The EF-S 15-85mm f/3.5-5.6 IS USM zoom lens is one of two lenses announced by Canon in September when details of the EOS 7D were revealed. It's offered with the 7D body in the Platinum kit and covers a wide-to-telephoto zoom range of roughly 5.6 times. A built-in image stabiliser claims a four f-stop advantage in shutter speed settings and an ultrasonic motor (USM) provides quick and quiet autofocusing.
Designed specifically for EOS EF-S mount bodies, this lens covers wide angle and portrait focal ranges. Its optical system is made from lead-free glass and consists of 17 elements in 12 groups. High precision aspherical lenses have been used to correct aberrations, with one UD (ultra-low dispersion) element to minimise chromatic aberrations.
Canon's EF-S 15-85mm f/3.5-5.6 IS USM zoom lens. (Source: Canon.)
Canon's Super Spectra coating have been used to minimise the effects of flare and ghosting and achieve accurate colour rendition and natural-looking contrast in images. The seven-bladed iris diaphragm closes to a circular aperture for attractive bokeh, while the ring type USM allows full-time manual focus override enabling users to fine-tune focus manually without having to switch out of AF mode.
Although constructed mainly from plastic, the build quality of the review lens was very good - and not unlike the quality of the EF-S 18-135mm f/3.5-5.6 IS lens, which was released at the same time (and which we have also reviewed). The stainless steel mounting plate provides a secure fit on the camera body it is attached to and the two inner tubes fit together snugly without any slackness. Internal focusing allows the use of angle-critical attachments like polarisers and graduated filters.
The IS (image stabilisation) system can compensate for both vertical and horizontal movements and includes automatic panning and tripod detection. Consequently, only two settings are provided: on and off. When the slider is set to on, the stabiliser engages when the shutter button is half-pressed.
Unlike many zoom lenses, the focusing ring on this lens is located close to the mounting plate. It's approximately 8mm wide with a finely-ridged rubber coating. Behind it is a distance scale, which tucks in under the flash housing and can, consequently, be difficult to read. Slider switches on the side of the lens barrel handle AF/MF switching and turn the stabiliser on and off.
In front of the focusing ring is a 40mm wide zoom ring with a 28mm wide, thickly-ridges rubber collar. The trailing edge of this ring is engraved with focal length markings for 15mm, 24mm, 35mm, 50mm, 70mm and 85mm. No zoom lock is provided and none appears necessary as we noticed no tendency for zoom creep in the course of our tests.
The lens is supplied with end caps but, in line with Canon's normal practice for ‘budget' lenses, no lens hood is provided. (The optional EW-78E lens hood has an RRP of $75.)
Handling
Being designed for the EOS 7D this lens fits the camera body very comfortably and is well balanced in the hands. Both focusing and zoom rings showed no slack yet moved smoothly and positively. The zoom ring moves through approximately 45 degrees of rotation and we found the markings on the lens barrel to be accurate for the indicated focal length settings.
Zooming in from 15mm to 85mm extends the inner barrel by approximately 40 mm. The maximum and minimum apertures change with focal length as follows:
|
Focal length
|
Max. aperture
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Min. aperture
|
|
15mm
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f/3.5
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f/22
|
|
24mm
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f/4.0
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f/25
|
|
35mm
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f/4.5
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f/29
|
|
50mm
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f/5.0
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f/32
|
|
70mm
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f/5.6
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f/36
|
|
85mm
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f/5.6
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f/36
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The focusing ring moves through just over 45 degrees in MF mode, making precise manual focusing relatively easy. No rotation was observed during autofocusing and the front element remains motionless.
Performance
The built-in USM focusing motor provided fast and very accurate autofocusing and near-silent operation. When the viewfinder was used for framing shots, AF accuracy was generally very good and we found little tendency for the lens to hunt in a wide range of light levels. Live View autofocusing with the 7D body was, as expected, slow.
The image stabiliser was slightly better than we found in the EF-S 18-135mm lens. It enabled us to use shutter speeds as slow as 1/6 second with a focal length of 85mm, which is slightly better than Canon's claim of four f-stops stabilisation advantage. More than 90% of shots taken in our stabilisation tests at shutter speeds between 1/10 and 1/4 second were acceptably sharp at between three and four f-stops below the shutter speeds we would expect from an unstabilised lens.
Imatest showed resolution to be much more consistent across different focal lengths than we found with the EF-S 18-135mm lens. Edge softening at wide aperture settings was also somewhat less - although still noticeable, particularly with shorter focal lengths. The 15mm focal length produced the highest overall resolution with best results at between f/5.0 and f/6.3. The graph below shows the results of our Imatest tests, based on JPEG files.
Lateral chromatic aberration varied with focal length setting, with the lowest levels at the 35mm and 50mm focal lengths and the highest at 15mm and 85mm. It is very well controlled in the middle focal length settings but rises into the ‘moderate' level at 15mm and 85mm. The graph below shows the results of our Imatest tests.
Rectilinear distortion was also a problem at the shorter focal lengths, with barrel distortion being quite obvious at 15mm. Distortion became negligible by 35mm and the pincushioning that could just be discerned at 85mm was slight enough to be negligible.
Vignetting could be seen in shots taken at wide apertures with all focal lengths. (No lens hood or filter was used for our test shots.) It was most pronounced with the 15mm and 85mm focal lengths, where it equated to approximately 1EV, and least obvious at 35mm. Stopping down to f/5.6 removes most of the darkening with the shorter focal lengths but f/8 or f/9 is required to remove it at the 85mm setting.
Backlit subjects were handled very well, with very little loss of contrast due to veiling flare. Bokeh in close-up shots was slightly more attractive than we found with the EF-S 18-135mm lens. However, this lens is unsuitable for macro photography as it can only focus down to 35 cm.
Buy this lens if:
- You want a high-resolution, general-purpose lens to match the 7D body.
- You'd like a lens that requires no readjustment when you fit polarisers and graduated filters.
- You want effective image stabilisation.
Don't buy this lens if:
- You require excellent flatness of field.
- You can't tolerate vignetting.
- You need close focusing and macro capabilities.
IMATEST GRAPHS
SAMPLE IMAGES
15mm focal length, ISO 100, 1/125 second at f/7.1.
85mm focal length, ISO 100, 1/125 second at f/6.3.
85mm focal length, ISO 100, 1/160 second at f/5.6.
85mm focal length, ISO 100, 1/1579 second at f/5.6.
15mm focal length, ISO 100, 1/125 second at f/6.4.
Enlarged crop from the above image showing edge softening and coloured fringing.
Image stabilisation test; hand-held at 85mm focal length, ISO 100, 1/4 second at f/5.6.
Distortion at 15mm: ISO 100, 1/125 second at f/7.1.
Distortion at 85mm: ISO 100, 1/166 second at f/5.6.
Vignetting at 15mm: ISO 100, 1/1328 second at f/3.5.
Vignetting at 35mm: ISO 100, 1/790 second at f/4.6.
Vignetting at 85mm: ISO 100, 1/664 second at f/5.6.