Patent Application
20060139481
The present invention relates to illumination apparatuses, which are provided in image-taking apparatuses such as digital cameras, and illuminates objects.
Illumination apparatuses used in image-taking apparatus generally comprise a light source, reflector which leads a luminous flux emitted from the light source forward (object side), and an optical member, such as a Fresnel lens, which is arranged in front of the light source for obtaining a predetermined light distribution characteristic.
In such illumination apparatuses, unevenness of light distribution tends to occur because of forming errors of the reflector and optical member, and displacements between the light source, reflector and optical member. An illumination apparatus has been disclosed in which a plurality of cylindrical lens surfaces having a concave shape are formed on the entrance surface of an optical member (protector) in Japanese Patent Laid-Open Application No.2001-337372. The cylindrical lens surface is generally extends in a direction parallel to a rod-like light-emitting tube, and diverges the flash light from the light-emitting tube to reduce the unevenness of light distribution.
The miniaturization of illumination apparatuses is required according to the miniaturization of image-taking apparatuses, and the improvement of light use efficiency (light condensing efficiency) is particularly required while reducing the height of the image-taking apparatus. An illumination apparatus has been proposed in which the improvement of light condensing efficiency and the reduction of the height of the optical system are achieved by using an optical member utilizing total reflection, such as a prism and light guide.
Moreover, recent image-taking apparatuses are designed so that the inside of the illumination apparatus (the light-emitting tube, terminals, or the like) cannot be seen from the outside.
In the illumination apparatus disclosed in Japanese Patent Laid-Open Application No.2001-337372, since the plurality of cylindrical lens surfaces for reducing the unevenness of light distribution are formed on the entrance surface of the optical member, the inside of the illumination apparatus is hard to be seen from the outside. However, it is difficult to obtain the required light distribution characteristic and light condensing efficiency in a case where the plurality of cylindrical lens surfaces are formed on the entrance surface of the above-mentioned optical member utilizing total reflection. In other words, the structure is not adequate to the illumination apparatus in which the reduction of its height is particularly required.
One object of the present invention is to provide an illumination apparatus having a structure which can make the inside of the apparatus hard to be seen from the outside without deterioration of the light distribution, and is applicable to illumination apparatuses having an optical member utilizing total reflection. Another object of the present invention is to provide an image-taking apparatus with the illumination apparatus.
An illumination apparatus as one aspect of the present invention comprises a light-emitting tube which extends in a first direction; and an optical member which includes an entrance portion where a luminous flux from the light-emitting tube enters and an exit portion where the luminous flux exits. The exit portion includes a plurality of surfaces which are arranged in a second direction orthogonal to the first direction, the surfaces being orthogonal or inclined with respect to the optical axis direction of the illumination apparatus, and located at different positions in the optical axis direction.
Other objects and further features of the present invention will become readily apparent from the following description of the preferred embodiments with reference to accompanying drawings.
Preferred embodiments of the present invention will hereinafter be described with reference to the drawings.
10 denotes an image-pickup element such as a CCD sensor and a CMOS sensor. The image-pickup element 10 converts an object image formed by the taking lens into electronic signals to generate image-taking signals. An image processor, not shown in the figure, processes the image-taking signals to generate video signals. When the release button is operated, a part of the video signals is captured and recorded to a recording medium such as a semiconductor memory. A silver-halide film may be used instead of the image-pickup element 10 in this embodiment.
The illumination unit 5 includes a cylindrical flash discharge tube (light-emitting tube) 6 such as a xenon tube, and a reflector 7. The reflector 7 reflects forward (toward the object) the luminous flux that has progressed in the backward direction (opposite to the object) other than the forward direction and in the vertical direction among luminous fluxes emitted radially from the flash discharge tube 6. The reflector 7 has a one-dimensional curvature in the vertical direction, and is made of a metallic material, such as bright aluminum, that has an inner, high-reflectance surface, or a resin material that has an inner, high-reflectance, metallic evaporated surface, etc.
Furthermore, the illumination unit 5 includes an optical member 8. The optical member 8 converts the luminous flux directly entering from the flash discharge tube 6 or reflected on the reflector 7 into a luminous flux having a predetermined light distribution characteristic to lead it efficiently to the object. The optical element 8 is made of an optical resin material having a high transmittance, such as acrylate resin, or a grass material.
In the above-described camera, a CPU (not shown) determines whether the illumination unit 5 is to emit light or not, based on the object brightness measured by a photometric unit (not shown) and a measurement result of the image-pickup element or the sensitivity of the film, in response to the first stroke operation (half-press operation) of the release button 4, for example, when the camera is set to a “flash automatic mode”.
