JP2617908B2 - Projection optics - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical apparatus suitable for use in a television image projection apparatus for enlarging and projecting an image projected on a picture tube onto a screen, and particularly to a projection image apparatus. And a projection optical device having good contrast.

2. Description of the Related Art Configuration and Problems There is a method of obtaining a large-screen television image by enlarging an image projected on a picture tube onto a screen by a lens.

In this case, since it is desirable that the projected image on the screen is as bright as possible, it is necessary to make the picture tube emit light with high luminance and to use a bright lens. As such a lens having an F of about 1.0, a six-group, six-element lens made entirely of glass, and a three-group, three-element lens made of acrylic resin and using an aspheric surface are already known.
When plastic is used, the temperature dependence of the refractive index of plastic is one order of magnitude greater than that of glass, so that the image plane moves due to changes in the surrounding temperature, thereby causing defocus and misconvergence. Therefore, a three-group three-lens hybrid lens combining a glass lens and a plastic lens is disclosed in Japanese Patent Laid-Open No. 58-12 / 1983.
Proposed in 5007.

Japanese Patent Application Laid-Open No. 58-181009 discloses that the load on the field curvature correction is reduced by combining with a picture tube having a phosphor surface of a face plate having a convex surface, and other aberrations are improved, a large aperture ratio, A projection lens with a large angle of view has been proposed.

In this way, the performance of the projection lens has been improved, but the problem remains that the contrast of the projected image is not good. To cope with this problem, Japanese Patent Application Laid-Open No. 58-194234 proposes a method for improving the contrast by interposing a medium having substantially the same refractive index as glass between the face plate of the picture tube and the projection lens. However, if a conventional projection lens is placed in front of the picture tube, and a medium having almost the same refractive index as glass is interposed between the two, the state of aberration changes, and the image quality is greatly improved, although the contrast is improved. There is a problem that it is deteriorated.

When the image projected on the picture tube is simply subjected to horizontal and vertical deflection, a pincushion-like distortion is generated. For example, a picture tube with a 70 degree deflection produces about 10% distortion. Therefore, a distortion correction circuit is actually added to the deflection circuit, but its power consumption cannot be ignored.

SUMMARY OF THE INVENTION An object of the present invention is to provide a projection optical device having good contrast of a projected image and good aberration correction.

It is another object of the present invention to provide a projection optical device in which a distortion correction circuit for a picture tube is reduced in power consumption.

Constitution of the Invention The projection optical device according to the present invention comprises, in order from the screen side, a first lens composed of a plastic positive lens having at least one aspheric surface and a surface having a high curvature directed to the screen side, and a second lens composed of a biconvex glass lens. A lens, a third lens made of a plastic lens with an aspherical concave surface facing the screen is arranged, a picture tube is arranged behind the third lens, and a transparent body is provided between the third lens and a face plate of the picture tube. In the space from the concave surface of the third lens on the screen side to the phosphor of the face plate of the picture tube, unnecessary reflection is reduced by reducing the refractive index difference at the boundary of each medium, As a result, the contrast of the projected image is improved. Also,
The first lens, the second lens, and the third lens are configured to generate positive, negative, and positive distortions, respectively, and the distortion at the maximum image height viewed from the picture tube side is Ee [%], and 2 <Ee < In order to satisfy the condition (10), a pincushion-shaped image is projected on the picture tube, and the power consumption of the distortion correction circuit is reduced. Further, the projection optical device of the present invention is characterized by satisfying the following conditions.

(1) 0.45 <f / f ₁ <0.7 (2) 0.65 <f / f ₂ <0.85 (3) −1.3 <f / f ₃ <−0.85 where f is the first lens, the second lens, and the third lens ,
The combined focal length of the optical system composed of the transparent body and the face plate, f ₁ and f ₂ are the focal lengths of the first lens and the second lens, respectively, and f ₃ is the combined focal length of the third lens and the face plate.

