Canon doesn't have a lot of lenses available for its mirrorless system. That makes the existence of the EF-M 15-45mm f/3.5-6.3 IS STM ($299.99) a bit of a head scratcher—after all, the company already has a kit lens in the form of the EF-M 18-55mm f/3.5-5.6 IS STM ($299.99 at Amazon) . But the 15-45mm is smaller and covers a wider field of view, making it a more appealing starter option. In that capacity it's a good lens when purchased in a bundle with a camera body, but EF-M 18-55mm owners probably don't want spend full price to add it to their kit. The EF-M 11-22mm f/4-5.6 IS STM is a stronger option if you want to buy a wider lens.

Design
The 15-45mm ($299.00 at Amazon)  features a collapsible design, measuring about 1.8 by 2.4 inches (HD) at its smallest, and extending its height by an inch to an inch and a half when ready to shoot. The barrel and mount are plastic and finished in your choice of silver or black, so it weighs just 4.6 ounces. It supports 49mm front filters. There's a bayonet around the front element for a lens hood, but it's not included—you'll need to spend another $29 to get one from Canon.

The zoom ring occupies the bulk of the barrel. It's finished with a knurled texture, making it comfortable to grip, and is marked at 15, 18, 24, 28, 35, and 45mm. A narrow manual focus ring sits at the front of the barrel. Like most mirrorless lenses, the focus system is by wire—the ring is an electronic control for the internal focus motor. You won't get the same tactile feel that you expect from a lens with a mechanical focus ring.

Canon mirrorless cameras use APS-C image sensors, so keep that in mind when thinking about the 15-45mm's zoom range. If you're used to thinking about field of view in full-frame terms, understand that it covers an equivalent field of view as a 24-72mm zoom on a full-frame system. When zoomed out that's slightly wider than your typical smartphone camera—the iPhone 6S ($149.00 at Amazon) matches the view of a 28mm full-frame prime.

Canon lists the close focus distance at 9.8 inches. That's measured from the image sensor, and applicable when zoomed all the way out. The distance extends a couple of inches when zoomed all the way in, but you'll be able to capture photos with higher magnification at 45mm.

Image Quality
I used Imatest to check sharpness when paired with the 18-megapixel EOS M10 ($378.99 at Amazon) . At 15mm f/3.5 the lens notches 2,062 lines per picture height on a center-weighted sharpness test—better than the 1,800 lines we look for in a photo. Edge performance is solid here, with the periphery of the frame scoring an excellent 1,944 lines. You see modest gains in the overall score as you stop down—2,083 lines at f/4, 2,299 lines at f/5.6, and a peak of 2,328 lines at f/8. There's a slight drop in image quality at f/11 (2,167 lines) due to diffraction. You'll want to avoid shooting at apertures narrower than that.

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At 28mm the maximum aperture is f/5. The lens scores 1,928 lines averaged across the frame, but edges are noticeably soft at 1,387 lines. The story is about the same at f/5.6, but there are significant gains in image quality at f/8—the overall score jumps to 2,408 lines and edges hit 2,125 lines. Again, there's a drop at f/11, with diffraction cutting the average score to 2,260 lines.

The f-stop closes down to f/6.3 when zoomed all the way to 45mm. The center-weighted average score holds up well, 1,966 lines, but edges are on the soft side—1,647 lines. Again, stopping down to f/8 brings up the scores all around—2,220 lines across the frame with edges that hit 1,925 lines. There's only a slight drop at f/11 (2,186 lines), along with signifcantly better edge crispness (2,172 lines), so you may want to consider stopping down that far when shooting a scene where sharpness across the frame is paramount.

Imatest can also detect distortion. The lens shows a lot of barrel distortion at 15mm—3.6 percent—which gives straight lines an outwardly curved appearance. It's not as extreme as a fish-eye lens, but is definitely noticeable in the field. Distortion is absent at 28mm, but at 45mm you'll have to contend with barrel distortion again, about 1.5 percent. It's not as noticeable as what you get at 15mm, but you'll see it in some shots. Lens distortion of this type is easily corrected using software; Adobe Lightroom ($9.99/Month at Adobe) can remove it with a single click.

The last aspect of lens performance we evaluate is the evenness of illumination across the frame. I used an ExpoDisc to capture an evenly-lit gray frame, and Imatest's Uniformity tool to see if the corners and edges are dimmer than that of the center. At the widest angle, the lens has issues here. When shooting Raw the corners are almost 4 stops (-4EV) dimmer than the center of the image at 15mm f/3.5, although in-camera correction cuts that deficit to 2.5 stops when shooting in JPG format.

Stopping the lens down improves things. At f/4 Raw images show a 3-stop drop at the corners, and a 2-stop dip in JPG format. At f/5.6 the corners are just a little dimmer (-0.8EV) in JPG format, but still -2.4EV in Raw. At f/8 and beyond the JPG illumination is corrected to the point where it's not worth talking about, but Raw shots still show a -1.8EV drop and a -1.4EV drop at f/8 and f/11, respectively. If you do shoot in Raw, Lightroom also corrects for this using the same lens profile that removes distortion.

Illumination is much more even at 28mm. The M10's JPG engine removes it almost entirely from images, and even if you're shooting in Raw you'll really only notice it when shooting wide open—at 28mm f/5 the corners show a -1.3EV drop. Beyond that it's limited to a stop or less, which is not an issue for most shots. At 45mm, whether you shoot in Raw or JPG format, illumination is even across the frame.

Conclusions
The Canon EF-M 15-45mm f/3.5-6.3 IS STM is a pretty typical example of a starter zoom lens. It doesn't offer the build quality or high-end optics of a premium zoom. Instead it makes compromises in order to manage a small size and a cost that allows it to be bundled with a camera body. The EOS M system doesn't currently offer any zooms that will deliver the optical quality that make serious shutterbugs happy, but it does have another kit lens in the form of the EF-M 18-55mm. If you already have that one, and are thinking about the 15-45mm as an alternative due to its wider field of view, consider sticking with what you have and adding the 11-22mm to round out your kit. On the other hand, if you're buying a new EOS M camera and it's bundled with the 15-45mm, or you're without a zoom lens at all and in the market for one, rest assured that that 15-45mm is a good starter that shares the same drawbacks you get with most kit lenses.

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