Off-photometric-range indicator for exposure meter

Abstract

An off-photometric-range indicating device for photometric circuits for cameras visually indicates to a photographer when the brightness of an object to be photographed is off the set photometric range of the photometric circuit. The indicating device includes a detection circuit to detect the brightness of the object and to produce an output signal when the detected value of the brightness is out of the photometric range of the photometric circuit, a switching circuit connected to the detection circuit and operated by said output signal, and a circuit connected to the switching circuit and actuated by the operation of the switching circuit to scale out the indicator, which may be visually observed by the photographer.

I claim: 
     
       1. In a device for indicating off-photometric-range of a photometric circuit in an exposure indicator, the indicating device including: a photometric circuit .[.(1, 2).]. adapted to generate a first voltage in correspondence to the object brightness of an object to be photographed;   an exposure factor introduction circuit .[.(5, 6).]. adapted to generate a second voltage which varies according to exposure factors; and   an indicator .[.(9) connected at one input terminal to said photometric circuit and at its other input terminal to said exposure factor introduction circuit and.]. adapted to indicate a proper value of exposure corresponding to the difference between said first and second voltages,   the improvements comprising: a. a detection circuit .[.(11, 12, 13, 13, 15, 16, 19).]. connected to said photometric circuit and adapted to detect the object brightness and issue an output signal when the detected value of the object brightness is off the photometric range of said .[.indicator,.]. .Iadd.photometric circuit;.Iaddend.   b. a switching circuit .[.(17, 25).]. connected to said detection circuit and arranged to operate when receiving said output signal; and   c. a circuit .[.(18, 26, 27).]. connected between said switching circuit and said indicator and actuated by operation of said switching circuit to scale out said indicator thereby to give the off-photometric-range indication.     
     
     
       2. The device set forth in claim 1, wherein said detection circuit comprises: a. a reference voltage generating circuit .[.(11, 12).]. which generates a fixed voltage equal to the output voltage produced by the photometric circuit when the object brightness is at the limit of the photometric range; and   b. a comparison circuit .[.(13, 14, 15, 16, 19).]. which receives the outputs from said reference voltage generating circuit and from said photometric circuit as inputs and compares said inputs and issues a signal to actuate said switching circuit when the object brightness is detected to be off the photometric range.   
     
     
       3. The device set forth in claim 2, wherein said comparison circuit is a differential amplifier. 
     
     
       4. The device set forth in claim 2, wherein said switching circuit, when made conductive, operates said scaling-out circuit. 
     
     
       5. The device set forth in claim 2, wherein said switching circuit, when made non-conductive, operates said scaling-out circuit. 
     
     
       6. The device set forth in claim 4, wherein said scaling-out circuit, when energized, generates a predetermined output voltage at one of the input terminals of said indicator to scale-out said indicator. 
     
     
       7. The device set forth in claim 5, wherein said scaling-out circuit, when energized, shuts off the output at one of the input terminals of said indicator to cut off electric current flowing to said indicator thereby to scale-out said indicator.