Canon EF-S 24mm f/2.8 STM Lens Review

For those of us closely following Canon's lens line, the Canon EF-S 24mm f/2.8 STM Pancake Lens looks exactly like a successful lens we have seen before. That lens is the first Canon pancake-designed lens compatible with EOS DSLR cameras, the Canon EF 40mm f/2.8 STM Lens. When first introduced, we were all amazed at the tiny size and light weight of the EF 40mm STM lens and even more amazed when we saw the image quality and overall performance it delivered for a price equally as small and light as its size and weight.

The EF-S 24mm STM lens first hit the streets in mid-November 2014, and it appears to be an exact duplicate of the EF 40 STM in an APS-C-format-only mount with a wider focal length that provides a near-40mm-equivalent 38.4mm angle of view on these smaller sensor cameras. With 40 STM-similar mechanical and optical performance, the 24 STM would be an incredible value at the same price point as the 40 STM. That this lens, in the USA at least, has a price tag of only 75% of the 40 STM's current/normal street price assures me that this lens is going to land in a significant number of kits.

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Focal Length / Focal Length Range

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As you have likely already figured out, this is a 24mm fixed focal length (prime) lens. To say that the 24mm focal length is popular could be considered an understatement as Canon's lens lineup alone includes 4 prime 24mm lenses and 15 zoom lenses with the 24mm focal length included. That is 19 out of about 78 total current lenses or about 25% of Canon's lenses containing the 24mm focal length.

With the "EF-S" qualification, we know that this lens provides an image circle large enough to cover only an APS-C sensor. APS-C format cameras compatible with EF-S lenses include the Rebel (***D and ****D) models, **D models (such as the 70D) and the 7D series. These cameras have a 1.6x FOVCF that provides an angle of view from a 24mm lens that is similar to that of a 38.4mm lens on a full frame camera. This is what that angle of view looks like:

Shown in this picture is the US Coast Guard Taney docked in Inner Harbor, Baltimore. A 20 second f/8 exposure at ISO 100 was used for this image.

A 38.4mm lens is modestly wider angle than the 50mm focal length that is most often considered the "normal" or "standard" focal length and only slightly longer than the also-wildly-popular 35mm focal length. These focal lengths are not greatly dissimilar and their lists of uses have significant overlap, but there is a perspective difference when framing a subject similarly. Below is a full frame comparison I created for the EF 40mm STM Lens review that shows this difference. APS-C-equivalent focal length angle-of-views are included in parenthesis after the actually-used focal lengths with the 25mm example being the relevant example for this review.

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In this example, the sides of the frame are nearly identical for each shown focal length, but the large trees in the background change size greatly in proportion to the foreground due to the different focus distances required for the similar framing. The wider angle lens will emphasize what is closer to the camera in relation to the background. The wider angle lens will also emphasize human subjects' closest parts - often noses - making them noticeably larger in relation to the rest of bodies if used at a close distance. A 24mm lens is not a good choice for head shots (unless a distorted perspective is what you are going for).

Step back and your subjects will be happier with their portraits. Portraits not framed tightly are going to be only one of a huge range of great uses for this lens. The 24mm focal length is one that you could leave mounted for general purpose needs.

Aperture

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Adding to the 24 STM's multipurpose capabilities is the relatively wide f/2.8 aperture. While not especially wide for a prime lens in this focal length, f/2.8 is as wide as zoom lenses get with the Sigma 18-35mm f/1.8 DC HSM Art Lens being the sole exception at review time. To get a wider aperture lens into a kit is a great reason for selecting a prime lens and f/2.8 is a full stop wider (letting in twice as much light) than a typical kit lens covering 24mm (the EF-S kit lenses are typically f/4 max at 24mm).

An f/2.8 aperture is usually what I consider to be the minimum for stopping motion indoors or for night sky photography.

Following is an example showing the depth of field at full stop aperture changes.

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Having only a 24mm focal length available generally disqualifies a lens for bird photography, but the 24 STM performed stellarly in this case. To keep this review a reasonable length, I'll share the complete cardinal picture story here. Notable is that the f/2.8 aperture can create some background blur with a close subject and a distant background, but the amount of blur is not extreme.

