LESSON 3
(3) Thin negatives result from underexposure or underdevelopment.
(4) Dense negatives result from overexposure or overdevelopment.
e. Mechanical and chemical print defects.
These defects often occur
for the same reasons that negative defects occur.
In addition to
underexposure, overexposure, and flat or contrasty prints, some of the more
common print defects are:
(1) Yellow stain - caused by insufficient agitation in the fixing
bath.
(2) Yellow-brown stain - caused by the use of an exhausted fixing
bath.
(3) Yellow-orange
stain
-
caused
by
underexposure
and
overdevelopment.
(4) Purple stain - results from lack of agitation or insufficient
time in the stop bath.
Learning Event 2:
QUALITY CONTROL DURING PROCESSING
1. Gamma. Gamma is a numerical value representing the contrast produced in
a negative through development.
Changes in development (in time,
temperature, and agitation) will vary contrast. An increase in development
produces a higher gamma; a decrease in development produces a lower gamma.
Materials capable of producing widely different gamma values are available.
Normal photographic subjects call for film with a gamma value around 1.0,
varying from 0.5 to 1.5. Such emulsion will record the wide range of tones
which are present in outdoor scenes. In practice, each of the main groups
of negative materials has its own individual characteristics.
Gamma is
useful to the photographer because it tells him how his photographic
material will respond to corresponding changes in exposure and processing.
a. Controls in processing. The gamma value of photographic material is
not fixed. It can be varied within wide limits by the choice of developer
and the methods of development. The time of development is only one of the
processing factors affecting gamma. Other factors are the type of developer
used, dilution of the developer, processing temperature, and the method and
cycle of agitation.
If the gamma is measured and found to be high, an
appreciable amount of development was obtained, even though the developing
time may have been correct. Gamma is one of the most important tools used
in processing control. Negatives developed to the same gamma, for example,
show comparable tone
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