LCD projection lens

Abstract

A projection lens for use with a pixelized panel (LCD) is provided. The lens has two positive lens units 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 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. The ratio of f1 to f2 is preferably less than about 0.75.

Description

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 FIG. 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 f1 is substantially shorter than f2, where f1 and f2 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 f1 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, f1 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

FIGS. 1-6 are schematic side views of projection lenses constructed in accordance with the invention.

FIG. 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

FIGS. 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: ##EQU1## 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 FIGS. 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 DataSurf. Clear ApertureNo. 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 Aperture 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 83.6010 a -57.0000 Space 1 93.6511 c -927.4539 29.50000 ACRYLIC 119.7712 a -79.0000 Space 2 124.9913 cf 185.6000 4.00000 ACRYLIC 237.0614 .infin. Image distance 236.86__________________________________________________________________________Symbol Description a -- Polynomial asphere c -- Conic section f -- Fresnel__________________________________________________________________________Conics Surface Number Constant__________________________________________________________________________ 11 -7.1739E+01 13 -1.7000E+00__________________________________________________________________________Even Polynomial AspheresSurf.No. D E F G H I__________________________________________________________________________ 1 -7.0051E-08 -6.3254E-12 -2.9530E-14 7.5364E-19 9.4792E-21 -3.0013E-24 2 7.7762E-08 1.2679E-11 1.0260E-13 -3.2966E-17 -1.6803E-21 1.6991E-23 9 4.1171E-07 2.1244E-10 1.0122E-14 4.0619E-18 4.4932E-21 -1.0666E-2410 2.4362E-07 1.2454E-10 1.2955E-14 1.0067E-17 1.8340E-21 3.0151E-2412 1.3759E-07 5.0414E-11 -2.7910E-15 1.1423E-18 3.9343E-23 -3.3950E-27__________________________________________________________________________Variable SpacesZoom Space 1 Space 2 Focal ImagePos. T(10) T(12) Shift Distance__________________________________________________________________________1 1.500 182.411 -1.425 10.0212 0.500 190.200 -1.000 10.0153 2.000 175.350 -1.800 10.013__________________________________________________________________________First-Order Data Zoom Position 1 2 3__________________________________________________________________________f/number 3.50 3.50 3.50Magnification -0.0645 -0.1000 -0.0322Object Height -1830.8 -1180.0 -3660.0Object Distance -3048.7 -1998.8 -6010.2Effective Focal Length 198.28 202.52 194.61Image Distance 10.021 10.015 10.013Overall Length 3391.4 2348.3 6346.5Forward Vertex Distance 342.78 349.56 336.21Barrel Length 332.76 339.55 326.20Stop Surface Number 6 6 6Distance to Stop 0.00 0.00 0.00Stop Diameter 55.244 56.621 54.042Entrance Pupil Distance 40.838 40.838 40.838Exit Pupil Distance -2564.2 -2859.8 -2270.8__________________________________________________________________________First Order Properties of ElementsElement SurfaceNumber Numbers Power f' lpp l'pp__________________________________________________________________________1 1 2 -0.70980E-02 -140.88 5.1374 -0.210472 3 4 0.18681E-01 53.532 8.2520 -8.25203 4 5 -0.88988E-02 -112.38 0.20149 -2.42614 7 8 -0.10095E-01 -99.059 -2.6268 -5.60255 9 10 0.29494E-02 339.06 35.393 26.0636 11 12 0.57837E-02 172.90 21.342 1.81797 13 14 0.26604E-02 375.88 -0.51716E-08 -2.6778__________________________________________________________________________First-Order Properties of DoubletsElement SurfaceNumbers Numbers Power f' lpp l'pp__________________________________________________________________________2 3 3 5 0.11187E-01 89.389 1.5277 -16.542__________________________________________________________________________First Order Properties of GroupsGroup SurfaceNumber Numbers Power f' lpp l'pp__________________________________________________________________________1 1 10 -0.26248E-03 -3809.7 495.35 349.412 11 12 0.57837E-02 172.90 21.342 1.81793 13 14 0.26604E-02 375.88 -0.51716E-08 -2.6778__________________________________________________________________________First Order Properties of the LensZoom PositionNumber Power f' lpp l'pp__________________________________________________________________________1 0.50433E-02 198.28 223.78 -199.632 0.49377E-02 202.52 228.97 -211.763 0.51385E-02 194.61 218.81 -189.07__________________________________________________________________________ TABLE 2__________________________________________________________________________Lens DataSurf. Clear ApertureNo. 