click for bigger image click for bigger image For the zoom lens, focus shift does occur when fitted with either EF Extender units, meaning whatever focus that was achieved at a given focal length of the EF 70-200mm f/2.8L USM zoom lens will be undone if the lens was zoomed to another focal length. It is best to focus again whenever the lens is zoomed if using the camera in its One-Shot AF mode. You don't have to refocus again if you are using your EOS camera in its AI Servo AF mode since the constantly AF focus tracking mode of the camera will automatically adjust the focus as it change during zooming operations. However, rest assured that the focus shift only occurs when the zoom lens is fitted with any of the two EF Extenders and for normal shooting that doesn't require the use of the Extenders concerned, there won't be any shifts in the focus after zooming. Shooting with zoom lenses can be pretty exciting -- pictures snapped at the various zooming angles can both be informative or selective, depending on the circumstances. These photos, for instance, can demonstrate on the points described: The photo on the left was shot at 70mm to show the area where the Malaysian flags were hanging from. The second photo shot at the 200mm gave an abstract shot of the flags - strong artistic concept. << Back to Main . 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 .