Best zoom lens upgrades

It's not often that an independently manufactured lens costs more than some camera manufacturers' own-brand rivals, but this Sigma is a bit special. Unlike the Canon and Nikon lenses on test, the Sigma 17-50mm boasts a fast, constant aperture of f/2.8 that remains fixed throughout the zoom range.

Street price : around £575

Read the full Sigma 17-50mm f/2.8 EX DC OS HSM review

Image tests

Sharpness Test

Best dslr zoom lens upgrades: 8 tested

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At all focal lengths, the Sigma optic shows good sharpness at the centre and middle frame, but there's a slight softening towards the edges.

Fringing test

Best zoom lens upgrades

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At all focal lengths, there's a little sign of fringing at the centre frame, but towards the edges there's a mild influence of blue and red.

Distortion test

Best zoom lens upgrades

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At 17mm and 21mm there's slight barrel distortion, and above this, pinch distortion is only minimal and barely visible.

Image test verdict

Sharpness at all focal lengths, and especially at the centre of the frame, is very good. Fringing and distortion are also minimal.

Score: 4/5