Photography – With object illumination for exposure – Having preexposure illumination
Reexamination Certificate
2003-06-03
2004-09-07
Perkey, W. B. (Department: 2851)
Photography
With object illumination for exposure
Having preexposure illumination
C396S159000, C396S161000, C348S364000, C348S371000
Reexamination Certificate
active
06788892
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a strobe light-emission control apparatus.
2. Description of the Related Art
An autodimming strobe emits strobe light toward a subject and receives reflected light from the subject by a photoreceptor sensor. The signal that is output from the sensor is integrated by an integrating circuit and the light emission from the strobe is halted when the integrated value attains a predetermined threshold value.
When a light source (extraneous light) falls within a range in which it is sensible by the photoreceptor sensor, however, not only reflected strobe light but also light emitted from the light source is received by the photoreceptor sensor. A signal obtained based upon the light emitted from the light source also is integrated by the integrating circuit. As a consequence, the integrated value attains the predetermined threshold value earlier than the time at which the strobe light emission should be terminated and, hence, there are instances where the image obtained is too dark.
Further, when the subject is a short distance away, it is required that the autodimming strobe control the light emission comparatively accurately so as to reduce the total amount of light that illuminates the subject. However, since it is comparatively difficult to accurately control the light emission of a strobe flash unit, often accurate control of the total amount of light that illuminates the subject is difficult to achieve.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to exclude the effects of extraneous light in control of a strobe light emission.
Another object of the present invention is to control, in comparatively accurate fashion, the total amount of light that illuminates a subject.
Accordingly to a first aspect of the present invention, the foregoing objects are attained providing a strobe light-emission control apparatus comprising: a photoreceptor for outputting a signal that conforms to amount of received incident light; a strobe light-emission control circuit for controlling a strobe flash device in such a manner that a subject is illuminated with strobe light; a subtracting circuit for subtracting, from a first signal that is output from the photoreceptor at emission of strobe light from the strobe flash device, a second signal that was being output from the photoreceptor during non-emission of strobe light from the strobe flash device; an integrating circuit for integrating a signal obtained by subtraction by the subtracting circuit; and a strobe light-emission halt control circuit for controlling the strobe flash device so as to halt emission of strobe light based upon amount of integration by the integrating circuit.
A control method suited to the strobe light-emission control apparatus of the present invention may also be provided. Specifically, there is provided a method of controlling a strobe light-emission control apparatus having a photoreceptor for outputting a signal that conforms to amount of received incident light, and a strobe light-emission control circuit for controlling a strobe flash device in such a manner that a subject is illuminated with strobe light, the method comprising the steps of: subtracting, from a first signal that is output from the photoreceptor at emission of strobe light from the strobe flash device, a second signal that was being output from the photoreceptor during non-emission of strobe light from the strobe flash device; integrating a signal obtained by subtraction; and controlling the strobe flash device so as to halt emission of strobe light based upon amount of integration.
In accordance with the first aspect of the present invention, a signal conforming to amount of incident light is output from the photoreceptor. The second signal is output from the photoreceptor when strobe light is not being emitted by the strobe light-emission control circuit. (If necessary, a detection circuit for detecting the second signal would be provided.) If extraneous light falls within the light-receiving range of the photoreceptor, the second signal indicates the amount of this extraneous light. The first signal is output from the photoreceptor when strobe light is being emitted by the strobe light-emission control circuit. The first signal indicates the total of extraneous light and strobe light that has been reflected from the subject.
The second signal is subtracted from the first signal by the subtracting circuit, and the signal that results from the subtraction operation is integrated by the integrating circuit. When the amount of integration by the integrating circuit attains a predetermined threshold value, the emission of strobe light is halted.
The subtracting circuit integrates the signal from which extraneous light has been excluded, i.e., the signal indicating the reflected strobe light. Control for halting the emission of light by the strobe flash device can be performed comparatively accurately.
Preferably, the subtracting circuit subtracts the second signal, which was being output from the photoreceptor at non-emission of strobe light immediately prior to emission of the strobe light, from the first signal for a period of time from emission of strobe light that is based upon control by the strobe light-emission control circuit to halting of emission of strobe light that is based upon control by the strobe light-emission halt control circuit. Thus, the effects of extraneous light can be excluded during emission of the strobe light.
Accordingly to a second aspect of the present invention, the foregoing objects are attained providing a strobe light-emission control apparatus comprising: a photoreceptor for outputting a photoreception signal that conforms to amount of received incident light; a first strobe light-emission control circuit for controlling a strobe flash device so as to illuminate a subject with strobe light and halt emission of light in response to a strobe light-emission halt signal applied thereto; an integrating circuit, which is reset with start of light emission by the strobe flash device and is reset in response to a reset signal applied thereto, for integrating the photoreception signal output from the photoreceptor; a comparison circuit for comparing an integrated value from the integrating circuit and a first reference signal and outputting a detection signal in response to the first reference value being surpassed by the integrated value; and a first control circuit for outputting the reset signal to the integrating circuit in response to output of the detection signal, which is output from the comparison circuit, prior to elapse of a first predetermined time from start of light emission by the strobe flash device, and outputting the strobe light-emission halt signal to the first strobe light-emission control circuit in response to output of the detection signal after elapse of the first predetermined time from start of light emission by the strobe flash device.
A method of controlling the strobe light-emission control apparatus of the second aspect of the present invention may also be provided. Specifically, there is provided a method of controlling a strobe light-emission control apparatus having a photoreceptor for outputting a photoreception signal that conforms to amount of received incident light, a first strobe light-emission control circuit for controlling a strobe flash device so as to illuminate a subject with strobe light and halt emission of light in response to a strobe light-emission halt signal applied thereto, and an integrating circuit, which is reset with start of light emission by the strobe flash device and is reset in response to a reset signal applied thereto, for integrating the photoreception signal output from the photoreceptor; the method comprising the steps of: comparing an integrated value from the integrating circuit and a first reference signal and outputting a detection signal in response to the first reference value being surpassed by the integrated value; and outputting the reset sig
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