A zoom lens includes, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power. The first lens unit includes a negative lens and a positive lens. The zoom lens satisfies the following conditional expression (1):
d.sub.13/f.sub.t<0.4(1)
where d.sub.13 is the total sum of the thickness of the lenses included in the first to third lens units of the zoom lens on the optical axis, and f.sub.t is the focal length of the entire zoom lens system at the telephoto end.

A zoom lens includes, in order from an object side to an image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and three or more lens units. A distance between adjacent lens units varies during zooming. A predetermined condition is satisfied.

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.

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.

The present disclosure is directed to an optical system internally having an intermediate imaging position that is conjugate with each of a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, the optical system comprising: a magnification optical system including a plurality of lens elements and positioned on the magnification side with respect to the intermediate imaging position; and a relay optical system including a plurality of lens elements and positioned on the reduction side with respect to the intermediate imaging position; wherein a first lens element positioned closest to the magnification side of the magnification optical system has a positive power, and the optical system satisfies the following condition (1): 0.9f1/f21.5 . . . (1), where f1 is a focal length of the magnification optical system, and f2 is a focal length of the relay optical system.

The present disclosure is directed to an optical system internally having an intermediate imaging position that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including: a magnification optical system having A (A is an integer of three or more) pieces of lens elements, positioned on the magnification side with respect to the intermediate imaging position; and a relay optical system having B (B is an integer of two or more) pieces of lens elements, positioned on the reduction side with respect to the intermediate imaging position. A first lens group composed of pieces ( is one or more and less than B) of lens elements positioned first from the magnification side in the relay optical system has a negative power.

A zoom lens includes a first lens unit having negative refractive power, a second lens unit, an intermediate unit including one or more lens units, and a final lens unit, which are arranged in this order from an object side to an image side and in which an interval between adjacent lens units changes during zooming, wherein the first lens unit includes two or more lenses, wherein the intermediate unit includes a first intermediate lens unit and a second intermediate lens unit arranged adjacent to the image side of the first intermediate lens unit, and wherein the first lens unit and the first intermediate lens unit do not move during zooming.

A projection zoom lens is constituted by: a negative first lens group; a positive moving second lens group; a positive moving third lens group; a positive final lens group; at least one lens group positioned between the final lens group and the third lens group; and an aperture stop provided between adjacent moving lens groups. The aperture stop is a variable stop, of which the aperture diameter changes such that the numerical aperture of the zoom lens becomes constant. The zoom lens satisfies Conditional Formulae below:
2.8<Bf/Im(1)
L/Im<12(2) wherein Bf is the back focus of the entire system at the reduction side at the wide angle end, Im is the maximum effective image circle diameter at the reduction side, and L is the distance from the lens surface most toward the magnification side to the lens surface most toward the reduction side when the projection distance is infinity.

A zoom optical system that is suitable for moving image capturing, has a small size and a light weight, and can obtain favorable optical performance, an optical apparatus, and a method for manufacturing the zoom optical system are provided.

A zoom optical system ZL included in an optical apparatus such as a camera 1 includes, sequentially from an object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3, and a fourth lens group G4 having positive refractive power, an space between adjacent lens groups changes at zooming, with the first lens group G1 fixed relative to an image plane and the fourth lens group G4 moving along an optical axis, at least the second lens group G2 moves along the optical axis at focusing, and the zoom optical system ZL satisfies a condition expressed by a predetermined conditional expression.

A zoom lens L0 consists of a first lens unit L1 having negative refractive power, a middle group Lm including one or more lens units, and a last lens unit having positive refractive power. The first lens unit L1 includes a first negative lens, a second negative lens, and a third negative lens that are arranged sequentially in an order from an object side to an image side. The number of negative lenses included in the first lens unit L1 is four or less. The middle group Lm includes a plurality of cemented lenses each having a cemented surface that is convex toward the object side, and includes a lens element Ln that is disposed closest to the image side among lens elements having negative refractive power included in the middle group Lm. The zoom lens L0 satisfies a predetermined inequality.