| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a downsized projection optical system which achieves a brightness of f number 2.0 or so, has properly corrected aberrations, and is less affected by temperature variation and provide a projection device having the same. <P>SOLUTION: A projection optical system comprises an aperture diaphragm, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power, and a polarization separation element in this order from a side of a projection plane. The fourth lens and the polarization separation element may be separated, integrated, or bonded. The projection optical system will satisfy a conditional expression 0.8<f1/f<2.0 (1), where f1 represents a focal length of the first lens and f represents a focal length of an entire system of the projection optical system. <P>COPYRIGHT: (C)2012,JPO&INPIT |
