KR100234193B1 - Projection optical system - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical system in which chromatic aberration is corrected, wherein the projection optical system comprising a first lens group, a second lens group, and a third lens group has at least one spherical lens and has a high refractive index. A first lens group G1 provided with a first lens L1 having power; The second lens L2, which is at least one aspherical lens for removing aperture aberration and longitudinal chromatic aberration, and the third and fourth lenses L3, which are dual lenses that combine positive power and negative power to form the main power of the whole optical system. A second lens group G2 provided with L4 and a fifth lens L5 which shares power with the third and fourth lenses L3 and L4; A third lens group (6) of the aspherical lens having a relatively weaker power than the second lens group (G2) is provided to correct spherical aberration and longitudinal chromatic aberration at the center, and to correct axle aberration at the peripheral portion ( G3) and; A fourth seventh lens group G4 that provides strong negative power by providing negative seventh and eighth lenses L7 and L8 positioned to face the cathode ray tube is provided.

Description

PROJECTION OPTICAL SYSTEM

1 is a lens arrangement of a conventional projection optical system.

2 is a lens arrangement diagram of a projection optical system according to the present invention.

3 is a spherical aberration diagram of FIG.

4 is a top view curvature, chromatic aberration and distortion aberration of FIG.

5 is a lens arrangement of the second embodiment.

6 is a spherical aberration diagram of FIG.

FIG. 7 is a diagram showing top surface curvature, chromatic aberration, and distortion aberration of FIG.

<Explanation of symbols for the main parts of the drawings>

Li: i th lens element Si: i th surface number

The present invention relates to a projection optical system, and more particularly to a projection (REAR TYPE PROJECTION) optical system.

Projection television systems typically use red, blue, green, and three monochromatic cathode ray tubes. Images formed on the three monochrome cathode ray tubes are projected onto a screen, and the three separate images are combined on the screen to form a full color screen.

Optical systems used in these applications generally include a strong negative lens near the cathode ray tube and a strong positive power (POWER: inverse of the focal length) provided at a predetermined distance from the negative lens. And a weaker lens farther away from the cathode ray tube. Examples of such optical systems are described in US Pat. No. 4,300,817; 4,348,081 and 4,526,442.

In fact, the fluorescent films used in each cathode ray tube do not emit complete monochromatic light. In particular, the emission spectrum of the green cathode ray tube has important side bands in addition to the main peak (MAIN PEAK) in the red and blue portions of the spectrum. If the projection optics are not corrected for color, this chroma spread causes color contrast and sometimes color interference.

Therefore, in order to achieve high image quality in applications such as data display, IDTV (INTERMEDIATE DEFINITION TV), HDTV (HIGH DEFINITION TV) and the like, it is desirable to make sure that the chromatic aberration of the lens is corrected.

Especially in the case of rear type projection optics that require a short throw distance and a wide field of view, chromatic aberration needs to be improved, and MTF (MODULATION TRANSFER FUNCTION) for lens systems for data display or HDTV broadcast reception. It should have good resolution power of 10 line pairs / mm (meaning that 10 black and white line pairs are included in 1mm).

In the case of general optical systems such as US Patent Nos. 4,300, 817, 4,348, 081 and 4,526, 442, a configuration without chromatic aberration correction is required and a good resolution of MTF 5 line pairs / mm is required. In this case, due to the side bands (490 nm, 590 nm, and 625 nm) of the green cathode ray tube, contrast reduction of an image and color interference of visible light occur.

In recent years, interest in HDTV has been increasing, and in addition, a rear-type projection optical system having a compact size is required in anticipation of the demand for home high definition rear-type projection TVs. In order to meet these demands, the rear type projection optical system must also maintain a large field of view with a large aspect ratio having a short TCL (TOTAL CONJUGATE LENTH), which represents a distance from a cathode ray tube to a transmission screen. It is necessary to attain a good resolution of 1,500 (≒ MTF 6.1 line pairs / mm) or more by satisfactorily correcting the above, and a high definition rear type projection optical system having a slim (SLIM) size for home use is possible in the future.

Patents for high-resolution projection optics with chromatic aberration correction include US Pat. Nos. 5,015,076 and 4,976,525, which are applied to front-type projection optics.

