digital scouting cameras

Focusing is fast and sharp as with the $300 canon lenses. I own two and pretty much use them more than most other lenses. Focus falloff is just like a Sonnar, with the sharp central image and lovely dissolve into nonfocus. Optimum aperture is f / 4. Focus is achieved by front element extension. The ring - type USM motor dives the small front elements easily, resulting in extremely fast AF.

Optically all three lenses are very similar. The two non - IS lenses have identical optics but the IS lens has additional optical elements as part of the IS mechanism. Optical performance is noticeably better than my cheap telephoto zoom. When used with the Canon EF 14X teleconverter, the maximum focal length becomes about 560mm, and optical quality is still excellent. Optically it ' s almost on a par with the 300mm f / 2. 8L. In other words, this is as good as it gets.