JPS61226720A - Projection lens - Google Patents

Abstract

PURPOSE:To obtain a compact projection lens by composing the lens of a positive meniscus lens, a positive biconvex lens, and a negative meniscus lens successively from a screen side and specifying the power distribution ratio of the 1st and the 2nd lenses. CONSTITUTION:The projection lens consists of the 1st, the 2nd, and the 3rd lenses successively from the screen side; the positive meniscus lens having its convex surface on the screen side, the biconvex lens having its convex surface on the screen side, and the negative meniscus lens having its large-curvature concave surface on the screen side. Then, the power distribution ratio of, specially, the 1st and the 2nd lenses is specified as shown by inequalities. Further, the 1st and the 3rd lenses are made of plastic and at least one surface is preferably made aspherical to correct aberrations; and the 2nd lens is made of glass to suppress the quantity of focus movement due to variation in ambient temperature within a range of practical use. Consequently, the lens is compacted and the spherical aberration, astigmatism, curvature of field are compensated excellently although the aperture ratio is large.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a projection lens, and particularly to a projection lens for a video glo projector that projects a CRT image to obtain a large screen.

(Prior Art) Conventionally, projection lenses for enlarging and projecting the CRT image of a television receiver onto a screen have been made entirely of glass lenses, made entirely of glass lenses, or made entirely of glass lenses. When a projection lens is constructed with a lens, a large focal point shift occurs due to a change in the ambient temperature, so projection lenses of a hybrid construction, which is a combination of a glass lens and a plastic lens, are known. In general, in a video glo projector using three CRTs, the monochromatic CRT images of green, red, and back are enlarged and projected using a projection lens, so there is no need for chromatic aberration correction. Therefore, a simple configuration of 3 elements in 3 groups consisting of the first lens with positive power, the @2 lens, and the third lens with negative power for correcting the curvature of the surface is possible, so it is possible to achieve a large aperture. For example, JP-A-55-1241
No. 14, JP-A-57-34515, JP-A-Sho 5
It is known from JP-A No. 8-118616, Japanese Patent Application Laid-open No. 59-219709, etc.

(Problems to be Solved by the Invention) However, such conventional projection lenses have a small number of lenses, and although they have achieved a large aperture ratio, they lack compactness.In recent years, video projectors have been developed. As the applications expand, there is an increasing need to reduce the size of the video projection lens, especially its depth.One of the ways to achieve this is to make the projection lens a conduit.For example, If we define the relative lens length as the length from the screen-side apex of the first lens to the CRT-side apex of the third lens divided by the focal length f of the entire system (Llf), then this relative lens length is the projection lens's focal length (Llf). / Indicates ducting]
It serves as an indicator of In the conventional example described above, Llf = 1.
Ashi in the range of 36 to 2.22, not small enough, video! There was a problem in converting Rozoecta into a hut.

(Means for Solving the Problems) Next, the projection lens of the present invention which solves the above problems includes a first lens which is a positive meniscus lens with a convex surface facing the screen side; The second lens is a positive biconvex lens with a weakly convex surface facing the screen, and the third lens is a negative biconvex lens with a strongly concave surface facing the screen. By appropriately adjusting the power distribution ratio of the second lens, the relative lens length can be reduced, that is, conductivity can be realized.

(Function) By satisfying the above configuration and each of the following conditions, the aperture ratio]: 1.04, half angle of view 28°, relative lens length 1.1
68 to 1.174, which is high performance and has achieved connectivity.

Condition 1.1 <f1/f2 <1.2
(1) 0. e<f/f1<0.7s
(2) 0.75<f/f2<0.85
(3) However, f: focal length of the lens, f2: focal length of the second lens, f: focal length of the entire system.

Condition (1) defines the power distribution between the @luns and @2 lenses. If the lower limit is exceeded, it is advantageous for compactness, but it becomes difficult to correct sycoma aberration, which requires a large share of the power of the fJEI lens. If the upper limit is exceeded, the controller/
This is disadvantageous for ducting.

Condition (2) is a'? of the first lens with respect to the entire system. This stipulates the distribution of funds. If the lower limit is exceeded, it will be disadvantageous for conducting/ducting. Beyond the upper @, it is advantageous to conduct/duct, but the off-axis lower rays are strongly refracted and significant comatic aberration occurs, making correction difficult.

Condition (3) defines the power distribution of the second lens to the entire system. If the lower limit is exceeded, it will be advantageous to reduce the number of squares to four, but it will be difficult to correct coma aberration. If the upper limit is exceeded, it will be disadvantageous for conducting/ducting.

In order to make the video glossor smaller, the relative lens length should be made smaller and the projection lens f should be made more compact.
It is better to widen the angle of view and shorten the distance from the screen to the tip of the projection lens.@K, which aims to improve performance by suppressing the increase in astigmatism that accompanies widening the angle of view, should have a concentric lens configuration. desirable. That is, it is necessary to use a lens shape and arrangement that can reduce the angle of incidence of the principal ray with respect to the lens surface. For this purpose, it is desirable to satisfy each of the following conditions.

Condition 3.5 (r2 / r 1(5,5(')4
, 5(r6/r5(7,s (5), r: radius of curvature of the lens surface on the screen side of the first lens, r2: radius of curvature of the lens surface on the CRT side of the first lens, r5: II 3 Radius of curvature of the lens surface on the screen side of the lens, r6: Radius of curvature of the lens surface on the CRT side of the third lens.

Condition (4) is the screen-side curvature radius of the first lens and C
This defines the ratio of the radius of the RT side curved car.

Similarly, condition (5) defines the ratio of the screen side radius of curvature to the CRT side radius of curvature of the third lens.

If the lower limit of the conditions (4) or 5) exceeds the upper limit, the concentric state will be deviated from, and off-axis performance with a large astigmatism difference will deteriorate.

In order to achieve even higher performance, it is better to increase the degree of freedom in design and improve the aberration correction ability. In the projection lens according to the present invention, the first lens and the third lens are made of glass lenses, at least one surface of the first lens is an aspherical surface, and at least one surface of the third lens is an aspherical surface. It is desirable to correct the aberrations. On the other hand, by using a glass lens as the second lens that shares the power of the optical system with respect to the entire system, the amount of focus movement due to changes in ambient temperature can be kept within a practical range.

(Example) Examples of the present invention are shown below.In each example, rl #
12 e r3... represents the radius of curvature of each lens surface in order from the screen side, d, , d2. d...
is the lens thickness and lens spacing% of each lens nl *
n2 * n4... is the wavelength λ of each lens = 546
Refractive index for am, C4. C2. C5 has wavelength λ=54
Atsube's number for 6 nm, fl z f2 is the focal length of each lens, the second lens, I is the focal length of the entire system, and L is the distance from the screen side apex of the first lens to the CRT of the third lens.
This is the length to the side apex. Also, the surface marked with * is an aspherical surface, and its shape is as follows in a rectangular coordinate system with the original axis direction as the X axis:
The vertex curvature radius 'ir+K is the conic constant, AD, AE
.

When AF and AC are high-order constants, it is a rotationally symmetric aspheric surface with ρ=5 ears 7. F represents the 7th grade of CRT.

Tatami tatami tatami tatami mat
, 3, 5, and 7, and the aberrations of each example are shown in FIGS. 2, 4, and 6.

Each is shown in FIG. Figures 1, 3, and 5.

In the lens power distribution diagram of each embodiment shown in FIG. 7, 1 is the first lens, 2 is the second lens, 3 is the third lens, and 4 is the face plate of the CRT.

(Effects of the Invention) As described above, according to the present invention, it is possible to realize a compact lens, and even with a large aperture ratio, spherical aberration, astigmatism, and curvature of the surface are favorably corrected. , the distortion aberration is positively shifted in accordance with the characteristics of the CRT deflection system, thereby reducing the correction burden on the circuit. These make it possible to downsize the video projector, which has great industrial value.

[Brief explanation of the drawing]

11EI and FIG. 2 are lens arrangement diagrams and aberration diagrams in the first embodiment of the present invention, and FIGS. 3 and 4 are diagrams. Lens arrangement ■ and aberration diagrams in the second embodiment, Figures 5 and 6 are lens arrangement diagrams and aberration diagrams in @3 embodiment,
The 1ET diagram and FIG. 8 are lens arrangement diagrams and aberration diagrams in the fourth embodiment. 1...GL lens, 2...2nd lens, 3...3rd lens, 4...CRT face plate. Figure 1 1 - 1st Shinmata 1 2... 2nd Lens 3... Cliff 3 Shinde 4 - CRTq 7c4 Soubret Plan 2 Figure 3 Shout M4 Figure Figure 5 6 Figure 11 Mebet Non-port history Kinkyoku Tore Figure 7

Claims (3)

[Claims] (1) In order from the screen side, a first lens is a positive meniscus lens with a convex surface facing the screen side, and a second lens is a positive biconvex lens with a weakly convex surface facing the screen side,
A projection lens comprising a third lens of a negative meniscus lens with a strongly concave surface facing the screen side, and satisfying the following conditions: Condition 1.1<f_1/f_2
<1.2 (1) 0.6<f/f_1<0.75 (2
) 0.75<f/f_2<0.85 (3) However, f_1 is the focal length of the first lens, f_2 is the focal length of the second lens, and f is the focal length of the entire system. (2) The first, second, and third lenses meet the condition (1),
A projection lens according to claim (1), which satisfies (2) and (3) and further satisfies the following condition: Condition 3.5<r_2/r_1<5.5 ( 4) 4.5<
r_6/r_5<7.5 (5) However, r_1 is the radius of curvature of the lens surface of the first lens on the screen side, r_2 is the radius of curvature of the lens surface of the first lens on the CRT side, and r_5 is the radius of curvature of the lens surface of the first lens on the CRT side. r_6 is the radius of curvature of the lens surface of the third lens on the CRT side. (3) At least one surface of the first lens is an aspherical surface, at least one surface of the third lens is an aspherical surface, the first lens and the third lens are plastic lenses, and the second lens is a glass lens. A projection lens according to claim (1), characterized in that: