Fast Sigma ultra-wide zoom for Canon EF with constant f/2.8 from 20mm, excellent for astro and interior work.
The Sigma 20-40mm f/2.8 EX DG is a fast ultra-wide zoom for Canon full-frame with a constant f/2.8 aperture throughout its range. The 20mm ultra-wide starting point provides dramatic perspectives, and the constant f/2.8 makes it one of the fastest ultra-wide zooms available for the Canon EF system.
The 20-40mm range covers from genuine ultra-wide through to standard wide-angle, providing a useful range entirely within the wide-angle spectrum. The constant f/2.8 is particularly valuable for astrophotography and low-light architectural work where wider apertures capture more light in the same exposure time.
Build quality is Sigma EX premium tier with quality construction and smooth mechanical operation. The DG designation confirms full-frame coverage, and the lens produces a large, bright image even in the viewfinder. The autofocus operates through the Canon EF mount electronics.
The Sigma 20-40mm f/2.8 offers exceptional value on the used market for Canon shooters who need a fast ultra-wide zoom. The constant f/2.8 at 20mm provides capability that most competing ultra-wide zooms cannot match, making it particularly valuable for astrophotography and interior work.