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,ย 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. ย 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. ย 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
  • Irene, there’s probably a bent or backed out screw and collar on the barrel inside the tripod collar. Unfortunately, that requires lens disassembly to repair so is best sent in to Canon.

  • Irene Vejar

    Having done this can you give me any idea why my tripod collar will not rotate? I’ve removed the foot, put a little silicone around the edges and tried to just physically loosen it up a bit. It will not budge!

  • Mike Hamra

    Fantastic teardown and great to learn. But, for gods sake, please stop down your lens, turn up the lights, and get everything in focus.

  • E A H K

    Thank you Aaron! I’d tell you later why the question. Have a good day ๐Ÿ˜‰

  • AaronClosz

    The mount sleeve is a sized ring that the lens mount fits into (the rubber weather seal would be in between these two parts). The final three digits in this particular part number give you the thickness of the sleeve. Sleeves at the mount are used in place of shims to achieve accurate flange distance.

  • E A H K

    Interesting article! Thank you for taking the time to write and picture it. One question here, what would be this part number? CY3-2359-000-260 Sleeve Mount, can you please point it in one of your pictures?

  • abo

    Could you do a test comparison with Nikon AF-s 80-400?

  • Roger Cicala

    Chris, it’s just pink lactate.

  • chrisnosleep

    Can you tell us what the pink adhesive is that is on most of the screws? It seems it has a rubber cement elasticity to it. Is it some kind of Loctite? Thank you.

  • Roger Cicala


    It’s a bit more difficult than that. The front element has to be taken out by removing the front ring, then taking out the side mount collars. If you’re handy and used to working with lenses it’s not awfully difficult, but it’s not one I would consider an easy dusting.

    That being said, I haven’t really experienced dust affecting AF accuracy.

  • chrisnosleep

    I too have the question about the front element. Is it possible to take out the front element by removing the front lens retaining ring with a spanner wrench. If not, what is the easiest/safest way to get into the front chamber for dust issues? I have read your other articles (which were excellent) about how much dust/particles it takes to affect the image. However I’m not having issues with the IQ, my issues are with focusing.

    I completely understand the risks involved here, but paying Canon $200-300 twice a month for cleaning isn’t something that’s feasible for me. And there are no camera shops anywhere even remotely close to my location.

    Thank you!

  • Roger Cicala

    It seems to be a pretty common problem with the front element dust, but it’s not nearly as easy to get out as the older version. I wouldn’t tackle it unless you’re really comfortable with disassembling lenses.

  • Balb0wa


    ive had my 100-400mk2 a month now, i have a lot of dust under the front element.

    How easy is it to get to it? can you take it apart from the front?


  • I, like Photonius, have concern of relying 0n four tiny screws to support the lens, & whatever is attached to it.

    I was contemplating rotating the foot up, and toting it with a “Sling”-Strap; but in view of the above, I’m having second thoughts.

  • Photonius

    As follow-up to Laurence. I’d also be interested in the foot. A strip-down of the foot (at a post in dpreview) did show these tiny four M2 screws. It would indeed be interesting to know how much these screws would hold when the lens is carried on tripod, or is attached at the tripod mount to a shoulder strap and swinging around.

  • Chris


    As this lens uses a shim as the mount spacer, does this mean that the lens uses one set size & thickness mount/bayonet? The previous model had something like 10 different thickness mounts in 0.1mm increments.

  • Christer Almqvist

    Sorry, I posted that in the wrong forum, should have been in the 200 mm comparison.

  • Laurence


    A great insight into the construction and quality of the product ๐Ÿ™‚

    I have the MkI version and must admit I was puzzled by the new tripod mounting point assembly? I currently use a Black Rapid strap as you likely know this holds the lens (and Canon body) inverted I also mount the combo onto a Wimberley Sidemount Gimbal so the strain is either a “pull” in the case of the BR strap or lateral with the Gimbal. So with the MkI as it is a single casting the load is spread across the whole ring with no obvious weak points.

