JPH11142731A - Projection lens and projection device having same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert the scan rate of a projection device by a projection lens of simple constitution. SOLUTION: This is a projection lens used for a projection device in which a conjugation distance between an original image displayed on a liquid crystal display element LC and a screen SC where the original image is projected, is substantially fixed and is provided with a 1st lens group I with negative refracting power and a 2nd lens group II with positive refracting power in order from the side of the screen SC, when the projection magnification is transited relatively from high magnification to low magnification, the 1st lens group I is fixed and the 2nd lens group II is moved toward the screen SC side to switch a focal distance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a projection lens,
In particular, it is suitably used for a rear projection device in which the conjugate distance between the original image and the screen is substantially fixed at a finite distance.

[0002]

2. Description of the Related Art Conventionally, there has been known a rear projection television in which an original image displayed on a CRT or a liquid crystal display element is rear-projected onto a screen fixed at a finite distance by a projection lens.

FIG. 9 is a schematic structural view of a general rear projection television. The rear projection television shown in FIG. 9 includes an image display unit 2 disposed in a housing 1,
It is composed of a projection lens 3, a reflection mirror 4, a screen 5, and the like. The light from the original image displayed on the image display means 2 is magnified by the projection lens 3 and
Is projected on the screen 5 via the. Screen 5
It is composed of a Fresnel lens and a lenticular lens (not shown), and the user can observe a bright image at a position in front of the screen 5.

On the other hand, in recent years, as image display means (specifically, a CRT, a liquid crystal display element, or the like) has become higher definition, not only display of moving images (NTSC images) for television but also still images for computers. There is a need for a projection device that can project (VGA, XGA, etc.).

[0005]

However, since the resolution is different between an NTSC image for a television and a still image for a computer, it is necessary to use a conventional apparatus to project each image to the screen at the same size. It was necessary to convert the scan rate using a converter. For example, in order to display both an NTSC image and a VGA image on the screen at the same size, a signal conversion process must be performed so that the NTSC image is displayed by overscan and the VGA image is displayed by underscan. However, since a scan converter for converting an image signal is expensive, the cost of the projection apparatus itself has been increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a projection lens having a simple configuration that realizes conversion of a scan rate by scaling.

[0007]

In order to solve the above-mentioned problems, the present invention relates to a projection lens used in a projection apparatus in which a conjugate distance between an original image and a screen on which the original image is projected is substantially fixed. There is a first lens unit having a negative refractive power and a second lens unit having a positive refractive power in order from the screen side. When the projection magnification is relatively changed from a high magnification to a low magnification, the first lens group is used. Fixing the lens group,
By moving the lens group to the screen side,
It is characterized by switching the focal length.

[0008]

1, 3, 5, and 7 are sectional views of projection lenses according to Numerical Examples 1 to 4 of the present invention.

In each figure, I is a first lens group having a positive refractive power, II is a second lens group having a negative refractive power, III is a third lens group having a positive refractive power, and ST is a stop. And LC
Denotes a liquid crystal display element, SC denotes a screen on which an original image displayed on the liquid crystal display element LC is projected, and CG denotes a cover glass. The liquid crystal display element LC is a transmissive element that is subjected to Koehler illumination by an illumination system (not shown).

The projection lens of each numerical example is a projection lens for a rear projection apparatus in which the distance between the original image and the screen is substantially fixed at a finite distance, and moves the second lens group II in the optical axis direction. By doing so, the focal length is switched between two focal lengths (hereinafter, for convenience, the shorter focal length is referred to as the wide-angle end, and the longer focal length is referred to as the telephoto end), thereby shifting the projection magnification. In each numerical example, when switching from the wide-angle end to the telephoto end, the second lens group II moves to the screen side as illustrated, but the first lens group I and the third lens group III are fixed.

As described above, the projection lens of the present embodiment can change the scanning magnification of a plurality of types of images having different resolutions by changing the projection magnification with a simple configuration that only moves the second lens group II. it can. The projection lens of the present embodiment can be used for a general rear projection television as shown in FIG.

