Sigma's 17-70mm f/2.8-4 DC Macro OS HSM lens is an upgrade to the AF 17-70mm f/2.8-4.5 DC Macro lens released in 2006. Designed for the smaller imaging circle of cameras with APS-C sized sensors, it is slightly larger and heavier than its predecessor and has a more complex optical construction. It also includes Sigma's Hyper Sonic Motor (HSM) technology for fast and quiet autofocusing.
The new Sigma 17-70mm f/2.8-4 DC Macro OS HSM lens. (Source: Sigma.)
Covering a 4x optical zoom range equivalent to 25.5-105mm on most compatible DSLRs (or 27.2-116mm on Canon DSLRs), Sigma's latest 17-70mm lens provides an affordable alternative to the kit lenses provided by the camera manufacturers. Not only is it faster than most kit lenses; it's also more solidly built.
Although an optical stabilisation system is built into this lens, it can still be used with DSLR cameras made by Pentax and Sony that include built-in sensor-shift stabilisation. With these cameras, photographers can choose which stabilisation system they wish to use: the camera's or the lens's. When the OS function in the lens is used, the stabiliser in camera body should be switched off.
The maximum aperture of f/2.8 at the wide position and f/4 for the tele end provide a bright image through the viewfinder. In addition, the inclusion of a macro function that focuses to 22 cm and provides a maximum magnification ratio of 1:2.7, makes this lens more versatile than many kit lenses. The 4.7 cm working distance between the front of the lens and the subject adds convenience for close-up work.
The diagram above shows the position of the various lens elements. (Source: Sigma.)
The optical construction comprises 17 elements in 13 groups (compared with 15 elements in 12 groups in the previous lens). There are three aspherical lenses and one Extraordinary Low Dispersion (ELD) glass element to correct for common of aberrations plus a Super Multi-Layer Coating to reduce the effects of flare and ghosting and deliver high-contrast images.
An internal focusing system eliminates front element rotation, allowing angle-critical attachments to be fitted without requiring re-adjustment when the lens is re-focused. An HSM (Hyper-Sonic Motor) drives autofocusing and provides fast and almost silent operation but won't work with Pentax ist* series and K100D DSLR cameras. Full-time manual focusing is also supported. A rounded seven-bladed diaphragm creates an attractive blur in the out-of-focus areas, giving a nice bokeh effect.
Measuring 88.9 mm in length, this lens has a diameter of 79 mm and accepts 72 mm diameter filters. Build quality is excellent; the lens has a ‘quality' look and feel, with the characteristic matte finish of recent Sigma lenses. It looks classy and isn't as prone to dust and fingermarks as you might expect. A zoom lock is provided to prevent unwanted lens creep when the lens is being carried pointing downwards.
The focusing ring, which is approximately 22 mm wide, is located towards the front of the lens. It has an 11 mm wide ridged, rubber coating and rotates through roughly one sixth of a turn when manual focus mode is engaged. On its leading edge is an engraved distance scale in bright white with seven settings in metres and feet, ranging from the closest point of 0.22 m to infinity.
The zoom ring is a 35 mm wide band behind the focusing ring. It has a prominent 21mm wide, ridged rubber grip with a 9 mm wide band behind it that carries the zoom lock plus engraved markings for the 17mm, 24mm, 28mm, 35mm, 50mm and 79mm focal length positions. These are lined up against a dot on the main barrel.
The main barrel carries two sliders, the upper one for switching between AF and MF and the lower one for turning the internal stabilisation system on and off. The mounting plate is solid stainless steel. It carries contacts for the camera interface plus a red reference dot to help users to attach the lens to the camera. The lens is supplied with a petal-shaped hood plus end caps.
Handling
The review lens was a comfortable match to the Canon EOD 40D body we used for our tests. The metal mounting plate fitted snugly, without being either tight or too loose and it was easy to fit and remove the lens when required.
The zoom movement was smooth and positive throughout the focal length range. The zoom lock was never required because the review lens showed no tendency to creep. The inner barrel extends approximately 43 mm as you move the zoom ring from the 17mm position to 70mm. In the process, the maximum aperture changes with focal length as shown in the table below. The minimum aperture remains fixed at f/22.
