This large-aperture wideangle zoom hits the sweet spot for Sony full-frame mirrorless users, says Andy Westlake
Tamron 17-28mm F/2.8 Di III RXD – Build and handling
One theoretical advantage of mirrorless systems is that the short lens-to-sensor distance allows wideangle lenses to be made considerably more compact than their DSLR equivalents. Tamron appears to have taken full advantage of this, and as a result the 17-28mm is surely the smallest and lightest f/2.8 full-frame wideangle zoom on the market, aided by the use of lightweight polycarbonate for the external barrel. However it still appears perfectly well made, and while it’s perhaps not as solid-feeling as the metal-barrelled Sony 16-35mm f/4, it should be much less prone to scratching. The mount is metal, and surrounded by a rubber seal to prevent moisture getting into the camera.
In terms of design, the lens follows the template of most full-frame E-mount lenses, with a narrow-diameter section immediately adjacent to the mount that flares outwards to the main barrel. However at 73mm in diameter, it’s comparatively slim. It sports a rather understated matte-black finish, with just a slim pale-gold ring around the mount to provide a cosmetic flourish.
With its compact size and light weight, the 17-28mm is an excellent companion to Sony’s Alpha 7 bodies. The zoom ring has a large rubberised grip, while the focus ring is a harder plastic; both rotate smoothly. However I must admit that I’m not a fan of Tamron’s decision to place the zoom ring towards the front of the barrel, and found myself twisting the focus ring instead more than once. It’s not a huge problem, but counts as a minor demerit compared to the Sony 16-35mm f/4.
Tamron 17-28mm F/2.8 Di III RXD – Autofocus
Lens makers delight in formulating obscure acronyms for autofocus motors, with Tamron here deploying its RXD (Rapid eXtra-silent stepping Drive) system, which is also used by the 28-75mm f/2.8. In keeping with the requirements for modern mirrorless cameras, this is super-fast and essentially silent in operation, so it works well for both stills and video shooting. It’s fully compatible with Sony’s Eye AF, should you wish to shoot wideangle portraits.
In practical use I found the AF worked pretty much flawlessly, only failing in exceptionally dark conditions where there was insufficient light for the camera to focus. Here the answer is to use manual focus; sadly the lens lacks a physical AF/M switch, so you need to use a function button or the Fn menu.
Manual focus works perfectly well, with rotation of the focus ring bringing up a magnified view for the most precise results. But as always with Sony it’s worth bearing in mind that the camera stops the lens down to the taking aperture, which compensates for any possible focus shift, but makes the viewfinder image noisy in low light.