Canon PowerShot G15 review
here are three different autofocus modes on the Canon PowerShot G15. The first is Face AiAF, an intelligent autofocus mode that automatically selects one or more from a choice of nine AF points and will prioritise any faces it detects in a scene. While the focusing is fast, the system obviously doesn't know exactly what the intended subject is, so it doesn't get it right every time. It is useful, however, in social situations for photographing people.
The next mode is tracking AF. Again, this works well, and is useful for choosing a subject and then recomposing the image. The AF target is placed in the centre of the frame and then the camera is moved so the target is over the subject. A half-press of the shutter button then locks the focus to this target, and the AF point will move and stay focused on this target if either the subject or the camera moves. Again, it is useful for portraiture where you may wish to focus on the subject's eyes and make sure they remain in focus even when recomposing the image slightly. Similarly, it is handy for tracking a moving subject, such as a child or a pet. While tracking AF is fairly responsive when subjects are moving at moderate speed, don't expect it to perform well with sports or fast-moving vehicles.
Finally, Flexi-Zone is the mode that will most commonly be used. This allows any one of up to 493 AF points to be selected on the rear LCD. Given the number of points available, switching between them is relatively fast, although the very edges of the image frame don't contain any points.
As most images won't have the subject that close to the edge of the frame, this shouldn't be of any concern. Overall, the focusing is very snappy when the lens is at its widest focal length. It tends to slow at the 140mm equivalent setting, and I found that a few times it was hunting back and forth. However, for the camera's intended market, the focusing is as comprehensive as it is fast.