Review by Klaus Schroiff, published April 2011

Introduction

The lens has an very good build quality based on a metal body - it shows no wobbling whatsoever even when zooming out to 400mm. Unlike most modern tele zoom lenses it relies on a a push-pull zoom mechanism which has both its pros and cons. You can zoom very fast if necessary but this comes at cost of accuracy. The amount of zoom friction can be adjusted using a dedicated control ring. It´s also possible to lock the lens at a certain zoom position so zoom creeping is not an issue. At the time I picked up the lens the rental service guy welcomed me like "so you wonna have the air pump". Yes, the push-pull design sucks in dust which isn't exactly a favorable aspect. The tested sample showed some dust particles near the front element. However, this is actually a general problem in this lens class because such lenses are simply big and they simply don't have a constant physical length - see e.g. also the Nikkor AF 80-400mm f/4.5-5.6 ED and the Sony 70-400mm f/4.5-5.6 SSM. The Canon lens has a rear-focusing mechanism resulting in a non-rotating front element. The focusing action is very smooth.

One of the primary selling argument is the IS (Image Stabilizer). It is a 1st generation variant (or v1.5 depending how you look at it) which gives you the equivalent of two extra f-stops in handholdability - this is certainly dated by now regarding the much higher efficiency of current IS versions. The claimed efficiency is about right based on some field experience with the lens. The IS cannot be used on tripods because it tries to detect motion where there is none causing the IS to produce erratic effects. There are two IS modes (which is why I referred to a v1.5 IS above) - mode one corrects motion in both vertical and horizontal axis whereas mode two corrects vertical motion only. The latter is meant for action photography when you´ve to track objects. Mode one is intended for static scenes only.

The lens features a ring-type USM drive resulting in a very fast and virtually silent AF operation. Full-time manual focusing is possible in one-shot AF mode. To avoid unnecessary hunting there's a focus limiter where you can choose between 1.8m-infinity or 6.5m-infinity. It's worth mentioning that it takes advantages of a so-called floating focusing system which optimizes the close-focus performance.