Hereinafter, more preferable embodiments for realizing the projection lens of the present invention will be described. (A) In each numerical example, the first lens group I has a strong concave surface (second surface) on the liquid crystal display element LC side of the lens located closest to the screen as an aspheric surface. The shape of the aspheric surface is such that the negative refractive power is weakened in the periphery so as to reduce barrel distortion generated by the concave lens. (B) In the rear projection device, the shorter the focal length of the projection lens, that is, the wider the angle of view, the shorter the conjugate distance to the screen and the smaller the size. However, from the viewpoint of aberration correction, the first lens group I
It is desirable that the off-axis oblique light beam be bent as gently as possible. Therefore, in each numerical example, the first lens unit I
Is constituted by a negative meniscus lens having a convex surface facing the screen SC side, and the occurrence of aberration is favorably suppressed. (C) In order to efficiently project the light from the liquid crystal display element LC onto the screen, the pupil position of the projection lens as viewed from the liquid crystal display element LC is located at infinity, in other words, on the liquid crystal display element LC side. It is desirable to configure the projection lens to be substantially telecentric. Therefore, in the projection lens of each numerical example, the focal length at the wide-angle end of the entire lens on the liquid crystal display element LC side from the stop ST is f.
r, and when the distance from the stop ST to the front principal point of the entire lens on the liquid crystal display element LC side from the stop ST is L, the conditional expression 0.85 <L / fr <1.0 (1) is satisfied. Each lens group is constituted as follows.

If the lower limit of conditional expression (1) is exceeded, the pupil position will be relatively close, and the matching with the illumination system will be poor.
There is a problem that the illuminance of the peripheral image on the screen SC is reduced. In particular, in a single-panel projection television using microlenses, phenomena such as color unevenness are not good. If the upper limit of conditional expression (1) is exceeded, the stop S
The refractive power of the entire lens on the liquid crystal display element LC side from T becomes too strong, which makes it difficult to correct aberrations, which is not preferable. (D) The third lens group III is conditional expression (1) in order to achieve both miniaturization and telecentricity (pupil position at infinity).
It is desirable to have a strong positive refractive power within a range satisfying the following. Since the third lens group III is closest to the liquid crystal display element LC, it greatly affects off-axis image plane characteristics, and requires a negative refracting surface which cancels out a strong positive refractive power component on an aberration basis. The chief ray before and after this negative refraction surface,
Since it is desirable that the liquid crystal display element LC is close to parallel and that the screen SC is concentric, a negative lens having a strong concave surface on the screen SC is effective. Here, the “strong concave surface” refers to 2 which constitutes the lens.
This is a relative value when two refraction surfaces are compared. (E) In the projection lens of each numerical example, the paraxial lateral magnifications of the first lens group I and the second lens group II at the wide-angle end are β1w and β2w, the zoom ratio (scan ratio) is Z, and
The amount of movement of the lens group II from the wide-angle end to the telephoto end is represented by M,
From the screen SC side focus of the lens group I to the screen SC
X, the first lens group I and the second lens group II
Are respectively f1 and f2, and the distance between the principal points of the first lens group I and the second lens group II is ew,

[0014]

[Outside 2] M = f2 × β2w × (1-Z) (3) β1w = f1 / x (4) ew = f1 + f2-f1 × β1w-f2 / β2w (5)

Here, the change in the scan rate of the projection device is about 10% due to the change in magnification of the projection lens. That is, from the equations (2) and (3), it can be seen that the paraxial lateral magnification used by the second lens group II is near unity, and conversely, the position sensitivity of the second lens group II is low. . Therefore, even if the second lens group II is slightly moved, the change in focus is small, and it is not necessary to move another lens group for focus correction, which is very convenient. Therefore, even when the projection lens of this embodiment is incorporated in a rear projection television as shown in FIG. 9, fine adjustment of the projection magnification can be performed by adjusting the position of the second lens group II. (F) It is desirable to adjust the focus of the conjugate distance between the original image (liquid crystal display element) and the screen by moving the entire projection lens system or the third lens group in the optical axis direction. If the screen size changes and the image deteriorates during focusing, it is desirable to correct the image by a floating mechanism in the first lens group.

