Sigma 18-35mm f/1.8 DC HSM A Lens Review

Sigma 18-35mm f/1.8 DC HSM A Performance

At 18mm and maximum aperture, sharpness in the centre of the frame is already outstanding with clarity towards the edges of the frame being just a shade short of excellent, which is impressive for a lens with an f/1.8 maximum aperture. Stopping down a little improves sharpness further, with peak performance being achieved between f/2 and f/2.8 for this focal length.

Zooming to 24mm results in a slight reduction in sharpness, although this lens is still very sharp at this focal length. At maximum aperture sharpness is still outstanding in the centre of the frame and the clarity towards the edges has fallen to very good levels. Stopping down to f/4 results in peak performance across the frame for this focal length, with outstanding sharpness being achieved from edge to edge.

Finally, at 35mm there is a slight further reduction in overall sharpness, although clarity is still very good across the frame at maximum aperture. Peak sharpness across the frame is achieved between f/4 and f/5.6 for this focal length.

Resolution @ 18mm

Resolution @ 24mm

Resolution @ 35mm

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 remarkably well controlled for a zoom lens with such a bright maximum aperture. The strongest fringing can be found towards the edges of the frame at maximum aperture at 24mm, although the level of CA is still low enough to cause very few issues here.

Chromatic aberration @ 18mm

Chromatic aberration @ 24mm

Chromatic aberration @ 35mm

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 Canon EOS 600D using Imatest.

Falloff of illumination towards the corners of the frame isn't as strong as you may expect from a lens with a fast f/1.8 aperture throughout the zoom range. At 18mm and f/1.8 the corners are only 1.25 stops darker than the image centre and at 35mm the corners are only 1.5 stops darker. Visually uniform illumination is achieved with the aperture stopped down to f/4 or beyond throughout the zoom range.

Distortion at both ends of the zoom is noticeable, but not overly strong with 2.71% barrel at 18mm and 1.06% pincushion at 35mm. The distortion pattern is uniform across the frame, so should be relatively straightforward to correct in image editing software afterwards.

A petal-shaped hood is supplied with this lens, which does a reasonable job of shielding the lens from extraneous light that may cause loss of contrast or flare. Even when shooting into the light, contrast remains good.

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