1. Field of the Invention
The disclosures generally relate to an optical projection system configured to enlarge an image and project the enlarged image on a projection surface, and an image projector including such an optical projection system.
2. Description of the Related Art
Liquid-crystal projectors are widely utilized as image projectors. Recent liquid-crystal projectors generally implement a higher definition of liquid crystal panels, higher luminance owing to improved efficiency of light source lamps, and reduction in price. Further, smaller and lightweight image projectors utilizing a digital micro-mirror device (DMD) are widely utilized not only in an office environment or a school environment but also at home. In particular, since recent front-type projectors have improved portability, they are frequently utilized in small conferences of several people.
In such image projectors, various focus-adjusting technologies have been disclosed for adjusting the focus on the screen. Japanese Patent Application Laid-Open Publication No. 2009-251457 (hereinafter referred to as “Patent Document 1”), for example, discloses a focus adjusting technology for an optical projection system. In this technology, the focus is adjusted by moving lens groups that form an optical projection system. In addition, Japanese Patent Application Laid-Open Publication No. 2009-229738 (hereinafter referred to as “Patent Document 2”), for example, discloses another focus adjusting technology for the optical projection system. In this technology, the focus is adjusted by moving focus lens groups in a lens system forming the optical projection system and an aspherical mirror, independently.
However, the focus adjusting technology disclosed in Patent Document 1 does not disclose directions in which respective lens groups are moved. Accordingly, distortion occurring during the focus adjustment may not be corrected by the technology disclosed in Patent Document 1. Further, in the focus adjusting technology disclosed in Patent Document 2, the aspherical mirror is moved. However, it is undesirable to move the aspherical mirror that performs distortion correction as a main function, because moving the aspherical mirror may accumulate positional errors between the aspherical mirror and other components. Accordingly, distortion occurring during the focus adjustment may not be corrected by the technology disclosed in Patent Document 2, similar to the technology disclosed in Patent Document 1.
It is a general object of at least one embodiment of the present invention to provide an optical projection system capable of correcting distortion that occurs while the focus is adjusted and an image projector including such an optical projection system.