Depth of Field
Closely related to an understanding of the aperture is depth of field. This concept refers to the amount of sharp focus around the subject that the camera is focused on. While most people think of sharpness as always being desirable, this is not true. Experienced photographers use depth of field to produce stunning images, often with areas deliberately out of focus.
There are several important things to keep in mind with depth of field:
The higher the f-number (the smaller the opening), the greater the depth of field.
The lower the f-number, the shallower the depth of field.
The shorter the focal length, the greater the depth of field.
The longer the focal length, the shallower the depth of field.
The farther the camera is from the subject, the greater the depth of field.
The closer the camera is to the subject, the shallower the depth of field.
A higher f-number will be sharper in terms of focus but requires a corresponding drop in shutter speed, which may cause blur.
A lower f-number will always have less in focus but requires a corresponding increase in shutter speed.
The maximum aperture used in this close shot allows much of the tablecloth to be in focus.
The minimum aperture used in this close shot causes much of the tablecloth to go out of focus both before and beyond the point of focus.
In portraiture, an out-of-focus background will often provide a soft setting for a sharp picture of a person's face. This can be achieved using a portrait lens of about 100 mm (35 mm equivalent) and a lower f-number. In another example, under low light with a slow shutter speed, a hand-held camera may produce a slightly blurred subject, yet that subject can appear quite sharp when contrasted with an out-of-focus background.
With experience, depth of field can be judged in the review mode on the LCD screen. Take a test picture and then view what you shot. Look first at the point of focus (the subject) and then the sharpness in front of and behind the subject.