    However, the MkII as shown in the teardown has the tripod screw going into a plate that is held with four much smaller screws………….so my concern is just how strong is this multi layered (so to speak) connection when used in the situations I mount such a lens?

    Clearly in when mounted in an upright position all the parts are in compression and little actual load is on the various screws and connections but just how good is the strength and durability or lifespan of the weakest ‘link’ in the chain?

    I ask because I am looking to upgrade my MkI to this newest MkII but as there is no published data (as far as I can find out) I suppose I am looking for the reassurance that the mechanical failure of this mounting is as unlikely as winning the Lotto in my lifetime ๐Ÿ˜†

    TIA for the insight & feedback ๐Ÿ™‚

  • Ruprecht

    How does this lens compare to the older but slightly more versatile zoom range Sony 70-400 G2? Are there a couple valid pros and cons about each you could name quickly and concisely?

  • Roland

    Thanks so much for the teardown Roger!
    Can you let us know what the inner barrel (i.e. the one that extends when you zoom to 400mm) is made of?
    Plastic or metal?

  • Daniel

    Great teardown. Business suggestion: LR for Lens Rentals, and LR II for Lens Repair. Your company has total credibility, and sending a lens in to be adjusted for service and optical centering would definitely be something your company would find willing clients. D.

  • Its superb as your other articles : D, appreciate it for posting .

  • mrc4nl

    @Roger Cicala, now i understand the conditions a little better, and the lack of time to do them properly. i was just giving ideas to do them better

    I guess nobody does the teardown in their free time, otherwise somebody could do blogposts about the less popular lenses (with sharp pictures) ๐Ÿ˜‰

  • bdbender4


    I think you are missing the point: more teardowns with adequate photos vs. fewer teardowns with studio-standard photos, given the amount of time Roger has. I vote for more teardowns, every time!

    Every time Roger does a lens test, some people pile on asking “why didn’t you do this or that” or “could you please test these other lenses”. These folks are missing the point, too, in a different context. Roger has politely explained about his time limitations quite a few times.

  • Roger Cicala

    mrc4ni some of it is contortions – trying to work around Aaron’s body to get the shot can be difficult. A lot of it is exposing to get black on black parts to show up. Most of it is priorities: we’re doing this to learn the lens for future work, and usually with lenses that are ‘hot’ and in great demand so time is of the essence. Taking shots during the teardown is fine and I write them up after work. It’s not the priority.

  • Well done! I recently stumbled on your site and I am already a big fan of your lens teardowns, including your first-class humor. ๐Ÿ™‚
    As a Canon user I am very pleased to see the splendid engineering they’ve put into a number of lenses. I recently bought this lens and my first impressions of holding it was: Massive but silent when shaken. Reading your thoughts about the construction is like pouring hot cloud-berry jam on top of vanilla ice cream. I love this lens, it’s simply amazing to work with.

  • mrc4nl

    i just find it odd there are also some great shots with excellent sharpness and (micro)contrast.

    If they were taken in the same lighting conditions, why is the “ringoff” picture so blurry and the “backoff” picture as sharp as it can be? they look similar in light.

    i dont expect fantastic product shots under diffuse light ,but ample light to make the pictures not so blurry would be nice. (maybe provide extra lights on the repair department ceiling? )

  • @mrc4nl, bad form.

  • Thank you for taking the time to post your findings on this new lens. As a photographer who knows how to use a lens, but not how to repair one, I found it very interesting to see one taken apart. As for the person who commented on blurry pictures I have to say. Come on? I feel like they missed the point of this post, plus I disagree. The photos are fine. Job well done, thanks again!

  • Roger Cicala

    mrc4ni, I invite you to take apart a lens under halogen spotlights, doing it as quickly as you can because it needs to be back in stock as soon as possible, and take great product shots over the shoulder of the person doing the disassembly. It can be damn hard. We have a superb product photo section with plenty of diffuse, reflected light, tripods, acrylic stands, etc. The repair area ain’t it.


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