Teardowns and Disassembly

Canon 100-400mm IS L Mk II Teardown: Best Built Lens Ever?

Published February 12, 2015
Canon 100-400mm IS Mk II, Lensrentals.com, 2015


You know Aaron and I love doing teardowns of almost anything. The two types we look forward to most, though, are Sony cameras and Canon lenses, because those tend to be on the cutting edge of engineering elegance. For a couple of weeks now, we’ve been wanting to sink our screwdrivers into the new Canon 100-400mm IS Mk II lens, and yesterday we finally got a few free hours to do it.

For those two or three of you who don’t like a little lens strip-tease I’ll give you the quick summary: the build quality on this thing is amazing. I usually laugh when people describe a lens as “built like a tank” because what I know is the lens they are describing has a thick, heavy outer metal shell filled with tiny delicate pieces that break and wear out with great frequency. But this lens is built like a tank inside and out.

The New Tripod Mount

Yeah, I know, taking off the tripod mount isn’t part of the teardown. But this mount is entirely new and different, plus it kind of gives notice of the build quality to come. The actual foot removes, of course, via the little thumbwheel.


All images credit Roger Cicala, Lensrentals.com, 2015


It’s just a foot, but note that there are two large and four small locking posts to keep it from slipping. It also can’t be mounted in reverse fashion, but I’m sure not too many people will want to do that anyway. It’s also nice that where the foot mounts to the ring is a replaceable locking plate, meaning that if you are strong enough to strip out the female threads, just the plate can be replaced, not the entire ring. That’s the difference between a $10 part and a $150 (my guess on costs, but probably accurate) part replacement.


All images credit Roger Cicala, Lensrentals.com, 2015


With the plate removed you can loosen the ring and slide it around to reveal the large screws that mount the ring to the barrel. I’ll note here that you can’t remove the ring without partial disassembly of the barrel, so no need to try taking them out at home. Again, I’ll point out those are big screws with washers around them, double the size of the screws we usually see assigned to this kind of task.


All images credit Roger Cicala, Lensrentals.com, 2015


Taking the Back Off

The lens mount comes off in the usual fashion so I won’t take up bandwidth with pictures of that. Once it’s off, though, we saw one thing we’d never seen before. The shim (red arrow) that is used to space the mount properly for infinity focus has screws (green arrows) holding it in place. I have no idea why, the mount screws pass through the shim and would hold it just fine, but there must be some purpose.


All images credit Roger Cicala, Lensrentals.com, 2015


With the shim removed, a normal Canon main circuit board is revealed.


All images credit Roger Cicala, Lensrentals.com, 2015


Underside of the PCB. All images credit Roger Cicala, Lensrentals.com, 2015


Removing the board gives access to the eight large screws (four to six is what we would have expected) holding the rear barrel in place.


All images credit Roger Cicala, Lensrentals.com, 2015


Removing these lets the rear barrel slide right off.


All images credit Roger Cicala, Lensrentals.com, 2015


The design here, like most Canon designs, is nice and modular.  The rear barrel assembly includes the tripod ring (which could now be removed if we wished) and all of the switches, meaning the flexes and connections are all contained in this replaceable assembly.


All images credit Roger Cicala, Lensrentals.com, 2015


Taking the rear barrel off lets us see one of the first examples of the robustness engineered into the new 100-400 Mk II. The rollers (red arrow) that the focusing assembly rotates on are huge metal bearings, about twice the size of what we see in most telephoto zooms. These are more the size we’d expect in big super telephoto prime.


All images credit Roger Cicala, Lensrentals.com, 2015


Back to disassembling now. Removing the focus rubber gives access to small openings that let us remove the collars under the focusing ring.


All images credit Roger Cicala, Lensrentals.com, 2015


All images credit Roger Cicala, Lensrentals.com, 2015


With those out of the way the USM motor assembly lifts right off in one modular piece.


All images credit Roger Cicala, Lensrentals.com, 2015


After which the focus ring can be taken off.


All images credit Roger Cicala, Lensrentals.com, 2015


With all of the back assemblies off, the bulk of the lens looks like this. You can start to notice how large the various collars and rollers are. And everything we’ve removed up until now has been an electrical or mechanical assembly. All of the glass and optics are still intact.


All images credit Roger Cicala, Lensrentals.com, 2015


Smooth-Tighten Ring

Normally I wouldn’t spend so much time on this assembly, but in the original 100-400 IS L, the smooth-tighten ring was a part destined to fail eventually, using about 1,000 tiny ball bearings to move friction pads around. The new lens has a very different and much more durable (at least in appearance) mechanism, which is entirely different.

Looking up into the smooth-tighten ring from below you can see the spring clips that hold it in place at the stop.


All images credit Roger Cicala, Lensrentals.com, 2015


Removing a plastic stop lets us rotate the assembly and remove it from the lens.


All images credit Roger Cicala, Lensrentals.com, 2015


Back on the lens barrel, you can see how thick and firmly attached the spring clips are – and those are just so you feel when the ring moves into certain positions, they don’t have a tightening function.


