Sigma 135-400mm f/4.5-5.6 APO DG - Sigma SA, Canon EF, Nikon F, Sony A, Pentax K Mount

The Sigma 135-400mm f/4.5-5.6 APO DG is a long-reach telephoto zoom lens compatible with both full-frame and APS-C cameras. The 'DG' designation indicates coatings optimised for digital sensors to reduce flare and ghosting. It features a rotating tripod collar and a rear-focusing system. This lens provides a cost-effective way to reach 400mm for wildlife and aviation photography where light levels are sufficient. When inspecting a used 135-400mm, it is vital to check the zoom tension, as these lenses can be prone to zoom creep when pointed up or down. SDS tests the autofocus speed and accuracy, noting that this model uses a mechanical drive rather than HSM in some mounts. We also check for internal dust, which is common in older external-zoom designs, and ensure the tripod foot threads are not stripped.