Optical: systems and elements – Lens – Eyepiece
Reexamination Certificate
1999-12-13
2001-05-08
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Eyepiece
C359S686000, C359S689000
Reexamination Certificate
active
06229653
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable-power eyepiece optical system which is used in combination with an objective optical system of binoculars, telescopes or microscopes.
2. Description of the Related Art
Various types of variable-power eyepiece optical systems having a magnification ratio of about 2 have conventionally been proposed. For example, Japanese Unexamined Patent Publication No. Hei-4-204616 has disclosed an afocal variable-power optical system including an objective optical system, an erecting optical system and a variable-power eyepiece optical system. Further, Japanese Unexamined Patent Publications Nos.Sho-62-134617 and Hei-6-175048 have solely disclosed variable-power eyepiece optical systems, i.e., the variable-power eyepiece optical systems have been disclosed without being accompanied by an objective optical system and an erecting optical system. With respect to each of the above publications, the variable-power eyepiece optical system is formed as a three-lens-group variable-power eyepiece optical system including a negative first moveable lens group, a field diaphragm, a positive second moveable lens group and a positive third immoveable lens group, in this order from the object. According to this arrangement, upon variable-power the first and second moveable lens groups are moved in the opposing directions, and at the same time, the change in diopter is corrected; however, the change in the exit pupil distance (i.e., the eye relief: the distance between the most viewer's eye-side surface and the eye point) cannot be corrected. In particular, if an attempt is made to obtain a higher magnification ratio of more than 2, the change in the exit pupil distance becomes extremely large, so that variable-power causes an eclipse.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a variable-power eyepiece optical system which can attain a magnification ratio of more than 2, can have a variable power function with a minimum positional change in the eye relief, and can prevent an eclipse.
The present invention is applied to a variable-power eyepiece optical system including a negative first moveable lens group, a positive second moveable lens group and a positive third immoveable lens group, in this order from an objective optical system. A conception of the present invention is to divide the positive second lens group into at least two moveable sub lens groups so that by independently moving these sub lens groups, the resultant power of the second lens group is varied, and thereby the object-image distance of the pupils (the distance between the entrance pupil and the exit pupil) is varied, and the position of the exit pupil is moved. Consequently, the change in the eye relief upon variable power is reduced, and an eclipse due to variable power is prevented.
In order to achieve the above mentioned object, there is provided a variable-power eyepiece optical system, which is used in combination with an objective optical system, including a negative first lens group, a second lens group having a positive first sub lens group and a positive second sub lens group, and a positive third lens group, in this order from the objective optical system. The first lens group, and the first and second sub lens groups of the second lens group are made moveable along the optical axis upon variable power, while the third lens group is made immoveable. More concretely, at the time of variable power, the first sub lens group and the second sub lens group move independently of each other in a direction opposite to the direction along which the first lens group moves, and thereby the resultant power of the first and second sub lens groups is varied.
In order to vary the resultant power of the second lens group suitably upon variable power, the variable-power eyepiece optical system according to the present invention preferably satisfies the following condition:
0.7 <
f
2
a/f
2
b <
1.4 (1)
wherein
f2a designates the focal length of the positive first sub lens group; and
f2b designates the focal length of the positive second sub lens group.
In order to obtain a longer eye relief along the overall variable-power range, the positive first sub lens group preferably includes a cemented sub lens group having a negative lens element and a positive lens element, and the positive second sub lens group and the positive third lens group preferably include a single lens element respectively. In the above cemented lens elements, the order of the negative and positive lens elements is not required.
The present disclosure relates to subject matter contained in Japanese Patent Application No.Hei-10-357881 (filed on Dec. 16, 1998) which is expressly incorporated herein by reference in its entirety.
REFERENCES:
patent: 5311355 (1994-05-01), Kato
patent: 5504624 (1996-04-01), Kato
patent: 5576888 (1996-11-01), Betensky
patent: 5576892 (1996-11-01), Hotta et al.
patent: 5663834 (1997-09-01), Koizumi
patent: 5734509 (1998-03-01), Ueno
patent: 62-134617 (1987-06-01), None
patent: 4-204616 (1992-07-01), None
patent: 5-5840 (1993-01-01), None
patent: 6-175048 (1994-06-01), None
An English Language abstract of JP 62-134617, Jun. 17, 1987.
An English Language abstract of JP 4-204616, Jul. 27, 1992.
An English Language abstract of JP 6-175048, Jun. 24, 1994.
Asahi Kogaku Kogyo Kabushiki Kaisha
Epps Georgia
Greenblum & Bernstein P.L.C.
Schwartz Jordan M.
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