Canon 40mm f2.8 STM Pancake Review

Just a few days ago I took delivery of this exciting new lens. I posted an article outlining some initial impressions which I’m sure many of you have read. If you haven’t read it then be sure to watch the short video below which gives you an excellent idea of the size of the lens in my hands. I’ve now had a short time to take some simple images with it and draw some conclusions. I went up to London to find a few subjects that could test the usual things like sharpness, vignetting and chromatic aberration. Unfortunately the weather wasn’t really cooperating with me and it rained heavily most of the day. I was able to step out into the elements a few times though and get some shots that whilst artistically anything special, do prove the points we all want to know about.

Physical Build

I always have some preconceptions based on a price point but of course I’m willing to adjust them when I get the product in my hand! This is exactly what was necessary with this lens. I wouldn’t have been surprised to see a build that resembled that of the nifty fifty but in fact I was a long way off! This lens actually feels nicer than the 50mm f1.4 which costs twice as much! In fact it feels on a par with the new 24mm f2.8 IS and 28mm f2.8 IS that I was able to handle at a Canon event in the winter, and those lens start at $750 ! Most importantly for me is the inclusion of a metal lens mount. You also get a super smooth and slightly rubberized focus ring. The lens body itself is of court polycarbonate but it feels the same as the 100mm f2.8 Macro IS , NOTHING like the cheap crappy plastic of previous lower-end Canon primes. It’s also nicely dense and solid, whereas the 50mm f1.8 feels quite hollow. I’d have no issues at all slipping this lens in the pocket of my pants and leaving it there all day, something which you can actually do!  

Optional (and mostly pointless) lens hood. ES-52

Whilst I was in London for the day I happily carried my 5D MKIII over my shoulder the entire day. I think that is the first time that I have EVER carried a pro body on my shoulder all day without complaint. I would typically take my Fuji X100 for such a day out, but it really was no trouble to take my 5D this time! What in incredible difference to have the power of the 5D all of a sudden in such a small package that you can use all day. The lens doesn’t come with a lens hood but an optional one is available. , the ES-52.  Due to the size of the lens it has to be a screw on hood not a ‘rotate-and-click’ type. Personally I just can’t see why you would bother with a lens hoot on this. The hood is the same size as the lens! You can also easily shade the front element if you are getting extraneous lens flare because whilst the front of the lens is 52mm , the front optical element is really only about 12mm in diameter! I could shade that with my pinky finger if I need to.


40mm Focal Length

This does require some thought and discussion because it is Canon’s only 40mm lens. Why did they choose 40mm ? This is something I have wandered but so far I can’t figure it out. I’m not saying it’s a bad thing, it just would have seemed far far more obvious to make a 35mm or a 50mm which are the two accepted ‘standard’ lenses. Perhaps that’s it right there, at 40mm, sitting between the two then you get a little bit of the best of both worlds. At this focal length though I think it’s particularly prone to differences in opinion on its usefulness and application based on which crop factor of camera you have. Wide lenses are wide and often there is no wider alternative. Telephoto lenses are long and seem ‘a bit longer’ on a crop body. A 40mm though is somewhere in between. On a full frame camera it does offer a reasonably wide-ish view and I actually really enjoyed it. It lends itself slightly better to people shooting than a 35mm does, but much more to capturing a scene than a 50mm does. On an APS-C camera though you’d have an equivalent of 64mm and because this focal length transcends the accepted 50mm standard view I can see the small difference seeming to be a lot greater. This (at 64mm equiv.) is the sort of focal length that works well for people and if you’re on a family vacation then you’ll put this to good use. My feeling is though that on an APS-C camera you probably won’t be happy with this as a one lens solution if you want to capture any scenic landscape or travel shots. Alongside a kit lens though you’ll be in good shape which isn’t such a bad thing as the majority of APS-C cameras are purchased with the kit lens and Canon of course knows this. I’m personally quite drawn to the 35mm focal length and never used a 50mm as my ‘standard’ but Canon has broken the long running traditions here and I think it was a good decision.

STM Focus system

This 40mm and the latest 18-135 kit lens that is now shipping with the Rebel T4i, are the first Canon lenses to feature STM motors. STM stands for stepping motor and the need has arisen from the desire to shoot video with DSLRs and also improved focusing technology in the same area. Continuous phase-detect auto focus has been missing from Canon’s DSLRs in video mode until the introduction of the Rebel T4i. Other companies have launched cameras that have this feature but none have so far been acceptably good in my book. I haven’t tried the new Rebel T4i either so I won’t pass comment on it’s functionality yet though. What STM is designed to do is smooth out the focusing process. All of Canon’s previous lenses, with the exception of some L series lenses have a slightly rough feel to to their focusing when powered by their motors. Of course in manual focus mode, as all professionals use when shooting video with DSLRs, they are buttery smooth but with this new technology we’re seeing first in the T4i there is now a requirement for something a little smoother when driven my the motor. The secondary purpose of the STM motor is to make it quieter than other lenses. Having played with this lens for a few days now I would say that it’s definitely quieter than any of the other Canon lenses at the low end of the market but I would still not call it quiet.

