An optical system comprises a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power, arranged in order from an object side. When focusing, the second lens group moves along an optical axis. The optical system satisfies the following conditional expressions

0.100<BFa/f<0.500 and

−5.000<(−G1R1)/f<500.000

where BFa is an air equivalent distance on the optical axis from a lens surface on an image side to an image surface for the lens disposed farthest on the image side in the optical system,

f is a focal length of the optical system, and

G1R1 is a radius of curvature of the lens surface on the object side for a lens component disposed farthest on the object side in the first lens group.

An optical system includes one or more positive lenses and one or more negative lenses. The first positive lens is a positive lens disposed closest to an object among the one or more positive lenses. The first negative lens is a negative lens that is disposed on an image side of the first positive lens and disposed closest to the object among the one or more negative lenses. At least one of an object side surface and an image side surface of the first positive lens is an aspherical surface. At this time, a relationship between a total lens length of the optical system L0, a focal length of the optical system L0, and a distance Dpn on an optical axis from the image side surface of the first positive lens to an object side surface of the first negative lens is defined.

The invention relates to a correction objective (10), comprising a first lens group (12) of positive optical power, a second lens group (14) of positive optical power, a third lens group (16) of negative optical power, and a fourth lens group (18) of positive optical power, which are arranged in this order from the object side, the second lens group (14) being movable along the optical axis (O) in such a way that the sum of the distance (V1) between the second lens group (14) and the first lens group (12) and the distance (V2) between the second lens group (14) and the third lens group (16) is constant. The image scale of the second lens group (14) lies in a range of 0.9 to 1.1.

An imaging lens and an imaging device furnished with same, including a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, disposed in sequence from the object side, wherein zooming from a point at infinity to an object at the near point is performed by moving the second lens group along an optical axis toward the object side while affixing the first lens group and third lens group, and satisfying predetermined conditional expressions.

An optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. The second lens unit moves during focusing and a distance between adjacent lens units changes. The second lens unit includes a cemented lens closest to an object. The cemented lens includes a positive lens and a negative lens disposed on the image side of the positive lens. A predetermined condition is satisfied.

The imaging lens consists of, in order from the object side, a first positive lens group, a stop, a second positive lens group, and a third negative lens group. During focusing, the first lens group and the second lens group move integrally. The first lens group consists of three or less lenses. The first lens group includes a cemented lens in which a negative lens and a positive lens are cemented in order from the object side. The third lens group consists of, in order from the object side, a negative aspheric lens, a negative lens, and a positive lens. The lens closest to the image side in the second lens group is a biconvex lens, and the imaging lens satisfies a predetermined conditional expression regarding the radius of curvature of the surface of the biconvex lens.

An embodiment provides an imaging lens comprising first to third lens groups arranged sequentially from an object side to an image side and having refractive power, wherein the distances of the second lens group and the third lens group from the first lens group are variable such that a tele mode having a narrow angle of view and a wide mode having a wide angle of view can be implemented, the EFL in the tele mode is no more than 2.5 times the EFL in the wide mode, 2<F.sub.number<5 and 15 mm<TTL40 mm.

An imaging lens comprises in order from an object, a first lens group of positive refractive power, a second lens group of positive refractive power, and a third lens group of negative refractive power. In focusing from infinity to a close object, the first lens group is fixed in position, and the second lens group and the third lens group are moved so that the distance between the first lens group and the second lens group is reduced, and the distance between the second lens group and the third lens group is increased. Further, the following conditional expression (1) is satisfied:

1.0<f1/f<2.5(1) where f1: is the focal length of the first lens group, and f: the focal length of the entire system.

A lens system is provided. The lens system includes a positive first lens group, an aperture diaphragm, a positive second lens group, and a third lens group, disposed sequentially from a subject side. The first lens group includes at least three positive lenses and at least one negative lens. The second lens group includes four or more lenses including at least one cemented lens. A negative lens with a concave surface toward the subject side is disposed at the subject side. The third lens group includes three or more lenses including at least one positive lens and at least one negative lens. When focusing is moving from an infinity-distance subject to a short-distance subject, the first lens group, the aperture diaphragm, and the second lens group move integrally toward the subject side, while the third lens group is fixed with respect to an image surface.

The imaging lens consists of, in order from an object side, a positive first lens group, a positive second lens group, and a negative third lens group. During focusing, only the second lens group moves. The number of lenses included in the second lens group is two or less. The lens on the most object side is a negative lens having a convex surface toward the object side. The lens surface on the most image side is a convex surface. The first lens group includes a stop. Predetermined conditional expressions related to the first lens group and the second lens group are satisfied.