JP2004046010A - Method of regulating prism stage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a regulating method capable of regulating a prism stage on which cross dichroic prisms are to be installed by easy operation with high accuracy. <P>SOLUTION: The laser beam from a light source 4 for regulation is projected to the cross dichroic prisms 2 and the reflected beam is deflected 90° by a pentagonal prism 5 and is projected to a screen 3. The prism stage is rotated around a Z-axis and is so regulated that the beam projected to the screen 3 is projected onto the reference axis of the screen by which the installation surface of the prism 2 is made exactly flush with a plane consisting of the Z-axis and X-axis. Next, the laser beam from the light source 4 for regulation is deflected 270° by the three pentagonal prisms and is projected to the prisms 2 and the position in the X-axis direction and the rotating angle around the Y-axis are so regulated that the beam reflected by the same are passed through a pinhole and is aligned with the center of the screen 3. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for adjusting a prism stage used for alignment adjustment of a liquid crystal panel combined with a cross dichroic prism in a three-panel liquid crystal projector.
[0002]
[Prior art]
As a projector using a liquid crystal panel, there is a type called a three-panel type in which liquid crystal panels for R, G, and B are respectively installed on three surfaces of a cross dichroic prism for color synthesis. In this type of projector, the light from the projection light source is split into three colors of R, G, and B, and the images are modulated by liquid crystal panels for each color, and then the colors are synthesized by a cross dichroic prism, and then projected by a projection lens. Enlarged projection on the screen.
[0003]
The alignment adjustment of an optical prism block in which a liquid crystal panel for three colors of R, G, and B and a cross dichroic prism are combined includes focus adjustment and registration adjustment. In recent years, as image devices have become smaller and lighter for mobile use, liquid crystal panels used in projectors have become 0.9 inch or 0.7 inch in size, and their pixel sizes have also become smaller. Therefore, these alignment adjustments are performed by enlarging and projecting the reference pattern image onto the screen.
[0004]
FIG. 9 is a conceptual diagram of a projector alignment adjustment device using a liquid crystal panel. In the alignment adjusting device shown in FIG. 9, a cross dichroic prism 2 is fixed to a center prism stage 1, and R, G, B projection light sources 11a, 11b, 11c are respectively applied to three surfaces of the cross dichroic prism 2. Light is incident through the optical systems 12a, 12b, and 12c, respectively. The R, G, and B light components that have entered the cross dichroic prism 2 are combined by the cross dichroic prism 2 and are enlarged and projected from the projection lens 13 to the screen 14.
[0005]
The image enlarged and projected on the screen 14 is captured by the CCD camera 15 and subjected to image processing and the like. On the basis of the processed image, alignment of liquid crystal panels (not shown) of three colors of R, G, and B is performed by panel stages 13a, 13b, and 13c, respectively, and panel fixing devices 14a, 14b, 14c, and 14d fixes the cross dichroic prism 2 at a predetermined position.
[0006]
Here, in registration adjustment for performing color matching of the three liquid crystal panels of R, G, and B, it is required that the amount of shift between pixels of three colors be less than half a pixel. Therefore, in registration adjustment, it is necessary to detect a shift amount by 100 to 200 times magnification projection, and an adjustment mechanism with high accuracy of several μm level is required.
[0007]
[Problems to be solved by the invention]
In order to perform such precise adjustment, first, it is necessary to set the reference prism stage 1 with high precision with respect to the optical axis of the projection optical system. Conventionally, this setting is performed by measuring the displacement of the optical axis using an expensive autocollimator or reflecting mirror. In addition, in order to secure the measurement accuracy by the conventional method, it is necessary to increase the accuracy of the adjusting mechanism of the holding unit of the autocollimator or the reflecting mirror and perform a precise operation.
[0008]
FIG. 10 is an explanatory diagram of a deviation between the position of the cross dichroic prism 2 and the optical axis of the projection optical system. FIG. 3A shows an ideal state. If the cross dichroic prism 2 is shifted in the X-axis direction with respect to the optical axis of the projection optical system as shown in FIG. Since the center of the image on the image 14 is shifted and trapezoidal distortion occurs in the horizontal direction, the R and B liquid crystal panels cannot be set at the correct positions.
[0009]
If the cross dichroic prism 2 is tilted, as shown in FIG. 3C, the optical path lengths of the R, G, and B colors are different, and the colors are combined and the image projected on the screen 14 is blurred. Will occur. Thus, in registration adjustment, it is extremely important to set the reference prism stage 1 with high accuracy with respect to the optical axis of the projection optical system.
