Overview

The Canon EF 400mm f/4 DO IS USM is a unique telephoto lens that uses diffractive optics to reduce size and weight, making it more handholdable than comparable f/2.8 lenses. It offers fast, quiet autofocus and image stabilization with about 2 stops of effectiveness. However, its apparent sharpness does not match its price point. Build quality is solid with weather sealing, but the protruding switches are prone to accidental bumps. It suits photographers prioritizing portability over ultimate optical performance.