LCD PROJECTION LENS

Abstract: A projection lens for use with a pixelized panel (LCD) is provided. The lens has two positive lens units (U1, U2) with an aperture stop between them. The optical powers of each of the units are such that f1 is substantially shorter than f2, where f1 and f2 are the focal lengths of the first lens unit (U1) and the second lens unit (U2), respectively, the first lens unit (U1) being on the system's long conjugate side and the second lens unit (U2) being on the short conjugate side. The ratio of f1 to f2 is preferably less than about 0.75.

Description: LCD PROJECTION LENS FIELD OF THE INVENTION This invention relates to projection lenses and, in particular, to projection lenses which can be used, inter alia, to form an image of an object composed of pixels, such as, a liquid crystal display (LCD). BACKGROUND OF THE INVENTION Projection lens systems (also referred to herein as "projection systems") are used to form an image of an object on a viewing screen. The basic structure of such a system is shown in Figure 7, wherein 10 is a light source (e.g., a tungsten-halogen lamp), 12 is illumination optics which forms an image of the light source (hereinafter referred to as the "output" of the illumination system), 14 is the object which is to be projected (e.g., a matrix of on and off pixels of a LCD panel), and 13 is a projection lens, composed of multiple lens elements, which forms an enlarged image of object 14 on viewing screen 16. Projection lens systems in which the object is a LCD or other pixelized panel are used in a variety of applications, including data display systems. Such projection lens systems preferably employ a single projection lens which forms an image of either a single panel having, for example, red, green, and blue pixels, or three individual panels, one for each color. For ease of reference, the following discussion will be in terms of a projection lens system that employs a single LCD panel, it being understood that the invention can also be used in systems which employ multiple panels and/or other types of pixelization. SUMMARY OF THE INVENTION The projection lenses of the invention comprise two positive lens units with an aperture stop between them. The optical powers of each of the units are such that fl is substantially shorter than £2, where fl and £2 are the focal lengths of the first lens unit and the second lens unit, respectively, the first lens unit being on the system's long conjugate side and the second lens unit being on the short conjugate side. In particular, the ratio of fl to f2 is less than about 0.75. (See Table 7 and note that when the second unit includes a field lens, e.g., a Fresnel field lens, the value of f2 is calculated without the field lens.) In contrast, for a classical double gauss form, fl is about the same as f2, or longer than f2. The projection lenses of the invention are capable of covering a wide field of view. They have a back focal length approximately equal to the focal length of the lens. Each of the first and second lens units has at least one aspherical surface. The first lens unit on the long conjugate side of the stop may consist of a single positive element. However, to obtain a better correction of residual astigmatism and chromatic aberrations, this unit may include a leading negative element closely followed by a positive component which may be a color correcting doublet. As illustrated in Tables 1-5, the spacing between the leading negative element and the positive component is at most about 5% of the focal length of the first lens unit. The second lens unit behind the aperture stop includes a color correcting doublet and a single positive element with at least one aspherical surface. Most of the correction of spherical aberration is obtained in the first lens unit, while off-axis aberrations including coma and distortion, as well as chromatic aberrations, are corrected predominantly in the second lens unit. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1-6 are schematic side views of projection lenses constructed in accordance with the invention. Figure 7 is a schematic diagram showing an overall projection lens system in which the projection lens of the present invention can be used. The foregoing drawings, which are incorporated in and constitute part of the specification, illustrate the preferred embodiments of the invention, and together with the description, serve to explain the principles of the invention. It is to be understood, of course, that both the drawings and the description are explanatory only and are not restrictive of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 1 to 6 illustrate various projection lenses constructed in accordance with the invention. Corresponding prescriptions and optical properties appear in Tables 1 to 6, respectively. The correspondence between the lens units discussed above and the various elements and surfaces of the lenses of Tables 1-6 is set forth in Table 7. HOYA or SCHOTT designations are used for the glasses employed in the lens systems. Equivalent glasses made by other manufacturers can be used in the practice of the invention. Industry acceptable materials are used for the styrene and acrylic elements. The aspheric coefficients set forth in the tables are for use in the following equation: 2 * = — l + [ ;l - (l ° + ' k, )c • 2 >y 2 2 ],ι ι / u » + Dy J 4 + Ey J " + F y J 8 + Gy J 10 + Hy J 12 + Iy J lΛ where z is the surface sag at a distance y from the optical axis of the system, c is the curvature of the lens at the optical axis, and k is a conic constant. The designation "a" associated with various surfaces in the tables represents an aspheric surface, i.e., a surface for which at least one of D, E, F, G, H, or I in the above equation is not zero. The designation "c" represents a conic surface for which the k value in the above equation is not zero. The designation "f" represents a Fresnel lens surface (the Fresnel lens is identified by the designation "FL" in Figures 1 and 3). All dimensions given in the tables are in millimeters. The tables are constructed on the assumption that light travels from left to right in the figures. In actual practice, the viewing screen will be on the left and the LCD panel will be on the right, and light will travel from right to left. Although specific embodiments of the invention have been described and illustrated, it is to be understood that a variety of modifications which do not depart from the scope and spirit of the invention will be evident to persons of ordinary skill in the art from the foregoing disclosure. TABLE 1 Lens Data Surf. Clear Aperture No. Type Radius Thickness Glass Diameter 1 a -1770.1750 8.00000 ACRYLIC 84.11 2 a 72.5195 10.00000 71.77 3 63.3660 25.00000 SK18 68.98 4 -63.3660 4.00000 KF6 65.89 5 762.9749 9.16228 60.48 6 Ap> erture stop 35.18800 57.72 7 -38.4192 5.00000 SF14 63.38 8 -81.9407 