Illumination – Light source and modifier – Adjustable or repositionable modifier
Reexamination Certificate
1998-02-18
2001-01-30
Husar, Stephen (Department: 2875)
Illumination
Light source and modifier
Adjustable or repositionable modifier
C362S018000, C362S333000, C362S339000, C362S322000, C362S308000
Reexamination Certificate
active
06179447
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light distribution lens of a strobe device which is located in front of a light emitter and a zoom strobe device using the same.
2. Description of the Related Art
A strobe device, and particularly a strobe device incorporated in a zoom lens camera should be small and have a large guide number and a uniform emission distribution over the entire zoom range from the telephoto extremity to the wide-angle extremity (i.e., least loss of the quantity of light at the periphery of the lens), in accordance with an increase in the focal-length at the telephoto extremity. Attempts have been made to improve a light emitting tube, a reflector, and a Fresnel lens (light distribution lens). In particular, the Fresnel lens can have theoretically the same power of an equivalent convex lens, though it be made thinner in size; therefore is useful in reducing the entire thickness of the strobe system. However, a light loss occurs due to the concentric cylindrical surfaces of the annuluses of the Fresnel lens, axes of which being the optical axis, and hence it is difficult to obtain a large guide number. If a bi-convex lens which has no light loss is used, it is possible to obtain a large guide number. However, the bi-convex lens has a large thickness at the center portion thereof, thus resulting in an increase in volume. In addition, it is difficult to obtain the necessary thickness at the peripheral portion. Thus, the bi-convex lens makes it difficult to miniaturize the strobe device.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a light distribution lens for a strobe wherein the thickness can be made thinner than an equivalent bi-convex lens; to reduce the light loss due to the annuluses (concentric grooves); and an increased guide number.
Another object of the present invention is to provide a zoom strobe device using the above-mentioned light distribution lens.
According to an aspect of the present invention, there is provided a light distribution lens for a strobe which is located in front of a strobe light emitter, including a convex surface which is provided on one of the opposed lens surfaces of the light distribution lens; and a convex Fresnel surface which is provided on the other lens surface of the light distribution lens.
According to another aspect of the present invention, there is provided a zoom strobe device including a light emitter unit including a light emitter and a reflector; a light distribution lens provided in front of the light emitter unit to distribute strobe light; and a zoom mechanism for varying the distance between the light emitter unit and the light distribution lens. One of opposed lens surfaces of the light distribution lens is made of a convex surface, and the other lens surface is made of a convex Fresnel surface. The convex Fresnel surface faces the light emitter unit while the convex surface is located so that it faces outward.
Preferably, the Fresnel surface is provided with annuluses, each being defined by a cylindrical surface having an axis coincident with the optical axis and a conical surface to define a wedge shape in section. Consequently, a molding die used to mold the Fresnel lens can be easily machined or produced.
The strobe light distribution lens preferably satisfies the following relationship:
&thgr;≦10 H
wherein H (mm) represents the distance of each annulus of the convex Fresnel surface from the optical axis, and &thgr;(° ) represents the angle defined by the wedge surface of each annulus and a plane perpendicular to the optical axis.
The radius of curvature of the convex surface is preferably larger than that of the basic curved surface of the Fresnel surface (at the center portion thereof). This is because if the radius of curvature of the convex surface is small, the lens must be thick to obtain a necessary thickness of the lens at the peripheral portion thereof. In order to provide a thin lens without decreasing the power, it is preferable that the power be chiefly provided by a Fresnel surface.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 09-34889 (filed on Feb. 19, 1997) which is expressly incorporated herein by reference in its entirety.
REFERENCES:
patent: 5055976 (1991-10-01), Arai
patent: 5160192 (1992-11-01), Sugawara
patent: 5280315 (1994-01-01), Nomura et al.
patent: 5539622 (1996-07-01), Ishikawa
patent: 5641218 (1997-06-01), Sakurai
patent: 7-110513 (1995-04-01), None
Iida Minoru
Ishikawa Tuyoshi
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Husar Stephen
Zeade Bertrand
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