KR100692810B1 - Projection Optical Lens System - Google Patents

Abstract

The present invention relates to a projection optical lens system. The projection optical lens system of the present invention comprises a total reflection lens provided between a first lens group having a negative refractive power and a second lens group having a positive refractive power, a first lens group, and a second lens group; And a variable aperture installed between the total reflection lens and the second lens group, wherein the variable aperture can adjust the f-stop by adjusting the size of the aperture. According to the present invention, by applying a variable aperture, the contrast ratio of the system can be adjusted in the projection optical system, especially the rear projection television system using the sFPD as a device to improve the image quality.

Projection optical lens, sFPT, f-stop, variable aperture, ultra wide angle lens

Description

Projection Optical Lens System

1 illustrates a projection optical lens system according to an embodiment of the present invention.

2 illustrates an aperture applied to a projection optical lens system according to an exemplary embodiment of the present invention.

3 shows an example of the structure of a projection optical lens system according to an embodiment of the present invention.

4 illustrates an embodiment in which a projection optical lens system according to an embodiment of the present invention is applied to a projection optical system.

5A and 5B graphically illustrate lens aberrations of a projection optical lens system according to an embodiment of the present invention.
<Explanation of symbols for the main parts of the drawings>
11: first lens group 12: second lens group
20, 20a: Aperture 30: Total reflection mirror
31: Actuator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical lens system for a rear projection system, and more particularly, to a projection optical lens system that can improve contrast by applying a variable aperture with adjustable brightness.

Conventional large screen displays have been the PRT type projection television has led the large display market, but the size and weight of the PRT CRT itself has a problem due to the miniaturization and thinning of optical components. Therefore, there are limitations in the weight and volume of the device for realizing a large-sized home display, and also in the disadvantage that the required luminance cannot be obtained in a high resolution specification such as HDTV.

In order to solve the above problems, a rear projection television for a micro device using a sFPD (samll flat panel display: LCD, DLP, LCoS) has been proposed. Since the system uses a method of projecting an image of a small panel of about 0.5 to 2 inches on the screen through a projection lens, the system can be miniaturized and lightweight, and it is easy to implement a large screen display. In addition, since high luminance can be obtained in comparison with PRT, development is being progressed as a representative display device of the HDTV era as a large-screen display for home use.

However, when used as a projection display device using a micro device (LCD, DLP, LCoS) in the same system as the above system, due to the characteristics of the system and the device itself, Light, etc.) is transmitted to the screen, so that the black level value of the system background is increased, and thus, the contrast ratio of the system is lowered, thereby degrading the image quality. In order to solve such a problem and to improve image quality, it is necessary to adjust the black level value according to the state of an image.

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An object of the present invention is to provide a projection optical lens system that can be applied to the variable aperture to adjust the black level value on the screen.

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Projection optical lens system of the present invention for achieving the above object is the first lens group having a negative refractive power and the second lens group having a positive refractive power; A total reflection lens provided between the first lens group and the second lens group; And a variable aperture installed between the total reflection lens and the second lens group, wherein the variable aperture can adjust an f-stop by adjusting the size of the aperture.

The variable diaphragm may include a circular diaphragm including two or more wings or a spatula-type diaphragm including one wing.
The variable diaphragm may include an actuator for varying the diaphragm.

The first lens group may include one or two aspherical plastic lenses.
The second lens group may include a two-ply lens having a positive refractive power, an aspherical plastic lens, a two-ply lens having a negative refractive power, and two spherical single lenses.
The first lens group and the second lens group have the following conditions, 3.5 <bf1 / f1 <5.0; 0.55 <| f1 / f2 | <075; And 8.0 <d8 / f1 <12.0, wherein bfl is the back focal length, f1 is the focal length of the entire lens, f2 is the focal length of the second group, and d8 is the first lens group and first It is characterized by showing the air gap between two lens groups.

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The total reflection mirror is made of glass or plastic, characterized in that the reflective surface is formed in a flat or aspherical surface.

The pre-reflective mirror is installed so that the optical path is changed in the range of the angle of the light reflected from the first lens group to the second lens group 30 degrees to 90 degrees with respect to the optical axis.
The first lens group or the second lens group includes a method of moving the lens focal formation forward and backward through the entire first lens group and the second lens group, or by moving a part of the first lens group or the second lens group back and forth. It is characterized by.

