Lenses 101: Depth-of-Field Concepts

Today’s Post by Joe Farace, photo by Mark Toal

The basic laws of imaging state that only one part of a three-dimensional object can be truly in focus at the image plane. This means areas in front of and behind the focus plane still appear more or less in focus or acceptable focus.

Depth-of-field is that area that your eyes perceive as being in focus and is affected by several things, including the distance to the subject. Depth of field increases as the lens aperture is stopped down and decreases as the lens aperture gets larger and the camera to subject distance decreases. At the point of critical focus, there is a range of acceptable focus that is one-third in front of that point and two-thirds behind it.

Some lenses for mirrorless cameras, especially when adapting those from other formats, for have an aperture ring. Most vintage lenses even have a depth-of-field scale, which can be helpful when using hyperfocal focusing.

The Hyperfocal Distance is the specific point of focus where any object that is between that distance and infinity is in focus. After you pick an aperture you rotate the lens’ focusing ring setting that aperture opposite the infinity mark so that everything from what’s at the opposite end of the focusing mark will be in acceptable focus.