The function of an enlarging light source is to provide enough light to cast the shadow of the negative onto the printing paper. Condenser and diffusion enlargers differ in terms of the quantity and the quality of the light they present to the negative.
The light from a condenser enlarger is usually provided by a tungsten bulb. The light from this bulb is focused on the negative through a series of large lenses called condensers. This focused light strikes the film in very straight, or collimated, rays.
The effect of a diffusion enlarger is much different. The light source is usually a fluorescent tube patterned into a grid. These tubes give off very little heat and thus are nicknamed cold lights. The light from this grid is diffused through a piece of translucent glass or plastic so that the light striking the negative is scattered as much as possible.
When light passes through a negative, it is scattered by the density of silver in the emulsion. The greater the density, the more the light is scattered. This is called the Callier effect. Collimated light from a condenser enlarger exaggerates this effect, giving the print more overall contrast and greater tonal separation. Because diffusion enlargers scatter the light more evenly across the surface of the emulsion, they render the true contrast of the negative more faithfully.
The advantages and disadvantages of condenser versus diffusion light sources can be summarized as follows.
CONDENSER ENLARGERS. The more a negative is enlarged, the more contrast is lost due to the scattering of light between the enlarging lens and the printing paper. Condenser enlargers compensate for this to a certain extent, which makes them very useful for printing small negatives, but there is a noticeable loss of tonal gradations, especially in the highlight areas of the print. Grain and dust are also more apparent with condenser enlargers. The extra contrast you can expect from condenser-enlarging light sources means that your Normal Development Times will be shorter when compared to photographers printing with diffusion enlargers. It usually requires approximately 15% less development to compensate for this factor. DIFFUSION ENLARGERS. As a rule, diffusion enlargers require that you produce negatives with more contrast than if you were printing with a condenser enlarger. This means that your Normal Development Time is likely to be longer. They are also dimmer and thus require slightly longer printing times. On the other hand, diffusion light sources render much more subtle tonal gradations in the highlights and obscure dust and scratches. This makes them ideal for printing medium- or large-format negatives. Add 15% to your Normal Development Times if you switch from printing with a condenser enlarger.
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