Sigma's hugely popular APS-C constant f/2.8 standard zoom — sharp, stabilised, and excellent value.
The Sigma 17-50mm f/2.8 EX DC OS HSM was released approximately 2010 as a constant f/2.8 standard zoom for APS-C bodies, providing 25.5-75mm equivalent range with OS (optical stabilisation) and HSM autofocus. DC designation confirms APS-C-only image circle. At 565g and 77mm filter thread. Seven rounded aperture blades. 0.28m MFD at all zoom positions.
The optical design uses 17 elements in 13 groups. Seven rounded aperture blades. The 77mm filter thread. At 565g the lens is moderate. Minimum focus distance of 0.28m throughout the zoom range. OS provides optical stabilisation. HSM provides fast, quiet AF with full-time manual override. Constant f/2.8 aperture. DC = APS-C only.
The constant f/2.8 at 17-50mm on APS-C covers the standard photojournalism and event zoom range: from 25.5mm environmental wide-angle through standard to short telephoto at f/2.8 for indoor low-light and background separation. The OS provides stabilisation for video and stills handheld at the longer focal lengths. The 0.28m MFD enables close environmental compositions throughout the zoom range.
On the used market the Sigma 17-50mm f/2.8 EX DC OS HSM is affordable as a constant f/2.8 APS-C standard zoom. Condition checks: OS engagement, HSM AF response, 77mm front element for marks, zoom ring smoothness. DC = APS-C only — vignettes on full-frame. Compatible with Canon EF, Nikon F, and other APS-C mount versions.