|Title of Invention
LENS SYSTEM FOR AN IMAGER TO IMAGER RELAY
|A lens system for use in a two-stage projection system that relays light output from a first imager on a pixel-by pixel basis onto a second imager. The lens system includes a double gauss lens set having a distortion of less than about 0.015% with at least about 90% of the light energy of a specific pixel projected within about a 15.4 micrometer square.
|FIELD OF TftE INVENTION
The present invention is related generally to a lens system for use in a projection system and more particularly to a low distortion, 1 -to-1 projection lens for projecting an image from a first imager onto a second imager in a two stage projector
Liquid crystal displays (LCDs), and particularly liquid crystal on silicon
COS) systems using a reflective light engine or imager, are becoming increasingly nre\ alent in imaging devices such as rear projection television (RPTV). In an LCOS system, projectcd light is polarized by a polarizing beam splitter (PBS) and directed onto a LCOS
mager or light engine comprising a matrix of pixels. Throughout this specification, and consistcnt with the practice of the relevant art, the term pixel is used to designate a small area
not of an image, the corresponding portion of a light transmission, and the portion of an imager producing that light transmission.
Each pixel of the imager modulates the light incident on it according to a gray-
scale factor input to the imager or light engine to form a matrix of discrete modulated light signals or pixels. The matrix of modulated light signals is reflected or output from the imager
nd directed to a system of projection lenses which project the modulated light onto a display screen, combining the pixels of light to form a viewable image. In this system, the gray-scale
anation from pixel to pixel is limited by the number of bits used to process the image signal.
the contrast ratio from bright state (i. e. maximum light) to dark state (minimum light) is
limited by the leakage ot light in the imager. U.S Fatent No. 5,023,4oo to Dietzsch represents ele\ant art disclosing a telecentric lens system including a double Gauss lens.
One of the major disadvantages of existing LCOS systems is the difficulty in reducing the amount of light in the dark state, and the resulting difficulty in providing outstanding contrust ratios. This is, in part, due to the leakage of light, inherent in LCOS systems.
In addition, since the input is a fixed number of bits (e. g. , 8,10, etc. ), which must describe the full scale of light, there tend to be very few bits available to describe subtle differences in darker areas of the picture. This can lead to contouring artifacts.
One approach to enhance contrast in LCOS in the dark state is to use a
OLORSWITCHTM or similar device to scale the entire picture based upon the maximum
value in that particular frame. This improves some pictures, but does little for pictures that
contain high and low light levels. Other attempts to solve the problem have been directed to
making better imagers, etc. but these are at best incremental improvements.
What is needed is a projection system that enhances the contrast ratio for video .mages, particularly in the dark state, and reduces contouring artifacts.
The present invention provides a lens system configured to project an image from a list imager on a pixel-by-pixel basis onto a second imager in a two stage projector ciutecture. To project an image from a first imager on a pixel-by-pixel basis onto a second mager, a double-gauss lens system is provided according to an embodiment of the present invention having a distortion of less than about 0.015% and projecting at least about 90% of the light energy of a specific pixel on the first imager within about a 15.4 micrometer square The second imager. In an exemplary embodiment of the invention, the magnification of the
lens system is very precisely controlled at about -1 and teieceatricity is maintained at both the input and the output of the lens system.
The invention will now be described with reference to the accompanying figures, of which:
Figure 1 shows an exemplary lens system according to an embodiment of the present invention;
Figure 2 shows the calculated distortion for the leas system of Figure 1; and
Figure 3 shows the calculated ensq uared energy for the leas system of Figure 1.
The inventors have determined that, by projecting the output of a first imager onto a second imager such that the output of a particular pixel in the first imager is projected onto a corresponding pixel in the second imager, a projection system can be provided with enhanced contrast and reduced contouring. The inventors have determined that this two-stage .irehitecture requires a lens system with very low distortion and highly ensquared energy. I he light from a pixel on the first imager must be centered on its corresponding pixel. Also, most of the light must fall within the area of the corresponding pixel.
