LEARNING OBJECTIVE: Recognize the purpose of projection printing, identify the main difference between projection and contact printing, and summarize the advantages of projection printing.
Projection printing is the process of making positive prints by projecting the negative image onto photosensitive paper. The projected image may be enlarged, the same size as the negative image, or reduced in size. When the print images are larger than the negative images, the process is called enlarging. When the print images are smaller than the negative images, the process is called reducing. Because projection printing is usually used to make positive prints with images larger than the negative, projection printers are usually referred to as enlargers. The term enlarging generally refers to all forms of projection printing.
DIFFERENCES BETWEEN PROJECTION AND CONTACT PRINTING
Projection printing differs from contact printing because the negative is separated from the paper and the image is projected by a lens onto the sensitized material. The negative is placed between an enclosed light source and a lens. The lens receives the light that passed through the negative and projects the image onto the paper. Changing the distance between the lens and the paper controls the size of the image. The image is focused on the paper by adjusting the distance between the negative and the lens. It is possible to enlarge or reduce the size of the projected image by changing and adjusting these distances.
Enlarging is a very adaptable and versatile process because considerable image and exposure control can be used The main advantage of enlarging over contact printing is that large prints can be made, but there are several other important advantages. The advantages of projection printing areas follows:
l Cropping (selecting the main area of interest in a negative) can be done and enlarged to any suitable size. This gives you the opportunity to eliminate unwanted and distracting elements from around the point of interest of the picture.
l Local fogging with a small external light, such as a penlight, to darken selected areas. For example, to darken the background of a portrait to direct viewer attention to the face.
l Special effects. You can change the appearance of the image by use of diffusers or patterns between the lens and paper.
l Image distortion correction or introduction can be done by tilting the enlarger easel. An easel is the device used to hold the paper during exposure.
In general, all enlargers are similar in design and operation. They have an enclosed light source, some method of providing an even distribution of light over the negative, a negative carrier, a lens, and a means of adjusting the lens-to-negative and lens-to-paper distances. There are two types of enlargers - condenser and diffusion.
The condenser enlarger (fig. 11-32) is the one most commonly used in Navy imaging facilities. It has a set of condensing lenses between the printing light and the negative. These lenses align and project the light rays evenly through the negative. Since all features of the negative are being enlarged, any flaws also will be enlarged.
The diffusion enlarger (fig. 11-33) has a diffusing medium (usually a ground glass) between the light source and the negative to spread the light evenly over the entire surface of the negative. Light emitted from the lamp, as well as that reflected from the parabolic reflector, strikes the diffuser, which, in turn, scatters it in all directions. Thus, when the light reaches the negative, it is traveling in a nondirectional pattern.
Most enlargers have a tungsten lamp as a light source. The lamp is enclosed in a lighttight housing that
Figure 11-32. - Condenser enlarger.
Figure 11-33. - Diffusion enlarger.
is ventilated to prevent excessive lamp heat from damaging the negative. Some enlargers have blowers to circulate air and cool the inside of the lamp housing.
The negative carrier used in an enlarger may be either a dustless type or a glass sandwich type. The dustless type of carrier is made of two metal plates with an opening in the center large enough to hold the negative. The negative is placed between these plates and held in position by its edges. This type of carrier is good for negatives 4 x 5 inches or smaller since these negatives are stiff enough to remain flat. The glass sandwich type of carrier is a holder where the negative is placed between two sheets of glass. This type of holder is used for larger negatives since they have a tendency to sag in the center if they are not supported by glass.
The lens used in an enlarger should have an angle of field large enough to cover the negative being printed. A lens with a focal length approximately equal to the diagonal of the largest negative to be printed will provide sufficient angle of field.
The bellows of an enlarger should be capable of extending at least twice the lens focal length. This amount of bellows extension is necessary for making 1:1 reproductions. Although it is possible to make reductions to any desired size, the bellows on most enlargers cannot be extended far enough to make reductions smaller than 1:1. Smaller reductions can be made by using a longer final-length lens, but a better method is to use a reducing attachment. A reducing attachment consists of a section of supplementary bellows fitted with a longer focal-length lens.