Canon EF-S 17-85 mm F4-5.6 IS USM Lens Review...

Canon EF-S 17-85mm 1:4-5.6 IS USM review
Andy Westlake, January 2008

First announced in August 2004 to coincide with the launch of the EOS 20D, the EF-S 17-85mm F4-5.6 IS USM is Canon’s logical upgrade from the basic 18-55mm kit lens supplied with its APS-C dSLRs. With a 35mm-equivalent focal length of 27-136mm, it covers a decent wideangle to telephoto range, making it a useful ‘walkaround’  lens which will cover a wide range of photographic opportunities. It also sports Canon's 2nd-generation optical image stabilizer, which allows hand-holding at slower shutter speeds than usual before the image-degrading effects of camera shake become apparent. This lens is clearly an attempt by Canon to replicate the success of their earlier 28-135mm F3.5-5.6 IS USM, which gained a strong reputation as an excellent performer on 35mm film; so is the 17-85mm up to scratch?
Headline features
27-136mm equivalent focal length range; F4-5.6 maximum aperture Optical image stabilisation – 3 stops  Ring-type USM focusing with full-time manual override EF-S mount for Canon APS-C dSLRS only
Angle of view
The pictures below illustrate the focal length range from wide to telephoto:

17mm (27mm equivalent) 85mm (136mm equivalent)
Canon EF-S 17-85mm 1:4-5.6 IS USM specifications
Street price • US: $520
• UK: £360
Date introduced August 2004
Maximum format size APS-C
Focal length 17-85mm
35mm equivalent focal length
(APS-C) 27-136mm
Diagonal Angle of view (APS-C)
78º - 18º
Maximum aperture F4-5.6
Minimum aperture F22-32
Lens Construction
• 17 elements/12 groups
• 1 Aspherical element
Number of diaphragm blades 6
Minimum focus 0.35m
Maximum magnification
0.20x at 85mm
AF motor type • Ring-type Ultrasonic Motor
• Full-time manual focus
Focus method Internal
Image stabilisation
• 3 stops
• Single mode (no panning)
Filter thread • 67mm
• Does not rotate on focus
Supplied accessories
• Front and rear caps
Optional accessories • EW-73B Hood,
• LP1116 Case
Weight 475 g (16.7 oz)
Dimensions 78.5 mm diameter x 92 mm length
(3.1 x 3.6 in)
Lens Mount Canon EF-S only
Other Supplies distance information for E-TTL II flash metering
* Supplied accessories may differ in each country or area
Foreword / notes
If you're new to digital photography you may wish to read some of ourDigital Photography Glossary before diving into this article (it may help you understand some of the terms used).
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Dpreview use calibrated monitors at the PC normal gamma 2.2, this means that on our monitors we can make out the difference between all of the grayscale blocks below. We recommend to make the most of this review you should be able to see the difference (at least) between X,Y and Z and ideally also A, B and C.
Design

The 17-85mm is a member of Canon’s  family of mid-range zooms, and as such the build quality is a clear step up from the lightweight plastic of the 18-55mm kit lens, if not quite up to the standards of Canon’s professional-level ‘L’ series. The lens mount is metal, and the barrel plastic; unfortunately it's not quite as solid as Canon's other mid-range zooms such as the 28-135mm F3.5-5.6 IS USM, and the plastic feels a bit thin and creaky, and deforms a little under pressure, which isn't terribly reassuring. However to its credit, and unlike the 18-55mm, the 17-85mm does have a proper manual focusing ring and distance scale. At 475g in weight, this lens is also perfectly light enough to carry around with you all day long.
On the camera

The lens feels well-balanced on both the small EOS Rebel XTi/400D and weightier EOS 40D. Controls are well-placed; the zoom ring is positioned perfectly for operation by the thumb and forefinger, with the slim manual focus ring then operated by the middle finger. When held in landscape format, only a slight shift in grip is required to reach either the IS switch, or the AF/MF switch on the side of lens barrel with the thumb, although they are somewhat less easy to find with the camera in portrait orientation. Overall, a well thought out, balanced design.
Lens body elements

The lens uses Canon’s all-electronic  EF-S mount. The ‘S’ designation means it is designed exclusively for APS-C digital SLRs, and the grey rubber ring on the rear prevents it from fitting on 1.3x or full-frame cameras. Owners of Canon’s pre-EF-S era APS-C models (i.e. the D30, D60 or 10D) beware: this lens won't fit those cameras either.

