Illumination – Photographic lighting – Including specific light modifier
Reexamination Certificate
2001-03-14
2003-06-10
O'Shea, Sandra (Department: 2875)
Illumination
Photographic lighting
Including specific light modifier
C362S003000, C362S309000, C362S327000
Reexamination Certificate
active
06575582
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination device capable of varying an illumination angle thereof, and to a photographing apparatus using the illumination device.
2. Description of Related Art
There have heretofore been known a variety of kinds of technical art concerning an illumination device for use with a photographing apparatus, such as a camera, so as to efficiently collect light fluxes emitted in various directions from a light source into a necessary illumination range (an angle of view required to be illuminated). In particular, in recent years, there has been known an illumination device in which an optical member utilizing total reflection, such as a prism or a light guide, is disposed in place of a Fresnel lens, which would conventionally be disposed in front of a light source, for the purpose of improving the efficiency of light collection and reducing the size of the illumination device.
On the other hand, in an illumination device of the fixed illumination range type, when a photographing apparatus having a high-magnification zoom ratio is in a telephoto state, in which the required illumination range is narrow, an unnecessary range would be illuminated, thereby causing large loss of energy. In order to solve such a phenomenon, there have been known a variety of variable-illumination-angle illumination devices capable of performing illumination corresponding to a photographing range.
As illumination devices adopting the above-mentioned two kinds of technical art, there has been known, as disclosed in Japanese Laid-Open Patent Application No. Hei 4-138439, an illumination device in which an optical prism arranged to perform total reflection is used as a light-collecting optical system and the positional relationship between the optical prism and a light source is relatively varied to change the total-reflection surface between reflection and transmission so as to vary the illumination range. Further, as disclosed in Japanese Laid-Open Patent Application No. Hei 8-262538, there has been known an illumination device in which an optical prism is divided into a plurality of prism members and the prism members disposed on the upper and lower sides are rotated to change over the illumination range.
In recent years, in the case of photographing apparatuses, such as cameras, the reduction in size and weight of the apparatus itself has advanced, and, on the other hand, a photographic lens shows a tendency to have a high-magnification zoom ratio. In general, such a reduction in size of the photographing apparatus and such a high-magnification zoom ratio of the photographic lens cause the photographic lens to tend to gradually become dark. If a photograph is taken without using any auxiliary light source, there is a possibility that the photograph becomes an unexpected failure due to the camera shake.
In order to resolve such a situation, normally, an illumination device (flash device) serving as an auxiliary light source is incorporated in most photographing apparatuses, such as cameras. Then, owing to the above-mentioned situation, the frequency of use of the illumination device increases greatly as compared with cases in the past, and the amount of light emission required for one photo-taking operation tends to increase.
Such being the background, in the case of the flash light emitting device (illumination device) disclosed in the above Japanese Laid-Open Patent Application No. Hei 4-138439, the optical prism, serving as a light-collecting optical system, is an optical member composed of upper and lower surfaces arranged to cause, mainly, light fluxes emitted sideward from the light source and entering the optical member to be totally reflected so as to be collected in a predetermined direction, and a front surface formed separately from the upper and lower surfaces and having a positive refractive power to collect light fluxes, and is arranged to cause the light fluxes collected by the respective surfaces to exit from one and the same exit surface toward an object side. Then, the positional relationship between the optical prism and the light source is relatively varied to change the total-reflection surfaces between reflection and transmission so as to vary the illumination range. However, there remain such problems difficult in design that, because of large limitations of the surface shape for change-over between total reflection and transmission to vary the illumination angle accurately, the degree of freedom of designing the shape of the optical prism is small, the loss in amount of light for transmitted light components entering and exiting from the optical prism becomes large, and the magnitude of an effective light emitting part of the light source has a considerable influence on the light distribution.
On the other hand, in the case of the illumination device disclosed in the above Japanese Laid-Open Patent Application No. Hei 8-262538, the optical prism is divided into a plurality of prism members and the prism members disposed on the upper and lower sides are rotated to change over the illumination range. However, since such a rotation of the prism members essentially causes only illumination directions of total-reflection light components to shift as a whole and does not vary the light distribution characteristic itself, it is not always possible to obtain the even light distribution in every zoom point. More specifically, in the method of widening the illumination range, from the most light-collecting state, which is brought about when three illumination areas, i.e., the upper, lower and middle areas, overlap one another, the prism members are rotated to cause the light distributions of the upper and lower illumination areas to gradually shift outward. In such a process of varying the illumination range, there occurs a discontinuous point in the overlapping portion of the light distributions of the upper, lower and middle areas, so that it is not necessarily possible to obtain the even light distribution over the entire illumination range and there exist points where the illuminance becomes uneven in part. Further, since three, i.e., upper, lower and middle, optical prism members are required and the two optical prism members have to be moved in synchronism with each other, the arrangement of mechanical parts of the illumination device becomes complicated, disadvantageously causing an increase in cost.
Further, as the related art of the invention, there are, for example, U.S. patent application Ser. No. 09/644,701 filed on Aug. 24, 2000 now U.S. Pat. No. 6,400,905, Japanese Laid-Open Patent Application No. Hei 4-275537, U.S. patent application Ser. No. 09/454,452 filed on Dec. 6, 1999, U.S. patent application Ser. No. 08/581,333 filed on Dec. 29, 1995, etc.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to reduce the size of the entire shape of an illumination optical system capable of varying the illumination angle.
It is another object of the invention to make the light distribution characteristic of the illumination optical system even in every zoom point and to decrease the amount of movement required for varying the illumination angle.
It is a further object of the invention to reduce the number of constituent parts of the illumination optical system, thereby causing a reduction in cost.
It is a still further object of the invention to provide a variable-illumination-angle illumination device which is reduced in size, thickness and weight.
It is a still further object of the invention to provide an illumination device, adapted for a still camera, a video camera, etc., arranged to be capable of utilizing energy obtained from a light source with high efficiency and of obtaining the even light distribution characteristic in every zoom point, and having the simple and inexpensive construction, and to provide a photographing apparatus using the illumination device.
To attain the above objects, in accordance with an aspect of the invention, there is provided an illumination device
Canon Kabushiki Kaisha
O'Shea Sandra
Robin Blecker & Daley
Truong Bao Q.
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