some days ago I daring duck had approached while I was taking photos of her and her friends in a pond. I was testing my new 70-200 2.8 VRII and I was a bit worried about the autofocus while working with autofocus and VR (camera was handheld).
The was duck at my feet and given that I was standing and I'm 1.76m tall, I think more or less the distance between the first lens and the duck was 1.20m.
I managed to take some perfectly focused picture of the head of the animal while I was using 120mm (again, at the moment I'm not totally sure since I haven't the foto with me).
I was using the "FULL" range of autofocus, but having read in the instruction that it would go much faster if I set the switch to "< 5m" I tried it. Results? The Autofocus couldn't "find" the head of the duck anymore. I switched back, it worked again. Again to "< 5m" and it didn't.
What the hell was wrong? Do I have a flawed objective?