부산대학교 도서관

A zoom lens includes a cam roll, straight-forward units, lens groups, a driving unit, a detecting unit and a micro-processing unit. The lens groups moved by the cam roll sequentially varies from a receiving status to a zeroing status, a macro shooting-distance status and a wide shooting-distance status. A datum point of the cam roll corresponds to the zeroing status of the lens groups. The detecting unit includes an impeller, a detecting portion and a photonic sensor. When the photonic sensor detects the datum point of the cam roll, the micro-processing unit determines the position of the datum point of the cam roll and to reset the rotation count of the impeller. When the photonic sensor detects a skew point of the cam roll, the micro-processing unit determines and amends the rotation count of the impeller to be equal to a predetermined value.