Image Stabilization

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This lens does not have it. Not surprising is that a lens this small and inexpensive does not include the image stabilization, but the relatively wide f/2.8 aperture allows this lens to be handheld in low light levels even without IS.

Image Quality

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Before an actual lens is in hand, determining expected image quality usually involves reviewing the theoretic MTF chart(s) provided by the manufacturer. Here is the MTF chart for the Canon EF-S 24mm f/2.8 STM Lens along with comparison charts from the focal length and max-aperture-sharing Canon EF 24mm f/2.8 IS USM Lens and Canon's other current pancake lens, the EF 40mm f/2.8 STM Lens.

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The thick lines show contrast while the thin lines show resolution. The solid lines show sagittal (lines radiating from the center to the outer image circle) results while the dashed lines show meridional (lines perpendicular to the sagittal lines) results. The black lines indicate a wide open aperture while the blue lines show results at f/8. The left side of the chart shows center-of-the-image-circle measurement and the right side shows peripheral measurement. The higher the lines, the better the lens is expected to perform.

The 24 STM's chart is cut short (the right side is missing) due to its APS-C-sized image circle, but the chart predicted that this lens was going to compete well with the other two well-regarded lenses compared here. With a wide open aperture, it appeared that the 24 STM was going to be nicely sharper than even the 40 STM with meridional performance in the corner perhaps being an exception. At f/8, it appears that the two lenses will perform nearly identical with meridional performance in the corner again being slightly worse for the 24 STM.

With a 24 STM in hand, shooting the enhanced ISO 12233 resolution test chart was the first order of business (right after the product images were captured). What we learn from these results is that this lens is nicely sharp with a wide open f/2.8 aperture and the results at f/4 are sharp. Stopping down to f/5.6 brings some minor sharpness improvements, primarily in the corners. Stopping down to narrower apertures makes little difference in sharpness until diffraction rears its ugly head. See the f/16 results to clearly see the diffraction's effects on sharpness.

My next immediate next task was to compare the EF-S 24 STM to the EF 40 STM. The 40 set the benchmark for inexpensive lens image quality and from these test results, we see that the 24 is right there with the 40 in this regard. What I see is that the 40 STM is slightly sharper in the APS-C corners at f/2.8, though that is not especially surprising since the 40 is delivering a full frame image circle. By f/4, the sharpness difference is erased and the 24 STM's barrel distortion remains the primary differentiator. At f/4, these lenses are producing impressive image quality – image quality that is approaching some fine lenses.

Field use has primarily confirmed what the lab is showing us, but looking at the results from a longer subject distance, we see more improvement in corners when stopping down. The following images were captured in RAW format and processed in Canon DPP using the Standard Picture Style with sharpness set to "1" (very low). The buildings run at an angle through the plane of sharp focus, so I included an image of the entire scene to help you see where that sharp plane should be. The point of focus is on the above-deck cabin portion of the ship. These crops were from high on the right side of the frame.

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While improvement in corner sharpness can be seen at a one or two stop narrower aperture, the biggest difference seen is the reduction in vignetting. The 24 STM corners have approximately 2.5 stops of shading at f/2.8. This amount is not unusual for an APS-C-format lens used at its widest aperture. At f/4, the shading is significantly reduced to about .8 stops with a generally-negligible .4 stops showing f/5.6.

Also negligible is the amount of flare this lens shows. Even with the sun in the corner of the frame, only a tiny amount of flare can be seen at f/11 and f/16.

More than negligible is the CA (Chromatic Aberration) this lens shows in the corners. With strongly contrasting subjects in the mid and corner areas of the frame, expect to see a modest amount of CA. CA is a relatively easy lens defect to correct in post processing (or in-camera with some models) and relatively little image degradation is caused by the correction process.

More destructive to correct is distortion and as I revealed above, this lens has some barrel distortion. The amount is modest, but if you have straight lines paralleling your borders, those lines may not appear straight or parallel without correction. Frame slightly wider than necessary if you plan to correct the distortion.

