KR20010011949A - Projecting Optical System - Google Patents

Abstract

PURPOSE: A projection optical system is provided to compensate a chromatic aberration and a spherical aberration by using a DOE(Diffraction Optical Element) lens, so as to implement a high resolution of a rear projection device, and to distribute a refractive index to the DOE lens to maintain a capacity of the projection optical system. CONSTITUTION: The first lens(110) has a positive refraction index. The second lens(120) has a negative refraction index. The third lens(130) has a positive refraction index. A diffraction optical element(DOE) lens(140) has a positive refraction index. The fifth lens(90) has a negative refraction index. The first and the second lens(110,120) composed of plastic materials have functions of compensating spherical aberrations. The third lens(130) composed of a glass material manages an entire refraction index of a projection optical system. A fourth lens(80) and the fifth lens(90) composed of plastic lenses have functions of compensating an astigmatism and a field curvature. The DOE lens(140) has a structure of forming a diffraction optical surface(140a). The DOE lens(140) compensates a color aberration.

Description

Projecting Optical System

The present invention relates to a projection optical system of a rear projection device, and more particularly to a projection optical system configured to implement high resolution and high brightness.

In recent years, in the display device, a projection type device for displaying a desired image by expanding and projecting a small image using a projection lens has been rapidly spreading in response to the demand for large screen and high image quality. Such projection apparatuses are roughly classified into front projection apparatuses which project light beams to the front of the screen to display a desired image, and rear projection apparatuses which project light beams to the rear of the screen to enlarge and display a desired image. . Among them, the rear projection is spreading more due to the advantage of displaying a relatively bright image even in a bright environment. A representative example of such a projection display device using the rear projection method may be a projection television (hereinafter referred to as a "projection TV"). In projection TVs, cathode ray tubes (CRTs) or liquid crystal display panels (LCDs) for realizing an image corresponding to an image signal are mainly used. The internally implemented image is enlarged and projected by the projection lens and displayed on the screen. Hereinafter, the front and side internal structures of the projection TV using the rear projection method will be described with reference to FIGS. 1A and 1B.

Referring to FIGS. 1A and 1B, the rear projection displays a CRT 10 for displaying an image corresponding to an image signal, a projection optical system 20 for enlarging and projecting an image displayed on the CRT 10, and a projection optical system ( A reflector 30 reflecting the light beam projected by the light toward the screen 40, and a screen 40 for displaying the light beam enlarged by the projection optical system 20. As shown in FIG. 1A, three CRTs 10R, 10G, and 10B corresponding to red (R), green (G), and blue (B) converge on the G CRT (10G) from left to right. It is arranged to maintain the angle. Each CRT 10 is provided with a projection optical system 20 composed of a plurality of plastic lenses and glass lenses to enlarge and project an image. 2, the conventional projection optical system 20 will be described.

Referring to FIG. 2, the conventional projection optical system 20 includes a first lens 50 having a positive refractive power, a second lens 60 having a negative refractive power, and a third lens 70 including a doublet. And a fourth lens 80 having a positive refractive power and a fifth lens 90 having a negative refractive power. The first and second lenses 50 and 60 are made of a plastic material to correct spherical aberration. In addition, the fourth and fifth lenses 80 and 90 may be made of a plastic material to perform a function of correcting astigmatism. On the other hand, it is composed of a double lens (Doublet) of the third lens glass material to correct the chromatic aberration. In this case, the doublet can correct chromatic aberration by combining a lens having a positive refractive power and a lens having a negative refractive power, but the cost increases. As described above, the projection optical system 20 is composed of three to five lenses and is applied to the National Television System Committee (NTSC) class. In this case, when the projection optical system is composed of three pieces, the number of lenses can be reduced, so that the cost can be reduced, but the optical performance is deteriorated. Accordingly, the projection optical system usually consists of 4-5 lenses.

On the other hand, the configuration of the projection optical system shown in Figure 2 can be applied to NTSC class, but according to the trend that the display is high resolution, the rear projection apparatus also requires HD (High Definition) class to cope with this. In this case, if the existing NTSC-class projection optical system is applied to the HD level as it is, the ability to decompose the scanning line on the CRT is degraded due to aberration, distortion, etc. of the projection optical system, and the image quality of the image displayed on the screen is reduced overall. . In order to solve this problem, the number of lenses of the projection optical system should be increased, which is difficult to increase the cost and thickness of the rear projection apparatus. As a result, a new projection optical system capable of realizing high resolution and high brightness while reducing the number of lenses is required.