DESCRIPTION OF THE EMBODIMENTS Embodiments of a projection optical device according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows the configuration of an embodiment of the projection optical apparatus according to the present invention. A first lens L1, a second lens L2, and a third lens L3 are arranged in this order from the screen (not shown) side, and the picture tube 1 is arranged close to and behind the third lens L3. A frame 2 is disposed between the third lens L3 and the picture tube 1, and the third lens L3 and the frame 2, and the face plate 3 of the frame 2 and the picture tube 1 are bonded with an adhesive. A closed space is formed between the lens L3 and the face plate 3. The transparent space 4 is filled in the closed space. The first lens L1 and the second lens L2 are incorporated in one lens barrel 5, and the focus of the optical system is adjusted by changing the distance between the lens barrel 5 and the third lens L3.

The first lens L1 is a plastic lens having at least one aspheric surface having a positive power with a surface having a strong curvature facing the screen, the second lens L2 is a biconvex glass lens,
Lens L3 is a plano-concave plastic lens with the aspheric concave surface facing the screen. Generally, a plastic lens has a large refractive index change due to a change in the ambient temperature, and the image plane movement is problematic. However, the positive power is shared between the plastic lens and the glass lens, so that the image plane movement due to the change in the ambient temperature can be practically used. It is kept within the range that does not cause a problem. The introduction of an aspherical surface facilitates aberration correction. The face plate 3 of the picture tube 1 has an inner phosphor surface 6 that is convex and an opposite surface 7 that is flat. By making the phosphor surface 6 convex, the curvature of field of the lens system can be slightly corrected. It is easy to do.

In the projection optical device according to the present invention, the third lens L3 is not limited to a plano-concave lens as shown in FIG.
As shown in FIG. 2, the third lens L3 may be a meniscus lens having a concave surface facing the screen. As shown in FIG. 3, the third lens L3 is a plano-concave lens, a flat glass 10 is bonded to a flat surface 9 of the plano-concave lens with a transparent adhesive, and a transparent body 4 is provided between the flat glass 10 and the face plate 3.
May be filled. If the total of the refractive indexes of the flat glass 10 and the face plate 3 and the center thickness of the flat glass 10 and the face plate 3 are the same as the refractive index and the center thickness of the face plate 3 shown in FIG. 1, respectively, FIG. The first lens L1, the second lens L2, the third lens L3, the air gap between them, and the center thickness of the transparent body 4 can be made exactly the same as those shown in FIG.

The transparent body 4 is made of a transparent liquid such as ethylene glycol or silicone oil, and has a refractive index of 1.4 to 1.49. If the third lens L3 is made of acrylic resin, its refractive index is
1.49, and the refractive index of the face plate 3 is 1.5 to 1.55
Since the difference in the refractive index at the boundary surface is small, reflection at the boundary between both end surfaces of the liquid can be extremely reduced. In addition, since the screen-side surface 8 of the third lens L3 is a concave surface having a strong curvature, the ratio of the light emitted from the phosphor surface 6 reflected by the concave surface and returning to the phosphor surface 6 can be reduced. As a result, it is possible to suppress a decrease in contrast due to the light returning to the phosphor surface 6 being reflected by the phosphor surface 6.

The transparent body 8 shown in FIGS. 1, 2 and 3 may use a transparent solid or a transparent adhesive instead of the liquid. However, it is necessary to select a refractive index close to that of the third lens L3.

Next, the projection optical device according to the present invention introduces a unique concept for distortion, and this will be described.
The image projected on the picture tube has a pincushion-like distortion when simply performing horizontal and vertical deflection. In view of this, a positive distortion is generated in the lens system when viewed from the picture tube side, so that the burden on the distortion correction circuit of the picture tube is reduced. In order to realize this, it is preferable that the distortion of the projection optical device satisfies the following condition. Assuming that the magnitude of the distortion at the maximum image height viewed from the picture tube side is Ee [%] and the magnitude of the distortion at the image height of 60% of the maximum image height is Em [%], 2 <Ee <10 0.2 < It is recommended that Em / Ee <0.6. Further, if the distortion aberration curve is a monotonically increasing curve, even if a relatively simple distortion correction circuit is used, the distortion of the projected image can be prevented from causing a practical problem. The distortion at the image height of 60% of the maximum image height is defined as follows: When the aspect ratio of the image projected on the picture tube is 3: 4, the dimension of the image in the vertical direction is a diagonal dimension. This is because the fact that the distortion of the projected image is conspicuous near the upper and lower ends of the projected image is taken into consideration.

