The present disclosure is related to a projection optical system and a projection type display device. Particularly, the present disclosure is related to a projection optical system which is favorably suited for use in a projection type display device having light valves such as liquid crystal display elements or DMD's (Digital Micromirror Devices®), and a projection type display device that employs this projection optical system.
Recently, projection type display devices (also referred to as “projectors”) which are equipped with light valves such as liquid crystal display elements and DMD's (Digital Micromirror Devices®) are in wide use, and the performance thereof is increasing.
Accompanying the improved performance of recent light valves, there is demand for projection optical systems to favorably correct aberrations so as to be compatible with the resolutions of the light valves. Further, projection optical systems having wider angles of view are in great demand, taking the fact that projectors are utilized in comparatively small interior spaces for presentations and the like.
Projection optical systems that form an intermediate image with a first optical system constituted by a plurality of lenses, then perform refocusing operations with a second optical system also constituted by a plurality of lenses have been proposed, in order to meet these demands (refer to Japanese Patent No. 4210314 and Japanese Unexamined Patent Publication No. 2006-330410).
In a projection optical system constituted by an ordinary optical system that does not form an intermediate image, if a widening of the angle of view is achieved by shortening the focal length thereof, the lenses toward the magnification side will become excessively large. In contrast, a projection optical system that forms an intermediate image as described above is capable of shortening the back focus of the second optical system while decreasing the diameters of lenses of the second optical system toward the magnification side, and is favorably suited to increasing the angle of view by shortening the focal length thereof.
However, Japanese Patent No. 4210314 discloses an optical system that forms an intermediate image with a first optical system, then projects the intermediate image by magnifying and reflecting it with an aspherical mirror. Although the use of the aspherical mirror is suited for widening the angle of view, the size of the mirror will be large, which is extremely disadvantageous from the viewpoint of cost. In addition, aberrations are corrected independently by a first optical system and a second optical system with an intermediate image at the boundary therebetween in the projection optical system of Japanese Unexamined Patent Publication No. 2006-330410. Therefore, a widening of the angle of view cannot be achieved to a degree which is becoming required recently.
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