proportional to the temperature. When the temperature
is too low, evaporation is slowed down. When it is too
high, the emulsion may be damaged.
Roller transport processors provide very consistent
processing results and can be converted easily to a new
process. The disadvantages of roller transport
processors are: they can leave scratches and scuffs from
dirty rollers touching the film, they require a high
amount of maintenance due to the large number of
moving parts, and oxidation can be a problem due to the
churning action of the rollers in the chemistry.
QUALITY PROCESSING
The processing required to produce a quality
product of any particular film varies with different
developer and film combinations, time and temperature
of the process, agitation, the film exposure, and the skill
of the darkroom worker. A good, high-quality image is
one that is free from all processing faults, including
scratches and dirt, and so forth.
When processing black-and-white film, your goal is
to produce a "normal" negative that is as fault-free as
possible. Normal is a rather vague term; however, a
normal negative is one that yields a pleasing print or
reproduction of the original scene when printed without
a printing filter or with a No. 2 printing filter.
When film is exposed and processed properly, it is
a normal negative. However, when a negative varies
from normal, you should be able to determine what
conditions caused the deviation.
A negative has several basic characteristics to
consider when evaluating quality. These basic
characteristics are as follows:
General negative density or opacity to light.
Image highlights or areas of greatest density.
The shadows or areas of least density.
Contrast or the differences between highlight and
shadow densities.
Tonal gradation or the range of grays between the
highlights and the shadows.
Graininess or the appearance of silver grains in a
negative that have clumped together. The size of the
clumps determines the degree of graininess in the
processed material.
All the basic characteristics of a negative are
affected to some extent by a combination of exposure
and development. By studying these characteristics, you
can usually determine the cause of an error or poor
quality in a negative.
DENSITY
Density determines how much of the incident light
falling upon a negative passes through the image. When
a small amount of silver is present in the negative, the
image appears thin (transparent), and it has low density.
When there is a large amount of silver present, only a
small amount of light passes through the image, and the
negative is said to have high density.
A low density, thin negative can be caused by
underexposure or underdevelopment or by a
combination of the two. A heavy or dense negative is the
result of either overexposure or overdevelopment or a
combination of the two.
HIGHLIGHTS
The highlights, or dark areas, of a negative for most
purposes should not lack detail. When detail is lacking
because the highlights are too dark, the highlights are
too dense or blocked up. Excessive highlight density is
caused by overexposure and/or overdevelopment.
When both the highlights and the shadow areas are too
thin and lack detail, the negative is probably
underexposed. Thin highlights are caused by
underexposure and/or underdevelopment.
This may seem like a repetition of the previous
discussion on density. However, a negative could and
may have overall good density except in the highlight
areas. This situation is a result of exposure latitude that
is not great enough for the scene brightness range.
SHADOWS
The shadows, or the more clear areas of the
negative, also should contain image detail. If these areas
are so thin and weak that they are transparent or nearly
so, the shadow areas are said to be lacking in detail. Loss
of shadow detail is caused normally by underexposure.
The need for detail in both the highlights and the
shadows for photographs of most subjects cannot be
stressed too strongly. One is as important as the other in
the production of good photographs.
CONTRAST
Contrast is the difference in density between the
highlights and the shadows in a negative. When this
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