The illumination device has a simple structure and a small size, can obtain a sufficient illumination light amount, and can improve illumination ability, with high reliability and high performance at low costs. A kaleidoscope is arranged such that its center axis substantially corresponds to the optical axis of a light bulb. The kaleidoscope includes a diffusive reflection surface in its rear side, and a laser beam is irradiated on the diffusive reflection surface from the opening side of the kaleidoscope, so that reflection light from the diffusive reflection surface is used as at illumination light source.

A compact work light that generates a light beam having high brightness and high illumination uniformity is disclosed. The work light includes a housing that houses a light source, a light homogenizer and an imaging lens in an operational relationship. The housing is attached to an adjustable mount, which can be attached to a fixed region such as wall, or to a movable support member such as a lamp base. The light source generates light that is uniformized by the light homogenizer. The homogenized light is then imaged by the imaging lens as a highly uniform, bright beam spot having a sharp boundary. The beam spot is formed at a selectable distance from the work light by varying the imaging lens and/or the adjustable mount. The work light is useful for a variety of industrial, professional and personal applications, including but not limited to a reading light, a dentist light, a head lamp, a head light and an optical projector.

An imaging method. A light beam passes through a first lens set, a second lens set, an imaging device and a projection lens set. The light beam is focused in a first position. The focused light beam converges in a first relay position via the first lens set and in a second relay position via the second lens set. The optical path from the first position to the principal plane of the first lens set is defined as a first optical path, and the principal plane of the second lens set to the second relay position as the fourth optical path. The length of the first optical path is longer than twice the focal length of the first lens set, and the length of the fourth optical path is longer than twice the focal length of the second lens set.

An arrangement in which light is directed onto a surface proceeding from a light source by first optics, so that an image is formed which can be detected by second optics, the arrangement having first, second and third partial optics and an optical axis as common optical axis for the first partial optics (22) and second partial optics (24) by which the second optics are formed. The light coming from the third partial optics and incident in the second partial optics encloses an angle relative to the common optical axis at which the third partial optics lie outside of an area traversed by the light reflected by the reflecting surface from the second partial optics (24) to the first partial optics (22).

An illumination optical device is provided with a light source device and a uniform illumination optical system. To a light flux emission side of an expanded portion of the light source lamp of the light source device, which is opposite to a reflector of the illumination optical device, a reflection member is provided. An effective reflection plane diameter of an elliptical reflector of the light source device is 30 mm or more but 50 mm or less, Furthermore, assuming that a first focal distance of the elliptical reflector is f1, and a second focal distance thereof is f2, f1 becomes equal to or more than 5 mm, but equal to or less than 50 mm, and f2/f1 becomes in a range from 4 to 7 inclusive. With such a structure, it becomes possible to provide an illumination optical device and a projector with which a solution can be provided to achieve further system downsizing, reducing or preventing light use efficiency from lowering, keeping a light quantity at a predetermined level or more, and reducing or preventing a manufacturing cost increase.