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 .infin. 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 83.8810 a -57.0000 0.50000 94.2611 c -927.4539 30.50000 ACRYLIC 119.0412 a -79.0000 194.22819 124.60__________________________________________________________________________Symbol Description a -- Polynomial asphere c -- Conic section Focal Shift = -1.97869__________________________________________________________________________Conics Surface Number Constant__________________________________________________________________________ 11 -7.5322E+01__________________________________________________________________________Even Polynomial AspheresSurf.No. D E F G H I__________________________________________________________________________ 1 -8.1680E-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 1.0984E-14 7.6281E-18 5.6048E-21 -1.6720E-2410 2.7112E-07 1.4686E-10 1.7530E-14 1.0200E-17 1.4695E-21 2.8348E-2412 1.1260E-07 4.4374E-11 -2.9777E-15 1.1981E-18 4.3134E-23 -6.5187E-27__________________________________________________________________________First-Order Dataf/number 3.50 Overall Length 3505.33Magnification -0.0645 Forward Vertex Distance 340.731Object Height -1830.8 Barrel Length 146.503Object Distance -3164.60 Entrance Pupil Distance 40.9073Effective Focal Length 198.998 Exit Pupil Distance -145.903Image Distance 194.228 Stop Diameter 57.224Stop Surface Number 6 Distance to Stop 6.43__________________________________________________________________________First Order Properties of ElementsElement SurfaceNumber Numbers Power f' lpp l'pp__________________________________________________________________________1 1 2 -0.68364E-02 -146.28 5.2411 -0.110472 3 4 0.18530E-01 53.965 8.2460 -8.24603 4 5 -0.90617E-02 -110.35 0.26468 -2.36164 7 8 -0.99405E-02 -100.60 -2.6199 -5.59265 9 10 0.29494E-02 339.06 35.393 26.0636 11 12 0.57859E-02 172.83 22.057 1.8788__________________________________________________________________________First Order Properties of DoubletElement SurfaceNumbers Numbers Power f' lpp l'pp__________________________________________________________________________2 3 3 5 0.10898E-01 91.762 1.1692 -6.833__________________________________________________________________________First Order Properties of the Lens Power f' lpp l'pp__________________________________________________________________________ 0.50252E-02 199.00 119.64 -15.627__________________________________________________________________________FIRST ORDER DATA, SURF 1 TO 5K PP1 PP2 f'__________________________________________________________________________0.490176E-02 30.3186 -1.10148 204.00__________________________________________________________________________FIRST ORDER DATA, SURF 7 TO 12K PP1 PP2 f'__________________________________________________________________________0.232360E-02 147.569 172.803 430.37__________________________________________________________________________ TABLE 3__________________________________________________________________________Lens DataSurf. Clear ApertureNo. Type Radius Thickness Glass Diameter__________________________________________________________________________1 a -148.4666 6.00000 ACRYLIC 51.922 a 54.4747 0.50000 45.043 40.0292 15.00000 SK18 45.074 -130.3723 6.26676 42.155 Aperture stop 21.40605 34.586 -23.1527 3.00000 SF13 39.967 -64.2034 1.50000 54.398 -54.0449 16.67610 ACRYLIC 54.699 a -35.8273 0.50000 63.6810 a -3465.3279 24.66862 ACRYLIC 93.0911 a -54.7193 121.94030 95.7412 cf 120.0000 4.00000 ACRYLIC 166.7913 .infin. 9.99997 166.48__________________________________________________________________________Symbol Description a -- Polynomial asphere c -- Conic section f -- Fresnel Focal Shift = -1.94463__________________________________________________________________________Conics Surface Number Constant__________________________________________________________________________ 12 -2.0085E+00__________________________________________________________________________Even Polynomial AspheresSurf.No. D E F G H I__________________________________________________________________________ 1 -1.0532E-06 -1.0364E-09 1.3079E-12 -2.2637E-15 4.0754E-18 -2.4681E-21 2 -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-1S 6.7032E-19 -5.6155E-2210 -2.1332E-07 2.4887E-11 3.2458E-14 8.2905E-18 2.9285E-22 -1.2661E-2511 5.7413E-07 4.5720E-11 4.8259E-14 2.5315E-17 -1.5472E-20 9.1310E-24__________________________________________________________________________First-Order Dataf/number 3.50 Overall