The Camera

Essentially, any camera is simply a device that uses a lens to focus the light reflected by an object onto a piece of photographic film. It's very important to understand and remember that only a certain amount of this reflected light must be allowed to expose the film. When this is done properly, we say that the film has been given the correct exposure.

The Aperture

The camera has two mechanisms that control the amount of light that's allowed to expose the film. The first is called the diaphragm. The diaphragm is simply a metal membrane in front of the film with an adjustable hole in it called the aperture. The larger the aperture, the more light it will let into the camera to expose the film.

FIGURE 162 Camera and diaphragm.

The various aperture sizes are measured with numbers called f/stops. Typical f/stop numbers are f/1.4, f/2, f/2.8, f/4, f/5.6, and f/8. You must remember two rules relating to f/stops:

1. The larger the f/stop number, the smaller the opening of the aperture. Thus, f/8 represents a smaller aperture (and less exposure) than f/5.6. A simple way to remember this is to consider f/numbers as you would ordinary fractions: 1/16 of a pie is smaller than 1/2 of a pie.

2. The second rule relates to what is called depth of field.

When you focus a camera on a given object, any object that is equally distant from the camera will also be in focus. This distance is called the plane of sharp focus (Figure 163).

FIGURE 163 Objects A and B are in focus.

Any object that is within a certain distance in front of or behind this plane will also appear to be in focus. This range of distance within which objects appear to be in focus is called the depth of field. The farther an object is from this depth of field, the more out of focus it will be.

FILM PLANE

FILM PLANE

FIGURE 162 Camera and diaphragm.

PLANE OF SHARP FOCUS

PLANE OF SHARP FOCUS

DEPTH OF FIELD -

FIGURE 164 Objects C and D are in focus. Objects E and F are out of focus.

The amount of depth of field depends on the size of the aperture. The smaller the aperture, the greater the depth of field. Thus, f/8 will give you more depth of field than f/5.6.

APERTURE: f/5.6

APERTURE: f/5.6

APERTURE: f/11

APERTURE: f/11

PLANE OF SHARP FOCUS

DEPTH OF FIELD

PLANE OF SHARP FOCUS

WIDE DEPTH OF FIELD

FIGURE 165 Depth of field increases from f/5.6 to f/8.

This is important to know because there are times when you will want as much depth of field as possible and others when you will want to use a selective focus to isolate objects in a given scene.

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