Patent Publication Number: US-9417443-B2

Title: Projector, projecting lens of the projector and method of projecting images

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a projection device, and more particularly to a projector, a projecting lens of the projector, and a method of projecting images. 
     2. Description of the Related Art 
     With advancement in technology, projectors have become the most popular devices used in a presentation. A projecting lens in a projector is the most important element to clearly show images on a screen. 
     In order to use the projector in a limited space, short-throw projection is a common requirement in the modern projector. A conventional projecting lens for short-throw projection usually has a lot of large lenses to obtain short-throw projection and high optical performance. 
     Therefore, the size and weight of the conventional projecting lens for short-throw projection conflicts with the current design focus of projectors, which is miniaturization and lightweight. Besides, it takes a high cost to manufacture the conventional projecting lenses because of their sizes. 
     In conclusion, the conventional projecting lens of the short-throw projector needs to be improved. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide a projecting lens of a projector, which has a small size, low cost, and high optical performance. 
     According to the objective of the present invention, the present invention provides a projector, which includes an image ray generator and a projecting lens. The image ray generator generates image rays; the projecting lens receives the image rays from the image ray generator and projects the image rays onto a screen, wherein the projecting lens includes a projection optical system and a relay optical system which is closer to the image ray generator than the projection optical system. The relay optical system has a plurality of lenses, through which the image rays from the image ray generator pass to the projection optical system. The projection optical system includes a lens group and a reflector, and the lens group is between the relay optical system and the reflector; the lens group includes at least one lens, and has a first optical side facing the relay optical system and a second optical side facing the reflector. The image rays enter the lens group through the first optical side and leave through the second optical side, and then the image rays is reflected by the reflector to enter the lens group again through the second optical side; the image rays are projected onto the screen after leaving the lens group through the first optical side. 
     The present invention further provides a projecting lens, which includes a relay optical system and a projection optical system. The relay optical system includes a plurality of lenses; the projection optical system includes a lens group and a reflector, wherein the lens group is between the relay optical system and the reflector; the lens group includes at least a lens, and has a first optical side facing the relay optical system and a second optical side facing the reflector; wherein image rays pass through the relay optical system, enter the lens group through the first optical side, and then leave through the second optical side to be reflected by the reflector to enter the lens group again through the second optical side and then leave through the first optical side. 
     The present invention further provides a method of projecting an image onto a screen, which includes the steps of: generating image rays which contain an image; making the image rays pass through a relay optical system, wherein the relay optical system has a plurality of lenses; making the image rays pass through a lens group, wherein the image rays enter the lens group through a first optical side thereof and leave through a second optical side thereof; reflecting the image rays back into the lens group again, wherein the reflected image rays enter the lens group through the second optical side and leave through the first optical side; and projecting the image rays onto a screen after the image rays leaving the leas group. 
     Therefore, the projecting lens of the projector and the method of projecting images can reduce the size of the projector, and lower the cost of manufacturing. In addition, the projector would have high optical performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sketch diagram of the projector of a first preferred embodiment of the present invention; 
         FIG. 2  is a sketch diagram of the arrangement of the lenses of the projecting lens of the first preferred embodiment of the present invention; 
         FIG. 3  is a sketch diagram of the first preferred embodiment of the present invention, showing the light paths between the projecting lens and the screen; 
         FIG. 4  is a sketch diagram of the arrangement of the lenses of the projecting lens of a second preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1 , a projector  100  of the first preferred embodiment of the present invention includes an image ray generator  10  and a projecting lens  20 . The image ray generator  10  generates image rays P which contain an image. The image ray generator  10  has a prism F where the image rays P emit through. The image rays P emit through the projecting lens  20  to be projected onto a screen. The projecting lens  20  includes a relay optical system  22  and a projection optical system  24  in an order from an image source side, which is closer to the image ray generator  10 , to an image formation side, which is closer to the screen. 
     As shown in  FIG. 2 , the relay optical system  22  includes eleven lenses L 1 -L 11  in sequence, in which the first lens L 1  is closest to the image source side, and the eleventh lenses L 11  is closest to the image source side. The first, second, fifth, sixth, seventh, eighth, ninth, tenth, and eleventh lenses L 1 -L 2  and L 5 -L 11  are single lenses, and the third and fourth lenses L 3  and L 4  are bonded together to form a compound lens. The relay optical system  22  receives the image rays P from the image ray generator  10 , changes the optical characteristics of the image rays P, and then emits it to the projection optical system  24 . The number of the lenses in the relay optical system  22  and the formation of each lens may differ according to different optical requirements. 
     As shown in  FIG. 1  and  FIG. 2 , the projection optical system  24  includes a lens group G and a reflector R. The lens group G is closer to the relay optical system  22  than the reflector R. In other words, the lens group G is between the relay optical system  22  and the reflector R. The lens group G includes two lenses L 11  and L 12 , in which the lens L 11  is a single lens, and the lens  12  is a compound lens. The lens group G has a first optical side S 1 , which is closer to the relay optical system  22 , and a second optical side S 2 , which is closer to the reflector R. The first optical side S 1  is a surface of the lens L 12  facing the relay optical system  22 , and the second optical side S 2  is a surface of the lens L 13  facing the reflector R. The reflector R has an aspheric concave surface facing the lens group G. A diameter of reflector R is in a range between 0.5 times and 1.5 times of a diameter of the largest lens of the relay optical system  22  and the projection optical system  24 . In practice, the surface of the reflector R could be a spherical surface or any other surfaces as well. In the first preferred embodiment, the diameter of the reflector R is 62 mm, and the largest lens of the projection optical system  24  is the lens L 11  with a diameter of 80 mm, which means, the diameter of the reflector R is 0.775 times of the diameter of the largest lens of the relay optical system  22  and the projection optical system  24 . 
     The projecting lens  20  further satisfies the following condition:
 
