Sigma's second-gen 12-24mm ultra-wide zoom — 12mm rectilinear coverage with improved coatings over the original.
The Sigma 12-24mm f/4.5-5.6 DG HSM II was released in 2010 as the second-generation ultra-wide full-frame zoom, revising the original 12-24mm with an updated optical formula and improved corrections. The 12mm minimum provides approximately 120° diagonal field of view on full-frame. The bulbous front element prevents conventional screw-in filter use. At 670g HSM provides fast, quiet AF. DG confirms full-frame image circle. Available in Canon EF, Nikon F, and other mounts.
The optical design uses 17 elements in 13 groups. Six aperture blades. No front filter thread — the bulbous front element prevents standard screw-in filter use; specialist holder systems are required for ND and polariser use. At 670g the lens is moderate for its focal range. Minimum focus distance of 0.28m. HSM motor provides fast, quiet AF with full-time manual override. Variable aperture from f/4.5 at 12mm to f/5.6 at 24mm. DG confirms full-frame coverage.
The 12-24mm range on full-frame covers the ultra-wide architectural and landscape field of view unavailable from standard wide zooms: at 12mm the approximately 120° diagonal field enables full interior room coverage and dramatic landscape panoramas. The second-generation formula improved upon the original's edge performance and chromatic aberration control. As a rectilinear design at 12mm, the bulbous front element and absence of filter thread are inherent to correcting straight lines at extreme wide angles.
On the used market the Sigma 12-24mm DG HSM II is affordable as a full-frame ultra-wide zoom. Condition checks: front element for marks — no filter thread means no front protection — HSM AF response, and zoom ring smoothness. Confirm the mount version — available in Canon EF, Nikon F, and other mounts. Compatible with full-frame and APS-C bodies in the specified mount; on APS-C the range becomes approximately 19-38mm equivalent.