Sigma's early DX ultra-wide — the 10-20mm f/4-5.6D version with screw-drive AF for Nikon.
The Sigma 10-20mm f/4-5.6 EX DC HSM is an ultra-wide zoom lens designed for APS-C Nikon DSLR cameras, providing a 15–30mm full-frame equivalent field of view. The 'D' suffix in the Nikon version denotes distance encoding compatibility. This is the original f/4-5.6 version, predating the later constant f/3.5 variant.
The lens spans 10–20mm with a variable f/4–5.6 aperture, EX professional-grade build quality for its era, HSM autofocus motor for fast and quiet operation, and a DC image circle sized for APS-C sensors only. It uses multi-layer coatings to manage flare across its wide field of view.
The f/4-5.6 variable aperture is its primary limitation compared to the later f/3.5 version, particularly at the wide end. However, its EX build quality and HSM autofocus give it an advantage over many consumer-grade ultra-wides. It was a popular landscape and architectural lens for Nikon APS-C shooters on a budget.
Inspect the HSM autofocus motor for smooth, accurate operation — listen for any grinding or hesitation. Check corner sharpness at 10mm, as extreme ultra-wides often show corner softness wide open. Examine the front element for coating abrasion and verify the zoom ring moves without binding.