Teardowns and Disassembly

Some Holiday Lens Mutilation

Published July 3, 2014

A couple of weeks ago I got an email asking if we would be willing to take some lenses, remove the electronics, fix the aperture wide-open, and permanently lock them at infinity focus. It seems the person who needed this done was having trouble finding a legitimate repair shop or service center that was willing to do it.

Well, illegitimate is our specialty, so I started negotiations about just how exorbitant a fee we would charge for this work. We quickly arrived at a fair price (no money, but we get to take pictures) and yesterday received brand new copies of the Canon 100mm f/2 and Sigma 35mm f/1.4 Art to work on. If you’re the kind of person who slows down to view car wrecks or spent $200 on fireworks for the 4th of July holiday, you might like this.

(For those of you who aren’t American, the 4th of July is when we celebrate our Independence by getting sunburned, making burnt offerings of animal parts in our backyards, and then eating said offerings. During the entire day, we drink massive quantities of American beer and once it gets dark we shoot off massive quantities of Chinese fireworks. All too often, the results of mixing alcohol and explosives prove that Darwin was correct — but hey, that’s what celebrating is all about, right?)

If torn apart camera lenses make you squeamish, then you won’t like this, and I suggest you not read further. You won’t miss learning anything; it’s just for fun. As best I can determine, this post has absolutely no practical use whatsoever. It’s just something to amuse and entertain those of you who are amused and entertained by such things.

Canon 100mm f/2.0

Being an older lens, we assumed this one would be simple to do. The plan was to remove the aperture assembly and electronics, then solder the focusing key at infinity. You know how plans go, though, so that isn’t exactly how it happened.

We started with removing the bayonet mount and rear barrel.


Then disconnected the flexes and removed the circuit board.

The mount removes as a single subassembly along with the rear focusing group. The focusing collar (red arrow pointing to it) sits in a fork connected to the focusing ring. Turning the ring moves the focusing element up and down in its helicoid. We had planned on soldering the fork in place, but with the lens disassembled, we couldn’t accurately check the infinity focus position so we had to go with our fallback plan.

Examining the front half showed the aperture assembly was going to be a problem to remove. One lens element is within the assembly, and it also has two light baffles that were important.

So instead of taking it out, we just put a drop of solder on the mechanics of the aperture ring, locking it in place wide open.

When we reassembled the front and rear halves we noted a lot of openings in the lens mount plate. Since this lens has something of a reputation for getting internal dust, Aaron decided to seal the openings up with double sided tape.  Mostly, Aaron likes opportunities to fall back on his Fine Art degree. He spent 30 minutes carefully cutting out tape shapes.

For the same dust control reasons, we replaced the electrical connectors. They no longer connect to anything, but do plug up what would otherwise be a large hole at the rear mount.

We decided to set infinity focus using the MTF bench. Since the bench delivers collimated light (appearing to come from infinity) we just manually focused the lens until we had maximum MTF and minimum astigmatism. (As expected, this was not quite at the infinity mark on the distance scale.)

Once we had infinity focus locked on, we glued the focusing barrel to the rear lens barrel.

And, for good measure, glued it to the front barrel, too.

It’s not as slick and elegant as we would have liked, but it sure works.

Sigma 35mm f/1.4 Art

We thought the Sigma, with its more modern and modular construction, would be simpler to do and it was. As usual, we removed the bayonet to expose the PCB.

Then removed the PCB, exposing the aperture motor and controls.

The rear barrel then comes off by removing a few side screws.

Soldering the aperture lever worked well on the other lens, so we repeated it here.

After which we remounted the bayonet, but left the rear barrel off.

That let us mount it to the MTF bench with part of the focusing mechanism still exposed.

Once we had infinity focus locked on, we filled the focusing stays with Loctite silicone.

Once it dried, the focusing mechanism wouldn’t move with a pry bar.

We put the barrel back on before sending it to its new owner, of course.

Roger Cicala and Aaron Closz


July, 2014

Author: Roger Cicala

I’m Roger and I am the founder of Lensrentals.com. Hailed as one of the optic nerds here, I enjoy shooting collimated light through 30X microscope objectives in my spare time. When I do take real pictures I like using something different: a Medium format, or Pentax K1, or a Sony RX1R.