I don’t have a Rebel T4i so I can’t demo this with the continuous focus but the video below is designed to let you listen to the sound created by the STM motor when the cameras audio is set to auto. I had to manually focus the lens as you cannot focus automatically during recording with the 5D MkIII that I currently have with me. As you can see, there is still a huge amount of audible noise, though it’s much improved on what most people have probably experienced before with cheaper lenses. Adding a more directional microphone such as a Rode Videomic Pro would likely eliminate a lot of it but I still feel that it is too noisy for using for video if focus needs to be adjusted mid shot though.

Here then is probably the biggest problem with this lens.  With any other Canon lens, if you think the AF motor is making too much noise you can either switch to manual focus mode to disengage the focus motors or with Canons l-series lenses and their ultrasonic motors you simply just turn the focus ring manually yourself and it doesn’t engage the noise producing AF motor.  Unfortunately though, the STM motor works in a different way as you will have seen in my hands on video.  Even when you switch to manual focus mode, rotating the the focus ring engages the STM motor to move the lens elements as the whole thing is a focus by wire system.  This means that there is absolutely no way for you to get a silent video.  Whether you let the camera do the focusing, as with the new cameras like the 650D/T4i , or whether you do it yourself, you are going to get the background hum as demonstrated in my video below.

I can’t help thinking that this is one step forwards (smoother focusing) and then one huge step backwards and for this reason I’m unlikely to recommend this lens to people who are shooting video.  If you aren’t intending to capture audio then you might be able to work around it but given that the lens is indicated as being designed and optimized for video shooting with the new Rebels I think it has fallen well well short in that department.

It’s always nice to save some bulk and weight but the further problem is that I can’t figure out how you’d use a follow focus with this lens either. To have any chance at all you’d need one with a reversible gear, then you might be able to get the gear close enough to the camera body. I own the O’Connor O-Focus DM myself and that does have a reversible gear so I’ll have to check this out when I get back home. If this is a consideration for you I certainly wouldn’t guarantee that you’ll be able to use a follow focus though.

Full Sized Samples

I have uploaded a selection of test images to a a set on FLICKR in their full resolution for those that want to have a good old pixel peep.

Detail & Sharpness

All of these samples are converted from RAW using the default Lightroom setting.  No extra sharpening has been applied.

I’ll lump contrast into this area of the discussion as well because perceived sharpness is  related to contrast.  The first thing that we want to look at is wide open sharpness because things will only get better from there, at least until diffraction kicks in.  As you can see in the 100% samples below, wide open sharpness is very good, again better than it has any right to be for what I had assumed was a ‘novelty lens.  A stigma that I have now banished from discussions about this lens.  I would happily shoot all day wide open if I needed to.  On a full frame camera you can still get some reasonable background blur as you can see behind the ‘girl with flowers’ photo (even at f4) below.  Stopping the lens down to f4 gives a small improvement and I think the sweet spot is at about f5.6 , though the difference between is that and f8, f9 is almost imperceptible and you have to hunt at a pixel level to see any differences.  In the full sized FLICKR gallery there is a series of images of an ornate lamppost at various apertures which you can take a look at.

Contrast is reasonable but I would not call it great, particularly in the corners at wider apertures.  This is an area where you really see the improvements that an L-series lens can provide.  At a fraction of the price though, this lens is still more than adequate.

What I’m trying to show here with this example is the remarkable consistency of the sharpness.  Right out of the gate at f2.8 it’s pretty darn good and though there is improvements to be had by stopping down , it is minimal.

Focus Speed

Focus speed is faster than other lenses in the price range, much much faster than a 50mm f1.8, but slower than L-series lenses like my 24mm f1.4 MKII.  I got the impression that it was a touch faster in the mid range of its focusing for some reason.  In this category there can be nothing to complain about.  Once again, for a lens costing $200 is performs admirably in my opinion.

Chromatic Aberration

The one benefit of the crappy weather on my day in London is that it provided ample opportunity to evaluate the chromatic aberrations produced by the lens.  You can spot them a mile off when they are on a white/grey background.  The sample image below if at f2.8, so it’s wide open, and foliage against a bright white sky is always a reasonable test for CA.  As you can see though, the resulting aberrations are quite minimal, a touch of magenta can be seen in some areas near the corners but once again the little 40mm seems to be punching well above its weight.  Like vignetting, if you are shooting in JPEG then CA can be corrected automatically and on-the-fly by the camera.  In Lightroom it can correct the RAW images but quite honestly for the majority of people I don’t think they will ever have to do anything about it.  More noticeable is a decrease in edge contrast when wide open with high contrast ratio subjects like the leaves on the sky.   CA seems to be essentially gone by the time you stop down to


The 40mm f2.8 STM will only stop down to f22.  The image doesn’t soften a huge amount by this point BUT it does loose considerable contrast.  I’ve included an image below which shows the difference at its greatest between f5.6 and f22.

