The Canon EF-S 18-55mm f/3.5-5.6 IS STM ($249.99 direct)($96.18 at Amazon) is the latest iteration of Canon's basic 18-55mm kit lens. Most folks will get one bundled with a new camera, like the EOS Rebel T5i, but some shooters may want to consider it as an upgrade to an existing lens, or to replace an older 18-55mm that was damaged or lost. It offers STM focusing, which the EF-S 18-55mm f/3.5-5.6 IS II does not, and its front element doesn't rotate when adjusting focus. It doesn't offer the zoom range of the EF-S 18-135mm f/3.5-5.6 IS STM($304.00 at Amazon), but it is smaller and lighter.

The lens measures 3 by 2.7 (HD) inches and weighs only 7.2 ounces. It has an internal focus design, but it does extend when zooming in and out. The front element accepts 58mm filters, and while there's a bayonet hood available, it's not included with the lens—you'll have to budget an extra $30 for the hood. The lens mount is plastic, which saves cost and weight, but isn't as sturdy as a metal mount. The focus motor is nearly silent, and if you're shooting with a compatible body you'll get smooth video autofocus—non-STM lenses tend to be a bit choppy when adjusting the focus during video recording.

I used Imatest to check the sharpness of the lens when paired with the T5i($469.98 at Amazon). It's a good performer in that regard. At 18mm f/3.5 it manages 2,160 lines per picture height, which is better than the 1,800 lines we require for a lens to be considered sharp. Zooming to 35mm drops the maximum aperture to f/4.5, but the lens still manages 2,080 lines. At 55mm f/5.6 it records 1,909 lines. Stopping down about a stop improves the sharpness across the board.

Sharpness isn't the only thing that matters in a lens. The 18-55mm records a significant amount of barrel distortion at its widest angle. Imatest measures it as 3.2 percent, but you don't need software analysis to notice that straight lines curve outward significantly at this focal length. It's not an atypical result for an 18-55mm zoom; the curved rendering is one of the optical compromises that go hand in hand with designing a compact, inexpensive zoom. It's something that can be remedied in Lightroom, and is more noticeable if the lens is closer to the subject. The distortion goes away quickly as you zoom in; it's negligible at 35mm and 55mm.

There's also a noticeable amount of light fall-off, which causes corners to be a bit darker than the center of the image, but that's only if you're shooting in Raw; the T5i corrects for it when shooting in JPG mode. There's also some color fringing in the corners of the image. It's most apparent at 18mm, but is also there at 35mm and 55mm. It's something that you're able to remove with a few clicks in a software tool like Lightroom if it's a major concern.

Despite its flaws, which are pretty common in 18-55mm designs, the Canon EF-S 18-55mm f/3.5-5.6 IS STM is a pretty decent performer. It's sharp throughout, and you can always make some quick edits in software if you are serious enough about your shots to be bothered by distortion, light fall-off, and fringing. The STM focus motor delivers smooth video autofocus when paired with the EOS T4i, T5i, or SL1, and future Canon SLRs are likely to support that feature. Most shooters will probably look to the EF-S 18-135mm f/3.5-5.6 IS STM as an upgrade to an older 18-55mm, as it has a longer zoom ratio, is also quite sharp, and also delivers STM focusing, but if that's out of your budget or if you'd like something that isn't as heavy, this is the basic Canon zoom to get.

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