Length 1401.46Magnification -0.1083 Forward Vertex Distance 231.458Object Height -762.00 Barrel Length 221.458Object Distance -1170.00 Entrance Pupil Distance 20.3913Effective Focal Length 129.271 Exit Pupil Distance 5729.90Image Distance 9.99997 Stop Diameter 34.576Stop Surface Number 5 Distance to Stop 0.00__________________________________________________________________________First Order Properties of ElementsElement SurfaceNumber Numbers Power f' lpp l'pp__________________________________________________________________________1 1 2 -0.12511E-01 -79.928 2.9100 -1.06772 3 4 0.20219E-01 49.458 2.2234 -7.24143 6 7 -0.19987E-01 -50.032 -0.99970 -2.77224 8 9 0.60514E-02 165.25 25.425 16.8555 10 11 0.89025E-02 112.33 16.739 0.264326 12 13 0.41148E-02 243.03 -0.82019E-08 -2.6778__________________________________________________________________________First Order Properties of the Lens Power f' lpp l'pp__________________________________________________________________________ 0.77357E-02 129.27 152.58 -131.33__________________________________________________________________________ TABLE 4__________________________________________________________________________Lens DataSurf. Clear ApertureNo. 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 .infin. 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 64.8910 a -2367.8999 24.39444 ACRYLIC 92.9211 a -54.6713 134.17166 95.59__________________________________________________________________________Symbol Description a -- Polynomial asphere Focal Shift = -1.24114__________________________________________________________________________Even Polynomial AspheresSurf.No. D E F G H I__________________________________________________________________________ 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-2210 -2.4379E-07 2.3325E-11 3.2535E-14 8.2976E-18 2.0542E-22 -2.1158E-2511 6.0221E-07 5.9205E-11 4.6922E-14 2.3851E-17 -1.6076E-20 8.9490E-24__________________________________________________________________________First-Order Dataf/number 3.50 Overall Length 1473.17Magnification -0.1083 Forward Vertex Distance 231.169Object Height -762.00 Barrel Length 96.9976Object Distance -1242.00 Entrance Pupil Distance 20.8429Effective Focal Length 129.736 Exit Pupil Distance -136.607Iinage Distance 134.172 Stop Diameter 36.897Stop Surface Number 5 Distance to Stop 0.45__________________________________________________________________________First Order Properties of ElementsElement SurfaceNumber Numbers Power f' lpp l'pp__________________________________________________________________________1 1 2 -0.12684E-01 -78.838 2.8906 -1.08622 3 4 0.19996E-01 50.010 2.1178 -7.33183 6 7 -0.18289E-01 -54.677 -1.2146 -2.99834 8 9 0.53197E-02 187.98 28.371 20.3495 10 11 0.88539E-02 112.94 16.659 0.38462__________________________________________________________________________First Order Properties of the Lens Power f' lpp l'pp__________________________________________________________________________ 0.77080E-02 129.74 85.332 -8.3775__________________________________________________________________________FIRST ORDER DATA, SURF 1 TO 4K PP1 PP2 f'__________________________________________________________________________0.825105E-02 11.8672 -1.63760 121.20__________________________________________________________________________FIRST ORDER DATA, SURF 6 TO 11K PP1 PP2 f'__________________________________________________________________________0.412919E-02 105.968 138.422 242.18__________________________________________________________________________ TABLE 5__________________________________________________________________________Lens DataSurf. Clear ApertureNo. 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 .infin. 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 93.1810 a -54.6936 133.38308 95.54__________________________________________________________________________Symbol Description a -- Polynomial asphere Focal Shift = -1.06757__________________________________________________________________________Even Polynomial AspheresSurf.No. D E F G H I__________________________________________________________________________ 1 -6.2558E-07 -6.6007E-10 1.3377E-12 -2.7764E-15 3.6207E-18 -1.7047E-21 2 -4.7729E-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-2510 5.3589E-07 1.0862E-10 4.8657E-14 2.7503E-17 -1.4201E-20 9.3743E-24__________________________________________________________________________First-Order Dataf/number 3.50 Overall Length 1471.80Magnification -0.1083 Forward Vertex Distance 229.807Object Reight -762.00 Barrel Length 96.4234Object Distance -1241.99 Entrance Pupil Distance 19.6498Effective Focal Length 129.598 Exit Pupil Distance -136.742Image