# Lens Angle and Field of View

Field of view may be calculated by substituting film aperture size for image size; the field of view is then the object size. (Lens angle may be calculated with the aid of a table of tangents or a pocket scientific or slide-rule calculator; see tangents table.)

For 2:1 anamorphic lenses, the field or object size is double in the horizontal dimension.

A = Aperture (height or width) in inches f = focal length of a lens in inches

XA A

The tangent of Vi viewing angle can be converted to degrees by consulting a tangent table. Multiply this angle by two to obtain the full viewing angle. For Cinemascope, or other two times squeeze wide screen processes, the formula is simply the aperture divided by the focal length of the lens, since 2 times Vi equals 1. Other squeeze ratios should use the following formula:

I/2 A x Squeeze Ratio

Tangent Vi viewing angle =-

Using the above sketch one may calculate camera distance, object size, lens focal length or image size if any three are known.

O = object size in front of camera D = distance from object to lens of camera F = focal length of lens used A - image size and: a = lens angle when A = film aperture size O = field of view when A = film aperture size