JPH0395512A - Projection lens - Google Patents

Abstract

PURPOSE:To obtain the bright projection lens which has a wide view angle by composing the lens system of six lens elements in five groups and composing a 3rd group of a high-dispersion concave lens and a low-dispersion convex lens. CONSTITUTION:The lens system consists of six elements in five groups, i.e. a 1st convex lens group 8, a 2nd lens group 7 with relatively weak refracting power, the 3rd cemented lens group 6 with has the majority of the positive refracting power of the whole system, a 4th lens group 5 with relatively weak refracting power, and a 5th lens group 4 which is concave to the screen side in order from the screen side. Then the concave lens 6b in the 3rd group is formed by cementing the lens 6a of a high-dispersion material which has the largest positive refracting power and a <=45 Abbe number to the lens 6b of a low-dispersion material which has a >=55 Abbe number. Consequently, the bright lens with the wide view angle is obtained and a sufficiently compact projection TV can be realized by using one mirror.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a projection lens suitable for projection television.

[Conventional technology]

In order to reduce the set size of a projection television, it is necessary to significantly shorten the projection distance (distance from the tip of the lens to the screen) of the projection lens used. When the projection distance of the projection lens is shortened, the angle of view increases, making the design difficult in the following respects.

(2) For a lens having principal refractive power, the angle of incidence of the light beam that forms an image at the circumferential section of the screen increases, and the amount of aberration that occurs increases. ■Peripheral illuminance ratio decreases significantly.

Generally, the amount of peripheral light is given by the following equation.

Q' = Q ・(1 −V) ・Cow'θ However,
Q′2 peripheral light amount. Q: Light amount on the optical axis θ: Lens angle of view,
(2)=Vignetting As mentioned above, the amount of circumferential light is proportional to the fourth power of the angle of view θ, so in order to obtain a sufficient amount of peripheral light with a projection lens having a high angle of view, it is necessary to make the vignetting sufficiently small. In other words, it is necessary to capture as much of the light rays that form an image at the periphery of the screen as possible into the projection lens, which makes it even more difficult to correct aberrations.

In order to solve these problems, various projection lenses have recently been studied in which plastic aspherical lenses are frequently used to increase the degree of freedom in correcting aberrations. This type of projection lens includes, for example, US Pat. No. 4,682,862. In the embodiment of the invention, a high half-field angle of 29 degrees to 44 degrees and a bright lens with an F number of about 1.0 are achieved with a relatively small number of lenses, but chromatic aberration is not sufficiently corrected. The focus performance was insufficient.

[Problem to be solved by the invention]

The above-mentioned conventional projection lenses have achieved a high angle of view, and a compact set can be realized with just one folding mirror. No consideration was given to reducing chromatic aberration, and focus performance was inadequate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bright, high-focus projection lens that has a high angle of view and can realize a sufficiently compact projection television with a single folding mirror.

[Means to solve the problem]

In order to achieve the above object, the lens is composed of five groups, and in order from the screen side, the first group corrects aberrations caused by the aperture. In the second group, a part of the positive refractive power of the third group is shared with respect to the light rays that form an image in the peripheral area of the screen by providing a lens that has a larger condensing effect in the peripheral area than in the center area. The third group shares most of the positive refractive power of the entire lens system, and corrects chromatic aberration by using the lens with the largest refractive power as a composite lens consisting of a high dispersion concave lens and a low dispersion convex lens.

At this time, in order to increase the chromatic aberration correction effect, a concave lens made of a high dispersion material is placed on the cathode ray tube side, and the shape of the cathode ray tube side lens surface of the concave lens is made flat or convex toward the screen side. The fourth group corrects aberrations caused by the angle of view.

#! The fifth group shares negative refractive power. With the above configuration, a projection lens with a high angle of view, brightness, and high focus can be realized. Furthermore, by using the projection lens, a sufficiently compact set can be realized even with a single folding mirror.

