A projection zoom lens is constituted essentially by: a plurality of lens groups that include at least two lens groups that move when changing magnification; the distances among all pairs of adjacent lens groups changing when changing magnification; the reduction side being configured to be telecentric; and a negative first lens group, which is fixed when changing magnification, being provided most toward the magnification side. The first lens group is constituted essentially by, in order from the magnification side to the reduction side, a negative first lens, which is a meniscus lens having a convex surface toward the magnification side, a biconcave second lens, and a positive or negative third lens. Conditional Formula (1) related to fw, which is the focal length of the entire projection zoom lens at the wide angle end, and f3, which is the focal length of the third lens, is satisfied:
−0.070<fw/f3<0.070  (1).

A zoom lens includes a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and two or more additional lens units. In zooming, the first lens unit moves, and an interval between adjacent lens units changes. The refractive index of a negative lens A disposed on a most object side of negative lenses included in the first lens unit is higher than or equal to 1.89, and the negative lens A and a lens B disposed adjacent to an image side of the negative lens A satisfy a predetermined relationship.

A projection zoom lens is configured by a first group having a negative refractive force, a second group having a positive refractive force, a third group having a positive refractive force, an aperture diaphragm, a fourth group having a positive refractive force, and a fifth group having a positive refractive force. The groups are arranged in aforementioned order from an enlarged-side to a reduced-side in the projection zoom lens, wherein the reduced-side is telecentric, wherein the first group is configured by a first sub-lens group having a positive or a negative refractive force, a second sub-lens group having a negative refractive force, and a third sub-lens group having a negative refractive force, wherein the sub-lens groups are arranged sequentially from the enlarged-side to form a focusing group, wherein the second group to the fifth group constitute a zooming group.

An imaging optical system includes, in order from an enlargement conjugate side, a front unit, a diaphragm, and a rear unit. The front unit includes, in order from the enlargement conjugate side, a first lens having a negative refracting power, a second lens having at least one aspherical surface and a meniscus shape with a negative refracting power, and a third lens having an aspherical surface on the enlargement conjugate side and a negative refractive power. The second lens has a positive refractive power at a periphery, and a surface in which the periphery and a center have curvatures with different signs. The third lens has a concave surface on the enlargement conjugate side. A predetermined condition is satisfied.

In the zoom lens, a first optical system is formed on the magnification side, and a second optical system is formed on the reduction side, with the intermediate image formed between the first optical system and the second optical system. The first optical system has a 5-group configuration, where the second to fourth lens groups move during zooming. In the first optical system, three or more negative lenses are disposed continuously in order from a position closest to the magnification side. The first optical system has a first cemented lens that is formed by cementing a negative lens and two positive lenses, of which Abbe numbers are larger than that of the negative lens, in order of positive, negative, and positive powers.

A projection zoom lens is configured by a first group having a negative refractive force, a second group having a positive refractive force, a third group having a positive refractive force, an aperture diaphragm, a fourth group having a positive refractive force, and a fifth group having a positive refractive force. The groups are arranged in aforementioned order from an enlarged-side to a reduced-side in the projection zoom lens, wherein the reduced-side is telecentric, wherein the first group is configured by a first sub-lens group having a positive or a negative refractive force, a second sub-lens group having a negative refractive force, and a third sub-lens group having a negative refractive force, wherein the sub-lens groups are arranged sequentially from the enlarged-side to form a focusing group, wherein the second group to the fifth group constitute a zooming group.

A projection zoom lens constituted by: a negative first lens group; a positive final lens group; and moving lens groups between the first and the final lens groups that move independently while changing magnification, satisfies the conditional formulae below:
1.00<(Rf2Rr2)/(Rf2+Rr2)(1)
0.00(Rr2Rf3)/(Rr2+Rf3)<0.15(2)
2.5<Bf/Im(9) wherein Rf2 and Rr2 respectively are the radii of curvature of the front and rear surfaces of the second lens from the magnification side within the most reduction side moving lens group, Rf3 is the radius of curvature of the front surface of the third lens from the magnification side within the most reduction side moving lens group, Bf is the back focus of the entire system at the reduction side at the wide angle end as an air converted length, and Im is the maximum effective image circle diameter at the reduction side.

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.