Depth of Field:
The depth of field is the distance between the parts of the picture that are acceptably sharp. The blue vintage jewellery shown here is sharp. Outside the depth of field, on either side, the other pieces are un-sharp.
The ‘Depth of Field’ is the distance across the part of the picture that is acceptably sharp to the eye. When a lens focuses on a subject it creates only one point of clarity in the image. There is a gradual fall-off of sharpness either side of that point. Within the ‘depth of field’ the image appears sharp to the eye. The edges of the ‘depth of field’ are defined by the two points where the loss of sharpness becomes noticeable.
The depth of field is dependent on a number of factors. These are the focal length of the lens; the lens aperture; sensor format size; the ‘Circle of Confusion‘ and the camera-to-subject distance.
Depth of field is sometimes confused with depth of focus. However the two concepts relate to the same phenomenon, but on either side of the lens. Depth of field is used to describe the concept of the sharpness range in the area beyond the lens, outside of the camera. The ‘Depth of Focus’ is used to describe the same phenomenon on the imaging plane (the sensor face). The term depth of focus applies exclusively to the inside of the camera.