Zoom lens system

Details Zoom lens system Zoom lens system

1995-12-20

1998-05-12

Nelms, David C.

Optical: systems and elements

Lens

With variable magnification

359689, 359691, G02B 1514

Patent

active

057514984

ABSTRACT:
A zoom lens system includes a first lens group having a positive focal length and a second lens group having a negative focal length, arranged in this order from the object side. A zooming operation of the lens system is carried out by varying the distance between the first and second lens groups. The first lens group may include a first sub-group and a second sub-group. The first sub-group and the second sub-group may each be provided with at least one negative lens element. The zoom lens system preferably satisfies the relationships defined by (1) 3.5<f.sub.L /f.sub.1 <5.0; (2) 1.77<N.sub.1 a N ; (3) 35<.upsilon..sub.1 a N <50; (4) 1.77<N.sub.1 b N ; and (5) 35<.upsilon..sub.1 b N <50; wherein "f.sub.L " represents the focal length of the whole lens system at a telephoto extremity, "f.sub.1 " represents the focal length of the first lens group, "N.sub.1 a N " represents the refractive index of the negative lens element of the first sub-group at the d-line, ".upsilon..sub.1 a N " represents the Abbe number of the negative lens element of the first sub-group, "N.sub.1 b N " represents the refractive index of the negative lens element of the second sub-group at the d-line, and ".upsilon..sub.1 b N " represents the Abbe number of the negative lens element of the second sub-group, respectively.

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