CANON EF 16-35mm f/2.8l USM III £1849/$1899

Launched nearly three years ago, this Mk III zoom received a major overhaul

Canon’s most ideal zoom lens for full-frame astrophotography, this one isn’t as wide-angle as the EF 11-24mm f/4l USM, but is an all-important f-stop faster. The maximum viewing angle is slightly less than the 14mm and 15mm full-frame lenses on test, equating to 108 degrees compared with 114 or 110 degrees.

This lens gains a large and complex double-surface GMO (Glass Moulded) aspherical element at the front, adding to two UD (Ultra-low Dispersion) elements and a ground aspherical element at the rear. Upgraded, high-tech coatings include both SWC (Subwavelength Coating) and ASC (Air Sphere Coating) for greater resistance to ghosting and flare. Weather-resistant attributes are extended to include moisture- and greaserepellent fluorine coatings on the front and rear elements.

The lens is quite long at 128mm, considering that it doesn’t have a built-in fixed hood. Unlike with most lenses

here, the separate bayonet-fit hood enables the easy attachment of filters, via an 82mm thread. Build quality is up to Canon’s usual robust L-series standards.

Performance

Sharpness and contrast are impressive across the zoom. The Mk III has much improved corner-sharpness compared with the previous edition, but still lags behind the competing Sigma 14-24mm zoom on test. There’s very little spherical aberration at f/2.8, but coma and astigmatism can be quite visible near the extreme corners of the frame.