Canon EF-S 15-85mm f/3.5-5.6 IS USM

Name: Canon EF-S 15-85mm f/3.5-5.6 IS USM
Brand: Canon
Rating: 9.1 (21 reviews)

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Lens Review
Specifications
Description

15-85mm	$799 average price

Lab Test Results

Canon 20D

Blur
Chromatic Aberration
Vignetting
Geometric Distortion

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Buy the Canon EF-S 15-85mm f/3.5-5.6 IS USM

SLRgear Review
November 10, 2009
by Andrew Alexander

The Canon EF-S 15-85mm ƒ/3.5-5.6 IS USM was released in September of 2009, as a replacement for the EF-S 17-85mm ƒ/4-5.6 IS USM.

With its EF-S specification, the lens was designed specifically to fit the APS-C sensor, making it incompatible with film or full-frame digital camera bodies. The lens offers an equivalent 24-136mm field of view. 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:

Focal length	15mm	24mm	35mm	50mm	70mm	85mm
Max. aperture	ƒ/3.5	ƒ/4	ƒ/4.5	ƒ/5	ƒ/5.6	ƒ/5.6
Min. aperture	ƒ/22	ƒ/29	ƒ/29	ƒ/32	ƒ/36	ƒ/36

The lens takes an optional petal-shaped lens hood, 72mm filters, and is available now for approximately $800.

Sharpness
The 15-85mm shows very sharp results, even at its widest apertures. Used wide open at its widest angle (ƒ/3.5 at 15mm) we note a very sharp sweet spot of sharpness in the center, between 1 and 1.5 blur units. There is very light corner softness, approaching 2 blur units in the corners. As the lens is stopped down at 15mm this corner softness reduces, at the expense of the central sharpness; however, we're still looking at tenths-of-blur units, and by ƒ/5.6-8, the lens shows on average just less than 1.5 blur units across the frame.

The lens also shows excellent performance throughout the mid-range and telephoto range of focal lengths. For the most part the results are similar throughout, a little less than 1.5 blur units in the center and less than 2 blur units in the corners. As before, stopping down improves sharpness performance: by ƒ/8, the lens shows almost tack-sharp results, at just over 1 blur unit at most focal lengths.

Diffraction limiting sets in around ƒ/11, but sharpness is still good to even ƒ/16, showing 2 blur units or less across the frame. By ƒ/22 the lens begins to show somewhat soft results - at least 3 blur units, unevenly across the frame - and it gets softer as the lens is stopped down further. Fully stopped-down performance, up to ƒ/36 by 85mm, is very soft - 6 blur units.

Chromatic Aberration
CA is well-controlled by the lens, particularly between 24mm and 70mm. At 15mm and 85mm, chromatic aberration results are statistically significant. At 15mm CA shows up a bit in the corners regardless of the aperture; at 85mm, CA is more prominent as the lens is stopped down.

Shading (''Vignetting'')
Corner shading is fairly prominent with this lens. At 15mm, corner shading is a factor regardless of the aperture selected, but is most noteworthy when used wide open at ƒ/3.5; at this setting, the corners are almost a full stop darker than the center. This improves to a half-stop by ƒ/5.6, and evens out at 1/3EV by ƒ/11 or smaller - thus, corner shading is always a factor.

At other focal lengths, corner shading is only a factor at ƒ/8 or wider. At these settings we see a half-stop or less when the lens is used wide open at 24mm or 35mm; at other settings, corner shading is not an issue.

Distortion
As with most all-in-one zoom lenses, distortion results are complicated. Distortion is typically high for the widest angle setting (15mm) - almost +1% barrel distortion in the corners, and +0.5% on average. This barrel distortion evens out by about 20mm, where the corners then go towards pincushion distortion (-0.5%) at 24mm. After this focal length, there is some convergence, but distortion never comes to zero on either spectrum.