Distance 133.383 Stop Diameter 37.137Stop Surface Number 5 Distance to Stop -0.86__________________________________________________________________________First Order Properties of ElementsElement SurfaceNumber Numbers Power f' lpp l'pp__________________________________________________________________________1 1 2 -0.11992E-01 -83.389 3.2180 -0.768952 3 4 0.18904E-01 52.899 1.5196 -7.84493 6 7 -0.17354E-10 -57.623 -1.3444 -3.13474 7 8 0.63978E-02 156.30 26.344 18.4715 9 10 0.80676E-02 123.95 17.207 2.1256__________________________________________________________________________First Order Properties of DoubletsElement SurfaceNumbers Numbers Power f' lpp l'pp__________________________________________________________________________3 4 6 8 -0.76835E-02 -130.15 -25.890 -48.110__________________________________________________________________________First Order Properties of the Lens Power f' lpp l'pp__________________________________________________________________________ 0.77162E-02 129.60 83.934 -9.1868__________________________________________________________________________FIRST ORDER DATA, SURF 1 TO 4K PP1 PP2__________________________________________________________________________0.754490E-02 10.2057 -3.41220__________________________________________________________________________FIRST ORDER DATA, SURF 6 TO 10K PP1 PP2__________________________________________________________________________0.446394E-02 93.0606 115.413__________________________________________________________________________ TABLE 6__________________________________________________________________________Lens DataSurf. Clear ApertureNo. Type Radius Thickness Glass Diameter__________________________________________________________________________1 a 94.4760 15.00000 STYRENE 42.782 a -528.9612 0.50000 37.323 .infin. 21.29889 36.844 -27.7690 3.00000 STYRENE 40.465 a -407.8987 4.00000 53.216 -74.3345 12.15783 BK7 53.557 -42.4453 0.50000 61.028 a 164.4718 26.97190 ACRYLIC 92.869 a -62.3055 135.01787 95.37__________________________________________________________________________Symbol Description a -- Polynomial asphere Focal Shift = -0.74200__________________________________________________________________________Even Polynomial AspheresSurf.No. D E F G H I__________________________________________________________________________1 -2.1948E-07 -3.1161E-09 7.4142E-12 -1.0377E-14 -2.2299E-17 3.2858E-202 -1.5111E-06 -5.1899E-09 -8.6485E-12 2.3336E-14 2.8430E-17 -1.0133E-195 -3.9131E-07 -6.8333E-10 5.5582E-13 6.5433E-16 1.3386E-20 -7.1347E-228 -2.9686E-07 -3.7064E-12 9.5859E-15 4.9355E-18 1.5459E-21 5.8285E-259 5.6173E-07 1.1183E-10 1.3209E-14 1.5832E-17 -1.7718E-20 7.9237E-24__________________________________________________________________________First-Order Dataf/number 3.50 Overall Length 1460.42Magnification -0.1083 Forward Vertex Digtance 218.446Object Height -762.00 Barrel Length 83.4286Object Distance -1241.97 Entrance Pupil Distance 14.3855Effective Focal Length 128.370 Exit Pupil Distance -110.515Image Distance 135.018 Stop Diameter 35.707Stop Surface Number 3 Distance to Stop 3.27__________________________________________________________________________First Order Properties of ElementsElement SurfaceNumber Numbers Power f' lpp l'pp__________________________________________________________________________1 1 2 0.73555E-02 135.95 1.4381 -8.05182 4 5 -0.19908E-01 -50.232 -0.13781 -2.02433 6 7 0.59254E-02 168.76 16.511 9.42764 8 9 0.10498E-01 95.259 13.631 -5.1638__________________________________________________________________________First Order Properties of the Lens Power f' lpp l'pp__________________________________________________________________________ 0.77900E-02 128.37 71.383 -7.9999__________________________________________________________________________FIRST ORDER DATA, SURF 4 TO 9K PP1 PP2__________________________________________________________________________0.444232E-02 92.8040 107.813__________________________________________________________________________ TABLE 7______________________________________ Unit 1 Unit 2Ex. No. Surf. Nos. Surf. Nos. f1 f2 f f1/f2______________________________________1 1 to 5 7 to 12 199.16 448.33* 198.99* 0.4442 1 to 5 7 to 12 204.00 430.37 199.00 0.4743 1 to 4 6 to 11 115.38 257.84* 129.60* 0.4474 1 to 4 6 to 11 121.20 242.18 129.74 0.5005 1 to 4 6 to 10 132.56 224.02 129.60 0.5926 1 to 2 4 to 9 135.95 225.11 128.37 0.604______________________________________ *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 minimal effect on the overall focal length of the lens, but a large effec on the value of f2, which effect is not representative of the actual functioning of the f2 unit.