In order to satisfy the above-mentioned condition relating to distortion, in the projection optical device according to the present invention, the power of the second lens L2 is made smaller than that of the conventional administration lens. That is, the first
The lens L1 and the third lens L3 share positive distortion,
The lens L2 shares the negative distortion, and when the power of the second lens L2 is small, the negative distortion is reduced, and the total positive distortion is increased.

To realize the projection optical device according to the present invention, it is necessary to satisfy the following conditions.

(1) 0.45 <f / f ₁ <0.7 (2) 0.65 <f / f ₂ <0.85 (3) −1.3 <f / f ₃ <−0.85 where f is the first lens L1, the second lens L2, and the 3 lenses
L3, the combined focal length of the optical system composed of the transparent body 4 and the face plate 3, f ₁ and f ₂ are the first lens L 1 and the second lens
L2 focal length of, f ₃ is the composite focal length of the third lens L3, transparent body 4 and face plate 3.

The conditions (1) and (2) relate to the distribution of the positive power, and generate the required distortion, correct other aberrations in a well-balanced manner, and keep the image movement due to a change in the ambient temperature within an allowable value. This is a condition provided for suppression. When the value exceeds the upper limit of the condition (1), the power of the first lens L1 becomes too large, and it is difficult to suppress the image plane movement due to a change in the ambient temperature to an allowable value or less. Condition (1)
When the lower limit is exceeded, the power of the second lens L2 must be increased, and the spherical aberration generated by the second lens L2 becomes too large, so that the on-axis aberration and the off-axis aberration are corrected in a well-balanced manner. It becomes difficult. Next, condition (2)
When the upper limit is exceeded, the spherical aberration generated by the second lens L2 becomes too large, and it becomes difficult to correct the spherical aberration while suppressing the generation of the off-axis aberration in other portions. Further, it becomes difficult to obtain the required distortion. If the lower limit of the condition (2) is exceeded, the power of the first lens L1 must be increased, and it becomes difficult to suppress the image plane movement due to a change in the ambient temperature to an allowable value or less.

Condition (3) is a condition provided for correcting curvature of field while maintaining the balance of various aberrations. Condition (3)
If the lower limit is exceeded, it is easy to correct the curvature of field, but the peripheral rays of the off-axis rays are liable to generate flare, and it is difficult to improve the image quality of the peripheral portion of the projected image. When the value exceeds the upper limit of the condition (3), the reduction of Petzval sum becomes unsatisfactory, and it becomes difficult to satisfactorily correct the field curvature.

Next, in order to realize a bright lens having an F-number of about 1.0, it is desirable to satisfy the following conditions.

(4) 0.65 <r ₃ / | r ₄ | <1.6 (5) 0.4 <d ₄ /f<0.7 where r ₃ and r ₄ are the first lens L of the second lens L2, respectively.
1-side surface and the radius of curvature of the opposite surface, d ₄ is the second lens L
This is the air gap between the second lens L3 and the third lens L3.

Condition (4) relates to the vertices of curvature r ₃ and r ₄ of the second lens L2. When the value exceeds the lower limit of the condition (4), it becomes difficult to satisfactorily correct coma over the entire angle of view. If the value exceeds the upper limit of the condition (4), the second lens L2
It is difficult to correct a light beam passing around the area.