When determining that the “illumination unit is to emit light” under the current image-taking condition, the CPU instructs to take an image (and record the image), outputs an emission signal to cause the flash discharge tube 6 to emit light via a trigger lead (not shown) attached to the reflector 7, in response to the second stroke operation (full-press operation) of the release button 4.
The most object side surface of the optical member 8 constituting the illumination unit 5 does not have a Fresnel lens surface or the like that controls the light distribution characteristic in the horizontal direction in this embodiment. However, adequate setting of the shapes of the optical member 8 and reflector 7 optimizes the light distribution characteristic in the horizontal direction. Moreover, adequate setting of the shapes of the entrance surface of the reflector 7 and optical member 8 also optimizes the light distribution characteristic in the vertical direction.
In
In
On the other hand, a second luminous flux emitted from the flash discharge tube 6 at an angle equal to or larger than a predetermined angle with respect to the optical axis AXL enters the optical member 8 from the first entrance surface 8a, emerges from the second exit surfaces 8d and 8d′ into the spaces 8c and 8c′ once, and then reenters the optical member 8 from the second entrance surfaces 8e and 8e′. After that, the second luminous flux emerges from the first exit surface 8b.
The second exit surfaces 8d and 8d′ are formed as a cylindrical lens surface having a positive refractive power (or optical power, that is, the inverse of the focal length) in the vertical direction (direction orthogonal to the paper of
Although the actual light distribution characteristic entirely changes in a slightly spreading direction due to the luminous fluxes emitted from the periphery of the discharge tube 6 in addition to the illustrated representative luminous flux, the actual light distribution characteristic is almost equal to the representative luminous flux's one. Therefore, the following description follows this representative luminous flux.
In
The luminous flux emitted forward from the discharge tube 6 at an angle larger than the first angle and smaller than a second angle with respect to the optical axis AXL directly enters the first entrance surface 8a, is refracted by the first entrance surface 8a, is totally reflected by reflective surfaces 8g and 8g′, and then emerges from the first exit surface 8b. The luminous flux is converted into a luminous flux having a desired light distribution characteristic in the process.
The luminous flux emitted forward from the discharge tube 6 at an angle larger than the second angle with respect to the optical axis AXL enters the first entrance surface 8a after reflection on the reflector 7, is refracted by the first entrance surface 8a, and then emerges from the first exit surface 8b. The luminous flux is also converted into a luminous flux having a desired light distribution characteristic in the process.
The combined radiation range of these three luminous fluxes becomes the angle range meeting the image-taking range through the taking lens.
Here, the description will be made of the optical path of the luminous flux emitted backward from the flash discharge tube 6 though it is not shown in the figure. Part of the reflector 7, which has a semi-cylindrical shape concentric to the flash discharge tube 6, is disposed behind the flash discharge tube 6. The grass tube of the flash discharge tube 6 has a cylindrical shape concentric to the flash discharge tube 6. Therefore, the luminous flux emitted backward from the center of the discharge tube 6 and reflected on the reflector 7 returns to the center of the discharge tube 6 without being affected by the refraction at the glass tube. The action of the luminous flux that has returned to the center of the discharge tube 6 is approximately the same as the luminous flux shown in
In the illumination unit 5 whose each surface has the above-mentioned shape, the luminous flux from the discharge tube 6 is converted into a luminous flux having a substantially even light distribution characteristic by the optical member 8 and reflector 7. The converted luminous flux emerges from the illumination unit 5 toward the object. Therefore, it is possible to produce a small illumination unit capable of reducing loss of light amount caused by radiation to the outside of the required radiation range, that is, the illumination unit having an extremely good efficiency.
Next, the description will be made of the shape of the first exit surface (exit portion) 8b in the optical member 8 with reference to
A plurality of rectangular groove portions 8f are formed at a substantially constant pitch in the Z-direction (second direction) on the first exit surface 8b. In other words, the first exit surface 8b is constituted by first and second planes (planar surfaces) 8f1 and 8f2 arranged alternately in the Z-direction. The first plane 8f1 is formed at a front position in the optical axis direction. The second plane 8f2 is formed at a position posterior to the first plane 8f1.
Both of the first and second planes 8f1 and 8f2 are orthogonal to the optical axis direction (Y-direction). As shown in
Furthermore, in this embodiment, a third plane 8f3 parallel to the optical axis direction is formed between the first and second planes 8f1 and 8f2 closest to each other in the Z-direction. The third plane 8f3 extends over the entire first exit surface 8b in the X-direction.
