A self-temperature focus compensation device adapted to cooperate with a lens group and including at least one Fresnel lens group is provided. Each Fresnel lens group has zero focal power at a specific temperature and is a cemented lens. Each Fresnel lens group includes a first Fresnel lens and a second Fresnel lens. The first Fresnel lens has positive focal power. The second Fresnel lens has negative focal power. A sum of a focal power change of the at least one Fresnel lens group with a temperature change and a focal power change of the lens group with the temperature change is zero.

The present disclosure discloses a telephoto optical imaging system and zoom camera apparatus. The telephoto optical imaging system includes, sequentially from an object side to an image side along an optical axis, a first lens having positive refractive power, a second lens having negative refractive power, an optical path turning prism, and a triangular prism. A total effective focal length F1 of the telephoto optical imaging system may satisfy F1>40 mm. The zoom camera apparatus includes the telephoto optical imaging system and a short-focus optical imaging system arranged in parallel with the telephoto optical imaging system. A total effective focal length F1 of the telephoto optical imaging system and a total effective focal length F2 of the short-focus optical imaging system satisfy F1/F2>5.

This invention provides a lens assembly for a vision system, allowing for a constant magnification at various focal distances. The lens assembly resides movably/adjustably along the optical axis relative to the sensor. In an embodiment, the lens assembly includes a fixed rear lens and a front lens that is moved mechanically to focus the object image on the image sensor. The lens assembly can alternatively include a liquid lens that is controlled to adjust magnification with respect to a fixed front lens so as to maintain a constant system magnification. The liquid lens resides between the (fixed) front lens assembly and the image sensor and can be controlled to focus the image onto the image sensor.

An image forming lens includes a first lens group and a second lens group. The first lens group has positive refractive power moved toward the object side when focusing from a long distance to a short distance. The second lens group has positive refractive power arranged closer to the image side than the first lens group. The second lens group includes, in order from the object side to the image side, a negative lens having a concave surface on the image side, a negative meniscus lens having a concave surface on the object side, and a positive lens. The focal length f21 of the negative lens and the focal length f22 of the negative meniscus lens satisfy the following conditional expression: (1) 0.1<f21/f22<0.5.

An optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, and a second lens unit having a positive refractive power. An interval between the first lens unit and the second lens unit changes during focusing. The second lens unit includes, in order from the object side to the image side, a first subunit having a positive refractive power, an aperture stop, and a second subunit having a positive refractive power. A predetermined condition is satisfied.

An optical system includes a first lens unit having a positive refractive power disposed closest to an object, a first focus lens unit having a positive refractive power disposed on an image side of the first lens unit, and a second focus lens unit having a negative refractive power disposed on the image side of the first focus lens unit. The first lens unit is fixed during focusing. The first focus lens unit and the second focus lens unit are movable during focusing so that a distance between the first focus lens unit and the second focus lens unit changes. The first lens unit includes a single negative lens disposed closest to the object. A predetermined condition is satisfied.

An imaging optical system includes, in order from an enlargement conjugate side to a reduction conjugate side, first and second optical systems both having positive refractive power. An enlargement conjugate point is imaged on an intermediate imaging position between the first and second optical systems. An image imaged on the intermediate imaging position is reimaged on a reduction conjugate point. The first optical system includes a first lens unit disposed closest to the enlargement conjugate side among lens units moving in an optical axis direction during focusing. The second optical system includes at least one lens unit fixed during focusing and moving in the optical axis direction during zooming. The first lens unit includes a meniscus lens disposed closest to the enlargement conjugate side and having a negative refractive power. The meniscus lens has an aspheric surface and is convex to the enlargement conjugate side.

A zoom lens includes, in order from a reduction conjugate side to an enlargement conjugate side, a first optical system having a positive refractive power, and a second optical system having positive refractive power. The second optical system reimages an intermediate image formed by the first optical system. The second optical system does not move during zooming. The first optical system includes a first lens unit that moves during zooming and has a positive refractive power, a second lens unit that moves during zooming and has a negative refractive power, and a third lens unit that moves during zooming and has a positive refractive power. A distance between adjacent lens units in the first optical system changes during zooming.

An optical system comprises a lens satisfying the following conditional expressions.

2.0100<ndLZ+(0.00925dLZ)<2.0800

28.0<dLZ<40.0 where, ndLZ: a refractive index of the lens relative to a d-line dLZ: a d-line based Abbe number of the lens.

A variable power optical system 3 used in a parallel stereoscopic microscope apparatus 100 and the like includes a plurality of optical paths in which optical axes are arranged substantially parallel, includes a plurality of lens groups that change the magnification of a diameter of a luminous flux entering substantially parallel to each of the optical paths to eject the luminous flux as substantially parallel luminous fluxes, and at least two lens groups move along the optical axis in each optical path according to the change in the magnification. At least two lens groups of at least one optical path among the plurality of optical paths move in a direction including a component perpendicular to the optical axis according to the change in the magnification at at least part of a section where the magnification is changed from a high-power end state to a low-power end.