Sigma 170-500mm f/5-6.3 APO DG - Sigma SA, Nikon F, Canon EF, Sony A, Pentax K Mount

The Sigma 170-500mm f/5-6.3 APO DG is a versatile long-reach telephoto zoom for DSLR cameras. It provides a significant focal range for birding and distant subjects in a relatively portable package for its reach. The APO (Apochromatic) design uses low-dispersion glass to minimise colour fringing, while the DG coating helps reduce ghosting and flare from digital sensors. On the used market, these lenses can often show 'zoom creep' where the barrel extends under its own weight; check that the zoom tension is acceptable. The external finish can be prone to scuffs. SDS checks the mechanical linkages of the zoom mechanism, ensures the autofocus is responsive throughout the range, and verifies that the internal elements are free from dust and debris.