An all-reflective or reflective and cata-dioptric optical system includes a concave primary mirror having a central aperture and a radius, the primary mirror having one of a parabolic, non-parabolic conical, or aspherical surface, a convex secondary mirror facing the primary mirror, the secondary mirror having an aspherical surface, where an optical axis extends from a vertex of the primary mirror to a vertex of the secondary mirror, a concave tertiary mirror arranged behind the primary mirror, the tertiary mirror having one of a parabolic, non-parabolic conical or aspherical surface, a concave quaternary mirror arranged in the central aperture of the primary mirror or behind the primary mirror, the quaternary mirror having one of a spherical, parabolic, non-parabolic conical or aspherical surface, and/or at least one image plane having one or more aggregated sensors. Additional multispectral imaging may utilize beam splitter(s), folding mirror(s), focal length optimizer(s) and/or additional image planes.

A flat-plate lens and an optical imaging system are provided. The flat-plate lens, includes a first face and a second face, the first face includes a ring-shaped light-transmitting region and a first reflective region surrounded by the ring-shaped light-transmitting region, and the second face includes an imaging region and a second reflective region surrounding the imaging region. The second reflective region is configured to reflect light to the first reflective region, and the first reflective region is configured to reflect light to the imaging region; the second reflective region includes a first mirror. The first mirror is one selected from the group consisting of a free-form curved mirror, an aspheric mirror and a spherical mirror, and the first reflective region includes at least one selected from the group consisting of a free-form curved mirror, an aspheric mirror, a spherical mirror and a plane mirror.

A system comprises a sensor subsystem for imaging an object space, and a telescope for coupling electromagnetic energy from the object space to the sensor subsystem. The system comprises a bypass optical path that bypasses the telescope on the way to the sensor subsystem in order to provide a larger field of view of the object space. The bypass path and the telescope path merge at a merging point between the telescope and the sensor subsystem, and are disjoint upstream of the merging point. A simple bypass configuration is therefore provided, with possibly just a single fold mirror at the merging point. A sensor may form an intermediate image, and a frame is placed at the intermediate image to reject stray radiation and provide a real and accessible intermediate pupil for the sensor. Other features are also provided.

A virtual image display device includes a display element, which is an image light generating unit that generates an image light, a first mirror that reflects the image light, a second mirror that reflects the image light reflected by the first mirror, and a third mirror that transmits external light and that reflects part of the image light reflected by the second mirror to guide the image light to a position of an exit pupil, wherein the first mirror has an angular dependence on a reflective surface.

A freeform surface off-axial three-mirror imaging system is provided. The freeform surface off-axial three-mirror imaging system comprises a primary mirror, a secondary mirror, and a compensating mirror. The primary mirror, the secondary mirror, and the compensating mirror are located adjacent and spaced away from each other. A surface shape of each of the primary mirror and the secondary mirror is a quadric surface. The primary mirror is used as an aperture stop. A surface shape of the compensating mirror is a freeform surface. A light emitted from a light source is reflected by the primary mirror, the secondary mirror, and the compensating mirror to form an image on an image plane.

A freeform surface off-axial three-mirror imaging system comprising a primary mirror, a secondary mirror, a tertiary mirror, and a detector. The secondary mirror defines a first location and a second location. Each reflective surface of the primary mirror, the secondary mirror and the tertiary mirror is an xy polynomial freeform surface. A working distance of the freeform surface off-axial three-mirror imaging system is greater than 125 mm.

A vehicular projection display apparatus includes: an intermediate image forming optical member; a display device disposed to project light including a display image to the intermediate image forming optical member, and to form an intermediate image as a virtual image or a real image, and an HUD optical system which receives the light of the intermediate image formed by the intermediate image forming optical member, which guides the light to a reflecting face of a windshield of a vehicle or a light reflecting member in a vicinity of the windshield, and which projects the light to allow the display image to be visually recognized as a virtual image at a predetermined eye point. The intermediate image forming optical member forms the intermediate image in a state in which at least part of the intermediate image is curved from a flat plane with respect to the display device.

An off-axis three-mirror optical system with freeform surfaces comprised an aperture, a primary mirror, a secondary mirror, a tertiary mirror, and a detector. The aperture is located on an incident light path. The primary mirror is located on an aperture side. The secondary mirror is located on a primary mirror reflected light path.

The tertiary mirror is located on a secondary mirror reflected light path. The detector located on a tertiary mirror reflected light path. The primary mirror and the tertiary mirror have a same fifth-order polynomial freeform surface expression. The primary mirror reflected light path, the secondary mirror reflected light path and the tertiary mirror reflected light path overlap with each other.

A freeform surface off-axial three-mirror imaging system comprising a primary mirror, a secondary mirror, a tertiary mirror, and a detector. The secondary mirror comprises a first freeform surface and a second freeform surface. Each reflective surface of the primary mirror, the first freeform surface, the second freeform surface and the tertiary mirror is an xy polynomial freeform surface. The freeform surface off-axial three-mirror imaging system comprises a first field of view formed by the first freeform surface and a second field of view formed by the second freeform surface.

An imaging optical system includes a primary reflecting mirror, a secondary reflecting mirror, a tertiary reflecting mirror, and an aperture stop. The imaging optical system has a field of view, a focal length of the field of view that is defined as FFL, and an effective aperture of a field of view entrance pupil that is defined as FEPD. The FFL and the FEPD at a central field of view are greater than that at the edge field of views, and the FFL and the FEPD change continuously.