Conclusion

The Sigma 28-70mm F2.8 DG DN Contemporary is an amazingly lightweight and very compact standard zoom lens for Sony Alpha and L-mount full-frame cameras.

Obviously intended as a clear riposte to the considerable success that Tamron have had with the 28-75mm F2.8 Di III RXD, the new Sigma 28-70mm F2.8 gives up a little extra reach to crucially be even lighter and shorter than its main rival.

Compared to its big brother, the Sigma 24-70mm F2.8 DG DN, this Sigma 28-70mm is significantly shorter and almost half the weight, but it has to give up a in order to achieve that.

It isn't as wide, has a much simpler design with fewer external controls, isn't as well-constructed or well-sealed, is slower to auto-focus, isn't as sharp, doesn't produce quite as nice bokeh, and doesn't ship with either a lockable lens hood or a lens bag.

In short, if we had to choose between the two Sigma lenses, the 24-70mm F2.8 DG DN is the clear winner and well worth the extra £300 / $200, unless size is absolutely your number one priority.

The contest between the new Sigma 28-70mm and the popular Tamron 28-75mm is a much closer one. The Tamron has slightly more reach, but it isn't quite as well-built as the Sigma or as sharp at the edges of the frame. We'd give the Sigma the slight edge overall, but then again the Tamron is £60/$100 cheaper, though, which may well prove more decisive for a lot of buyers.

In terms of its optical performance, the Sigma 28-70mm F2.8 DG DN Contemporary is tack-sharp in the centre throughout all of the zoom range, with sharpness only falling off a little at the very edges of the frame. It also produces some nice bokeh effects thanks to the 9-blade iris diaphragm.

There's some obvious vignetting at wide-open apertures, barrel distortion at 24mm and slight pincushioning at 70mm, but all of this can be corrected either in-camera or during post-processing. Importantly chromatic aberrations, which are much harder to correct, are very well-controlled.

Auto-focusing proved to be quick on the Sony Alpha A7 III that we tested the lens with, and manual focus over-ride at any time is a great feature.

Build quality is excellent, with the brass lens mount and sober all-black design adding to the premium feel, and Sigma have also included a good lens hood. The Sigma 28-70mm F2.8 DG DN Contemporary lens is usefully weather-sealed, but only at the mount and not also throughout the barrel as on the Sigma 24-70mm.

This lens doesn't have a built-in optical image stabilisation system, instead relying on Sony's in-camera system, which will be fine for everyone except those who own a first generation Alpha camera (which don't feature built-in OIS).

Overall, the new Sigma 28-70mm F2.8 DG DN Contemporary is a well-built, fast standard zoom lens that delivers excellent image quality in a very small, lightweight package.

It isn't as good as our favourite Sony full-frame standard zoom, the Sigma 28-70mm F2.8 DG DN, in any aspect except size, but it does out-perform its main rival, the Tamron 28-75mm F2.8 Di III RXD, albeit at a slightly higher price-point, which makes choosing between them a close-run thing.

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