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How does a photographic enlarger make a positive print from a negative?

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Diagram showing the negative-positive photographic process: a scene is captured on film in a camera, developed into a negative, projected onto paper with an enlarger, and developed again to produce a positive print.
technology of photography Figure 1: Sequence of negative–positive process, from the photographing of the original scene to enlarged print (see text).

A photographic enlarger creates a positive print from a negative by using a projection system to expose light-sensitive printing paper.

The process functions as follows:

  • Projection: The negative is placed in a holder within the enlarger’s projection assembly. An illumination system—typically a lightbulb paired with a condenser or diffuser—directs light through the negative.12
  • Magnification and Focus: The assembly is raised or lowered on a vertical column to determine the print size, while the lens is adjusted to focus the image onto photosensitive paper placed on the baseboard.12
  • Exposure: The light projects the negative image onto the paper, creating a latent image. Because the negative is tonally reversed, the dense areas block light and the thin areas allow it to pass, effectively re-creating the original scene's light values on the paper.3
  • Processing: After exposure, the paper undergoes a sequence of development, rinsing, fixing, and washing to produce a permanent positive silver image.34