Light emission control circuit of flash device

Abstract

An optical sensor receives light of a light emitting tube. A photoelectric current output from the optical sensor is integrated by a capacitor. A stop signal output part compares the generated voltage of the capacitor with a comparison voltage and outputs a light emission stop signal when the generated voltage exceeds the comparison voltage. A voltage setting part predicts, from target amount of light, an amount of overrun light from when the light emission stop signal is output until when light emission of the light emitting tube terminates and sets the comparison voltage so that a total amount of light emission including the amount of overrun light is a target amount of light emission.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by identical reference numbers, in which:

FIG. 1 is a circuit diagram showing the principle of a photometric circuit;

FIG. 2 is a diagram showing the state of overrun light emission or light increase;

FIG. 3 is a diagram showing the relationship (a) between a target amount of light and a comparison voltage and the relationship (b) between the target amount of light and (the amount of light emission/comparison voltage);

FIG. 4 is a diagram showing an example of a curve of a correction coefficient when the target amount of light/amount of full light emission (light emission ratio) is taken as a parameter;

FIG. 5 is a diagram showing another example of a photometric circuit;

FIG. 6 is a diagram showing an example of a state of photometric range switching of the photometric circuit shown in FIG. 5; and

FIG. 7 is a sequence diagram between a camera and a flash device.

Claims

1. A light emission control circuit of a flash device, comprising: an optical sensor that receives light of light emission from a light emitting tube;a capacitor that integrates a photoelectric current output from said optical sensor;a stop signal output part that compares a generated voltage of said capacitor with a comparison voltage and outputs a light emission stop signal when said generated voltage exceeds said comparison voltage; anda voltage setting part that predicts, from a target amount of light of light emission, an amount of overrun light from when said light emission stop signal is output until when light emission of said light emitting tube terminates and sets said comparison voltage so that a total amount of light emission including said amount of overrun light is a target amount of light.

2. The light emission control circuit of a flash device according to claim 1, wherein said target amount of light is defined by a ratio to an amount of full light emission.

3. The light emission control circuit of a flash device according to claim 2, comprising: a correction table that stores a correction coefficient of a comparison voltage as an input parameter of said ratio; andan operation part that finds an uncorrected comparison voltage by multiplying the generated voltage of said capacitor at the time of full light emission and said ratio to obtain said comparison voltage by multiplying said uncorrected comparison voltage and the correction coefficient obtained from said correction table.

4. The light emission control circuit of a flash device according to claim 1, wherein said capacitor includes:a plurality of capacitor elements;a selection part that selects at least one capacitor element from said plurality of capacitor elements; anda connection part that connects in parallel a plurality of capacitor elements selected by the selection part.

5. A light emission control circuit of a flash device, comprising: an optical sensor that receives light of light emission from a light emitting tube;a capacitor that integrates a photoelectric current output from said optical sensor; anda stop signal output part that compares a generated voltage of said capacitor with a comparison voltage and outputs a light emission stop signal when said generated voltage exceeds said comparison voltage,wherein said capacitor has a configuration in which a plurality of series circuits of a capacitor element and a switching element are provided and are connected in parallel, and controls a time until the generated voltage of said capacitor exceeds said comparison voltage by changing the capacitance of said capacitor by the turning on/off control of said switching element.