Projection optical system and head-up display

1. A projection optical system comprising an eyepiece optical system configured to refract and reflect image light emitted from an image forming unit for forming image information to display a virtual image, wherein

the eyepiece optical system includes at least a concave lens, a folding mirror, and a concave mirror which are successively placed in order from the image forming unit,

of the concave lens and the folding mirror, at least the folding mirror has a free curved surface shape, the folding mirror being arranged separately from the concave lens,

the concave lens is arranged, relative to an emission direction of the image light, downstream of an image plane of a liquid crystal display panel of the image forming unit and has a focal distance corresponding to a distance between the image plane and a condensing position that is upstream of the image plane,

the concave lens has a first surface which is concave and a second surface which is not concave, and the second surface is arranged adjacent to and facing the liquid crystal display panel, and

a polarization unit is positioned between the liquid crystal display panel and the concave lens, the polarization unit being configured to attenuate polarization light different from the image light emitted from the image forming unit.

2. A head-up display comprising:

an image forming unit configured to emit image light including image information; and

an eyepiece optical system configured to refract and reflect the image light emitted from the image forming unit to display a virtual image, wherein

the image forming unit includes a backlight and a liquid crystal display panel,

the eyepiece optical system includes at least a concave lens, a folding mirror, and a concave mirror which are successively placed in order close to the liquid crystal display panel along an emission direction of the image light,

of the concave lens and the folding mirror, at least the folding mirror has a free curved surface shape, the folding mirror being arranged separately from the concave lens,

the concave lens is arranged, relative to the emission direction of the image light, downstream of an image plane of the liquid crystal display panel of the image forming unit and has a focal distance corresponding to a distance between the image plane and a condensing position that is upstream of the image plane,

the concave lens has a first surface which is concave and a second surface which is not concave, and the second surface is arranged adjacent to and facing the liquid crystal display panel, and

a polarization unit is positioned between the liquid crystal display panel and the concave lens, the polarization unit being configured to attenuate polarization light different from the image light emitted from the image forming unit.

3. A head-up display comprising:

an image forming unit configured to emit image light including image information; and

an eyepiece optical system configured to refract and reflect the image light emitted from the image forming unit to display a virtual image, wherein

the image forming unit includes a relay optical system configured to form an image of a light valve and a screen plate having a diffusion capability,

the eyepiece optical system includes at least a concave lens, a folding mirror, and a concave mirror which are successively placed in order close to the image forming unit along an emission direction of the image light,

of the concave lens and the folding mirror, at least the folding mirror has a free curved surface shape, the folding mirror being arranged separately from the concave lens,

the concave lens is arranged, relative to the emission direction of the image light, downstream of an image plane of a liquid crystal display panel of the image forming unit and has a focal distance corresponding to a distance between the image plane and a condensing position that is upstream of the image plane,

the concave lens has a first surface which is concave and a second surface which is not concave, and the second surface is arranged adjacent to and facing the liquid crystal display panel, and

a polarization unit is positioned between the liquid crystal display panel and the concave lens, the polarization unit being configured to attenuate polarization light different from the image light emitted from the image forming unit.

4. A head-up display comprising:

an image forming unit configured to emit image light including image information; and

an eyepiece optical system configured to refract and reflect the image light emitted from the image forming unit to display a virtual image, wherein

the image forming unit includes:

a laser light source;

an optical scanning unit configured to perform optical scanning of the laser light source by rotation of a reflection surface; and

a screen plate configured to diffuse an emission light from the laser light source,

the eyepiece optical system includes at least a concave lens, a folding mirror, and a concave mirror which are successively placed in order close to the image forming unit along an emission direction of the image light,

of the concave lens and the folding mirror, at least the folding mirror has a free curved surface shape, the folding mirror being arranged separately from the concave lens,

the concave lens is arranged, relative to the emission direction of the image light, downstream of an image plane of a liquid crystal display panel of the image forming unit and has a focal distance corresponding to a distance between the image plane and a condensing position that is upstream of the image plane,

the concave lens has a first surface which is concave and a second surface which is not concave, and the second surface is arranged adjacent to and facing the liquid crystal display panel, and

a polarization unit is positioned between the liquid crystal display panel and the concave lens, the polarization unit being configured to attenuate polarization light different from the image light emitted from the image forming unit.