In contrast, a conventional projection optical system for a rear type projection optical system having a short throw distance and a large field of view is described in US Pat. It is an optical system. 1 is a lens arrangement constituting such a conventional projection optical system.

Referring to FIG. 1, a conventional projection optical system includes a positive first lens L1 spaced apart from the positive first lens L1 at least one surface by an aspherical surface and has a higher dispersion than the positive first lens L1. A first lens group G1 consisting of a negative second lens L2 which is HIGH DISPERSION; At least one positive third lens L3 and a negative fourth lens L4 that is spaced apart from the positive third lens L3 and is more dispersed than the positive third lens L3, and provides positive power. Second lens group G2; It is composed of a third lens group G3 positioned to face the cathode ray tube and provided with strong negative sixth and seventh lenses L6 and L7 to provide negative power.

The fifth lens L5, which is an aspherical correction lens CORLECTOR LENS, is provided between the second lens group G2 and the third lens group G3, and the sixth lens L7 is provided in the seventh lens L7. L6) is matched with the refractive index and the cooling liquid is inserted in preparation for the temperature rise of the cathode ray tube, and the first, second, fourth, fifth and sixth lenses L1, L2, L4 and L5 Five sheets are made of plastic, and two sheets of the third and seventh lenses (L3) and L7 are made of a hybrid type manufactured by using glass materials simultaneously.

However, in the conventional projection optical system configured as described above, the first lens group including the first lens and the second lens and the fifth lens as the correction lens are made of plastic, and the thickness difference between the central part and the peripheral part is large, so that the temperature change In addition, the manufacturing error is greatly affected during the injection molding of the lens manufacturing.

In other words, by using a plastic lens with a large difference in thickness between the center and the periphery of the first lens group for removing chromatic aberration, the non-uniform contraction and the distortion of the lens structure generated during injection molding are easily received. Therefore, the correction of chromatic aberration is not effective, and the production thereof is difficult.

Furthermore, considering that the temperature of the cathode ray tube, which is a component of the projection optical system, is increased by 80 ° C. or more, the first lens group and the correction lens having a large difference in thickness between the center and the periphery are made of a plastic having a large thermal expansion coefficient according to the temperature. It is not suitable to use to remove chromatic aberration as a material. The larger the aperture ratio, the more difficult it is to remove the LONGITUDINAL CHROMATIC ABERRATION. Therefore, the correction of chromatic aberration is not effective even in large-diameter projection optical systems.

In addition, the prior art and the conventional technology can not increase the angle of view any longer by maintaining a focal length of 138 mm or more in order to have a high-definition resolution, and because of this, the TCL becomes longer, so it is adopted for home high-definition rear type projection optical system. In this case, the equipment becomes large and the miniaturization thereof occurs.

Accordingly, an object of the present invention is to provide a high-resolution projection optical system that removes chromatic aberration corresponding to the visible light of the entire area at a wide angle of view, minimizes the thickness ratio of the plastic lens in consideration of the injection molding conditions of the plastic lens, and maintains the large diameter ratio. .

In order to achieve the above object, the present invention provides a projection optical system composed of a first lens group, a second lens group, a third lens group and a fourth lens group, having at least one spherical lens and having a high refractive index. A first lens group provided with a first lens having power; The second lens, which is at least one aspherical lens to remove aperture aberration (aberration as spherical aberration generated as the diameter of the lens increases) and longitudinal chromatic aberration, and positive power and negative power are combined to provide the main power of the whole optical system. A second lens group including third and fourth lenses that constitute a double lens and a fifth lens that shares power with the third and fourth lenses; A third lens group having a sixth lens of an aspherical lens having a relatively weak power compared to the second lens group, correcting spherical aberration and longitudinal chromatic aberration at the center, and correcting axle aberration (coma and astigmatism) at the periphery; ; A fourth lens group providing a strong negative power by providing negative seventh and eighth lenses positioned to face the cathode ray tube is provided.