[Effect]

The projection lens of the present invention has a five-group configuration, and most of the positive refractive power of the entire system is shared by the third group lens. Here, the third lens group is a laminated lens consisting of a high dispersion concave lens and a low dispersion convex lens.In order to enhance the effect of reducing chromatic aberration, the high dispersion concave lens is placed on the cathode ray tube side, and The side lens surface is either flat or concave toward the cathode ray tube. On the other hand, in order to obtain the same breaking power as a biconvex lens, it is necessary to reduce the radius of curvature of the screen-side lens surface of the third group lens. As a result, the monochromatic aberration that occurs increases. This tendency appears more prominently in image light that forms an image around the screen. Therefore, in the present invention, the second lens group shares the refractive power for the image light formed around the screen, thereby achieving good imaging performance.

〔Example〕

Examples thereof will be described below. FIG. 1 is a sectional view showing the main part of a lens of an optical system for a projection television as an embodiment of the present invention.

In the figure, P1 is a cathode ray tube phosphor screen, 1 is a cathode ray tube panel, 2 is a coolant, 4 is a fifth group lens, 5 is a fourth group lens, 6a and 6b are 317# lenses, and 7 is a second group. , and 8 is the first lens group. The first to fourth groups are assembled into the inner lens barrel 11, and the outer mirror [10 is made slidable for focus adjustment. Further, the outer lens barrel 10 is screwed and fixed to the bracket 3 via the fixing plate 9.

The optical system of this example has a 5.4
An inch raster is displayed on the screen in inches (9.3
It is configured so that the best performance can be obtained when it is enlarged to

The distance from lens 8 of the first group to the screen is 790m
m, and the half angle of view is 39 degrees. The lens 8 of the first group has an aspherical shape mainly to correct aberrations caused by the aperture. Second group lens 7
In order to share part of the positive collapsing power against ambient light,
The shape has a stronger light-concentrating effect at the periphery than at the center. The lenses 61L and 6b of the third group are glass lenses that reduce focus drift due to temperature changes, and include a concave lens 6a made of a high dispersion material and a convex lens 6b made of a low dispersion material.
This reduces chromatic aberration. Moreover, this lens shares most of the positive refractive power of the entire system. The lens 5 of the fourth group has an aspherical shape to minimize the refractive force in order to eliminate high-order comatic aberrations that occur due to the high angle of view. The fifth # lens 4 is a lens for correcting field curvature, and has an aspheric air-side interface in order to correct sagittal aberration caused by light rays at the peripheral portion of the screen. Further, the cathode ray tube phosphor screen P1 has a curvature to correct field curvature. In particular, if an aspheric surface is used to correct high-order field curvature, even more excellent correction becomes possible.

Generally, the phosphor screen P1 of the cathode ray tube panel 1 is manufactured by press molding without any post-processing. Therefore, whether the molded shape is spherical or aspherical,
The manufacturing method itself remains unchanged.

On the other hand, the lenses of this lens system are designed to minimize the power of plastic lenses, making them thin and
By reducing the difference in wall thickness between the center and periphery, we aim to improve moldability. Specific lens data that this lens system can take is shown in Table 1 (A) and (B). How to read Table 1 and Table (A) will be explained below. Data is shown divided into a spherical system mainly dealing with the lens region near the optical axis and an aspherical system dealing with the outer periphery. First, the screen has a radius of curvature of oo (that is, a plane). The distance wA on the optical axis from the screen to the surface S+ of the lens 8 of the first group
It is shown that the surface spacing) is 790 mm, and the refractive index of the medium (air) between them is 1.0. The radius of curvature of the S1 surface of the lens 8 of the first group is 85,726 mm (the center of curvature is on the phosphor screen side), and the distance between the lens surfaces S1 and S on the optical axis (plane distance) is 8.874 tnm. It has been shown that the refractive index of the medium between them is 1.58890. In the same way, the last one is CRT panel 1.
The radius of curvature of the phosphor screen P1 is 341.28 mm. The thickness of the cathode ray tube panel l on the optical axis is 13.4 mm, and the refractive index is 1.
．． 53983. Next, how to read Table (B) of Table 1 will be explained below.

Surface s of lens 8 of the first group. e 82 #Surface Ss of lens 7 of second group. 84 and #i 4th group < 7) L/ ance 5 (7) surface Ss, Ss (!: 5th group lens 4
surface S1. The aspherical coefficients are shown for and phosphor screen P. Here, the aspheric coefficient is a coefficient when the surface shape is expressed by the following equation.

