Optical: systems and elements – Compound lens system – Telescope
Reexamination Certificate
2002-07-12
2003-08-05
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Compound lens system
Telescope
C359S432000, C359S831000
Reexamination Certificate
active
06603603
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Application No. 11-328781 filed Nov. 18, 1999.
Japanese Patent Application No. 2000-319435 filed Oct. 19, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a real image viewfinder optical system for a camera, a digital still camera, and the like.
2. Description of Related Art
A real image viewfinder optical system includes an objective lens system having a positive refractive power as a whole, an eyepiece lens system having a positive refractive power for observing a real image formed by the objective lens system, and an image inverter optical system for erecting an inverted image formed by the objective lens system. In a compact type real image viewfinder used for a camera and the like, a reflection type image inverter optical system is commonly used.
In the reflection type image inverter optical system, there are a Porro type for inverting an image by reflection elements, such as a single or a plurality of Porro prisms having more than four reflection surfaces and a roof type for inverting an image by reflection elements, such as a roof prism having roof reflection surfaces.
Coordinates crossing at right angles with each other in a plane perpendicular to an optical axis of an incident light into a viewfinder optical system or a plane perpendicular to an optical axis of a light reflected by each reflection surface are to be called a vertical direction and a horizontal direction, respectively. A direction parallel to only the optical axis of the incident light into the viewfinder optical system is to be called a thickness direction. A direction in the horizontal direction relative to the optical axis of the incident light into the viewfinder optical system is to be called a width direction.
In the Porro type, the reflection type image inverter optical system is liable to become large in the horizontal direction when used for inverting an image in the horizontal direction, and in the vertical direction when used for inverting an image in the vertical direction. Therefore, an optical system according to the Porro type is liable to become large, so that it is not suitable for miniaturization.
Then, in a roof type, a projected direction of a roof ridgeline of a roof type reflection element on a plane perpendicular to the optical axis of the incident light or a plane perpendicular to the optical axis of the light reflected by each reflection surface is defined to be a horizontal direction. A direction perpendicular to the horizontal direction is defined to be a vertical direction. In this case, since an image inversion in vertical direction is performed on the roof surfaces composing the roof ridgeline, the dimension of the optical element in vertical direction can be small in comparison with the Porro type. Therefore, the roof type is advantageous for miniaturization relative to the Porro type.
There have been known an optical system using a pentagonal prism and an optical element using a combination of two triangle or trapezoidal prisms for performing an image inversion in horizontal direction by using an optical system of a roof type. Hereinafter the former is called a reflection type image inverter optical system using pentagonal and a roof prisms and the latter is called a reflection type image inverter optical system using triangular and roof prisms.
As for reflection type image inverter optical system using pentagonal and roof prisms, there have been optical systems proposed in Japanese Patent Application Laid-Open Nos. 4-63313 and 8-304880. In an optical system disclosed by Japanese Patent Application Laid-Open No. 4-63313, an optical axis of an incident light to a roof mirror makes an angle of approximately 45° with a roof ridgeline. Accordingly, the roof mirror reflects the incident light in the width direction making an angle of approximately 90° with the optical axis of the exit light. The exit light is incident to a pentagonal prism, and is led to an eyepiece via two reflections in the pentagonal prism. In an optical system disclosed by Japanese Patent Application Laid-Open No. 8-304880, an optical axis of an incident light to a roof prism makes an angle of more than 45° with a roof ridgeline. Accordingly, the roof prism reflects the incident light in the width direction making an angle of less than 90° with the optical axis of the exit light. The exit light is incident to a pentagonal prism, and is led to an eyepiece via two reflections in the pentagonal prism.
On the other hand, as for reflection type image inverter optical system using triangular and roof prisms, there have been optical systems proposed in Japanese Patent Application Laid-Open No. 8-179400 and the like. In an optical system disclosed by Japanese Patent Application Laid-Open No. 8-179400, an optical axis of an incident light to a roof prism makes an angle of less than 45° with a roof ridgeline. Accordingly, the roof prism reflects the incident light in the width direction making an angle of more than 90° with the optical axis of the exit light. The exit light is incident to a first triangular prism, to a second triangular prism via two reflections in the first triangular prism, and is led to an eyepiece.
However, in the optical system disclosed by Japanese Patent Application Laid-Open No. 4-63313, since the roof mirror reflects the incident light in the width direction making an angle of approximately 90° with the optical axis of the exit light, the pentagonal prism is arranged at right besides the roof mirror. Accordingly, the eyepiece is located to an exit pupil side of the pentagonal prism, so that it is difficult to reduce the dimension of the whole optical system of the real image viewfinder optical system including the image inverter optical system in the thickness direction.
Moreover, in the optical system disclosed by Japanese Patent Application Laid-Open No. No. 8-304880, since the roof prism reflects the incident light in the width direction making an angle of less than 90° with the optical axis of the exit light, the pentagonal prism is arranged to the object side relative to the roof prism. Accordingly, the position of the eyepiece in the thickness direction can be the same as that of the roof prism, so that it is possible to reduce the dimension of the whole optical system of the real image viewfinder optical system including the image inverter optical system in the thickness direction. However, in the object side of the eyepiece, the pentagonal prism protrudes to the object side, so that it is difficult to reduce the dimension in the thickness direction to the object side of the eyepiece.
Furthermore, in an optical system disclosed by Japanese Patent Application Laid-Open No. 8-179400, since the roof prism reflects the incident light in the width direction making an angle of more than 90° with the optical axis of the exit light, the first and second triangular prisms are located to the exit pupil side relative to the roof prism. Accordingly, the eyepiece is arranged to the exit pupil side of the second triangular prism, so that it is difficult to reduce the dimension of the whole optical system of the real image viewfinder optical system including the image inverter optical system in the thickness direction.
SUMMARY OF THE INVENTION
The present invention is made in view of the aforementioned problems and has an object to provide a real image viewfinder optical system with high optical performance and compactness, whose dimension of whole optical system including an image inverter optical system is small in the thickness direction, and whose dimension to an object side of an eyepiece lens system is small in the thickness direction.
In order to solve the aforementioned problems, the present invention provides a real image viewfinder optical system comprising, in order from an object side, an objective lens system having a positive refractive power as a whole, an eyepiece lens system that observes a real image fo
Miles & Stockbridge P.C.
Nguyen Thong
Nikon Corporation
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