As a specific embodiment type, the first lens group satisfies a condition of f / f1 &lt; 0.25 (f: focal length of the entire optical system, f1: focal length of the first lens); The second lens group is -0.52 &lt; f / f2 &lt; -0.35 and 2+> 50, 2- <40 (f: focal length of the whole optical system, f2: focal length of the second lens, 2 ±: satisfies the condition of the third and fourth lenses, i.e., the Abbe number of the bi-lens ± power lens; The third lens group satisfies the condition of -0.28 &lt; f / f6 &lt; 0.028 (f: focal length of the entire optical system, f6: focal length of the sixth lens).

In order to maintain the large angle, the distance between the first lens group and the second lens group is limited as follows.

d12 / f &lt; 0.26 (d12: interval between the first lens group and the second lens group, f: focal length of the whole optical system).

In addition, a cooling oil having a refractive index of 1.4 or more is inserted into the eighth lens to match the refractive index of the seventh lens and to prepare for a rise in temperature of the cathode ray tube, and the first, third, and third lenses are four lenses among the eight lenses. The fourth and fifth lenses are made of a glass material, and the remaining three lenses, the second, sixth and seventh lenses, are made of a plastic material and are manufactured in a hybrid type.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the illustrated drawings.

2 is a lens bezel diagram of a projection optical system according to the present invention, FIG. 3 is a spherical aberration diagram of FIG. 2, and FIG. 4 is a top surface curvature, chromatic aberration, and distortion aberration diagram of FIG.

Referring to FIG. 2, the projection optical system according to the present invention includes a first lens group G1 provided with a first lens L1 of glass material having a positive power of high refractive index as a spherical lens; The second lens L2 of the plastic aspherical lens to remove the aberration and longitudinal chromatic aberration, and the third and fourth lenses of the glass material, which are the dual lenses combining the positive power and the negative power to form the main power of the whole optical system ( A second lens group G2 provided with L3) (L4) and a fifth lens L5 of glass material which shares power with the third and fourth lenses L3 and L4; A third lens L6 of a plastic aspherical lens having a relatively weaker power than the second lens group G2 is provided to correct spherical aberration and longitudinal chromatic aberration at the center thereof, and to correct axle aberration at the periphery thereof Lens group G3; The negative seventh and eighth lenses L7 and L8 positioned to face the cathode ray tube are provided to constitute the fourth lens group G4 that provides strong negative power.

In addition, a cooling oil having a refractive index of 1.4 or higher is inserted into the eighth lens L8 to match the refractive index of the seventh lens L7 and to prepare for the increase in the temperature of the cathode ray tube, thereby reducing the increase in heat generation of the cathode ray tube.

And the first lens group G1 satisfies a condition of f / f1 &lt; 0.25 (f: focal length of the entire optical system, f1: focal length of the first lens L1); The second lens group G2 is -0.52 &lt; f / f2 &lt; -0.35 and 2+〉 50, 2- <40 (f: focal length of the entire optical system, f2: focal length of the second lens L2, 2 ±: satisfies the conditions of the third and fourth lenses L3 (L4), that is, the Abbe number of the ± power lens which is a dual lens; The third lens group G3 satisfies the condition of -0.28 &lt; f / f6 &lt; 0.028 (f: focal length of the entire optical system, f6: focal length of the sixth lens L6).

In addition, the interval between the first lens group G1 and the second lens group G2 is limited as follows to maintain the large angle.

d12 / f &lt; 0.26 (d12: interval between the first lens group and the second lens group, f: focal length of the whole optical system).

Lens data of Example 1 according to the present invention shown in FIG. 2 is summarized in Table 1 below.

Table 2 below shows lens data of the second embodiment shown in FIG. 5, FIG. 6 is a spherical aberration diagram of FIG. 5, and FIG. 7 is a top surface curvature, chromatic aberration, and distortion aberration diagram of FIG.

The operation of the projection optical system of the present invention configured as described above is as follows.

It has a positive power of high refractive index and low dispersion > 50) The first lens group G1 provided with the spherical lens made of a material partially shares the power of the entire optical system together with the third lens group G3 in order to correct distortion of an image.