+AE-r◆+AF-r'+AG-r'+AH-r"°
However, as shown in FIGS. 9 and 10, 2 represents the height of the lens surface (r relationship) when the optical axis direction is taken as the two axes and the radial direction of the lens is taken as the r axis, and r indicates the radial distance, and RD indicates the radius of curvature. Follow me, CC
, AE. AF. A.G. If each coefficient of AH is given, the height, that is, the shape of the lens surface is determined according to the above equation. Figure 10 is an explanatory diagram of an aspherical surface, and each ? By substituting the values, a lens surface that is shifted by S, (■) - Asω] from the lens surface of only the spherical system can be obtained.

Also, in Table 1 and Table (B), the surface 8 of the lens 4 of the fifth group
11 indicates that the aspherical coefficients are all zero and it is a spherical surface. The above is how to read the data shown in Table 1, Table (A), and Table (B).

l5 16 In this projection lens, most of the positive refractive power of the entire system is shared by lenses 6a and 6b of the third group. Lens 6a is a concave lens made of a high dispersion material, and lens 6b is made of a low dispersion material. This is a convex lens made up of two types of lenses, and chromatic aberration is reduced by bonding the two together.

FIG. 4 shows calculated longitudinal chromatic aberration occurring in the projection lens described above. The coordinates of the side cross-sectional view of the lens shown in the same figure are the optical axes t and t' of the lens, and if the direction from t to t' is the positive direction, then the radius of curvature is positive if the center is in the positive direction. , the radius of curvature of surface B has a positive sign. The horizontal axis in FIG. 4 is the reciprocal of the radius of curvature of the bonding surface B, and it can be seen from the figure that in order to reduce longitudinal chromatic aberration, the radius of curvature of the B surface can be reduced. However, if the radius of curvature of the B surface is made smaller, the amount of sag at the outermost peripheral portion of the lens increases. For this reason, if the lens edges are secured, the convex lens becomes a very thick lens. For this reason, the radius of curvature of the B surface cannot be made very small. Therefore, when the radius of curvature of surface B is fixed, as is clear from FIG. However, the effect of the concave lens becomes greater, and the ability to correct chromatic aberration is greatly improved. In the projection lens of the present invention, chromatic aberration can be significantly reduced by making the cathode ray tube side lens surface of the aforementioned high dispersion concave lens flat or convex toward the screen side. However, on the other hand, it becomes difficult to correct monochromatic aberrations because it is necessary to increase the refractive power of the laminated convex lens. Below, we will use diagrams to explain the reasons for this and how technical means to solve the problem will work. FIG. 5 is a side sectional view showing the projection lens of the present invention. For convenience of explanation, the cathode ray tube 1, the fifth group of lenses 4, and the third group of lenses are arranged as a single convex meniscus lens 6 having a convex surface on the screen side. It is said that

On the other hand, the function of each lens group is that the third group shares most of the positive refractive power of the entire system, and the fifth group uses a negative lens with a concave surface on the screen side to reduce the Betsuval sum of the entire system. are doing. In a projection lens with a high angle of view,
The image light emitted from the periphery of the phosphor screen P of the cathode ray tube 1 passes through the coolant 2 and is then diverged by the concave lens 4 of the fifth group and then
The light enters the lens 6 of the group. At this time, the upper limit light RAYI and the lower limit light RAY2 enter the lens 6 of the third group at an incident angle θ,, θ,
incident at FIG. 6 is an enlarged view of FIG. 5, and (a) shows that the upper limit light RAYI is in the third group. (b) is a diagram showing a state in which the lower limit light RAY2 enters the lens 6. FIG. In the conventional projection lens, as shown by the broken line in the figure, the lens that shares most of the positive refractive power is convex toward the cathode ray tube, and the incident angles θl and θt of the upper and lower limit rays are large. For this reason, it has great refractive power. On the other hand, since the projection lens of the invention is convex or flat on the screen side as shown by the solid line in the figure, the incident angle of the upper and lower limits of light is θ! , θ, are small, and the refractive power obtained at the side surface of the cathode ray tube is small. For this reason, in order to obtain the necessary refractive power with the third lens group 6, it is necessary to reduce the radius of curvature on the screen side. Therefore, the amount of aberration occurring on the screen-side lens surface increases. Therefore, in the present invention,
As shown in Figure 7, by making the shape of the lens constituting the second group stronger at the periphery (indicated by A in the figure) than at the center, the refractive power for the image light at the periphery of the screen can be increased. By sharing a part of the lens, the radius of curvature of the screen-side lens surface of the third group of lenses 6 is prevented from becoming small.

