Canon EF-S 24mm f/2.8 STM

SLRgear Review
December 16, 2014
by Andrew Alexander

Canon's release of a 40mm pancake lens for full-frame sensor camera bodies perhaps prompted the release of the Canon EF-S 24mm ƒ/2.8 STM - essentially, an APS-C equivalent of the 40mm. The optical layout is almost the same, and the form factor is equally small.

The 24mm ƒ/2.8 STM will not mount on regular Canon EF-mount bodies, but provides a similar field of view to its full-frame pancake-style brother -- almost 40mm. The lens takes 52mm filters, does not ship with a lens hood, and is available now for a very affordable price of around $150.

Sharpness
For its price point, the lens is much sharper than it has any right to be; there's just a trace of corner softness when shot wide open at ƒ/2.8, but stop down to just ƒ/4 and it's tack-sharp across the frame. Diffraction limiting technically begins to set in at ƒ/8, but it's not noticeable until ƒ/16, where we note some slight generalized softness across the frame. It's much more noticeable at ƒ/22, though.

Chromatic Aberration
There isn't much in the way of chromatic aberration to complain about, and it's not affected by the aperture selected. When it does manifest we see it as magenta-green fringing in areas of high contrast, primarily in the corners of the image.

Shading (''Vignetting'')
There is some corner shading to speak of when using this lens at its largest aperture (ƒ/2.8) -- the extreme corners are three-quarters of a stop darker than the center. Stop down to ƒ/4 and this differential lowers to a quarter of a stop; any other aperture, and there is no corner shading visible.

Distortion
As you'd expect with a wide-angle lens, there is some distortion present in images shot with the 24mm ƒ/2.8 STM. It's not overly objectionable, thought -- just +0.5% barrel distortion in the corners, and easily correctable in post-processing, if that's your thing.

Autofocus Operation
The EF 40mm ƒ/2.8 STM uses Canon's newer Stepping Motor Technology focusing system, which, according to Canon, allows the lens to smoothly and silently focus, and when used in combination with Canon's Movie Servo AF feature, achieve continuous AF while recording video. In practice the lens is indeed much quieter to focus than previous lenses, and is still very quick to focus, taking about one second to go from close focus to infinity. Attached 52mm filters will not rotate during focus operations.

Macro
Unlike its full-frame brethren, the EF-S Canon 24mm ƒ/2.8 STM actually provides reasonable macro performance: it can deliver 0.27x magnification at a minimum close-focusing distance of just 16cm (just over six inches).

Build Quality and Handling
The Canon EF-S 24mm ƒ/2.8 STM shaves off five grams from the size of its full-frame 40mm brother, making it even smaller and pocketable. The lens is less than an inch deep and weighs around 4.5 ounces -- this is a lens that can easily fit into the smallest crook of your camera bag, if not your pants pocket. It doesn't make your dSLR any less pocketable, but it sure makes it a lots less imposing.

The lens itself is painted in a matte black with a light stippled finish, and has a metal mount and plastic filter threads. The lens has very little in the way of control surfaces; there are two, the focusing ring, and a AF/MF switch to enable or disable autofocus.

The focusing ring is polycarbonate, and only 1/8'' wide. The STM focusing system is a focus-by-wire design, as the ring will turn forever in either direction with no increase in resistance to let you know you are at the end of the focusing range. The lens has a dedicated manual focus mode, but it also allows for MF override while AF is enabled, but there is a slight caveat compared to Canon's other USM-type lenses. With AF enabled, simply hold the shutter button half way and smoothly rotate the focus ring. The lens will extend by about 1/4'' when focused to infinity.

The compatible ES-52 lens hood is not included with the lens, but you can purchase it separately for $30.

Alternatives

Canon EF 40mm ƒ/2.8 STM ~$200
If you're using a full-frame body, this is the full-frame equivalent version of this lens. It's just as sharp, although the larger frame shows some more softness in the corners of the image.

Canon EF 24mm ƒ/2.8 IS USM ~$600
You can mount EF lenses on EF-S cameras, so this lens is also a candidate if you're looking for a 24mm prime that includes image stabilization. It's a much larger lens, but it produces as sharp images, with only a bit more chromatic aberration present.

Canon EF 24mm ƒ/1.4L II USM ~$1,650
If you're looking for the thinnest depth-of-field possible, you'll be paying more than ten times the price for the luxurious L-glass of this lens -- but it does gives you two extra stops of light-gathering ability. Ironically it's not actually a lot sharper - once the 24mm ƒ/1.4 is set to ƒ/2.8, they're about as sharp.

Sigma 30mm ƒ/1.4 DC HSM "A" ~$500
It's not 24mm, but Sigma's 30mm could also do the job for you - it's small and light, reasonably inexpensive and offers that fast ƒ/1.4 aperture. At ƒ/2.8 it's almost as sharp as the Canon.

Conclusion
There's not a lot to add that the above paragraphs don't spell out in glowing detail -- it's small, it's economical, and it has great test results. I see it ending up in a lot of presents this holiday season.

Product Photos

Sample Photos

Click here for Real-world Gallery Images on our Flickr page!

The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.

Still Life shot

VFA target

As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.