−20≦CRA≦20
 
     where CRA is a chief ray angle of the projection optical system  24 . 
     In the first preferred embodiment, the chief ray angle is 7.542 when a normalized field at a testing position T (the edge of projection, as shown in  FIG. 2 ) is 1.0. 
     As shown in  FIG. 3 , after the image rays P from the image ray generator  10  enter the projecting lens  20 , they pass through the relay optical system  22 , enter the lens group G through the first optical side S 1 , and then leave the lens group G through the second optical side S 2  to the reflector R. The reflector R reflects the image rays P back to the lens group G. Next, the reflected image rays P enter the lens group G through the second optical side S 2 , and leave through the first optical side S 1 . The image rays P continuously pass through the eleventh lens L 11 , which is the lens of the relay optical system  22  closest to the projection optical system  24 , and the eleventh lens L 11  projects the image rays P onto a screen  200 . Some of the image rays P continuously pass through the lenses L 10 , L 9 , and L 8 , and then are projected onto the screen  200 . More specifically, the image rays P pass through the lens group G twice with the reflection of the reflector R to obtain short-throw projection and high optical performance with lesser and smaller lenses. 
     The number of lenses L 1 -L 11  in the relay optical system  22  is larger than the number of lenses L 12 , L 13 , and the reflector R in the projection optical system  24 . The purpose of such design is to provide high optical performance with the relay optical system  22 , and therefore the projector  100  is able to project a clear image onto the screen in a short distance. 
     In addition, an area of a portion on the first optical side S 1  of the lens group G where the image rays P pass through is smaller or equal to a half of an area of the entire first optical side S 1 . The image rays P from the image ray generator  10  (before being reflected by the reflector R) and the image rays P from the projection optical system  24  (after being reflected by the reflector R) do not cross in the lens L 11 , which is the last lens for the image rays P passing through before leaving the projecting lens  20 . It may avoid optical interference to ensure higher image quality. 
       FIG. 4  shows a projecting lens of the second preferred embodiment of the present invention, which is similar to the first preferred embodiment, except that some of lenses L 8 ′, L 9 ′, and L 10 ′ are ground or cut at predetermined portions to allow the image rays P from the projection optical system  24  being projected onto the screen directly. Therefore, the projecting lens of the second preferred embodiment would have even higher optical performance, and furthermore, the projecting lens is thinner and lighter. 
     The description above is a few preferred embodiments of the present invention and the equivalence of the present invention is still in the scope of claim construction of the present invention.