As described above, the projection lens of each numerical example includes: (a) the first lens group has at least one aspherical surface; and (b) a plurality of negative meniscus lenses having the first lens group having a convex surface facing the screen. (C) Conditional expression (1) must be satisfied. (D) The third lens unit having a positive refractive power has a negative lens having a strong concave surface on the screen side. (E) Conditional expression (2) (F) Satisfy all of the requirements for moving the entire projection lens system or the third lens group in the optical axis direction to perform focus adjustment, but satisfy the requirements of the projection lens of the present invention. In, even if only at least one of the above requirements is satisfied, the effect of each requirement can be expected.

Next, each numerical embodiment will be described.

(Numerical Example 1) Table 1 shows numerical data of the projection lens of Numerical Example 1 shown in FIG. In the table, ri
Is the radius of curvature of the i-th lens surface in order from the screen side, di is the distance between the i-th and (i + 1) -th lens surfaces, ni is the refractive index for the d-line of the glass constituting the i-th lens, and νi Represents the Abbe number of the glass constituting the i-th lens.

The aspherical shape has an X axis in the optical axis direction, a Y axis in a direction perpendicular to the optical axis, a positive traveling direction of light, a point of intersection between the vertex of the lens and the X axis as an origin, and r as the surface of the lens. When the paraxial radius of curvature, k, B, C, D, and E are aspheric coefficients,

[0020]

[Outside 3] Can be expressed as

The indication of "D-03" is "1".
0 ^-3 ], and the unit of length is (mm).

FIG. 2 shows an aberration diagram of the projection lens of this embodiment when the conjugate distance is 820 mm. FIG. 2A shows the wide-angle end,
FIG. 2B is a diagram showing various aberrations at the telephoto end. In this embodiment, the focus adjustment is performed by extending the entire projection lens system.

[0023]

[Table 1]

(Numerical Embodiment 2) Table 2 shows numerical data of the projection lens of Numerical Embodiment 2 shown in FIG. The meanings of the reference numerals in the table are the same as in Numerical Example 1, and the description is omitted.

In the present embodiment, the aberration generated by the convex lens on the screen SC side of the stop ST in the second lens group II,
In order to mainly correct coma well, the convex lens is a cemented lens with a concave lens. Also, by introducing a negative meniscus lens having a convex surface facing the screen SC at the head of the second lens group II, aberration fluctuation due to zooming is suppressed.

FIG. 4 shows an aberration diagram of the projection lens of this embodiment when the conjugate distance is 820 mm. FIG. 4A shows the wide-angle end,
FIG. 4B is a diagram showing various aberrations at the telephoto end. In this embodiment, the focus adjustment is performed by extending the entire projection lens system.

[0027]

[Table 2]

(Numerical Embodiment 3) Table 3 shows numerical data of the projection lens of Numerical Embodiment 3 shown in FIG. The meanings of the reference numerals in the table are the same as in Numerical Example 1, and the description is omitted.

FIG. 6 shows an aberration diagram of the projection lens of this embodiment when the conjugate distance is 820 mm. FIG. 6A shows the wide-angle end,
FIG. 6B is a diagram showing various aberrations at the telephoto end. In this embodiment, the focus is adjusted by extending the third lens group III.

[0030]

[Table 3]

(Numerical Embodiment 4) Table 4 shows numerical data of the projection lens of Numerical Embodiment 4 shown in FIG. The meanings of the reference numerals in the table are the same as in Numerical Example 1, and the description is omitted.

In this embodiment, the focus is adjusted by extending the third lens group III. However, the curvature of field generated when the screen size changes is corrected by the floating mechanism of the first lens group. I have.

