| 摘要 |
PURPOSE: To correct tolerance between the nominal and actual focal distance of a lens by constituting the positioning means of a long and narrow cam member provided with a curved cam surface and of a cam follower that is connected to the lens and that moves in contact with the cam surface. CONSTITUTION: A cam surface is extended across the vertical axis of a cam member 23, while the curved cam surface of the cam member 23 is provided with a twisted appearance and formed with plural different arches with the same hyperbola arranged successively and adjacently across the plane of the hyperbola. The cam surface is provided with a contour suitable to a lens with a nominal focal distance as shown in dotted lines. In addition, a cam follower 29 moves in contact with a cam surface 24 on the level of a zero error contour 21; therefore, the contour of the cam provided for the cam follower 29 changes by displacing the cam member 23 in the direction perpendicular to the vertical axis (direction vertical to the scanning surface) against the cam follower 29. As a result, tolerance can be corrected for the plus and minus focal distance. |
