An electronic device includes a movable mirror system to selectively reflect an incident image projection beam traveling along a first path toward a second path different than a first path. The image projection beam displays a corrected image at a first location but would otherwise display an uncorrected image at a second location when the movable mirror system reflects the image projection beam toward the second path. The electronic device also includes an optical correction system having at least one corrective optic element to correct the image projection beam to display a corrected image at the second location when the movable mirror system reflects the image projection beam toward the second path.

An optical system includes a reflective optical system on a magnification side along an optical path of the projection optical system and a refractive optical system on a reduction side along the optical path. The reflective optical system includes one reflective optical element having a power. The refractive optical system includes a front group on the magnification side and a rear group on the reduction side. The front group having, in order from the magnification side toward the reduction side, a first lens group with a positive or negative refractive power, a second lens group, and a third lens group with a positive refractive power. The rear group has a positive refractive power. The first lens group moves to the magnification side, and the second lens group and the third lens group move to the reduction side in a change in focus from a long distance to a short distance.

A projection device to magnify and project, on a screen, an image displayed at an image display element, includes: a dioptric system including at least one positive lens and at least one negative lens; and a reflection optical system having at least one reflection optical element.

A projection device to magnify and project, on a screen, an image displayed at an image display element, includes: a dioptric system including at least one positive lens and at least one negative lens; and a reflection optical system having at least one reflection optical element.

A spectrograph that includes a first mirror having flat a mirror reflective surface and positioned to reflect light traversing a prism, a second mirror having a concave-shaped reflective mirror surface and positioned to reflect light received from the first mirror, a third mirror having a convex-shaped reflective mirror surface and positioned to receive light reflected by the second mirror, a fourth mirror having a spheroidal reflective mirror surface and positioned to receive light reflected by the third mirror, and a field lens comprising a concave mirror surface in combination with a convex mirror surface, wherein light received by said field lens from said fourth mirror enters said convex mirror surface, traverses said field lens, and exits from said concave mirror surface. The fifth mirror is positioned such that the second mirror, third mirror, fourth mirror, and fifth mirror share a common vertex axis.

In a 1-2nd lens group, a reduction-side fixed lens group (first fixed lens group) as a fixed group is disposed on the outermost reduction side, an enlargement-side fixed lens group (second fixed lens group) as a fixed group is disposed on the outermost enlargement side, moving lens groups (lens groups), which move when focusing is performed in response to a magnification change, are disposed between the fixed groups, and thereby it is possible to perform effective correction in order to suppress aberration fluctuation to be reduced. Even in a case where the second optical group is configured of one mirror, it is possible for a primary image to have appropriate aberration and to hereby reduce aberration for a good image which is finally projected onto a screen through the second optical group.

A projection optical system comprises an image forming unit that forms an image; a refractive optical system including a plurality of lenses that enlarges and projects the image on a screen; and a reflecting surface, wherein an intermediate image is formed between the refractive optical system and the reflecting surface, and the projection optical system satisfies conditions of 0.6<D/Did<0.8 and 2.5<Did/F<6, where Did represents a maximum paraxial image height of the intermediate image in a focusing state in which a projection image is maximum, D represents a maximum value of a distance between an optical axis and an intersection of a paraxial image surface and a light beam passing center of an aperture stop of the refractive optical system, and F represents a focal length of the refractive optical system in a focusing state in which the projection image is maximum.

A spectrograph that includes a first mirror having flat a mirror reflective surface and positioned to reflect light traversing a prism, a second mirror having a concave-shaped reflective mirror surface and positioned to reflect light received from the first mirror, a third mirror having a convex-shaped reflective mirror surface and positioned to receive light reflected by the second mirror, a fourth mirror having a spheroidal reflective mirror surface and positioned to receive light reflected by the third mirror, and a field lens comprising a concave mirror surface in combination with a convex mirror surface, wherein light received by said field lens from said fourth mirror enters said convex mirror surface, traverses said field lens, and exits from said concave mirror surface. The fifth mirror is positioned such that the second mirror, third mirror, fourth mirror, and fifth mirror share a common vertex axis.

Disclosed is a projection optical system including a first optical system configured to form a first image conjugate to an object and have an optical axis and a second optical system configured to project a second image conjugate to the first image onto a surface to be projected on, wherein the first image satisfies a condition of:
ImTr1.70
wherein Im denotes a length of the first image in a direction of an optical axis of the first optical system, normalized by a focal length of the first optical system, and Tr denotes a throw ratio for the projection optical system.

A projection lens including a reflective unit and a refractive unit is provided. The projection lens is disposed between an object side and an image side. The reflective unit is disposed between the object side and the image side and has a negative refractive power. The refractive unit is disposed between the object side and the reflective unit and has a positive refractive power. The refractive unit includes a first lens group and a second lens group. The first lens group is disposed between the object side and the reflective unit and includes at least one cemented lens and an aperture stop. The at least one cemented lens is disposed between the object side and the aperture stop. The second lens group is disposed between the first lens group and the reflective unit and includes at least one aspheric lens. A projection apparatus including the projection lens is also provided.