According to another aspect of the present invention, a rear projection optical lens system includes an sFPD for outputting light having image information, a projection optical lens system for receiving the image information to form a focal point for forming an image, and from the lens system. A rear projection optical system comprising a reflector for reflecting light of a light and a screen for forming an image using light from the reflector, wherein the projection optical lens system comprises a first lens group having negative refractive power And a second lens group having positive refractive power; A total reflection lens provided between the first lens group and the second lens group; And a variable aperture installed between the total reflection lens and the second lens group, wherein the variable aperture becomes an ultra wide-angle projection optical lens system capable of adjusting the size of the aperture by an actuator.

The sFPD is characterized in that any one of LCD, DLP, LCoS.

Hereinafter, the lens system according to the present invention will be described in detail with reference to the accompanying drawings as an embodiment. The examples presented are exemplary and are not intended to limit the scope of the invention.

As used herein, the term “ultra wide angle lens” refers to a lens having a focal length of 21 mm to 14.15 mm and a focal length of more than 85 degrees, especially among wide angle lenses having a shorter focal length and a wider angle of view than a standard lens. Generally, a standard lens refers to a lens having an angle of view of about 46 to 47 degrees and a focal length of 38 mm to 58 mm. In addition, unless otherwise specified in the present invention, a lens means an ultra wide-angle lens.

1 illustrates a projection optical lens system according to an embodiment of the present invention.

As shown in FIG. 1, the lens system according to the present invention includes a first lens group 11 and a second lens group 12 arranged on an optical axis OX. The first lens group 11 includes two negative aspherical plastic single lenses convex in an object direction, for example, an input light direction. In the following, the radius of curvature of each lens is denoted by rx and the thickness and air gap of each lens is denoted by dx. Where x represents the number of any corresponding lens. The second lens group 12 includes a double-layer lens having a positive refractive power, a plastic lens, a double-layered lens having a negative refractive power, and two spherical single lenses having a positive refractive power. Are arranged in order. That is, in the second lens group 12, a total of seven lenses are arranged in the order shown above. A total reflection mirror may be installed between the first lens group 11 and the second lens group 12 to convert an optical path, and a variable aperture may be installed between the front reflection mirror and the second lens group 12. Can be. The diaphragm may be changed in size by an actuator, and a stop position of the variable diaphragm is illustrated in FIG. 1.

The first lens group 11 and the second lens group 12 are ultra wide-angle lenses and are formed to satisfy the following conditions.

3.5 <bf1 / f1 <5.0.. … Conditional Expression (1)

0.55 <| f1 / f2 | <075. … Conditional Expression (2)

8.0 <d8 / f1 <12.0... … Conditional formula (3),

In the above description, bfl represents a back focal length, f1 represents a focal length of the entire lens, f2 represents a focal length of the second group, and d8 represents an air gap between the first lens group and the second lens group.

Conditional expression (1) becomes a condition regarding the ratio of bf1 and f1, that is, the Retro ratio, and determines the size at which the projection lens system according to the present invention can be installed. If the retro ratio exceeds the upper limit of 5.0, the aberration correction becomes difficult because the projection lens system becomes larger than necessary. On the other hand, if the lower limit is less than 3.5, the aberration characteristics and optical performance will be improved when designing the system, but the air gap will be narrowed, which reduces the insertion space of the system for color synthesis, making the system impossible. Therefore, the retro ratio must satisfy the given conditional expression (1).

And conditional expression (2) relates to the refractive power between the first lens group 11 and the second lens group 12. If the given condition is not satisfied and the value is smaller than the lower limit, the refractive power of the first lens group 11 is increased, which is advantageous in miniaturizing the projection lens and making the projection lens an ultra wide-angle lens, but using the r2 of the first lens. The problem is that cotton becomes close to the hemisphere, making it impossible to produce. In addition, the Petzval Sum increases in the negative direction and has a disadvantage that the upper surface curvature becomes large. On the other hand, when f1 / f2 is greater than or equal to the upper limit, the refractive power of the second lens group 11 is weakened, causing a problem in that coma aberration occurs due to spherical aberration correction. Therefore | f1 / f2 | must satisfy the given value.

