Sigma's early ultra-wide zoom for full-frame — the 15-30mm f/3.5-4.5 EX with constant wide aperture.
The Sigma 15-30mm f/3.5-4.5 DG EX Aspherical IF is an early full-frame ultra-wide zoom released around 2000. It was one of the first affordable ultra-wide zooms to cover full frame, competing against the expensive Canon 16-35mm and Nikon 17-35mm. The EX designation indicates Sigma's professional tier with the bulbous front element characteristic of extreme wide-angle designs.
Optical performance is decent for the era. Sharpness is good in the centre throughout the range. The aspherical element helps control distortion and aberrations. The variable aperture starts at a useful f/3.5 at the wide end. As an early ultra-wide zoom design, it represented good value against expensive first-party alternatives that cost significantly more.
Available in Canon EF, Nikon F, and Sony A mounts. The bulbous front element prevents standard filter use. Weight is approximately 750 grams. Build quality is solid with the EX designation. No image stabilisation. The IF (Internal Focusing) design is a practical advantage. DG coatings reduce digital sensor reflections.
Available on the used market at very low prices. Check the bulbous front element for scratches. Thoroughly superseded by modern ultra-wide zooms from Sigma and competitors. Only worth considering at a very low price for budget ultra-wide full-frame coverage. The Sigma 14-24mm f/2.8 Art is the modern equivalent with dramatically better optics.