It is therefore an object of the present invention to provide a projection optical system configured to realize high resolution and high brightness.

1A and 1B schematically illustrate a rear projection.

2 is a diagram showing the configuration of a conventional projection optical system.

3 shows a projection optical system of the present invention.

FIG. 4 is a diagram illustrating diffraction characteristics with respect to the wavelength of the diffraction optical element of FIG. 3. FIG.

5 is a diagram showing a phase amount curve of a diffraction optical surface of the diffraction optical lens of FIG. 3;

6 is a characteristic diagram showing field-specific MTF characteristics of the projection optical system of the present invention.

7 is a characteristic diagram showing MTF characteristics of the projection optical system of the present invention.

8 is a characteristic diagram showing chromatic aberration characteristics of the projection optical system of the present invention.

<Description of the code | symbol about the principal part of drawing>

10: cathode ray tube 20: projection optical system

30: reflector 40: screen

50,110: first lens 60,120: second lens

70,130: third lens 80,150: fourth lens

90: fifth lens 140a: diffractive optical surface

In order to achieve the above object, the projection optical system of the present invention includes a diffractive optical element formed on at least one surface of the refractive lens.

Other objects and features of the present invention other than the above object will become apparent from the description of the embodiments with reference to the accompanying drawings.

With reference to Figures 3 to 8 will be described a preferred embodiment of the present invention.

Referring to FIG. 3, the projection optical system according to the present invention includes a first lens 110 having a positive refractive power, a second lens 120 having a negative refractive power, and a third lens 130 having a positive refractive power. And a diffraction optical element ("DOE") lens 140 having a positive refractive power, and a fifth lens 90 having a negative refractive power. The first and second lenses 110 are made of plastic and have a function of correcting spherical aberration. The third lens 130 is made of a glass material to cover most of the total refractive power of the projection optical system. The fourth lens 80 and the fifth lens 90 are made of plastic lenses and have a function of correcting astigmatism and field curvature.

On the other hand, the diffraction optical lens 140 has a structure in which the diffraction optical surface 140a is formed on a lens having positive refractive power. In this case, the DOE lens 140 corrects chromatic aberration. This will be described with reference to FIG. 4. As shown in FIG. 4A, the light beam having the color signal via the refractive lens has a focal length f of B shorter than a focal length of R. On the other hand, as shown in FIG. 4B, the light beam having the color signal via the DOE surface 140a can be seen that the focal length of R is shorter than the focal length of B. That is, the color signal dispersion characteristics of the refractive lens and the diffractive lens are opposite to each other. Accordingly, chromatic aberration is corrected using the DOE lens 140 having a DOE surface having diffraction characteristics formed on a surface of the plastic lens having positive refractive power. At this time, the corrected chromatic aberration characteristics in each field are shown in Figs. 8A to 8E.

On the other hand, in the DOE, diffraction occurs due to the interference between the object source and the reference source, and the aspherical phase of the DOE when the diffraction occurs is shown in Equation (1).

Here φ (r) means the phase at height r. c1 to c4 mean coefficients of phase terms having an aspherical effect. The characteristic diagram with respect to the phase amount of a DOE surface at this time is shown in FIG. The phase quantity characteristic graph is related to the number of revolutions of the diffractive optical surface, and the optimum design of the lens system by setting the phase amount in charge of the diffractive lens system is preferable to improve the optical performance considering the diffraction efficiency and the processability of the lens. In addition, referring to Equation 1, it can be seen that the phase of the DOE surface is changed at intervals of 2π. That is, the DOE lens 140 is formed to properly combine the characteristics of the aspherical surface and the diffractive optical element surface, thereby correcting chromatic aberration, spherical aberration, and distortion aberration. At this time, a plurality of concentric grooves are formed on the DOE surface to have rotational symmetry. In addition, the pitch of the DOE groove becomes smaller from the center of the DOE toward the periphery. In addition, since the DOE lens 140 does not have to use a lens of an expensive material having a separate negative refractive power and high dispersion for chromatic aberration correction, cost is reduced.

