Real-image finder having variable power

Details Real-image finder having variable power Real-image finder having variable power

1995-07-25

1997-12-02

Nguyen, Thong

Optical: systems and elements

Compound lens system

Variable magnification

359422, 359431, 359690, G02B 2300, G02B 1514

Patent

active

056942443

ABSTRACT:
A real-image finder having variable power includes an objective lens system of positive power, a condenser lens, and an ocular lens system. The objective lens system includes a first positive lens group, a second negative lens group, and a third positive lens group from an object side towards an image side. The second lens group is moved toward an image side and the third lens group is moved toward an object side, when the magnification changes from a wide angle side to a telephoto side. Thus, the distance between the first and second lens groups increases, the distance between the second and third lens groups decreases, and the distance between the third lens group and the condenser lens increases. The real-image finder meets the requirements defined by the relationships 0.5<.vertline.m.sub.2w .vertline.<1.0; 1.1<.vertline.m.sub.2T .vertline.; 0.5<.vertline.m.sub.3w .vertline.1,0; and, 1.1<.vertline.m.sub.3T .vertline., where "m.sub.2w " and "m.sub.2T " designate the lateral magnification of the second lens group on the wide angle and telephoto sides, and "m.sub.3w " and "m.sub.3T " designate the lateral magnification of the third lens group on the wide angle and telephoto sides.

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