a. Adjusting light assemblies.
Adjust the light assemblies as follows:
(1) Position your head in front of the lens assembly (figure 14) and
study the illumination of the item to be copied.
(2) Readjust the light assemblies (para 2-5b) to produce an even
illumination with no glare or hotspots.
b. Determine exposure. The exposure required for the type of copy and
the image size used may be determined by the operator based upon experience.
Normally, however, an exposure meter must be used. When an exposure meter
is used, proceed as follows:
(1) Operate the exposure meter to measure the light from the material
to be copied, and to determine the exposure setting (f/stop and time) for
the light measured and for the film used.
(2) The exposure setting obtained [(1) above] is correct for objects
at infinity (a lens operating at a distance from the film equal to the lens
focal length).
However, the lens used with the camera set operates at a
distance from the film much greater (due to the bellows extension) than its
12-inch focal length.
As a result, a corrected exposure setting must be
determined (calculated).
(3) Calculate the corrected exposure setting as follows:
(a) Measure the bellows extension (distance from the center of the
lens to the film plane).
(b) Use the following formula to calculate the corrected exposure
setting:
Where:
CES is the corrected exposure setting in seconds.
BE is the bellows extension distance in inches [(a) above].
FL is the focal length of the lens in inches.
EM is the exposure meter setting in seconds [(1) above].
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