Condition (5) relates to an air gap d ₄ between the second lens L2 third lens L3. If the lower limit of the condition (5) is exceeded, the effect of reducing Petzval sum will be reduced. When the value exceeds the upper limit of the condition (5), although it is advantageous to reduce the Petzval sum, the position where the off-axis ray enters the third lens L3 may be high, so that the off-axis aberration may be favorably reduced. It becomes difficult to correct.

In the configuration shown in FIG. 2, when a liquid is used for the transparent body, it is desirable to satisfy the following conditions.

(6) r ₆ /f<0.6 where r ₆ is the radius of curvature of the surface of the third lens L3 on the image tube 2 side.

When the condition (6) is not satisfied, the peripheral portion of the liquid becomes too thick compared to the central portion, so that a change in the refractive index due to a change in the temperature of the liquid cannot be ignored, and the image quality of the peripheral portion of the projected image deteriorates. There is.

Hereinafter, specific numerical examples of the projection optical device according to the present invention will be described. Here, r _j is the radius of curvature of the vertex of the j-th surface, d _j is the surface interval from the j-th surface to the next surface, and n _i and v _i are the refractive index and Abbe number of the i-th lens at the e-line, respectively. n _L , ν _L
Is the refractive index and Abbe number of the transparent body 8 at the e-line, and n _p , v _p , n _p , and v _p are the refractive index and the Abbe number of the face plate 4 and the flat glass 10 of the picture tube 1 at the e-line, respectively. . The surface marked * is an aspherical surface, and X is the aspherical surface coefficient K _j , D _j , E _j , where X is the amount of deviation from the lens vertex at the position of a radial distance Y of the aperture from the optical axis of the lens. , F _j , G _j
Using, Indicated by

The first to fifth embodiments have the configuration shown in FIG. 1 and have both surfaces of the first lens L1 aspherical. In the sixth embodiment, only the screen-side surface of the first lens is aspherical in the configuration shown in FIG. Example 7 has the configuration shown in FIG. 1 in which both surfaces of the first lens are aspherical, and the radii of curvature of both surfaces of the second lens are the same. Embodiment 8 is based on the configuration shown in FIG.

