JPH02111909A - Lens for projection type television image receiver - Google Patents

Abstract

PURPOSE:To correspond to a change of use magnifications over a wide range at a low cost without degrading focus performance while using the same lens barrel by changing the face shape of either the front or rear face or both of a 1st group lens constituting a 1st group to change the spacing between the constituting group lenses at the time of changing the magnification. CONSTITUTION:The required focus performance corresponding to the magnification after the change is maintained while the same lens barrel is used by changing the face shape of either the front or rear face of the 1st group lens 1 constituting the 1st group or both thereof or changing the shape of both faces of the 1st group lens 1 and the 2nd group lens 2 or partly changing the spacing between the lenses at the time of the magnification change. Namely, the ability to correct the spherical aberrations of the 1st group lens 1 is partly divided for correcting comatic aberrations and astigmatism by changing the face shape of the 1st group lens, by which the aberrations are well corrected over the entire image lane in the case of using this lens at 10.2 times magnification. The high-focus lens is thus obtd. The lens for projection type television image receivers, which has the good image quality up to the large image plane, is obtd. by a minor change of the face shape of the lens and the spacing between the lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a lens for a projection type television receiver used for enlarging and projecting an image on a cathode ray tube phosphor screen onto a screen.

[Conventional technology]

Due to various improvements, the image quality of projection type television receivers has made great progress compared to a few years ago, and is now approaching that of a direct view type. In particular, there has been remarkable progress in projection lenses, which are the key device that determines image quality. Under these circumstances, the present inventors have developed a set using a projection lens with a short projection distance that can simultaneously improve image quality and make the receiver set more compact. Patent documents related to this type of projection lens include Japanese Patent Application No. 1985-085070.

Although FIG. 1 is a side cross-sectional view useful for explaining one embodiment of the present invention, reference is made to FIG. 1 as it is a diagram that can also be used to explain the prior art.

As can be seen in FIG.
4 group lenses 2, 3rd group lens 3, and 4th group lens 4
This is an excellent lens that achieves the required focus and contrast performance with a small number of lens elements.

Furthermore, as shown in FIG. 2, which is a side sectional view of a conventional projection television receiver, even with a single folding mirror 10, a sufficiently compact receiver set can be obtained. The receiver lens had a short projection distance and was excellent in compactness.

The center magnification of such a lens is 8°4x (
Assuming that there is a lens (compatible with a 45-inch screen size), when modifying it to a lens compatible with another screen size, as explained in FIG. The projection distance, which is the distance from I was responding by doing this.

[Problem to be solved by the invention]

However, with this method, the screen size that can be used while maintaining focus performance is from 7.5x (compatible with 40 inches) to 9.3x (compatible with 50 inches); If you use , focus performance will drop significantly. This is shown in FIGS. 5 and 6.

In other words, in Figures 5 and 6, the dashed line shows the case where the conventional lens described above is used at 1000x (compatible with 55 inches), and the broken line shows the case where it is used at 8 and 4 times (compatible with 45 inches), which is the focus of the design. The solid line indicates the case, and the focus performance is 300TV.
Book M T F (ModulaLionTransf
Figure 5 shows the MERI characteristic, and Figure 6 shows the MERI characteristic.
It shows the characteristics.

As is clear from these figures, when conventional lenses are used outside of the design center, focus performance (especially sagittal in Figure 6) deteriorates at high relative angles of view, and this poses a problem. It had become.

The purpose of the present invention is to use the lens for projection television receivers based on the original design (even when used at other magnifications, the same lens barrel can be used by changing the lens shape, To provide a lens for a projection television receiver that does not cause deterioration in focus performance and can accommodate a wide range of changes in magnification in the order of low cost I.

In other words, lenses for projection television receivers are desired to have a variety of magnifications corresponding to various screen sizes, but if lenses of each magnification were manufactured with a separate OA design, The cost is high. A lens designed for that magnification, and a lens for another magnification;
To provide a lens for a projection type television receiver that clarifies how to rebuild it with minimal modification at no cost (while using the same lens barrel, without causing deterioration in focus performance). This is the object of the present invention.

