JPH03131808A - Projection lens - Google Patents

Abstract

PURPOSE:To obtain a projection image which has a bright peripheral part by composing the projection lens of 1st - 7th lenses, i.e. seven lenses in order and compensating aberrations under specific conditions. CONSTITUTION:The 1st lens L1 compensate a spherical aberration and a comatic aberration, the 2nd lens L2 compensates a chromatic aberration, and the 3rd lens L3 compensates an aberration pertaining to an increase in the diameter; and the 4th lens L4 and 5th lens L5 has refracting power which is the majority of the refracting power of the whole system, and compensates a chromatic aberration by the combination of the positive lens with the negative lens, the 6th lens L6 compensates the aberration of the circumferential part of a picture plane, and the 7th lens L7 compensates curvature of field. Then requirements shown by inequalities I - IV are met and at least one surface of the lenses L1, L3, and L6 is made aspherical. In the inequalities I - IV, nu2 is the Abbe number of the 2nd lens L2, nu4 and nu5 are the Abbe numbers of the positive and negative lenses of the 4th and 5th lenses L4 and L5, (f) is the focal length of the whole system, f2 is the focal length of the 2nd lens L2, and f5 is the focal length of the negative lens of the 4th and 5th lenses L4 and L5. Consequently, an image with high definition can be projected brightly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a projection lens for a projector suitable for enlarging and projecting a high-definition image on a screen of a cathode ray tube.

[Prior art] In recent years, with the advent of high-definition television, the F value has increased to 1.0.
There is a need for a projection lens for a projector that is reasonably bright and capable of enlarging and projecting 100 OTV images.

In general, a projector projects images from three independent red, green, and blue cathode ray tubes using three different projection lenses for each color, so correction of chromatic aberration has been considered unnecessary. However, when projecting 100 OTV images, it is necessary to correct chromatic aberration caused by the emission spectrum of the phosphor.

JP-A-61-249014, JP-A-64-322
No. 15 describes a projection lens that is corrected for chromatic aberration with an F value of about 1.05.

However, these lenses are insufficiently corrected for chromatic aberration due to their large apertures, and their imaging performance is insufficient when projecting high-quality images of about 100 OTVs.

For example, in the first example of JP-A-61-249014, the longitudinal chromatic aberration of the d-line and FIIA for a lens with a focal length of 100- is about 0.8 m regardless of the height of ll. However, as the pupil height increases, the lateral chromatic aberration that affects imaging performance also increases, so as the pupil height increases, it is necessary to reduce the longitudinal chromatic aberration.

[Problems to be Solved by the Invention] The above-mentioned conventional techniques are insufficient in correcting aberrations, and in particular, are insufficient in correcting chromatic aberrations associated with larger apertures.

The present invention has a bright F value of 1.051i degrees, and enables the projection of high-quality images.Furthermore, an interference film is provided in close contact with the inner surface of the glass panel and between it and the phosphor layer.

It is an object of the present invention to provide a projection lens capable of obtaining a projected image with a bright peripheral area even when combined with a cathode ray tube having directivity in the light emission direction.

[Means to solve the problem] In order to achieve the above object, the present invention.

From the screen side, a positive first lens with an aspherical surface on at least one surface, a negative second lens, a positive third lens with an aspherical surface on at least one surface, a positive lens and a negative lens, or a negative lens and a positive lens. the fourth and fifth lenses, at least one
The structure consists of seven lenses arranged in the following order: a negative sixth lens with an aspheric surface, and a seventh lens with a strongly concave surface facing the screen, and despite its large aperture and wide angle, it eliminates various aberrations. I have made sufficient corrections.

[Effect]

The first lens of the lens of the present invention corrects spherical aberration and coma, and the second lens corrects chromatic aberration.

The third lens corrects aberrations caused by increasing the aperture.

The fourth and fifth lenses have most of the refractive power of the entire system, and correct chromatic aberration by a combination of a positive lens and a negative lens. The sixth lens corrects aberrations in the peripheral areas on both sides,
The seventh lens is for field curvature correction.

