Types | Components | Operating
Steps | Film | Line Photography
| Halftone Photography
The process camera is able to produce high contrast film images
from other 2 dimensional images such as line art, text, black and white photographs,
and full-color photographs. The lens on a process camera is specially designed
to provide excellent results with 2-dimensional (flat) artwork. The lens on
a process camera differs from the lens on a regular snapshot camera which is
designed to photograph 3-dimensional objects.
The two types of process cameras are the horizontal and vertical
Horizontal Camera: The lens of a horizontal camera
faces parallel with the floor and the components are built in a horizontal
line. The camera is also known as the "Darkroom Camera" and can
be installed through a wall between a darkroom and an adjacent room with
normal lighting. The portion of the camera that holds the film is located
in the darkroom and the major portion of the camera is in the lighted room
where artwork and copy, lens adjustments, and exposure settings can be accomplished.
Having the major portions of the camera in the lighted room saves space
in the darkroom and makes camera operation and film processing more efficient,
although the entire camera can be located in a darkroom if necessary.
Most horizontal cameras accept single sheets of film only,
but there are models that operate with film contained within a roll which
dispenses a film sheet for each exposure. Horizontal cameras also have a
wide range of enlargement and reduction ability.
There are two types of horizontal cameras: floor models
and overhead models. The major components of the floor models are mounted
to a camera bed which is positioned on a heavy base. The base is carefully
secured to the floor so that the unit is as level as possible and so that
vibration is reduced. An overhead model is even better for reducing vibration
because the camera is attached to an overhead frame. The overhead model
also provides better access around the copyboard and lensboard.
Vertical Camera: Also known as the "Gallery
Camera", the vertical camera is much like a horizontal camera turned
on end. The components are built in a vertical line and the lens faces the
floor. The vertical configuration is useful when space is at a premium,
but it requires that the vertical camera be housed in a darkroom. There
are daylight models that have special film holders that allow the the camera
to be used outside of the darkroom.
The smaller size of the vertical camera does not allow
for enlargements or reductions as great as the horizontal camera. They also
cannot accommodate film sizes as large as horizontal cameras. In order to
create the same range of enlargements and reductions as the horizontal camera,
the vertical camera would have to be built much higher than would be practical
in order to get the required spacing between the larger film and the copy.
The vertical camera can accept only single film sheets.
Horizontal and vertical cameras contain many of the same components
such as the copyboard, lensboard, and focusing controls. Listed below are descriptions
of the major components and their functions:
Copyboard: The copyboard consists of a frame with
a hinged glass door. The hinged door is closed over the artwork or "copy"
to hold it in place while it is being photographed. The copyboard is mounted
on a track to enable it to move back and forth, toward or away from the
lens in order to perform enlargements or reductions.
Copyboard Lights: The copy is illuminated with banks
of lights mounted at a 45 degree angle and positioned at the proper distance
from the copy to ensure the best results. The lights are connected to the
copy board or to the same track onto which the copyboard is mounted. Being
mounted on the same track ensures the proper spacing between the lights
and the copy regardless of how much the copy will be enlarged or reduced.
There are several types of lamps available for copyboard
lights. Each type varies in the part of the visible spectrum that is emitted
and in the intensity of light that is delivered. An important point to remember
is that when one lamp burns out, all of the lamps should be replaced. Replacing
all of the lamps will ensure that all of the lamps are emitting the same
intensity of light onto the copyboard. Lamps for process cameras are divided
into two main groups: incandescent and gas discharge.
Incandescent: A constant output of light is produced
by incandescent light sources. The wavelengths emitted are throughout
the visible spectrum. The intensity of light and the type of wavelengths
emitted depends upon the temperature attained when the light sources are
Carbon Arc: The light from a carbon arc
covers the entire visible spectrum and it is extremely intense. The
light produced by carbon arcs is not the result of a bulb burning, but
is the result of electric current passing through two lengths of a carbon
rod. A very bright arc of light is produce when the two pieces come
together. Carbon arcs are rarely used except in the oldest cameras,
but at one time it was very popular. The burning carbon rods gradually
get shorter as they are burned and they produce smoke and ash which
produce health concerns.
Tungsten: Some lamps for process cameras
are made with tungsten filaments which are also used in regular light
bulbs. The light emitted is high in red wavelengths and low in the blue-violet
end of the spectrum, so they are not a good choice if a wider spectral
range is required. They are inexpensive, but the total light output
is gradually reduced because some of the tungsten filament burns away
as the lamps are used.
Quartz-Iodine: A quartz-iodine lamp uses a tungsten
filament surrounded by iodine and inert gases enclosed in a quartz bulb.
The color temperature is greater than regular tungsten filament lamps
and the the bulbs do not darken with use.
Gas Discharge: The nature of the gas within the
lamp and not the temperature at which the lamp burns determines the wavelengths
of light emitted. The different gas discharge light sources have separated
spectral wavelengths known as a discontinuous spectrum.
Pulsed Xenon: The pulsed xenon lamp is
similar to an electronic flash used with photography. The light output
is close to that of daylight. They provide a clean and constant level
of light, but they have a high initial cost.
Mercury Vapor: An electrical current passes
through gaseous mercury within the lamp in order to emit light. The
light is high in ultra-violet radiation and is useful when longer periods
of exposure are required.
Metal Halide: Providing a good source of blue-violet
wavelengths, metal halide lamps are mercury lamps with a metal halide
additive. The light intensity emitted from the lamps is 3 to 4 times
stronger than most other types of lamps.
