Process Cameras Printing Knowledge
Process Cameras

Description | Types | Components | Operating Steps | Film | Line Photography | Halftone Photography


 

Description

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.

 

Types

The two types of process cameras are the horizontal and vertical cameras.

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.

 

Components

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 operating.

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 the film.

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 is required.

 

Operating Steps

There are several steps that are required in order to create images with the process camera:

  1. Load the copyboard with the artwork: line art, black and white photographs, color photographs, or text.
  2. Set the light source.
  3. Adjust the exposure settings.
  4. Adjust the focus.
  5. Mount the film on the vacuum back.
  6. Set the exposure time.
  7. Perform the exposure.
  8. Develop the film.

 

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 be produced.

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 darkness.

 

Line Photography

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.

 

Halftone Photography

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 screens.

 


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