Basic Photography Course

negatives, or negatives containing many heavily
exposed areas, contain less water and dry faster than thin
negatives. When you think about this for a moment, you
can see that since the heavily exposed and lightly
exposed areas are distributed randomly throughout the
average negative, drying occurs rapidly in the dense

areas, more slowly in the intermediate areas, and most
slowly in the thin or unexposed areas. Obviously, then,
film does not dry uniformly.

When gelatin dries, the water it contains must first

migrate to the surface and then evaporate into the air.
Ideally, these processes should take place
simultaneously and at the same rate. However, when the
surface moisture evaporates too rapidly, the surface
becomes hard, and the internal moisture is unable to
escape it. In addition, when drying is too rapid, the outer
surface shrinks while the rest of the gelatin layer is in an
expanded state. This causes strains that can have a
harmful effect upon the emulsion.

For a negative to dry, it must be surrounded by dry

air; that is, air that contains a lower relative percentage

of moisture than the gelatin. When the heated air
circulates, the damp air moves away from the surface of
the wet film and replaces it with dry air that permits the
drying process to continue. This is the principle behind
the air impingement dryers currently in use. Heated air

accepts more moisture than cool air. When the air does
not move, air can become heated and rapidly reach a
state of equilibrium with the moist film, and drying
stops.

In an air impingement drying system, air is warmed

and blown against (impinges upon) the surface of the
wet film. The warm, dry air picks up moisture and moves

on. It is immediately replaced by more warm, dry air,
and the process continues until the film is dry. The rate
of drying is controlled by adjusting the velocity,
temperature, and humidity of the air in the drying
chamber. In hot and humid climates where the air is
saturated with moisture, the air must be passed through
a dehumidifier before it enters the drying chamber.
When this is not done, the film does not dry. In dry
climates, you must reduce both the heat and the air
velocity to prevent overdrying.

Photographic films begin drying at the corners and

edges as well as in the areas of heaviest density. This
introduces strains in the direction of the dry areas. As a
film continues to dry, the strains gradually begin to
equalize, and the film, when dried properly, ultimately
lies flat. The surface is not moist to the touch, but it is
firm and soft enough that flexing does not damage it. If

10-9

overdried, the film curls toward the emulsion and can
become brittle.

The rate of drying and the amount of curl also

depend upon how thick the emulsion layer is and
whether or not the film has a gelatin backing. Naturally,
the thicker the layer, the longer the drying time. A gelatin
backing takes time to dry, but it introduces an opposing
curl and causes the dried negative to lie quite flat.

FILM PROCESSING EQUIPMENT

Hand processing of photographic film is best carried

out in a darkroom that is properly equipped. Whether
the darkroom is large or small, certain essentials are
necessary for good quality processing.

The darkroom must be clean and well ventilated.

Shelves, bottles, racks, processing equipment, walls,
and floors that are spotted with dried chemicals are
harmful to photographic images. Navy photo lab
equipment, therefore, must always be spotlessly clean.

The arrangement of a darkroom should be

convenient, "a place for everything and everything in its
place." There should be adequate and correct safelights
placed at recommended working distances. Only
necessary sensitized material should be in the darkroom.
Temperatures in the lab should be maintained as closely
as possible to the normal processing temperature-about
70°F to 75°F. The well-equipped darkroom should
contain the following items: sink, graduates, required
chemicals, waterproof aprons to protect clothing, clean
towels, accurate thermometer and timer, and the
necessary film hangers, trays, reels, and tanks. All
darkrooms should be well stocked with prepared
chemicals in containers that are labeled properly. In
general, good photographic quality demands that all
work must be conducted in a clean, orderly, and
systematic manner.