[0010]
Therefore, in the present invention, an adjustment method capable of adjusting a prism stage on which a cross dichroic prism is installed with high accuracy by an easy operation for alignment adjustment when combining a liquid crystal panel with three surfaces of the cross dichroic prism. The purpose is to provide.
[0011]
[Means for Solving the Problems]
In the method of adjusting a prism stage according to the present invention, a cross dichroic in which an optical axis of a light source is a Z axis, an X axis and a Y axis perpendicular to the X axis are provided on a surface perpendicular to the Z axis, and the prism is mounted on the prism stage. A method of adjusting a prism stage so that the center of the prism coincides with the X-axis, the Y-axis, and the Z-axis. A cross dichroic prism is installed on the prism stage, and the cross dichroic prism allows a light beam from a light source to reach 90 degrees. A pentaprism is arranged in the direction to be deflected, and a light beam deflected by 90 degrees by this pentaprism and projected on a screen arranged on a plane perpendicular to the Z axis is projected on the X axis of the screen. Adjusting the prism stage by rotating it around the Z axis, and rotating the prism stage by 90 ° around its Y axis. A pentaprism is arranged in a direction in which the light beam from the light source is deflected by 90 ° by the cross dichroic prism, and a light beam deflected by 90 ° by this pentaprism and projected on the screen is projected on the X axis of the screen. Rotating the prism stage around its X axis to adjust it, reversely rotating the adjusted prism stage around its Y axis by 90 °, and setting a pinhole between the exit side of the cross dichroic prism and the screen. And adjusting the position of the pinhole so that the light from the light source passes through the pinhole and is projected to the center of the screen with the cross dichroic prism removed, and between the light source and the cross dichroic prism. A first pentaprism is disposed on the first pentaprism. A second pentaprism is arranged on the X axis where the light from the light source is deflected by 90 °, and the light deflected by 90 ° by the second pentaprism is deflected by 90 ° so as to be incident on the cross dichroic prism. A third pentaprism is disposed on the X-axis and the rotation of the prism stage about the Y-axis so that the light beam deflected by 90 ° by the cross dichroic prism passes through the pinhole and is projected on the center of the screen. Adjusting.
[0012]
By installing a cross dichroic prism on the prism stage, arranging a pentaprism in a direction in which the light from the light source is deflected by 90 ° by the cross dichroic prism, and rotating and adjusting the prism stage around the Z axis, If a light beam deflected by 90 degrees by the pentaprism and projected on a screen arranged on a plane perpendicular to the Z axis is projected on the X axis of the screen, the light beam is deflected by 90 degrees by the cross dichroic prism and is deflected by 90 degrees. Light rays incident on the prism are in a plane formed by the Z axis and the X axis, and the reflection film surface of the cross dichroic prism is orthogonal to this plane.
[0013]
In addition, the prism stage is rotated by 90 ° around its Y axis, a pentaprism is arranged in a direction in which the light from the light source is deflected by 90 ° by the cross dichroic prism, and the prism stage is rotated around its X axis for adjustment. By doing so, if the light beam deflected by 90 ° by the pentaprism and projected on the screen is projected on the X axis of the screen, the light beam deflected by 90 ° by the cross dichroic prism and incident on the pentaprism will be It is in the plane defined by the X axis, and the reflecting film surface of the cross dichroic prism is orthogonal to this plane. Further, by reversely rotating the adjusted prism stage around the Y axis by 90 °, the installation surface of the cross dichroic prism on the prism stage is accurately coincident with the plane formed by the Z axis and the X axis. .
[0014]
A pinhole is arranged between the exit side of the cross dichroic prism and the screen, and a pinhole is formed so that the light from the light source passes through the pinhole and is projected to the center of the screen with the cross dichroic prism removed. Is adjusted, the position where the cross dichroic prism should be accurately arranged is set on the Z axis.
[0015]
Here, a first pentaprism is arranged between the light source and the cross dichroic prism, and a second pentaprism is arranged on the X axis where the light beam from the light source is deflected by 90 ° by the first pentaprism. By arranging the third pentaprism so that the light beam deflected by 90 ° is deflected by 90 ° by the second pentaprism and enters the cross dichroic prism, the light beam from the light source is deflected by 270 °. The light enters the cross dichroic prism. Then, the position of the prism stage in the X-axis direction and the rotation angle around the Y-axis are set so that the incident light beam is deflected by 90 ° by the cross dichroic prism, passes through the pinhole, and is projected on the center of the screen. By performing the adjustment, the cross dichroic prism is arranged in an accurate posture on the Z axis.
