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.

An objective optical system for endoscope includes a first lens having a negative refractive power, a second lens having a positive refractive power, an aperture stop, a third lens having a positive refractive power, a fourth lens having a positive refractive power, a fifth lens having a negative refractive power, and a sixth lens having a positive refractive power. The second lens is a meniscus lens having a convex surface directed toward an image side and the third lens is a meniscus lens having a convex surface directed toward the image side. A cemented lens having a positive refractive power is formed by the fourth lens and the fifth lens. The sixth lens is cemented to an image sensor, and the following conditional expression (1′″) is satisfied:
1≤(r3f+r3r)/(r3f−r3r)≤5  (1′″).

The present invention relates to the field of optical lenses and provides a zoom lens consisting of, from an object side to an image side in sequence, a first lens having negative refractive power, a second lens group having positive refractive power, a fifth lens having positive refractive power, and a sixth lens having negative refractive power. During zooming, a distance between adjacent lenses or between lens and adjacent lens group in a direction of an optic axis varies. The second lens group consists of a second lens having positive refractive power, a third lens having negative refractive power, and a fourth lens having negative refractive power, and following conditions are satisfied: f_Tele/f_Wide≥1.80; −1.75≤f3/f2≤−1.35; −1.75≤f4/f2≤−1.35. The present invention becomes compact when contracted, while during imaging, FNO is bright, and has good optical properties.

A variable magnification projection optical system includes, in order from an enlargement side: a first lens group having negative refractive power; a second lens group having negative refractive power; and a third lens group having positive refractive power. During zooming, the first lens group is fixed, and the second lens group and the third lens group move. The second lens group includes a plurality of lenses each having positive refractive power. All lenses each having positive refractive power in the first lens group and the second lens group are made of a glass material having a transmittance greater than 0.98 per thickness of 10 mm with respect to light having a wavelength of 440 nm.

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); a third lens group (G3); a fourth lens group (G4) having a negative refractive power; and a fifth lens group (G5) having a positive refractive power, the system performing varying magnification by changing the distance between the first and second lens groups, the distance between the second and third lens groups, the distance between the third and fourth lens groups, and the distance between the fourth and fifth lens groups, and the fourth lens group including a 42nd lens group (G42) configured to be movable so as to have a component in a direction orthogonal to an optical axis and a 41st lens group (G41) disposed at an object-side of the 42nd lens group.

This variable power optical system (ZL(1)) has a plurality of lens groups (G1-G7), and the intervals between the respectively adjacent lens groups change during power variation. The plurality of lens groups include a first focusing lens group (G6) that moves during focusing, and a second focusing lens group (G7) that is disposed closer to the image surface than is the first focusing lens group and moves so as to follow a track different from that of the first focusing lens group. The first focusing lens group (G6) and the second focusing lens group (G7) each have a negative refractive power and satisfy conditional expression: 0.40<MTF1/MTF2<1.00, where MTF1 represents an absolute value of the movement amount of the first focusing lens group during shifting, in a telephoto end state, from an object-at-infinity focusing state to an object-at-extremely-close-distance focusing state, and MTF2 represents an absolute value of the movement amount of the second focusing lens group during shifting, in a telephoto end state, from the object-at-infinity focusing state to the object-at-extremely-close-distance focusing state.

An optical system comprising a plurality of lens groups arranged on an optical axis and comprising a leading lens group, a first focal lens group, and a second focal lens group. The leading lens group is arranged further on the object side than the first focal lens group and the second focal lens group is arranged further on the image side than the first focal lens group. The first focal lens group has positive refractive power and moves along the optical axis to the image side when focusing from an infinite object to a short-distance object. The second focal lens group: has a negative refractive power; travels along the optical axis to the object side when focusing from an infinite object to a short-distance object; and has, between the first focal lens group and the second focal lens group, an intermediate lens group that includes at least one lens.

An attachment optical system attachable to and detachable from an imaging optical system includes a first converter optical system attachable to an object side of the imaging optical system, and a second converter optical system attachable to an image side of the imaging optical system. The first converter optical system includes a first unit consisting of a dome-shaped cover. A predetermined condition is satisfied.

Provided is a camera optical lens including, sequentially from an object side to an image side: a first lens having a negative refractive power; a second lens; a third lens having a positive refractive power; a fourth lens having a negative refractive power; a fifth lens; a sixth lens having a positive refractive power; and a seventh lens having a negative refractive power. At least one of the first to seventh lenses comprises a free-form surface. The camera optical lens satisfies following conditions: −5.00≤f1/f≤−1.00; and 1.50≤d1/d2≤7.00. The camera optical lens can achieve high optical performance while satisfying design requirements for ultra-thin, wide-angle lenses.

A variable magnification optical system used in an optical apparatus is configured to include a plurality of lens groups such that upon varying magnification the distances between the lens groups are varied; a final lens group closest to an image side of the lens groups includes at least one lens surface having a pole; and the following conditional equation (1) or (2) is satisfied.

0.50<TL/fw<10.00  (1)

where TL denotes the shorter of the total optical length in a wide-angle end state and the total optical length in a telephoto end state of the variable magnification optical system, and fw denotes the focal length of the variable magnification optical system in the wide-angle end state.

−5.00<fRI/fR<5.00  (2)

where fRI denotes the focal length of a lens in the final lens group including a lens surface having a pole, and fR denotes the focal length of the final lens group.