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 – Performance
What we’re always most concerned about from a lens, of course, is how the images look. With this kind of ultra-wide zoom that’s liable to be used for subjects such as landscapes and architecture, we’re hoping for high resolution right across the frame, low distortion, and strong resistance to flare. The Tamron 17-28mm f/2.8 delivers strongly on all these counts.
Indeed sharpness is particularly impressive, with the lens describing excellent levels of detail into the corners even at f/2.8. It outperforms most DSLR equivalents, illustrating the inherent advantages of mirrorless mounts for wideangle zooms and vindicating Tamron’s decision to restrict the zoom ratio. Stop down to normal working apertures of f/8 to f/16 and you’ll get images that are super-sharp from corner to corner.
This perceived sharpness is also helped by very low levels of lateral chromatic aberration: even if you decide to disable in-camera compensation for some reason, you’ll see very little colour fringing in the corners of the frame. Adobe software corrects this by default when developing raw files, too.
Curvilinear distortion is much as we’d expect; at 17mm lines that should be straight along the long edge of the frame adopt a noticeably wavy appearance. Across most of the rest of the zoom range, you’ll see pincushion distortion that gets increasingly pronounced as you zoom in. A lot of the time this is nothing to worry about, but it has the potential to be troublesome for architectural photography, or landscapes with a clean horizon.
For raw shooters, the complex distortion pattern seen at 17mm really demands the use of profiled corrections to remove properly, rather than those based on simple sliders. At the time of writing, there’s no profile yet available for Adobe Camera Raw or Lightroom, but doubtless one will appear in due course. Enable in-camera lens compensation and distortion will be perfectly corrected in the camera’s JPEG output.
Flare resistance is very impressive, which is important for such a wide lens. Even when shooting directly into the light, I saw no hint of ghosting or veiling flare. Stop down to f/11 or smaller, and you’ll get 18-point sun-stars thanks to the 9-blade aperture diaphragm.
Tamron 17-28mm F/2.8 Di III RXD – Image Quality
Our Image Engineering MTF tests, shot on the 42.4MP Sony A7R III, reveal a lens that’s remarkably sharp in the centre of the frame at all focal lengths, even at the maximum aperture of f/2.8. The measurements are not quite so spectacular in the corners, but still very good indeed. The odd behaviour at small apertures, with the corners appearing sharper than the centre, is probably an artefact of using a flat test chart at relatively close focus distances, and is not generally reflected in real-world use.
At 17mm the lens shows fairly strong vignetting of almost two stops, which will be plainly visible in images with clear blue skies. But its relatively gradual fall-off profile means that’s not too objectionable. This light falloff decreases to about 1 stop on closing the aperture down to f/5.6, but doesn’t reduce any further at smaller settings. Longer focal lengths show a similar pattern, but with lower levels of vignetting, with just 1.3 stops measured at 28mm and f/2.8.
At its wideangle setting, the lens exhibits moderate moustache distortion, with barrel distortion in the centre of the frame re-correcting to pincushion distortion towards the edges. Zoom in slightly to around 19mm and this neutralises, before turning to pincushion distortion through the rest of the focal-length range. Turning on lens compensation will effectively fix this distortion in the camera’s JPEG processing.