Photography – With object illumination for exposure – Variable intensity control
Reexamination Certificate
2000-07-05
2002-11-12
Gray, David M. (Department: 2851)
Photography
With object illumination for exposure
Variable intensity control
C396S200000, C362S017000, C362S018000
Reexamination Certificate
active
06480679
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a strobe device, incorporated with a silver-halide camera, a lens-fitted film unit and a digital camera, and specifically, relates to a strobe device which is suitable for a camera equipped with a wide angle lens, an image capturing apparatus equipped with a strobe device and a reflector of the strobe light.
FIG. 1
shows distribution characteristics of the luminous intensity for a conventional strobe device. As shown in
FIG. 1
, in a conventional strobe device, luminous intensity of strobe lighting is substantially constant within a predetermined illuminating angle, or the luminous intensity at the center position is greater than that at the peripheral positions, so as to increase the guide number in regard to the illuminating distance along the center axis.
In the distribution characteristics of the luminous intensity described above, however, when capturing a subject, like as a flat surface, directly opposite the camera or subjects aligned in the vertical direction, the larger the angle of view, the larger the distance between the peripheral subject and the strobe device, and thereby, luminous intensity for the peripheral subject would decrease due to the low of inverse square, and the reflected light from the subject would also decrease according as the distance becomes larger.
In addition, the amount of light components, coming toward the camera after being reflected and scattered on a plane object such as a wall, etc., would also decrease, due to the large angle of incident of the light illuminated by the strobe device.
Further, since the peripheral subjects are usually located at distant positions in almost all conventional snapshot images, compared to the subject located in the center position, the reflected light intensity from such peripheral subjects will decrease considerably.
Owing to the multiple-effects of the adverse factors mentioned above, the periphery portion is apt to be dark in the photograph shot with conventional strobe lighting, resulting in a lack of liveliness, in which only the center portion is remarkably bright, while the periphery portion is a flat and expressionless field. This tendency will become remarkable according as the illuminating angle of strobe device is getting larger with the increase of the angle of view, by employing a wide-angle lens for the camera.
Now, referring to
FIG. 6
, an example of the relationship, between viewing angle a of a photographic lens in a camera employing a strobe device and illuminating angle &bgr; of the light coming to subject M from the strobe device, will be described in the following.
As shown in FIG.
6
(
a
), when viewing angle a is relatively small (for instance, 60 degrees) as a standard type, it is possible to adequately illuminate subject M existing within viewing angle a, even if illuminating angle &bgr; of the strobe device is not so wide.
As shown in FIG.
6
(
b
), however, when a wide-angle photographic lens having a wide viewing angle a (for instance, 90 degrees) is employed in the camera, it becomes almost impossible to adequately illuminate the overall region covered by viewing angle a with illuminating angle &bgr; of a conventional strobe device, resulting in difficulties of improving photographic effects of subject M.
SUMMARY OF THE INVENTION
To overcome the abovementioned drawbacks in conventional strobe devices, it is an object of the present invention to provide a strobe device, which could brightly illuminate a periphery of the subject and, specifically, makes it possible to obtain a desirable distribution characteristics of the luminous intensity, even when an image capturing is conducted with a wide-angle photographic lens.
Accordingly, to overcome the cited shortcomings, the abovementioned objects of the present invention can be attained by strobe devices and image capturing apparatus described as follow.
(1) A strobe device, comprising a reflector to reflect a strobe light, a light-emitting tube, mounted in an interior of the reflector, to emit the strobe light and an optical panel, mounted in front of the light-emitting tube, to transmits the strobe light, wherein a maximum luminous intensity of the strobe light, illuminated by the strobe device, is arranged in a direction being different from a direction of a strobe light axis which is orthogonal to a longitudinal direction of the light-emitting tube.
(2) The strobe device of item 1, which fulfills a following conditional equation,
[4×{(cos(
K
P
))
−4
−1
}×Q
C
]+Q
C
≧Q
KP
≧[0.1×{(cos(
K
p
))
−4
−1
}×Q
C
]+Q
C
where: K
P
; an illumination angle for the maximum luminous intensity with reference to the strobe light axis, Q
C
; a luminous intensity in a direction of the strobe light axis Q
KP
; the maximum linous intensity.
(3) The strobe device of item 1, wherein the reflector comprises a concave reflection surface and a side reflection surface arranged at each side of the concave reflection surface, the side reflection surface is inclined to the light-emitting tube at such an angle that the side reflection surface reflects the strobe light, emitted from the light-emitting tube, so as to emit the strobe light toward a direction of being apart from the strobe light axis located at a center of the light-emitting tube, instead of toward a direction of crossing the strobe light axis.
(4) The strobe device of item 3, wherein each of the side reflection surfaces comprises a sub-reflection surface being orthogonal to a longitudinal direction of the light-emitting tube.
(5) The strobe device of item 1, which fulfills a following conditional equation,
1.5
≦W/L
≦2.0,
where: L; an effective illuminating length of the light-emitting tube, W; a length of the strobe panel in a longitudinal direction of the light-emitting tube.
(6) The strobe device of item 1, wherein the light-emitting tube is formed in a cylindrical shape and the reflector comprises a concave reflection surface, the strobe device fulfills following conditional equations,
3.0
U<W
1
<5.2
U
1.2
U<W
2
<3.5
U
2
U<D
<5
U
where: W
1
; a width at a front end of the concave reflection surface, W
2
; a width of the concave reflection surface at a center axis of the light-emitting tube, D; a distance from a front end of the concave reflection surface to a center axis of the light-emitting tube, and U; a distance from a center axis of the light-emitting tube to a rear end of the concave reflection surface.
(7) The strobe device of item 1, wherein the light-emitting tube is formed in a cylindrical shape and the reflector comprises a concave reflection surface, and in regard to a cross-sectional view of the concave reflection surface in a direction orthogonal to a longitudinal direction of the light-emitting tube, when a front end point of the concave reflection surface, an intersection of the concave reflection surface and a straight line, which goes through a center axis of the light-emitting tube and is perpendicular to the strobe light axis, and a rear end point of the concave reflection surface on the strobe light axis, are defined as P, Q and V, respectively, all of points, residing on the concave reflection surface between points P and Q, are located opposite a center axis of the light-emitting tube with respect to a line P-Q, while all of points, residing on the concave reflection surface between points Q and V, are located opposite a center axis of the light-emitting tube with respect to a line Q-V, and under the above condition, the strobe device fulfills following conditional equations,
0.05<&Dgr;
1
/
U
<0.4
0.07<&Dgr;
2
/
U
<0.5
where: &Dgr;
1
; a maximum distance from a point, residing on the concave reflection surface between points P and Q, to the line P-Q, &Dgr;
2
; a maximum distance from a point, residing on the concave reflection surface between points Q and V, to the line Q-V, and U; a distance from a center axis of the light-emitting tube to a rear end of the concave
Hosaka Takao
Ishida Ken
Masuda Takuro
Mori Nobuyoshi
Blackman Rochelle
Gray David M.
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