G - Physics – 03 – B
Patent
G - Physics
03
B
88/16, 88/43
G03B 13/26 (2006.01) G02B 27/02 (2006.01) G02B 27/40 (2006.01)
Patent
CA 1049820
FOCUSING DEVICE AND METHOD OF USE THEREOF FOR PHOTOGRAPHIC ENLARGER ABSTRACT The present invention is an optical aid especially applicative as a focuser for use with photographic enlargers. The structure of the device makes it possible to focus at any point on the projected image at the easel surface. The focuser can be hand held by the operator with one reference point placed on the easel surface in an area where the image is to be focused. The focuser has a mirror which reflects the light of the enlarging apparatus onto an integral viewing surface with the distance from the reference point to the center of the mirror along a reference axis being precisely the same as the distance from the center of the mirror to the center of the viewing surface along a viewing surface axis. The angle of the viewing axis relative to the mirror surface must be the same as the angle of the reference axis to the mirror surface. By maneuvering the focuser while keeping the reference point in contact with the desired focusing point on the easel surface, the distance that a light ray would travel from the enlarging lens to the focusing point is equal to the distance from the enlarging lens to the midpoint of the mirror surface plus the distance from the midpoint of the mirror surface to the viewing surface. The maneuvering or tilting of the focuser changes the normal height of the midpoint of the mirror with reference to the easel surface and changes the angle that the planar mirror makes with a horizontal axis. However, by maintaining the reference point generally in the center of the shadow cast by the mirror it is possible to maintain the equality in the above distance equation.
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