Canon EF-S 18-135mm f/3.5-5.6 IS

The Canon EF-S 18-135mm ƒ/3.5-5.6 zoom lens was announced alongside the 7D camera in September 2009.

Designed for the Canon APS-C sensor, the lens provides an effective field of view of 29-216mm. This lens isn't a "constant" lens, in that as you increase the focal length, both the maximum and minimum aperture sizes decrease. The following table reflects the change in aperture available for the lens:

A petal-shaped lens hood is available for but does not ship with the lens. The lens is available now for around $400.

Sharpness
Looking at the lens at its widest aperture settings, it performs quite well for the price tag. Wide open at ƒ/3.5 at its widest angle of 18mm, the lens is sharp in the middle, tapering out to slightly soft corners; zooming in to 24-50mm produces even sharper results, even wide open at ƒ/4-5 at those focal lengths. At 85mm corner softness ramps up quickly, while still providing a sharp center; the corners are actually slightly better at 135mm than 85mm, both of which offer an aperture of ƒ/5.6.

Stopping down the lens improves sharpness results across all focal lengths, and the optimal sharpness settings are 50mm and ƒ/8, where the lens is tack-sharp across the frame. The effects of diffraction limiting are noticeable by ƒ/16 (at 50mm and wider, it's noticeable by ƒ/11) but even then images are still quite sharp at 50mm and lower. At ƒ/16 and 85-135mm, we note some slightly softer images. Fully stopped-down performance is fair at wide angle, average at 50mm, and quite soft at 85-135mm.

Chromatic Aberration
CA is noticeable as magenta-green fringing on edges of high-contrast areas, at wide and telephoto focal lengths: in the mid-range, between 35mm and 50mm, chromatic aberration is quite well-controlled. Below 35mm, CA is controlled slightly better with the lens used at wider aperture settings rather than stopped-down; above 50mm, it really doesn't make a difference what aperture you use.

Shading (''Vignetting'')
Corner shading is only significant when the lens is used with wider aperture settings; the worst-case scenario sees the corners 2/3 EV darker than the center when the lens is used at 18mm and ƒ/3.5. At any other setting wide open it's less than that, and with the exception of 18mm, any other focal length stopped down to ƒ/8 or smaller essentially produces no light falloff.

Distortion
The complex array of lens elements that allows the range of focal lengths in this lens leads to some dramatic results for distortion. When used in the wide angle configuration, the lens provides uniform barrel (''bloat'') distortion up to around 21mm, with dramatic distortion in the corners (1.25%, quite significant). After 21mm, distortion across the frame remains consistently barrel-distorted, but at a moderately low level (around 0.2%, on average) and the extreme corner distortion turns into the pincushion (''squeeze'') style. The worst pincushion distortion shows at 35-50mm, where the corners show -0.6% pincushion distortion. Post-processing would be required to correct for these effects.

Autofocus Operation
The Canon 18-135mm ƒ/3.5-5.6 IS is not a USM lens, with AF being driven by a DC motor and gears. As a result the lens focuses fairly fast, but is noticeably slower than a USM lens. As well, the lens makes a slight, low frequency whizz as it focuses. Manual focus override is unavailable while the lens is set to autofocus operation: in order to focus manually, autofocus must be overriden with the ''AF/MF'' switch.

Macro
With a reproduction ratio of 1:4.8 (0.21x), the 18-135mm has fair macro capability, but it won't replace a macro lens any time soon. Its minimum close focusing distance is 45mm (just under 18 inches).

Build Quality and Handling
At 16 ounces, the Canon 18-135mm ƒ/3.5-5.6 IS makes a light package for the versatile range of focal lengths it offers. To accomplish this the lens is largely plastic, though it is of a high-quality construction. The lens mount is metal, and the 67mm filter threads appear to be plastic. There is no flexing or rattling when using the lens: the exterior of the lens has a spatter-painted appearance, while the lens barrel, visible when the lens extends towards 135mm, are smooth. The only information available on the lens are marked focal lengths: there are no distance scales or depth-of-field indicators.