Posted in Teardowns and Disassembly
  • pallermo

    Hello, please can you tell me what type of Loctite u are using? Thanks

  • Oskar Ojala

    On industrial macro lenses there are usually screws for locking the aperture and focus. Would a screw through the outer body of the lens had been possible here? I’m mostly thinking of the scenario that focus drifts due to environmental conditions and a readjsutment is required.

  • Roger Cicala


    Not really overthinking at all – it’s why we only do these things open and leave the lenses open overnight. Even then we had an episode about a year ago when we tried a new type of glue and found that it did indeed outgas and leave a film on the nearest two elements. (Actually that’s the other reason we chose to use silicon rather than glue on the Sigma. We’ve used that enough to know it’s inert.)

  • Fred

    Having seen many used lenses advertised on eBay to have “haze” on some of their elements, I’m concerned about outgassing of haze-depositing substances from the likes of DIY camera bag inserts, neoprene sleeves, plastic storage containers, etc. Boy, does the stuff you nice folks are sticking and glopping inside those lenses make me cringe. Am I over thinking this, Roger?

  • Mad Hungarian

    It’s no good for astrophotography — while we are indeed focused approximately somewhere around infinity, we always have to finetune the focus to compensate for temperature and atmospheric variations.

  • Gábor Ember

    I just used this article as a guide to open up my Sigma 17-35 that I bought used and the aperture didn’t work on it. Found out that the aperture cable had snapped. Either I’m going to replace the flex cable or find out where f8 is and fix the aperture lever in that position. Sadly the cables are soldered on in this older Sigma, there are no clips.

  • Adrian Sun

    “… by getting sunburned, making burnt offerings of animal parts in our backyards, and then eating said offerings. During the entire day, we drink massive quantities of …… beer and once it gets dark we shoot off massive quantities of Chinese fireworks. All too often, the results of mixing alcohol and explosives prove that Darwin was correct — but hey, that’s what celebrating is all about, right?)”

    Thought that was just Australia Day.

  • Roger Cicala

    Sean, it’s for laboratory use in a temperature controlled environment. But even then, they have a few microns of final focus capability.

  • It’s too bad that thermal expansion shifts infinity focus. Hopefully the user never visits a location with a different temperature than your warehouse…

  • Chris Bourne

    Interesting set of photos – thanks Roger.

    Is there any reason they didn’t start with a samyang 35 rather than butchering a much more expensive sigma?

  • Roger Cicala

    obican, since I wasn’t certain what conditions they might be operating under, I wanted to make sure the aperture was fixed wide-open, not just held there by a small spring that might get jarred or magnetized loose.

  • Tim

    For the NSA, for use on a drone?


  • obican

    I have a Canon 28-105 3.5/4.5 lens, probably from the same era as the 100/2 that you’ve worked on. Mine had its aperture stuck at wide open, due to a faulty flex. You could have probably simulated the same by removing the flex that goes to the aperture from the rear assembly.

  • Bill Adkins

    Roger and Aaron, WELL DONE

  • Nqina Dlamini

    While reading, I was thinking “I hope this is reversible”.
    Nice reflections on the open Sigma.

  • glasswalker

    A problem I see with fixed focus for astro use is that focus varies quite a bit temperature. This may not be a problem if used with an external focusing system moving the sensor. Fast apertures like these may also cause problems with filters and astro use.

  • Jeff

    Wow, you ShoulD offer the service with the rokinon 14 mm pain in the a..

  • Bruce in Toronto

    Owner to Canon rep – “Honestly, it just stopped working one day.” 🙂

  • Bruce in Toronto

    Owner to Canon rep – “Honestly, it just stopped working one day.” 🙂

  • Mike G.

    Grrr, “see”, not “seem”….

  • Mike G.

    I seem I’m late in asking “but why???”

    For instance, how would this help astrophotography? By reducing power usage and keeping focus perfect?

  • asad

    Wow. Did the owner give any indication of exactly why he wanted this work done?

  • Mike

    For the love of God, why would someone want to do that?

  • I’d guess this modification was intended for astrophotography?

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