A projection lens system projects an image of a reduction side into a magnification side in an image projection device, a back glass being disposed on the reduction side. In the projection lens system, all of one or more negative lenses that satisfy, in a surface on the reduction side or a surface on the magnification side, condition |h/H|<2.0 defined by height h of a most off-axis principal ray and height H of an axial ray passing through a highest pupil position satisfy conditions Tn≥98.5% and Dn/Db≤0.05 defined by transmittance Tn, thickness Dn of the negative lens on an optical axis, and total thickness Db of the back glass.

The lens apparatus includes an optical system, a voltage transformation unit, and an actuator. A first lens unit of the optical system is moved toward the object side during zooming from a wide-angle end to a telephoto end. The voltage transformation unit includes coils. The actuator is configured to be driven by a voltage output from the voltage transformation unit and to move a part of the lens units in the optical system during focusing. The coil is disposed at a position that is separated from a position of a most object-side surface of the optical system at the wide-angle end, toward the image side by a maximum or more moving amount of the first lens unit, and is closer to the object side than a most image-side surface of the optical system at the wide-angle end.

A lens apparatus includes zoom lens units configured to move in an optical axis direction for zooming, and a correction lens unit configured to move in the optical axis direction to correct change in a focal position due to change in an atmospheric pressure. The lens apparatus satisfies an inequality 0.4<|fair_t/fw|<6 where fair_t is a composite focal length of an air lens included in one of the zoom lens units having a smallest absolute value of the composite focal length among the zoom lens units and fw is a focal length of the lens apparatus at a wide-angle end.

A zoom lens includes, in order from an object side, a first lens group that is positive, a second lens group that is negative, a third lens group that is positive, and a fourth lens group that is positive. During zooming from a wide angle end to a telephoto end, at least the first lens group and the third lens group are fixed and an interval on an optical axis of an adjacent lens group relative thereto is changed. In the zoom lens, the fourth lens group includes at least one positive lens and satisfies a predetermined conditional expression. In addition, an imaging device includes the zoom lens and an image sensor.

A variable magnification optical system consists of, in order from an object side to an image side, a first lens group, a second lens group, and a subsequent lens group. The variable magnification optical system satisfies a predetermined conditional expression for a partial dispersion ratio related to F line, C line, and a wavelength of 1970.09 nm, a d-line back focus of the variable magnification optical system at a telephoto end, a back focus in any one wavelength from a wavelength of 1300 nm to a wavelength of 2325.42 nm at the telephoto end, and a d-line focal length of the variable magnification optical system at the telephoto end.

A zoom lens includes a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group in order from an object side. In a case of magnification, the first lens group, the second lens group, and the third lens group move. The third lens group consists of a third a lens group that does not move in a case of image shake correction, a third b lens group that moves in the case of the image shake correction, and a third c lens group that does not move in the case of the image shake correction in order from the object side. The third b lens group consists of a positive lens and a negative lens. A predetermined conditional expression related to the third b lens group is satisfied.

A lens apparatus includes two optical systems. Each of the two optical systems includes, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a first reflective surface, a second reflective surface, and a rear lens unit having positive refractive power. At least a distance between the first lens unit and the second lens unit and a distance between the second lens unit and the first reflective surface are changed during magnification variation. A predetermined condition is satisfied.

An optical imaging system includes a first lens group, a second lens group, a third lens group, and a fourth lens group sequentially disposed in ascending numerical order along an optical axis of the optical imaging system from an object side of the optical imaging system toward an imaging plane of the optical imaging system, wherein at least one lens group among the first lens group to the fourth lens group is configured to be movable along the optical axis, the first lens group has a positive refractive power and comprises a reflective member and at least one lens disposed between the object side of the optical imaging system and the reflective member, and the at least one lens is configured to refract light passing through the at least one lens to converge the light to be incident on the reflective member.

Provided is a zoom lens. The zoom lens includes a fixed lens group having a positive optical power, a first zoom lens group having a negative optical power, a second zoom lens group having a positive optical power, and a compensation lens group having a positive optical power which are sequentially arranged along an optical axis from an object side to an image side, where the first zoom lens group and the second zoom lens group are capable of reciprocating along the optical axis. The fixed lens group includes a first lens, and the first zoom lens group includes a second lens, a third lens, and a fourth lens which are sequentially arranged along the optical axis from the object side to the image side.

Provided is a zoom lens, comprising, in order from an object side to an image side, first to fourth lens units having positive, negative, positive, and positive refractive powers. During zooming, first lens unit does not move, and second to fourth lens units move. Third lens unit comprises, in order from the object side to the image side, first and second lens subunits each having a positive refractive power. Second lens subunit moves in a direction having a component of a direction perpendicular to an optical axis during image blur correction. Third lens unit comprises at least two positive lenses and at least two negative lenses. Second lens subunit comprises a positive lens and a negative lens. A focal length (f2) of second lens unit, a focal length (f3) of third lens unit, and a focal length (f3b) of second lens subunit are each appropriately set.