1.00000 80.13 9 a -77.4031 18.00000 ACRYLIC 83.60 10 a -57.0000 Space 1 93.65 11 c -927.4539 29.50000 ACRYLIC 119.77 12 a -79.0000 Space 2 124.99 13 cf 185.6000 4.00000 ACRYLIC 237.06 14 Image distance 236.86 Symbol Description a Polynomial asphere c Conic section f Fresnel Conies Surface Number Constant 11 -7.1739E+01 13 -1.7000E+00 Even Polynomial Aspheres Surf. No. D I H I 1 -7 0051E-08 • 6.3254E-12 -2.9530E-14 7.5364E-19 9.4792E-21 0013E-24 2 7.7762E-08 1.2679E-11 1.0260E-13 -3.2966E-17 -1.6803E-21 6991E-23 9 4.1171E-07 2.1244E-10 1.0122E-14 4.0619E-18 4.4932E-21 0666E-24 10 2.4362E-07 1.2454E-10 1.2955E-14 1.0067E-17 1.8340E-21 0151E-24 12 1.3759E-07 5.0414E-11 -2.7910E-15 1.1423E-18 3.9343E-23 3950E-27 Variable Spaces Zoom Space 1 Space 2 Focal Image Pos. T(10) T(12) Shift Distance 1 1.500 182.411 -1.425 10.021 2 0.500 190.200 -1.000 10.015 3 2.000 175.350 -1.800 10.013 TABLE 1 (continued) First-Order Data Zoom Position 1 2_ 3 f/number 3.50 3.50 3.50 Magnification 0.0645 -0.1000 -0.0322 Object Height 1830.8 -1180.0 -3660.0 Object Distance 3048.7 -1998.8 -6010.2 Effective Focal Length 198.28 202.52 194.61 Image Distance 10.021 10.015 10.013 Overall Length 3391.4 2348.3 6346.5 Forward Vertex Distance 342.78 349.56 336.21 Barrel Length 332.76 339.55 326.20 Stop Surface Number 6 6 6 Distance to Stop 0.00 0.00 0.00 Stop Diameter 55.244 56.621 54.042 Entrance Pupil Distance 40.838 40.838 40.838 Exit Pupil Distance 2564.2 -2859.8 -2270.8 First Order Properties of Elements Element Surface Number Numbers Power Ipp I'pp 1 1 2 ■ -0. .70980E-02 • 140.88 5.1374 -0.21047 2 3 4 0. .18681E-01 53.532 8.2520 -8.2520 3 4 5 • -0. .88988E-02 ■ 112.38 0.20149 -2.4261 4 7 8 ■ -0. .10095E-01 -99.059 -2.6268 -5.6025 5 9 10 0. .29494E-02 339.06 35.393 26.063 6 11 12 0. .57837E-02 172.90 21.342 1.8179 7 13 14 0. .26604E-02 375.88 -0.51716E-0£ -2.6778 First-Order Properties of Doublets Element Surface Numbers Numbers Power Ipp I'PP 0.11187E-01 19.389 1.5277 ■ 16.542 First Order Properties of Groups Group Surface Number Numbers Power Ipp I'PP 1 1 10 -0. .26248E-03 -3809.7 495.35 349.41 2 11 12 0. .57837E-02 172.90 21.342 1.8179 3 13 14 0. .26604E-02 375.88 -0.51716E-08 -2.6778 First Order Properties of the Lens Zoom Position Number Power f Ipp I'pp 1 0. .50433E-02 198.28 223.78 -199.63 2 0..49377E-02 202.52 228.97 -211.76 3 0..51385E-02 194.61 218.81 -189.07 TABLE 2 Lens Data Surf. Clear Aperture No. Type Radius Thickness Glass Diameter 1 a -3501.6551 8.00000 ACRYLIC 83.97 2 a 73.8047 10.00000 72.07 3 63.9262 25.00000 SK18 69.86 4 -63.9262 4.00000 KF6 67.04 5 570.3825 2.53228 60.39 6 41.97092 59.72 7 -39.0852 5.00000 SF14 64.45 8 -83.4350 1.00000 80.90 9 a -77.4031 18.00000 ACRYLIC 83.88 10 a -57.0000 0.50000 94.26 11 c -927.4539 30.50000 ACRYLIC 119.04 12 a -79.0000 194.22819 124.60 Symbol Description Polynomial asphere Conic section Focal Shift = -1.97869 Conies Surface Number Constant 11 -7.5322E+01 Even Polynomial Aspheres Surf. No. D E H 1 1680E-08 -9.0415E-12 -2.8846E-14 9.7292E-19 9.4877E-21 -2.8507E-24 2 6.1549E-08 5.4266E-12 9.8518E-14 -3.4835E-17 -1.5392E-21 1.7744E-23 9 3.8615E-07 1.8759E-10 .0984E-14 7.6281E-18 5.6048E-21 1.6720E-24 10 2.7112E-07 1.4686E-10 7530E-14 1.0200E-17 1.4695E-21 2.8348E-24 12 1.1260E-07 4.4374E-11 9777E-15 1.1981E-18 4.3134E-23 6.5187E-27 First Order Data f/number 3.50 Overall Length 3505.33 Magnification -0.0645 Forward Vertex Distance 340.731 Object Height -1830.8 Barrel Length 146.503 