The color temperature of light used to expose the color material must match the spectral sensitivity of the color material. This is true when making the original camera exposure, and it is also true when you are printing color materials. In color printing equipment, color temperature is usually regulated by adding filters to balance the light source and by regulating the voltage source supplying the lamp.

Corrective Filters

In color printing, three emulsion layers in the printing material must be correctly exposed from the three color images in the negative. The exposure of these three layers is manipulated by both exposure time and the color quality of the exposing light reaching the paper. The color or quality of light is altered by placing color filters in the light beam of the enlarger. You can use color printing (CP), color compensating (CC), or dichroic filters. CP and dichroic filters are placed between the light source and the negative. Generally, dichroic filters have replaced CP filters. Dichroic filters more accurately control the light, and unlike gelatin filters, do not fade over time. CC filters are placed between the lens and the light-sensitive paper.

The filters that control the exposing light are called the filter pack The basic filter pack differs among each characteristic of color negative film; that is, film size, manufacturer, film type, and film speed. For example, the basic filter pack for 35mm Kodak Vericolor III differs from the basic filter pack of 120 Kodak Vericolor

III. The basic filter pack for 35mm Scotchcolor differs from the basic filter pack of 35mm Fuji color. The basic filter pack for Kodacolor Gold differs from Kodak Vericolor III. The basic filter pack for Kodacolor 100 differs from the basic filter pack of Kodacolor 400.

In addition to CP, CC, and dichroic filters, a CP2B or equivalent filter is usually built into the enlarger to absorb ultraviolet radiation emitted by the light source.

Voltage Regulation

Fluctuations in line voltage are more common than most people realize. Power fluctuations affect both the intensity and color quality of a light source. As little as a 5-volt variation in the normal operating range (l00-125volts) can change the output of a lamp by about 15 percent. This change in voltage results in a change in the color quality of the light source. This variation is about the equivalent of a CC10 filter.

To prevent voltage fluctuations, you must connect the enlarger to a voltage regulator. Most voltage regulators provide a constant voltage between 95 to 120 volts.

Two main types of color enlargers are in common use by the Navy. The two color enlargers differ in the way they control the exposing light. They are the subtractive and additive printers.