Sigma's budget APS-C ultra-wide zoom — 15-30mm equivalent coverage at a very affordable price.
The Sigma 10-20mm f/4-5.6 EX DC HSM is an APS-C ultra-wide zoom for Pentax K-mount (also available in Canon EF, Nikon F, Sony A, and Sigma SA mounts), covering 15-30mm equivalent on APS-C. DC designation confirms APS-C-only image circle. Variable aperture from f/4 at 10mm to f/5.6 at 20mm. At 470g and 77mm filter thread. Six aperture blades. 0.24m MFD.
The optical design uses 14 elements in 10 groups. Six aperture blades. The 77mm filter thread. At 470g the lens is moderate. Minimum focus distance of 0.24m. HSM provides fast, quiet AF. Variable aperture from f/4 (10mm) to f/5.6 (20mm). DC = APS-C only — vignettes on full-frame. 15-30mm full-frame equivalent.
The 15-30mm equivalent on APS-C covers extreme ultra-wide to moderate wide in a single lens: 15mm provides the widest rectilinear perspective practical for APS-C bodies, useful for interiors, astrophotography, and environmental landscape. The 0.24m MFD enables very close environmental foreground placement at ultra-wide focal lengths.
On the used market the Sigma 10-20mm f/4-5.6 EX DC HSM is affordable as a vintage APS-C ultra-wide zoom. Condition checks: HSM AF response, 77mm front element for marks, zoom ring smoothness. DC = APS-C only. Available in Canon EF, Nikon F, Pentax K, Sony A, and Sigma SA mounts.