[0016]
Further, if the first pentaprism, the second pentaprism, and the third pentaprism are arranged symmetrically with respect to the Z axis and the position of the prism stage in the X axis direction and the rotation angle around the Y axis are adjusted, it is easier. It can be adjusted so that the light beam deflected by 90 ° by the cross dichroic prism passes through the pinhole and is projected on the center of the screen.
[0017]
When the screen is not arranged in advance on a plane perpendicular to the Z axis, the screen is arranged on the Z axis, and a pentaprism is arranged between the light source on the Z axis and the screen. By rotating the pentaprism around the Z axis and adjusting the X and Y axes of the screen so that the distance between the light beam deflected by 90 ° by the pentaprism and the screen is constant, the screen is moved with respect to the Z axis. It can be placed on a vertical plane.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram showing a coordinate system of the prism stage in the present embodiment.
In FIG. 1, an optical axis of a light source (not shown) is defined as a Z axis, and a rotation angle around the Z axis is defined as Zθ. The X axis and the Y axis perpendicular to the X axis are set on a plane perpendicular to the Z axis, and the rotation angles around the X axis and the Y axis are Xθ and Yθ, respectively. A 100-inch screen 3 having a plane perpendicular to the Z-axis is arranged ahead of the Z-axis. The vertical direction of the screen 3 coincides with the Y-axis direction, and the horizontal direction coincides with the X-axis direction.
[0019]
As shown in FIG. 1, the cross dichroic prism 2 according to the present embodiment has a structure in which four prisms each having a right-angled isosceles triangular prism shape are connected at an apex angle. A film has been deposited. The surface on which the red reflecting film is deposited is referred to as an R reflecting film surface, and the surface on which the blue reflecting film is deposited is referred to as a B reflecting film surface. When the cross dichroic prism 2 is installed at a predetermined position on the prism stage 1 (see FIG. 9), a work of mounting a liquid crystal panel including alignment adjustment is performed.
[0020]
The red light incident from the surface of the cross dichroic prism 2 in the positive direction of the X axis (hereinafter referred to as “R surface”) is deflected by 90 ° in the positive direction of the Z axis by being reflected by the R reflecting film surface. Blue light incident from a surface of the cross dichroic prism 2 in the negative direction of the X axis (hereinafter referred to as “surface B”) is reflected by the surface of the B reflection film, and is reflected in the positive direction of the Z axis. Green light incident from the surface of the cross dichroic prism 2 in the negative direction of the Z axis (hereinafter referred to as “G surface”) is directly transmitted in the positive direction of the Z axis and deflected by the R reflection film surface and the B reflection film surface, respectively. The red light and the blue light are combined and projected on the screen 3.
[0021]
FIG. 2 is an explanatory diagram illustrating a method of adjusting the screen 3 in the present embodiment.
To adjust the prism stage 1 in the present embodiment, an adjustment light source 4 that emits a red visible light laser beam and a pentaprism (pentagonal prism) 5 are used. The distance from the optical axis base point of the adjustment light source 4 to the screen 3 is 5 m.
[0022]
The pentaprism 5 is a roof-shaped prism having a pentagonal cross section. The pentaprism 5 is a constant deflection prism that performs total internal reflection twice and deflects all light incident on the effective surface by 90 ° and emits it. That is, the deflection of the light by the pentaprism 5 is constant, and the incident light is deflected by 90 ° regardless of the direction of the prism.
[0023]
Adjustment of the screen 3 is performed according to the following procedure.
(1) In a state where the cross dichroic prism 2 and the pentaprism 5 are not arranged, a laser beam is projected on the screen 3 and the position of the screen 3 is adjusted so that the center of the screen 3 matches the projection point.
(2) As shown in FIG. 2, a pentaprism 5 is arranged in front of the center of the screen 3, and a laser beam is projected and deflected by 90 ° by the pentaprism 5.
(3) The pentaprism 5 is rotated about the Z axis, and the distance between the laser beam deflected by 90 ° by the pentaprism 5 and the surface of the screen 3 is measured by the scale 6 in each direction on the screen 3. The angle of the screen 3 is adjusted so that the values become the same.
