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Canon EF 40mm f/2.8 STM

The Canon EF 40mm f/2.8 STM offers solid image quality in a well built package that comes with the novelty of being a diminutive pancake design and at a low price point. However, slightly odd 40mm focal length might not be a great fit for your artistic vision regardless of sensor size.

I’ve had this lens sitting in my drawer for a couple of years now, and honestly, I can’t think of when the last time was that I took it out and used it. Which to be honest, makes writing this review quite a bit more difficult than it probably needs to be.

Worse, it’s not like we’re talking about a bad lens here. Though diminutive in size, the EF 40mm f/2.8 STM packs solid image quality and a reasonably fast aperture into a tiny package with an eminently reasonable price point.

40 mm
Canon EF

EF 40mm f2.8 stm front quarter view.


4.6 oz.
0.9 x 2.7⌀ in.

One thing that can be said about Canon’s lenses for the last 8 years, or so, is that they’re being built well. There was a time, not that long ago, where I would have expected a lens like this to feel cheap and plastic-y, and have an underwhelming plastic lens mount to go with it. That’s not something that Canon seems to be doing anymore. Even the similarly inexpensive EF 50mm f/1.8 STM isn’t built cheaply.

Build wise, the EF 40mm f/2.8 STM is quite nice, even if there’s very little lens be concerned with. The outer lens barrel is finished in a finely textured black coating that’s closer in appearance to an L lens than the smoother finish of many of the other consumer grade lenses.

On the rear, there’s a metal lens mount. This is a feature I always want to see in lenses, but maybe not for the reasons some would expect. Because the lens mount interfaces with it’s counterpart on the camera body, this is a wear surface. Plastic mounts are much softer than metal ones which means that they’ll wear faster. And ultimately, it’s the accuracy of these mating surfaces that hold lens in the correct optical alignment on the camera.

EF 40mm f2.8 stm rear quarter view.


As one would expect on such a small lens, the controls are equally small. In many cases, I would consider something like a narrow focus ring, or a tiny AF/MF switch to be a negative factor. However, this case is an exception. The simple reality is that there really isn’t that much lens to start with, and making the focus ring bigger would have negatively impacted other aspects.

A perfect example of this problem can be seen in Canon’s EF-M 22mm f/2 STM for their EOS M platform. On that lens, the focus ring covers half of the overall depth of the lens. As a result, one of the complaints I had wit that lens when I was using it is that it’s hard to mount and dismount from the camera. With so much of the front of the lens being free turning focusing ring, it’s easy to grab the lens by the focusing ring while trying to mount it and not be able to turn the in the mount.

With the EF 40mm f/2.8 STM, the focus ring is only 0.2 in. (5 mm) and only takes up 21% of the overall 0.91 in. (23 mm) depth of the lens. Quite simply, there’s much more meat to grab on to when trying to mount and dismount the lens.

Additionally helping matters, Canon didn’t go for a super smooth overall design like the have with the EF-M lenses. There’s pronounced ridges along the back of the lens by the mount. These provide both a solid tactile indication that you’re holding something that isn’t going to spin freely on you, as well as providing good traction for turning the lens.

Of course, that still does leave a quite narrow focusing ring. However, on this lens it’s not necessarily a problem either.

Canon located the focus ring around the front edge of the lens. In fact, the focus ring here doesn’t just wrap around the perimeter of the lens, it also is the outer 6mm of the front face.

Finally, the circumference of the focusing ring is textured with a straight ridge “knurling” to provide better traction when focusing.

That said, like all STM lenses, the EF 40mm f/2.8 STM is a focus-by-wire lens, meaning that there’s no mechanical connection between the focusing ring and the part of mechanism that moves the lens elements.

The biggest consequence of electronic focusing is that the feel of turning the ring depends entirely on how the encoder and bearing system for the ring is designed. In some lenses, the focus ring feels almost identical to the focus ring of a really high end manual focus lens; in other lenses, the feel fall a bit short.

The focus ring on my EF 40mm f/2.8 STM is free spinning and smooth with no indication of grit or the rotary encoding that is being done behind the scene. Compared to other STM and electronically focusing lenses I have, it feels a bit freer spinning than most of the others. However, that might also be a consequence of the front edge placement and that when rotating it you don’t end up rubbing as much of the barrel as you do on other lenses.

The only other control on the lens is the slightly smaller than normal AF/MF selector switch. Following Canon’s current design trends, the AF/MF switch on the EF 40mm f/2.8 STM is a flat flush mounted switch that sits in a slightly raised area in the housing. Though flat and flush with the surface, the switch is easy to flip when you want too.

Though this is a consumer lens, and so there is less focus on manual focusing, I felt it was at least worth putting the lens through my winter glove tests. For these tests, I’ll be using two different gloves; a set of Marmot PreCip gloves, and a set of Freehands Stretch Thinsulate gloves.

Wearing either pair of gloves there’s no perceptible feedback that you’re touching the focus ring, at least not from the texturing. However, because of it’s position on the lens, this really isn’t necessary. You can easily feel the corner of the lens, and since that’s the focusing ring that’s all you really need.

The front filter threads are 52 mm, and don’t rotate.