Next, using the projection lens of the present invention described above, the 5.4-inch image on the phosphor screen is enlarged and projected onto the screen.
FIG. 11 shows the evaluation results of the focus characteristics using the 'ransfar function'. The phosphor emission spectrum shown in FIG. 8 was used at this time. As the evaluation frequency, the black and white striped signal on the screen was set to 300
This shows the case of TV main display. From the same figure, sagittal (displayed by S in the figure), meridional (displayed by M in the figure)
It can be seen that good MTF characteristics are obtained in both cases. or,
Tables (A) and (B) of Table 2 are lens data of the second embodiment shown in FIG. The lens surface is flat. The focus performance of this projection lens is
Shown in Figure 2. By reducing the addition of chromatic aberration, sagittal. It can be seen that both meridional and meridional focus characteristics are excellent, similar to the first embodiment.

The embodiment of the present invention described above has a high half angle of view of 39 degrees, and as shown in FIG. 3, a sufficiently compact set can be realized even with one folding mirror 14.

〔Effect of the invention〕

As described above, according to the present invention, a projection lens with a high angle of view, high focus, and brightness can be realized. moreover,
A projection television employing an optical system using the projection lens of the present invention can be made sufficiently compact even with a single folding mirror.

[Brief explanation of drawings]

1 and 2 are side sectional views of a projection lens used to explain an embodiment of the invention, FIG. 3 is a longitudinal sectional view of a projection television using the projection lens of the invention, and FIG.
7 to 7 are explanatory diagrams used when explaining the present invention,
FIG. 8 is an emission spectrum characteristic diagram of the edge phosphor, FIGS. 9 and 10 are explanatory diagrams used to explain the definition of the lens shape, and FIGS. FIG. 3 is a characteristic diagram showing MTF characteristics of a projection lens. l Ni cathode ray tube 2: Coolant 3: Bracket 4: 5th group lens 5: 4th group lens 6.6m, 6b: 3rd group lens 7: 29th lens 8: 1st group lens 9: Fixed plate 1o: Outer mirror 11: Inner barrel 12: Screen 13: Outer frame 14.14-0. 14-1. 14-2: Reflection mirror 15: Projection lens 16: Braun tube P1:
Fluorescent screen edict M 〇1- LN^) Marie G Tonu 0 Pini C Punishment 5 Figure Punishment 4 Figure JP-A-95512 (8) Frost 5 Figure? 6 Figure 6 (α) No C axis top shell ゛j (b) Punishment 7 Figure Kouka Yushita Seki lJ Congee 6 Figure 3 Blank 10 Figure Otsuyuki axis) Punishment 11 Figure OO Waj T I Natsume Chuuriki 12 figure

Claims (1)

