| 摘要 |
PURPOSE:To enable fixed point macro photographing keeping the macro close distance always at a constant distance, by providing part of the macro region in the cam groove of a zoom lens in parallel arrangement so as to avoid relative movement in the direction of optical axis. CONSTITUTION:A cam groove 6'' is set parallel to a cam groove 5' at the final end. Therefore, with respect to rotation of a cam ring 4, the moving elements in the regions of grooves 5', 6'' are unchanged in the relative positions on the optical axis. When a zoom ring Z is rotated, the moving lens group advances the front group lens by means of helicoid screw provided on the outer circumference of the outer tube having linear key groove, while keeping the engaged state of the groove part of the cam ring 4 and guide pin. In this constitution, the subject distance for fixed point macro photographing may be set accurately by using zoom lens. |
