| 摘要 |
To provide means for correctly and quickly detecting the focusing lens of an auto focusing mechanism located at its focusing position. MEANS FOR CARRYING OUT THE INVENTION In the process of moving a focusing lens ( 21 b) by a motor ( 41 ) along the optical axis of a collimating optical system (telescope ( 20 )), the image of a staff ( 1 ) sighted by the telescope ( 20 ) is converted into an electric signal by a line sensor ( 24 ). The output signal of the line sensor ( 24 ) is further converted into a digital signal by an A/D converter ( 27 ) and stored in a RAM ( 28 ). Based on the data stored in the RAM ( 28 ), a microcomputer ( 3 ) monitors frequencies of the component signals, or wavelets, contained in the output signal of the line sensor ( 24 ) stored in the RAM ( 28 ). When a particular frequency of the output signal associated with the position of the focusing lens ( 21 b) is detected while varying the position of the focusing lens ( 21 b), a decision is made that the focusing lens ( 21 b) is located at a substantial focusing position, and the distance from the telescope ( 20 ) to the staff ( 1 ) is calculated based on the output signal of the line sensor ( 24 ). Positioning of the focusing lens to the focusing position can be attained by comparing the position of the focusing lens ( 21 b) calculated from the distance with the position of the focusing lens ( 21 b) determined by the position sensor 5.
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