FIG. 8 is an aberration diagram of the projection lens of this embodiment when the conjugate distance is 931 mm. FIG. 8A shows the wide-angle end,
FIG. 8B is a diagram showing various aberrations at the telephoto end.

[0034]

[Table 4]

Table 5 shows the value of L / fr for each numerical example.
Shown in

[0036]

[Table 5]

[0037]

As described above, according to the present invention,
The conversion of the scan rate can be realized by a projection lens having a simple configuration.

[Brief description of the drawings]

FIG. 1 is a sectional view of a projection lens of Numerical Example 1.

FIG. 2 is a diagram illustrating various aberrations of the projection lens of Numerical Example 1 at a wide-angle end and a telephoto end.

FIG. 3 is a sectional view of a projection lens according to Numerical Example 2.

FIG. 4 is a diagram illustrating various aberrations of the projection lens of Numerical Example 2 at the wide-angle end and the telephoto end.

FIG. 5 is a sectional view of a projection lens of Numerical Example 3;

FIG. 6 is a diagram illustrating various aberrations of the projection lens of Numerical Example 3 at the wide-angle end and the telephoto end.

FIG. 7 is a sectional view of a projection lens of Numerical Example 4.

FIG. 8 is a diagram illustrating various aberrations of the projection lens of Numerical Example 4 at the wide-angle end and the telephoto end.

FIG. 9 is a schematic configuration diagram of a general rear projection television.

[Explanation of symbols]

 I first lens group II second lens group III third lens group LC liquid crystal display element SC screen ST stop

Claims (11)

[Claims] 1. A projection lens for use in a projection apparatus in which a conjugate distance between an original image and a screen on which the original image is projected is substantially fixed, wherein the projection lens has a negative refractive power in order from the screen side. A first lens group, a second lens group having a positive refractive power, and when the projection magnification is relatively changed from a high magnification to a low magnification, the first lens group is fixed and the second lens group is fixed.
By moving the lens group to the screen side,
A projection lens characterized by switching a focal length. 2. When the focal length at the wide-angle end of the entire lens on the original image side from the stop is fr, and the distance from the stop to the front principal point of the entire lens on the original image side from the stop is L, 0.85. The projection lens according to claim 1, wherein a conditional expression of <L / fr <1.0 is satisfied. 3. The projection lens according to claim 1, wherein the first lens group has at least one aspherical surface. 4. The first lens group has a negative meniscus lens having a convex surface facing the screen side closest to the screen side, and the original image side of the negative meniscus lens is aspherical. 3. The projection lens according to 3. 5. The projection lens according to claim 1, wherein the first lens group includes at least two negative meniscus lenses whose convex surfaces face the screen. 6. The projection lens according to claim 1, further comprising a third lens group having a positive refractive power. 7. The third lens group according to claim 6, wherein the third lens group has at least one positive lens and at least one negative lens, and the negative lens has a strong concave surface on the screen side. Projection lens. 8. moving the third lens group on the optical axis,
8. The projection lens according to claim 6, wherein focus adjustment is performed. 9. When the size of the screen changes,
Using the floating mechanism in the first lens group,
9. The projection lens according to claim 1, wherein deterioration of an image plane on the screen is corrected. 10. The paraxial lateral magnifications of the first lens group and the second lens group at the wide-angle end are respectively β1w, β2w,
The zoom ratio is Z, the amount of movement of the second lens group from the wide-angle end to the telephoto end is M, the distance from the screen-side focal point of the first lens group to the screen is x, the first lens group and the When the focal lengths of the two lens groups are f1 and f2, respectively, and the distance between the principal points between the first lens group and the second lens group is ew, The projection lens according to claim 1, wherein the following relationship is satisfied: M = f2 × β2w × (1-Z) β1w = f1 / x ew = f1 + f2-f1 × β1w-f2 / β2w 11. A projection apparatus, comprising: the projection lens according to claim 1; wherein the projection lens projects an original image onto a screen.