Review by Klaus Schroiff, published December 2010

Lens kindly provided for testing purposes by Christoph Siegwart!

Introduction

Compared to its predecessor it has been improved in a number of aspects. The most significant change is a redesign of the optical construction which now features a UD element. The AF speed has been significantly improved to a very decent level although it doesn't quite reach the speed of Canon's ring-type USM lenses. Thanks to a micro-USM drive the noise level is very low. The lens does not feature FTM (full-time manual focusing in AF mode) though.
One key selling factor for this lens is naturally the Image Stabilizer (IS). Camera motion is detected by 2 gyro sensors which measure the angle and speed of the shake. This information is used to shift a lens group off the optical axis (basically a forced decentering) to counteract this motion. The result is a significant improvement of handholdibility under extreme conditions. Canon improved the efficiency of the mechanism to an equivalent of 3 f-stops (up from 2 f-stops).
The IS now offers 2 different modes (instead of just one):

• mode (1) for static scenes where the IS corrects shake both vertically as well as horizontally
• mode (2) for action photography (object tracking) where only vertical shake is corrected

The build quality of the lens is about average. Neither the focus nor the zoom control ring is especially damped but it operates quite smooth. The various switches feel a little cheap. As you can see in the product shot below the lens extends significantly during zooming (typical in the lens class) and the front element rotates during focusing operations so using a polarizer is a little cumbersome at best. Another new feature is a transport lock that prevents zoom creeping.

Here's a comparison with its nearest cousins: