Illumination – Light source and modifier – Plural serial lens elements or components
Reexamination Certificate
1999-03-10
2002-10-15
O'Shea, Sandra (Department: 2875)
Illumination
Light source and modifier
Plural serial lens elements or components
C362S242000, C362S331000
Reexamination Certificate
active
06464375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens element mainly used for illumination, an illumination optical apparatus for mainly illuminating a spatial optical modulator, and a projection display apparatus for projecting a large-screen image on a screen by using the illumination optical apparatus, a spatial optical modulator for forming an optical image when a video signal is supplied from an external unit, and a projection lens.
2. Description of the Related Art
Various types of projection display apparatuses respectively using the spatial optical modulator have been known so far as video units for a large screen. Each of these projection display apparatuses enlarges an optical image corresponding to a video signal supplied from an external unit with a projection lens and projects the image on a screen by using a transmission- or reflection-type liquid-crystal panel as a spatial optical modulator, illuminating the liquid-crystal panel with a light source, and forming the optical image on the liquid-crystal panel.
It is necessary for an illumination optical apparatus used for a projection display apparatus to have high uniformities of brightness and color, a high light-utilization efficiency, and a large light output on a light-receiving surface (spatial optical modulator).
A projection display apparatus using two lens arrays is disclosed as means for improving the uniformities of brightness and color (e.g. Japanese Patent Application Laid-Open Nos. Hei 3-111806 and Hei 5-346557).
FIG. 26
shows a basic configuration of the projection display apparatus. The white light emitted from a lamp
280
is condensed by a concave reflector
281
to become a luminous flux advancing along and in parallel with an optical axis
288
, pass through lens arrays
283
,
284
and a field lens
285
, and illuminate the display region of a liquid-crystal panel
286
. A UV-IR cut filter
282
is used to remove unnecessary and harmful infrared light and ultraviolet light from illumination light. An optical image is formed on the liquid-crystal panel
286
, which is enlarged by a projection lens
287
and projected on a screen (not illustrated).
It is generally known that the brightness of a luminous flux condensed by a concave reflector increases at a position closer to its optical axis because the luminous flux density rises and decreases at a portion farther from an optical axis because the density lowers. The lens arrays
283
and
284
are used to improve the brightness irregularity of a luminous flux condensed by a concave reflector. The first lens array
283
and the second lens array
284
are respectively constituted by two-dimensionally arranging a plurality of first lenses
283
a
and a plurality of second lenses
284
a
. A luminous flux emitted from the concave reflector
282
is divided into a plurality of micro luminous fluxes and these micro luminous fluxes are led in the superimposing configuration each other so that each micro luminous flux illuminates the entire display region of the liquid-crystal panel
286
.
The conventional illumination optical apparatus shown
FIG. 26
constituted by combining a concave reflector with two lens arrays completely meets the display uniformity requested for a projection display apparatus but it has the problems described below.
When constituting an illumination optical apparatus with lens arrays, the image of the illuminant of the lamp
280
is formed on the apertures of a plurality of second lenses
284
a
. This state is schematically shown in FIG.
27
. When applying a luminous flux having a large brightness irregularity condensed by the concave reflector
282
to the first lens array
283
, plural illuminant images
290
at a position closer to the optical axis where the luminous flux density is higher increase in size and the plural illuminant images
290
at a position farther from the optical axis where the luminous flux density is lower decrease in size. when the aperture of the second lens
284
a
is smaller than the illuminant images
290
formed there, the light leaking from the aperture results in a loss. When applying a large-enough aperture to the illuminant images
290
, the illuminant images
290
decrease in size toward the circumference as shown in FIG.
27
. Therefore, the number of unnecessary regions increases, the effective aperture
291
of the second lens array
284
increases, and a projection lens having a large converging angle is required. Increase of a converging angle causes the size of a projection lens to increase and results in increase of the cost. To decrease the irradiation angle of the light used for illumination, it is possible to increase an illumination optical path. However, the interval between the second lens array
284
and the liquid-crystal panel
286
increases and the entire size of a projector increases.
When an illuminant formed by the lamp
280
is small enough, the degree of a problem is low. However, an illuminant formed by a metal halide lamp or xenon lamp actually used for the above purpose has a problem because the illuminant has a size of a certain degree.
A projection display apparatus using a plurality of lamps is disclosed as means for increasing the light output of an illumination luminous flux (e.g. Japanese Patent Application Laid-Open Nos. Hei 6-242397 and Hei 6-265887 and Hei 9-50082).
FIG. 28
shows a configuration of the above projection display apparatus.
Parabolic mirrors
303
and
304
, UV-IR cut filters
305
and
306
, first lens arrays
307
and
308
, and second lens arrays
309
and
310
are arranged for a plurality of lamps
301
and
302
respectively. The light emitted from the second lens arrays
309
and
310
is divided into three primary color lights of red, green, and blue by dichroic mirrors
311
and
312
and thereafter, passes through field lenses
318
,
319
, and
320
and enters their respectively-corresponding liquid-crystal panels
321
,
322
, and
323
. Relay lenses
313
and
314
correct the intensity difference of illumination light due to the difference between the illumination optical path lengths which are the distances between the second lens arrays
309
and
310
on one hand and the liquid-crystal panels
321
,
322
, and
323
on the other. Moreover, plane mirrors
315
,
316
, and
317
are arranged to bend the optical path of each color. Primary color lights of red, green, and blue emitted from the liquid-crystal panels
321
,
322
, and
323
are synthesized by dichroic prism
324
and then, enter a projection lens
325
. The projection lens
325
enlarges optical images formed on the liquid-crystal panels
321
,
322
, and
323
and projects them on a screen (not illustrated).
Vicinities of surfaces of the second lens arrays
309
and
310
are almost conjugate with the pupil surface
326
of the projection lens
325
and the sizes and distribution of a plurality of illuminant images formed on the second lens arrays
309
and
310
are focused on the pupil surface of the projection lens
325
.
FIG. 29
schematically shows the state of illuminant images
340
and
341
formed on the pupil surface
326
of the projection lens
325
. In
FIG. 29
, broken lines are virtual lines showing outlines of the second lens arrays
309
and
310
. The illuminant images
340
and
341
corresponding to lamps
301
and
302
are formed on the pupil surface
326
of the projection lens
325
at both the sides of the optical axis
331
of the projection lens
325
.
Vignetting is generally provided in the projection lens
325
, in which the circumferential illuminance becomes lower than the central illuminance on a screen. This is because the illuminant images
340
and
341
on the pupil surface
326
of the projection lens
325
cause an eclipse due to vignetting. Therefore, when the luminous characteristics of two lamps
301
and
302
arranged at both the sides of the optical axis
331
are different from each other as shown in
FIG. 29
, illuminant images contributing to the brightness of the circumferen
Tanaka Takaaki
Wada Mitsuhiro
Matsushita Electric - Industrial Co., Ltd.
O'Shea Sandra
Smith Gambrell & Russell, LLP.
Ward John Anthony
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