On the other hand, the third lens 130 having a positive refractive power is responsible for most of the total refractive power of the projection optical system. At this time, the shorter the focal length of the projection optical system becomes thinner the rear projection. To this end, the third lens preferably has a large refractive power, but when the refractive power is large, spherical aberration occurs. In order to solve this problem, the refractive power of the third lens 130 is distributed to the DOE lens 140 to increase the refractive power of the projection optical system, thereby reducing the overall focal length. This makes it possible to thin the rear projection apparatus. In addition, the pitch interval of the DOE surface 140a may be adjusted to correct spherical aberration according to the designer's intention. As described above, the projection optical system of the present invention can correct the chromatic aberration by the DOE lens 140 and reduce the rear projection value.

On the other hand, the projection optical system according to the present invention is to improve the resolution. This will be described with reference to FIGS. 6 and 7. Referring to FIG. 6, the MTF (Modulation Transfer Function) characteristic according to the height of the lens in the projection optical system of the present invention is illustrated. In this case, 1 'is an MTF characteristic diagram in the tangential direction when the spatial frequency is 3LP / mm and 3' is an MTF characteristic diagram in the sagittal direction when the spatial frequency is 3LP / mm. Meanwhile, referring to FIG. 7, the MTF characteristic of the projection optical system of the present invention is shown. In this case, T means a tangential direction and S means a sagittal direction. In addition, 0.0, 0.4, 0.6, 0.8, 1.0 mean the field of a projection optical system. As shown in FIG. 7, in the conventional NTSC-class rear projection apparatus in the projection optical system MTF characteristic diagram, the spatial frequency has an MTF characteristic of 50% at 3LP / mm, but the projection optical system of the present invention has a 50 to 3LP / mm range. MTF characteristics in the 75% range. It can be seen that the resolution is significantly improved compared to the resolution of the conventional NTSC rear projection apparatus. As described above, the projection optical system of the present invention is applicable to HD class.

In addition, the brightness of the lens is improved by the DOE lens 140. This is due to the brightness of the lens when the focal length is reduced by using the DOE lens 140. In this case, the focal length f and the brightness f # of the lens have a relationship as in Equation 2.

Here, D means the aperture of the lens. As shown in Equation 2, the brightness F / # of the lens is inversely proportional to the aperture D of the lens and is proportional to the focal length f. In other words, when the overall focal length of the projection optical system becomes smaller, F / # becomes smaller. Accordingly, the projection optical system of the present invention realizes high brightness.

As described above, the projection optical system of the present invention employs the DOE lens 140 to correct chromatic aberration, spherical aberration, and the like, thereby magnifying and projecting the scanning line of the CRT at high resolution. That is, it has a configuration suitable for high resolution. In addition, the projection optical system of the present invention reduces the overall focal length to realize a thinner and higher luminance of the rear projection device. In addition, the projection optical system of the present invention can be applied to high resolution without increasing the number of lenses, thereby reducing the manufacturing cost.

Hereinafter, application examples implemented using the projection optical system having the same configuration as the present invention will be described. The curvature radius, distance, refractive index, focal length and refractive power of each lens for constructing the projection optical system of the first application example are shown in Table 1.

Radius of curvature, distance refractive index, focal length, refractive index of projection optical system Si r d n fi ?? S1 111.000 8.600 1.494000 f1 = 351.9 f0 / f1 = 0.225 S2 299.109 14.400 S3 -140.000 8.200 1.494000 f2 = -3651.3 f0 / f2 = -0.0210 S4 -155.321 3.600 S5 74.500 25.000 1.492000 f3 = 97.2 f0 / f3 = 0.813 S6 -220.500 9.863 S7 -415.000 7.000 1.494000 f4 = 287.5 f0 / f4 = 0.275 S8 -115.876 33.000 S9 -50.782 3.500 1.430000 f5 = -155.4 f0 / f5 = -0.508 S10 -45.000 9.000

On the other hand, in the configuration of the projection optical system of the present invention, the first, second, fourth, and fifth lenses 110, 120, 140, and 150 are formed as aspherical surfaces. Aspherical lenses are defined by the aspherical formula shown in equation (3).

X is the Seg (Sag) value for the aspherical surface at height r from the optical axis, C is the curvature of the lens surface from the optical axis, K is the Conic constant, a1 to a5 is the aspherical coefficient. In addition, the coefficients of the aspherical surface and the DOE surface for each lens surface of the projection optical system are shown in Table 2.