In order to fully perform the above correction function, the first lens,
It is desirable to use an aspherical surface on at least one surface of each of the third lens and the sixth lens.If the fourth and fifth lenses are made of glass, it is possible to realize a lens with small focus shift due to temperature.

In order to effectively remove chromatic aberration, it is desirable to satisfy the following conditions.

ν, kuν, ...(1) ν, <ν, ...(2) -0,5<f/f, <-0,3...(3) -0,6<
f/f, <-0,4. (4) However, ν3 is the Abbe number of the second lens, and ν is the fourth lens. Each of the fifth lenses is a positive lens.

The Abbe number of the negative lens, f is the focal length of the entire system, and f3 is the second
The focal length of the lens, f, is the focal length of the negative lens among the fourth and fifth lenses.

Equations (1) and (2) are conditions for correcting longitudinal chromatic aberration. Equations (3) and (4) are conditions for correcting lateral chromatic aberration that accompanies an increase in aperture. If the lower limit of equations (3) and (4) is exceeded,
The refractive index of the negative lens increases, and the chromatic aberration of light rays away from the paraxial axis increases.

If the value exceeds 1 in equations (3) and (4), the ability to correct chromatic aberration decreases.

In order to reduce the F value of the lens, it is desirable to satisfy the following conditions.

0.4<f/f, <0.6 ・ (5) 0.6<D/
f<0.8 (6) where f is the focal length of the entire system, fl is the focal length of the first lens, and D is the distance between the fifth lens and the fluorescent surface of the cathode ray tube.

Equation (5) defines the power distribution of the first lens in the entire system, and Equation (6) defines the positions of the fourth and fifth lenses. According to formula (5), if the first lens has a large power, the power of the entire system will depend on the screen side. The fifth lens can be moved closer to the fluorescent surface side. This effect makes it possible to widen the angle at which light from the center of the fluorescent surface is taken in by the lens.

If the upper limit of equation (6) is exceeded, the angle at which the light at the center of the phosphorescent surface is captured by the lens becomes small, making it impossible to reduce F[. If the lower limit of equation (6) is exceeded, it becomes impossible to reduce aberrations at the periphery of the screen.

A cathode ray tube that adheres closely to the inner surface of the glass panel of the tube and has an interference film between it and the phosphor layer to provide directivity in the direction of light emission is the Niss I Day-88 Digest (SID).
DIGEST 88), pages 218-221. This cathode ray tube with a lamp has the characteristic of increasing the brightness in a direction close to perpendicular to the fluorescent surface and reducing the brightness in a direction that is significantly different from that direction, and by using this cathode ray tube, the brightness of a projector can be greatly increased. .

Figure 2 shows the brightness distribution of a cathode ray tube with an interference film, which was created from Figure 4 of the SID data, at an angle α between the normal to the panel's fluorescent surface.
The vertical axis shows the brightness of a cathode ray tube without an interference film at 1
When α is 0 to 35 degrees, which indicates the relative brightness when
Cathode ray tubes with interference films have higher brightness than regular cathode ray tubes.
With an F1.0 lens, the light emitted from the center of the phosphor screen and captured by the lens will spread by up to 26 degrees before reaching the cathode ray tube panel glass, so if you use a cathode ray tube with an interference film, It is possible to project brighter images than with ordinary cathode ray tubes.

However, when the light from the periphery of the screen is incident at an angle of 35 degrees or more with respect to the normal to the cathode ray tube panel surface.

There is a possibility that the amount of peripheral light will deteriorate. In order to avoid this, in the present invention, the effective radius H of the seventh lens on the screen side is
1 and the distance H2 from the optical axis of the light beam of the fluorescent surface object height 1.

