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Canon 40mm Pancake – How Did They Do That??

Published June 21, 2012

We got our first batch of the Canon 40mm f/2.8 pancake lenses in today and, as with all new lenses, I had to run them through Imatest to establish our acceptable standards for the lens. Let me start by saying I had low expectations. I don’t particularly like pancake lenses except on tiny cameras. They’re usually compromises between size and image quality and I’m an image quality guy, mostly. And, come on, it’s a $200 lens. But duty calls, so test them I must.

My first impression was the build quality was better than I expected. It has a metal mount, not plastic. The aperture blades appear more curved than most of the Canon 7 blade aperture rings, making a more circular opening. The little STM motor is not silent, but it’s pretty quiet. It’s also not lightning fast (as expected) but autofocus is certainly quicker than a Canon 85mm f/1.2 lens. And it’s amazingly tiny — the rear lens cap is about half as big as the lens. So far, so good, if the image quality doesn’t suck too bad.

Imatest Results

As always, these are Imatest MTF 50 results, so they reflect the performance at about 12 feet distance in our lab. Infinity and close-up results could be different to some degree. But the little 40mm has amazingly good numbers. To give some perspective, I’ve put it in a table with results for some other f/2.8 lenses. The higher number is MTF 50 at the center point, the lower number is average across the entire lens front measured at 20 points.

 Lens  Center  20 pt
Canon 40mm f/2.8 870 775
Canon 24-70 740 610
Canon 16-35 770 635
Canon 45 TS-E 785 660


You can see the average number is really excellent, which is especially surprising since pancakes often have poor corners. This is sooo not the case here that I’ll show you a graphed printout of a typical copy. Notice it retains excellent sharpness right out to the absolute corners on a 5D II.


One thing I have to note: the results were VERY consistent. We only had a dozen copies to test but there was  little lens-to-lens variation. As a rule pancake lenses don’t have lots of optical calibration adjustments inside, so they may depend on the manufacturing tolerances of the housing more than most lenses. Take this with a bit of a grain of salt, though, all the copies we tested were close in serial number, so there could be more variation when we get another dozen copies.

The 40mm f/2.8 lens is near peak sharpness wide open. The graph below shows 8 copies I tested at both f/2.8 and f/5.6. There’s only a slight increase in sharpness (I’m not certain that difference would be visible in a photograph, it’s within 5 SQF points.) That’s wonderful, but I want to point out that a lot of lenses that do improve stopped down (like the 3 in the table above) would ending up being sharper than the 40mm at f/4 or f/5.6.

The only other comment I have about the little lens is that manually focusing, while possible, is rather difficult: the focusing ring is really thin and I found a fingernail moves it better than my whole fingertip. Mostly, though, it has a small range so a tiny movement can move the focus a lot. But then, one of the main purposes of this lens was to provide smooth video autofocusing.

Overall, though, I’m extremely impressed. I’d be impressed if a lens this size and price was just decent, but this one is excellent. I might as well go ahead and get in trouble with the business manager: if you think you want this lens, just go ahead and buy it. At this price, unless some of the more thorough reviewers find something I missed on this quick overview, you can’t go wrong.

Roger Cicala

June 2012

Author: Roger Cicala

I’m Roger and I am the founder of 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.

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  • l_d_allan

    My interest in the 40mm pancake isn’t just academic / curiousity.

    I am still pondering trying to use MtfMapper to get actual lp/ph numbers that had some probability of being reasonably valid / accurate / repeatable. I’m having correspondence with the developer … Frans van den Bergh.

    If there was some level of interest in something like a “MtfMapper User Group”, I’m wondering if something could be worked out with LensRentals / LensAuthority to purchase the super highly consistent 40mm pancake that had actual OLAF numbers for that specific lens.

    That might a a “known baseline” to refine “best practice” on using MtfMapper. The idea might be to check how well user of MtfMapper was making progress on getting the “over the top attention to detail” in order to get values that were in reasonably close correspondence to OLAF numbers.

