Conclusion

The new Tamron 20mm F/2.8 Di III OSD M1:2 is a unique ultra-wide-angle lens for Sony shooters, but some notable optical issues prevent us from recommending it more highly.

This lens produces sharp images in the centre and offers 1:2 macro shooting, weather-proofing and a compact, lightweight design, all at a budget price.

Unfortunately, as with the other Tamron FE primes that we've recently reviewed, the auto-focusing system is fairly slow and quite noisy, the maximum aperture isn't particularly fast, it offers very few features, it requires a a worryingly stern twist to lock it into place.

More seriously, there's an awful lot of barrel distortion that you'll need to remove either in post-processing or by turning the in-camera correction on.

Center sharpness is excellent throughout the entire aperture range and very good at the edges from f/5.6 onwards. Chromatic aberrations are virtually non-existent and flare is only ever an issue when shooting directly into the sun.

Unfortunately, the barrel distortion is very obvious indeed, even in the JPEG files. The other notable optical issue is very obvious corner shading at the maximum aperture.

The ability to shoot at 1:2 at just 11cms away from your subject is one of the main reasons for considering this lens, as is the fact that Sony don't make a native 20mm lens for their full-frame cameras (yet).

Much less appealing is the auto-focusing. Tamron claim that it's fast and near silent, hence the silent bit of the OSD acronym, but we found it be anything but, especially in low-light situations.

Overall, this is a very interesting prime lens thanks to its unique ultra-wide 20mm focal length, compact and lightweight design and its wallet-friendly price-tag, but the very high levels of distortion and slow auto-focusing ultimately prevent us from recommending it more highly.

Ratings (out of 5)
Design	4
Features	4
Ease-of-use	3.5
Image quality	3.5
Value for money	4.5