Also, conditional expression (3) relates to the air gap between the first lens group 11 and the second lens group 12. If d8 / f1 is smaller than the lower limit value, the air gap is reduced, which makes it impossible to install the total reflection mirror between the first lens group 11 and the second lens group 12. On the other hand, if d8 / f1 is above the upper limit value, the projection lens system becomes longer than necessary, and this causes a problem that it is difficult to thin the whole system. Therefore, the optical lens system according to the present invention must satisfy the given conditional formula (3).

In the projection optical lens system according to the present invention that satisfies the conditional expressions (1), (2) and (3) as described above, focusing is performed by the first lens group 11 or the second lens group ( 12) is moved back and forth to correct the plane on which the image is formed. Another possible method is to move some lenses of the second lens group 12 back and forth. In the case of the L-shaped lens according to the present invention, a lens focusing method such as correcting a plane on which an image is formed by moving the entire lens is not appropriate. This is because when the lens focus forming method is applied in the projection optical lens system according to the present invention, the center of the screen and the image forming surface may not coincide according to the position of the projection lens, and the image projected on the screen moves up and down the screen. Has the disadvantage of being able to escape. Therefore, there is a need for a separate alignment device (Align Apparatus) to correct this, which causes problems such as increased production cost and reduced productivity.

The radius of curvature rx of the respective lens surfaces of the first lens group 11 and the second lens group 12 shown in FIG. 1, which can be applied in the projection optical lens system according to the present invention below, the distance between the lenses Example of (dx) and the refractive index of the lens is illustrated in Table 1. In the embodiment shown in Table 1, the focal length f = 1.0 mm, the F number = 2.9 and 2ω = 85.88 degrees. ω represents the angle of view between the projection lens system and the screen.

Radius of curvature (r) Thickness / Period (d) Index of Refraction One -4.97647 0.628499 1.492623 2 -18.40562 1.517066 3 -2.99332 0.476792 1.492623 4 9.41899 10.630518 5 Aperture (Midpoint) 1.517066 6 3.92630 0.869149 1.855066 7 -2.65084 0.108362 1.839306 8 8.28200 0.704352 9 -16.85010 0.384555 1.492623 10 -9.63205 0.010836 11 37.67994 0780206 1.489144 12 -2.13643 0.108362 1.855066 13 4.37912 0.011400 14 4.59383 0.879465 1.489144 15 -3.04220 0.010836 16 4.93339 0.759346 1.489144 17 -5.17345 0.325086 18 Image plane 0.0

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Table 2 shows coefficient values for the shape of the aspherical lens.

Lens surface S1 S2 S3 S4 S9 S10 K -6.8370E + 00 -3.2617E + 02 -3.9905E + 00 -1.1421E + 02 -6.3784E + 01 -2.1090E + 01 AR3 3.7369E-02 3.9851E-02 2.9250E-02 2.0807E-02 1.8152E-03 -2.0179E-04 AR4 -1.4804E-02 -4.1641E-03 7.4524E-02 1.0692E-01 -8.4199E-04 1.3935E-02 AR5 1.3959E-02 -8.3248E-03 -2.1131E-02 -3.2990E-02 7.5241E-03 -2.5727E-02 AR6 -4.6727E-03 1.3070E-02 -9.5918E-03 2.8505E-02 -6.0956E-03 3.6463E-02 AR7 1.4326E-04 -3.1390E-03 1.4184E-03 -3.4174E-02 7.1886E-03 -1.5327E-02 AR8 1.5130E-04 -3.1250E-04 1.0518E-03 1.9030E-03 -1.6531E-03 -8.6046E-03 AR9 -8.3572E-06 2.1071E-06 -1.0001E-04 8.8688E-03 8.8686E-03 1.1595E-02 AR10 -2.7432E-06 3.8938E-05 -3.7712E-05 -2.7550E-03 -2.7550E-03 -4.8137E-03 AR11 -2.0664E-08 -1.6813E-06 -2.8077E-07 4.5417E-05 4.5417E-05 6.6071E-04 AR12 2.4931E-08 -3.1759E-07 4.0539E-07 2.3768E-05 2.3768E-05 3.0178E-04 AR13 5.3963E-09 -6.4598E-07 2.0866E-07 2.6981E-06 2.6981E-06 8.1397E-05 AR14 -1.6045E-10 -1.6376E-08 -1.6376E08 1.3813E-06 1.3813E-06 -1.5622E-04

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The nonspherical equations for odd terms are given by:

Z = Cr ² / (1 + (1- (1 + K) x c ² x r ² ) ^1/2 ) + AR1 x r + AR2 x r ² + AR3 x r ³ . …

Where r ² = x ² + y ² .