Lensboard: Like the copyboard, the lensboard is
mounted on a track which allows the lens assembly to move back and forth
in relation to the copy.
Lens: The lens is the most important part of the
camera. It controls the amount of light reaching the film and the overall
quality of the photographed image. When the lens is rotated, the metal blades
of the iris inside the barrel of the lens, open or close creating a larger
or smaller opening through which light can pass.
Special lenses can be used on the process camera to create
different effects. One such lens is the anamorphic lens which is also known
as a variable squeeze lens. The anamorphic lens enlarges or reduces an image
in one direction only, rather than affecting the width and height proportionately.
Bellows Extension: Shaped like an accordion, the
bellows extension forms a light tunnel between the lens and the film. The
accordion shape allows the bellows to expand and contract with the lensboard
as it is moved. It should be checked for cracks occasionally because even
the smallest crack will allow unwanted light to enter the chamber and reach
Ground Glass: Mounted on a hinged frame on the back
of the camera case, the ground glass is swung into place in order to check
the positioning and focus of the copy. The frame can then be swung out of
the way after use.
Vacuum Back: Mounted on the back of the camera,
the vacuum back is a door which contains a series of holes on the back side.
When a vacuum pump is switched on, any film that has been placed over the
holes will be held in place by the vacuum. There are several sets of markings
and guides to assist in correctly positioning the film on the vacuum board.
Focusing Controls: The process camera has controls
for adjusting the lensboard and the copyboard. Cameras with manual
controls have dials that are used to move the lensboard and the copyboard
into the proper position. Steel tape rules, which move as the dials are
turned, are used as guides to indicate the enlargement or reduction percentage.
There are separate tapes for the copyboard and the lensboard and each tape
must be set at the same percentage in order for the enlargement or reduction
to be correct. When an image is enlarged, the lens is farther away from
the film and closer to the copy than it is when set at 100%. When an image
is reduced, the lens is closer to the film and farther from the copy than
it is when set at 100%.
Computerized controls have taken the place of manual controls
for enlargement and reduction, lens focusing, and exposure settings. The
computer can store the settings to be repeated whenever the same exposure
There are several steps that are required in order to create
images with the process camera:
- Load the copyboard with the artwork: line art, black and white photographs,
color photographs, or text.
- Set the light source.
- Adjust the exposure settings.
- Adjust the focus.
- Mount the film on the vacuum back.
- Set the exposure time.
- Perform the exposure.
- Develop the film.
Film for process cameras is made of a transparent plastic or
acetate base coated with an emulsion sensitive to light. The emulsion is made
of gelatin and light sensitive silver salts. Photographic paper is similar to
film except that it is opaque and is used for producing high resolution positives.
Structure: Most types of film contain the same general
components. Film used with the process camera has a base made from cellulose,
polystyrene, or ester. An adhesive bonds the gelatin emulsion, containing
the silver compound, to the base. A protective layer covers the emulsion
and an antihalation layer is bonded to the bottom of the base material.
The antihalation material prevents light from reflecting back to the emulsion
side during the exposure period, so that a shadow or double image will not
Color Sensitivity: The color sensitivity of film
describes the wavelengths of light that will expose the emulsion of the
film. There are three types of light sensitive film emulsions used in film
for process cameras: monochromatic, orthochromatic, and panchromatic.
Monochromatic: Also known as blue sensitive film,
monochromatic film is sensitive only to blue light and not the red or
green parts of the visible spectrum. Green and red wavelengths record
as black. The emulsion has a silver emulsion base and all emulsions containing
silver are sensitive to blue light. Monochromatic film is an excellent
choice for copying black and white photographs.
Orthochromatic: Orthochromatic film is not sensitive
to red light but it is sensitive to all other visible spectrum wavelengths.
This allows it to be used for a greater range of applications. The emulsion
of orthochromatic film is faster acting than monochromatic.
Panchromatic: Also known as pan films, panchromatic
film is sensitive to all visible wavelengths. The color sensitivity of
panchromatic film comes closet to the color sensitivity of the human eye.
The film is used for reproducing color originals. Because it is sensitive
to all visible wavelengths, it is necessary to process the film in total
Line art is defined as any artwork consisting of lines such as original drawings
and text characters. The copy does not contain any continuous tones such as
in photographs. The copy can be photographed and the resulting negative can
be used to produce a printing plate. The plate is used to reproduce the line
art on the press in the same color as the original or any other color that is
required. If the original line art contains several different colors, then a
separate negative and plate are necessary for each of the colors, but only if
all the colors are required for the finished printed piece. If all the colors
are not required, then the entire image can be printed in one color.
A halftone is a reproduction of a continuous tone image, such as a photograph,
using patterns of printed dots. The dots can be in rows and columns and vary
in size in order to simulate the image. Another option is that the dots can
all be the same size, but they are scattered in groups of different quantities.
The halftone negative is produced by placing a special screen over the film.
During the exposure, the light from the original image passes through the open
areas of the screen to the film, resulting in a negative of the image consisting
of many dots. This dot pattern enables the image to be reproduced as a printed
item using a plate made from the negative.
If a full-color image is required, then a separate halftone negative for each
of the three primary color components (cyan, magenta, and yellow) plus black
must be made in order to reproduce the image in full-color. The halftone records
of each of the primary color components of the image are know as color
separations. For more on halftones and screens see line
Back to Top