The Sigma 17-40mm F1.8 DC Art for Canon RF brings an F1.8 zoom to Canon's APS-C mirrorless cameras, something Canon itself does not make. With the 1.6x crop it covers a 27.2-64mm equivalent range, from a moderate wide angle to a short portrait length, and it keeps F1.8 the whole way. On an EOS R7 or R10 it replaces a set of fast primes for events, weddings and video.
Image quality
Inside are 17 elements in 11 groups, including four SLD and four aspherical elements, which keep it sharp and free of obvious colour fringing at F1.8 across the whole range. An 11-blade rounded aperture gives smooth, round background highlights, and the front element has a water- and oil-repellent coating that makes it easier to wipe clean.
Autofocus and video
Sigma's HLA linear motor gives fast, quiet focusing and works with Canon's Dual Pixel AF, including eye and subject detection. The zoom is internal, so the lens keeps its length and balance, and focus breathing is kept low for clean focus pulls.
Canon-style control ring
In place of an aperture ring, the RF version has a control ring that works like the one on Canon's own RF lenses. You can set it in the camera menu to adjust aperture, ISO or exposure compensation.
Who it's for
This is the lens for R7 and R10 owners who shoot in low light and do not want to keep swapping primes. It is a big lens for a small body, at 535g and 115.9mm long, so if you mainly want a light everyday zoom the Sigma 18-50mm F2.8 for Canon RF is the better fit. The R7 has in-body stabilisation; the R10 and R50 do not, and the lens has none of its own.
Also available for Sony E, Fujifilm X and L-Mount.
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