Optical tool used as a focus assist for photographic enlargers. Such tools allow the operator of the enlarger to view the actual film grain and focus the enlarger precisely. (achieve grain focus)
Achieving correct focus of the light projecting onto the paper surface of an enlarger can be difficult, and grain focussers can help immeasurably in this regard. They are simple tubes equipped with lenses which can multiply the image by 10 to 20x. They also contain carefully positioned mirrors which reflect light entering from above (from the enlarger head) towards the eye of the operator.
The distance from the eyepiece to the mirror is exactly equivalent to the distance from the mirror to the paper surface, so when the image is correctly in focus in the eyepiece of the grain focusser it will also be correctly in focus on the paper.
cf. enlarger, grain, grain sharp.
Entry last updated 2002-04-11. Term 568 of 1487.
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