Shel Belinkoff mused: > > So, here's a question about these multipoint autofocus systems. How does > one change the focus point? I'd imagine that it's a time consuming > operation, pushing buttons or turning wheels or some such > electro-mechanical modal interface <LOL>.
Depends on the camera. In the MZ-S it just about requires two hands, as you have to push up a spring-loaded slider and turn a control wheel. On the *ist-D, in normal shooting mode, the 4-way controller is what you use to change focus-point selection; a normal right-eyed person can probably do it almost instantaneously with the camera to the eye. > Seems then that for scenes where > there's any quickness of action required on the part of the photographer, > adjusting autofocus preferences might be a hindrance, and that using just > one focus point and slightly shifting the camera may be a faster > alternative. That's how I use my camera when I'm shooting motorsports. > But, if one does that, as noted by Vic, how does that effect > the point of focus? Is it changed because the camera has moved? That depends on whether you're using AF-S (focus once when you first half- depress the shutter) or AF-C (continually update focus while the shutter is half depressed). > And, can > one focus with autofocus on an area where there's no contrast or even a > subject? No. You need contrast. In fact, you even need the right sort of contrast. Some AF sensors work well with horizontal lines, but not with verticals. Some work the other way. And some (referred to as "cross sensors") are basically one of each kind looking at the same part of the image. (IIRC, the *ist-D has 9 cross sensors, plus two verticals, one at each edge)
