with his permission, all rights retained by Paul Janosi

What is depth of field?

When the camera is focused on an object, there is an area in front of and behind the object that also appears to be in sharp focus. This area extending in front and behind the plane of the sharpest focus is referred to as "Depth of Field". Contrarily to regular photography, when the object distance is less than 8 times the focal length of the lens, the depth of field becomes approximately the same in front of the focused distance as behind. The greater the extension of the lens from the camera, the greater the magnification and the more shallow will be the depth of fields. Since at 1:1 reproduction ratio the depth of field at f22 is only about 1/4 inch, at 1:2, 1/2 inch, at 1:3, 3/4 inch and at 1:4, about 1 inch, it is clear that a small aperture and careful placement of the subject, if it has depth, will be necessary.

What controls depth of field?

Depth of field can be controlled by the aperture size, focal length and lens to subject distance. Stopping down the lens to a smaller aperture for instance going from f2.8 to f 22 will increase depth of field. As the aperture gets smaller, more of the image will be sharper. For macro photography in the 1:4 reproduction ratio, I recommend shooting at f22. Focal length also has an effect on depth of field. When photographing the same subject from the same location depth of field decreases as the focal length of the lens is increased. For example when switching from a 50 mm macro lens to a 200 mm macro lens. If the image size remains the same, all the lenses at the same f-stop will yield pictures with the same depth of field. The lens to subject distance will also effect depth of field. The closer you are to the subject the grater the magnification the shallower the depth of field. The farther from the subject, the less the magnification the greater the depth of field.

Paul Janosi
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