    But I’d think it would take some conversion factors to go from OLAF numbers to MtfMapper numbers that involve a sensor … non trivial?

  • l_d_allan

    I looked around for a “Just the Lens” type article that had OLAF’ish numbers for the 40mm pancake … including variance/consistency back when you were reporting that single “figure of merit” number for variance.

    Did I miss a link to the variance number (with MTF charts)?

    I did find the variance number for the Canon EF 50mm f/1.8 STM, which was in the “stellar category” with variance of 9.3:

    IIRC, the variance number for the 40mm pancake was over 10, but I can’t find the actual link to an article with the specifics. Careless / lazy on my part?

    I remain hopeful that LR works out how to more validly report on the concept of consistency / variance of specific lens models. Any progress on that? (and if that comes about, please consider having a lower number of variance be better than a higher number).

  • jpsi

    They probably have done it in the same way Pentax made their 40mm F2.8 XS for less than $200 :P.

  • Jeremy

    The focus issue can be resolved by ensuring the lens is fully retracted before turning off the camera. You can do this by focusing to infinity and manually rotating the focus ring, if needed, until it is fully retracted. I read about this before purchasing the lens and have only had it not focus for me once or twice after forgetting to fully retract before turning off.

    Hope that helps. Love the lens! Good intro to a prime. Not a walk around for me, I missed some good shots in Jamaica because I couldn’t walk back enough to fit everything I wanted in the shot.

    I partially got it in the hopes that I would get better pics at night but the way I was shooting, I would have preferred to have the IS on my kit 18-55. When I got back from my trip, I bought a flash for those low light situations.

    The compact size is great! I did not worry as much about smacking my camera into things while walking around with it hanging on a rapid strap. It also didn’t get in the way much when walking around with my fiancé.

    Being a beginner photographer, I don’t know as much as some others on here and don’t have as good of an eye for quality I guess. When comparing shots taken with the 40mm and the 18-55 is kit at 40mm, I did not notice much difference. Yes, the 2.8 gives better focus control and bokeh but in terms of overall image quality, my eye couldn’t see much of a difference.

    I am definitely going to keep playing with this lens. It will be used for certain situations and is easy to carry in my bag in case I want to use it but if I have to leave the house with one lens, I will choose the 18-55 over the 40mm. At least until I save up for a 17-55, 17-50, 15-85 or possibly an 18-125. I want to spend a good amount of time using the 18-55 and 40 before I buy another lens. You won’t really know what you value in a lens until you’ve spent some quality time taking and reviewing photos in various settings.

    Do I recommend this? Absolutely! This over the 50/1.8? I haven’t used the 50 but I’m happy I chose the 40. Yes, it’s not 1.8 but 50mm on an crop sensor would be too limiting for my use, take away from the overall compact size and honestly, I wasn’t a fan of the 1.8 performance I saw of the 50 and the 40 seemed to be better at 2.8 and up.

  • Thanks, am planning to buy one soon 😛

  • Roger Cicala


    Both are good lenses and great values. Both make enough noise that you would hear it using on camera mic for video. Image quality is excellent. The 40mm will AF more accurately.


  • James

    I have read so many reviews on this lens, and am getting kinda confused.

    I have the 50mm 1.8, and would be buying this lense for video and still work.

    I am hearing a lot of people say that the STM motor is not as quiet as canon say and still produces noticable noise…

    I am using a 650d, and I know the STM tech is optimised for this camera.

    I suppose the question would be, am I really going to see a difference between the 40mm and the 50mm?!

  • Daryl McMullen

    I bought this lens too – and placed it on my Canon 7D. Nothing happened… Didn’t act powered at all. Unmounted and remounted and nothing. My 7D read 00 for Aperture.

    Wound up finding that there is a firmware update for the lens. This update can be applied when mounted on specific cameras (like the 5d MIII) but very unstable and not possible on a 7D.

    So I sent it in to have the update applied for me.