[Claims] 1. A five-group lens used in a projection television optical system that enlarges and projects an image on a cathode ray tube onto a screen, in which the central part is convex and the peripheral part is convex with respect to the screen, in order from the screen side. A first group that includes at least one lens that is convex toward the screen and has at least one surface that becomes concave as it goes along, a second group that includes at least one lens that has a relatively weak refractive power, and a large a third group including at least one plano-convex or convex meniscus lens having positive refractive power and convex toward the screen side;
The fourth group includes at least one lens with a relatively weak refractive power, and the fifth group includes a negative lens having a concave surface on the screen side. Atsbe number ν for lenses with strong positive refractive power
Concave lens made of high dispersion material with d of 45 or less and Atsube number ν
A projection lens characterized in that it is a laminated lens of convex lenses made of a low dispersion material with d of 55 or more. 2. The projection lens according to claim 1, wherein a half angle of view of the lens formed by a line segment connecting the front end of the lens and a diagonal of the screen and the optical axis is 30 degrees or more. 3. The radius of curvature of both surfaces of the bonded lens having the strongest positive refractive power among the lenses constituting the third group satisfies the following conditions. Projection lens. |γ_1|<|γ_2| However, γ_1: radius of curvature γ_ of the lens surface on the screen side
2: A radius of curvature of the lens surface on the cathode ray tube side is 4, and at least one surface of the lenses constituting the first group, second group, fourth group, and fifth group is an aspheric surface. The projection lens according to claim 3. 5. According to claim 4, the lens action of the screen-side lens surface of at least one of the lenses constituting the second group is an aspherical shape that has a stronger light-converging action at the periphery than at the center of the lens. projection lens. 6. In the laminated lens constituting the third group, a concave lens made of a high dispersion material having an Abbe number νd of 45 or less is provided on the cathode ray tube side. Projection lens. 7. The projection lens according to claim 6, wherein the radius of curvature of both surfaces of the concave lens of the laminated lens constituting the third group satisfies the following condition. |γ_3|<|γ_2| However, γ_2: Radius of curvature of the bonded surface γ_3: Radius of curvature of the side surface of the cathode ray tube 8, The radius of curvature of both surfaces of the convex lens of the bonded lens constituting the third group satisfies the following conditions. 7. The projection lens according to claim 6. |γ_2|>|γ_1| However, γ_1: Radius of curvature of the side surface of the screen γ_2: Radius of curvature of the bonded surface 9, The radius of curvature of each surface of the bonded lens constituting the third group satisfies the following conditions. 7. The projection lens according to claim 6. |γ_3|>|γ_2|>|γ_1| However, γ_3: Radius of curvature of the side surface of the cathode ray tube γ_2: Radius of curvature of the bonded surface γ_1: Radius of curvature of the side surface of the screen 10. A projection television that enlarges and projects the image on the cathode ray tube onto the screen. A 5-group lens used in a commercial optical system, in order from the screen side, the lens has at least one surface that is convex at the center and becomes concave toward the periphery, and is convex toward the screen. The first group includes at least one lens, the second group includes at least one lens with relatively weak refractive power, and the plano-convex or convex lens has a positive refractive power for most of the entire system and is convex toward the screen. The third group includes at least one meniscus lens, the fourth group includes at least one lens with relatively weak refractive power, and a negative lens with a concave surface on the screen side and a phosphor glass with a convex surface on the electron gun side. It consists of a fifth group, and among the lenses constituting the third group, the lens with the strongest positive refractive power is a concave lens made of a high dispersion material with an Abbe number νd of 45 or less, and a concave lens made of a high dispersion material with an Abbe number νd of 55 or more. A projection lens characterized in that it is a laminated lens of convex lenses made of a dispersive material. 11. The projection lens according to claim 10, wherein the phosphor glass constituting the fifth group has a center of curvature on the screen side, and a radius of curvature is larger at the periphery than at the center. 12. A first group including, in order from the screen side, at least one lens that is convex toward the screen and has at least one surface that is convex at the center and becomes concave toward the periphery; A second group including at least one lens with a relatively weak refractive power, a plano-convex lens that has a positive refractive power for most of the entire system, and is convex toward the screen;
A third group includes at least one convex meniscus lens, and a fourth group includes at least one lens with relatively weak refractive power.
and a fifth group consisting of a negative lens having a concave surface on the screen side and a fluorescent screen glass having a convex surface on the electron gun side, and among the lenses constituting the third group, the lens having the most positive refractive power This projection television is characterized by using a projection lens constructed by a strong lens made of a concave lens made of a high dispersion material with an Atsube number νd of 45 or less and a convex lens made of a low dispersion material with an Atsube number νd of 55 or more. 13. Consisting of a display unit that reproduces video signals, a screen, and an optical system that projects the image reproduced on the display unit onto the screen at a half angle of view of 39 degrees or more, this optical system has positive refractive power. Most of the area is occupied by a laminated convex lens provided in the optical system, and this laminated convex lens includes a concave lens element having a first surface facing the display side and a second surface facing the screen side, and a concave lens element. It consists of a convex lens element having a first surface bonded to the second surface of the element and a second surface facing the screen side, and the Atsbe number of the material forming the concave lens element is the Atsbe number of the material forming the convex lens element. A projection device characterized in that the first surface of the concave lens element is flat or has a surface shape close to a flat surface.