Object Distance ■ 3164.60 Entrance Pupil Distance 40.9073 Effective Focal Length 198.998 Exit Pupil Distance -145.903 Image Distance 194.228 Stop Diameter 57.224 Stop Surface Number 6 Distance to Stop 6.43 TABLE 2 (continued) First Order Properties of Elements Element Surface Number Numbers Power f Ipp I'PP 1 1 2 -0.68364E-02 -146.28 5.2411 -0.11047 2 3 4 0.18530E-01 53.965 8.2460 -8.2460 3 4 5 -0.90617E-02 -110.35 0.26468 -2.3616 4 7 8 -0.99405E-02 -100.60 -2.6199 -5.5926 5 9 10 0.29494E-02 339.06 35.393 26.063 6 11 12 0.57859E-02 172.83 22.057 1.8788 First-Order Properties of Doublets Element Surface Numbers Numbers Power f Ipp I'pp 2 3 3 5 0.10898E-01 91.762 1.1692 -16.833 First Order Properties of the Lens Power r Ipp •'PP 0.50252E-02 199. 00 119.64 -15.627 FIRST ORDER DATA, SURF 1 TO 5 K PP1 PP2 f 0.490176E-02 30.3186 -1.10148 204.00 FIRST ORDER DATA, SURF 7 TO 12 - K PP1 PP2 f 0.232360E-02 147.569 172.803 430.37 TABLE 3 Lens Data Surf. Clear Aperture No. Type Radius Thickness Glass Diameter 1 a -148.4666 6.00000 ACRYLIC 51.92 2 a 54.4747 0.50000 45.04 3 40.0292 15.00000 SK18 45.07 4 -130.3723 6.26676 42.15 5 Aperture stop 21.40605 34.58 6 -23.1527 3.00000 SF13 39.96 7 -64.2034 1.50000 54.39 8 -54.0449 16.67610 ACRYLIC 54.69 9 a -35.8273 0.50000 63.68 10 a -3465.3279 24.66862 ACRYLIC 93.09 11 a -54.7193 121.94030 95.74 12 cf 120.0000 4.00000 ACRYLIC 166.79 13 9.99997 166.48 Symbol Description a Polynomial asphere c Conic section f Fresnel Focal Shift = -1.94463 Conies Surface Number Constant 12 -2.0085E+00 Even Polynomial Aspheres Surf. No. D I H -1.0532E-06 -1.0364E-09 1.3079E-12 -2.2637E-15 4.0754E-18 2.4681E-21 -1.0077E-06 1.3853E-10 -5.4208E-12 1.3555E-14 -3.2354E-18 5.1055E-21 9 -7.2513E-07 1.8571E-09 -2.8477E-12 1.3532E-15 6.7032E-19 5.6155E-22 10 -2.1332E-07 2.4887E-11 3.2458E-14 8.2905E-18 2.9285E-22 1.2661E-25 11 5.7413E-07 4.5720E-11 4.8259E-14 2.5315E-17 -1.5472E-20 9.1310E-24 First Order Data f/number 3.50 Overall Length 1401.46 Magnification -0.1083 Forward Vertex Distance 231.458 Object Height -762.00 Barrel Length 221.458 Object Distance -1170.00 Entrance Pupil Distance 20.3913 Effective Focal Length 129.271 Exit Pupil Distance 5729.90 Image Distance 9.99997 Stop Diameter 34.576 Stop Surface Number 5 Distance to Stop 0.00 TABLE 3 (continued) First Order Properties of Elements Element Surface Number Numbers Power f ipp i'pp 1 1 2 -0. .12511E-01 -79.928 2.9100 -1.0677 2 3 4 0, .20219E-01 49.458 2.2234 -7.2414 3 6 7 -0. .19987E-01 -50.032 -0.99970 -2.7722 4 8 9 0. .60514E-02 165.25 25.425 16.855 5 10 11 0. .89025E-02 112.33 16.739 0.26432 6 12 13 0. .41148E-02 243.03 - 0.82019E-08 -2.6778 First Order Properties of the Lens Power f Ipp I'pp 0.77357E-02 129.27 152.58 -131.33 TABLE 4 Lens Data Surf. Clear Aperture No. Type Radius Thickness Glass Diameter 1 a -143.9480 6.00000 ACRYLIC 52.57 2 a 54.0933 0.50000 46.45 3 39.9766 15.00000 SK18 47.01 4 -138.3967 6.26676 44.55 5 23.26477 37.09 6 -23.3945 3.00000 SF13 41.34 7 -57.7517 1.50000 55.58 8 -50.6040 16.57162 ACRYLIC 56.00 9 a -36.2946 0.50000 64.89 10 a -2367.8999 24.39444 ACRYLIC 92.92 11 a -54.6713 134.17166 95.59 Symbol Description a - Polynomial asphere Focal Shift - -1.24114 Even Polynomial Aspheres Surf. No. H 1 -7.8786E-07 -7.4301E-10 1.2284E-12 -2.6558E-15 3.7917E-18 -1.8308E-21 2 -4.9688E-07 6.2284E-10 -5.5378E-12 1.2528E-14 -4.7256E-18 -2.2320E-21 9 -6.7035E-07 1.6035E-09 -2.8384E-12 1.4275E-15 6.5802E-19 -6.1437E-22 10 -2.4379E-07 