Canon EF 40mm f/2.8 STM

Canon EF 40mm f/2.8 STM

This review covers


» Image Quality «


» Sample Pictures «

» Conclusion «

» Further Information «

Table of contents

Canon's first-ever "pancake" EF lens is small in size but great in features and quality. In many ways the EF 40mm f/2.8 STM is a unique lens that you'll immediately like once you hold it in your hands. Read about what it does great and where its weakest spots are in this review and find out whether or not it is for you.

Intended Use

Street & Travel

With its tiny size the EF 40mm f/2.8 STM is well suited for unobtrusive street photography and general travel. The focal length and maximum magnification (0.18 x) is good to cover anything from tight portraits to (small) groups of people. Obviously it is not a wide angle lens and thus cannot cover broader scenes. The good maximum aperture of f/2.8 supports the fast shutter speeds required for some street photography.


When used with an APS-C camera the EF 40mm f/2.8 STM has an effective focal length of 64 mm which is good for nice portraits. Also the maximum aperture of f/2.8 is well suited for portrait photography though some portraits might require even lower f-stops - which is where an EF 85mm f/1.8 USM or an EF 50mm f/1.4 USM is better suited. Notably the EF 40mm f/2.8 STM creates very nice and smooth background blur which is great for portraits as well.


Well the EF 40mm f/2.8 STM is one of the first two Canon lenses to feature an STM focusing motor which was initially developed to allow continuous autofocus operation during video recording. If you are shooting video you will certainly need more than one lens but this one works quite well with video and even the manual focus operation is very smooth.

Weight and Dimensionstop


The EF 40mm f/2.8 STM is the smallest EF lens Canon have ever produced and at 4 oz it's also among the lightest.

Lens Weight [oz]  
Canon EF 40mm f/2.8 STM 4

Compare with the weight of other lenses:


Canon EF-S 10-22mm f/3.5-4.5 USM 14
Canon EF-S 15-85mm f/3.5-5.6 IS USM 20
Canon EF 16-35mm f/2.8L II USM 22
Canon EF 17-40mm f/4L USM 17
Canon EF-S 18-55mm f/3.5-5.6 IS II 7
Canon EF-S 18-135mm f/3.5-5.6 IS 16
Canon EF 24mm f/2.8 IS USM 10
Canon EF 24-70mm f/2.8L II USM 28
Canon EF 24-70mm f/2.8L USM 32
Canon EF 24-105mm f/4L IS USM 23
Canon EF 28mm f/1.8 USM 11
Canon EF 28mm f/2.8 IS USM 9
Canon EF 50mm f/1.2L USM 19
Canon EF 50mm f/1.4 USM 9
Canon EF 50mm f/1.8 II 4
Canon EF 50mm f/2.5 Compact Macro 10
Canon EF-S 55-250mm f/4-5.6 IS 14
Canon EF-S 55-250mm f/4-5.6 IS II 14
Canon EF-S 60mm f/2.8 Macro USM 12
Canon EF 70-200mm f/2.8L IS II USM 52
Canon EF 85mm f/1.8 USM 14
Canon EF 100mm f/2.8 Macro USM 21
Canon EF 100mm f/2.8L Macro IS USM 22
Canon EF 100-400mm f/4.5-5.6L IS USM 52
Canon EF 300mm f/2.8L IS II USM 83
Canon EF 300mm f/2.8L IS USM 90
Tamron AF 70-300mm F/4-5.6 Di LD MACRO 1:2 (for Canon) 16


The EF 40mm f/2.8 STM's dimensions are 2.7 " (diameter) by 0.9 " (length).


Compare with these values:

Length in
Diameter: in

Handling and Build Qualitytop

Apart from its incredibly tiny dimensions you'll immediately notice the EF 40mm f/2.8 STM's superior build quality. It feels rock solid and comes with a metal lens mount that will last much longer than lower-cost plastic mounts. The plastics its made of have a decent look and the focus ring - while tiny (0.2 ") - has a very nice grip and rotates as smooth as I can imagine.

Canon do not ship any accessories with the EF 40mm f/2.8 STM (except for the dust and lens cap) but a lens hood is available for purchase. Like with the EF 50mm f/1.8 II the lens hood needs to be attached to the filter thread (and has another filter thread to use) because the lens doesn't have a separate fixture for lens hoods. Circular polarizing filters and other filters that need to be adjusted for each shot can easily be used with the EF 40mm f/2.8 STM because the lens's front element doesn't rotate while focusing. The 52 mm filter size is as small as it gets and is shared with the EF 50mm f/1.8 II, the EF-S 60mm f/2.8 Macro USM and other lenses (if you'd like to use your existing bigger filter you can use a cheap step-up filter adapter).

Stepping motor (STM)

The EF 40mm f/2.8 STM is one of the first two Canon lenses to feature an STM focusing motor (the other one being the EF-S 18-135mm f/3.5-5.6 IS STM. Canon have designed this motor to be faster and less noisy than conventional micro motors - and indeed it is. However STM motors are not quite as fast as modern USM type motors and nor are they as silent. But then again it depends on what generation USM motor you have. The one in the EF 50mm f/1.4 USM for example is a lot noisier and (somewhat) slower than the EF 40mm f/2.8 STM's motor.

But why would anyone even bother about the sound an AF motor makes? Well, first of all an old-style micro motor can really catch attention if you shoot in a silent athmosphere (such as a wedding ceremony). And then, many people now use their DSLRs to record great video footage. Even if external microphones are used the focusing motor can often be heard if the camera is close to the action. Whether the sound of an STM motor is quiet enough to use the camera's build-in microphone during autofocus operation is something I would certainly doubt but as said before it's at least less noisy than micro motors.


The focusing ring does not mechanically connect to the lens's focusing parts. Instead it's an electrical connection and a turn of the ring just tells the focusing motor to focus closer or farther. That's great for video because the focus transition is very smooth but of course it's also bad because even with MF you will have to cope with some (in this case actually very little) of the STM motor's noise. In addition the STM motor needs the camera's battery to work so you'll have to press down the shutter half way in order to wake the camera up from sleep mode and even the lens itself can fall into sleep mode (not during live-view) and needs to be woken-up in the same manner.

Full-Time Manual

As with USM lenses STM lenses also allow manual override of the autofocus operation which is great when your autofocus is just not focusing where you want it to (e.g. you want the eyes of an animal to be in perfect focus) and you are too lazy (or don't have the seconds required) to switch over to MF mode. While this is most useful in One-Shot AF mode it can (rarely) also be helpful in AI-Servo to "show" the lens whether you want it to focus on something in the foreground or background (while the shutter is not pressed down). STM lenses however don't allow manual override of the autofocus operation during AI-Servo mode (USM lenses do). Note that Canon could change this with a different camera firmware in the future.

Autofocus during video

Probably the lens's most unique feature is that the STM motor can continously autofocus during a video recording (or during live-view photography). This however requires a hybrid CMOS AF system to be present in the camera and currently only the EOS Rebel T4i (called "EOS 650D" in Europe and "EOS Kiss X6" in Japan) uses this system. That camera also features a touch-to-focus display which in combination with STM lenses makes it very simple to keep the focus on a moving person's face (the camera tracks the movement throughout the image frame). This works very well with the EF 40mm f/2.8 STM and the autofocus is certainly fast enough for this purpose. It is also silent enough for home videos but I doubt that serious videographers will accept the still audible focusing noise when the camera's built-in mikes are used.




Image Quality