Autofocus Operation
With USM focusing, the 15-85mm ƒ/3.5-5.6 is very fast to focus, and nearly silent. Focusing from infinity to close-focus took just under one second. Autofocus results can be overridden by just turning the focus ring. The front element doesn't rotate during focus operations.

Macro
Macro performance is average - 0.21x magnification, with a close-focusing range of 35cm (a little over one foot).

Build Quality and Handling
For fit and finish, the 15-85mm certainly doesn't measure up to Canon's pro-grade glass, but then, the price tag doesn't measure up either. The lens construction may be plastic, but for its size it's fairly heavy - 575 grams (over 20 oz) - suggesting a durable interior chassis. The 15-85mm has a few more trimmings than less expensive lenses, including a distance scale set behind a plastic window, showing distance in feet and meters. There are no depth-of-field or infrared index indicators. There are two switches: one enables image stabilization, the other enables autofocus on the lens.

The prominent zoom ring (1 1/8'' wide) is composed of a durable rubber, with a texture of segmented raised ribs. The ring takes only a turn of approximately 45 degrees to go through its entire range of focal lengths. The ring is fairly stiff and resistant to zoom creep. The design of the lens is such that as the lens extends its focal length the barrel physically extends, adding a further 1 5/8'' to the overall length at 85mm.

The focus ring is much less prominent than the zoom ring - only 1/4'' wide - and is positioned rather at odds with much of the Canon lineup by placing it before the zoom ring rather than on the other side of it. The ring uses the same rubber ribbed texture, and offers a substantial range of movement - about ninety degrees of turning action. Either end of the focusing spectrum is bounded by a soft stop, and the lens will focus slightly past infinity. The front element doesn't rotate during focus.

The main draw for this lens is its image stabilization feature, which Canon advertises will allow a shutter speed four stops slower than required for a shake-free image. Your mileage may vary with regard to image stabilization, but in our limited testing it does work as advertised. In-lens stabilization has the advantage over in-body stabilization systems in that you can see the effect working through the viewfinder, though with live view systems gaining prominence (and stabilization results being visible through them at the time of shooting), this technological advantage may become more marginal.

The optional EW-78E lens hood is petal-shaped, and attaches to the lens with a bayonet mount. The lens hood can be reversed and mounted on the lens for easy storage. The interior of the hood is flocked to reduce stray light from hitting the front element.

Alternatives

Canon EF-S 17-85mm ƒ/4-5.6 IS USM ~$520
The new 15-85mm is definitely an improvement over the 17-85mm, offering sharper results at every focal length as well as distinct improvements with regard to chromatic aberration, corner shading and distortion. As well, you get 2mm wider, and a half-stop faster at the wide end.

Sigma 17-70mm ƒ/2.8-4.5 DC Macro ~$350
While not offering the same level of wide-angle as the Canon (17mm instead of 15mm), the Sigma offers a slightly faster lens with macro capability (0.43x magnification). The lenses are both quite sharp, with a nod to slightly sharper performance from the Canon; in the other categories (CA, corner shading and distortion) the Sigma fares slightly better. The Sigma doesn't feature image stabilization, though the price tag is lower.

Tamron 17-50mm ƒ/2.8 XR Di II LD Aspherical IF SP AF ~$450
One of our perennial favorites, the Tamron 17-50mm is neither as wide or as long as the Canon, though it does offer a constant ƒ/2.8 aperture, and vibration-controlled (VC) model offers image stabilization, though at the time of writing, the Canon-mount model is not yet shipping from Tamron. Optically, the Tamron is as sharp or sharper than the Canon at the same focal lengths and apertures, and the same applies to resistance to chromatic aberration. Corner shading is also better with the Tamron, though distortion is about the same.

Conclusion
With very good, if not excellent results for sharpness, resistance to chromatic aberration, distortion and corner shading, Canon has released an excellent general purpose lens. If you were looking for an upgrade to a kit lens and can't decide between wide angle and telephoto, this could be an excellent choice.

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.