Designed for use with Canon’s APS-C sized sensors....
The lens consists of twelve elements in eight groups, and offers a close focusing distance of just 20cm, with 1:1 magnification. The lens uses an Ultra Sonic Motor for AF movement, which is quiet and quick. This is especially useful if you’re shooting live subjects, such as insects. Switching between auto and manual focus is facilitated by a switch on the lens, which is marginally less quick than the two-position focus ring seen on some other lenses, as you have to move your hands from the focus ring to the switch and back to focus ring.
The lens produces the best performance at around f/5.6, and holds that well through the middle of the aperture range before dipping down at f/16. Similarly the chromatic readings in the corners drop as the aperture is reduced, but still within limits of acceptability.
A great 'true' macro lens
see sample image gallery