The filter thread is 67mm. It does not rotate on autofocusing, which should please filter users.
A bayonet-type mount is provided for the petal-style EW-73B hood, but the bad news is that Canon don’t supply this in the box, instead it’s a pricey optional extra. Shame on Canon; I would argue that the lens hood should always be a standard accessory.

The zoom ring rotates 60 degrees anti-clockwise from wide to telephoto. The ribbed rubber grip is 20mm wide, and the zoom action smooth and precise.
The front element extends 26mm on zooming, and stays solidly positioned when set to 85mm, with no lateral play whatsoever. It can be made to wobble around a bit at shorter focal lengths, but this is unlikely to be a problem in real-life use.

The 9mm-wide focus ring rotates 90 degrees clockwise from infinity to 0.35m. It does not rotate during autofocus, and the full-time manual system allows tweaking of the focus even when the lens is set to AF. Again the action is smooth and precise; unlike the kit 18-55mm, this is a lens you can manually focus perfectly happily. Very nice.
A distance scale is provided with markings in both feet and meters, but there’s no depth-of-field markings or infra-red correction mark. The focus ring travels slightly past the infinity mark, apparently to allow for the effects of ambient temperature variations.
Two small but positive switches adorn the side of the lens barrel; the lower turns the image stabiliser on or off, and the upper switches between autofocus and manual focus. The IS switch is the larger of the two, and slightly recessed to prevent accidental movement. Both are within easy reach of your left thumb with the camera up to your eye.
Reported aperture vs focal length
Here we show the maximum and minimum apertures reported by the camera at the marked focal lengths.
Studio Tests
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NOTE the line marked 'Nyquist Frequency' indicates the maximum theoretical resolution of the camera body used for testing. Whenever the measured numbers exceed this value, this simply indicates that the lens out-resolves the sensor at this point - the calculated MTF values themselves become meaningless.
The 17-85 gives what can only be described as mixed results in our studio tests. Its performance is rather disappointing at wideangle, where it serves up a witch’s brew of corner softness, green/magenta chromatic aberration, barrel distortion and light falloff; however it becomes very much better at telephoto, and in the 35-70mm range is really very good indeed.
Resolution Best results are obtained in the normal to telephoto range, where the lens gives consistently high MTF readings from 35mm to 85mm. Unfortunately things go downhill towards wide angle, especially in the corners which are distinctly soft at 17mm.  The lens appears to be optimized to perform wide open at all focal lengths, and shows no systematic increase in quality on stopping down to smaller apertures; at F11 and beyond the sharpness drops rapidly due to diffraction, as expected.  We’d certainly advise against using apertures much smaller than F16, except in those rare cases where extreme depth of field is important.
Chromatic Aberration Chromatic aberration is distinctly worst at 17mm, where the almost-overlapping red and blue lines indicate green-magenta fringing, which is visually the most intrusive (see also the example below). The story is similar at 24mm, but at 35mm and beyond CA becomes much less of an issue.
Falloff We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the centre. Once again, the lens gives a poor showing at 17mm, with 1.7 stops of falloff wide open; you’ll need to stop down to around F8-11 to reduce it completely below perceptible  levels. However aside from that, there’s nothing too much to worry about, with just a hint of falloff wide open at 24mm.
Distortion
The 17-85mm also shows unusually high barrel distortion at wide angles, measuring a whopping 2.4% at 17mm. This is also not ‘pure’ barrel distortion but a more complex ‘wave’-type, with the barrel effect most pronounced towards the centre, then pinched in again towards the edges, which makes it relatively difficult to correct in software. At 24mm and longer the pattern changes to pincushion, and at its worst reaches -1.5% at 50mm; again pretty pronounced, and readily visible if the image should contain straight lines.
Macro Focus