All images credit Roger Cicala, Lensrentals.com, 2015


The smooth-tighten ring itself separates into two parts.


All images credit Roger Cicala, Lensrentals.com, 2015


Which lets us see how friction is generated by two thick ramps (one on each piece) – sliding the ring increases tension. No ball bearings to fail. I guess the metal ramps could wear over time, but that shouldn’t have a great effect; you just slide them a bit further.

The Optical Assembly

This is where things get fun. Before we do anything else, let’s just take a look at the back of the lens, where the various barrels, helicoids, and helicoid collars are largely visible.  First, look at the helicoid collars for the focusing and zoom groups (I believe) identified by the red arrows. Those are huge and robust things; I’ll show you a comparison in a second. Additionally, look at the lower helicoids – there are six channels, of which two are visible (one marked with the lower red arrow). Most lenses have three channels and collars. That’s a huge amount of increased stability when the barrel extends away from the lens.


All images credit Roger Cicala, Lensrentals.com, 2015


Next look at the eccentric optical adjustment screws identified by the green arrows. Those are much larger than usual, which allows for much finer adjustments. They’re also separated into tilting and centering screws at each of three locations around the lens. This should allow not only more accurate adjustments, but adjustments that are less likely to slip over time. I’m extremely impressed.

Below is a size comparison from one of the smaller 100-400 Mk II collars and the largest collar in the original Canon 24-70 f/2.8 lens, which until now I would have called a fairly large collar. Notice the 100-400 collar (the white one) is not only larger and thicker, it’s made of a very tough nylon and has a brass center, compared to the simple composite of the 24-70 collar.


All images credit Roger Cicala, Lensrentals.com, 2015


OK, back to our regularly scheduled disassembly. Removing the front makeup rings and a stop key lets us slide the last outer barrel (zoom ring) off of the lens.


All images credit Roger Cicala, Lensrentals.com, 2015


Which now looks like this with the barrel fully extended.


All images credit Roger Cicala, Lensrentals.com, 2015


We have to remove the zoom locator brush, and then a series of screws and sliders (the black screw below the brush Aaron is removing in this picture is one of them) to remove the front barrel.


All images credit Roger Cicala, Lensrentals.com, 2015


Here is a close-up of the thick brass sliders that are under the screws. They keep the barrel straight when it zooms, which is critical for keeping the optics in line. Most zoom lenses just have plastic guides, not brass, and not nearly this robust.


All images credit Roger Cicala, Lensrentals.com, 2015


That’s got everything disassembled down to the individual lens elements. The front element is still in the extending barrel in Aaron’s right hand. The front element in this lens is not adjustable other than a distance slider, the optical adjustments are in the other elements.


All images credit Roger Cicala, Lensrentals.com, 2015


All of the other elements and all of the adjustable collars are in the main optical assembly in Aaron’s left hand.


All images credit Roger Cicala, Lensrentals.com, 2015


You can’t see all of them in one view, but there are a number of different optical adjustment locations. It will take us a while to figure out which control what types of issues. The IS unit, by the way, is the top group in the optical assembly, the second group overall from the front.


All images credit Roger Cicala, Lensrentals.com, 2015


I know I can’t really, without showing you dozens of other lenses, do a good job of impressing you with just how robustly engineered this lens is. I will say that the insides look more like what we’d expect to see in a 500mm f/4 or 600mm f/4 lens, rather than a telezoom. It’s by far the most heavily engineered zoom lens Aaron and I have ever seen; and we’ve seen the insides of dozens of lenses in this range.

Well done, Canon engineers, well done!


Roger Cicala and Aaron Closz


February, 2015

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
  • mrc4nl

    this being a blog about the technical side of photography:Why are there so many pictures blurry, or plain shaken (taken at a too slow shutter speed)

    how hard can it be?

  • KeithB

    As someone who has worked closely to a wafer fab, there are *plenty* of chemicals involved in electronics.

  • Impressive ! to see what comes around to make such a lens… ( and that you all @LR can make it work again!)
    This is what i have always liked about photography ; that so many skills come together.
    (The chemical part however has been lost…but the electronics part has come to take its place)

  • Eric Tung

    Also interesting in teardown of canon 70-300L. I know Roger is not a fan of this lens. But before 100-400L II came out, this lens was a lot people’s choice since the old 100-400L has not weather sealing and only 2 stops for its image stabilization.

  • Henrik Sandstrom

    Always interesting to see the inside. How about the 70-300L? Have you done a teardown of that too and if does the inside look sturdy enough? I was stupid enough to buy one that has a dent (hard to see but big enough to prohibit filters) close to the front lens from being dropped on the floor. The pictures seemes sharp but i have not looked really close.

  • Roger Cicala

    Jeet, it has all of the usual rubber seals and taped over holes. So it’s like most L Canon lenses.

  • Jeet

    Hi Roger,

    What is your take on the weather-sealing of the lens? Dust/moisture resistance etc.?

  • SteveNobody

    Fabio: Yes…the tripod foot itself is a tad flexy. If you *really* tighten the foot down it will minimize it, but it ain’t the collar on the 70-200 f/2.8.

