| 摘要 |
PURPOSE:To prevent the failure of photography, by generating a warning signal when the output of a photoelectric converting circuit becomes a reference value or less corresponding to a minimum of the luminance of the object to be photographed which is required for accurate photometry. CONSTITUTION:The reflected light from an object to be photographed is detected by a photodiode 1, and a voltage VBE1 is inputted to an operational amplifier 6 from a photoelectric converting circuit consisting of a logarithmic conversion transistor TR2 and an operational amplifier 3. Meanwhile, a reference voltage VBE2 corresponding to a reference photocurrent ISS based on a minimum of the luminance of the object to be photographed which is required for accurate photometry is inputted from a reference value generating circuit, which consists of a constant current source IS, a logarithmic conversion TR4, an operational amplifier 5, to the operational amplifier 6, and both inputs are compared with each other; and if the voltage VBE1 is lower than voltage VBE2, a signal VC is outputted to generate an alarm. Consequently, the failure of photography due to impossibility of focusing is prevented. |
