Condenser Enlargers

Figure 11-8.–Condenser enlarger. 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 when 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 provides sufficient angle of field. The bellows of an enlarger should be capable of extending at least twice the focal length of the lens. 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 focal-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. The systems used to distribute the light evenly over the negative divide enlargers into three general types–condenser, diffusion, and condenser-diffusion enlargers. CONDENSER ENLARGERS A condenser enlarger has a set of condensing lenses between the light source and the negative. The condensing lenses concentrate or focus the light from a light bulb and direct the light rays straight through the negative to the lens (fig. 11-8). Figure 11-9.–Diffusion enlarger. The condenser lenses are a pair of planoconvex lenses mounted as a unit with their convex surfaces face to face. A condenser enlarger produces a sharp, brilliant image and produces higher contrast and detail than diffusion enlargers. Negative defects and scratches are more apparent in the print when made on a condenser enlarger. The characteristics of a condenser enlarger are as follows: It produces maximum tone separation. It is suitable for making prints to a high degree of enlargement, because of its optical characteristics. It produces a higher image contrast with a given negative than printing with a diffusion enlarger. It is not recommended for negatives that have been retouched, because the edges and ridges of the retouched areas may print as dark lines. It may be used to emphasize negative defects and silver grain structure. DIFFUSION ENLARGERS A diffusion enlarger has a diffusion screen (usually ground or optical glass) between the light source and the negative. Light from the lamp, as well as the light reflected from the reflector of the lamp housing, falls on the diffuser that scatters the light. After the light passes through the diffuser, it travels in many directions when it falls upon the negative (fig. 11-9). 11-10