    I also don’t care for the window in the hood. You can’t turn the filter that much at a time and it gets knocked open by accident a lot. I may try to find a way to hold mine shut forever.

    But other than that the lens is AMAZING…easily one of my favorites now.

  • Frank S.

    Excellent work, both on you and Canon.

    I can’t wait to see what your I impressions are when you finally get your hands on Pentax’s new DFA* 70-200 and the DFA 150-450.

  • DOC

    Roger, How ’bout stirrin’ the pot a little. Please think about stripping down a new Nikon 80-400 and compare it to the Canon. This new Canon lens which has a magnesium barrel is a few hundred less than Nikon’s new 80-400, which is all engineering plastic. Can the cost be that dramatic between alloy and plastic? Yes, we all know construction materials do not affect the optical quality, it’s just that all the new Nikon glass keeps getting more cheaply made with every new release. I wonder if their execs would like plastic wood dashboard panels and body panels on their Lexus cars!(Just guessing) For my hard-earned money, I really do expect more from Nikon. Their legacy is lenses, and they should be ashamed of themselves. BTW, how about as Zeiss Otus 85mm teardown? Thanks, Doc

  • The only bad thing i have read about this lens is the softness of the tripod collar.

  • Doctor Ed

    Jean-Paul, the lens also zooms by push-pull if you wish to operate it that way. You just grasp the base of the lens hood and push or pull. (You really need to have the lens hood on for this.) To me push-pull is awkward with this lens because you have to reach a bit, so I twist to zoom.

  • Awesome Roger.
    Loving this lens, it is more than everything we hoped for in a replacement for the old standard.

    I am eying your tear down intensely and looking to see what sort of machining it would require to convert to “One touch” zoom.

    thanks for your insightful post!

  • NancyP

    Thank you. Most of us have no idea how complex the designs can get.

  • Roger Cicala

    Obican, yes, we looked at that as we reassembled.

  • Jean-Paul Landry: Set the slip ring to the loosest setting, grab a hold of the hood, and push-pull all you want.

    I’ve seen several former Version 1 owners doing this and being OK with it given the vast IQ improvements they gained by giving up the old one.

    For me, I prefer the ring-zoom since I never liked or owned Version 1….. This one, however, is a keeper…. Sharpest lens I’ve seen in this range. I’m even thinking about selling my 400 5.6L which I’ve had for 20 years.

  • Bradford Griswold

    Roger – I’m curious to hear your thoughts on the Mark II vs the Mark I. Is it that big an improvement where a real photo nerd should consider upgrading? Heading off to Africa in October to do some game spotting – I remember the last time I was there I almost never took off the 100-400…makes me wonder about upgrading…

  • Tim

    It’s always great to see your lens teardowns. Thanks!

  • obican

    Question: Can you partially assemble the lens so that it is still possible to reach all the adjustment locations while having the lens mounted to a camera?

  • Renaud

    Thank you for this teardown. Some say that the 4-5.6/70-300 LIS is also build like a tank. You probably have repaired some of them, is it your opinion too?

  • Roger Cicala

    Mark, they go right back into stock after they get reassembled and retested. Remember we have to disassemble lenses to repair them all day every day, it’s what we do. We have 4 full-time repair technicians and during a typical work day we’ll disassemble a couple of dozen lenses and cameras to repair or optically adjust them.

  • Eugene Mitchell (aka “Houndog”)

    Fantastic. I recently bought one. It has superbly done everything I have asked it to do. Quick focusing on my 70D. A bit heavy, but I quickly got used to that. Got good BIF shots of wild ducks on my first outing. Can’t wait for warmer weather in the mid-Atlantic States (more birds).

  • Ray

    I’m really curious. Have you ever disassembled one of the 4/3 SHG lenses like the 90-250mm f2.8? I’ve had one for years now from new and it’s not had an easy life, yet seems as good as the day I bought it.

  • Matt

    Matteo, I believe that is the “environmentally friendly use period” (EFUP), 10 years.
    Roger, thanks to you and Aaron for all the great info. Your articles are a pleasure to read.

  • Mark Olwick

    Great info. I’m curious, what happens to these teardown units? Do they get thrown back into the rotation or are the sacrificed for parts? Or sold on Lens Authority?

  • Jean-Paul Landry

    Too bad you can’t convert it to push-pull.

  • Gosh, great job to all designers 😉
    And of course to Roger for bringing it to us !

  • Matteo

    Hi Roger, will you or some users please explain to me exactly what the circle symbol with the “10” inside visible in the third photo from the upper part of the topic means? Thank you a lot

  • The lens handles nicely too. Though you are right about it being built like a tank. Handholding it for a day of Eagle watching and musical event photography adds up to some serious soreness the next day. Maybe in a year or two you will have a few up on your(lens authority) black Friday sale, and I will have saved up the money for it. Looks like it will still be in good shape, being engineered so well. Thanks for the tear down!

  • That zoom locator resolves 49 different focal lengths, right? Tapering looks nicely non-linear, just like the changes in focal length probably are. Gray code is mandatory 🙂

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