Canon's original L-series professional zoom, the predecessor to the legendary 24-70mm f/2.8L.
The Canon EF 28-70mm f/2.8L USM was launched in 1993 as Canon's first professional standard zoom for the EF mount. With a constant f/2.8 aperture and L-series build, it established the professional zoom standard that the 24-70mm f/2.8L would later inherit. It was the zoom Canon professionals relied on for nearly a decade.
Optical quality is good with strong sharpness particularly in the 35-60mm sweet spot. Build is classic L-series with weather sealing and a robust metal and plastic construction. Ring USM autofocus is fast and reliable with full-time manual override. The 28mm wide end is narrower than the 24mm of its successor.
Canon EF mount only, 77mm filter thread. Replaced by the EF 24-70mm f/2.8L USM in 2002 which extended the wide end to 24mm. The 28-70mm is now a legacy lens but remains optically capable. It was the professional Canon zoom of the 1990s.
Cheap used as it is thoroughly superseded. Check the USM motor, zoom ring stiffness, and overall condition. The lens is well-built and durable. At used prices it offers professional f/2.8 capability at a fraction of the 24-70mm's cost. The 28mm limitation is the main practical concern.