| 摘要 |
PURPOSE:To prevent photography based upon wrong range finding operation when a photographer himself is a subject by detecting whether or not there is a subject which radiates infrared rays, e.g. a human body within a range measurable range. CONSTITUTION:When the human body as a subject is positioned at a point A outside a range which by an angle theta in a figure and where infrared rays are converged, so none of infrared rays from said subject is incident on an infrared detecting element 2 and any part does not operate. Consequently, a transistor 14 never turns on to cause an LED 15 to illuminates and the subject at the position A can appreciate by himself that he is outside the measurable range. On the other hand, when the subject moves to a point B within the measurable range or when a subject at the position B moves in said range, infrared rays incident on the infrared detecting element 2 through the window member 1 vary, so the infrared detecting element 2 detects the variation of the infrared rays to generate a chane of charge.
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