0.77<H1/H2...(7) In the present invention, when a normal cathode ray tube is used, a peripheral illuminance ratio of 30% can be secured if the light beam at an object height of 1 is spread by 25 degrees on the fluorescent surface. Available for use. When using a cathode ray tube with an interference film, in order for the luminous flux at object height 1 to spread to 25 degrees and the light intensity not to decrease, from Figure 2, it is necessary to capture light whose luminous flux at object height 1 is 20 degrees or less. be. Therefore, between Hl and H2 (
7) Eq.

[Example] FIG. 1 is a block diagram of a lens according to a first example of the present invention. In addition, the lens data is shown in Table 1 on page 11. In order from the screen side, the second lens L2, the second lens L2, and the third lens
Lens I, 3, fourth lens L4, fifth lens L5. 6th
Lens L6, seventh lens L7. It consists of a cooling liquid (mixture of ethylene glycol and glycerin) E and a cathode ray tube glass panel P. In Table 1, f is the focal length of the entire system, R is the radius of curvature, T is the interplanar spacing, CL is the effective radius, N is the refractive index of the medium at a wavelength of 545 nm, and ν is the Abbe number of the d-line. CG, AD, AE, AF, and AG are aspheric coefficients, which are included in the following equation when the displacement amount 2 of the lens surface in the optical axis direction is expressed by the distance r from the optical axis.

The lens of the first example is for a 110-inch screen, with a magnification of 17.7 times, an F value of 1.06, and a half angle of view of 22.4.
degree. 1st. The third, sixth, and seventh lenses are lenses that use aspheric surfaces, and the first and third lenses eliminate comatic aberration and spherical aberration, the sixth lens eliminates aberrations at the periphery of the screen, and the seventh lens eliminates field curvature. Corrected Table 1 [I implementation wholesale f=183. o F value=1.06 Double L17.7 Half stroke*22. [ Na RT CL N ν
o O,03397,0 book 1 133,85 29.0 g6 1.
4935 57.8* 2 423.74 18
．． 981 863 -800.0 4.0 86
1.7921 25.74 800.0
45.579 86*5 -4974.6 17.
0 86 1.4935 57. Jl Ne 6 -72
5.47 2.833 86? 117.09
60.0 84 1.6229 60.38
-185.0 4.0 &4 1.7921
6.79 -594.80 32.172 84
$10 813.46 10.687 72 1
．． 4935 57.8$11 732.91 46
．． 715 67 pieces 12 -82.844 6
．． 5 64 1.4935 57.8
13 -100.0 17.625
67 1.444714 G, 0
14.0 1.539915 -1000.
0...Aspherical surface Aspherical surface coefficient CCAD AE AF A
Gl-6,590893,01610X104-4
．． 49745X10-"5.19540X10"-
4,36065X10””2 -7.15697-4.
221137X10'-4,74774X10-"
3,98515xlO"-9,76709X10"5
-3254.50-2.84813XlO” -9,
19185X10”-8, 17676X1O”2.
44160X10"6 -25.2782-2.361
77X10'-1, 20170X10-” 8.E1
641XlO"'2.85166X10"10 1
20.11O5-6,01091X10°'-5,6
2218XlO"3.70942X1σ"-3,72
439XIG”11 44.7333-3.05116
XlO'-2,88778XlO" 3.40735
110”-2,93989X10”12-2.67
658-1.67016xlO°' -1,03298
xlO"2.97026xlO" -4,42624
The second and fifth concave lenses, which have an angle of xlO'', perform chromatic aberration correction together with the first and fourth convex lenses.

The spherical aberration and astigmatism on the fluorescent surface of this lens are shown in FIGS. 3(a) and 3(b), respectively, and the lateral aberration at zero extra height is shown in FIG. 4.

For comparison, Japanese Patent Application Laid-Open No. 61-249014
Spherical aberration of lenses described as examples.

The astigmatism is shown in FIGS. 5(a) and 5(b), and the lateral aberration at a special height of 0 is shown in FIG. 6. The lens of the first embodiment of the present invention has a focal length that is smaller than that of the conventional lens. Despite being 1.8 times longer, the paraxial chromatic aberration is about half that.

