Optical: systems and elements – Compound lens system – Telescope
Reexamination Certificate
2000-03-31
2001-08-21
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Compound lens system
Telescope
C359S422000, C359S432000, C359S676000
Reexamination Certificate
active
06278544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a real-image zoom finder optical system.
2. Description of the Related Art
A real-image zoom finder optical system is provided with an objective lens system, an erecting optical system which erects an inverted image formed through the objective lens system, and an eyepiece lens system. In a wide-angle real-image zoom finder optical system of the prior art, the apparent visual angle is not sufficiently large, and the eyerelief is not sufficiently long. In other words, it is difficult for a conventional wide-angle real-image zoom finder optical system to suitably correct aberrations over the entire field-of-view while maintaining an enough apparent visual angle and a long eye relief.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a wide-angle real-image zoom finder optical system suitable for a still camera, a video camera and the like, and in particular, to provide a real-image zoom finder optical system having suitable performance, and having a wider apparent visual angle and a longer eyerelief.
In order to achieve the above-mentioned object, there is provided a real-image zoom finder optical system in which a condenser lens system is arranged to lead a bundle of rays carrying an object image formed by an objective lens system to an eyepiece lens system, and along the optical path from the objective lens system to the eyepiece lens system, an erecting optical system for erecting the image formed by the objective lens system is provided; and the objective lens system, the condenser lens system, the erecting optical system and the eyepiece lens system are arranged in this order from the object. The objective lens system includes a negative lens group O
1
and a positive lens group O
2
, in this order from the object, and these lens groups are moveable along the optical axis upon zooming. Further, the negative lens group O
1
includes a negative meniscus single lens element O
11
having a convex surface facing towards the object, and a meniscus single lens element O
12
having a convex surface facing towards the image, in this order from the object.
The real-image zoom finder optical system according to the present invention preferably satisfies the following condition:
SF
1
<−1.1 (1)
wherein
SF
1
=(r
2
+r
1
)/(r
2
−r
1
);
SF
1
designates the shaping factor of the negative meniscus single lens element O
11
;
r
1
designates the radius of curvature of the object-side surface of the negative meniscus single lens element O
11
; and
r
2
designates the radius of curvature of the image-side surface of the negative meniscus single lens element O
11
.
As understood from condition (1), a feature of the present invention resides in the surface configuration of the most object-side negative meniscus single lens element in the real-image zoom finder optical system in which the objective lens system includes a negative lens group and a positive lens group, in this order from the object.
The real-image zoom finder optical system according to the present invention preferably satisfies the following condition:
−0.2<ØO
12
/ØOC<0.1 (2)
wherein
ØO
12
designates the power of the meniscus single lens element O
12
; and
ØOC designates the resultant power of the objective lens system and the condenser lens system at the short focal length extremity.
The real-image zoom finder optical system according to the present invention preferably satisfies the following condition:
−3.5<r
4
×ØOC<−0.4 (3)
wherein
r
4
designates the radius of curvature of the image-side surface of the meniscus single lens element O
12
.
The condenser lens system preferably includes at least one positive lens element and a negative single lens element LCn having a concave surface facing towards the object. According to this arrangement, the apparent visual angle can be made larger, and the eyerelief can be made longer.
The negative single lens element LCn of the condenser lens system preferably satisfies the following condition:
1≦SFCn (4)
wherein
SFCn=(r
2
′+r
1
′)/(r
2
′−r
1
′)
SFCn designates the shaping factor of the negative single lens element LCn;
r
1
′ designates the radius of curvature of the object-side surface of the negative single lens element LCn; and
r
2
′ designates the radius of curvature of the image-side surface of the negative single lens element LCn.
Furthermore, the negative single lens element LCn of the condenser lens system preferably satisfies the following condition:
−0.5<ØLCn/ØOC<0 (5)
wherein
ØLCn designates the power of the negative single lens element LCn.
ØOC designates the resultant power of the objective lens system and the condenser lens system at the short focal length extremity.
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patent: 3-4217 (1991-01-01), None
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Nguyen Thong
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