The 24 STM shows an average amount of coma in the frame corners. Coma is perhaps most easily seen in night sky photographs. Coma causes the stars closest to the corners of the frame to appear more like little comets with their tails stretching toward the corners.

This lens's bokeh (referring to the quality of the out of focus blur in an image) is decent. The corners can become a little busy, but specular highlights appear nice. Having an odd number (vs. an even number – not as in an unusual number) blade count, the 24 STM's 7-bladed aperture shows 14-pointed stars radiating from points of light.

From an image quality perspective, I can say that my expectations for this lens have been realized.

Focusing

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The 40 f/2.8 STM Lens I keep referring to was the first available Canon lens with an "STM" (stepping motor) AF implementation. The Canon EF-S 18-135mm f/3.5-5.6 IS STM Lens was simultaneously announced, but the 40 STM Lens was the first available on the street. With the 24 STM and the announced-at-the-same-time Canon EF 24-105mm f/3.5-5.6 IS STM Lens, there are now 7 STM lenses in Canon's lineup. Canon has obviously found success in the STM technology.

The 24's STM implementation is nearly identical to the 40's STM implementation:

The STM design is a focus-by-wire AF implementation. The focusing ring does not turn during AF and FTM (Full Time Manual) focusing is supported. In AF mode, manual focusing is supported only while the shutter release is half-pressed as long as the camera is enabled for electronic manual focusing lens via the camera's menu when this option is present (this feature is enabled by default). The lens's switch must be in the "MF" position and the camera meter must be on/awake for manual focusing to be available. As is typical for "focus-by-wire" designs, the meter does have to be active for MF to be functional.

The focusing ring size, like the rest of this lens, is tiny. However, being located at the outer-most position on the lens barrel, the MF ring remains quite usable. The MF ring is easy to rotate and is nicely smooth. Expect some modest subject size change in the frame when pulling focus using this lens.

The 24 STM's front filter threads do not rotate with focusing. This lens uses a front-focusing design and the lens's inner barrel extends modestly at minimum focus distance (you can see this in the product images below).

There are no focus distance or DOF markings provided on this lens. There is no room for a distance window, and since the focusing ring is not directly connected to the focusing gears (same as with most USM AF implementations), printed markings are not an option. Most AF lenses produced today have no significant DOF markings and I doubt that many using this lens will care about either of these missing features.

The Canon EF 40mm f/2.8 STM Lens was introduced with the Canon EOS Rebel T4i / 650D DSLR and the T4i press release mentioned that "When used with Canon’s new EF and EF-S STM lenses, the camera can provide smooth and quiet continuous AF while recording video." AF performance during video recording continues to grow in importance, especially with Dual Pixel CMOS AF recently introduced and especially with Dual Pixel CMOS AF being included in the Canon EOS 7D Mark II announced alongside the EF-S 24mm f/2.8 STM Lens. The "smooth" portion of Canon's claim has held true over all of the released-to-date STM lenses, and the "quiet" claim has also been true with the exception of the 40 STM.

The 40 STM is not a silent focusing lens. While it is not as noisy as the Canon EF 50mm f/1.8 II Lens for example, the 40 STM emits a buzz sound when focusing. The noise is not bad, but some buzzing motor noise is picked up by an in-camera microphone including that on the Rebel T4i/650D. In normal use, the 24 STM has the same noise level as the 40 STM.

However, on the newer Dual Pixel AF DSLRs, the 24 and 40 STM lenses are much quieter than most non-STM lenses in Movie Servo AF mode (though some AF sound will still be picked up by the camera's built-in mic). Notable is that the STM lenses are smoother in focus transitions than the non-STM lenses in Movie Servo AF mode and the micro-stepping drive closing/opening aperture is quiet.

While the 40 STM is not the fastest-focusing lens, it performs quite well in AI Servo mode and I expected the 24 STM to perform the same. I was nicely surprised to see the 24 STM focusing significantly faster than the 40 STM in side-by-side comparison. You will not call the 24 STM a fast-focusing lens when performing a full-extent focus adjustment, but in more-normal subject distance changes, this lens focuses with nice speed.