In a frustrating, but typical, move from Canon, the EF 40mm f/2.8 STM doesn’t include a lens hood. Instead it’s a ridiculous $29 part that screws into the front filter threads to mount. While I might not complain much about the $29 price if we were talking about a $1000 lens, at $130, the hood adds a further 22% to the cost of the lens if you want one.

Video Tests

Canon introduced the STM motor in conjunction with their greater focus on video DLSRs. The motor replaced the traditional, and loud, micro motors, and silent, but less than smooth, micro-USM motors with something that could silently make smooth focus transitions.

With the focus on video for the motor system, it’s worth at least looking at the rest of the lens in that context.

The first question goes to manual focus. Controlled smooth focus pull is an important aspect of cinematography. And that’s also a place where this lens falls down a bit.

To start with, the manual focus ring is pretty small, though the texturing is gear-tooth like and may mesh with some follow focuses. However, the diminutive size is going to make it hard to mount a follow focus in the first place.

Secondly, because the lens is purely electronic, there are no stops for infinity and close focus. In fact, in my testing, the electronic focusing system seems to take things a step further and vary the relationship between ring rotation and focusing shift based on the speed at which the ring is turned. That is, turn the ring slowly, and the lens focuses in smaller increments making it more sensitive. Turn the ring quickly, and the lens jumps faster but with less sensitivity.

The result of this is that while the lens can easily be manually focused, and focused accurately, its not repeatable. It also means that focus pulls can be somewhat erratic.

With that out of the way, lets move on to breathing. Breathing is caused by the lens’s angle of view shifting while focusing.

This lens breathes.

I don’t even have to test for it, as this is an overall linear extension focusing design. That means that the to focus closer to the camera, all of the lens elements move away form from the sensor. This has the effect of changing the effective focal length and therefore the angle of view.

What is it good for?

Well, the answer certainly isn’t, “absolutely nothing.”

40 mm is a bit of an odd ball focal length, at least in the traditional context of lenses. It’s about 14% longer than the traditional 35 mm, and about 20% wider then the next step up at 50 mm.

That said, I believe it was Ernst Leitz, the man who founded Lecia Camera, that argued that the proper “normal” focal length was for the focal length to equal to the diagonal of the film frame, and only later settled on 50 mm. For a 24 x 35 mm frame, that would be 43.26 mm, and 40 mm is a lot closer to that than 50 mm.

In many ways, this lens is right in a sweet spot, all be it a non-traditional one, for normal to slightly-wider-than-normal lenses.

All that said, as I noted at the start, my copy has largely lived in my lens drawer, and that’s something of a contradiction given that I keep saying the lens isn’t a bad performer. This is where lens choices become something of a personal decision.

To start with, the 40 mm focal length doesn’t really do much for me artistically. Normal and slightly wide lenses just don’t add much in the way of interest to images. And while the resulting images may be more reflective of reality, or how my eye supposedly saw the world at the time, they image they produce certainly isn’t reflective of how my brain perceives the world.

Compounding matters, I also own Canon’s very good EF 24-70mm f/2.8L II USM zoom. Optically, the two are very close. Though with the prime being a prime it does beat the zoom in terms of resolution. However, with both lenses being f/2.8, the choice, for me, ends up being between a zoom that has focal lengths I like to shoot at, and a prime that doesn’t. Under those conditions, the choice really isn’t that hard for me to make.

Does this mean that you should avoid the EF 40mm f/2.8 STM? Absolutely not.

EF 40mm f2.8 stm along side extender ef 1.4x iii
Smaller than a 1.4x teleconverter, the diminutive size of the EF 40mm f/2.8 STM makes does have a novelty factor.

The lens has a lot of things going for it. It’s small size makes is a unimposing lens for things like street photography or really anywhere you might want to have a lower profile camera. At f/2.8 it’s reasonably fast, though it is still a stop-and-a-half slower than the slightly cheaper EF 50mm f/1.8 STM. And rounding out the package, it’s relatively inexpensive at around $130.

It was the solid optical performance, small size, and low price that got me to buy one of these lenses, and it’s the small size and solid performance that has me keeping it around, even after I’ve sold other lenses.

That just leaves the question, where does the EF 40mm f/2.8 STM fit, and is it a good lens to have in your bag?

This is a question that’s somewhat hard for me to answer. In some respects the lens is very much just a novelty due to the pancake design. The EF 50mm f/1.8 STM is faster and slightly cheaper, and honestly not all that much bigger.

I would say that the EF 40mm f/2.8 STM is a reasonably poor-man’s 35mm prime, and in many ways it is. But at the same time, Canon does make a 35mm f/2 IS USM that is both actually 35mm, a stop faster, and image stabilized.

Aside from the novelty factor, I’m rather hard pressed to come up with a compelling reason to have one of these.

One place where it might really shine is on an EF-EOS-M mount adapter and attached to an EOS-M. The pancake design, even with the mount adapter, keeps it reasonably small on the small mirrorless bodies. Moreover, on an APS-C camera the lens gives an 64mm equivalent angle of view, making it more of a short portrait lens. Though it’s still a bit of an odd focal length.

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