A wide-angle lens assembly includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens and a tenth lens arranged in order from an object side to an image side along an optical axis. The first lens has negative refractive power and includes a convex surface facing the object side and a concave surface facing the image side. The second lens has negative refractive power. The third lens has refractive power and includes a convex surface facing the image side. The fourth lens has positive refractive power and includes a convex surface facing the object side. The fifth lens has refractive power. The sixth lens has refractive power and includes a concave surface facing the object side. The seventh lens has positive refractive power. The eighth lens is a biconvex lens with positive refractive power. The ninth lens has negative refractive power. The tenth lens has refractive power and includes a convex surface facing the image side.

A projection system has a zooming function and is configured that light rays from a telecentric system enter. The projection system is formed of seven lens groups. The first and seventh lens groups are fixed when the projection magnification is changed, and the second, third, fourth, fifth, and the sixth lens groups move along the optical axis when the projection magnification is changed. The second lens group is formed of one positive lens. The third lens group is formed of one positive lens. The fourth lens group is formed of one or two positive lenses and one negative lens having the center of curvature located at the magnifying side. The fifth lens group is formed of one negative lens having a magnifying-side aspheric surface and a demagnifying-side aspheric surface with each of the surfaces having the center of curvature located at the demagnifying side.

A projection system including seven lens groups sequentially arranged from an enlargement side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power, a fifth lens group having positive refractive power, a sixth lens group having positive refractive power, and a seventh lens group having positive refractive power, wherein dR that is a dispersion value of a lens that forms the seventh lens group out of the seven lens groups and is closest to a reduction side and dF that is a dispersion value of a lens that forms the first lens group out of the seven lens groups and is closest to the enlargement side satisfy a following conditional expression: 5<dRdF<30.

An objective optical system for endoscope includes a first lens having a negative refractive power, a second lens having a positive refractive power, an aperture stop, a third lens having a positive refractive power, a fourth lens having a positive refractive power, a fifth lens having a negative refractive power, and a sixth lens having a positive refractive power. The second lens is a meniscus lens having a convex surface directed toward an image side and the third lens is a meniscus lens having a convex surface directed toward the image side. A cemented lens having a positive refractive power is formed by the fourth lens and the fifth lens. The sixth lens is cemented to an image sensor, and the following conditional expression (1) is satisfied:

1(r3f+r3r)/(r3fr3r)5(1).

A wide-angle lens assembly comprises sequentially from an object side to an image side along an optical axis a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens, a seventh lens, an eighth lens, and a ninth lens. The first lens is a meniscus lens with refractive power. The second lens is a meniscus lens with refractive power. The third lens has refractive power and includes a concave surface facing the object side. The fourth lens has positive refractive power and includes a convex surface facing the image side. The fifth lens has refractive power. The sixth lens is a biconvex lens with positive refractive power. The seventh lens has refractive power. The eighth lens has positive refractive power. The ninth lens has positive refractive power.

A zoom lens consists of, in order from an object side, a focusing group, a zoom group, and a subsequent group. The focusing group consists of, in order from the object side, a front focusing group which does not move with respect to the image plane during zooming and focusing, a middle focusing group which consists of one or two positive lens groups each moving during focusing, and a rear focusing group which consists of a negative lens group moving during zooming and focusing. The rear focusing group has a zoom range in which the amount of movement during focusing changes in accordance with the zoom position and the rear focusing group moves to the image side during focusing from the object at infinity to the closest object. Predetermined conditional expressions relating to the amount of movement of the rear focusing group are satisfied.

The zoom lens consists of, in order from an object side: a positive first lens group that does not move during zooming; a middle group that consists of two or more movable lens groups moving during zooming; and a subsequent group that has a lens group including a stop at a position closest to the object side. The middle group has at least two negative movable lens groups. The subsequent group includes at least one positive LA lens that satisfies predetermined conditional expressions relating to the refractive index, the Abbe number, and the partial dispersion ratio.

The zoom lens consists of, in order from an object side: a positive first lens group that does not move during zooming; a middle group that consists of two or more movable lens groups moving during zooming; and a subsequent group that has a lens group including a stop at a position closest to the object side. The middle group has at least two negative movable lens groups. At least one negative movable lens group in the middle group includes at least one negative LN lens which satisfies predetermined conditional expressions relating to the refractive index, the Abbe number, and the partial dispersion ratio.

A projection system includes a first lens group that does not move when the projection magnification is changed with the aid of the zoom function, and the first lens group includes a correction lens group that is moved in the direction of the optical axis to correct worsened astigmatism. The projection system satisfies the following conditional expressions (1) and (2):
|BF20|<PFNO2(1)
1.5<|f1/f|(2)
where P represents the pixel pitch in an image displayed by liquid crystal panels, FNO represents the F number of the entire lens system, BF represents the amount of movement of the back focus position in a case where the correction lens group is moved by the amount of movement for correction of the aberration that changes when the temperature changes by 20 C., f represents the focal length of the entire lens system, and f1 represents the focal length of the correction lens group.

A variable magnification optical system includes: a first lens group (G1) having a negative refractive power; a second lens group (G2) having a positive refractive power; an intermediate group (Gn) disposed closer to an image side than the second lens group (G2); and a vibration-reduction lens group (VR) disposed closer to the image side than the intermediate group (Gn) and configured to be movable so as to have a component in a direction orthogonal to an optical axis. The system performs varying magnification by changing at least the distance between the first lens group (G1) and the second lens group (G2) and the distance between the second lens group (G2) and the intermediate group (Gn), and the system satisfies Conditional Expression (1).

1.500<(Gn)t<100.000(1) where (Gn)t: an imaging magnification of the intermediate group (Gn) in a telephoto end state