(Example 1) f = 100, F0.99, β = −0.140 r ₁ = 95.758 ^* d ₁ = 19.24 n ₁ = 1.494 ν ₁ = 57.2 r ₂ = −555.971 ^* d ₂ = 64.82 r ₃ = 164.598 d _{3 = 13.99 n 2 = 1.662 ν 2} = 50.6 r 4 = -183.745 d 4 = 49.44 r 5 = -44.594 * d 5 = 3.50 n 3 = 1.494 ν 3 = 57.2 r 6 = ∞ d 6 = 4.81 n L = 1.40 ν _{L = 58 r 7 = ∞ d} 7 = 9.88 n p = 1.507 ν p = 50.7 r 8 = -2054.807 aspheric coefficients ^{_{K 1 = -6.45282 × 10 -1 K}} 2 = 0.0 D 1 = -2.41362 × 10 -7 D ₂ = -5.72433 × 10 ^-8 E ₁ = 4.63542 × 10 ^-11 E ₂ = 4.94034 × 10 ^-11 F ₁ = −2.32568 × 10 ^-14 F ₂ = −1.96549 × 10 ^-14 G ₁ = 1.53141 × 10 ^-18 G ₂ = 1.69014 × 10 ⁻¹⁸ K ₅ = −5.97814 × 10 ⁰ D ₅ = −5.78769 × 10 ⁻⁶ E ₅ = 2.07267 × 10 ⁻⁹ F ₅ = −6.15447 × 10 ⁻¹³ G ₅ = 1.04525 × 10 ⁻¹⁶ _{f / f 1 = 0.599 f /} f 2 = 0.750 f / f 3 = -1.079 ( example 2) f = 100, F0.99, β = -0.142 r 1 = 86.679 * d 1 = 17.80 n 1 = 1.494 ν ^{_{1 = 57.2 r 2 = -3300.094 *}} d 2 = 56.57 r 3 = 164.967 d 3 = 13.46 n 2 _{1.662 ν 2 = 50.6 r 4 =} -199.638 d 4 = 53.50 r 5 = -52.085 * d 5 = 3.47 n 3 = 1.494 ν 3 = 57.2 r 6 = ∞ d 6 = 6.85 n L = 1.40 ν L = 58 r 7 = ∞ d ₇ = 9.81 n _p = 1.507 ν _p = 50.7 r ₈ = −2040.000 Aspherical surface coefficient K ₁ = −4.15551 × 10 ⁻¹ K ₂ = 0.0 D ₁ = −1.8882 × 10 ⁻⁷ D ₂ = 6.49 126 × 10 ^-8 E ₁ = 4.77615 × 10 ^-11 E ₂ = 3.13528 × 10 ^-11 F ₁ = −2.42754 × 10 ^-14 F ₂ = −1.23574 × 10 ^-14 G ₁ = 1.71915 × 10 ^-18 G ₂ = 8.45 260 × 10 ^-19 K ₅ = -3.08905 x 10 ⁰ D ₅ = -4.68538 x 10 ^-6 E ₅ = 1.43842 x 10 ^-9 F ₅ = -6.47043 x 10 ^-13 G ₅ = 1.64181 x 10 ^-16 f / f ₁ = 0.584 f / f ₂ = 0.722 f / f ₃ = −0.920 (Example 3) f = 100, F0.99, β = −0.142 r ₁ = 94.526 ^* d ₁ = 19.29 n ₁ = 1.494 ν ₁ = 57.2 r ₂ = ^{_{-565.960 * d 2 = 65.31 r 3}} = 161.846 d 3 = 14.03 n 2 = 1.662 ν 2 = 50.6 r 4 = -190.719 d 4 = 49.08 r 5 = -44.623 * d 5 = 3.51 n 3 = 1.494 ν 3 = 57.2 _{r 6 = ∞ d 6 = 4.74} n L = 1.40 ν L = 58 r 7 = ∞ d 7 _{9.91 n p = 1.507 ν p =} 50.7 r 8 = -2060.953 aspheric coefficients ^{_{K 1 = -6.07149 × 10 -1 K}} 2 = 0.0 D 1 = -2.33232 × 10 -7 D 2 = -4.52352 × 10 -8 E 1 = 4.65257 × 10 ^-11 E ₂ = 4.64427 × 10 ^-11 F ₁ = −2.27747 × 10 ^-14 F ₂ = −1.93136 × 10 ^-14 G ₁ = 1.42096 × 10 ^-18 G ₂ = 1.65208 × 10 ^-18 K ₅ = −6.91543 × 10 ⁰ D ₅ = −6.08408 × 10 ⁻⁶ E ₅ = 2.09362 × 10 ⁻⁹ F ₅ = −5.55175 × 10 ⁻¹³ G ₅ = 8.50045 × 10 ⁻¹⁷ f / f ₁ = 0.604 f / f ₂ = 0.744 f / f ₃ = −1.079 (Example 4) f = 100, F0.99, β = −0.142 r ₁ = 103.298 ^* d ₁ = 17.14 n ₁ = 1.494 ν ₁ = 57.2 r ₂ = −401.761 ^* d _{2 = 66.51 r 3 = 184.627 d} 3 = 13.62 n 2 = 1.662 ν 2 = 50.6 r 4 = -152.382 d 4 = 48.55 r 5 = -41.724 * d 5 = 3.52 n 3 = 1.494 ν 3 = 57.2 r 6 = ∞ d ₆ = 6.68 n _L = 1.40 ν _L = 58 r ₇ = ∞ d ₇ = 9.93 n _p = 1.507 ν _p = 50.7 r ₈ = −2065.512 Aspherical coefficient K ₁ = −7.99251 × 10 ⁻¹ K ₂ = 0.0 D ^{_{1 = -2.19610 × 10 -7 D 2}} = -1.00800 × 10 -8 E 1 = 7.16297 × 10 -1 ² E ₂ = -1.43379 × 10 ^-11 F ₁ = −2.33490 × 10 ^-14 F ₂ = −2.54580 × 10 ^-15 G ₁ = 5.80384 × 10 ^-18 G ₂ = 3.34299 × 10 ^-18 K ₅ = −3.38508 × 10 ⁰ D ₅ = −4.20336 × 10 ⁻⁶ E ₅ = 1.45394 × 10 ⁻⁹ F ₅ = −5.41178 × 10 ^-13 G ₅ = 9.64214 × 10 ⁻¹⁷ f / f ₁ = 0.594 f / f ₂ = 0.780 f / f ₃ = −1.155 (Example 5) f = 100, F 0.99, β = −0.142 r ₁ = 90.921 ^* d ₁ = 19.08 n ₁ = 1.494 ν ₁ = 57.2 r ₂ = −813.559 ^* d ₂ = 63.02 r _{3 = 139.699 d 3 = 13.88 n} 2 = 1.591 ν 2 = 61.0 r 4 = -187.594 d 4 = 50.42 r 5 = -44.236 * d 5 = 3.47 n 3 = 1.494 ν 3 = 57.2 r 6 = ∞ d 6 = 4.77 n _L = 1.40 ν _L = 58 r ₇ = ∞ d ₇ = 9.80 n _p = 1.507 ν _p = 50.7 r ₈ = -2038.307 Aspheric coefficient K ₁ = -5.25626 × 10 ^-1 K ₂ = 0.0 D ₁ = -2.24405 × 10 ⁻⁷ D ₂ = −2.93590 × 10 ⁻⁸ E ₁ = 5.74635 × 10 ⁻¹¹ E ₂ = 5.73430 × 10 ⁻¹¹ F ₁ = −2.46801 × 10 ⁻¹⁴ F ₂ = −2.07700 × 10 ⁻¹⁴ G ₁ = 1.51322 × 10 ^-18 G ₂ = 1.67919 × 10 ^-18 K ₅ = −3.60780 × 10 ⁰ D ₅ = −4.72438 × 10 ^-6 E ₅ = 1.80837 × 10 ⁻⁹ F ₅ = −7.86544 × 10 ⁻¹³ G ₅ = 1.76583 × 10 ⁻¹⁶ f / f ₁ = 0.600 f / f ₂ = 0.727 f / f ₃ = −1.088 (Example 6) f = 100, F1.05, β = -0.142 r 1 = 91.766 * d 1 = 19.07 n 1 = 1.494 ν 1 = 57.2 r 2 = -673.529 d 2 = 63.64 r 3 = 166.857 d 3 = 13.87 n 2 = 1.662 ν 2 _{= 50.6 r 4 = -193.161 d 4} = 49.95 r 5 = -44.199 * d 5 = 3.47 n 3 = 1.494 ν 3 = 57.2 r 6 = ∞ d 6 = 4.77 n L = 1.40 ν L = 58 r 7 = ∞ d _{7 = 9.79 n p = 1.507 ν} p = 50.7 r 8 = -2036.625 aspheric coefficients ^{_{K 1 = -5.25860 × 10 -1 K}} 5 = -5.52339 × 10 0 D 1 = -2.22574 × 10 -7 D 5 = -5.68908 × 10 ^-6 E ₁ = 3.99679 × 10 ^-11 E ₅ = 2.07717 × 10 ^-9 F ₁ = −2.44869 × 10 ^-14 F ₅ = −6.96600 × 10 ^-13 G ₁ = 3.09552 × 10 ^-18 G ₅ = 1.34247 × 10 ⁻¹⁶ f / f ₁ = 0.606 f / f ₂ = 0.728 f / f ₃ = −1.089 (Example 7) f = 100, F0.99, β = −0.142 r ₁ = 