[Means to solve the problem]

To achieve the above object, the present invention provides a lens for a projection television receiver used when enlarging and projecting an image on a cathode ray tube phosphor screen onto a screen, the lens having a meniscus convex on both sides with respect to the screen, starting from the screen side. A first group including a lens, a second group including a biconvex positive lens, a third group including a lens having a weak positive refractive power with a biconvex center, and a negative lens having a concave surface on the screen side. In a lens for a projection television receiver, which has lens groups arranged in the order of 4 groups, when changing the magnification, the surface shape of one or both of the front and back of the first group lens constituting the first group is changed. By doing so, or by changing the shape of both surfaces of the first group lens and the second group lens or partially changing the lens spacing, it is possible to maintain the required focus performance corresponding to the changed magnification while using the same lens barrel. This is achieved in this way.

Furthermore, in order to use a common lens barrel, the edge thickness dimensions of the individual lenses should be the same.

[Effect]

How the above-mentioned means works will be described below using the diagram. When the projection lens has a magnification of 8.4 times (compatible with 45 inches) as shown in Figure 1 with a 4-group configuration, the burden of aberration correction is mainly for the first group lens 1, which corrects spherical, coma, and astigmatism. The third group lens 3 corrects high-order comatic aberration, and the fourth group lens 4 corrects field curvature and astigmatism.

Next, when trying to use such a lens at a magnification of -10.2 times (compatible with 55 inches), the projection distance and lens spacing (distance between lenses 3 and 4) 1b,
If , the correction of spherical aberration becomes overcorrection, and the correction of coma and astigmatism becomes insufficient. Therefore, in the present invention, by changing the surface shape of the first group lens 1, a part of its spherical aberration correction ability is divided into coma and astigmatism correction, and good aberration correction is performed over the entire screen, You get a high focus lens.

[Example] The present inventors studied the division of aberration correction in a lens having a four-group configuration as shown in FIG. As a result, by changing the projection distance and lens apertures 2 and 7 using the conventional method, a lens with a 4-group configuration as shown in Figure 1 with a design center magnification of 8.4 times was converted into a lens with a magnification of 10.2 times. (hereinafter, such conditions will be referred to as Condition I),
It has been found that the correction of spherical aberration in the first group lens 1 becomes overcorrection, and conversely, the correction of coma and astigmatism is insufficient.

Therefore, as mentioned above, the focus performance improves near the optical axis where the relative angle of view is small, as shown in Figures 5 and 6, and the MTF performance improves in areas where the relative angle of view is large. , MTI" performance has decreased significantly (especially in 5AGI).

In order to improve the imbalance of aberration correction and optimize the balance of aberration correction, instead of changing the magnification by changing the projection distance and lens distance Lff as in the conventional method, the first group It has been found that it is better to realize the change in magnification by changing the shape of the lens l.

FIG. 17 is a cross-sectional view of the lens shape when the shape of the first group lens l is changed based on the findings of the inventors. In the figure, the shapes of the S1 surface and the 82nd surface of the first lens group l and the lens distance ff16 for focus adjustment?
FIG. 7 compares the focusing performance when the condition (hereinafter referred to as condition ①) of changing the condition (hereinafter referred to as condition ①) (that is, the embodiment of the present invention) with that of the conventional example in which the above-mentioned condition ② is implemented. It is shown in FIG. Further, the lens data at this time is shown in Table 1.

In FIGS. 7 and 8, the focus performance (solid line) when condition (2) is implemented (that is, the embodiment of the present invention) is better.
It will be appreciated that this is a marked improvement over that of the conventional example (broken line) in which Condition I was implemented.

Next, according to the present invention, the shape of only 32 surfaces of the first group lens 1 is changed, and the lens spacing is improved! 1. and! FIGS. 9 and 10 show the focusing performance when the condition (hereinafter referred to as condition (2)) of changing 23 is implemented in comparison with that of a conventional example in which the above-mentioned condition (2) is in effect. Further, the lens data at this time is shown in Table 2.

Similarly, the conditions shown in the lens data (Table 3) (this is the condition
The focusing performance under the conditions shown in the lens data (Table 4) (this is referred to as condition ①) was compared with that of the conventional example under the above-mentioned condition I. 12.

