Conclusion

The new Sigma 100-400mm F5-6.3 DG OS HSM telephoto zoom lens offers very good image quality throughout its versatile focal range, whilst being light and compact enough to make it suitable for hand-holding. 

Build quality is very good, with the sober all-black design adding to the high-quality feel and the dust/splash-proof construction adding some peace of mind, plus there's a decent lens hood included, although the lack of a case/soft bag and even more importantly a tripod collar are clearly concessions made to hit the aggressive price-point. Auto-focusing was acceptable rather than quick on the Canon EOS 5DS R that we tested the lens with, but manual focus over-ride is a great feature, as is the effective built-in optical image stabilisation system.

The Sigma 100-400mm F5-6.3 DG OS HSM is tack-sharp at both the centre and edges of the frame when stopped down by one-stop at all the focal lengths, even at 400mm. Obvious vignetting at wide-open apertures is the only real optical issue of note, and this can be easily corrected in post-production.

The very affordable price-tag of the Sigma 100-400mm F5-6.3 DG OS HSM significantly undercuts the main rival lenses from Canon (EF 100-400mm F4.5-5.6 L IS II USM) and Nikon (80-400mm F4.5-5.6G VR). The Sigma 100-400mm F5-6.3 DG OS HSM brings the 100-400mm focal range to a much wider audience without sacrificing image quality, and, despite a few glitches in performance and specification, is therefore a deserved winner of our Highly Recommended award...

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