Abstract:
A projection display device includes a lens module, a light source and an adjusting device. The lens module has a first lens and a second lens. The light source emits light through the first lens and the second lens to a surface. The adjusting device is used to change the distance between the first lens and the second lens, thereby adjusting brightness and uniformity of the projected pictures on the surface.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to a projector with adjustable brightness and uniformity. 
     2. Description of the Related Art 
     The portable digital projectors commercially available in the market include DLP (Digital Light Processing) projectors and LCD panel (Liquid Crystal Display panel) projectors. The two kinds of projectors have a common defect: either the picture brightness or the uniformity of brightness produced by the projectors is poor. FIGS. 1A and 1B depict this conundrum. In FIG. 1A, the brightness on the central portion of a projection surface (xy-plane)  100  is strong but the brightness on the side portions of the projection surface  100  is weak. That is, the brightness is good but the uniformity of brightness is poor. In FIG. 1B, the uniformity of brightness on the projection surface  100  is greatly improved. However, the brightness on the central portion of the projection surface  100  is weakened. 
     Generally, a portable digital projector is connected to a computer for a user to make a briefing, or is connected to an image output device such as a video tape recorder, a VCD player, an LD player or a DVD player to show films. In the case of a briefing, the user prefers the brightness rather than the uniformity of brightness because the briefing room generally is not dark enough. In the case of showing films, however, the user prefers the uniformity of brightness rather than the brightness so as to produce clear and beautiful pictures. Taking both cases into consideration, the projector manufacturers generally compromise between the brightness and the uniformity in design. As a result, the projection picture produced by the projector is not bright enough when the user makes a briefing, and the uniformity of brightness is not good enough when the user watches a film. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a projection display device that solves the above-mentioned problem. 
     The projection display device of the present invention includes a lens module, a light source and an adjusting device. The lens module has a first lens and a second lens. The light source emits light through the first lens and the second lens to a projection surface. The adjusting device is used to change the distance between the first lens and the second lens, thereby adjusting the brightness and the uniformity of brightness on the projection surface to meet the needs of users in various applications. 
     In conclusion, the projection display device of the present invention allows the user to adjust the brightness and the uniformity of brightness so as to produce good projection quality in different situations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
     FIG. 1A depicts a case of good brightness but poor uniformity of brightness on a projection surface; 
     FIG. 1B depicts a case of good uniformity of brightness but poor brightness on a projection surface; 
     FIG. 2A depicts a projection display device of a first embodiment of the present invention, in which the distance between the lenses of a relay lens module is short; 
     FIG. 2B depicts a projection display device of the first embodiment of the present invention, in which the distance between the lenses of the relay lens module is long; 
     FIG. 3A depicts a projection display device of a second embodiment of the present invention, in which the distance between the lenses of a relay lens module is short; 
     FIG. 3B depicts a projection display device of a second embodiment of the present invention, in which the distance between the lenses of the relay lens module is long; 
     FIG. 4A is a sectional view of a means for adjusting the distance between the lenses of the relay lens module in accordance with an example of the present invention; 
     FIG. 4B is a side view of FIG. 4A; 
     FIG. 4C is a perspective diagram of FIG. 4A; and 
     FIG. 4D is also a perspective diagram of FIG. 4A, in which, however, the inner cylinder is rotated with respect to the outer cylinder to adjust the distance between the lenses of the relay lens module. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 2A and 2B depict a projection display device of a first embodiment of the present invention, the arrangement of which is applicable to a DLP projector. The projection display device includes a lamp  1 , a reflector  2 , a front converging lens  3 , a color wheel  4 , a relay lens module  5 , a rear converging lens  6 , a digital micromirror device (DMD)  7  and a projection lens  8 , all of which are arranged in series to form an optical path (OL). It is noted that the relay lens module  5  includes two lenses  5   a ,  5   b.    
     In operation, the lamp  1  is turned on to emit light. The reflector  2  reflects the light, through the front converging lens  3 , to the color wheel  4 . The color wheel  4  generally is provided in a color projector and consists of three filters for generating red, green and blue lights. As soon as the lamp  1  is turned on, the color wheel  4  is rotated at a predetermined speed so that the light passing therethrough is filtered to alternately generate red, green and blue lights. Furthermore, the speed of rotation of the color wheel  4  is adjustable. 
     The colored light generated by the color wheel  4  goes through the relay lens module  5  and the rear converging lens  6  and then arrives at the digital micromirror device  7 . In the present invention, the distance between the two lenses  5   a ,  5   b  of the relay lens module  5  is adjustable by using an adjusting means. The adjusting means will be introduced later. 
     The lenses  5   a ,  5   b  of the relay lens module  5  are converging lenses and thus the power of the lenses  5   a ,  5   b  are positive. If the distance (indicated by symbol “a”) between the two lenses  5   a ,  5   b  of the relay lens module  5  is short as shown in FIG. 2A, then the total power of the lenses  5   a ,  5   b  is great. Thereby, the emergent angle (indicated by symbol “u”) of the light is also great, so that the light beam is narrow while passing through the DMD  7  (the light beam is focused at the position P). As a result, the brightness is strong on the central portion of the DMD  7  but rapidly decreases in the directions away from the central portion of the DMD  7 . The uniformity of the brightness on the whole DMD  7  is not so good. 