[0024]
Since the pentaprism 5 has a function of accurately deflecting 90 ° with respect to incident light having an incident angle in a certain range, the laser beam is fixed and the pentaprism 5 itself is rotated around this optical axis (Z axis). Thus, a light beam deflected by 90 ° with high accuracy is obtained without being affected by the rotational whirling accuracy. Thus, even if the reading accuracy of the scale 6 is ± 1 mm, it is possible to arrange the screen 3 on a plane perpendicular to the Z axis while ensuring the accuracy equal to or higher than the flatness of the screen 3.
[0025]
Next, the tilt of the prism stage 1 is adjusted.
FIG. 3 is an explanatory diagram showing a method of adjusting the Zθ angle of the prism stage 1.
[0026]
The cross dichroic prism 2 and the pentaprism 5 are arranged in the positional relationship shown in FIG. 3 in a state where the laser beam and the center of the screen 3 match. At this time, the cross dichroic prism 2 is set on the prism stage 1 such that the G surface is on the adjustment light source 4 side. Further, the pentaprism 5 is installed in a direction in which the laser beam is deflected by 90 ° by the R reflection film surface of the cross dichroic prism 2.
[0027]
A laser beam is incident on the G surface of the cross dichroic prism 2. The laser beam is reflected by the back surface of the R reflecting film surface of the cross dichroic prism 2, is deflected by 90 degrees by the pentaprism 5, and is projected on the screen 3. Here, when the R reflecting film surface is rotationally displaced (Zθ) about the Z axis, the projection point of the laser beam moves up and down on the screen 3, and this projection point is moved to the X axis of the screen 3. Adjust Zθ to match.
[0028]
As a result, light rays deflected by 90 ° by the cross dichroic prism 2 and incident on the pentaprism 5 are in a plane formed by the Z axis and the X axis, and the R reflection film surface of the cross dichroic prism 2 is orthogonal to this plane. You will be doing.
[0029]
FIG. 4 is an explanatory diagram showing a method of adjusting the Xθ angle of the prism stage 1.
In order to change the state of the cross dichroic prism 2 from the state shown in FIG. 3 to the state shown in FIG. 4, the prism stage 1 is rotated clockwise by 90 ° around the Y axis so that the laser beam is incident on the R surface of the cross dichroic prism 2. . In addition, the pentaprism 5 is disposed at the position shown in FIG.
[0030]
When the laser beam is incident on the R surface of the cross dichroic prism 2, it is reflected on the R reflecting film surface, then enters the pentaprism 5, is deflected by 90 ° by the pentaprism, and is projected on the screen 3. Here, when the R reflection film surface is rotationally displaced (Xθ) about the X axis, the projection point of the laser beam moves upward and downward on the screen 3, and this projection point is moved to the X axis of the screen 3. Adjust Xθ to match.
[0031]
As a result, light rays deflected by 90 ° by the cross dichroic prism 2 and incident on the pentaprism 5 are in a plane formed by the Z axis and the X axis, and the R reflection film surface of the cross dichroic prism 2 is orthogonal to this plane. I will do it. Then, the adjusted prism stage 1 is rotated by 90 ° reversely around its Y axis. Thereby, the installation surface of the cross dichroic prism 2 on the prism stage 1 exactly coincides with the plane formed by the Z axis and the X axis.
[0032]
Next, the position of the prism stage 1 in the X-axis direction and the rotation angle (Yθ) around the Y-axis are adjusted. FIG. 5, FIG. 6, and FIG. 7 are explanatory diagrams showing this adjustment method.
[0033]
As shown in FIG. 5, a pinhole plate 8 having a pinhole 7 is arranged between the exit side of the cross dichroic prism 2 and the screen 3. Then, the position of the pinhole plate 8 is adjusted so that the laser beam passes through the pinhole 7 and is projected on the center of the screen 3 with the cross dichroic prism 2 removed. As a result, the position where the cross dichroic prism 2 should be accurately arranged is set on the Z axis.
[0034]
Next, the cross dichroic prism 2 and the three pentaprisms 5a, 5b, 5c are arranged as shown in FIG. The pentaprism 5 a is arranged between the adjustment light source 4 and the cross dichroic prism 2. The pentaprism 5b is arranged on the X axis where the laser beam from the adjustment light source 4 is deflected by 90 ° by the pentaprism 5a. The pentaprism 5c is arranged such that a light beam deflected by 90 ° by the pentaprism 5b is deflected by 90 ° and enters the cross dichroic prism 2.
