Sony's own 16-35mm F2.8 GM is widely respected glass, but it runs well over $2,000. Tamron's answer, the 17-28mm F2.8 Di III RXD released in July 2019, covers nearly the same range at a small fraction of the cost — and it isn't a fringe alternative. Alongside its 28-75mm and 70-180mm siblings, it forms what reviewers call Tamron's own "holy trinity": three constant-f/2.8 zooms covering 17-180mm that together cost roughly what a single comparable Sony GM lens does.
The tradeoffs are modest: a plastic-heavier build than Sony's metal barrels, and simple weather sealing rather than full professional-grade dust and moisture resistance. But at 420g and with a compact, constant-length zoom design, it's become one of the most recommended wide-angle options for Sony full-frame shooters who'd rather spend the savings on a second lens — or a second camera body.
