A zoom lens includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a rear group, sequentially from an object side. Intervals between lens groups varies when changing magnification. A lens group having a highest negative refractive power among a lens group having a negative refractive power in the rear group is a focusing lens group GF configured to move toward an image side when focusing from infinity to a close range. A lens group GFF having a positive refractive power and arranged adjacent to an object side of the focusing lens group GF among a lens group having a positive refractive power included in the rear group includes a positive lens component L1 positioned on a most image side, which includes a positive lens L1P having a refractive index NdL1P, and a conditional expression (1) 1.85<NdL1P is satisfied.

A zoom lens includes a negative first lens group, a positive second lens group, and a subsequent lens group in order from an object side. A focusing lens group closer to an image side than the first lens group moves during focusing. The first lens group consists of a first-a lens group and a first-b lens group in order from the object side. Assuming that an average of refractive indices of the negative lenses of the first-a lens group is Nd1ave, a focal length of the focusing lens group is ff, and a focal length of the first lens group is f1, Conditional Expression (1) of 1.73<Nd1ave<1.95 and Conditional Expression (2) of 1<|ff/f1|<3 are satisfied.

A zoom lens includes a negative first lens group, a positive second lens group, and a subsequent lens group in order from an object side. A focusing lens group closer to an image side than the first lens group moves during focusing. The first lens group consists of a first-a lens group and a first-b lens group in order from the object side. Assuming that an average of refractive indices of the negative lenses of the first-a lens group is Nd1ave, a focal length of the focusing lens group is ff, and a focal length of the first lens group is f1, Conditional Expression (1) of 1.73<Nd1ave<1.95 and Conditional Expression (2) of 1<|ff/f1|<3 are satisfied.

A lens driving apparatus is for driving a lens assembly and includes a base, a metal cover, a carrier, a first coil, at least one first magnet, at least one second magnet, a frame and a spring set. At least one lower leaf spring of the spring set includes a frame connecting section, a carrier connecting section and a resilient section. The carrier connecting section and the second magnet are arranged along the first direction. The carrier connecting section includes an opening portion and a shielding portion, and the opening portion and the shielding portion both corresponding to the second magnet along the first direction are respectively for a part of the second magnet to be exposed through the opening portion and another part of the second magnet to be shielded by the shielding portion.

An optical system includes a first optical subsystem disposed on an enlargement side and a second optical subsystem disposed on a reduction side with an intermediate image in between. The first optical subsystem includes: a first lens group that is disposed on the enlargement side of a first stop with a first distance, in which other lenses could be disposed but no other lenses are disposed, and is provided on the enlargement side with a first component with negative refractive power; and a second lens group that has positive refractive power, is disposed on the reduction side of the first stop with a second distance, in which other lenses could be disposed but no lenses are disposed, and forms the intermediate image so as to be adjacent on a reduction side of the second lens group and so as to be tilted toward the enlargement side.

An optical element includes a plurality of substrates, an adhesive configured to adhere the plurality of substrates to each other, and an antireflection film provided to at least one of an incident surface and an exit surface of the optical element. The antireflection film includes a first layer including alcohol having at least one of an ether bond and an ester bond in a branched structure with 4 to 7 carbon atoms. A content of the alcohol in the first layer is 0.5 mg/cm.sup.3 to 5.0 mg/cm.sup.3. The first layer has a refractive index of 1.1 to 1.3 for light with a wavelength of 550 nm.

A zoom lens consists of, 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 a rear group including one or more lens units. Each distance between adjacent lens units changes during zooming. The rear group includes a focus lens unit having a positive refractive power that moves from the image side to the object side during focusing from an infinite distance object to a close distance object. A lens closest to an object in the focus lens unit has a shape with a concave surface on the object side. The following inequalities are satisfied.

1.20<fLP/fL2<3.20

−3.00<fL1/fL2<−0.85

fLP represents a focal length of the focus lens unit, fL1 represents a focal length of the first lens unit, and fL2 represents a focal length of the second lens unit.

A zoom lens includes a plurality of lens units. The plurality of lens units consist of, in order from an object side to an image side, a first lens unit having a negative refractive power, a middle group including one or more lens units, and a final lens unit having a negative refractive power. Each distance between adjacent lens units changes during zooming. The first lens unit includes at least three negative lenses. Predetermined conditions are satisfied.

A projection optical system includes a first lens group having negative power, a second lens group having positive power and disposed at a reduction side of the first lens group, and a third lens group having positive power and disposed at the reduction side of the second lens group. The first lens group includes at least three negative lenses. The second lens group includes at least one positive lens. The third lens group includes a plurality of positive lenses. The at least three negative lenses of the first lens group are each a single lens. The third lens group includes a jointed lens including at least one of the plurality of positive lenses. NA is a reduction-side numerical aperture, Dst is a distortion aberration at a reduction-side maximum image height, and the projection optical system satisfies Conditional Expressions (1) and (2),
0.2<NA  (1)
−45%<Dst<−10%  (2).

A lens assembly includes a first lens group, a second lens group, and a third lens group, all of which are arranged in order from a first side to a second side along an optical axis. The first lens group is with positive refractive power. The second lens group is with positive refractive power. The third lens group is with positive refractive power. The first lens group is fixed, the second lens group can move along the optical axis, and the third lens group can move along the optical axis, so that the lens assembly is zoomed from a wide-angle end to a telephoto end to change an effective focal length.