Photography – With object illumination for exposure – Having flash built into camera
Reexamination Certificate
2000-07-19
2002-04-30
Gray, David M. (Department: 2851)
Photography
With object illumination for exposure
Having flash built into camera
C396S200000, C362S016000
Reexamination Certificate
active
06381415
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-206235, filed Jul. 21, 1999; and No. 11-206236, filed Jul. 21, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a flash apparatus and a camera using the same.
A flash apparatus is used for cameras and the like. Conventionally, various types of flash apparatuses are proposed, including a flash apparatus using a flash unit of small bulb type (called point light source type hereafter).
The following describes the first prior art and a problem thereof.
Jpn. Pat. Appln. KOKAI Publication No. 63-259527 discloses a flash apparatus of point light source type with a protector having light diffusion properties in a circumferential direction for preventing effects of shadow caused by a masking shield in the flash unit.
However, a method according to the above-mentioned Jpn. Pat. Appln. KOKAI Publication No. 63-259527 just spreads light distribution by using a protector having light diffusion properties, thus leaving a disadvantage of increasing a light volume loss.
The method according to the above-mentioned Jpn. Pat. Appln. KOKAI Publication No. 63-259527 provides light distribution characteristics in which the flash light distribution itself is uneven and a light volume concentrates on the flash center. Accordingly, a light volume tends to become insufficient on the periphery of a wide angle lens having a short focal length.
The following describes the second prior art and a problem thereof.
FIG. 22A
is a schematic illustration for a flash apparatus of the conventional point light source type. The flash apparatus comprises a xenon flash lamp
600
and a reflector
601
which is arranged almost concentrically (forming a rotational symmetry against a medial axis of the point light source) against the xenon flash lamp
600
for reflecting light flux from this xenon flash lamp
600
.
FIG. 22B
is a cross-sectional view of the flash apparatus shown in FIG.
22
A. As seen from the figure, the conventional flash apparatus has an oval or parabolic sectional form.
FIG. 23A
provides light distribution characteristics for the conventional flash apparatus. An abscissa axis shows angle &thgr; against the central optical axis. An ordinate axis shows a flash light volume irradiated from the flash apparatus. The reflector
601
is formed almost concentrically with respect to the xenon flash lamp
600
. Consequently, same light distribution characteristics are provided in both shorter-side and longer-side directions. As shown in
FIG. 23A
, this type of light distribution characteristics causes a largest light volume at the optical axis with angle &thgr;=0. The light volume drastically decreases as the angle deviates from the optical axis.
FIG. 23B
is a three-dimensional representation of light distribution characteristics for the conventional flash apparatus in FIG.
23
A.
Based on
FIG. 23B
,
FIG. 24
shows light distribution characteristics for the conventional flash apparatus with respect to relationship between a photographic angle of view and light distribution characteristics. In
FIG. 24
, angle “a” is a necessary angle of view in a shorter-side direction of the film exposure aperture. Angle “b” is a necessary angle of view in a longer-side direction of the film exposure aperture. Angle “c” is a necessary angle of view in a diagonal direction of the film exposure aperture. As seen from the figure, a light volume difference becomes large at ends of each of angles of view, “a”, “b”, and “c”, preventing provision of uniform light distribution characteristics.
With respect to the above-mentioned flash apparatus of the point light source type, Jpn. Pat. Appln. KOKAI Publication No. 63-259527 discloses a flash apparatus whose flash unit is provided with a protector having light diffusion properties in a circumferential direction for uniforming light distribution characteristics.
Conventional flash apparatuses including the above-mentioned Jpn. Pat. Appln. KOKAI Publication No. 63-259527 use a reflector forming a rotational symmetry against the medial axis for the point light source, also providing rotationally symmetrical light distribution. However, the light distribution forms a rectangular shape similar to a picture plane shape. Consequently, just part of the rotationally symmetrical shape is available, causing a problem of a large loss in the light volume.
The present invention has been made in consideration of the problems in the above-mentioned first and second prior arts. It is an object of the present invention to provide a flash apparatus and a camera using the same which can effectively use an energy from a xenon flash lamp of the point light source type.
BRIEF SUMMARY OF THE INVENTION
In order to achieve the above-mentioned object, the first aspect of the present invention relates to a flash apparatus comprising:
a flash tube of the point light source type;
a reflector which reflects light flux from the flash tube forward; and
a diffuser panel which is placed in a light flux passing position in front of the flash tube and the reflector for diffusing the light flux from the flash tube,
wherein the diffuser panel is so formed that a diffusion angle of the light flux varies with positions between a center corresponding to a light-emitting axis of the flash tube and a periphery concerning an area where light flux of the flash tube passes.
The diffuser panel is so formed that a diffusion angle of the light flux varies with positions between the center corresponding to the light-emitting axis of the flash tube and a periphery on an area where light flux of the flash tube passes.
The second aspect of the present invention relates to a flash apparatus comprising:
a flash tube of the point light source type;
a reflector which reflects light flux from the flash tube forward;
a diffuser panel which is placed in front of the flash tube and the reflector for diffusing light flux from the flash tube; and
transport means for moving the flash tube relatively to the diffuser panel between a first state irradiating light flux from the flash tube through the diffuser panel and a second state irradiating light flux from the flash tube without using the diffuser panel.
The third aspect of the present invention relates to a flash apparatus comprising:
a flash tube of the point light source type;
a reflector which reflects light flux from the flash tube forward; and
a diffuser panel which is placed in a light flux passing position in front of the flash tube and the reflector for diffusing the light flux from the flash tube,
wherein the diffuser panel is so formed that a diffusion degree of the light flux varies with positions between a center corresponding to a light-emitting axis of the flash tube and a periphery concerning an area where light flux of the flash tube passes, and the diffuser panel is so formed that a diffusion degree is varied between a vertical direction and a horizontal direction according to the aspect ratio of a square photographic picture plane of the camera.
The diffuser panel is so formed that a diffusion degree of the light flux varies with positions between the center corresponding to the light-emitting axis of the flash tube and a periphery on an area where light flux of the flash tube passes. In addition, the diffuser panel is so formed that a diffusion degree vertically and horizontally varies according to the aspect ratio of a square photographic picture plane of the camera.
The fourth aspect of the present invention relates to a camera having the flash apparatus comprising:
a flash tube of the point light source type for generating flashes; and
a reflector which reflects light flux from the flash tube forward,
wherein the reflector comprises a reflecting surface having a first curved-face portion for determining the vertical irradiating light distribution and a second curved-face portion for determining the horizontal irradiating li
Blackman Rochelle
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Gray David M.
Olympus Optical Co,. Ltd.
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