Furthermore, it has the characteristic that the longitudinal chromatic aberration becomes O at a position where the height of the lens is high, which is effective in reducing the lateral chromatic aberration, which indicates the imaging performance, at a position where the pupil height is high.

The fluorescent surface on the inner surface of the panel of the cathode ray tube used in combination with the lens of the present invention has a spherical shape with the convex surface facing the electron gun side, and is designed to take in a large amount of light per periphery. The lens of the first example secures a peripheral light amount ratio of 49%.

Even when using a cathode ray tube in which an interference film is provided between the inner surface of the cathode ray tube panel glass and the phosphor layer to improve brightness in a direction close to perpendicular to the phosphor surface, the extra-high 1. The light of 13.7~ to the cathode ray tube panel glass with respect to the normal to the fluorescent surface.
Since the light is incident at an angle of 49.2 degrees, a sufficient amount of peripheral light can be obtained.

FIG. 7 shows the MTF characteristics for the edge wall light body of the first embodiment. *The relative brightness ratio of the three wavelengths of 490 nm, 545 nm, and 590 nm was calculated as 1:3:l.

Spatial frequency was calculated using an aspect ratio of 16:9.

It shows good MTF characteristics even with 1000 TV lines, indicating that it is a lens that can be used for high-definition television.

Second. Third. The lens data of the fourth example is
The MTF characteristics are shown in Table 2 on page 4, Table 3 on page 15, and Table 4 on page 16, and FIGS. 8, 9, and 10, respectively.

f/f□, f/f, f/f, , D/f, H of each example
The values of 1/H2 are summarized in Table 5 on page 17. In the fourth example, the value of H1/H2 is (7) formula % formula % Table 3 (2) 3 implementation wholesale f = 181.3 FiE = 1.05 times ≠ 17.8
Half-stroke 422.4 degrees RTQ.

0.0 3397.0 129.16 26.0 86 328, +5 21. μ5186 -800.0 4.0 86 800.0 47.8'+2 86377.76
17.0 86 2・175.3 2. B33 86122.17
Shit, o g.

-1&5.0 4.0 8゜-614,8644,95880 1203,110,68760 614,2639,60260 -85,36,559,5 -100,013,625B1 0.0 14.0 -1000.0 ...Aspherical surface 1.4935 1.7921 1.4935 57.8 25.7 57.8 1.6229 ω, 3 1.7921 25.7 1.4935 1.4!11. '(5 1,4447 1,5309 57,8 57,8 Table 4 (2) 4 implementation wholesale f = 180.2 F value = 1.05 times L-17.
8 Half 1i square duck 2. [NaRTCLN ν o O, 03400, O ml 129.12 22.0 86 1.
4935 57.8 pieces 2 315.52 24.1
93 863 -900.0 4.0 86
1,7921 25.74 900.0 49
．． 829 Part 5 O2.36 13.0 8
6 1.4935 57.8*6 44g, 6
2.5 867 124.66 54.0
80 1.6229 60.38 -170.0
4.0 80 1.7921 25.79 -
526.89 44.717 Open book 10 B
274,9 10.687 60
1.4935 57.8to 11g3,5
38.994 60 pieces 12 -8:11.8
82 6.5 58.5 1.4
935 57.813 -100.0 13.
625 60 1.449714 0.0
14.0 1.539915 -1000.0 book...) Four-sided aspheric coefficient CCAD AE AF A
Gl-7,730733,91417×10”-6
,03Z34xtσ''6.85a55X10°14-4
．． 48169xlσ”2 1.06483-2,086
75X10'-9,12774X10"" 1,49
162X10-"-1,60838X10"'5 0
．． 0 -1.66115X104-5.73876X
10"-3,16367XlO°" 3.29654
xlO"6 0.0 -1.26032X1σ' -
1,46947X1σ"-1,41114X10"
1.84366X1σ"10205.764 -7.0
3739X104-5.65617X10" 5.45
082X10”-5,68017X10”11-44
．． 6086 -4.24523X10-7-6.449
69X10""4.19783X10-"-3,2
2195X10-12-3.36074-1.8789
7X10"-8,35774X10" 2.1862
6X10''-2,46664XIO-'' is not satisfied because it is not compatible with cathode ray tubes with interference films.