97.489 ^* d ₁ = 16.25 n ₁ = 1.494 ν ₁ = 57.2 r ₂ = -2316.876 ^* d ₂ = 57.10 r ₃ = 177.545 d ₃ = 14.05 n ₂ = 1.662 ν ₂ = 50.6 r ₄ = −177.545 d ₄ = 61.04 r ₅ = −48.311 ^* d ₅ = 3.51 n ₃ = 1.494 ν ₃ = 57.2 r ₆ = ∞d ₆ = 4.12 n _L = 1.40 ν _L = 58 r ₇ = ∞ d ₇ = 9.93 n _p = 1.507 ν _p = 50.7 r ₈ = −2064.209 Aspheric coefficient K ₁ = −6.30076 × 10 ⁻¹ K ₂ = 0.0 D ₁ = −2.39607 × 10 ⁻⁷ D ₂ = −2.16803 × 10 ⁻⁸ E ₁ = 5.84274 × 10 ⁻¹¹ E ₂ = 6.34962 × 10 ⁻¹¹ F ₁ = −2.64553 × 10 ⁻¹⁴ F ₂ = −2.28945 × 10 ⁻¹⁴ G ₁ = 4.60514 × 10 ⁻¹⁹ G ₂ = 8.23373 × 10 ⁻¹⁹ K ₅ = −4.77638 × 10 ⁰ D ₅ = −5.15458 × 10 ⁻⁶ E ₅ = 1.56966 × 10 ⁻⁹ F ₅ = −6.05097 × 10 ⁻¹³ G ₅ = 1.35551 × 10 ⁻¹⁶ f / f ₁ = 0.527 f / f ₂ = 0.733 f / f ₃ = −0.995 (Example 8) f = 100, F0.99, β = −0.140 r ₁ = 91.025 ^* d ₁ = 19.01 n ₁ = 1.494 ν ₁ = ^{_{57.2 r 2 = -765.802 * d 2}} = 62.62 r 3 = 161.096 d 3 = 13.83 n 2 = 1.662 ν 2 = 50.6 r 4 = -197.805 d 4 = 50.37 r 5 = -44.078 * d 5 = 5.19 n 3 = 1.494 ν ₃ = 57.2 r ₆ = −86.427 d ₆ = 3.02 n _L = 1.40 ν _L = 58 r ₇ = ∞ d ₇ = 9.77 n _p = 1.507 ν _p = 50.7 r ₈ = −2031.04 Aspheric coefficient K ₁ = −5.79979 × 10 ⁻¹ K ₂ = 0.0 D ₁ = −2.37 240 × 10 ⁻⁷ D ₂ = −5.00883 × 10 ⁻⁸ E ₁ = 5.47455 × 10 ⁻¹¹ E ₂ = 5.44340 × 10 ⁻¹¹ F ₁ = −2.59253 × 10 ⁻¹⁴ F ₂ = −2.08555 × 10 ⁻¹⁴ G ₁ = 1.58578 × 10 ⁻¹⁸ G ₂ = 1.56249 × 10 ⁻¹⁸ K ₅ = −3.97953 × 10 ⁰ D ₅ = −5.31545 × 10 ⁻⁶ E ₅ = 2.111712 × 10 ⁻⁹ F ₅ = −7.50059 × 10 ⁻¹³ G ₅ = 1.37462 × 10 ⁻¹⁶ f / f ₁ = 0.603 f / f ₂ = 0.734 f / f ₃ = −0.979 FIGS. 4 to 11 show examples 1 to 8 respectively.
FIG. This aberration diagram is viewed on the picture tube side. From the numerical table and the aberration diagram of each example, the F number is 0.
It is very bright at 99, indicating that the aberrations are sufficiently corrected except for the distortion. Since the distortion curve is a smooth curve or a monotonically increasing curve at a maximum image height of about 5%, it can be seen that the power of the distortion correction circuit of the picture tube can be reduced. Further, since the second lens L2 is made of glass and the distribution with the first lens L1 is selected to be an appropriate value, the problem of image plane movement due to a change in ambient temperature is suppressed to a level that cannot be practically used.

