Photography – Flash system responsive to focal length or distance
Reexamination Certificate
2001-08-23
2003-06-10
Perkey, W. B. (Department: 2851)
Photography
Flash system responsive to focal length or distance
C396S159000, C396S163000
Reexamination Certificate
active
06577820
ABSTRACT:
This application is based on patent application 2000-254549 filed in Japan, the contents of which are hereby incorporated by references.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a camera having an automatic flash light control system for controlling a quantity of flash light emitted from a built-in flash apparatus of the camera or an exterior type flash apparatus mounted on the camera.
2. Description of the Related Art
Conventionally, two types of flash light control system is known. In an automatic flash light control system, a quantity of reflected light component of the flash light reflected by an object is sensed by a flash light sensor while the flash light has been emitted from the flash apparatus. When the quantity of the reflected light component reaches to a predetermined value, the emission of the flash light is forcibly stopped.
In a flashmatic system, a quantity of flash light which will be emitted from the flash unit or apparatus is calculated with reference to a distance between the camera and the object and an aperture value of a taking lens which will be used for taking a photograph. The flash apparatus emits the calculated quantity of the flash light.
Furthermore, a first conventional flash light controller of a camera, for example, shown in U.S. Pat. No. 5,815,743 has a combination system of the automatic flash light control system and the flashmatic system. When a first stop signal through the automatic flash light control system is outputted faster than a second stop signal through the flashmatic system, the emission of the flash light by a flash unit or apparatus is forcibly stopped, even though the quantity of the flash light calculated in the flashmatic system has not been emitted, fully.
In a second conventional flash light controller of a camera, for example, shown in U.S. Pat. No. 6,085,040, an upper limit and/or a lower limit of a quantity of flash light emitted from a flash apparatus are/is calculated with reference to information such as a distance to an object, an aperture value of a taking lens, and the quantity of the flash light emitted from a flash apparatus is controlled through the automatic flash light control system by using the upper and/or the lower limit.
In the second conventional flash light controller of the camera, it is assumed that the upper limit and/or the lower limit of the quantity of the flash light include(s) only error component caused by sensing error of the distance to the object depending on information of a focal length of a taking lens. Thus, when the upper limit and/or the lower limit of the quantity of the flash light include(s) another error component caused by another factor, it is impossible to control the quantity of the flash light precisely.
For example, when the flash light is bounded on a ceiling or a wall, when a diffuser is used for diffusing the flash light, or when a plurality of flash apparatuses are used, an actual quantity of the flash light illuminating the object will be varied, even though the total quantity of the flash light emitted from the flash apparatus(es) is the same. Thus, the quantity of the flash light calculated in the flashmatic system (hereinafter, abbreviated as “criterion value”) will be improper. Furthermore, when the flash apparatus is apart from a camera body, the distance to the object sensed by the camera will be different from the actual distance between the object and the flash apparatus. Thus, the quantity of the flash light calculated with reference to the distance to the object sensed by the camera in the flashmatic system will include error component.
When a power of the flash apparatus is smaller such as the built-in flash apparatus of the camera, the distance to the object or the aperture value of the taking lens which can be controlled through the flashmatic system will be restricted. Furthermore, when a taking lens includes a factor for restricting the quantity of flash light, for example, when an open aperture value of a taking lens is larger, when a taking lens has a specific function such as a tilt function, or when a filter is adapted in an optical path of a taking lens, the flash light amount determined in the flashmatic system will include error component with respect to a proper quantity of the flash light.
When a specific timing for emitting the flash light is selected in the camera such as in a rear shutter blade synchro-flash mode or a self-timer photographing mode, the criterion value in the flashmatic system will be improper to be used as the upper limit and/or the lower limit of the quantity of the flash light controlled through the automatic flash light control system.
When the criterion value in the flashmatic system includes any error component, it will be the cause of the failure for taking a photograph that the quantity of the flash light controlled through the automatic flash light control system is restricted by the improper criterion value as the upper limit and/or the lower limit. Thus, it is necessary to correct the criterion value or to release the upper limit and/or the lower limit of the quantity of the flash light by the criterion value in the automatic flash light control system.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a camera having an automatic flash light control system in which an upper limit and/or a lower limit of a quantity of flash light by a criterion value, that is, flash light amount calculated in a flashmatic system will be corrected or released when the criterion value includes error component.
In a camera in accordance with an aspect of the present invention, a light quantity sensor senses a quantity of reflected flash light which is emitted from a flash light source, reflected by an object and reaches to a plane to be exposed. A flash light controller controls a quantity of flash light emitted from the flash light source by stopping emission of the flash light with reference to the quantity of the flash light sensed by the light quantity sensor. A distance sensor senses a distance to the object. A luminance sensor senses a luminance of the object. An aperture value selector selects an aperture value of a taking lens corresponding to the luminance of the object or selection by an operator. A limit quantity calculator calculates an upper limit and/or a lower limit of the quantity of the flash light which will be emitted from the flash light source with reference to the distance to the object and the aperture value selected by the aperture value selector. A quantity restrictor restricts the quantity of the flash light which will be controlled by the flash light controller corresponding to the upper limit and/or the lower limit of the quantity of the flash light calculated by the limit quantity calculator.
By such a configuration, when the quantity of the flash light sensed by the light quantity sensor reaches to a predetermined value, the emission of the flash light is forcibly stopped so that an object to be exposed such as a silver-halide film or a solid-state imaging device can be exposed by the predetermined quantity of the flash light. When the quantity of the flash light controlled by the flash light controller is larger than the upper limit or the smaller than the lower limit, the quantity of the actual flash light emitted from the flash light source is restricted by the upper limit or the lower limit. Thus, it is possible to prevent the occurrence of the erroneous photographing, for example, when a reflectance of the object is much higher or much lower than a standard value of the reflectance.
Furthermore, the camera further comprises an input unit for inputting parameter information with respect to parameters which will affect an accuracy of the upper limit and/or the lower limit of the quantity of the flash light calculated by the limit quantity calculator, and a compensator for compensating the upper limit and/or the lower limit of the quantity of the flash light calculated by the limit quantity calculator corresponding to the parameter informat
Akamatsu Norihiko
Hasegawa Yasushi
Ichikawa Tsutomu
Nakamaru Akio
Tsujimura Ichiro
Minolta Co. , Ltd.
Perkey W. B.
Sidley Austin Brown & Wood LLP
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