Furthermore, the focusing performance when the conditions shown in the lens data (Table 5) (this is referred to as condition ①) is compared with that of the conventional example under the above-mentioned condition I, is shown in Figs. 13 and 14.
As shown in the figure.

In addition, the conditions shown in the lens data (Table 6) (this is the condition
) and the conditions shown in the lens data (Table 7) (this is referred to as condition (2)), the focusing performance was compared with that of the conventional example in which the above-mentioned condition I was implemented. As shown in FIG.

In the above implementation, a phosphor having the emission spectrum as shown in FIG. 3 was used.

From the above FIGS. 7, 8 to 15, and 16, it is clear that by changing the lens shape according to the present invention, focus performance M
It can be seen that the decrease in TF has been improved.

Referring again to FIG. 17. FIG. 17 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 same figure, Pl is the cathode ray tube fluorescent screen,
6 is a cathode ray tube panel, 5 is a cooling liquid, 4 is a fourth lens group, 3 is a third lens group, 2 is a second lens group, and 1 is a lens group.

The optical system shown in Figure 17 (and Figure 1) provides the best performance when the 5.4-inch raster on the cathode ray tube phosphor screen P is enlarged to 55 inches (10.2 times) on the screen. It is configured as follows.

The distance from the Luns group l to the screen is 952,1
mm, and the angle of view is 36 degrees. The 1st lens group eliminates spherical aberration, coma, and astigmatism based on the aperture.
It has an aspherical shape. The second lens group 2 is made of glass lenses in order to reduce focus drift due to temperature changes, and its power is made as large as possible.

The third lens group 3 has an aspherical structure to eliminate high-order coma and astigmatism, and has a power as small as possible. The fourth lens group 4 is a lens for correcting field curvature. In addition, the distance between the phosphor screen and the concave lens is increased to achieve high contrast.

Furthermore, in order to dissipate the heat generated from the cathode ray tube by convection, a sufficient amount of 1γ of the cooling liquid is provided.

Further, the fluorescent screen P of the cathode ray tube 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.

1/'IQ, the phosphor screen P1 of the cathode ray tube panel 6 is manufactured by Blaine molding without any post-processing. Therefore, the manufacturing method itself does not change whether the molded shape is spherical or aspherical.

On the other hand, the lenses of this lens system are designed to minimize the power of the plastic lenses, resulting in thin walls, and by reducing the difference in thickness between the center and the periphery, we aim to improve moldability. There is.

Specific lens data that can be taken by this lens system is shown in Tables 1 to 7, which were referred to above. All lenses have an F number of 1 or less, making them extremely bright lenses.

Also, the angle of view is 36 degrees.

How to read Table 1 will be explained below. The 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 flat surface), an effective radius guaranteed in terms of optical performance (ramp radius) of 750 m + n, and a distance on the optical axis from the screen to the surface S1 of the luns group l (surface spacing). 952.1 mm, and the refractive index of the medium (air) between them is 1°0. Also, the radius of curvature of the S7 surface of the first lens group is -1
00,03+++m (the center of curvature is on the phosphor screen side), and the distance between lens surfaces S1 and 32 on the optical axis (plane distance) is 9.0 m
m, and the refractive index of the medium therebetween is 1.49345.

In the same way, the final step is the fluorescent screen P1 of the cathode ray tube panel 6.
The radius of curvature is 341.28+n@, the radius of the gangway is 72
．． 4 mm, and the thickness of the CRT panel 6 on the optical axis is 13.
4 mm and a refractive index of 1.53994.

Next, surfaces S, , S2 . Aspherical coefficients are shown for the surfaces S, , S of the third lens group 3, the surface S7 of the fourth lens group 4, and the phosphor surface P1.

Here, the aspherical surface coefficient is a coefficient when the surface shape is expressed by the following equation.

10AE-r'+AF-r'+AG-r"+AH-r"However, Z is the lens when the optical axis direction is taken as the Z axis and the radial direction of the lens is taken as the r axis, as shown in Figure 4. represents the height of the surface (a function of r), where r indicates the radial distance, and Ro
indicates the radius of curvature.

Therefore, if the CC, AE, AF, AC, and AH coefficients are given, the height, or shape, of the lens surface is determined according to the above formula.

