Sigma's first-generation ultra-wide zoom for APS-C DSLRs, covering a dramatic 15-30mm equivalent range.
The Sigma 10-20mm f/4-5.6 EX DC HSM was released around 2005 as one of the first affordable ultra-wide zooms designed specifically for APS-C DSLRs. Covering a 15-30mm equivalent range, it gave crop-sensor shooters access to dramatic wide-angle perspectives previously only available with expensive full-frame glass and adapters.
Optical performance is respectable for the era. Centre sharpness is good throughout the range, though corners are softer especially at 10mm wide open. Chromatic aberration is visible in high-contrast edges. The EX designation indicates Sigma's professional-tier build quality, though this lens sits at the affordable end of that range.
Available in Nikon F mount and other systems. Filter thread is 77mm — a professional standard size. Weight is approximately 470 grams. HSM motor provides quiet autofocus. The later Sigma 10-20mm f/3.5 replaced this with a constant aperture design, and the Sigma 10-18mm f/2.8 Art is the modern equivalent.
Affordable on the used market with good availability. Check for smooth zoom operation and clean front element. The variable aperture is a limitation in low light. A solid budget ultra-wide for APS-C DSLRs, though the constant f/3.5 version or modern alternatives are preferred if budget allows.