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 β pieces (β 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 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 zoom lens includes a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group having negative refractive power and a fourth lens group having positive refractive power. Upon varying magnification, distances between the first lens group and the second lens group, between the second lens group and the third lens group and between the third lens group and the fourth lens group vary. The second lens group includes a front lens group, an aperture stop, and a rear lens group. Each of the front lens group and the rear lens group includes at least one positive lens. At least a part of the lenses in the second lens group is moved as a group to have a component in a direction perpendicular to an optical axis.

A variable magnification optical system comprising, in order from an object side, a first lens group having negative refractive power, a first intermediate lens group having positive refractive power, a second intermediate lens group having negative refractive power and a rear lens group; upon varying a magnification from a wide angle end state to a telephoto end state, a distance between the first lens group and the first intermediate lens group being varied, a distance between the first intermediate lens group and the second intermediate lens group being varied, and a distance between the second intermediate lens group and the rear lens group being varied; the rear lens group comprising at least one focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expressions being satisfied, thereby the focusing lens group(s) being reduced in weight.

A zoom lens includes, in order from an object, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group. Zooming is performed by changing respective distances between the first and second lens groups, the second and third lens groups, and the third and fourth lens groups. The first lens group includes a negative lens disposed closest to the object, and a negative lens. Specified conditional expressions are satisfied.

A zoom optical system (ZL) includes: a first lens group (G1) having negative refractive power; a second lens group (G2) having positive refractive power, the second lens group (G2) being disposed further toward an image than the first lens group (G1); and a succeeding lens group (GL) having a vibration-isolating group (GVRb) that moves so as to have a displacement component in a direction orthogonal to an optical axis, the succeeding lens group (GL) being disposed further toward the image than the second lens group (G2), a distance between the first lens group (G1) and the second lens group (G2) changing and a distance between the second lens group (G2) and the succeeding lens group (GL) changing upon zooming, and the following conditional expression being satisfied:
4.899≤|f1VRaw/fw|<1000.000
where f1VRaw is a composite focal length in a wide-angle end state of a lens disposed further toward the object than the vibration-isolating group, and fw is a focal length of the whole system in the wide-angle end state.

A zoom lens includes: a first lens group having negative refractive power on a most object side; and a positive lens group Pa having positive refractive power, a negative lens group N having negative refractive power, and a positive lens group Pb having positive refractive power that are arranged in this order from the object side and provided on an image side with respect to the first lens group.

A zoom lens system (10) for imaging, includes, in order from an object side (11); a first lens group (G1) with negative refractive power that moves at the time of zooming; a second lens group (G2) with a positive refractive power that moves at the time of zooming, the second lens group including an aperture stop (St); a third lens group (G3) with a positive refractive power, the position of which is fixed relative to the image plane. The second lens group includes: a first sub-lens group (S1) with a positive refractive power arranged on the object side and having the aperture stop; and a second sub-lens group (S2) with a negative refractive power arranged on the image plane side and configured to move independently of the first sub-lens group at the time of focusing.

A lens assembly includes a first lens group, a second lens group, a third lens group, a fourth lens group, a fifth lens group, a sixth lens group, and a first reflective element. The first and third lens groups are with negative refractive power. The second and fourth lens groups are with positive refractive power. The fifth and sixth lens groups are with refractive power. The first, second, third, fourth, fifth, and sixth lens groups are arranged in order from a first side to a second side along an axis. The first reflective element includes a first reflective surface. A light from the first side sequentially passes through the first, second, third, fourth, fifth, and sixth lens groups to the second side. The first reflective element is disposed between the first lens group and the sixth lens group.

A variable magnification optical system includes, in order from an object: a first lens group (G1) having a negative refractive power; a second lens group (G2) having a positive refractive power; a third lens group (G3) having a negative refractive power; and a fourth lens group (G4) having a positive refractive power. The system performs varying magnification by changing the distance between the first lens group and the second lens group, the distance between the second lens group and the third lens group, and the distance between the third lens group and the fourth lens group. The third lens group includes a 32nd lens group (G32) configured to be movable so as to have a component in a direction orthogonal to an optical axis in order to correct image blur as a vibration-reduction lens group (VR) and a 31st lens group (G31) disposed at an object-side of the 32nd lens group. The 32nd lens group has negative refractive power, and the system satisfies Conditional Expression (1) below.
0.200<f1/f3<0.900  (1)