Sigma's stabilised 1:1 macro with HSM — the improved successor adding OS and improved optics.
The Sigma 105mm f/2.8 EX DG OS HSM Macro is the optically stabilised version of Sigma's full-frame macro prime, providing 1:1 magnification with OS (optical stabilisation) and HSM autofocus. For Sony A-mount, AF is driven by the HSM motor in the lens. At 725g and 62mm filter thread it is moderate for a full-frame 1:1 macro with stabilisation. The EX designation was Sigma's premium quality tier before the Art/Contemporary/Sports categorisation.
The optical design uses 16 elements in 11 groups. Nine rounded aperture blades. The 62mm filter thread is standard. At 725g the lens is moderate. Minimum focus distance of 0.31m at 1:1 magnification. OS provides approximately 2-2.5 stops of compensation in practice — Sigma did not publish an official stop figure for this lens. HSM provides fast, quiet AF with full-time manual override. f/2.8 maximum aperture.
The OS on the 105mm macro provides practical benefit for handheld work approaching 1:1: at macro distances below 0.5m, camera movement is magnified along with the subject, and OS compensation reduces blur during subject approach and framing. At 1:1 itself, a tripod or focusing rail is still preferred for extended sessions. Compared to the non-OS EX DG version (460g), the OS version is 265g heavier reflecting the optical stabiliser group.
On the used market the Sigma 105mm f/2.8 EX DG OS HSM Macro is affordable for a stabilised full-frame 1:1 macro prime. The Sony A-mount version is discontinued. Condition checks: HSM AF motor response, OS engagement, focus ring smoothness through the macro range, 62mm front element for marks, and aperture blade condition. Compatible with Sony A-mount bodies.