| 摘要 |
PURPOSE:To accurately measure the distance to an object of measurement by combining plural lens systems which differ in focal length with image detecting means arranged at their image formation parts. CONSTITUTION:When the distance between a preceding vehicle and a following vehicle is, for example, long distance L1, light reflected by the rail lamp 10a of the preceding vehicle forms a sharp tail lamp image S1 at the position P1 of an image sensor 35 through the long-distance lens 32 of the following vehicle. In this case, an intermediate distance lens 33 and a short distance lens 34 are out of focus, so images S2 and S3 formed by those lenses are inferior in contrast. The image sensor 35 detects a photodetection image on the photodetection surface 35a from its lower end Pl to its upper end Pu and detects the position P1 of the sharp formed image S1 by using a high-pass filter. A distance measuring circuit determines the vehicle distance to the preceding vehicle on the basis of the position P1.
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