I've been playing with AI Servo mode on my S90, and am experiencing something a bit odd -- when I half press the shutter and point the camera at something, say a book a few feet away -- the camera will beep and lock focus on it (with the blue box signaling its in servo mode). Then when I move the camera to another object and back to the book, the focus on the book starts pulsating in and out of focus about 5 times a second constantly.

Does anyone else experience this? If I go ahead and take a picture while its pulsating, the resulting image is hit or miss whether its in focus, even though the camera is fixed on a stationary object (the book). Its as if the camera is having a hard time focusing.

Interestingly, if I try the test again in Macro mode, the camera doesn't seem to do this...it will pulsate once or twice when I move the focus to different objects, but then the focus is steady and the pictures are sharp.

Any ideas? Thanks