Further, in Table 1, both surfaces of the second lens group 2 and the surface S8 of the fourth lens group 4 have aspherical coefficients of all zero, indicating that they are spherical surfaces.

The above is how to read the data shown in Table 1.

As already mentioned, Tables 2 to 7 show specific examples of other lens data.

As explained above, by using the lens of the present invention, it is possible to realize a lens that can handle up to high magnification without reducing the focus with minimal changes in the lens shape.

Next, we will discuss a method for processing the lens edge that can be used without changing the lens barrel dimensions even if the lens shape is changed.

FIG. 18 shows the state in which the lens group l is attached to the inner lens barrel 8. Due to a design change, the lens surface St (
(broken line) moves to the 32' plane (solid line), and the sag amount increases by l. In order to absorb this, the radius of curvature of the arc at the joint between the lens edge and the aspherical region (connected by a circular arc in the figure) is changed from R2 to R.

By setting (R2>R1), increases and decreases in edge thickness are absorbed.

FIG. 19 is an enlarged view of FIG. 18 and shows the case of connecting by an arc, and P+ and Pg each form the center of the circle of the arc connection.

FIG. 20 shows a case where the connection between the aspherical region and the lens surface diameter is a straight line. It goes without saying that the length of the straight part (indicated by diagonal lines in the figure) must be changed in order to absorb the increase or decrease in edge thickness.

〔Effect of the invention〕

According to the present invention, the lens barrel of a conventional lens can be used as is, and by making small changes to the lens surface shape and lens spacing, it is possible to obtain a lens for projection television receivers with good image quality up to a large screen of 55 inches. be.

Table 1 (Part 1) (Hereafter, margin)

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a lens for a projection television receiver that can be used to explain the present invention in detail, FIG. 2 is a longitudinal sectional view of the projection television receiver, and FIG. 3 is an emission spectrum of a phosphor. FIG. 4 is an explanatory diagram used to explain the definition of lens shape, FIGS. 5 and 6 are characteristic diagrams showing the MTF characteristics of conventional lenses, and FIGS. 7 to 16 are diagrams showing the MTF characteristics of conventional lenses, respectively. Characteristic diagram showing MTF characteristics of a lens as an example, No. 17
The figure is a side cross-sectional view of a lens for a projection television receiver that can be used to explain the present invention in detail, and FIGS. It is a sectional view showing an example. Explanation of symbols 1... 1st lens group, 2... 2nd lens group, 3...
3rd lens group, 4... 4th lens group, 5... Coolant, 6... Cathode ray tube panel, Pl... Fluorescent screen agent Patent attorney Akira Namiki 2 S Male 3 G Hen 4 Figure 2 (Ji90000 Mei 7 Ward 75 Zu Zuzo 6 Zu Chome) 1 stroke A Figure sl0ffi 1 day illness/Bird angle calculation 11 g 112 Figure Hawk 15E! ! 6 2 No. 133 Z I J S: A ; r J plexus 18E4 @20 figure

Claims (1)

[Claims] 1. A lens for a projection television receiver used when enlarging and projecting an image on a cathode ray tube phosphor screen onto a screen, comprising:
In order from the screen side, the first group includes a meniscus lens with convex surfaces on both sides relative to the screen, the second group includes a biconvex positive lens, and the third group includes a lens with a weak positive refractive power with a biconvex center. , and a fourth group including a negative lens having a concave surface on the screen side. In a lens for a projection television receiver, the first group constituting the first group is arranged in the following order when the magnification is changed. By changing the surface shape of either the front or back of the lens, or both, and changing the spacing between the constituent lenses, it is possible to maintain the required focus performance corresponding to the changed magnification while using the same lens barrel. Characteristic lenses for projection television receivers. 2. The lens for a projection television receiver according to claim 1, wherein the shape of both surfaces of the second lens group constituting the second group is also changed. 3. In the lens for a projection television receiver according to claim 2, when changing the magnification, only the shape of the lens surface facing the second group side of the first group lens constituting the first group is changed;
The edge thickness dimensions of the first group lens and the second group lens are made the same before and after the magnification change, and while using the same lens barrel before and after the magnification change, the required focus performance corresponding to the magnification after the change is achieved. A lens for a projection type television receiver, characterized in that: