a. Multiplying factor. The multiplying factor for a critical exposure is

determined in the following manner:

bellows extension 2

BE 2

Multiplying Factor = (

focal length

)

or ( FL )

Example:

If a 6-inch lens is used with a 12-inch bellows, the multiplying

factor is -

12 2

2

Multiplying Factor =

( 6) =2=4

b. Use of multiplying factor.

(1) As explained previously, each lens stop passes twice as much light

as the lens stop above it. For example, f/4 passes twice as much light as

f/5.6, four (2x2) times as much light as f/8, eight (2x2x2 ) times as much

light as f/11, sixteen (2x2x2x2) times as much light as f/16, etc.,

(2) The multiplying factor indicates the number of times that exposure

must be increased. For example, a multiplying factor of 4 (2x2) indicates

that the lens must be opened two lens stops beyond the exposure setting

for an object at a normal 6-foot distance; a multiplying factor of 8

(2x2x2) indicates that the lens must be opened three stops beyond the

normal exposure setting; and a multiplying factor of 16 ( 2x2x2x2 )

indicates a need for opening the lens four stops beyond the exposure

setting normally used at the 6-foot distance.

REVIEW EXERCISE

28.

You have an original document that is 8x10-inches and you must make a

reproduction that is 4x5-inches. What is the ratio?

_______________________________________________________________________________.

29.

You are given a chart that is 3x5-inches and asked to copy it at a ratio

of 2:1. What size will the copy be?

_______________________________________________________________________________.