     Now referring to FIG. 2B, if the distance (indicated by symbol “b”) between the two lenses  5   a ,  5   b  of the relay lens module  5  is long (b&gt;a), then the total power of the lenses  5   a ,  5   b  is small. Thereby, the emergent angle (u′) of the light is also small. Then, the light beam is wide while passing through the DMD  7  (the light beam is focused at the position P′ and the position P′ is behind the position P shown in FIG.  2 A). As a result, the brightness on the central portion of the DMD  7  is decreased, but the brightness on the side portions of the DMD  7  is increased. The uniformity of the brightness on the whole DMD  7  is improved. 
     In contrast to the conventional projection display device in which the distance between the lenses of the relay lens module is fixed, the projection display device of the present invention allows the user to adjust the distance between the lenses  5   a ,  5   b  so as to selectively improve the brightness or the uniformity of brightness. Therefore, the projection display device of the present invention always provides the best effect in various operating situations. 
     FIGS. 3A and 3B depict a projection display device of a second embodiment of the present invention, the arrangement of which is applicable to an LCD panel projector. The projection display device includes a lamp  1 , a reflector  2 , a front converging lens  3 , a relay lens module  5 , a rear converging lens  6 , a liquid crystal display (LCD) panel  9  and a projection lens  8 , all of which are arranged in series to form an optical path (OL). The relay lens module  5  includes two lenses  5   a ,  5   b.    
     In operation, the lamp  1  is turned on to emit light. The reflector  2  reflects the light, through the front converging lens  3 , the relay lens module  5  and the rear converging lens  6 , to the LCD panel  9 . If the distance (indicated by symbol “a”) between the two lenses  5   a ,  5   b  of the relay lens module  5  is short as shown in FIG. 3A, then the light beam is narrow while passing through the LCD panel  9 . As a result, the brightness is strong on the central portion of the LCD  9  but is rapidly decreased in the directions away from the central portion of the LCD  9 . The uniformity of the brightness on the whole LCD panel  9  is poor. On the other hand, if the distance (indicated by symbol “b”) between the two lenses  5   a ,  5   b  of the relay lens module  5  is long (b&gt;a) as shown in FIG. 3B, then the light beam is wide while passing through the LCD panel  9 . As a result, the brightness on the central portion of the LCD panel  9  is decreased, but the brightness on the side portions of the LCD panel  9  is increased. The uniformity of the brightness on the whole LCD panel  9  is thus improved. 
     For both of the DLP projector and LCD panel projector, the present invention allows the user to selectively improves the brightness or the uniformity of brightness via adjusting the distance between the lenses  5   a ,  5   b  of the relay lens module  5 . The use of the projection display device of the present invention is more flexible than a conventional one. 
     Now, the means for adjusting the distance between the lenses  5   a ,  5   b  of the relay lens module  5  is introduced. Referring to FIGS. 4A,  4 B and  4 C, the adjusting means has an outer cylinder  10   a  and an inner cylinder  10   b  coaxially received in the outer cylinder  10   a . The outer cylinder  10   a  has a flange  10   d  and an elastic ring  10   e  inside for holding the lens  5   a  therebetween, while the inner cylinder  10   b  also has a flange  10   f  and an elastic ring  10   g  inside for holding the lens  5   b  therebetween. Furthermore, three posts  10   h   1 ,  10   h   2 ,  10   h   3  spaced 120° to each other and equipped with wheels which are attached onto the inner cylinder  10   b , while three curved grooves  10   i   1 ,  10   i   2 ,  10   i   3  are provided on the outer cylinder  10   a  for receiving the wheels of the posts  10   h   1 ,  10   h   2 ,  10   h   3 . In operation, the user moves the post  10   h   1  along the groove  10   i   1  so that the inner cylinder  10   b  is rotated and axially moved with respect to the outer cylinder  10   a  as shown in FIG. 4D, with the wheels rolling in the grooves. Thereby, the lens  5   b  is moved far away from or close to the lens  5   a . As a result, the user can easily adjust the distance between the lenses  5   a ,  5   b  as he wishes by moving the post  10   h   1 . 
     It is understood that the projection display device of the present invention allows the user to adjust the brightness and the uniformity of brightness so as to produce good projection quality in different application situations. 
     Furthermore, the present invention does not use additional lenses to adjust the brightness and the uniformity of brightness. Instead, the present invention uses a simple mechanism to adjust the distance between the lenses of the relay lens module, which is relatively inexpensive. 
     Furthermore, in this preferred embodiment the distance between the lenses of the relay lens module is changed in the manner of stepless adjustment as disclosed above. However, it is understood that stepped adjustment is applicable to the present invention. 
     While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.