No, 15 ft. is going to give you a fairly wide focus area, probably from about 7-25 with decent focus. Since you don't have to wait for the autofocus to find your subject, theoretically you are able to snap a quick picture. I would trust this a lot more at fairly shallow depth in tropical water with a lot of ambient light, and the flash turned off. I think the preflash/flash setting process takes almost as much time as the autofocus. Where autofocus is really an issue is in dark water at greater depth or with poor vis, where the camera has to hunt for something to focus on. Sometimes illuminating the subject with your dive light or mounting a little UK mini or something like that on top of your housing can help a lot.