Photography – Flash system responsive to focal length or distance
Reexamination Certificate
1999-10-08
2001-05-15
Perkey, W. B. (Department: 2851)
Photography
Flash system responsive to focal length or distance
C396S164000, C396S176000
Reexamination Certificate
active
06233404
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic flash device for a camera. More particularly, the present invention relates to an electronic flash device for a camera in which flash light can be effectively applied to a photographic subject located at a very near distance in closeup photography.
2. Description Related to the Prior Art
There are various types of commercially available cameras. Many types of cameras incorporate an automatic focus changing mechanism and an automatic exposure adjusting mechanism for automated focusing and adjustment of exposure. Some flash-built-in type of camera is provided with an automatic light adjustor, which adjusts an emitted amount of flash light automatically according to a photographic subject distance and photographic subject brightness For flash photography of a photographic subject at a very near distance with such a camera, an aperture stop is stopped down, or an emitted amount of the flash light is reduced, to optimize exposure of the photographic subject.
If the camera is a low-cost type without the automatic exposure adjusting mechanism or the automatic light adjustor, the subject brightness is excessive if flash light is emitted at the very near distance, to result in an over-exposure photograph. Distribution of the flash light is predetermined for illumination to a photographic field at a normally used range of a subject distance in flash photography. If the photographic subject is located at a nearer distance than this normally used range, a central portion of one frame is illuminated considerably by the flash light, to create a great difference in the emitted light amount from peripheral portion of the frame. As a result, a photographic print is likely to have the excessively white central portion.
JP-A 9-138456 discloses an adapter attachable to the camera for a good condition of closeup photography even if the camera does not have the automatic exposure adjusting mechanism or the automatic light adjustor. In the document, an auxiliary lens is disposed in the adapter for changing a focal point to a position offset in the direction of the near distance from an initial focal point. The auxiliary lens is fixedly disposed in front of a taking lens of the camera, to enable the closeup photography of the photographic subject at the very near distance. Also the adapter is provided with a light reducing plate, which includes a light-shielding flat plate and a number of holes formed therein for passing of the flash light. For the closeup photography, a flash emitting component of the flash device is associated with the light reducing plate set in front thereof for restrict the amount of the flash light to be applied to the photographic subject. Note that the holes for passing of the flash light have a size and arrangement each determined in consideration of the emitted amount and distribution of the flash light emitted from the flash emitting component.
In the light reducing plate, there are formed a great number of holes for passing of the flash light. If a great amount of the flash light is emitted from the flash emitting component, the holes do not effectively operate for light reduction. The holes are very close to one another, so that fluxes of the flash light through the holes are overlapped on one another at the photographic subject at the very near distance. There occur bright and dark portions of photographic subject distinct apparently from one another. Differences between the bright and dark portions are so conspicuous according to greatness of the amount of the flash light, to lower evenness in the illumination.
Furthermore the light reducing plate of the prior art has a size totally covering the flash emitting component. If the light reducing plate is incorporated in the camera, a large space in the camera is required for retreat of the light reducing plate from the flash emitting component. There occurs unwanted enlargement of the camera.
SUMMARY OF THE INVENTION
In view of the foregoing problems, an object of the present invention is to provide an electronic flash device for a camera in which distribution of flash light can be optimally obtained in a subject distance region of the very near distance and also with a simple structure.
In order to achieve the above and other objects and advantages of this invention, an electronic flash device for a camera includes a flash emitting component, substantially quadrilateral, having vertical and horizontal side lines, for emitting flash light. A light reducing plate is disposed in front of the flash emitting component, extended in a vertical direction, and has a predetermined width in a horizontal direction. The predetermined width is shorter than the horizontal side lines. The light reducing plate intercepts a central portion of the flash emitting component. First and second lateral portions of the flash emitting component remain uncovered for illumination with a restricted amount of the flash light.
In a preferred embodiment, the light reducing plate substantially has a vertically symmetrical shape with reference to the central portion, and substantially has a horizontally symmetrical shape with reference to the central portion.
The flash emitting component includes a flash discharge tube disposed to extend horizontally. A reflector is disposed with a curve behind the flash discharge tube, for reflecting part of the flash light forwards after being emitted rearwards by the flash discharge tube. A transparent diffusing plate is disposed in front of the flash discharge tube, longer horizontally than vertically, for diffusion and forward emission of the flash light from the flash discharge tube and the reflector.
The flash emitting component has a size and a shape adapted to illumination of a photographic field at a first subject distance. The light reducing plate adapts the flash light to illumination of a photographic field at a second subject distance shorter than the first subject distance.
Furthermore, a retention mechanism retains the light reducing plate on the flash emitting component in a disengageable manner.
In another preferred embodiment, the light reducing plate, when in an effective position, intercepts the central portion. Furthermore, a changeover mechanism is operable externally, for moving the light reducing plate between the effective position and an ineffective position. The light reducing plate, when in the ineffective position, is located offset from the flash emitting component, for allowing the flash emitting component fully to emit the flash light.
The changeover mechanism, when a subject distance is within a first distance range, is set in the ineffective position, and when a subject distance is within a second distance range being a nearer distance than the first distance range, is set in the effective position.
Furthermore, the camera includes a front wall disposed in front of the flash emitting component. A flash emitting window is formed in the front wall, for illumination of the flash light from the flash emitting component. The changeover mechanism includes a sliding space, defined behind the front wall and in front of the flash emitting component, for receiving insertion of the light reducing plate, to keep the light reducing plate slidable. The light reducing plate, when in the ineffective position, is covered by the front wall, and when in the effective position, is positioned in the flash emitting window.
The changeover mechanism further includes a changeover button portion disposed with the light reducing plate, operated externally, for sliding the light reducing plate along the sliding space.
In still another preferred embodiment, the changeover mechanism includes a hinge portion, disposed to extend along one of the horizontal side lines of the flash emitting component, secured to a horizontal edge of the light reducing plate, for supporting the light reducing plate in a rotatable manner.
In another preferred embodiment, the light reducing plate is substantially quadrilateral, and has fir
Tobioka Takashi
Tobise Manabu
Fuji Photo Film Co. , Ltd.
Perkey W. B.
Young & Thompson
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