Electric lamp and discharge devices – With optical device or special ray transmissive envelope
Reexamination Certificate
2001-08-29
2004-05-25
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With optical device or special ray transmissive envelope
C313S114000, C313S112000, C359S834000, C362S016000, C362S328000, C396S021000, C396S200000, C348S337000
Reexamination Certificate
active
06741014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a light emitting device capable of changing an illumination range and a camera having the same.
2. Description of the Related Art
Conventionally, a variety of illuminating devices for use in a photographing apparatus such as a camera have been proposed in order to efficiently converge luminous fluxes, which are emitted from a light source in various directions, within a required illumination angle of view.
Particularly in recent years, the convergence efficiency have been improved and the size of a photographing apparatus has been reduced by providing an optical member that performs total reflection on a prism, a light guide, and the like in place of a Fresnel lens, which is conventionally disposed in front of a light source.
In recent years, a photographing apparatus such as a camera has been reduced in size and weight whereas the zooming magnification of a taking lens has been increasing. Generally, a full aperture f-number of the taking lens tends to gradually increase with the reduction in size of the photographing apparatus and the increase in the magnification. If a picture is taken without using an auxiliary light source, an image on the picture is unexpectedly blurred due to the motion of the photographer's hand or the motion of a subject, or a failed picture is produced due to underexposure. To address this problem, an illuminating device serving as an auxiliary light source is usually built in the photographing apparatus.
Under the circumstances, the frequency with which the illuminating device is used is increased to a large extent, and the quantity of emitted light required for one photography is increased. Thus, the illumination range is usually fixed correspondingly to the wide-angle photography, and an undesired range is illuminated in the telephotography. It is therefore disadvantageous to use an illuminating device with a fixed wide illumination range since a large amount of energy is lost.
Accordingly, a variety of illuminating devices have been proposed which are capable of changing the illumination range so as to illuminate only a range corresponding to a shooting angle of view to thus save power. In particular, some illuminating devices have been proposed which improve the luminous efficiency by total reflection.
For example, an illuminating device proposed in Japanese Laid-Open Patent Publication No. 4-138439 (Kokai) by the assignee of the present invention has a convergent optical system arranged at a front portion of the illuminating device and comprised of an optical prism having two upper and lower entrance surfaces having a positive refracting power and which luminous fluxes emitted mainly from a light source laterally with respect to an exit optical axis enter, two upper and lower total reflection surfaces upon which the luminous fluxes are totally reflected, and exit surfaces through which the totally reflected fluxes are emitted toward a subject. In this convergent optical system, the positions of the optical prism and the light source are relatively changed to cause the luminous fluxes to be reflected by or transmitted through the total reflection surfaces to thereby change the illumination range.
In an illuminating device proposed in Japanese Laid-Open Patent Publication (Kokai) No. 8-262538, an optical prism is divided into a plurality of parts, and the optical prism disposed vertically is rotated to change the illumination range.
However, the illuminating devices disclosed in the above publications provide a relatively easy convergence and diffusion control of directing the luminous fluxes in a diametrical direction of a cylindrical discharge arc tube as the light source, i.e. in a direction (vertical direction) orthogonal to the longitudinal direction of the light source (transverse direction with respect to the axis of illumination light), but do not provide a convergence diffusion control of directing the luminous fluxes in the longitudinal direction of the light source (transverse direction with respect to the axis of illumination light). Therefore, the illumination range cannot always be controlled in an ideal manner because the illumination range can be controlled only in the longitudinal direction.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a light emitting device that can be reduced in size as a whole, and that is capable of efficiently utilizing energy from a light source and changing the illumination angle in the transverse direction, and a camera incorporating the light emitting device.
It is another object of the present invention to provide a light emitting device that is capable of changing the illumination angle in the transverse and vertical directions, and a camera incorporating the light emitting device.
To attain the above objects, the present invention provides a light emitting device comprising an emission unit including at least an arc tube being elongated in a longitudinal direction thereof, the arc tube having opposite ends in the longitudinal direction thereof, and a reflection umbrella, and a light-permeable optical unit arranged in front of the emission unit at a side thereof closer to a subject in a manner such that a relative distance between the optical unit and the emission unit is variable, the optical unit having reflection surfaces for reflecting luminous fluxes emitted from the emission unit toward the subject, the reflection surfaces being located at locations corresponding to the opposite ends of the arc tube in the longitudinal direction thereof.
In a preferred form of the present invention, the optical unit has a plurality of cylindrical lenses formed at a central portion thereof and arranged in parallel with the longitudinal direction of the arc tube.
Preferably, the reflection surfaces of the optical unit are disposed such that they do not reflect the luminous fluxes when the optical unit is close to the emission unit but reflect the luminous fluxes when the optical unit is apart from the emission unit.
Also preferably, the emission unit comprises a light refracting section provided at a central portion thereof for refracting light from the arc tube and projecting the light to the subject, the light refracting section having opposite sides, and an optical member having a reflecting section for totally reflecting light from the arc tube to the opposite sides of the light reflecting section and projecting the light to the subject.
Preferably, the optical unit includes prism sections having prism surfaces and projecting from the optical unit toward the arc tube, and the reflection surfaces are the prism surfaces of the prism sections.
To attain the above objects, the present invention further provides alight emitting device comprising an emission unit including at least an arc tube being elongated in a longitudinal direction thereof, the arc tube having opposite ends in the longitudinal direction thereof, and a reflection umbrella, and a light-permeable optical unit arranged in front of the emission unit at a side thereof closer to a subject in a manner such that a relative distance between the optical unit and the emission unit is variable, the optical unit including a plurality of light refracting sections provided at a central portion thereof and arranged in parallel with the longitudinal direction of the arc tube, the light refracting sections having opposite sides in a longitudinal direction thereof, and reflection surfaces provided at the opposite sides in the longitudinal direction of the light refracting sections for reflecting luminous fluxes emitted from the emission unit toward a subject.
Preferably, the light refracting sections comprise cylindrical lenses.
To attain the above object, the present invention also provides a camera having a light emitting device constructed as above.
REFERENCES:
patent: 6011929 (2000-01-01), Fuke et al.
patent: 6404988 (2002-06-01), Tanabe
Japanese Patent Laid-Open Publication No. 04-138439, published May 12, 1992.
Japanese Patent Lai
Canon Kabushiki Kaisha
Patel Ashok
Robin Blecker & Daley
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