[0035]
The laser beam projected from the adjustment light source 4 in such an arrangement state is deflected 270 ° by the three pentaprisms 5a to 5c and is incident on the cross dichroic prism 2. The laser beam incident on the cross dichroic prism 2 is deflected by 90 ° by being reflected by the R reflection film surface. The position of the prism stage 1 in the X-axis direction (see FIG. 6) and the rotation angle Yθ around the Y-axis (see FIG. 7) so that the laser beam passes through the pinhole 7 and is projected on the center of the screen 3. To adjust.
[0036]
By this adjustment, the cross dichroic prism 2 is arranged in an accurate posture on the Z axis. FIG. 8 shows a state where the adjustment of the prism stage 1 is completed. In this method, since the incident position of the laser beam on the R surface of the cross dichroic prism 2 is not limited to the center of the prism cross, the position in the X axis direction and the rotation around the Y axis are fixed with the Z axis position fixed. Adjust the angle Yθ. The position of the cross dichroic prism 2 in the Z-axis direction is adjusted by the projection lens 13 because positional accuracy with respect to the projection lens 13 shown in FIG.
[0037]
Although not shown, the position of the prism stage 1 in the X-axis direction and the rotation angle (Yθ) around the Y-axis are adjusted, and the pentaprisms 5a to 5c are arranged symmetrically with respect to the Z-axis. By adjusting the position in the X-axis direction and the rotation angle around the Y-axis, the light beam deflected by 90 ° by the cross dichroic prism 2 passes through the pinhole 7 and is projected to the center of the screen 3 more easily. It is possible to adjust.
[0038]
【The invention's effect】
According to the present invention, the following effects can be obtained.
[0039]
(1) By adjusting the prism stage of the cross dichroic prism using a pentaprism, which is a constant deflection prism that deflects all light incident on the effective surface by 90 ° and emits the light, accuracy of the operation can be improved by an easy operation. High adjustments can be made. This eliminates the need for a high-precision fine-adjustment mechanism in the light source holding section, compared to an adjustment mechanism using a conventional autocollimator or a reflecting mirror, and therefore does not require expensive equipment, and thus, a pentaprism holding mechanism, The rotation angle determining mechanism can be simplified.
[0040]
(2) Since the screen is arranged on a plane perpendicular to the optical axis by using a pentaprism, the vertical accuracy of the screen with respect to the projection optical axis system can be ensured. This makes it possible to easily adjust even a projection optical system having a high magnification using a large screen. Further, even if the optical axis system is displaced due to vibration or the like, it can be easily checked using the pentaprism, so that the work time for resetting can be reduced.
[0041]
(3) Since adjustment by a visible laser beam is possible, skill in setting, measuring and adjusting the optical system is not required, and workability is improved.
[0042]
(4) Since the prism stage can be adjusted with high accuracy, alignment adjustment when combining a liquid crystal panel with three surfaces of the cross dichroic prism can be performed with high accuracy.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a coordinate system of a prism stage according to an embodiment.
FIG. 2 is an explanatory diagram illustrating a screen adjustment method according to the embodiment.
FIG. 3 is an explanatory diagram showing a method of adjusting a Zθ angle of a prism stage.
FIG. 4 is an explanatory diagram showing a method of adjusting an Xθ angle of a prism stage.
FIG. 5 is an explanatory diagram showing a method of adjusting a position of a prism stage in an X-axis direction and a rotation angle around a Y-axis.
FIG. 6 is an explanatory diagram showing a method of adjusting a position of a prism stage in an X-axis direction and a rotation angle around a Y-axis.
FIG. 7 is an explanatory diagram showing a method of adjusting the position of the prism stage in the X-axis direction and the rotation angle around the Y-axis.
FIG. 8 is a view showing a state where the adjustment of the prism stage is completed.
FIG. 9 is a conceptual diagram of a projector alignment adjustment device using a liquid crystal panel.
FIG. 10 is a diagram illustrating a deviation between the position of the cross dichroic prism and the optical axis of the projection optical system.
