Sigma 17-70mm f/2.8-4 DC Macro OS HSM C Lens Review

Sigma 17-70mm f/2.8-4 DC Macro OS HSM C Performance

At 17mm, sharpness is already outstanding in the centre of the frame and excellent towards the edges of the frame at maximum aperture. This high level of clarity across the frame is maintained as the lens is stopped down to around f/8.

Zooming the lens to 35mm results in similarly high performance in the centre of the frame, but a noticeable reduction in sharpness towards the edges of the frame. At maximum aperture sharpness towards the edges of the frame only reaches fairly good levels. This improves as the aperture is stopped down, peaking between f/8 and f/11 where the clarity towards the edges falls just short of excellent levels.

Finally, zooming the lens to 70mm results in a reduction in overall sharpness. At maximum aperture, clarity still approaches very good levels in the centre of the frame, but only reaches fairly good levels towards the edges. Stopping down to between f/8 and f/11 results in the best compromise between sharpness in the centre and towards the edges of the frame.

Resolution @ 17mm

Resolution @ 35mm

Resolution @ 70mm

How to read our charts The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges. Averaging them out gives the red weighted column. The scale on the left side is an indication of actual image resolution. The taller the column, the better the lens performance. Simple. For this review, the lens was tested on a Canon EOS 600D using Imatest.

Chromatic aberrations are fairly well controlled, just exceeding 0.75 pixel-widths towards the edges of the frame at 17mm and maximum aperture, although this level decreases as the lens is stopped down, or as the lens is zoomed in. This low level should pose few issues, even in images with high contrast edges close to the edges of the frame.

Chromatic aberration @ 17mm

Chromatic aberration @ 35mm

Chromatic aberration @ 70mm

How to read our charts Chromatic aberration is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software. Apochromatic lenses have special lens elements aspheric, extra-low dispersion etc. to minimize the problem, hence they usually cost more. For this review, the lens was tested on a Canon EOS 600D using Imatest.

Falloff of illumination towards the corners of the frame is well controlled for a zoom lens of this aperture and focal length range. At 17mm, the corners of the frame are 1.15 stops darker than the image centre and visually uniform illumination is achieved with the aperture stopped down to f/5.6 or beyond. At 70mm the corners are only 0.747 stops darker than the image centre and f/5.6 will also result in visually uniform illumination.

Reasonably strong barrel distortion can be seen in images take at 17mm. Imatest detected 3.71% barrel distortion at 17mm and 0.791% pincushion distortion at 70mm. Throughout the zoom range, the distortion pattern is uniform across the frame, which should make corrections relatively easy to apply in image editing software afterwards.

A petal shaped hood is supplied with the lens, which does a great job of shading the lens from extraneous light that may cause loss of contrast of flare. Contrast remains good when shooting into the light also.

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