Projection apparatus

Optics: image projectors – Composite projected image – Multicolor picture

Reexamination Certificate

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Details

C353S030000, C353S033000

Reexamination Certificate

active

06273568

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a projection apparatus, and is suitable for a color liquid crystal projector for enlarging and projecting, for example, the original picture of a projected image displayed on a color liquid crystal panel onto the surface of a screen.
2. Related Background Art
There have heretofore been proposed various projection apparatuses (liquid crystal projectors) adapted to enlarge and project the original picture of the projected image of a liquid crystal light valve or the like onto the surface of a screen.
Apparatuses of various types are used as projection apparatuses, and in a projection apparatus using color liquid crystal as the original picture of a projected image, a color combining system such as a reflecting mirror or a dichroic mirror is disposed in the space (back focus) from the last lens surface of a projection lens to a liquid crystal display element to thereby effect the color combination of a colored imaged.
In a color liquid crystal projector using three liquid crystal panels for R, G and B lights as a color liquid crystal projector, use is made of a color combining system for combining color lights transmitted through the three liquid crystal panels into an optical path.
As the color combining system, for example, in Japanese Laid-Open Patent Application No. 1-131593, use is made of a so-called cross dichroic prism comprising four triangular prisms cemented together, and a dichroic surface being designed to cruciformly cross the cemented surface thereof, and this cross dichroic prism is provided in an optical path leading from a liquid crystal panel to a projection lens.
Generally, when a color combining system is comprised of a prism, the thickness of a dichroic surface is very small and its influenced on the optical performance (imaging performance) of a projection lens is very little, and this is suitable for projecting an image of high image quality.
On the other hand,
FIG. 7
of the accompanying drawings is a schematic view of the essential portions of a color liquid crystal projector using three dichroic mirrors and a dichroic prism which is proposed in Japanese Laid-Open Patent Application No. 9-211750.
In
FIG. 7
, of the lights emitted from a light source
201
using a metal halide lamp, red light (light of about 600 nm to about 700 nm) is reflected by a red reflecting dichroic mirror
202
and the other lights are transmitted therethrough. The reflected red light has its travelling path changed by a reflecting mirror
203
and enters a liquid crystal light valve
206
for red. Of the lights transmitted through the red reflecting dichroic mirror
202
, green light (light of about 500 nm to about 600 nm) is reflected by a blue transmitting dichroic mirror
204
, and blue light (light of about 400 nm to about 500 nm) is transmitted therethrough. The green light reflected by the dichroic mirror
204
enters a liquid crystal light valve
205
for green, and the blue light transmitted through the dichroic mirror
204
enters a liquid crystal light valve
207
for blue. Each liquid crystal light valve has a polarizer
221
and an analyzer
222
mounted thereon, whereby light is modulated for each color to thereby form an image.
The blue light light-modulated by the liquid crystal light valve
207
for blue is reflected by a reflecting mirror
208
, and is made incident on a blue transmitting dichroic prism
227
to be transmitted therethrough, and is enlarged and projected by a projection lens
211
. The green light light-modulated by the liquid crystal light valve
205
for green is made incident on a red transmitting dichroic mirror
209
to be reflected therefrom, and is made incident on the blue transmitting dichroic prism
227
to be reflected therefrom, and is enlarged and projected by a projection lens
211
. The red light light-modulated by the liquid crystal light valve
206
for red is made incident on the red transmitting dichroic mirror
209
to be transmitted therethrough, and is made incident on the blue transmitting dichroic prism
227
to be reflected therefrom, and is enlarged and projected by the projection lens
211
. The combination of the red light and the green light is effected by the dichroic mirror
209
, and the combination of the aforementioned combined light and the blue light is effected by the dichroic prism
227
.
Liquid crystal projections in which a projection lens is comprised of a telecentric system are proposed, for example, in Japanese Laid-Open Patent Application No. 8-122699, Japanese Laid-Open Patent Application No. 10-10467, etc. Japanese Laid-Open Patent Application No. 8-122699 proposes an image projecting apparatus comprising a light source, a spatial light modulating element, an illuminating optical system for applying the light from the light source to the spatial light modulating element, and a projection optical system for projecting the image of the spatial light modulating element, and which is comprised of an illuminating optical system or a projection optical system. Japanese Laid-Open Patent Application No. 10-10467 proposes a projection display apparatus comprised of a light source device, an optical integrator for converting the light from the light source into a uniform light beam, a reflection type liquid crystal panel for modulating the light beam from the optical integrator and displaying an image, and a projection lens for enlarging and projecting the image displayed on the reflection type liquid crystal panel onto a screen.
A cross dichroic prism for color combination or color resolution suffers from the disadvantage that the deviation of liquid crystal pixels forming an image on a screen is caused by the inclination or level difference of two cemented surfaces when two prism surfaces are cemented together to form a dichroic surface performing a function (e.g. reflecting red light) into the two prism surfaces.
This disadvantage appears more remarkably as the number of the pixels of the liquid crystal used becomes greater and therefore, to solve this problem, the cementing step of very high accuracy becomes necessary, and it is feared that the costs of parts are increased.
On the other hand, in the liquid crystal projector shown in
FIG. 7
, a dichroic surface near the projection lens
211
is comprised of a prism and is made into a dichroic prism
227
, and dichroic surface and reflecting surfaces near the liquid crystal panels
205
,
206
and
207
are comprised of a dichroic mirror
209
and a mirror
208
, respectively. When such a construction is adopted, the problem in the manufacture of the dichroic surfaces in the dichroic prism is avoided and the weight is not increased. However, in the optical path transmitted through the dichroic mirror
209
, the dichroic mirror
209
is disposed obliquely relative to the optical path and therefore, there is the problem that astigmatism by the thickness of the dichroic mirror and the distortion of an asymmetrical image occur and in the optical path reflected by the dichroic mirror
209
, the distortion of an asymmetrical image due to the distortion of the reflecting surface occurs.
It is written that in the color liquid crystal projector shown in
FIG. 7
, the deterioration of performance occurs to the reflecting optical path and transmitting optical path of the dichroic mirror
209
, but the specific substance of the deterioration is not mentioned. The setting of the optical paths when a dichroic mirror is used need be considered with a phenomenon occurring in this dichroic mirror taken into account, and this will now be described with reference to
FIGS. 8 and 9
of the accompanying drawings. The distortion of an image occurring in the transmitting optical path is such that when as shown in
FIG. 8
, the principal ray of light is incident on the dichroic mirror
209
at different angles, the amounts of shift (&Dgr;′1, &Dgr;′2 and &Dgr;′3) of the ray of light by the thickness of the mirror differ from one another and non-uniform distortion occurs to a projected

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