Before April 2021, every ultra-wide zoom built for APS-C mirrorless cameras topped out at a variable aperture that narrowed as you zoomed — useful, but never fast enough for handheld low-light or shallow-depth work at the wide end. Tamron's 11-20mm F/2.8 Di III-A RXD changed that with a genuine first: a constant f/2.8 aperture held across the entire ultra-wide range, delivering a 17-30mm full-frame equivalent field of view with no compromise as you zoom.
At just 335 grams and 8.6cm long, it stays remarkably compact for what it does, helped by a quiet, fast RXD autofocus motor and full weather sealing despite a mostly high-grade plastic build. Reviewers have found sharp, impressive results throughout the range, with some geometric distortion and peripheral shading at the extremes — reasonable tradeoffs for a lens that opened up a category no other manufacturer had touched.
