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

SLRgear Review
August 20, 2012
by Andrew Alexander

Announced in June of 2012, the Canon EF-S 18-135mm ƒ/3.5-5.6 IS STM was designed to improve performance generally and more specifically in video applications. With a new STM ("Stepping Motor") autofocus mechanism, autofocus performance is both faster and quieter.

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 changes as you zoom:

The EW-73B petal-shaped lens hood is available for but does not ship with the lens. The lens is available now for around $600.

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 28mm, with dramatic distortion in the corners (1%, fairly significant). After 28mm, 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. Pincushion distortion is consistent from 35mm to 135mm (-0.5%), and post-processing would be required to correct for these effects.

Autofocus Operation
The Canon EF-S 18-135 ƒ/3.5-5.6 IS STM employs an autofocus system called a "Stepping Motor", which allows the lens to provide smooth and quiet autofocus operation, particularly during video capture. The lens took well under a second to focus from infinity to close-focus. While the lens does not offer full-time manual operation, it is possible to adjust focus manually without switching to manual focus mode by half-pressing the shutter button (this engages autofocus, which you can then override manually). Attached 67mm filters will not rotate during focus operations, making life easier for polarizer users.

Macro
The Canon EF-S 18-135mm offers average macro performance: a minimum close-focusing distance of 39cm (1', 4") and a magnification of 0.28x.

Build Quality and Handling
(At this point, perceptive readers may note a strong similarity between this review and that of the predecessor EF-S 18-135mm ƒ/3.5-5.6 IS. While the arrangement of lens elements has been redesigned, the new STM focusing motor has been added, and the 6-bladed aperture has been replaced by a 7-bladed aperture, the two lenses feel, and produce results, which are strikingly similar.)

At almost 17 ounces, the Canon EF-S 18-135mm ƒ/3.5-5.6 IS STM 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, is 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''). There is a very slight sound when image stabilization is active, but mostly only audible when your ear is next to the lens. We didn't have a chance to do a proper image stabilization test with this lens, but we will add one to this review in the future.

The large zoom ring is the prominent feature of the lens, at just over 1 1/4 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 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 plastic ridged knurl that is easy to turn. The ring is a half-inch in width: With the new STM focusing system, the lens focuses electrically, meaning there is no direct mechanical connection between turning the ring and the resulting focus. The focusing ring will turn forever in either direction, and offers a good amount of resistance for manual focus.

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 18-135mm ƒ/3.5-5.6 IS ~$400
The previous version of the 18-135mm ƒ/3.5-5.6 IS is very similar to the new STM version: optically, they provide nearly identical test results. The only real differences are the new STM motor and an additional diaphragm blade to make up the aperture.

Canon EF-S 18-200mm ƒ/3.5-5.6 IS ~$700
For a few dollars more you can get 65mm more "reach" to your telephoto end: optically, it's about the same quality, but you don't get the new STM focusing motor.

Sigma 18-125mm ƒ/3.8-5.6 DC OS HSM ~$350
If all you are looking for is a lens with the 18-135mm focal length, Sigma provides a similar lens complete with optical stabilization and an HSM focusing motor. We haven't tested the OS HSM model, but we did test the previous model, which provided almost as good performance optically as the Canon 18-135mm.

Conclusion
The 18-135mm zoom lens occupies an interesting position when it comes to consumer zoom lenses: it's not as long as the more convenient superzooms (18-200, for example), but it's longer and more capable than an 18-55mm kit lens. Canon's made an interesting decision to load the 18-135mm lens with its new STM motor.

Regarding the lens' actual performance, it's very good but not amazing - you'll need to go to the more expensive L-glass if you'd like some amazing. But for what it does, it does it very well, meaning you get what you pay for and then some.

Additional Links

• Shawn Barnett's review of the Canon T4i and 18-135mm STM
• Canon's website for this lens

Product Photos

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.