Overview

The Canon EF 100-300mm f/4.5-5.6 USM is an affordable telephoto zoom with decent optics when stopped down, especially at wider focal lengths. Sharpness is good at 100-135mm at f/8, but softens at 200-300mm and wide apertures. Chromatic aberration and vignetting are well controlled at shorter focal lengths but noticeable at the long end. Build quality is solid with a metal mount and plastic barrel, though the zoom ring can creep. Autofocus is fast and quiet thanks to ring USM, with full-time manual override. It suits budget-conscious users needing a lightweight, long telephoto for well-lit conditions.