The second lens L2 of the second lens group G2 is composed of an aspherical surface to eliminate aperture aberration and longitudinal chromatic aberration, and the third lens L3 and the fourth lens L4 are positive and negative power. The chromatic aberration is removed by the dual lens, and the fifth lens L5 forms the main power of the entire optical system together with the third and fourth lenses L3 and L4. As a result, the second lens group G2 corrects longitudinal chromatic aberration and LATERAL CHROMATIC ABERRATION, where the third lens L3 having positive power has a low dispersion ( 〉 50) and the fourth lens L4 having negative power has high dispersion ( A substance of <40 is used.

The third lens group G3 is composed of a plastic aspherical lens and has a weak power. The center lens of the third lens group G3 removes spherical aberration and longitudinal chromatic aberration, and the peripheral portion of the third lens group G3 removes axon aberration.

The fourth lens group G4 is composed of a seventh lens L7 of a plastic aspherical surface and an eighth lens L8 coupled to a cathode ray tube, and the eighth lens L8 is an oil layer and is formed by cooling oil having a refractive index of 1.4 or higher. In order to suppress the generated heat of the cathode ray tube and to correct the second lens group G2 and the image surface curvature with each other, the entire fourth lens group G4 has a strong negative power.

As described above, according to the present invention, a 7-inch small cathode ray tube can project a high-resolution image of a large screen of 50 inches or more, that is, chromatic aberration at a large angle (34.7 degrees) is improved, and MTF 10 in all fields. It is possible to realize an image having a high resolution of line pairs / mm. In consideration of the injection molding of the plastic lens, chromatic aberration can be effectively compensated for by using a lens having a small thickness difference between the center and the periphery of the lens, and a high resolution image can be realized while maintaining a large aperture ratio (f / ＃: 1.13). have.

In addition, with a short focal length (100.7 mm) and a large angle, the TCL can be reduced, thereby miniaturizing a high-definition rear type projection system.

Accordingly, the present invention provides a high-resolution projection optical system that removes chromatic aberration corresponding to the visible light of the entire area at a wide angle of view, minimizes the thickness ratio of the plastic lens in consideration of the injection molding conditions of the plastic lens, and maintains the large-diameter ratio.

Claims (6)

A projection optical system composed of four lens groups, comprising: a first lens group G1 having at least one spherical lens and provided with a first lens L1 having positive power of high refractive index; At least one aspherical lens (L2) that removes aberration and chrominance aberration, and a third lens and a fourth lens, which are dual lenses in which positive power and negative power are combined to form a main power of the whole optical system. A second lens group G2 provided with L3) L4 and a fifth lens L5 that shares power with the third and fourth lenses L3 and L4; A third lens group (6), which is an aspherical lens having a weaker power than the second lens group G2, is provided to correct spherical aberration and longitudinal chromatic aberration at the center, and to correct axle aberration at the periphery. G3) and; A fourth lens group G4 provided with negative seventh and eighth lenses L7 and L8 positioned to face the cathode ray tube to provide strong negative power; Wherein the distance between the first lens group G1 and the second lens group G2 is equal to the following condition, d12 / f &lt; 0.26 (d12: interval between the first lens group and the second lens group, f: And a focal length of the whole optical system). The method of claim 1, wherein the first lens group G1 satisfies a condition of f / f1 &lt; 0.25 (f: focal length of the entire optical system, f1: focal length of the first lens L1). Projection optical system. The method of claim 1, wherein the second lens group G2 is -0.52 &lt; f / f2 &lt; -0.35 and 2+〉 50, 2- <40 (f: focal length of the entire optical system, f2: focal length of the second lens L2, 2 ±: the projection optical system, which satisfies the conditions of the third and fourth lenses L3 (L4), that is, the Abbe number of the ± power lens which is a dual lens. The third lens group G3 satisfies the condition of -0.28 &lt; f / f6 &lt; 0.028 (f: focal length of the entire optical system, f6: focal length of the sixth lens L6). Projection optical system, characterized in that. The projection optical system according to claim 1, wherein the eighth lens (L8) is inserted with a cooling oil having a refractive index of 1.4 or more in accordance with the refractive index of the seventh lens (L7) and in preparation for the temperature rise of the cathode ray tube. The method of claim 1, wherein the first, third, fourth, and fifth lenses L1, L3, L4, and L5 are made of glass material, and the remaining second, sixth, and seventh lenses L2. Projection optical system characterized in that (L6) (L7) is made of a plastic material.