    Just got it back today – hoping all is well – still haven’t been home to test it.

    Good luck all!


  • ernesto

    I have a Panasonic AF 100 with a Kipon EOS-m4/3 Canon EOS to Micro Four Thirds Lens Adapter w/ Aperture Control
    Does anyone know if this lens works with this adapter? It seems that I would need an adopter that would have to power the lens electronically.

  • bip

    Great to read constructive comments and a v helpful review… Has to be said. Bip.

  • Tor-Arne

    I own this lens myself. And I can verify the focus issue.
    But now I know that Canon already has issued an FW update for the 7D to remedy this issue. And we’re already seeing FW updates rolling out to remedy the issue on other models as well.
    But so far I found the only solution is to unmount and remount the lens again.
    A minor niggle in the grand scheme of things.
    Whenever I’ve used the lens in AF mode I always switch it to MF and roll it back before putting on the lens cap. This has kept the issue from reappearing for me.

  • Ben

    I found some explanation in this video.

    It seems as though it goes to sleep before the camera itself goes to sleep, and it does need power from the camera to use manual focus. So it goes to sleep too soon.

  • Ben

    I sent Canon an email.

    I thought about buying this lens then gave up after reading the comments about focus.

  • zemitch

    Focus blocked after two shoots… Mounted on 5D2.

  • bullmoon

    I cannot repro the focus problem. I have had the lens for over 2 weeks and shot quite a bit with it – often “manually” retracting/pushing in the lens after powering off the camera – almost always in fact. Just tried it again following the steps Vu gave and no repro.

    I like it – handy lens, pictures look fine, 40mm works well for casual shooting out and about for a compact setup.

    Canon 5D MKII / latest firmware: 2.1.2

  • Sasham5

    In my totally “unscientific” tests, I found it much superior in sharpness to 50mm 1.8, especially wide open, but also at 2.8. No comparison…

    but it’s got a tiny hole, so the amount of light is an issue.

  • Joe

    Hi Robert,

    Do you think the 40mm pancake is better optically than the 50mm 1.8?


  • mrkgoo

    Airquotes: I’m suspecting it’s a weird quirk… that is, since the motor is not engaged with the focus ring, if the focus has shifted (by force for example) since the last time it stopped or was asleep or whatever, it requires a complete power down and reset (ie remount).

    That said, if that were the case, it should be fixable in a firmware for the lens, I would imagine. Otherwise, I wonder if firmware for teh cameras can be adjusted to ‘fix’ it?

  • Airquotes

    I’ve had the same focus problem with mine on a 5D MK II. It happened a couple times before I tried Vu’s method of pushing it in and was able to recreate the problem exactly. I think this is a quirk of the lens and not a problem with any one copy. With all the reports of this problem I’ve been reading I think exchanging it would make no difference as all copies of the lens have the problem. It’s really annoying but probably not a deal breaker for me. I’ve just been focusing at infinity so the lens is fully recessed before i put it back in my bag. I wonder if Canon will issue a recall if it truly affects all copies as I suspect it does.

  • mrkgoo

    I haven’t had the issue beyond the firs two, but admittedly, I ahven’t been out and using it all that much, jsut checking day to day. I wonder if it’s just a quirk, like it needs to be reset if bumped?

    I know the Canon 7D doesn’t fully power down with power off (the viewfinder actually goes dark when fully powered down), so maybe a proper power cycle (ie remove battery) might reset the lens too. I’ll give that a go if and when the next time it happens.

    It would help if we can get a consensus of when it’s happening, and what model camera people have.

    Again, I have a 7D, and it happened when I was either powering the device on or waking it.

  • Isaac

    Exact same thing here. Lens arrived yesterday and in general am very pleased with it (super sharpness at f2.8), but it’s already three times had the “will not focus” thing (including not even focusing manually) requiring a remount each time. I don’t think I was pushing at anything… unless pushing gently while putting the lens cap on counts.

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