The lens only has two switches to speak of: one to enable or disable autofocus (''AF/MF'') and one to activate or deactivate image stabilization (''Stabilizer ON/OFF''). Image stabilization works as advertised, providing several stops of steadiness in our hands, though as always the actual usefulness is going to depend largely on the capability of the individual camera user. There is a very slight sound when image stabilization is active, but mostly only audible when your ear is next to the lens.

The large zoom ring is the prominent feature of the lens, at just over 1 1/2 inches in width. The rubber texture is a series of raised ribs that provide an easy grip. The zoom action is smooth, going from 18mm to 135mm in a ninety-degree turn, with only a minor amount of force required to transition between focal lengths. The lens extends as it is zoomed out, adding an extra 1 1/2 inches to its overall length. Zoom creep was not a factor in our testing with this lens.

The focusing ring is mounted near the front of the lens, with a rubber ridged knurl that is easy to turn. The lens really isn't built for manual focus: the ring is only a half-inch in width, and doesn't offer much in the way of travel for manual focus operations (less than ninety degrees of turning action). The ring turns during autofocus operation, and can't be overridden in this mode: you must specifically disable autofocus to override the focus clutch. Note that while the focusing ring turns, the front element does not, so attached filters will stay in place during focusing operations. The focusing ring ends in hard stops at the close-focusing and infinity ends, and we cannot tell if it can focus past infinity.

The optional EW-73B lens hood is petal-shaped with a bayonet-mount, but we can't comment on its usefulness as it doesn't come with our test sample.

Alternatives

Canon EF-S 18-200mm ƒ/3.5-5.6 IS ~$600
For a few dollars more this lens extends your reach to 200mm, and does it surprisingly well; sharpness results for this lens were slightly better than the 18-135mm, though unsurprisingly results for distortion and corner shading are slightly worse, given the range the lens has to cover. Chromatic aberration is handled the same, if not slightly better, than the 18-135mm.

Sigma 18-250mm ƒ/3.5-6.3 DC OS HSM ~$480
For about the same price Sigma offers its own superzoom, with performance that is similar to the Canon 18-135mm for the ranges it covers. It's as sharp if not sharper in the mid-range up to about 80mm; above that, there is some extreme corner softness. CA is handled slightly more poorly, especially at the extremes. Results for distortion follow much the same pattern, and corner shading is handled much better in the Sigma.

Technically, the Sigma 18-125mm ƒ/3.8-5.6 DC OS HSM is a closer match to the focal lengths, but we haven't yet tested this lens.

Tamron 18-270mm ƒ/3.5-6.3 Di II VC LD Aspherical IF Macro AF ~$630
Tamron's superzoom offers the most wide-angle to telephoto reach of any superzoom, and its most recent update offers a new focusing motor technology which we haven't yet reviewed. The Tamron covers the same range and then some compared to the Canon; wide open, the Tamron is almost as sharp as the Canon, but not quite; stopped down, they're on par. The Tamron handles chromatic aberration quite well, at least in the same range of focal lengths as the Canon 18-135mm; light falloff is also fairly negligible, and distortion is typical for the superzoom category.

Conclusion
The Canon EF-S 18-135mm ƒ/3.5-5.6 is available as a kit lens option for several Canon camera bodies, and it makes an excellent all-purpose lens. For the money, it provides very good performance: it doesn't need to be stopped down excessively to provide sharp results, and results for distortion, light falloff and chromatic aberration aren't beyond the pale of what you'd expect in this category of lens.

With the array of lenses available to service this range of focal lengths, there's no clear reason to pick this particular lens over other choices, such as Canon's excellent 18-200mm superzoom, or a 15-85mm & 55-250mm combination (or, for that matter, superzooms offered by Sigma and Tamron). That said, owners of this lens should be more than satisfied with the performance it offers.

Sample Photos

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.