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?
_______________________________________________________________________________.
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