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Focal length
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17mm
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24mm
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28mm
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35mm
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50mm
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70mm
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Max. aperture
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f/2.8
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f/3.5
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f/4.0
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In MF mode, the focusing ring moves through approximately 25 degrees, which isn't much. However, precise manual focusing was reasonably easy, thanks to the large maximum aperture of this lens. Although this ring rotates during autofocusing, the front element remains motionless so there's no problem when angle-critical attachments are in place.
There's a working distance of approximately 47 mm between the front element and the subject when shooting close-ups. This appears to apply regardless of which focal length setting you use. It's not a true macro lens as it doesn't provide 1:1 magnification. However, its 1:2.7 magnification ratio is close to one quarter life size, which is adequate for shooting flowers and larger insects, such as dragonflies and cicadas.
Performance
The review lens provided a nice, bright view through the viewfinder of the Canon EOS 40D we used for our tests. Autofocusing was generally fast and accurate, even in relatively low light levels - provided the viewfinder was used for shooting - and the AF system was as quiet as you would expect from an ultrasonic motor drive.
Imatest showed pronounced edge and corner softening at the 17mm focal length setting but the differences between centre and edge resolution became gradually less as focal length was increased - although they never completely disappeared. At medium aperture settings, resolution was close to and above expectations for the test camera's potential resolution, which is quite impressive.
We obtained the highest resolution at the 50mm focal length with an aperture of f/5.6 and resolution at all focal lengths was highest several stops down from maximum aperture. The graph below plots the results of our Imatest tests.
Lateral chromatic aberration was mainly low, although it reached into the ‘moderate' band with the 17mm focal length setting. Coloured fringing was evident in shots taken at this focal length, although it was barely visible at longer focal lengths. The graph below shows the results of our Imatest tests.
Vignetting was quite pronounced at 17mm as well, although barely visible at longer focal lengths. Barrel distortion was noticeable in shots taken with the 17mm focal length but became relatively insignificant at 24mm. Contre-jour subjects were handled very well, with very little loss of contrast due to veiling flare.
Bokeh was also attractive in close-up shots at wide lens apertures, where the 47 mm working distance produced excellent results with the 70mm focal length, despite its smaller maximum aperture. Shooting close-ups at 17mm is only worthwhile with reasonably large subjects. And, even then, you need to take account of the pronounced edge softening at wide aperture settings.
The image stabiliser enabled us to use shutter speeds as low as 1/6 second with a focal length of 70mm and obtain more than 80% of acceptably-sharp images. With shutter speeds of 1/4 second, less than 50% of shots in our test sequence of 10 frames were acceptably sharp.
Buy this lens if:
- You want an affordable general-purpose lens to replace a standard kit lens.
- You'd like a lens that requires no readjustment when you fit polarisers and graduated filters.
Don't buy this lens if:
- You require a lens with excellent flatness of field and edge-to-edge sharpness.
- You need true macro capabilities.
IMATEST GRAPHS
SAMPLE IMAGES
How focal length changes the view of the subject. Top row, from left: 17mm, 24mm 28mm. Bottom row, from left: 35mm, 50mm 70mm.
17mm focal length, ISO 200, 1/362 second at f/13.5.
70mm focal length, ISO 200, 1/512 second at f/14.
Contre-jour lighting:17mm focal length, ISO 200, 1/512 second at f/16.
Close-up:17mm focal length, ISO 200, 1/125 second at f/4.
Close-up:70mm focal length, ISO 200, 1/181 second at f/4.
Stabiliser test: 70mm focal length, ISO 200, 1/6 second at f/4.
Vignetting at 17mm f/2.8; ISO 200, 1/362 second.
Vignetting at 24mm f/2.8; ISO 200, 1/362 second
Barrel distortion at 17mm; ISO 200, 1/362 second at f/9.5.
Negligible distortion at 35mm; ISO 200, 1/181 second at f/8.
Sample shot at 17mm; ISO 200, 1/250 second at f/8.
100% enlargement of a section of the above image showing noticeable coloured fringing and edge softening.
Sample shot at 35mm; ISO 200, 1/250 second at f/9.5.
100% enlargement of a section of the above image showing slight coloured fringing.
Sample shot at 70mm; ISO 200, 1/362 second at f/9.5.
100% enlargement of a section of the above image showing minimal coloured fringing.
24mm focal length, ISO 200, 1/181 second at f/8.
50mm focal length, ISO 200, 1/181 second at f/8.