You can expect this lens to be able to track most in-motion subjects that the 24mm focal length is appropriate for in AI Servo AF mode. One shot AF is consistently accurate.

Excluding the 0.5x and 1.0x maximum magnification full macro/micro/makro lenses, there are 118 prime lenses in the site's specifications database. Among these 118 lenses, the Canon EF-S 24mm f/2.8 STM Lens, at review time, ranks fifth for highest native maximum magnification (MM) with a 0.27x spec at the minimum 6.3" (160mm) focus distance. Here is a table showing some similar lenses.

Model	Min Focus Distance "(mm)		Max Magnification
Canon EF-M 22mm f/2 STM Lens	5.9	(150)	0.21x
Canon EF 24mm f/1.4L II USM Lens	9.8	(250)	0.17x
Canon EF 24mm f/2.8 IS USM Lens	7.9	(200)	0.23x
Canon EF-S 24mm f/2.8 STM Lens	6.3	(160)	0.27x
Canon EF 28mm f/2.8 IS USM Lens	9.1	(230)	0.23x
Canon EF 35mm f/2 IS USM Lens	9.4	(240)	0.24x
Canon EF 40mm f/2.8 STM Lens	11.8	(300)	0.18x

Filling the frame with the cardinal subject I shared earlier in the review was not a challenge for this lens. Image quality remains good at this distance (and the feather detail is great).

If even 0.27x is not enough magnification for you, extension tubes will be your ally. With a 12mm extension tube mounted, the magnification range becomes 0.77-0.50x and with a 25mm extension tube mounted, the magnification range is between 1.38-1.11x. These numbers show that with-extension tube focusing can only be accomplished within a short distance range, but the increase in magnification is significant. This lens is not compatible with Canon Extenders.

Build Quality & Features

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This is a bare bones lens, but like the 40 STM, it feels well made. The non-weather-sealed body is constructed of engineering plastic with a standard metal mount. The other external components include a single switch, an extending inner lens barrel and a tiny MF ring. The MF ring has little play/wobble in its design.

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As already indicated, this is a diminutive and featherweight lens. Here is a comparison table that will highlight these facts.

Model	Weight oz(g)		Dimensions w/o Hood "(mm)		Filter	Year
Canon EF-M 22mm f/2 STM Lens	3.7	(105)	2.4 x 0.9	(60.9 x 23.7)	43mm	2012
Canon EF 24mm f/1.4L II USM Lens	22.9	(650)	3.3 x 3.4	(83.5 x 86.9)	77mm	2008
Canon EF 24mm f/2.8 IS USM Lens	9.9	(280)	2.7 x 2.2	(68.4 x 55.7)	58mm	2012
Canon EF-S 24mm f/2.8 STM Lens	4.4	(125)	2.7 x 0.9	(68.2 x 22.8)	52mm	2014
Canon EF 28mm f/2.8 IS USM Lens	9.2	(260)	2.7 x 2.0	(68.4 x 51.5)	58mm	2012
Canon EF 35mm f/2 IS USM Lens	11.8	(335)	3.1 x 2.5	(77.9 x 62.6)	67mm	2012
Canon EF 40mm f/2.8 STM Lens	4.6	(130)	2.7 x 0.9	(68.2 x 22.8)	52mm	2012

For many more comparisons, review the complete Canon EF-S 24mm f/2.8 STM Lens Specifications using the site's Lens Spec tool. Here is a visual comparison of some of these lenses:

Positioned above from left to right in their fully retracted positions are the following lenses:

Canon EF-S 24mm f/2.8 STM Lens
Canon EF 24mm f/2.8 IS USM Lens
Canon EF 28mm f/2.8 IS USM Lens
Canon EF 35mm f/2 IS USM Lens
Canon EF 50mm f/1.4 USM Lens

The same lenses are shown below in their fully extended states with their lens hoods in place.

The tiny, not-included Canon ES-52 Lens Hood does not have a big price tag, but ... it is not an especially protective piece:

The hood is not thick enough to add significant impact protection to the front element and the angle of view difference for light blocking is small. I'm a huge proponent of using lens hoods, but I don't think this one is worth bothering with.

