Method for focusing telephoto type optical system

Claim 2

In a method for focusing, on an image plane, a telephoto-type objective lens system having front and rear lens groups disposed in rearward succession along an optical axis between an object and the image plane, the front lens group being of positive power and the rear lens group having at least two lens members, the improvement which comprises the step of simultaneously moving the frontmost and rearmost members of the rear lens group in respectively opposite axial directions while the front lens group is held stationary.

Claim 3

The improved method as defined in cLaim 1 in which the rear lens group is of negative power.

Claim 4

A telephoto-type objective lens system comprising a front lens group of positive power and a rear lens group of negative power disposed in rearward succession along a system optical axis between an object and an image plane, the rear lens group having movable frontmost and rearmost lens members, and means for simultaneously moving said movable lens members in respectively the opposite the axial directions independent of the front lens group.

Claim 5

A telephoto-type objective lens system comprising a front lens group of positive power and a rear lens group of negative power disposed in rearward succession along a system optical axis between an object and an image plane, the rear lens group having movable frontmost and rearmost lens members, and means for simultaneously moving said movable lens members in respectively the opposite the axial directions independent of the front lens group.

Claim 6

The improvement as defined in claim 3 in which the front lens group comprises a pair of axially spaced positive lens members.

Claim 7

The improvement as defined in claim 3 in which the frontmost movable lens member in the rear lens group has at least one divergent surface.

Claim 8

The improvement as defined in claim 3 in which the frontmost movable lens member in the rear lens group is of positive power.

Claim 9

The improvement as defined in claim 3, in which the frontmost movable lens member in the rear lens group is of negative power.

Claim 10

The improvement as defined in claim 3, in which the focal lens of the rearmost movable lens member in the rear lens group is fB, the focal length of the frontmost movable lens member in the rear lens group is fA, and in which the magnitude of fA is greater than the magnitude of fB.

Claim 11

The improvement as defined in claim 3 in which the rear lens group comprises a fixed lens member intermediate the frontmost and rearmost movable lens members.

Claim 12

The improvement as defined in claim 3 in which the front lens group comprises, in rearward succession, a biconvex lens, a biconcave lens, and a positive meniscus lens having a forward convex surface, and in which the frontmost and rearmost movable lens members in the rear lens group comprise first and second negative meniscus lenses each having a forward concave surface.

Claim 13

The improvement as defined in claim 10 in which the second negative meniscus lens comprises a forward biconcave lens and a rear biconvex lens cemented together.

Claim 14

The improvement as defined in claim 3 in which the front lens group comprises in rearward succession a first positive meniscus lens having a forward convex surface, a first negative meniscus lens having a forward concave surface, a second positive meniscus lens having a forward convex surface, and a positive lens; and in which the frontmost and rearmost movable lens elements in the rear lens group respectively comprise second and third movable negative meniscus lenses.

Claim 15

The improvement as defined in claim 12 in which the third negative meniscus lens comprises a forward biconcave lens and a rear biconvex lens cemented together.

Claim 16

The improvement as defined in claim 3 in which the front lens group comprises in rearward succession a first positive meniscus lens having a forward convex surface, a first negative meniscus lens having a forward concave surface, a second positive meniscus lens having a forward convex surface, and a positive lens; in which the frontmost and rearmost movable lens elements in the rear lens group respectively comprise second and third negative meniscus lenses each having a forward concave surface; and in which the rear lens group further comprises a third fixed positive meniscus lens having a forward concave surface.

Claim 17

The improvement as defined in claim 14 in which the third movable negative meniscus lens comprises a forward biconcave lens and a rear biconvex lens cemented together.