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).

When a diffusion enlarger is used, negative defects are not recorded as clearly in the print, compared to condenser enlargers. There is an apparent overall softening of the image sharpness and a reduction in image contrast.

Most of your negatives can he enlarged equally well with either a condenser or diffusion enlarger; however, for certain work the choice of enlarger may be an important factor.

The characteristics of a diffusion enlarger are as follows:

It should be used for printing negatives that have been retouched.

It subdues negative defects and grain.

It has less image contrast than that produced with a condenser enlarger.

It is not suitable for making large prints due to the softness of the image produced.

Diffusion enlargers should be considered for use in portraiture and when the negatives have been retouched.

CONDENSER-DIFFUSION ENLARGERS

A condenser-diffusion enlarger or semidiffusion enlarger is a compromise between the two extremes of condenser and diffusion. A condenser-diffusion enlarger uses a diffusion (frosted) bulb and condensers, or a diffusion bulb with either a diffusing glass over the condensers, or else one of the condensers itself acts as the diffuser.

A condenser-diffusion enlarger has the advantages of a diffusion enlarger to reduce the effects of negative defects, silver grain structure and dust, and it also uses the condenser system for speed and uniformity of light.

The enlargers in general use by most Navy imaging facilities are the condenser-diffusion type. They use frosted or diffusion bulbs with or without a diffusion screen placed above the condensers.