As described above, a variable aperture is provided between the total reflection mirror and the second lens group 12. The form of the aperture is shown in FIG. 2.

2 illustrates an aperture applied to a projection optical lens system according to an exemplary embodiment of the present invention.

As shown in FIG. 2, the diaphragm according to the present invention may have a spatula shape 20a as shown in (a) of the circular shape 20 or (b). In general, the diaphragms 20 and 20a are built in the lens and become f-stops or f-numbers and used to adjust the amount of light passing through. In the projection optical lens system according to the present invention, the diaphragms 20 and 20a are installed between the first lens group and the second lens group, and the mounting positions of the diaphragms 20 and 20a are shown in FIG. The apertures 20 and 20a according to the present invention are characterized by being variable by an actuator (see FIG. 3) to adjust the amount of light. As shown in FIG. 2A, the circular aperture may include two or more wings to adjust the amount of light. On the other hand, as shown in (b) of Figure 2, the spatula-type aperture adjusts the amount of light or f-number as one wing. The adjustment of the size of the apertures 20, 20a or the adjustment of the f-stops according to the invention can be made according to methods known in the art.

The projection optical lens system according to the present invention includes a first lens group, a second lens group, a total reflection mirror and a variable aperture. 3 illustrates an embodiment of a projection optical lens system according to the present invention.

3 shows an example of the structure of a projection optical lens system according to an embodiment of the present invention.

Referring to FIG. 3, image information of a micro device (not shown) is input to the first lens group 11. The first lens group 11 is composed of a non-spherical lens to correct spherical aberration for the incident light. At the same time, it has a negative refractive index to correct coma and astigmatism, and to correct chromatic aberration using two lenses. Incident light transmitted through the first lens group 11 is reflected by the total reflection mirror 30 to pass through the aperture 13. The total reflection mirror 30 may be a thin film coating to increase the reflectance according to methods known in the art. The total reflection mirror 30 may allow the optical path conversion to occur in a predetermined angle range. For example, the total reflection mirror 30 may be installed such that the axis of the light traveling direction, that is, the angle between the light incident on the total reflection mirror 30 and the reflected light is in a range of 30 degrees to 90 degrees with respect to the optical axis. This can be determined taking into account the size of the overall projection system, other components such as reflectors (see FIG. 4) and screens. As described with reference to FIG. 2, the diaphragm 13 according to the present invention may have a circular or spatula shape as a variable diaphragm. The size of the diaphragm 13 is adjusted by an actuator 31. The light with the image information incident to the second lens group 12 by adjusting the amount of light controlled by the aperture 13 is first refracted by the two-ply lens having positive refractive power to form a focal point. Aspheric aberration correction and field curvature correction are performed by the aspherical plastic lens. And coma and chromatic aberration are corrected by a two-ply lens having negative refractive power. The incident light, which has been corrected for image formation, is finally chromatic aberration corrected by two lenses having a positive refractive power of the second lens 12 and has a required refractive index for image formation. In this way, the light having the necessary corrected image information for forming the required image forms an image on a screen (not shown). The process of forming an image on the screen is shown in FIG.

4 illustrates an embodiment in which a projection optical lens system according to an embodiment of the present invention is applied to a projection optical system.

Referring to FIG. 4, light having image information incident from a micro device (not shown) is input to a projection optical lens system 40 according to the present invention. The lens system 40 corrects spherical aberration and chromatic aberration using the first lens group necessary for incident light. And the brightness is controlled by using a variable aperture to adjust the amount of light. As described above, the variable diaphragm is sized by an actuator. On the other hand, the incident light whose light amount is adjusted is changed into the second lens group by changing the light path by the total reflection mirror. The second lens group corrects astigmatism and coma, and also corrects chromatic and spherical aberration for the incident light. The incident light is refracted by the lens having a positive refractive power to form an image. The first lens group or the second lens group is provided so that all or part thereof can move back and forth. If focus formation is required, the focus formation may be adjusted by moving all or part of the first lens group or the second lens group back and forth. The movement of all or part of the first lens group or the second lens group may be performed according to methods known in the art. Incident light passing through the second lens group is incident on the rear reflector 41 to form an image necessary for the screen 42. The back reflector 41 may be made of total reflection thin film coating, if desired, according to methods known in the art.

