rack

Definition: Noun: (1) Track or bar with indents or teeth which engage in circular gear-wheel or pinion to create a rack and pinion: used for focusing or aligning optical equipment e.g. enlarger, bellows extension. (2) Hanger to hold roll or sheet film for processing, or for drying prints. Verb: (3) To focus or change position of an instrument or optical component e.g. enlarger, process camera.

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