An optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a first focus lens unit having a negative refractive power, and a second focus lens unit having a positive refractive power. The first lens unit is fixed during focusing. The first focus lens unit and the second focus lens unit move so that a distance between the first focus lens unit and the second focus lens unit changes during focusing. The first lens unit includes a single lens which is disposed closest to an object and has a negative refractive power. A predetermined condition is satisfied.

Provided are an optical lens, a camera module and a front camera. From an object side to an Imaging plane, the optical lens sequentially includes: a stop; a first lens having a positive focal power and a concave object side surface; a second lens having a negative focal power and a concave image side surface; a third lens having a positive focal power, a convex object side surface and a concave image side surface; a fourth lens having a positive focal power, a concave object side surface and a convex image side surface; a fifth lens having a negative focal power. An entrance pupil diameter EPD of the optical lens is smaller than 1.58 mm, and the maximum distance between the projection of an entrance pupil and the projection of the object side surface of the first lens on the optical axis is greater than 0.17 mm.

A zoom lens includes, in order from an object side, a first lens group that is positive, a second lens group that is negative, a third lens group that is positive, and a fourth lens group that is positive. During zooming from a wide angle end to a telephoto end, at least the first lens group and the third lens group are fixed and an interval on an optical axis of an adjacent lens group relative thereto is changed. In the zoom lens, the fourth lens group includes at least one positive lens and satisfies a predetermined conditional expression. In addition, an imaging device includes the zoom lens and an image sensor.

A zoom optical system comprises, in order from an object side: a first lens group having positive refractive power; a front-side lens group; an intermediate lens group having positive refractive power; and a rear-side lens group. The front-side lens group is composed of one or more lens groups and has a negative lens group. At least part of the intermediate lens group is a focusing lens group. The rear-side lens group is composed of one or more lens groups. Upon zooming, distances between the first lens group and the front-side lens group, between the front-side lens group and the intermediate lens group, and between the intermediate lens group and the rear-side lens group change. At least one of the following conditional expressions is satisfied:

0.010<fF/fXR<10.000

2.250<TLW/ZD1<10.000

where fF denotes a focal length of the focusing lens group, fXR denotes a focal length of a lens group closet to the image surface in the front-side lens group, TLW denotes an entire length of the optical system in a wide angle end state, and ZD1 denotes a movement amount of the first lens group upon zooming from the wide angle end state to a telephoto end state.

A variable magnification optical system capable of realizing a high-resolution observation image display system that can arbitrarily change an observation field of view without changing a working distance of an observation optical system while keeping the observation optical system small in size and an imaging apparatus including the variable magnification optical system.

A zoom lens includes, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, a fourth lens unit having positive refractive power, and a fifth lens unit having negative refractive power. During zooming from a wide-angle end to a telephoto end, a distance between adjacent lens units changes, the first lens unit and the third lens unit are fixed, and the second lens unit and the fourth lens unit move. The third lens unit includes a negative lens and a positive lens. A predetermined condition is satisfied.

Provided is a zoom lens including, in order from an object side to an image side: a positive first lens unit; a negative second lens unit; a positive third lens unit; a positive fourth lens unit; and a rear unit including at least one lens unit. An interval between each pair of adjacent lens units is changed during zooming. The first lens unit includes, in order from the object side to the image side, a negative lens and a positive lens. A focal length f1 of the first lens unit, a focal length f2 of the second lens unit, a focal length f3 of the third lens unit, and an average value Nd1ave of refractive indices at a d-line of respective materials of the negative lens and the positive lens of the first lens unit are each appropriately set.

The present disclosure relates to zoom lenses and optical devices using the same. A zoom lens may include in order from an object side to an image side: a first lens group; a second lens group; a third lens group; a fourth lens group; and a fifth lens group; wherein the zoom lens satisfies the following conditions: 1.7f.sub.2/f.sub.w0.3, 0.7f.sub.3/f.sub.w2.1, 1.1f.sub.4/f.sub.w2.5, and TTL/f.sub.w6.5, wherein f.sub.2 denotes a focal length of the second lens group, f.sub.3 denotes a focal length of the third lens group, f.sub.4 denotes a focal length of the fourth lens group, f.sub.w denotes a focal length of the zoom lens, and TTL denotes a total track length of the zoom lens.

An optical system comprises a lens satisfying the following conditional expressions.

2.0100<ndLZ+(0.00925dLZ)<2.0800

28.0<dLZ<40.0 where, ndLZ: a refractive index of the lens relative to a d-line dLZ: a d-line based Abbe number of the lens.

A zoom optical system (ZL) comprises, in order from an object: a first lens group (G1) having positive refractive power; an intermediate group (GM) including at least one lens group and having negative refractive power as a whole; an intermediate side lens group (GRP1) having positive refractive power; a subsequent side lens group (GRP2) having positive refractive power; and a subsequent group (GR) including at least one lens group. The subsequent side lens group (GRP2) moves upon zooming. The subsequent side lens group (GRP2) includes at least two lenses. A following conditional expression is satisfied.
0.2<fRP1/fRP2<0.8 where, fRP1 denotes a focal length of the intermediate side lens group (GRP1), and fRP2 denotes a focal length of the subsequent side lens group (GRP2).