2-24. REPRODUCTION RATIO.

When copying an object, the size of the reproduction compared with the

original, depends on the focal length of the lens and the distand between the

original and the camera. The greater the focal length, the larger the copy.

a.

A 400mm lens produces copy twice the size of copy.

made with a

200mm lens, if the original is the same distance from the lens. The farther an

object is from the camera, the smaller the copy.

However, in this case, the

size is not directly proportional (inversely) to the distance. An 11x14-inch

original copied so that the long side becomes 7 inches undergoes a linear

reduction of one-half (14 = 2 ). The number obtained by dividing any length in

7

the original by its length in the copy is the

reduction figure (ratio).

b. When speaking of reduction of size in copying, linear reduction is

always meant unless the contrary is stated. Reproduction ratio is defined as

any linear distance on the image divided by the corresponding distance on the

original.

Reproduction ratio refers to either reduction or enlargement,

whichever is applicable at the time. The following formula is used:

Image size = Ratio

Object size

c. Scale is the measurement of a reproduction as compared to the

corresponding measurement of the original. A scale of 1:1 means the scale of

reproduction is equal to the scale of the original. A scale of 1:2 means that

the reproduction is one-half the size of the original.

A scale of 2:1 means

that the reproduction is two times the size of the original.

2-25. CAMERA BELLOWS EXTENSION. Normally, a camera lens can be focused from 6

feet to infinity and retain its f/number value.

At close lens-to-subject

distances, however, the distance between the lens and focal plane becomes so

great that the film does not receive the amount of light indicated by the

marked f/number. When the camera is moved to a point closer than ten times the

focal length from the subject, compensation must be made for light lost due to

the bellows extension.

This compensation is made by application of a

multiplying factor.