5A and 5B graphically illustrate lens aberrations of a projection optical lens system according to an embodiment of the present invention.

5A shows spherical aberration in the longitudinal direction, (B) shows astigmatism, and (C) shows distortion. In the graph shown, CR represents the red wavelength, CG represents the green wavelength, and CB represents the blue wavelength, red (R) wavelength is 620 nm, green (G) wavelength is 546 nm and blue (B). ) Wavelength was measured using 450 nm. In each graph, the horizontal axis represents millimeters (mm) and the focus is the reference.

Referring to FIG. 5A, it can be seen that the spherical aberration is corrected as the distance increases, and the error value is insignificant above 3.0 mm. Astigmatism and distortion are unrecognizable for the red (R) and blue (B) wavelengths and insignificant for the green (G) wavelengths.

As described above, it can be seen that the projection optical lens system according to the present invention can improve the contrast ratio by forming a clear image on the screen.

FIG. 5B illustrates Ray Aberration of a projection optical lens system according to an embodiment of the present invention.

In each graph, CR, CG and CB represent Red wavelength, Green and Blue wavelength, respectively, and the wavelengths used are 620 nm, 546 nm and 450 nm, respectively.

Referring to FIG. 5B, it can be seen that aberration does not appear or is insignificant for green light and that aberration changes from positive to negative or negative to positive with respect to red and blue wavelengths. In FIG. 5B, (x, y) represents a measurement position and a relative field represents a wide angle. The unit used is millimeters (mm).

The projection lens optical system according to the present invention can improve the image quality by adjusting the contrast ratio of the system in the projection optical system, especially the rear projection television system using the sFPD as a device by applying a variable aperture.

The projection optical lens system according to the present invention has been described above in detail by way of example. The presented embodiments are exemplary and can be made by those skilled in the art without departing from the scope of the technical spirit of the present invention. The invention is not limited by the invention as such variations and modifications, but only by the claims below.

Claims (11)

A first lens group having a negative refractive power and a second lens group having a positive refractive power; A total reflection lens provided between the first lens group and the second lens group; And A variable aperture is provided between the total reflection lens and the second lens group, And the variable aperture can adjust the f-stop by adjusting the size of the aperture. The method of claim 1, The variable diaphragm includes a circular diaphragm including two or more wings or a spatula-type diaphragm including one wing. The method of claim 2, And the variable aperture includes an actuator for varying the aperture. The method of claim 1, And said first lens group comprises one or two aspherical plastic lenses. The method of claim 1, And the second lens group includes a two-ply lens having a positive refractive power, an aspherical plastic lens, a two-ply lens having a negative refractive power, and two spherical single lenses. The method of claim 1, The first lens group and the second lens group is the following conditions, 3.5 <bf1 / f1 <5.0; 0.55 <| f1 / f2 | <075; And 8.0 <d8 / f1 <12.0, where bfl is the back focal length, f1 is the focal length of the entire lens, f2 is the focal length of the second group, and d8 is the first lens group and the second A projection optical lens system, characterized in that it represents an air gap between lens groups. The method of claim 1, The total reflection mirror is made of glass or plastic, the projection optical lens system, characterized in that the reflective surface is formed in a planar or aspherical surface. The method of claim 1, And the pre-reflective mirror is installed such that the optical path is changed in a range of 30 degrees to 90 degrees with respect to the optical axis of the light reflected from the first lens group to the second lens group. The method according to any one of claims 1, 4, and 5, The first lens group or the second lens group moves the lens focus formation forward and backward in the direction of the total reflection mirror, or transfers some of the first lens group or the second lens group. And a method of moving back and forth in the direction of the reflecting mirror. An sFPD for outputting light having image information, a projection optical lens system for receiving the image information to form a focal point for image formation, a reflector for reflecting light from the lens system, and light from the reflector In a rear projection optical system comprising a screen for forming an image by using: The projection optical lens system includes a first lens group having negative refractive power and a second lens group having positive refractive power; A total reflection lens provided between the first lens group and the second lens group; And A variable aperture is provided between the total reflection lens and the second lens group, And the variable aperture is an ultra wide-angle projection optical lens system capable of adjusting the size of the aperture by an actuator. The method of claim 10, The sFPD is any one of LCD, DLP, LCoS rear projection optical lens system.

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