Luminous Landscape is featuring part one of a multi-part article on “http://www.luminous-landscape.com/tutorials/Digital%20Focusing.shtml“>Focusing in the Digital Era” by Gary Ferguson.

This article confirms some of what I have believed about the concept of depth of field. Many people seem to assume that objects within the depth of field at a given aperture (on a given camera) will be “in focus” and those outside of the depth of field will be “out of focus.” I’ve always thought it couldn’t really be quite that simple. It has seemed to me that there should be a plane of optimum focus with objects in front of or behind that gradually going out of focus at rates varying by aperture. In other words, an object that is not in the plane of focus may be “acceptably out of focus,” but it is not really in focus.

Ferguson explains the history of the depth of field scales on lenses, and points out that they were designed in an era when photographer did not think to enlarge images to the extent we do today. If one took a 35mm negative and enlarged it to, say, 4 x 6 inches, the fuzziness in front of and behind the plane of focus would not be visible. However, today many of us make quite large prints from images captured on sensors that are often smaller than 35mm film frames, and the focus issues become more critical.

He includes a series of photographs that clearly illustrate just how fuzzy objects that “should be in focus” turn out to be – important stuff to understand and think about.

—–