The Canon EF-S 18-135mm f/3.5-5.6 IS STM ($549.99 direct)£336.39 at Amazon UK is one of only two lenses from Canon that use STM focusing motors, the other being the EF 40mm f/2.8 STM£380.41 at Amazon UK. When paired with the new EOS Rebel T4i D-SLR these lenses provide smooth, silent autofocus during video recording. If bought in a kit along with the camera, you'll save a full $200 off of its retail price, but if you aren't a video shooter and are considering an 18-135mm purchase on its own, the older EF-S 18-135mm f/3.5-5.6 IS£399 at Amazon UK is a bit sharper, albeit slightly larger, lens.

It measures 3.8 by 3.1 inches (HD) and weighs just over a pound, which is fairly typical for an 18-135mm design. It's at its shortest at 18mm, and the barrel extends as you zoom. The front element doesn't rotate when zooming or focusing, so using a 67mm circular polarizer is no problem.

I used Imatest to check the sharpness and distortion characteristics of the lens when paired with the EOS Rebel T4iSEE IT. At 18mm f/3.5 it records an excellent 1,956 lines per picture height, which increases to 2,238 lines at f/5.6. Distortion is an issue at this focal length, as the lens shows 3.5 percent barrel distortion, which will make straight lines appear curved, especially when shooting an object that is close to the lens.

Sharpness dips below the 1,800-line threshold for a sharp photo at 50mm. It hits 1,698 lines at 50mm f/5, but does a much better job at f/8, where it records 2,139 lines. You'll get about 1,892 lines at 135mm f/5.6, and stopping down to f/8 there increases the score to 2,071 lines. At both 50mm and 135mm the lens shows 1.5 percent pincushion distortion, which can be noticeable in certain conditions. Some distortion is to be expected in a zoom lens, especially one that covers a long 7.5x range.

If you're buying a T4i, the 18-135mm STM lens is the way to go. Sure, the kit is a bit more costly than the one that is bundled with the EF-S 18-55mm f/3.5-5.6 IS II, but the longer zoom range and silent STM motor justify the cost. If you're simply looking for a nicer zoom lens for an existing D-SLR, opting for the older EF-S 18-135mm f/3.5-5.6 IS lens—notice that there's no STM designation for that one—will save you about $50 and give you a sharper image at the midpoint of the zoom range, but you may find yourself missing the STM motor if you later upgrade to a body that supports it.

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