The present invention provides a projection optical system including a first concave reflecting surface, a first convex reflecting surface, a second concave reflecting surface, and a third concave reflecting surface, wherein the first concave reflecting surface, the first convex reflecting surface, the second concave reflecting surface, and the third concave reflecting surface are arranged such that light from an object plane forms an image on an image plane by being reflected by the first concave reflecting surface, the first convex reflecting surface, the second concave reflecting surface, the first convex reflecting surface, and the third concave reflecting surface in an order named.

An optical apparatus for a near-eye display includes a microdisplay to emit image light and one or more field lenses positioned to receive the image light from the microdisplay. The one or more field lenses have a combined optical power to form a curved intermediate image. A freeform combiner, having an eyeward side and an external side, is positioned to receive the image light from the one or more field lenses and reflect the image light. A curved intermediate image is formed between the freeform combiner and the one or more field lenses.

A head up display can use a catadioptric collimating system. The head up display includes an image source. The head up display also includes a collimating mirror, and a polarizing beam splitter. The light from the image source enters the beam splitter and is reflected toward the collimating mirror. The light striking the collimating mirror is reflected through the beam splitter toward a combiner. A field lens can include a diffractive surface. A corrector lens can be disposed after the beam splitter.

An optical system configured to guide a light beam from a display element includes a positive lens, a negative lens, and an optical element having at least three optical surfaces. The light beam from the display element is reflected a plurality of times inside the optical element via the positive lens and the negative lens, and then travels to an exit pupil. A predetermined condition is satisfied.

A projection optical system (10) projects from a first image plane (5) on a reducing side to a second image plane (6) on an enlargement side. The projection optical system (10) includes a first optical system (11) that includes a plurality of lenses and forms a first intermediate image (51) formed inside the first optical system (11) by light incident from the reducing side into a second intermediate image (52) on the enlargement side of the first optical system (11); a second optical system (12) that includes a first reflective surface (M1) with positive refractive power which is positioned further to the enlargement side than the second intermediate image (52); and a glass block (30) that is disposed between the first optical system (11) and the first reflective surface (M1), the glass block (30) passing light rays from the first optical system (11) to the second intermediate image (52).

A first optical group that forms an intermediate image and a second optical group that enlarges and projects the intermediate image formed by the first optical group satisfy a variety of conditions. Therefore, the overall length of the entire lens system of the projection system is reduced in a linear arrangement, or the distance between the first optical group and the second optical group is increased and an optical path deflector that deflects the optical path is disposed at the middle of the optical path between the first and second optical groups to fold the optical path.

A variable magnification optical system consists of, in order from an object side, a first optical system remaining stationary during changing magnification and a second optical system including a plurality of lens groups moving during changing magnification. The first optical system includes a first mirror and a second mirror having reflective surfaces arranged to face each other. The first mirror is an optical element having a power at a position closest to the object side on an optical path and has a reflective surface concave toward the object side. The second mirror has a reflective surface convex toward the image side. An intermediate image is formed between the second mirror and the second optical system.

A beam expander apparatus includes a parabolic primary mirror that has a continuous surface. The continuous surface is configured to reflect, at least twice, a light beam. The parabolic primary mirror is further configured to deliver the light beam, in an expanded form, to a target object. The apparatus also includes a parabolic secondary mirror arranged with an orientation relative to the parabolic primary mirror. The parabolic secondary mirror has a continuous surface configured to reflect, at least twice, the light beam. The parabolic secondary mirror is further configured to receive the light beam via a port of the parabolic primary mirror.

A projection optical system (10) projects from a first image plane (5) on a reducing side to a second image plane (6) on an enlargement side. The projection optical system (10) includes a first optical system (11) that includes a plurality of lenses and forms a first intermediate image (51) formed inside the first optical system (11) by light incident from the reducing side into a second intermediate image (52) on the enlargement side of the first optical system (11); a second optical system (12) that includes a first reflective surface (M1) with positive refractive power which is positioned further to the enlargement side than the second intermediate image (52); and a glass block (30) that is disposed between the first optical system (11) and the first reflective surface (M1), the glass block (30) passing light rays from the first optical system (11) to the second intermediate image (52).

There is provided a projection optical system capable of projecting an image formed on an image forming unit on a projection plane, which has an extremely short projection distance and a small size.