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Abstract

An auto focusing mechanism is provided in a surveying instrument, such as an electronic level, that is capable of automatically focusing a telescope on a sighted staff.As a focusing lens (21b) is moved by a motor (41) along the optical axis of a telescope (20), the image of a staff (1) sighted by the telescope (20) is converted into an electrical signal by a line sensor (24). The output signal of the line sensor (24) is 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 (21b) is detected a determination is made that the focusing lens (21b) is located at a focusing position, and the distance from the telescope (20) to the staff (1) is calculated.

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First Claim