In the examples shown in Table 5 and above, the fourth lens is positive and the fifth lens is negative, but it is possible to obtain the same effect even if the fourth lens is negative and the fifth lens is positive. Effects As explained above, according to the present invention, a lens with an F value of about 1.05 that can brightly project a high f'#l image can be obtained, and in particular, the chromatic aberration that accompanies a large aperture is corrected. 10
This is effective when projecting high-quality images of about 0 OTV lines. Furthermore, by using an aspherical plastic lens, the number of lenses can be reduced by one and the weight can be reduced compared to an all-glass projection lens.

Also, when used in combination with a cathode ray tube with an interference film, 1
It is possible to project an image without deteriorating the amount of peripheral light.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the lens configuration of the first embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the angle α to the normal to the fluorescent surface of the cathode ray tube with an interference film and the relative brightness in that direction, and FIG. (a) is a spherical aberration diagram of the lens of the first example, and FIG. 3(b) is an astigmatism diagram of the lens of the first example. FIG. 4 is a diagram showing the transverse aberration of the lens of the first example at an extra height of O. Fig. 5(a) is a spherical aberration diagram of a comparative lens, Fig. 5(b)
) is an astigmatism diagram of the comparative example lens, Figure 6 is a lateral aberration diagram of the comparative example lens at special height 0, and Figure 7 is the MT of the first example lens.
F characteristic diagram, FIG. 8 is an MTF characteristic diagram of the second example lens,
FIG. 9 is an MTF characteristic diagram of the lens of the third example, and FIG. 10 is an MTF characteristic diagram of the lens of the fourth example. Ll...first lens, L2...second lens. L3...Third lens. L4... 4th lens. L5...Fifth lens, L6...Sixth lens. L7...Seventh lens, E...Cooling liquid, P...l1 triode tube panel. Nu 10 20th 5 0 5 0 Be (A) M3 Figure 4 Collection destination (goods 0) -・-4qO1lviewΣ)-LL Ward Σ%-LL MeΣ)-LL Me

Claims (1)

[Claims] 1. In a projection lens for a projection television that enlarges and projects a display image of a cathode ray tube onto a screen, from the screen side, a positive first lens having an aspherical surface on at least one surface, a negative lens having an aspherical surface on at least one surface; 2 lenses, a positive third lens having an aspherical surface on at least one surface, a fourth and fifth lens consisting of a positive lens and a negative lens or a negative lens and a positive lens, and a negative sixth lens having an aspherical surface on at least one surface. , has seven lenses arranged in order, with the seventh lens having a strongly concave surface facing the screen, and the second lens having a strongly concave surface.
A projection lens that satisfies the following conditions: ν_2<ν_4 ν_5<ν_4, where the Abbe number of the lens is ν_2, and the Abbe numbers of the positive lens and negative lens among the fourth and fifth lenses are ν_4 and ν_5, respectively. . 2. In the projection lens according to claim 1, when the focal length of the entire system is f, the focal length of the second lens is f_2, and the focal length of the negative lens among the fourth and fifth lenses is f_5, the following conditions are satisfied. A projection lens that satisfies -0.5<f/f_2<-0.3 -0.6<f/f_5<-0.4. 3. In the projection lens according to claim 1, when the focal length of the entire system is f, the focal length of the first lens is f_1, and the distance between the fifth lens and the fluorescent surface of the cathode ray tube is D, the following conditions are satisfied. A projection lens that satisfies the following: 0.4<f/f_1<0.6 0.6<D/f<0.8. 4. In the projection lens according to claim 1, when the effective radius of the seventh lens on the screen side is H1, and the distance from the optical axis of the light beam at object height 1 on the fluorescent surface is H2, the following condition 0.77 is satisfied. A projection lens characterized by satisfying <H1/H2.