A decidedly average performance here, with an image area of 10.5cm x 7cm, equating to a maximum magnification of 0.21x, close to Canon’s specified 0.2x. This is achieved at 85mm and the closest focus distance of 35cm, giving a working distance of about 19cm between the subject and the front of the lens.
The image shows strong barrel distortion, soft corners and yellow/blue chromatic aberration; this is a poor result, far worse than the kit 18-55mm and certainly no substitute for a true macro lens.
Macro - 105 x 70 mm coverage
Distortion: Strong barrel
Corner softness: Poor
Focal length: 85mm (135 mm equiv)
Specific image quality issues
Chromatic Aberration
By far the most problematic aspect of this lens’s performance in real-life shooting is chromatic aberration at wide angle. Strong green/magenta fringing is visible in 17mm shots even at modest magnifications, and stopping down the aperture has no effect. It remains a problem at 24mm, but is much less of an issue at longer focal lengths. This type of chromatic aberration can be ‘corrected’ in software, and particularly efficiently if you’re prepared to shoot RAW. For instance, using our standard converter, Adobe Camera RAW, processing with -30 Red/Cyan and +30 Blue/Yellow effectively eliminated CA.

100% Crop, left of frame 17mm F8.0, EOS 400D
Aberration correction using Digital Photo Pro (updated July 2008)
With version 3.4 of their free RAW conversion software Digital Photo Pro (DPP), Canon have added lens aberration correction support for the 17-85mm IS. This allows RAW shooters to eliminate (or at least reduce) the effects of chromatic aberration, falloff (which Canon refer to as 'peripheral illumination'), geometric distortion, and 'color blur' (which appears to be Canon's term for axial chromatic aberration).
DPP's aberration correction works by using profiles specific for each lens, making the software fairly straightforward to use, and with no major need to play with the slider settings (except perhaps for the occasional small tweak). Here's an example of chromatic aberration correction using default settings for the image above; DPP has effectively removed the ugly green and magenta fringing completely.

100% Crop, left of frame 17mm F8.0, EOS 400D
The corrections for peripheral illumination and geometric distortion are equally impressive; in the example below we can see clear correction for falloff even at F8 (however in more extreme cases, this will come at some cost to image noise). More importantly, the strong barrel distortion at 17mm is also well corrected; this is most obvious in the bowed line along the lower edge of the frame, but verticals also become properly parallel. Of course there's no such thing as a free lunch, and this kind of software distortion correction will require some localized 'stretching' of the image data resulting in a loss of resolution in affected regions, but overall this is a small price to pay when distortion is otherwise objectionable.
EOS 400D, 17mm F8

Original Peripheral Illumination PI + Distortion
Optical Image Stabilization
The 17-85mm features Canon's second generation optical image stabilization, which claims to allow handholding at shutter speeds 3 stops lower than usual before blur from camera shake becomes apparent. It's near-silent in use, with just a quiet whirring noise when operational, and with distinct clicks when it activates and deactivates, presumably due to the lens elements moving in and out of the 'at rest' position.
We've generally found the units in SLR lenses to be pretty effective in real-world use, and to quantify this, we subjected the 17-85mm to our studio image stabilization test at both wideangle and telephoto. With its effective focal length range of 27-136mm, we'd normally expect to be able to get good results handheld at 1/30 sec at wideangle, and 1/160 sec at telephoto without image stabilization. The subject distance for these tests was approximately 2.5m.

