| 摘要 |
PROBLEM TO BE SOLVED: To provide an illumination optical system and an image projection device that achieve miniaturization without reducing illumination efficiency.SOLUTION: An illumination optical system includes: a first optical system for emitting a luminous flux from a light source having a predetermined ark length in an optical axis direction of the illumination optical system as a convergent luminous flux; a second optical system for converting the convergent luminous flux into a luminous flux parallel with respect to the optical axis; a luminous flux dividing element for dividing the parallel luminous flux into a plurality of luminous fluxes; and a third optical system for superimposing the divided luminous fluxes on an illuminated region. The second optical system has a focal length of which a height h becomes larger than a height D within a predetermined plane, where D is a height from the optical axis of the second optical system to an end of an effective region of the luminous flux dividing element, and h is defined as a height from the optical axis of the second optical system to an end of an effective luminous flux of the parallel luminous flux emitted from the second optical axis. |
