Optics: image projectors – Reflector
Reexamination Certificate
2001-10-12
2003-07-01
Dowling, William (Department: 2851)
Optics: image projectors
Reflector
C099S278000
Reexamination Certificate
active
06585380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination apparatus, and a projection type display apparatus which modulates the output light from the illumination apparatus according to predetermined image information by using a light valve and projects thus modulated light onto a screen; and, in particular, to a configuration of an illumination apparatus comprising a plurality of light source sections.
2. Description of the Prior Art
Methods using a lens array or a lenticular plate have conventionally been known as an integrator type in illumination apparatus employed in projection type display apparatus. Even when a light source having uneven light-distributing characteristics such as a metal halide lamp, xenon lamp, or halogen lamp is used, this type of methods can yield an illumination apparatus which can eliminate the unevenness in illumination on the light valve caused by light-distributing characteristics of the light source.
Such an illumination apparatus comprises a first integrator plate (known as a second flyeye or the like in general) and a second integrator plate (known as a first flyeye or the like in general) successively disposed in this order downstream a light source section using a reflector. The first integrator plate is constituted by a plurality of two-dimensionally arranged lens elements, each having a form substantially similar to that of the liquid crystal display panel. A luminous flux with a large unevenness in brightness emitted from the light source section is divided by the first integrator plate into partial luminous fluxes whose number is identical to the number of lens elements in the first integrator plate. The unevenness in brightness of partial luminous fluxes is smaller than that of the undivided luminous flux. The partial luminous fluxes form respective secondary light sources on the surface of the second integrator plate (which becomes conjugate with the pupil surface of a projection lens), which are emitted toward the illuminating region by way of the second integrator plate and a field lens, so as to be superposed on each other, whereby illumination with a smaller unevenness in brightness can be realized.
Known as the projection type display apparatus using two integrator plates as mentioned above is one having a plurality of light sources arranged symmetrical about the optical axis in order to secure the quantity of illumination light, and so forth (Japanese Unexamined Patent Publication No. 6-265887).
In the case of an illumination apparatus comprising a single light source, the unevenness in illumination caused by light-distributing characteristics of the light source can effectively be eliminated by the above-mentioned integrator type. In an illumination apparatus in which a plurality of light sources are arranged symmetrical about the optical axis, however, a new intensity distribution occurs due to light-distributing characteristics of the light sources. Namely, since individual light sources having respective intensity distributions different from each other are arranged symmetrical about the optical axis, a part having a high intensity occurs at a position not near the optical axis but separated from the optical axis by a predetermined distance on the pupil surface of the projection lens, which becomes conjugate with the surface of the second integrator plate. However, the imaging performance of the projection lens is higher in the vicinity of the optical axis and becomes lower as being distanced further therefrom. If a part having a higher intensity, i.e., a part governing the imaging performance, exists at a position separated from the optical axis on the pupil surface by a predetermined distance as mentioned above, it becomes harder to fully exhibit the imaging performance inherent in the projection lens.
A conventional example which can deal with such a problem caused by a plurality of light sources is the illumination apparatus and the projection type display apparatus using the same disclosed in Japanese Unexamined Patent Publication No. 2000-3612. This illumination apparatus comprises a plurality of light source sections each comprising an ellipsoidal mirror having a first focal point near the center of gravity of a luminous body, whereas the luminous flux from each light source section is reflected toward the integrator by a reflecting prism having a reflecting surface near a second focal point of each ellipsoidal mirror. Therefore, the secondary light source of luminous body formed on the reflecting surface of the reflecting prism is located nearer to the optical axis of the illumination apparatus than is the luminous body itself, whereby the position of the secondary light source can be taken as the light source position in its downstream optical systems. Thus, while this apparatus is a bright illumination apparatus comprising a plurality of light sources, a light spot is formed by the luminous flux from each light source section at a position near the optical axis on the pupil surface of the projection lens, whereby the imaging performance of the projection lens can be made favorable.
However, the apparatus mentioned above aims at improving the uniformity in illuminance and color of the illumination light. Therefore, it is considered important for luminous body images formed on the projection lens pupil surface to be arranged substantially symmetrical about the optical axis even when a plurality of lamps are used. Namely, the luminous body images are arranged substantially symmetrical about the optical axis, whereby the light spot formed by the luminous flux from each light source section is resultantly positioned near the optical axis. Hence, this apparatus is not necessarily conceived to cause the above-mentioned projection lens to fully exhibit its imaging performance.
As mentioned above, the imaging performance of projection lens is higher in the vicinity of the optical axis and becomes lower as being separated farther therefrom. Therefore, in order to utilize the imaging performance of the projection lens most effectively, it is desirable that the part having a higher luminous flux intensity be transmitted through the pupil surface of the projection lens at a position as close to the optical axis as possible. Though the light spot formed by the luminous flux from each light source section can be formed at a position close to the optical axis to a certain extent in this conventional example, there is a limit. Namely, as the light spot approaches the optical axis, the position at which the luminous flux from the light source section is reflected on each reflecting surface of the reflecting prism inevitably approaches a vertex of the reflecting prism formed by reflecting surfaces of the reflecting prism. However, a certain area is necessary for reflecting a luminous flux even in the vicinity of the focal position of the luminous flux, whereby no luminous flux can be reflected by a vertex of the reflection prism.
Therefore, a paradigm shift is necessary for causing the part with a higher intensity of the luminous flux from a light source section to pass through the pupil surface of the projection lens at a position nearer to the optical axis, and further effectively utilizing the imaging performance of the projection lens.
Commonly assigned Japanese Unexamined Patent Publication No. 11-44920 discloses a projection type display apparatus proposed as one solving the above-mentioned problem caused by a plurality of light sources. This projection type display apparatus is configured such that the luminous fluxes from each light source section is moved in an integrator section so as to approach the optical axis of the integrator section while the rate of change in the distance from the luminous flux center to the optical axis becomes the rate of change in the diameter of the luminous flux or greater. As a consequence, in the pupil surface of the projection lens, the light spot caused by the luminous flux from each light source section is formed at a position near the optical
Dowling William
Fuji Photo Optical Co., Ltd.
Snider Ronald R.
Snider & Associates
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