| 摘要 |
PURPOSE:To eliminate the parallax between the optical axes of an electroacoustic transducer and a photographic lens system, to realize narrow directivity and to increase a measureable distance by arranging the electroacoustic transducer which operats as both a sound transmitter and a sound receiver annularly around the lens system. CONSTITUTION:The electroacoustic transducer 2 which has a parabolic horn 3 serving as a hood is arranged at the peripheral part of a photographic lens 1, an annular diaphragm 6 is provided onto a coupling shaft 5 arranged at the center part of a plural-sheet stuck type piezoelectric element 5, and the peripheral part of the annular diaphragm 6 is fixed elastically to the internal surface of an annular case 8 across a buffer material 7 such as elastic rubber. An ultrasonic wave signal which is sent by the electroacoustic transducer 2 and reflected by a subject is detected by the electroacoustic transducer 2 and sent to a detecting and processing circuit connecting with the transducer 2, and the circuit sends it to a focusing device as an output signal relating to the distance to the subject to control the lens system automatically, thus performing focusing operation. |
