Ease of operation in total darkness
A good quality enlarger is required to produce
high-quality color prints. Color enlargers used in Navy
imaging facilities are diffusion type of enlargers. Like
all image-forming equipment, the lens is an integral part
of the enlarging system. The lens used in a color enlarger
must be free of chromatic aberration; that is, it must be
a color-corrected lens.
COLOR TEMPERATURE
The color temperature of light used to expose the
color material must match the spectral sensitivity of the
color material. This is true when making the original
camera exposure, and it is also true when you are
printing color materials. In color printing equipment,
color temperature is usually regulated by adding filters
to balance the light source and by regulating the voltage
source supplying the lamp.
Corrective Filters
In color printing, three emulsion layers in the
printing material must be correctly exposed from the
three color images in the negative. The exposure of these
three layers is manipulated by both exposure time and
the color quality of the exposing light reaching the paper.
The color or quality of light is altered by placing color
filters in the light beam of the enlarger. You can use color
printing (CP), color compensating (CC), or dichroic
filters. CP and dichroic filters are placed between the
light source and the negative. Generally, dichroic filters
have replaced CP filters. Dichroic filters more
accurately control the light, and unlike gelatin filters, do
not fade over time. CC filters are placed between the
lens and the light-sensitive paper.
The filters that control the exposing light are called
the filter pack The basic filter pack differs among each
characteristic of color negative film; that is, film size,
manufacturer, film type, and film speed. For example,
the basic filter pack for 35mm Kodak Vericolor III
differs from the basic filter pack of 120 Kodak Vericolor
III. The basic filter pack for 35mm Scotchcolor differs
from the basic filter pack of 35mm Fuji color. The basic
filter pack for Kodacolor Gold differs from Kodak
Vericolor III. The basic filter pack for Kodacolor 100
differs from the basic filter pack of Kodacolor 400.
In addition to CP, CC, and dichroic filters, a CP2B
or equivalent filter is usually built into the enlarger to
absorb ultraviolet radiation emitted by the light source.
Voltage Regulation
Fluctuations in line voltage are more common than
most people realize. Power fluctuations affect both the
intensity and color quality of a light source. As little as
a 5-volt variation in the normal operating range
(l00-125volts) can change the output of a lamp by about
15 percent. This change in voltage results in a change in
the color quality of the light source. This variation is
about the equivalent of a CC10 filter.
To prevent voltage fluctuations, you must connect
the enlarger to a voltage regulator. Most voltage
regulators provide a constant voltage between 95 to 120
volts.
Two main types of color enlargers are in common
use by the Navy. The two color enlargers differ in the
way they control the exposing light. They are the
subtractive and additive printers.
SUBTRACTIVE PRINTERS
The subtractive type of color enlarger uses a dial-in
dichroic filtration system. This type of color enlarger has
three filtration controls that move yellow, cyan, and
magenta filters into the path of the exposing light.
Segments of the dichroic filters are moved in and out of
the exposing light beam on calibrated cams. This type
of filtration system provides accurate and repeatable
filter pack combinations.
Most color enlargers use a tungsten-halogen light
source. These light sources produce a great amount of
heat. When a tungsten-halogen light source is used, the
color printer must have forced-air cooling fans in
addition to the heat-absorbing glass. An ultraviolet
absorber, such as a Kodak Wratten Filter No. 2B
(CP2B), must always be included in the light beam,
preferably above the negative. The most common type
of subtractive printer used in the Navy is the Chromega
D dichroic enlarger.
NOTE:
Never touch a tungsten-halogen bulb.
Handle it only by the edges or reflector cone. Oil from
your fingers can heat up and create a hot spot on the light
bulb, causing it to burn out. If you touch the bulb, clean
it with a soft cloth and isopropyl alcohol. Allow the bulb
to dry thoroughly before energizing.
ADDITIVE PRINTERS
The additive type of color enlarger uses the additive
or primary colors of light (red, green, and blue) to
expose color printing paper. This type of enlarger uses
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