As described above, according to the present invention, it is possible to provide a projection optical device which has good contrast of a projected image, saves power in a distortion correction circuit of a picture tube, and has good aberration correction. Can be very effective.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a configuration of an embodiment of a projection optical device according to the present invention, FIGS. 2 and 3 are schematic configuration diagrams showing configurations of another embodiment of the present invention, and FIGS. FIG. 11 is an aberration diagram for each of Embodiments 1 to 8 of the present invention. 1 ... picture tube, 2 ... frame, 3 ... face plate,
4 ... Transparent body, L1 ... First lens, L2 ... Second lens,
L3 ... The third lens.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-194234 (JP, A) JP-A-59-121016 (JP, A) JP-A-59-111615 (JP, A) JP-A-58-194 140708 (JP, A) JP-A-58-139110 (JP, A) JP-A-58-125007 (JP, A) JP-A-58-111816 (JP, A) JP-A-57-177115 (JP, A) JP-A-57-108818 (JP, A) JP-A-57-34515 (JP, A) JP-A-56-131658 (JP, A) JP-A-56-125716 (JP, A) JP-A-50-145226 (JP, A) JP-A-50-87322 (JP, A)

Claims (6)

(57) [Claims] 1. A first lens composed of a plastic positive lens, a second lens composed of a biconvex glass lens, and a concave surface of an aspheric surface, in which at least one surface is aspherical and a surface having a high curvature is directed toward the screen in order from the screen side. A third lens made of a plastic lens with the lens facing the screen is arranged,
An image tube is arranged behind the third lens, and the third
At least one kind of transparent body is arranged so that no air layer is interposed between the lens and the face plate of the picture tube. The refractive index of the transparent body is close to the refractive index of the third lens, and the first lens , The combined focal length of the optical system composed of the second lens, the third lens, the transparent body and the face plate is f, and the focal lengths of the first lens and the second lens are f ₁ , f ₂ , The combined focal length of the third lens, the transparent body, and the face plate
As _{f 3, 0.45 <f / f} 1 < satisfy _{0.7 0.65 <f / f 2 <} 0.85 -1.3 <f / f 3 <-0.85 conditions, the first lens, said second lens and said third lens Are set to generate positive, negative, and positive distortions, respectively, and let the distortion at the maximum image height viewed from the picture tube side be Ee [%] so as to satisfy the condition of 2 <Ee <10. A projection optical device characterized in that an image distorted in a pincushion shape is projected on a tube to reduce the power consumption of a distortion correction circuit. 2. The lens according to claim 1, wherein a condition of 0.2 <Em / Ee <0.6 is satisfied, wherein Em [%] is a distortion at an image height of 60% of a maximum image height viewed from the picture tube side. The projection optical device according to item (1). 3. The projection optical apparatus according to claim 2, wherein the distortion seen from the picture tube side is a curve that monotonically increases with an increase in the angle of view. 4. The projection optical apparatus according to claim 1, wherein the following condition is satisfied. 0.65 <r ₃ / | r ₄ | <1.6 0.4 <d ₄ /f<0.7, where r ₃ and r ₄ are the apex radius of curvature of the first lens surface and the third lens surface of the second lens, respectively. d ₄ is the air space between the third lens and the second lens. 5. The method according to claim 1, wherein the transparent body is a liquid, and the face plate has a flat or substantially flat surface on the side of the third lens, and satisfies the following conditions. Item (2) or (4). r ₆ /f<−0.6 where r ₆ is the radius of curvature of the vertex of the surface of the third lens on the picture tube side. 6. The transparent body includes a flat glass and a liquid, and the flat glass is bonded to a surface of the third lens on a picture tube side with a transparent adhesive, and the flat glass and a face plate of the picture tube are connected to each other. The projection optical device according to claim 1, wherein the space between the projection optical devices is filled with a transparent liquid.