The terms ‘orthogonal’ and ‘parallel’ as used herein (in this specification and claims) mean not only being perfectly orthogonal and parallel, but also being deviated therefrom within an allowable error range not affecting optical characteristics.
a:b (aspect ratio)=1:5,
where a represents the depth of the groove portion 8f, that is, the width of the third plane 8f3 in the Y-direction, b represents the width of the groove portion 8f, that is, the width of the second plane 8f2 in the Z-direction.
As described above, in this embodiment, the groove portion 8f has a rectangular shape, and the first exit surface 8b is constituted by the first and second planes 8f1 and 8f2 orthogonal to the optical axis AXL and located at different anteroposterior positions, and the third plane 8f3 parallel to the optical axis AXL. This prevents the luminous flux from diverging, thereby making it possible to obtain a light distribution characteristic equivalent to that in a case where the first exit surface 8b is formed as a simple plane.
The light distribution characteristic diagram in the upper part of
The simulation of light distribution shown in
The light distribution characteristic diagrams are shown by circular graphs, the lateral axis thereof showing radiation angles and the vertical axis showing values of logarithm in which the luminous intensity is 1 when the radiation angle is 0 degree. The solid line shows the luminous intensity in the horizontal direction (X-direction), and the dashed line shows the luminous intensity in the vertical direction (Z-direction).
These diagrams show that approximately the same light distribution characteristic is obtained in this embodiment's case where the groove portions 8f are formed on the first exit surface 8b and the case where the first exit surface 8b is a simple plane having no groove portion. Therefore, according to this embodiment's illumination unit 5, it is possible to obtain approximately the same radiation range as the illumination unit that is different only in having no groove portion and its radiation range is set so as to meet the image-taking range of the taking lens.
In these figures, the rays RAY2 shown by the dashed line are totally reflected on the first exit surface 8b (first plane 8f1) due to an influence of changing the aspect ratio of the groove portion 8f from that in
As is shown from the comparison between
Specifically it is desirable to set the value as follows:
a/b≦0.35.
The configuration of the first exit surface 8b shown in
In the above embodiment, the description was made of the case where the third plane 8f3 constituting the groove portion 8f on the first exit surface 8b is a plane parallel to the optical axis direction. However, as shown in
For example, the above-mentioned inclined third plane 8f3 facilitates die removal from the resin molded optical member 8. However, it is necessary to suppress the inclination angle a with respect to the optical axis direction to a small angle so that the light distribution characteristic and radiation efficiency may not be deteriorated compared to those of the optical member having no groove portion.
The description was made of the case where two planes 8f1 and 8f2 located at different anteroposterior positions were formed alternately on the first exit surface 8b in the above-described Embodiment 1. However, as shown in
In
The description was made of the case where two planes 8f1 and 8f2 on the first exit surface 8b were planes orthogonal to the optical axis direction (Y-direction) in the above-described Embodiment 1. However, as shown in
In
The description was made of the case where two planes 8f1 and 8f2 on the first exit surface 8b were planes orthogonal to the optical axis direction (Y-direction) in the above-described Embodiment 1. However, as shown in
In
As described above, according to each embodiment, it is possible to obtain an even light distribution characteristic in the required radiation range and good radiation efficiency while reducing the vertical height of the illumination unit, and improve the exterior appearance with little influence on the light distribution characteristic. Also, loss of light amount is very small. Moreover, the present invention is easy to apply to an illumination apparatus including an optical member utilizing total reflection, and effective particularly in miniaturizing the illumination apparatus and an image-taking apparatuses with the same.
Although the pitch, height and depth of the groove portion 8f were constant in each above-described embodiment, they may be changed in the present invention. Moreover, the number of the groove portions is not limited to that of each embodiment. The pitch and number of the groove portions can be determined from a design standpoint.
Furthermore, the entrance surface of the optical member had an optical power, and the optical member had a reflective surface totally reflecting light in each above-described embodiment. However, in a case where a Fresnel lens is used as the optical member, a surface other than the Fresnel lens surface on the optical member may be formed in the shape described in each embodiment.
Moreover, although the illumination unit included a reflector having a function of surface reflection in each above-described embodiment, an optical element made of a transparent body leading light forward by internal total reflection can be used instead of the reflector.
Moreover, although the optical member had planes orthogonal to the optical axis and extending over the first exit surface in the X-direction in each above-described embodiment, planes located at different anteroposterior positions can be formed alternately, or planes orthogonal to the optical axis can be formed stepwise, in the X-direction.
The shape of the optical member in the present invention is not limited to that described in each embodiment, and any shape having the first entrance surface and the final exit surface can be acceptable.
This application claims a foreign priority benefit based on Japanese Patent Application No. 2004-381783, filed on Dec. 28, 2004, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-381783 (PAT. | Dec 2004 | JP | national |
