Zoom lens system

Details Zoom lens system Zoom lens system

1999-06-15

2000-10-03

Epps, Georgia

Optical: systems and elements

Lens

With variable magnification

359684, 359686, G02B 1514

Patent

active

061281409

ABSTRACT:
A zoom lens system which includes a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group. All of the lens groups move toward the object upon zooming from the short focal length extremity to the long focal length extremity. The positive third lens group includes at least a positive lens element and a negative lens element. The positive fourth lens group includes at least one negative lens element. When the object distance changes from infinity to a finite object distance, focusing is performed by moving the second lens group toward the object,and the following conditions are satisfied: (1)-1.23<m.sub.3-4W <-1.0, (2)0.02<d.sub.19 /fw<0.30, (3)1.6<n.sub.L13 <1.76; wherein m.sub.3-4W : the resultant lateral magnification of the third and fourth lens groups which are considered to be one lens group at the short focal length extremity; d.sub.19 : the distance between the positive lens element and the negative lens element in the third lens group; fw: the focal length of the entire lens system at the short focal length extremity; and n.sub.L13 : the refractive index of the negative lens element closest to the image in the fourth lens group.

REFERENCES:
patent: 4952039 (1990-08-01), Ito
patent: 5528423 (1996-06-01), Arimoto et al.
patent: 5699198 (1997-12-01), Inadome et al.
patent: 5815321 (1998-09-01), Shimo

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