2.3325E-11 3.2535E-1- .2976E-18 2.0542E-22 -2.1158E-25 11 6.0221E-07 5.9205E-11 4.6922E-14 2.3851E-17 -1.6076E-20 8.9490E-24 First Order Data f/number 3.50 Overall Length 1473.17 Magnification -0.1083 Forward Vertex Distance 231.169 Object Height -762.00 Barrel Length 96.9976 Object Distance -1242.00 Entrance Pupil Distance 20.8429 Effective Focal Length 129.736 Exit Pupil Distance -136.607 Image Distance 134.172 Stop Diameter 36.897 Stop Surface Number 5 Distance to Stop 0.45 First Order Properties of Elements Element Surface Number Numbers Power Ipp I'PP 1 1 2 -0.12684E-01 -78.838 2.8906 -1.0862 2 3 4 0.19996E-01 50.010 2.1178 -7.3318 3 6 7 -0.18289E-01 -54.677 -1.2146 -2.9983 4 8 9 0.53197E-02 187.98 28.371 20.349 5 10 11 0.88539E-02 112.94 16.659 0.38462 TABLE 4 (continued) First Order Properties of the Lens Power f Ipp I'pp 0.77080E-02 129.74 85.332 -8.3775 FIRST ORDER DATA, SURF 1 TO 4 K PP1 PP2 f 0.825105E-02 11.8672 -1.63760 121.20 FIRST ORDER DATA, SURF 6 TO 11 K PP1 PP2 f 0.412919E-02 105.968 138.422 242.18 TABLE 5 Lens Data Surf. Clear Aperture No. Type Radius Thickness Glass Diameter 1 a -215.0838 6.00000 ACRYLIC 50.10 2 a 51.3941 0.50000 44.84 3 39.5202 15.00000 SK18 45.08 4 -204.0199 6.26676 41.86 5 24.70386 37.34 6 -23.5819 3.00000 SF13 42.80 7 -54.9838 17.48359 SK5 58.11 8 -38.5513 0.50000 68.16 9 a -442.7462 22.96924 ACRYLIC 93.18 10 a -54.6936 133.38308 95.54 Symbol Description a - Polynomial asphere Focal Shift = -1.06757 Even Polynomial Aspheres Surf. No. D I H 1 -6.2558E-07 -6.6007E-10 1.3377E-12 -2.7764E-15 3.6207E-lc -1.7047E-21 2 -4.7729F-07 2.8390E-10 -5.2520E-12 1.3608E-14 -6.5024E-18 -3.3618E-21 9 -4.6643E-08 3.6819E-11 2.8968E-14 8.8163E-18 1.7148E-21 2.3288E-25 10 5.3589E-07 1.0862E-10 4.8657E-14 2.7503E-17 -1.4201E-20 9.3743E-24 First Order Data f/number 3.50 Overall Length 1471.80 Magnification -0.1083 Forward Vertex Distance 229.807 Object Height -762.00 Barrel Length 96.4234 Object Distance -1241.99 Entrance Pupil Distance 19.6498 Effective Focal Length 129.598 Exit Pupil Distance -136.742 Image Distance 133.383 Stop Diameter 37.137 Stop Surface Number 5 Distance to Stop -0.86 First Order Properties of Elements Element Surface Number Numbers Power f Ipp I'PP 1 1 2 ■ -0. .11992E-01 -83.389 3.2180 -0.76895 2 3 4 0..18904E-01 52.899 1.5196 -7.8449 3 6 7 - -0. , 17354E-01 -57.623 -1.3444 -3.1347 4 7 8 0..63978E-02 156.30 26.344 18.471 5 9 10 0..80676E-02 123.95 17.207 2.1256 TABLE 5 (continued) First-Order Properties of Doublets Element Surface Numbers Numbers Power f Ipp i'pp 3 4 6 8 -0.76835E-02 -130.15 -25.890 -48.110 First Order Properties of the Lens Power f Ipp i'pp 0.77162E-02 129.60 83.934 -9.186 FIRST ORDER DATA, SURF 1 TO 4 K PP1 PP2 0.754400E-02 10.2057 3.41220 FIRST ORDER DATA, SURF 6 TO 10 K PP1 PP2 0.446394E-02 93.0606 115.413 TABLE 6 Lens Data Surf. Clear Aperture No. Type Radius Thickness Glass Diameter 1 a 94.4760 15.00000 STYRENE 42.78 2 a -528.9612 0.50000 37.32 3 21.29889 36.84 4 -27.7690 3.00000 STYRENE 40.46 5 a -407.8987 4.00000 53.21 6 -74.3345 12.15783 BK7 53.55 7 -42.4453 0.50000 61.02 8 a 164.4718 26.97190 ACRYLIC 92.86 9 a -62.3055 135.01787 95.37 Symbol Description a - Polynomial asphere Focal Shift = 0.74200 Even Polynomial Aspheres Surf. No. D I H I -2.1948E-07 -3.1161E-09 7.4142E-12 0377E-14 2299E-17 3.2858E-20 ■ 1.5111E-06 -5.1899E-09 -8.6485E-12 3336E-14 8430E-17 -1.0133E-19 -3.9131E-07 -6.8333E-10 5.5582E-13 5433E-16 3386E-20 -7.1347E-22 -2.9686E-07 -3.7064E-12 9.5859E-15 9355E-18 5459E-21 5.8285E-25 5.6173E-07 1.1183E-10 1.3209E-14 5832E-17 7718E-20 7.9237E-24 First Order Data f/number 3.50 Overall Length 1460.42 Magnification -0.1083 Forward Vertex Distance 218.446 Object Height -762.00 Barrel Length 83.4286 Object Distance -1241.97 Entrance Pupil Distance 14.3855 Effective Focal Length 128.370 Exit Pupil Distance -110.515 Image Distance 135.018 Stop Diameter 35.707 Stop Surface Number 3 Distance to Stop 3.27 First Order Properties of Elements Element Surface Number Numbers Power Ipp I'pp 1 1 2 0 73555E-02 135.95 1.4381 -8 0518 2 4 5 -0 19908E-01 -50.232 -0.13781 -2 0243 3 6 7 0 59254E-02 168.76 16.511 9 4276 4 8 9 0 10498E-01 95.259 13.631 -5 1638 TABLE 6 (continued) First Order Properties of the Lens Power f Ipp I'PP 0.77900E-02 128.37 71.383 -7.9999 FIRST ORDER DATA, SURF 4 TO 9 K PP1 PP2 0.444232E-02 92.8040 107.813 -IT- TABLET * Value calculated without the Fresnel lens since the Fresnel lens is primarily a field lens which serves to couple the lens' entrance pupil to the exit pupil of the illumination system. As such, the Fresnel lens has a minimal effect on the overall focal length of the lens, but a large effect on the value of f2, which effect is not representative of the actual functioning of the f2 unit.

Claims: What is claimed is: 1. A projection lens for forming an image of an object, said lens having an aperture stop and comprising in order from its image end to its object end: (a) a first lens unit having a positive optical power and a focal length fl; (b) a second lens unit having a positive optical power and a focal length f2; wherein the aperture stop is located between the first and second lens units and fl is substantially shorter than f2. 2. The projection lens of Claim 1 wherein the ratio of fl to f2 is less than about 0.75. 3. The projection lens of Claim 1 wherein the lens has a back focal length approximately equal to the lens' focal length. 4. The projection lens of Claim 1 wherein each of the first and second lens units has at least one aspherical surface. 5. The projection lens of Claim 1 wherein the first lens unit consists of a single positive lens element. 6. The projection lens of Claim 1 wherein the first lens unit comprises in order from its image end: (a) a negative lens element; and (b) a positive lens subunit. 7. The projection lens of Claim 6 wherein the positive lens subunit is closely spaced to the negative lens element. 8. The projection lens of Claim 6 wherein the positive lens subunit is a color correcting doublet. 9. The projection lens of Claim 1 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface. 10. The projection lens of Claim 6 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface. 11. The projection lens of Claim 7 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface. 12. The projection lens of Claim 8 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface. 13. A projection lens system for forming an image of an object, said system comprising: (a) an illumination system comprising a light source and illumination optics which forms an image of the light source; (b) a pixelized panel which comprises the object; and (c) the projection lens of Claim 1.

Inventors: MOSKOVICH JACOB, MOSKOVICH, JACOB
Applicants: MOSKOVICH JACOB, US PRECISION LENS INC, MOSKOVICH, JACOB, U.S. PRECISION LENS INCORPORATED
Application year: 1997
Main classification: G02B3
IPC codes: G02B9, G02B13