17mm IS OFF 85mm IS OFF
17mm IS ON 85mm IS ON
Here we can see clearly the effectiveness of Canon's in-lens IS unit. At the wideangle end and shutter speeds of 1/6 sec, IS is delivering 70% critically sharp shots, compared to just 20% without. Even at very slow shutter speeds of 0.3 sec, IS is giving usable images with no more than mild blur 80% of the time, compared to just 10% without.
Performance is even better at the telephoto end; at 1/20 sec, IS gives 100% sharp images, in contrast to just 10% without IS. Even at 1/10 sec, 90% of images are usable (just mild blur) with IS on, compared to 10% with it switched off. Impressive stuff, the image stabilization is clearly delivering the goods here.
Conclusion - Pros
Decent build quality - much better than any of Canon's 18-55mm kit lenses Very useful focal length range, almost ideal for a walkaround lens Highly effective image stabilisation Excellent autofocus and manual override Consistently high image quality across almost all of the range
Conclusion - Cons
Poor performance at wideangle, with marked barrel disortion, high levels of light falloff, and intense green/magenta chromatic aberration Slow maximum aperture Very average close-up performance
Overall conclusion
The EF-S 17-85mm is a major step up from Canon’s EF-S 18-55mm F3.5-5.6 II kit lens, adding an extended focal length range, image stabilisation, fast and silent autofocus with a decent manual focus option, and substantially improved build quality. This makes it, at first sight at least, an ideal all-in-one ‘walkaround’ lens for Canon’s APS-C SLRs, which will cover the majority of photographic opportunities when travelling light.
And to a great extent it delivers on this potential, with good imaging performance over much of its range, especially in that extended telephoto region, plus effective image stabilisation which works as promised. But there’s no getting away from this lens’s Achilles’ Heel, which is comparatively poor optical performance at the wideangle end. Most intrusive is the green/magenta chromatic aberration at 17mm, which is highly visible in a wide variety of shooting situations. Now if you’re only planning on viewing files on screen or making small prints, this may not be a huge problem, but if you are making large prints or viewing at 100% it’s a clear issue. However it can be effectively overcome if you are prepared to shoot in RAW and eliminate the CA in post-processing, using either Canon's Digital Photo Pro (v3.4 or later) or third party software such as Photoshop.
The lens also exhibits significant barrel distortion at 17mm, making it far from ideal for photographing architecture, except perhaps Gaudi in Barcelona, or City Hall amd the ‘Gherkin’ in London. And with its relatively slow maximum aperture, this is also not an ideal lens for low light/indoor photography of people or other moving subjects. It’s important to appreciate that while image stabilisation will allow hand-holding at slower shutter speeds than usual without suffering image degradation due to camera shake, those shutter speeds are still slow, and moving subjects will therefore still be blurred. Likewise the slow maximum aperture will limit flash range, so for this kind of photography, a faster zoom or prime lens will be a better option.
So overall the judgement to be made is whether the attractive feature set of this lens offsets the negatives, and most importantly the problems with distortion and chromatic aberration at wide angle. If you shoot primarily towards the telephoto end, this lens will reward you with excellent results, but if your interests tend more towards the wideangle end of the spectrum and you don't want to shoot RAW, then it may well be a good idea to look away now. However overall it must be said this lens is really rather enjoyable to use; the zoom range is very flexible, the autofocus fast and silent, and the image stabilizer highly effective. So in balance its advantages probably outweigh its disadvantages, and despite its faults this lens is ultimately still one of our favourites for Canon's APS-C dSLRs. Therefore, as long as its limitations are appreciated, it just about earns our recommendation.
GOOD FOR:
Walkaround lens for outdoor shooting and travel use.
NOT SO GOOD FOR:
Indoor available light or flash shooting.
Architectual photography where distortion would be a problem.
Detail Rating (out of 10)
Build quality 7.5
Ergonomics & handling 8.0
Features 8.5
Image quality 7.5
Value 7.0
Recommended (with reservations)

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Samples Gallery
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Canon 17-85mm EF Samples Gallery - Posted 28th January 2008