Optical: systems and elements – Compound lens system – Telescope
Reexamination Certificate
1999-11-16
2001-08-28
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Compound lens system
Telescope
C359S831000, C359S835000
Reexamination Certificate
active
06282022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a real-image finder optical system, and in particular, relates to a diopter adjustment mechanism.
2. Description of the Related Art
In a compact camera (for example), a real-image finder optical system has the own optical axis which is separate from the optical axis of the photographing optical system. The real-image finder optical system includes a positive objective optical system which forms an object's inverted image which is upside down and reversed from left to right, an erecting optical system which erects the inverted image to the same orientation as the object, and a positive eyepiece optical system through which the erected image is viewed.
In a real-image finder optical system of this type, diopter adjustment is conventionally carried out by moving the eyepiece lens element along the optical axis thereof. In such a diopter adjusting mechanism in which the position of the eyepiece lens element is adjusted, there is an advantage of not increasing the number of lens elements. However, since a space is required in order to move the eyepiece lens element along the optical axis thereof, the thickness of the camera body has to be increased. Alternatively, if the camera body is made small and thin, a space to allow the eyepiece lens element to move cannot be secured, and thereby the diopter adjusting range cannot be made large.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a real-image finder optical system which can obtain a large diopter adjusting range while the thickness of the camera body does not increase. To achieve the above mentioned object, there is provided a real-image finder optical system including a positive objective optical system, an erecting optical system constituted by a combination of a plurality of reflection surfaces, and a positive eyepiece optical system, and thereby an inverted image of an object, which is formed by the objective optical system and is upside down and reversed from left to right, is erected to the same orientation as the object by the erecting optical system, and the erected image is viewed through the eyepiece optical system. At least two reflection surfaces of the erecting optical system are utilized for diopter adjustment, and wherein (i) a first diopter-adjusting reflection surface and a second diopter-adjusting reflection surface come into contact with each other to form a right angle therebetween, (ii) an optical axis extending from the side of the objective optical system to the first diopter-adjusting reflection surface and an optical axis being reflected by and extending from the second diopter-adjusting reflection surface are substantially parallel with each other, (iii) these two optical axes are substantially perpendicular to an optical axis being incident from the object to the objective optical system, (iv) diopter adjustment is performed by integrally moving the first and second diopter-adjusting reflection surfaces so that the optical path length from the image forming plane of the objective optical system to the eyepiece optical system is varied, and (v) the following condition is satisfied:
0.1<L
1
/L
2
<0.4 (1)
wherein
L
1
designates the distance, extending in the direction parallel with the optical axis being incident from the object to the objective optical system, between the optical axis reflected by and extending from the second diopter-adjusting reflection surface and the final surface of the eyepiece optical system; and
L
2
designates distances, extending in the direction parallel with the optical axis being incident from the object to the objective optical system, between the most-object side surface of the objective optical system and the final surface of the eyepiece optical system.
It is practical that the moving direction of the diopter-adjusting reflection surfaces is perpendicular with respect to the optical axis being incident from the object to the objective optical system.
The first and second diopter-adjusting reflection surfaces can be formed as a right-angle prism. The right-angle prism is preferably made of a synthetic resin material from the viewpoint of costs. The first and second diopter-adjusting reflection surfaces can also be formed by a mirror unit which integrally connects two plane mirrors. Preferably, the mirror unit is also made of a synthetic resin material from the viewpoint of costs.
The present disclosure relates to subject matter contained in Japanese Patent Application No.Hei-10-327234 (filed on Nov. 17, 1998) which is expressly incorporated herein by reference in its entirety.
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patent: 5621568 (1997-04-01), Hasushita et al.
patent: 5625487 (1997-04-01), Hasushita et al.
patent: 10282423 (1998-10-01), None
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Nguyen Thong
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