Asahi Kogaku Kogyo Kabushiki Kaisha

Asahi Corporation

Asahi Kogaku K.k.k.

Takuo Itagaki

Masaaki Niiho

Yukiyasu Nishikawa

Shinichi Suzuki

Kiyoshi Itoh

Koji Tsuda

A change-over shutter for an optical range finder employs at least two slits for measurement light, one of which is employed during long distance measurements and the other of which includes a light reduction member and is employed for short distance measurements. The arrangement advantageously eliminates measurement error caused in short distance measurements due to light secondarily reflected from the light emitting element.

Change-over shutter for light-wave range finder

An averaging circuit includes a number of sample/hold circuits which cyclically sample/hold an input signal, the outputs of the sample hold circuits being added and applied to a comparator. A further sample/hold circuit sample/holds an internal input signal at an increased rate and the output thereof is amplified by a factor equal to the number of cyclically operated sample/hold circuits before being applied as the other input to the comparator.

Averaging circuit

An exposure information quantizing circuit. A current signal source generates a signal current to be quantized. A controllable bidirectional shift register has a series of bit positions and corresponding signal receiving outputs and is operable to shift a bit sequentially from one position to the next. Each position corresponds to a different divisional range of the signal to be quantized. A unique signal appears only at the output corresponding to the position containing a bit. Means comprises at least one further reference current source responsive to the outputs of the shift register for forming at least a pair of signals corresponding to opposite ends of the divisional range for each output of the shift register. A first logarithmic compression means is coupled to the signal current source for forming a first reference voltage proportional to the logarithm of the signal current. At least one further logarithmic compression means is coupled to the at least one further reference current source for causing the pair of signals to form first and second reference signals proportional to the logarithm of the at least one further reference current source. A voltage comparator forms a direction of shift control signal for the shift register in accordance with comparison thereby of the magnitude of the signal voltage with that of the first and second reference voltages. A source of shift control pulses is provided for the shift register.

Exposure information quantizing circuit utilizing shift register

A closed-loop circuit arrangement sequentially operates in a tracking mode before the shutter of a single lens reflex camera is actuated, and then in a holding mode after the shutter is actuated. The circuit arrangement receives from a conventional photoelectric circuit a first analog signal that instantaneously represents exposure time so long as light entering the camera impinges on the photoelectric circuit. A register in the circuit arrangement provides a digital multi-bit signal that is converted to a second analog signal. The first and second analog signals are compared to produce an error signal used during the tracking mode in controlling the register so that the digital multi-bit signal varies until the first and second analog signals represent the same exposure time. After the shutter is actuated, the register serves as a memory thereby causing the second analog signal to statically represent exposure time.

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Wako, Japan

Takuo Itagaki