DARKROOM SINKS

Sinks in the photographic darkroom should be sized

adequately and constructed properly. Most sinks in
Navy labs are factory-made and meet all the
requirements for photographic work Sinks should be
big enough and built so they drain thoroughly. The sink
should have duckbords to keep trays and tanks off the
bottom and to permit water to circulate under and around
the solution tanks to maintain correct and constant
temperatures. Sinks, also, should have a mixing valve
to control the temperature of the water in the sink and a

contents

Basic Photography Course

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> negatives, or negatives containing many heavily exposed areas, contain less water and dry faster than thin negatives. When you think about this for a moment, you can see that since the heavily exposed and lightly exposed areas are distributed randomly throughout the average negative, drying occurs rapidly in the dense areas, more slowly in the intermediate areas, and most slowly in the thin or unexposed areas. Obviously, then, film does not dry uniformly. When gelatin dries, the water it contains must first migrate to the surface and then evaporate into the air. Ideally, these processes should take place simultaneously and at the same rate. However, when the surface moisture evaporates too rapidly, the surface becomes hard, and the internal moisture is unable to escape it. In addition, when drying is too rapid, the outer surface shrinks while the rest of the gelatin layer is in an expanded state. This causes strains that can have a harmful effect upon the emulsion. For a negative to dry, it must be surrounded by dry air; that is, air that contains a lower relative percentage of moisture than the gelatin. When the heated air circulates, the damp air moves away from the surface of the wet film and replaces it with dry air that permits the drying process to continue. This is the principle behind the air impingement dryers currently in use. Heated air accepts more moisture than cool air. When the air does not move, air can become heated and rapidly reach a state of equilibrium with the moist film, and drying stops. In an air impingement drying system, air is warmed and blown against (impinges upon) the surface of the wet film. The warm, dry air picks up moisture and moves on. It is immediately replaced by more warm, dry air, and the process continues until the film is dry. The rate of drying is controlled by adjusting the velocity, temperature, and humidity of the air in the drying chamber. In hot and humid climates where the air is saturated with moisture, the air must be passed through a dehumidifier before it enters the drying chamber. When this is not done, the film does not dry. In dry climates, you must reduce both the heat and the air velocity to prevent overdrying. Photographic films begin drying at the corners and edges as well as in the areas of heaviest density. This introduces strains in the direction of the dry areas. As a film continues to dry, the strains gradually begin to equalize, and the film, when dried properly, ultimately lies flat. The surface is not moist to the touch, but it is firm and soft enough that flexing does not damage it. If 10-9 overdried, the film curls toward the emulsion and can become brittle. The rate of drying and the amount of curl also depend upon how thick the emulsion layer is and whether or not the film has a gelatin backing. Naturally, the thicker the layer, the longer the drying time. A gelatin backing takes time to dry, but it introduces an opposing curl and causes the dried negative to lie quite flat. FILM PROCESSING EQUIPMENT Hand processing of photographic film is best carried out in a darkroom that is properly equipped. Whether the darkroom is large or small, certain essentials are necessary for good quality processing. The darkroom must be clean and well ventilated. Shelves, bottles, racks, processing equipment, walls, and floors that are spotted with dried chemicals are harmful to photographic images. Navy photo lab equipment, therefore, must always be spotlessly clean. The arrangement of a darkroom should be convenient, "a place for everything and everything in its place." There should be adequate and correct safelights placed at recommended working distances. Only necessary sensitized material should be in the darkroom. Temperatures in the lab should be maintained as closely as possible to the normal processing temperature-about 70°F to 75°F. The well-equipped darkroom should contain the following items: sink, graduates, required chemicals, waterproof aprons to protect clothing, clean towels, accurate thermometer and timer, and the necessary film hangers, trays, reels, and tanks. All darkrooms should be well stocked with prepared chemicals in containers that are labeled properly. In general, good photographic quality demands that all work must be conducted in a clean, orderly, and systematic manner. DARKROOM SINKS Sinks in the photographic darkroom should be sized adequately and constructed properly. Most sinks in Navy labs are factory-made and meet all the requirements for photographic work Sinks should be big enough and built so they drain thoroughly. The sink should have duckbords to keep trays and tanks off the bottom and to permit water to circulate under and around the solution tanks to maintain correct and constant temperatures. Sinks, also, should have a mixing valve to control the temperature of the water in the sink and a contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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