I'm also not sure that a lens this inexpensive justifies a protection filter, though I would be lost without circular polarizer filters for all of my lenses and also frequently find neutral density filters to be invaluable. For these filter types, the small 52mm size is also reflected in the relatively small prices and a small form factor for that is easy for taking with you.

No case is included in the box, but finding somewhere to stow this lens should not be challenging. Most clean pockets will work.

Price

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The Canon EF-S 24mm f/2.8 STM lens's price is definitely one of my favorite features of this lens. Few lenses cost this little and you can buy many of these lenses for the price of most other Canon lenses. As Sean pointed out, this lens is worth the price just to add its video capabilities to the kit.

When the 24 STM was introduced, the Canon EF 40mm f/2.8 STM Lens was in the #1 position on my Best Bargain Lens List. Based on my expected performance of this lens, I strongly believed that the Canon EF-S 24mm f/2.8 STM Lens would join the 40 STM at the top of this list and that expectation was correct. Which of these lenses should be #1? Flip a coin. I made it #2 because it was introduced after the 40. And it is not full frame compatible.

As pointed out by a friend of the site, exchange rates seem to have been ignored in Europe where this lens costs 60-90% more than in the USA. As I understand it, the review time street price for this lens is about 149 plus tax/VAT regardless of the £, € or $ currency. While paying more is not fun, I still think that this lens is easily worth the price even across the big pond.

Alternatives

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This is a 24mm prime (fixed focal length) lens, of which Canon currently offers four models. There are also a couple of 28mm lens models available right now. Why select the 24mm STM over these other lens options? Price, small size, light weight and Movie Servo video capabilities/performance are the easiest advantages to discern. The STM's disadvantages are the barrel distortion, the small focus ring and, in some cases, lack of fast Ring USM AF.

The Canon EF 24mm f/2.8 IS USM Lens adds image stabilization to its advantages. The image quality from these two lenses is similar with the STM having slightly better corner performance and less CA while the IS lens has less distortion.

The far-heavier and far-more-expensive Canon EF 24mm f/1.4L II USM Lens is in a different league with its 2-stop aperture allowing 4x as much light to reach the sensor and creating a much stronger background blur. If I had to rely on a lens to perform when I needed it to, the L lens would get my vote. Or, perhaps having a backup 24 STM would be adequate in this concern. The L lens is also in a different league from a price, size and weight perspective. At f/2.8, the L lens is sharper in the center of the frame, but the STM competes well in the corners and the STM has less CA. At f/4, the STM seems to have the edge in this comparison.

A downside to using a single focal length for all of your images is that your images can all begin to look similar. My preference is to use a range of prime lenses – in no more than 1/2 or 2x focal length increments when omitting a zoom lens covering a similar range.

The first prime lens that I would pair with this one is the nearly identical Canon EF 40mm f/2.8 STM Lens (shown compared above). This 2-lens combo would cost little, take up little space in the case and would barely be noticed when carried.

Prime lenses are, in my opinion, best in a kit that also contains zoom lenses. I expect that many buyers of the 24 STM will have one or more relatively narrow aperture zoom lenses that come packaged with DSLRs sharing a place in their kits. The little prime lens gives these kits a wide aperture not otherwise available.

The evaluation EF-S 24mm f/2.8 STM lens was an off-the-shelf retail model.

Summary

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Canon likes to promote the incredible number of lenses they have produced. This production figure far exceeds 100 million as I create the Canon EF-S 24mm f/2.8 STM Lens review. Providing lenses like this one in their lineup will, significantly, increase Canon's production figures and marketing will be reaching production milestones at an even higher frequency.

The Canon EF-S 24mm f/2.8 STM Lens is an extremely small and light lens that produces nice image quality and has accurate auto focus. The price will seal the deal and make this a must-have lens for any APS-C kit.

At the end of the 40 STM review, I made a statement that also applies to this pancake-style lens: "Overall, I’m finding "little" to not like about this tiny, inexpensive lens." It is fun to joke about this little lens, but ... it is the real deal. Not only will it get the job done, it will do the job as well or better than many other lenses. And for a lower price. It is not hard to justify this purchase.