Aspheric and DOE coefficients for each lens surface Si K A (a1) B (a2) C (a3) D (a4) E (a5) S1 -17.15900 1.162E-07 -1.313E-09 -4.585E-13 4.961E-16 -1.025E-19 S2 0.000000 6.029E-07 -7.796E-10 -5.599E-13 4.406E-16 -8.283E-20 S3 -10.000000 1.717E-06 -2.944E-10 -1.286E-12 4.009E-16 0.000E + 00 S4 -1.727000 1.612E-06 -3.750E-10 -1.096E-12 5.164E-16 -5.476E-20 S7 101.81000 5.163E-07 3.253E-10 -1.839E-14 4.097E-16 0.000E + 00 S7 (DOE coefficient) 0.000000 -2.546E-04 0.000000 0.000000 0.000000 0.000E + 00 S8 -41.46900 2.136E-06 3.747E-09 -3.142E-12 1.889E-15 -2.799E-19 S9 -0.77700 5.140E-06 2.687E-09 -3.730E-12 2.504E-15 -7.896E-19 S10 0.000000 0.000E + 00 0.000E + 00 0.000E + 00 0.000E + 00 0.000E + 00

To form an S1 aspherical surface having a radius of curvature of 82.962 to form an aspherical lens, a predetermined position (i.e., positions A to E) on a spherical lens having the same radius of curvature is processed to meet the data shown in Table 6 to form an aspherical lens. Done. In the same manner as described above to S10 aspherical surface to form an aspherical lens corresponding to the first application example.

Meanwhile, the curvature radius, distance, refractive index, focal length, and refractive power of each lens for constructing the projection optical system according to the second application example are shown in Table 3.

Radius of curvature, distance refractive index, focal length, refractive index of projection optical system Si r d n fi ?? S1 101.635 8.600 1.494000 f1 = 426.9 f0 / f1 = 0.185 S2 190.658 15.400 S3 280.338 8.200 1.494000 f2 = 1518.2 f0 / f2 = 0.052 S4 443.295 3.600 S5 78.280 25.000 1.492000 f3 = 97.7 f0 / f3 = 0.808 S6 -194.639 7.000 S7 -712.755 7.000 1.494000 f4 = 304.4 f0 / f4 = 0.259 S8 -137.901 33.562 S9 -48.084 3.500 1.430000 f5 = -143.6 f0 / f5 = -0.550 S10 -45.000 9.000

In addition, the coefficients of the aspherical surface and the DOE surface for each lens surface of the projection optical system are shown in Table 4.

Aspheric and DOE coefficients for each lens surface Si K A (a1) B (a2) C (a3) D (a4) E (a5) S1 -10.000000 2.963E-07 -1.925E-09 1.485E-14 3.251E-16 -6.104E-20 S2 0.000000 5.029E-7 -2.422E-09 6.559E-13 4.874E-17 -1.649E-20 S3 -10.000000 1.717E-06 -2.944E-10 -1.288E-12 4.009E-16 0.000E + 00 S4 0.000000 9.716E-07 1.142E-10 -1.612E-12 6.936E-16 -7.465E-20 S7 24.65800 2.926E-07 -3.045E-11 5.413E-14 2.714E-16 0.000E + 00 S7 (DOE coefficient) 0.000000 -2.000E-04 0.000000 0.000000 0.000000 0.000000 S8 -45.04800 1.117E-06 1.429E-09 -6.531E-13 4.908E-16 -1.380E-20 S9 0.000000 5.236E-06 3.978E-09 -4.788E-12 3.183E-15 -9.871E-19 S10 0.000000 0.000E + 00 0.000E + 00 0.000E + 00 0.000E + 00 0.000E + 00

As an example of forming an aspherical lens, in order to form an S1 aspherical surface having a radius of curvature of 111.000, a predetermined position (i.e., A to E position) on a spherical lens having the same radius of curvature is processed to fit the data shown in Table 2. Aspheric lenses are formed. In the same manner as described above to S10 aspherical surface to form an aspherical lens corresponding to the second application example.

Meanwhile, the curvature radius, distance, refractive index, focal length, and refractive power of each lens for constructing the projection optical system according to the third application example are shown in Table 5.