The present invention provides a low-distortion, higb-ensquared energy, relay lens system for use in a two-stage projection architecture. In an exemplary embodiment of the invention, a double gauss lens system is provided to relay light from a first imager lo a second imager 60 with distortion of less than 0.015% and at least 90% of the light energy from a specific pixel of the first imager 50 projected onto about a 15.4 micrometer square on the second imager. An exemplary two-stage projection system, as shown in Figure 1, comprises a
first imager 50 and a second imager 60, with two polarizing beam splitters (PBS's) 71, 72 and a lens set or lens system 80 disposed between the imagers 50, 60 to relay light images from the first imager 50 on a pixel-by-pixel basis onto correspoading pixels of the second imager 60.
As shown in Fig. 1, exemplary relay leas system 80 comprises a first aspherical lens S i and a first acromatic lens 82 between the Gift PBS 71 and the focal point of the lens system or system stop 83. Between the system stop 83 and the second imager 72, leas system 80 comprises a second acromatic lens 84 and a second aspherical lens 85. First aspberical lens 81 has a first surface 81a and secoad surface 81b which bead the diverging light pattern from the first PBS 71 into a light pattern converging toward the optical axis of lens system 80. First acromatic lens 82 has a first surface 82a, a secoad surface 82b, and a third surface 82c, which focus the converging light pattern from the first aspherical lens 81 onto the system stop
83. At the system stop 83, the light pattern inverts and diverges. The second acromatic lens
84, which has a first surface 84a, a second surface 84b, and a third surface 84c, is a mirror
image of first acromatic lens 82 (i.e., the same lens turned backward such that first surface 84a
of second acromatic lens 84 is equivalent to third surface 82c of first acromatic lens 82 and
third surface 84c of second acromatic lens 84 is equivalent to first surface 82a of first
acromatic lens 82). The surfaces 84a, 84b, and 84c of second acromatic lens 84 distribute the
diverging light pattern onto the second aspherical lens 85. The second aspherical lens 85,
which has a first surface 85a and a secoad surface 85b, is a mirror image of the first aspherical
lens 81. Surfaces 85a and 85b bend the light pattern to converge to form an inverted image on
the second imager 72 that has a one-to-one corresondenceo to the object or matrix of pixels
from the first imager 50. The surfaces of relay lens system 80 are configured to work with the
imagers 50, 60 and PBS's 71, 72 to achieve the one-to-one correspondence of the pixels of
first imager 50 and second imager 60. A summary of the surfaces of an exemplary two-stage
projection system 30 are provided in Table 1, and aspherical coefficients for surface 81a, 8 lb, 85a, and 85b are provided in Table 2. These exemplary tees siafaoes were developed by the inventors using ZEMAX™ software and novel characteristics determiaed by lie inventors. Various modifications can be made to this exemplary projection system based on such factors as: cost, size, luminance levels, and other design factors. In relay lens system 80 acromatic lenses 82 and 84 are equivalent and Mpherical leases 81 and 85 are equivalent. I herefore, fewer unique parts are required providing manufacturing efficiencies and reduced cost. Also, the acromatic lenses 82, 84 of the exemplary lens system 80, comprise inexpensive optical glass (SF15 having a cost approximately 2.25 times the cost of BK7 and BAK2 having a cost approximately 1.85 times the cost of BK7). (SP15, BK7, and BAK2 are commercially available from the Schott Corpontion of Yonkers, New York.)
TABLE 1 (dimensions in mm)
After the first light matrix 5 leaves the relay lens system 80, it enters into a second PBS 72 through a first surface 72a. Second PBS 72 has a polarizing surface 72p that reflects the s-polarity first light matrix 5 through a second surface 72b onto the second imager 60. In me exemplary embodiment, illustrated in Figure 1, second imager 60 is an LCOS imager which modulates the previously modulated first light matrix 5 on a pixel-by-pixel basis Proportional to a gray scale value provided to the second imager 60 for each individual pixel. The pixels of the second imager 60 correspond on a one-for-one basis with the pixels of the
first imager 50 and with the pixels of the display image. Thus, the input of a particular pixel (1,J) to the second imager 60 is the output from eorrespoadiag pixel (i j) of the first imager 50.
