SIGMA 100-400MM F5-6.3 DG OS HSM | C
It takes the weight off your neck, but not out of your wallet
this newcomer is the most compact lens in the group, and the cheapest to buy. Despite weighing barely more than the tamron, it has a more complex optical path based on 21 rather than 17 elements. these include four sLD (special Low Dispersion) elements.
High-performance components include a ring-type ultrasonic autofocus system that’s easily as fast and accurate as that of the Canon and Nikon lenses. the sigma also matches the Nikon in having three switchable focus modes, including auto-priority and manual-priority autofocus settings, as well as purely manual focus. A new-generation optical stabiliser senses and corrects for movement in horizontal, vertical and diagonal planes, and has a switchable panning mode that can work in any camera orientation.
particularly impressive is the inclusion of two custom modes, available via a switch on the lens barrel. You can set up any two combinations of autofocus speed, autofocus range limiter distance and stabilisation behaviour, with a more or less visible effect in the viewfinder. Custom setups are created and stored via sigma’s optional usB Dock (£40/$60), which can be used for fine-tuning AF accuracy and applying firmware updates.
Build quality is good throughout, although the only weather seal is a rubber ring on the mounting plate. Handling benefits from smooth-action zoom and focus rings. You can also adjust the zoom setting with a push-pull action, for which the hood is specially shaped.
Image quality is impressive with very good sharpness and contrast throughout the zoom range, even when shooting wide open. It beats the Canon lens at the long end but doesn’t quite match the Nikon and tamron for centre sharpness. However, sharpness is retained particularly well into the edges and corners of the frame.