Radius of curvature, distance refractive index, focal length, refractive index of projection optical system Si r d n fi ?? S1 82.962 8.600 1.494000 f1 = 495.7 f0 / f1 = 0.159 S2 121.163 15.381 S3 280.338 8.200 1.494000 f2 = 858.9 f0 / f2 = 0.092 S4 817.986 3.660 S5 71.753 25.000 1.492000 f3 = 95.2 f0 / f3 = 0.804 S6 -265.639 7.020 S7 -356.111 7.000 1.494000 f4 = 333.5 f0 / f4 = 0.237 S8 -127.715 33.000 S9 -52.782 3.500 1.430000 f5 = -164.5 f0 / f5 = -0.480 S10 -45.000 9.000

In addition, the coefficients of the aspherical surface and the DOE surface for each lens surface of the projection optical system are shown in Table 6.

Aspheric and DOE coefficients for each lens surface Si K A (a1) B (a2) C (a3) D (a4) E (a5) S1 -10.525000 1.446E-06 -2.585E-09 -2.577E-13 6.292E-16 -1.224E-19 S2 0.000000 5.697E-07 -2.303E-09 -1.592E-13 5.906E-16 -1.153E-19 S3 -10.000000 1.717E-06 -3.481E-10 -1.286E-12 4.009E-16 0.000E + 00 S4 0.000000 7.759E-07 -3.480E-10 -9.128E-13 2.923E-16 0.000E + 00 S7 -85.58500 3.547E-07 -1.366E-09 2.086E-12 4.252E-16 0.000E + 00 S7 (DOE coefficient) 0.000000 -2.546E-04 0.000000 0.000000 0.000000 0.000000 S8 -45.04800 1.599E-06 1.098E-09 4.231E-13 1.535E-16 0.000E + 00 S9 0.000000 6.856E-06 8.342E-09 -1.223E-11 8.706E-15 -2.530E-18 S10 0.000000 0.000E + 00 0.000E + 00 0.000E + 00 0.000E + 00 0.000E + 00

To form an S1 aspherical surface having a curvature radius of 101.635 to form an aspherical lens, a predetermined position (ie, A to E position) on a spherical lens having the same curvature radius is processed to meet the data shown in Table 4 to form an aspherical lens. Done. In the same manner as described above to S10 aspherical surface to form an aspherical lens corresponding to the third application example.

As described above, the projection optical system of the present invention corrects chromatic aberration and spherical aberration using a DOE lens, so that a high resolution of the rear projection apparatus can be realized.

In addition, the projection optical system of the present invention has the advantage that it is possible to implement a thinner and higher brightness of the rear projection apparatus because the optical power is distributed to the DOE lens to secure the performance of the projection optical system to reduce the overall focal length.

In addition, the projection optical system of the present invention can be applied to high resolution without increasing the number of lenses, there is an advantage that can reduce the manufacturing cost.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (11)

In the projection optical system consisting of a plurality of refractive lenses, And a diffraction optical element formed on at least one surface of the refractive lens. The first lens group having weak refractive power, the second lens group having weak refractive power, the third lens group having strong positive refractive power, and the third lens group are generated in the projection optical system configured to be aligned from the image side. In a projection optical system composed of a fourth lens for correcting aberration and a fifth lens having negative refractive power, And a diffractive optical element formed on at least one surface of the lenses. The method of claim 2, The projection optical system of claim 1, wherein one surface of the first lens is designed as an aspherical surface and the other surface is designed as a diffractive optical element surface. The method of claim 2, The projection optical system, characterized in that one surface of the second lens is designed as an aspherical surface and the other surface is designed as a diffractive optical element surface. The method of claim 2, The projection optical system, characterized in that one surface of the fourth lens is designed as an aspherical surface and the other surface is designed as a diffractive optical element surface. The method of claim 4, wherein And the fourth lens has weak refractive power. The method according to any one of claims 1 and 2, And the diffractive optical surface has a positive refractive power. The method of claim 2, The diffractive optical surface is a projection optical system, characterized in that the groove is formed with a plurality of concentric circles having rotational symmetry. The method of claim 8, And a pitch of the groove portion of the diffractive optical surface decreases from the center of the diffractive optical surface to the periphery thereof. The method of claim 2, And the second lens has negative refractive power. The method of claim 2, At least one of the lenses is a projection optical system, characterized in that the plastic. At least one of the lenses is a projection optical system, characterized in that the plastic.