Variable-power type observational optical system and a variable-

Details Variable-power type observational optical system and a variable- Variable-power type observational optical system and a variable-

1999-06-25

2000-10-17

Epps, Georgia

Optical: systems and elements

Lens

With variable magnification

396374, 396379, G02B 1514

Patent

active

061340529

ABSTRACT:
A variable-power type eyepiece lens system, in a variable-power type observational optical system, comprises, a positive first lens group including a negative meniscus lens element and a bi-convex positive lens element which are cemented together; a second lens group including a single plastic-made bi-convex lens element having at least one aspherical surface; a third lens group including a single plastic-made bi-concave lens element having at least one aspherical surface; wherein an object image by the objective lens system is formed between the second and third lens groups, and when variable power is performed from the long focal length extremity towards the short focal length extremity, the second lens group is moved closer to the first lens group, and the third lens group is moved away from the first lens group, and the following conditions are satisfied: 1.5<.DELTA.LD/M<3.0 . . . (1) 1.8<f2/fS<2.6 . . . (2) wherein M: the magnification ratio of the eyepiece lens system; .DELTA.LD: the change of the overall length of the eyepiece lens system upon variable power being performed; f2: the focal length of the second lens group; and fS: the focal length of the overall system of the eyepiece lens system at the short focal length extremity.

REFERENCES:
patent: 5504624 (1996-04-01), Kato
patent: 5734509 (1998-03-01), Ueno
patent: 5734930 (1998-03-01), Hagiwara
patent: 5983029 (1999-11-01), Yamada et al.

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