A variable magnification optical system includes, in order from the object side: a positive first lens group, which is fixed when changing magnification; a negative second lens group that moves from the object side to the image side when changing magnification from the wide angle end to the telephoto end; and a rearward lens group having a positive refractive power throughout the entire variable magnification range that includes at least one lens group that moves when changing magnification. The first lens group includes, in order from the object side, a positive first lens group front group, a positive first lens group middle group, and a first lens group rear group constituted by a negative lens. The first lens group front group and first lens group middle group include cemented lenses formed by cementing a negative lens and a positive lens, provided in this order from the object side, together.

A variable magnification optical system includes, in order from the object side: a positive first lens group, which is fixed when changing magnification; a negative second lens group that moves from the object side to the image side when changing magnification from the wide angle end to the telephoto end; and a rearward lens group having a positive refractive power throughout the entire variable magnification range that includes at least one lens group that moves when changing magnification. The first lens group includes, in order from the object side, a positive first lens group front group, a positive first lens group middle group, and a first lens group rear group constituted by a negative lens. The first lens group front group and first lens group middle group include cemented lenses formed by cementing a negative lens and a positive lens, provided in this order from the object side, together.

A zoom optical system includes a negative first lens group having a first deflection optical element, a positive second lens group, a positive third lens group, a positive fourth lens group, and a second deflection optical element, in that order from the object side. The first lens group is provided at a fixed position relative to an imaging plane. Zooming is performed by moving at least the second and third lens groups so that distances between adjacent lens groups of the first through fourth lens groups change. The third lens group is a focusing lens group which moves along the optical axis during focusing. The following condition (1) is satisfied:
0.2<f3/f4<1.0(1),
wherein f3 designates the focal length of the third lens group, and f4 designates the focal length of the fourth lens group.

An ophthalmic surgical microscope includes a beam coupler positioned along an optical path of the surgical microscope between a first eyepiece and magnifying/focusing optics, the beam coupler operable to direct the OCT imaging beam along a first portion of the optical path of the surgical microscope between the beam coupler and a patient's eye (an OCT image being generated based on a reflected portion of the OCT imaging beam). The surgical microscope additionally includes a real-time data projection unit operable to project the OCT image generated by the OCT system and a beam splitter positioned along the optical path of the surgical microscope between a second eyepiece and the magnifying/focusing optics. The beam splitter is operable to direct the projected OCT image along a second portion of the optical path of the surgical microscope between the beam splitter and the second eyepiece such that the projected OCT image is viewable through the second eyepiece.

A zoom lens system includes a positive first lens group, a negative second lens group, and positive third and fourth lens groups, in that order from the object side. Upon zooming from the short to long focal length extremities, the first lens group does not move along the optical axis direction, and the second lens group and the third lens group are movable in the optical axis direction. The first lens group includes at least one negative lens element, and the following conditions are satisfied:

vd1n<22.85

and

8.0<f3/f2<3.0,

wherein vd1n designates the Abbe number, with respect to the d-line, of the negative lens element, which is provided closest to the object side within the first lens group, and f2 and f3 designate the focal lengths of the second and third lens groups, respectively.

In a zoom lens in which the interval between adjacent lens units changes during zooming, a magnification-varying lens group includes a lens group V having a negative refractive power and a lens unit C having a negative or positive refractive power. The lens group V includes a first magnification-varying lens group V1 including a lens unit V1a having a negative refractive power and a lens unit V1b having a negative refractive power. The lens units V1a and V1b move toward the image side such that the interval between the two lens units is largest at the telephoto end. The lens unit interval m1 on the optical axis between the lens units V1a and V1b at the wide angle end and the maximum lens unit interval m2 on the optical axis between the lens units V1a and V1b during zooming are set as appropriate.

A zoom lens unit includes, in order from an object side to an image side, a first lens group having positive refractive power and a focus function, a second lens group having negative refractive power, which moves when changing a magnification, a third lens group which moves when changing a magnification, and a fourth lens group having positive refractive power, which is fixed when changing a magnification, wherein the following condition (1) is fulfilled:

|M.sub.2W.Math.M.sub.3W.Math.M.sub.4W|<0.14 (1) where M.sub.2W represents an imaging magnification of the second lens group at a wide-angle end, M.sub.3W represents an imaging magnification.the third lens group at the wide-angle end, and M.sub.4W represents an imaging magnification of the fourth lens group at the wide-angle end.

A zoom lens unit includes, in order from an object side to an image side, a first lens group having positive refractive power and a focus function, a second lens group having negative refractive power, which moves when changing a magnification, a third lens group which moves when changing a magnification, and a fourth lens group having positive refractive power, which is fixed when changing a magnification, wherein the following condition (1) is fulfilled:

|M.sub.2W.Math.M.sub.3W.Math.M.sub.4W|<0.14 (1) where M.sub.2W represents an imaging magnification of the second lens group at a wide-angle end, M.sub.3W represents an imaging magnification.the third lens group at the wide-angle end, and M.sub.4W represents an imaging magnification of the fourth lens group at the wide-angle end.

A zoom lens system includes first through fourth lens groups. Upon zooming from the short to long focal length extremities, the second and third lens groups move while the distance between the first and second lens groups increases, and the distance between the second and third lens groups decreases. The fourth lens group includes a positive lens element having a convex surface on the object side; a cemented lens having a positive lens element and a negative lens element; a biconvex positive lens element, and a negative meniscus lens element having a convex surface on the image side. The following condition (1) is satisfied:
1.6<f1/f4<3.0. . . (1),
wherein f1 and f4 designate the focal lengths of the first and fourth lens groups, respectively.

A zoom lens system includes first through fourth lens groups. Upon zooming from the short to long focal length extremities, the second and third lens groups move while the distance between the first and second lens groups increases, and the distance between the second and third lens groups decreases. The fourth lens group includes a positive lens element having a convex surface on the object side; a cemented lens having a positive lens element and a negative lens element; a biconvex positive lens element, and a negative meniscus lens element having a convex surface on the image side. The following condition (1) is satisfied:
1.6<f1/f4<3.0. . . (1),
wherein f1 and f4 designate the focal lengths of the first and fourth lens groups, respectively.