Depth of Field
Depth of field (DOF) is defined as the distance in front of and behind the plane of focus that still has an acceptable degree of sharpness. and can be described as shallow or deep, large or small, short or long. A camera, like the eye, can only focus on one structure at a time.
This is one of the best explanations of depth of field I’ve ever seen. It is worth your time to view it in its entirely.
Depth of field is important in medical photography in that a clinician desires clarity and accuracy in clinical photographs. Having a long depth of field provides more accurate information. In general, there is twice as much depth of field behind the plane of focus as in front of it. Another concept in medical photography related to depth of field is called “plane parallel” where the photographer keeps the plane of the sensor is parallel to the subject. By keeping the plane of the sensor parallel to the plane of the subject, this will minimize the clinical structures that are beyond the depth of field, thus out of focus.
Depth of field is a function of 1) the lens aperture size, 2) the lens focal length, and 3) camera-to-subject distance. In medical photography, lens aperture size is the easiest factor of these three to control. A small aperture will provide a longer depth of field. A similar phenomenon is seen when we use a pin hole to test a person’s vision. The small aperture minimizes the amount of stray light striking the sensor, sharpening the image.