Minimum Focus Distance

MFD for the 40mm is 300mm which is pretty good.  By comparison, the 50mm f1.8 is 450mm so it’s considerably better than that.  Lenses can often perform differently when focusing at their MFD so I have included some MFD samples on the Flickr page as well, some of which are wide open.  Wide open at the MFD is a worst case scenario and whilst it does show up a little big of softening, it handles it much better than many other lenses. You’re unlikely to be disappointed.


In short, this is something of an Achilles heel for this lens when it is used wide open. Vignetting at f2.8 is very heavy on a full frame camera. Of course if you shoot in JPEG then this is no issue as you can use the camera’s built in lens profiles to correct the vignetting entirely. Even in RAW shooting it’s only a minor annoyance as you can set up programs like Lightroom to automatically correct the RAWs as well. Even if you do it manually it’s as simple a one click to fix it. Some people do like vignetting so it might not even be something you want to correct. Personally I don’t like it so I will correct it. The good news though is that the vignetting improves very quickly as you stop the lens down. At f3.2 there is a considerable improvement and by f3.5 it’s to a point where I probably wouldn’t even feel the need to adjust it in post. At this point I’d say the majority of people just wouldn’t notice it unless you’re shooting white pieces of paper in a flat light. Mileage will obviously vary with APS-C cameras that will only be sampling the inner portion of the image circle. I’d bet most people shooting with an APS-C sensor camera will be shooting JPEG anyway so it is a non issue. At f2.8 though it does vignette considerably more than a 50mm f1.8 or 50mm f1.4 at f2.8. This might seem obvious as those lenses are considerably stopped down at that point but it is worth a mention.

Pros & Cons


  • Small Size (obviously!)
  • Excellent sharpness wide open
  • Even better sharpness stopped down a stop or two
  • Price; Up there with the best value Canon lenses
  • Metal mount not plastic , nice at this price
  • Reasonable AF speed, better than all the non-L primes and better than a couple of the L primes like the 85mm
  • STM motor is quieter and smoother than all but a few L lenses (which are only quieter and not smoother)
  • Did I mention this thing is small ?
  • Excellent resistance to Chromatic aberrations, even when wide open
  • Excellent corner sharpness when stopped to just f3.5, better than most wide open at f2.8


  • Focus element of lens doesn’t retract when you turn the camera off
  • Heavy vignetting at f2.8 but dramatically improved with even 1/3 stop difference
  • So small that I can’t see how you would be able to attach a follow focus to this lens!
  • ‘Only f2.8’ I’ve heard this mentioned several times by followers. To me, with today’s ISO qualities on new cameras this is a non-issue though.
  • STM system is still too noisy for continual focus in videos in my opinion
  • The focus ring only works when powered, meaning that there is NO manual focus with the AF motor disengaged.


By now you’ve probably gathered that I quite like this lens. I went into this review with high hopes but honestly, reasonably low expectations. Canon have been churning out some fantastic optics in the last few years (100mm f2.8 L IS Macro, 70-300 L IS, 70-200 f2.8 iS MKII, 24-70 MKII) but its been a long long time since they addressed the low end of the market price wise. It seemed unlikely to me that they would produce anything truly superlative, not just at that price point but in that pancake form factor as well. After all, it’s their first ever pancake lens and all the pancakes we’ve seen in recent years for M 43/3 cameras (Panasonic, Olympus etc) have really sacrifices image quality for the convenient form factor. Canon have actually created a lens that is not only better than all those mirrorless camera versions, but it also cheaper and better built! It’s strongly assumed that Canon is going to present a mirrorless solution of their own in the next month or two and this lens bodes VERY well for this. Why ? It means that Canon have got a handle on creating small, compact optics without making sacrifices in sharpness and I would bet that some lessons, if not a lot of what we see in this lens will be showing up in their mirrorless lens kit. Typically when someone comes to me and says they want to get their first DSLR I recommend that they get a zoom and a prime to start with. For beginners that prime used to be the venerable ‘nifty fifty’, the 50mm f1.8. It produced decent images albeit with a slow as heck AF motor. From now on I will be recommending the 40mm f2.8 STM instead for photography, though not for video work due to the poor implementation of a noisy focus system. The $100 price difference might be doubling the price but this lens IS one of Canon’s gems for photos and the price premium over the 50mm is well worth it in my book. You get an optical and physical build improvement and a considerable size reduction. The ‘nifty’ is something you keep for a short while and eventually upgrade. The ‘shorty’ is a lens you can keep for many years and still find a place for it in your kit, or even your pocket!

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Dan Carr

Founder of Shutter Muse, full time photographer and creative educator. Dan lives in the Canadian Yukon, but his wanderlust often sends him in search of images all around the world to meet the needs of clients and readers alike.

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