Claims

1. A projection lens for forming an image of an object, said lens having an aperture stop and consisting in order from its image end to its object end of:

(a) a first lens unit having a positive optical power and a focal length f1;

(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, f1 is shorter than f2, and the lens has a back focal length approximately equal to the lens' focal length.

2. The projection lens of claim 1 wherein the second lens unit has a negative lens element at its image end.

3. The projection lens of claim 1 wherein said lens has a focal length f and f1/f is less than or equal to 1.1.

4. The projection lens of claim 3, 1, or 2 wherein the ratio of f1 to f2 is less than about 0.75.

5. The projection lens of claim 3, 1 or 2 wherein each of the first and second lens units has at least one aspherical surface.

6. The projection lens of claim 3, 1 or 2 wherein the first lens unit consists of a single positive lens element.

7. The projection lens of claim 3, 1 or 2 wherein the first lens unit comprises in order from its image end:

(a) a negative lens element; and

(b) a positive lens subunit.

8. The projection lens of claim 7 wherein the positive lens subunit is spaced from the negative lens element by a distance which is less than or equal to 5% of f1.

9. 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.

10. 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.

11. The projection lens of claim 7 wherein the positive lens subunit is a color correcting doublet.

12. The projection lens of claim 11 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface.

13. The projection lens of claim 3, 1, or 2 wherein the second lens unit comprises a color correcting doublet and a positive lens element which has at least one aspherical surface.

14. 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 3, 1, or 2.

15. The projection lens system of claim 14 further comprising a field lens between the pixelized panel and the projection lens.

16. The projection lens of claim 2 wherein the lens has a focal length f and f1/f is less than or equal to 1.1.