing 3 Phillips screws which hold the mount and aperture control assembly down. Remove the screws and the rear assembly can be pulled straight off. These are the first 3 of a total of seven screws which must be removed, so don’t worry about mixing them up.


The next step is to remove the tapering trim ring, which is held in place with 3 setscrews. As before, just loosen them to the point where the ring can be pulled off. The photo shows just one of the three screws. Before removing it, it is convenient to use the guide printed on it to set the focus distance away from infinity. It will aid in the next step.

Gold limiting stops

After the previous step, you will see two gold-toned bits, each held on with two screws. These are the stops for the lens’ focusing assembly, and have tangs that slot into the helicoid assembly. Once the Philips head screws have been removed, the tangs can be removed. It is easier to remove them if the lens has been focused away from infinity as recommended in the previous step. Otherwise they bind, but may still be removed.

Prior to gut removal

This photo shows the lens just prior to removing its innards. With the stops removed, you can simply unscrew the inside parts from the outer shell/grip. Try to pay attention or mark the position of each of the 3 relative moving components relative to each other for reassembly. The grip and inside are directly related, but the ring to which the rear mount is attached can move independently of the other two, now that the tangs are removed.

Guts and gloryGuts and glory

The first of these two photos shows the entire inside assembly of the lens. The second shows the substantial front element assembly removed. It simply unscrews from the rest of the assembly. This is the part for which the gloves are required as the edges of the metal will cut you as you twist. [My hand is still healing at the time I write this].
The rearmost glass will also need to be removed but is a more simple task. If you cannot remove it with your hand, or while using a piece of rubber, then you should be able to use a metal ruler in the two grooves in the retaining ring for the glass.

Completely disassembled

This shows all of the main elements of the lens after being separated. This is as far as I went toward taking the lens completely apart, as I only needed to access the aperture assembly (contained in the piece with the male helicoid portion).

Cleaning the Aperture

To clean the aperture, I used Ronsonol lighter fluid. It is an effective solvent and evaporates quickly and without residue. It does have a strong smell and is of course highly flammable, so you would be wise to work in a well ventilated area, free of spark or flame.
Using the lever, I closed the aperture down. After dribbling a few drops of Ronsonol onto the leaves, I shuttered the aperture open and closed to help dissolve the oils. Using a Q-tip, I gently wiped the blades. It may help to keep a finger gently pressed against the opposite side so as to not damage the leaves. Furthermore, be careful to wipe in the overlapping direction of the blades. If you go the opposite way, you risk not only bending them, but getting fibers trapped into the assembly.
As you repeat the process, you should see the ends of each new Q-tip you use becoming less soiled. It will start off blackening the cotton, but as it improves will be only slightly gray. Eventually, the assembly will become free, and the spring will retract the blades as it should. Even after it seems done, I recommend a last cleaning, and then allowing the blades to retract and sit at least overnight. There is still a little oil inside which will take some time to migrate to the leaves.
After a final cleaning with Ronsonol, you can make the blades look really clean by dipping a clean Q-tip in acetone (nail polish remover) and gently wiping the blades. Be careful with that, because it removes paint and melts plastic. It is the most effective way I have discovered for establishing cosmetically clean blades.
While this entire cleaning process will restore your the aperture to operational condition, it is not the most effective at removing all the oil, and it may soil the blades in time. Furthermore, if you do not clean up excess oil throughout the lens, you run the risk of re-contaminating the iris.

Reassembly Notes

The reassembly is essentially the opposite of reverse. The hardest part will be reintegrating the helicoid assembly. Initial recombination of the two pieces will likely feel like it is not meshing, but it does require a surprising amount of force. There are also multiple positions they can mesh, which is why marking it earlier should help you put it back together. However, there is a limited number of positions, so if you made a mistake, you can solve it with trial and error.
Without markings, there are still some tips that can help with reassembly. The ring to which the mount attaches should be turned to the ‘infinity’ stopping point. The infinity position is when the lens assembly is closest to the camera’s sensor or film, so you can use that to determine which direction to turn it. The outer helicoid block has two slots for the tangs, and the inner piece has 3 slots. The two that are opposite need to be roughly aligned with the two in the outer block while it is being reassembled.
From there, there are only 3 positions which might be the correct angle for insertion; with the assemblies aligned straight, or with one helicoid groove offset to either side. From there, you can quickly reattach the mount (while skipping the intervening steps), and mount it on your camera to check infinity focus.

I hope some people will find use in this guide and be able to improve or repair their old 135mm F1.8 lenses.
If you have any questions about the lens or about the process, you’re more than welcome to use the site’s contact box to reach me with your inquiries or corrections.
Thanks for stopping by!


  1. Mark says:

    Thank you for a very good article. I have a Weltblick 135/1.8 with some dust inside. Not sure if I want to open it up or not but your page shows me what I would be getting into.

    • CPBurrows says:

      Most of the time internal dust, unless it’s extreme, won’t have any noticeable effect on the quality of images taken with it. As long as the dust is not too bad, and it’s mechanically working well, I would probably leave it be.
      I am glad you appreciated the guide and hope you enjoy the lens!

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