[Explanation of symbols]
Reference Signs List 1 prism stage 2 cross dichroic prism 3 screen 4 light source for adjustment 5, 5a, 5b, 5c pentaprism 6 scale 7 pinhole 8 pinhole plate

Claims (4)

The optical axis of the light source is the Z axis, the X axis is taken on a plane perpendicular to the Z axis, and the Y axis is taken perpendicular to the X axis. The center of the cross dichroic prism installed on the prism stage is the X axis and the Y axis. And adjusting the prism stage to coincide with the Z axis,
A cross dichroic prism is set on the prism stage, and a pentaprism is arranged in a direction in which the light beam from the light source is deflected by 90 ° by the cross dichroic prism. Rotating and adjusting the prism stage around the Z axis so that light rays projected on a screen disposed on a plane perpendicular to the screen are projected on the X axis of the screen;
The prism stage is rotated by 90 ° around its Y axis, a pentaprism is arranged in a direction in which the light from the light source is deflected by 90 ° by the cross dichroic prism, and the pentaprism is deflected by 90 ° to the screen. Rotating and adjusting the prism stage about its X axis so that the projected light beam is projected on the X axis of the screen;
Reversely rotating the adjusted prism stage by 90 ° about its Y axis;
A pinhole is arranged between the exit side of the cross dichroic prism and the screen, and the light from the light source passes through the pinhole and is projected to the center of the screen with the cross dichroic prism removed. Adjusting the position of the pinhole to;
A first pentaprism is arranged between the light source and the cross dichroic prism, and a second pentaprism is arranged on the X-axis where the light from the light source is deflected by 90 ° by the first pentaprism. A third pentaprism is arranged so that the light beam deflected by 90 ° by the second pentaprism is deflected by 90 ° and enters the cross dichroic prism, and the light beam deflected by 90 ° by the cross dichroic prism is Adjusting the position of the prism stage in the X-axis direction and the rotation angle about the Y-axis so that the light passes through the pinhole and is projected onto the center of the screen. Further, the first pentaprism, the second pentaprism and the third pentaprism are arranged symmetrically with respect to the Z-axis, and the light beam deflected by 90 ° by the cross dichroic prism passes through the pinhole and passes through the screen. 2. The method for adjusting a prism stage according to claim 1, further comprising the step of adjusting the position of the X-axis of the prism stage and the rotation of the prism stage around the Y-axis so that the light is projected on the center of the prism stage. The optical axis of the light source is the Z axis, the X axis is taken on a plane perpendicular to the Z axis, and the Y axis is taken perpendicular to the X axis. The center of the cross dichroic prism installed on the prism stage is the X axis and the Y axis. And adjusting the prism stage to coincide with the Z axis,
A screen is arranged on the Z-axis, a pentaprism is arranged between the light source on the Z-axis and the screen, and this pentaprism is rotated around the Z-axis. Adjusting the X axis and the Y axis of the screen so that the distance between the light beam and the screen is constant;
A cross dichroic prism is set on the prism stage, a pentaprism is arranged in a direction in which the light from the light source is deflected by 90 ° by the cross dichroic prism, and the pentaprism is deflected by 90 ° and projected on the screen. Rotating and adjusting the prism stage about the Z axis such that a light beam is projected on the X axis of the screen;
The prism stage is rotated by 90 ° around its Y axis, a pentaprism is arranged in a direction in which the light from the light source is deflected by 90 ° by the cross dichroic prism, and the pentaprism is deflected by 90 ° to the screen. Rotating and adjusting the prism stage about its X axis so that the projected light beam is projected on the X axis of the screen;
Reversely rotating the adjusted prism stage by 90 ° about its Y axis;
A pinhole is arranged between the exit side of the cross dichroic prism and the screen, and the light from the light source passes through the pinhole and is projected to the center of the screen with the cross dichroic prism removed. Adjusting the position of the pinhole to;
A first pentaprism is arranged between the light source and the cross dichroic prism, and a second pentaprism is arranged on the X-axis where the light from the light source is deflected by 90 ° by the first pentaprism. A third pentaprism is arranged so that the light beam deflected by 90 ° by the second pentaprism is deflected by 90 ° and enters the cross dichroic prism, and the light beam deflected by 90 ° by the cross dichroic prism is Adjusting the position of the X-axis of the prism stage and the rotation of the prism stage about the Y-axis so that the light passes through the pinhole and is projected on the center of the screen. Further, the first pentaprism, the second pentaprism and the third pentaprism are arranged symmetrically with respect to the Z-axis, and the light beam deflected by 90 ° by the cross dichroic prism passes through the pinhole and passes through the screen. 4. The method for adjusting a prism stage according to claim 3, further comprising the step of adjusting the position of the X-axis of the prism stage and the rotation of the prism stage around the Y-axis so that the light is projected on the center of the prism stage.

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