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.

That's quite an achievement for a lens that also includes optical image stabilisation. Other finery includes two of Sigma's FLD glass elements, which the company claims provides the very best low-dispersion performance to reduce chromatic aberration while enabling maximum light transmission.



Link: Techradar