The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Oct. 17, 2000
Filed:
Jun. 25, 1999
Takaaki Yano, Hokkaido, JP;
Asahi Kogaku Kogyo Kabushiki Kaisha, Tokyo, JP;
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.