Optical: systems and elements – Prism – With reflecting surface
Reexamination Certificate
2000-03-23
2002-09-24
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Prism
With reflecting surface
C359S633000, C359S634000
Reexamination Certificate
active
06456447
ABSTRACT:
This application claims the benefit of Japanese Patent application Nos.11-083899 and 2000-058899 which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color separating prism or a color separating and composing prism for color-separating a white light into a red component light, green component light, and blue component light (hereinafter called the R light, G light, and B light, respectively) or for color-composing the R light, the G light and the B light into one light, a full color projection display apparatus provided with reflection-type light valves respectively for the R light, the G light, and the B light, for modulating and emitting polarized light beams of the respective colors entering the respective light valves, for color-composing the respective modulated color light beams from the light valves through the color separating and composing prism so as to analyze to extract the color-composed light by use of an analyzing optical system, and for projecting the analyzed light by use of a projection lens, as well as a camera provided with such prism.
2. Related Background Art
As a conventional projection display apparatus, there is known, for example, a full color projection display apparatus disclosed in Japanese Patent No. 2505758.
FIG. 9
is a diagram for showing the constitution of the projection display apparatus disclosed in
FIG. 1
of the above patent. The conventional apparatus will be described below with reference to this diagram.
A light source beam emitted from a light source
23
is converted into a substantially parallel light beam through a shaping lens
22
to enter a polarizing beam splitter
21
. The light source beam entering the polarizing beam splitter
21
is polarized and split into an S-polarized light which is reflected by a polarization and separation unit of this polarizing beam splitter and a P-polarized light which progresses through this polarization and separation unit. The S-polarized light is emitted from the polarizing beam splitter
21
to enter a color separating and composing prism consisting of a prism
11
A, a prism
11
B, and a prism
11
C. Note that this color separating and composing prism comprises a dichroic film formed on a surface
11
e
of the prism
11
A for reflecting the B light and transmitting the G light and the R light and another dichroic film formed on a joint surface between the prism
11
B and the prism
11
C for reflecting the R light and transmitting the G light. In addition, a gap is formed between the prism
11
A and the prism
11
B.
The light beam entering from the surface
11
a
of the prism
11
A progresses through the prism
11
A, and enters the B light reflecting dichroic film formed on the surface
11
e
, and is color-separated into the B light to be reflected, and a mixed light of the R light and the G light which are transmitted through this dichroic film to enter the prism
11
B through the gap. The B light which is reflected by the B light reflecting dichroic film progresses through the prism
11
A to be totally reflected by the surface
11
a
, and further progresses to exit from an exit surface
11
b
, and then enters a B light reflection-type light valve
12
which is provided in the vicinity of the exit surface. On the other hand, the mixed light of the transmitted R light and G light enters an R light reflecting dichroic film. The R light reflected by this film progresses through the prism
11
B and is totally reflected by an entrance surface of the prism
11
B and then exits from the exit surface
11
c
to enter an light valve
13
for the R light which is provided in the vicinity of the exit surface. The G light progressing through the prism
11
C continues to progress through the prism
11
C as it is to exit from a surface
11
d
, and enters a G light reflection-type light valve
14
which is provided in the vicinity of the exit surface.
The S-polarized light incident on the light valve of each color is subjected to modulation by the use of a color signal of the color, and a predetermined part of this light is converted into a P-polarized light, and is reflected as a mixed light with the S-polarized light which is a non-modulated light, to exit therefrom. The mixed light emitted from each light valve goes back in the above optical path to exit as a color composed light from the surface
11
a
of the prism
11
A. This color composed light re-enters the polarizing beam splitter
21
, whereby only the P-polarized light which is a modulated light of each color is analyzed and extracted as a transmitted light from the polarizing beam splitter. The analyzed light enters a projection lens
24
to form a full color projection image on a screen
25
.
However, the conventional projection display apparatus mentioned above has a problem that pixels of the three light valves for the R light, the G light and the B light are projected on the screen in a shifted manner due to a change in the environment, vibration, or the like, that is, a so-called registration shift is generated. The present inventor has studied and examined a registration shift generated in the above projection display apparatus, to clarify the cause thereof. As a result, he found that such registration shift is caused by the air gap between the prism
11
A and the prism
11
B and a space between the polarizing beam splitter
21
and the prism
11
A.
More specifically, a relative positional relation between each prism member of the composite prism and the polarizing beam splitter for forming the gap or the space is changed due to a change in the ambient temperature, a vibration, or the like, thereby causing such registration shift.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a color separating prism with an improved arrangement of prisms or the like having the above gap or space in the color separating prism, to the exclusion of the registration shift, and to provide a projection display apparatus in which the composing prism and the polarizing beam splitter are used in combination, to the exclusion of the registration shift.
Another object of the present invention is to provide a camera which is capable of always obtaining a shot image having an excellent contrast.
In order to achieve the above objects, according to the present invention, there is provided a color separating prism which comprises:
a first prism provided with a first surface on which a light is incident, a second surface having a first color reflecting dichroic film for reflecting a first color light (B light) and transmitting a second color light (R light), and a third surface for emitting the first color light (B light);
a second prism provided with a first surface for transmitting the second color light (R light) which is transmitted through the second surface of the first prism, a second surface for reflecting the second color light (R light), and a third surface for emitting the second color light (R light) which is totally reflected by the first surface after being reflected by the second surface, and integrally fixed to the first prism by an adhesive; and
a total reflection supporting layer provided between the second surface of the first prism and the first surface of the second prism to allow total reflection on the first surface of the second prism.
In a preferred embodiment of the present invention, a refractive index of the total reflection supporting layer is preferably lower than that of the second prism.
Also, in a preferred embodiment of the present invention, the total reflection supporting layer is preferably an adhesive for binding the first prism to the second prism.
Also, in a preferred embodiment of the present invention, an absolute value of a photoelastic constant of a glass material for forming the first prism and the second prism is preferably within a range of 1.5×10
−8
cm
2
/N, at the wavelengths of the first color light (B light) and the second color light (R light).
According to the present invention, there is provided a
Cherry Euncha
Miles & Stockbridge P.C.
Nikon Corporation
Spyrou Cassandra
LandOfFree
Color separating prism, and projection display apparatus and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Color separating prism, and projection display apparatus and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Color separating prism, and projection display apparatus and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2829910