Figure 2-15.

Angle of view.

a.

To determine the angle of view, draw a line AB equal to the focal length

of the lens. Construct BC perpendicular to AB and locate point C so that BC is

equal to one-half of the diagonal of the negative, (fig 2-16).

Multiply the

size of the angle by two to determine the angle of view.

Figure 2-16.

Determining angle of view.

b.

While angle of field is an unalterable optical characteristic of a lens,

angle of view is a variable depending on focal length of the lens, film size of

the camera with which the lens is used, and subject distance.

(1) With a normal lens, the focal length is equal to the diagonal of the

negative size used. When a normal focal length is used with a negative having

a shorter