There is provided a projection optical system (1) that projects from a first image plane on a reducing side to a second image plane on an enlargement side, including a first refractive optical system (11) that includes eight lenses (L1) to (L8) and forms a first intermediate image (31) on the enlargement side using light that is incident from the reducing side, a second refractive optical system (12) that includes six lenses (L9) to (L14) and forms the first intermediate image (31) on the reducing side into a second intermediate image (32) on the enlargement side, and a first reflective optical system (20) that includes a first reflective surface (21a) with positive refractive power that is positioned closer to the enlargement side than the second intermediate image (32).

An optical system includes a first lens unit that has positive refractive power, a second lens unit that moves during focusing and that has positive refractive power or negative refractive power, and a third lens unit that has positive refractive power or negative refractive power. The first lens unit, the second lens unit, and the third lens unit are disposed in that order from an object side to an image side. During focusing, an interval between adjacent lens units changes. In the optical system, a focal length f of the entire optical system, a distance LD along an optical axis from a lens surface of the first lens unit that is closest to the object side to an image plane, and focal lengths of positive and negative lenses that are included in the first lens unit are appropriately set.

A variable-power optical system includes, in order from an object, an objective optical system (O), a relay optical system (R), and an eyepiece optical system (E), wherein the relay optical system is provided with, in order from the object, a first lens group (G1) having positive refractive power, a second lens group (G2) having positive refractive power, and a third lens group (G3) having positive refractive power, and is an optical system in which an image formed by the objective optical system with variable optical power, and the variable-power optical system is configured so as to satisfy expressions: 0.7<||.sub.min<1.4, and 12 (mm)<f.sub.min<15 (mm), where ||.sub.min denotes a minimum of absolute value of imaging magnification of the relay optical system, and f.sub.min denotes a shortest focal length.

An image forming lens is formed by sequentially arranging, from an object side to an image side, a first lens group having positive refractive power, an aperture stop, a second lens group having positive refractive power, and a third lens group having positive or negative refractive power. When focusing is performed from a long distance to a short distance, the third lens group is fixed relative to an image surface, and the first lens group, the aperture stop, and the second lens group are moved integrally to the object side. In the image forming lens, the third lens group is formed by sequentially arranging, from the object side to the image side, two lenses in order of a negative lens and a positive lens, and a conditional expression is satisfied:
0.20<D/L.sub.3F-I<0.60,
where D is an air space between the negative lens and the positive lens which form the third lens group, and L.sub.3F-I is a distance from an object-side surface of the negative lens of the third lens group to the image surface.

An optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. During focusing from infinity to a short distance, the first lens unit is fixed, and the second lens unit and the third lens unit are moved so that a distance between the second lens unit and the third lens unit changes. Predetermined conditions are satisfied.

An optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. During focusing from infinity to a short distance, the first lens unit is fixed, and the second lens unit and the third lens unit are moved so that a distance between the second lens unit and the third lens unit changes. Predetermined conditions are satisfied.

An imaging apparatus comprises an optical system that includes a plurality of lens groups, each lens group including one or more lenses, at least one of the lens groups being independently movable with respect to the other lens groups and including a focus lens group for focusing the subject and a lens control unit that controls movement of the plurality of lens groups to bring into focus based on a feeding position of the focus lens group.

A zoom lens for projection consists of a negative first lens group, which is fixed during magnification change, a middle group, which includes plural lens groups that move during magnification change, and a positive last lens group, which is fixed during magnification change, in this order from a magnification side. A reduction side is non-telecentric. Both of a lens group closest to the magnification side and a lens group closest to the reduction side in the middle group have positive refractive power, and move from the reduction side toward the magnification side during magnification change from a wide-angle end to a telephoto end. The last lens group includes at least two positive lenses and at least two negative lenses. A positive lens is arranged closest to the reduction side in the last lens group. A predetermined conditional expression about a focal length of the last lens group is satisfied.

The disclosure describes various aspects of techniques for elliptical beam design using cylindrical optics that may be used in different applications, including in quantum information processing (QIP) systems. In an aspect, the disclosure describes an optical system having a first optical component having a first focal length, a second optical component having a second focal length and aligned with a first direction, and a third optical component having a third focal length and aligned with a second direction orthogonal to the first direction. The optical system is configured to receive one or more optical beams (e.g., circular or elliptical) and apply different magnifications in the first direction and the second direction to the one or more optical beams to image one or more elliptical Gaussian optical beams. A method for generating elliptical optical beams using a system as the one described above is also disclosed.