How Active Autofocus Makes Pictures Sharp
Photographers can’t always rely on automatic focusing because it’s subject to the vagaries of any mechanism that cannot see but pretends it can. For the most part, autofocus has all but eliminated pictures of relatives with fuzzy faces and blurred birthday bashes, and it’s a must for action shots and subjects who won’t stand still for a portrait. The implementations of autofocus are as diverse as the minds of the ingenious engineers who invent them. We’ll look here at two types of active autofocus found on less expensive cameras. One is akin to the echo technology of radar and sonar; the other is based on the triangulation used in rangefinders. Over the next few pages, we’ll also take a look at passive autofocus designs and the motor that makes them all work.