The lens system 80 summarized in Tables 1 and 2 was designed using the ZEMET™ software package under system constraints devised by the inventors. The calculated distortion and the ensquared energy of the lens system 90 are shown in Figures 2 and 3, respectively. The distortion is less than 0.015%, causiag the light output from a particular pixel (ij) in the first imager 50 to be relayed or projected oato a corresponding pixel (ij) in the second imager 60, allowing a video image, for example, to be modulated by a combination of values provided to the first imager 50 and second imager 60 for that pixel (i j). The light energy from the first imager 50 is highly ensquared, with at least 90% of the light energy output from particular pixel (i,j) on the first imager 50 being projected onto a 15.4 micron square on the second imager 60. Since the pixel size for an exemplary LCOS imager is 12 microns, the inajority of light from a particular pixel (ij) oa the first imager 50 will fall on the corresponding pixel (i j) on the second imager 60.
The magnification for a one-to-one lens system should be approximately -1.0 when the imagers 50, 60 are the same size to project an image from the first imager 50 onto the second imager 60 on a pixel-by-pixel basis. The exemlary lens system 80 provides a magnification of -0.99977 as calculated by the ZEMAX™ software.
The exemplary lens system 80 also provides a low F-number of no greater than 2.8, and more particularly a calculated F-number of about 2.798. This low F-number is desired to ensure adequate illumination of the viewing screen. The exemplary lens system 80 is also compact, having an overall distance between imagers 50, 60 of about 161.25 mm. This overall length is a summation of the thickness values for the various surfaces of the lens system, the thickness values being the linear distance to the next surface.
Also, because the light input to the projection system is telecentric and the projection lens requires a telecentric image, the lens system 80 mast be highly teleceatric. The calculated maximum deviations from the chief ray in the center of the projected image for the exemplary lens system 80 are 1.03 degrees of input angle aad 1.00 degrees of output angle.
The foregoing illustrates some of the possibilities for practicing the invention. Many other embodiments are possible within the soope and spirit of the invention. It is, therefore, intended that the foregoing description be regarded as illustrative rather than limiting, and that the scope of the invention is given by the appended claims together with their full range of equivalents.
1. A projection system characterized by
a first imager;
second imager; and
a lens system having a double gauss lens set, the double gauss lens set having a distortion of less than about 0.015% with at least about 90% of the light energy of a specific pixel projected within a 15.4 micrometer square and light from the first imager being relayed on a pixel-by-pixel basis onto the second imager.
2. The projection system as claimed in claim 1, wherein said double gauss lens set has a magnification of between about -0.9997 and -1.0003.
3. The projection system as claimed in claim 1, wherein said double gauss lens set has a telecentricity with an input and output angle deviation of less than 1.05 degrees.
4. The projection system as claimed in claim 3, wherein said double gauss lens set has a telecentricity with an input angle deviation of less than 1.03 degrees and an output angle deviation of less than 1.0 degrees.
5. The projection system as claimed in claim 3, wherein said double gauss lens set consists of a pair of symmetrical aspherical lenses surrounding a pair of symmetrical acromatic lenses.
6. The projection system as claimed in claim 5, wherein said acromatic lenses comprise
7. The projection system as claimed in claim 1, wherein the total distance between the first and second imagers is less than 165 mm.
8. The projection system as claimed in claim 1, wherein the total distance between the first and second imagers is about 161.25 mm.
9. The projection system as claimed in claim 1, wherein the double gauss lens set has an F-number no greater than about 2.8.
10. An imager to imager relay lens system for use in a projection system as claimed in claim 1, characterized by a lens set consisting of one pair of equivalent acromatic lenses and one pair of equivalent aspherical lenses positioned and configured to project the light output from a particular pixel on a first imager onto a corresponding pixel on a second imager.
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|THOMSON LICENSING S.A.
|46, QUAI A LE GALLO, F-92648 BOULOGNE CEDEX, FRANCE
|PCT International Classification Number
|PCT International Application Number
|PCT International Filing date