condenser

Definition: Lens, fresnel lens or group of lenses used to collect light from a source to evenly illuminate a film or transparency for projection. * Used in slide, overhead and cine projectors, enlargers, etc.
Condenser milk
Condenser enlargers are commonly thought to produce completely undiffused light. In fact the light-housing for all condenser enlargers I've ever seen are painted white inside, thus creating a fairly diffused light-source - resulting in what is best referred to as a semi-condenser source.

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