JPH04256B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverted Galilean type finder capable of focusing a photographing apparatus using a zoom lens as a photographing optical system.

Conventionally, the first viewfinder system for cameras using zoom lenses, such as 8mm projectors and VTR cameras, was
A TTL finder like the one shown in the figure is often used. In the figure 101, 102, 103, 1
04 and 106 are lenses forming a zoom lens system, and 107 is an image forming position of the zoom lens. 1
05 is a beam splitter that splits the beam into the finder system, 108 is an imaging lens, 109 is a mirror, 110 is a focal plane formed by the imaging lens 108, and 111 is an image on the focal plane 110. 112 is the conjugate image position of the focus plane 10 by the relay lens 111, 113 is an eyepiece lens, and 114 is the pupil position of the finder system. In the figure, the finder system includes an imaging lens 108, a mirror 109, and a focusing surface 11.
0, a relay lens 111, a conjugate image position 112, and an eyepiece lens 113.As is clear from the figure, it has a complicated structure and has the disadvantage that the overall length of the finder system is long.

On the other hand, the inverted Galilean type finder conventionally used in lens shutter cameras and the like has an extremely simple structure as shown in FIG. Second
In the figure, 201 is a photographing lens system, and 202 is an imaging position. Further, 203 is a finder type objective lens, 204 is a finder type eyepiece lens, and 205 is a finder type pupil position. As is clear from FIG. 2, this type of reverse Galilean type finder has the disadvantage that parallax occurs between the photographing lens system and the finder system.

The present invention eliminates the drawbacks of the finder system shown in FIGS. 1 and 2, has a simple structure, is free from parallax, and is an inverse Galilean type finder with a short overall length of the finder system, and provides a focusable finder. The above purpose is to provide an optical device in which the photographing optical system is a zoom lens that has a portion where the light beam from the axis becomes almost afocal, and to transfer the light beam from the on-axis object to the afocal portion. A beam splitter 1 is provided to split the incident beam in a direction perpendicular to the optical axis up to the afocal part of the lens, and the beam splitter 1 bends a part of the incident light beam, and the afocal part of the zoom lens is included in the beam splitter 1. A subsequent lens system is provided to form a photographing system, and at least one concave lens is provided in a light beam passing through the beam splitter 1 in the same direction as the optical axis direction up to the afocal portion of the zoom lens, and the afocal portion of the zoom lens is provided with at least one concave lens. A composite lens system of the above lens system and the concave lens is used as an objective lens, and at least one lens is provided behind the concave lens.
Two convex lenses are provided, the convex lenses are used as eyepiece lenses, and the diameter of the lens is made large so that a beam of light with an F number brighter than the F number required for photography passes up to the afocal part of the zoom lens. A light beam with a bright F number passes through the outside of the semi-transparent part of the light beam splitter 1, and a light flux passing outside the semi-transparent part is sent between the light flux splitter 1 and the concave lens into the afocal part of the zoom lens. A mirror is provided between the beam splitter 1, the concave lens, and the mirror, and a portion of the beam from the mirror is bent perpendicularly to the optical axis up to the afocal portion of the zoom lens. A light beam splitter 2 that bends the light beam in a direction is provided so that the image of the light beam passing through the semi-transparent part of the light flux splitter 1 and the image of the light flux passing outside the semi-transparent part can be seen to match. This is achieved using an inverted Galilean type focuser that allows for focusing.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 3 shows an optical system according to an embodiment of the present invention, and FIGS. 3a and 3b show cross-sectional views of the same embodiment in directions perpendicular to each other.

In FIG. 3, lenses 301, 302, 30
3, 304 is a lens system up to the afocal portion of the zoom lens; 305 is a beam splitter 1;
The beam splitter 305 splits and reflects most of the incident beam at right angles to the optical axis direction, and forms an image on a focal plane 307 by a lens 306, which is an optical system after the afocal portion of the zoom lens.

On the other hand, a part of the light beam split and passed in the same direction as the optical axis by the light beam splitter 305 enters the finder system. A beam splitter 308 following the beam splitter 305 is used for focusing, and the next concave lens 309 is a lens system (lenses 301, 30) up to the afocal part of the zoom lens.
2, 303, 304) to form the objective lens of the finder. Behind this concave lens 309 is a convex lens 310 serving as an eyepiece, and together with an objective lens constitutes an inverted Galilean off-finder system, and 312 is the pupil position of this finder system.

311a and 311b shown in FIG. 3B are reflecting mirrors, which are used together with the beam splitter 308 for focusing. Only the shaded part of the beam splitter 305 is a semi-transparent part, and the outside thereof is transparent, and the light passing through the transparent part of the beam splitter 305 is reflected by the reflecting mirrors 311a, 311b and the beam splitter 30.
8 leads to the finder system.

Regarding the lens system up to the afocal part consisting of lenses 301, 302, 303, and 304,
The diameter of the lens is increased so that the light beam with an F number brighter than the F number necessary for shooting with the zoom lens passes through, and the light beam with an F number brighter than the F number necessary for shooting passes through the transparent part of the beam splitter 305. ing.

Further, between the beam splitter 305 and the concave lens 309, the beam passing through the transparent part of the beam splitter 305 is bent by reflecting mirrors 311a and 311b so as to be perpendicular to the optical axis up to the afocal part of the zoom lens. A part of the luminous flux from the reflecting mirrors 311a, 311b is directed to the afocal portion of the zoom lens by a splitter 305, a beam splitter 308 provided between the concave lens 309, and the reflecting mirrors 311a, 311b. Focusing is now done by bending the beam in the same direction as the optical axis of the beam splitter 305 and checking the match between the image of the beam passing through the diagonally shaded portion of the beam splitter 305 and the image of the beam passing through the transparent portion of the beam splitter 305. There is.

In FIG. 3b, when there is an object at a distance of ∞ with a zoom lens whose distance scale is ∞, out of the light flux from the on-axis object at a distance of ∞, the light flux near the optical axis and the light flux of the beam splitter 305. The light flux passing through the transparent portion comes to the pupil position 312 together. At the beam splitter 305, the axial beam is focused and becomes AFOCAL, so the two beams have the same angle and the finder images coincide.

On the other hand, assume that the distance scale of the zoom lens is ∞ and that the on-axis object is at a finite distance T. Now let f be the combined focal length of lenses 301, 302, 303, 304 and concave lens 309, and lens 30
Let H be the height from the axis of the maximum luminous flux of an axial object incident on the lens 301, and when that luminous flux passes through the transparent part of the luminous flux splitter 305, it has an incident angle of Θ=H/T, and , 302, 303, 304 and a concave lens 309, and has an image height of Y=fΘ. Since the luminous flux near the optical axis has an image height of 0, 2
The two images are separated by Y=fΘ. Also, the reflecting mirror 311
The light flux passing through a and the reflecting mirror 311b becomes an image separated by 2Y=2fΘ.

Now, if the distance scale of the zoom lens is set to T,
At the beam splitter 305, the beam from the axial object becomes afocal, and the plurality of images coincide.

As explained above, it has been possible to obtain an inverted Galilean type finder which is free from parataxis and capable of focusing with a short overall length using a simple structure.

In this embodiment, the light beam splitter 305 is provided with a transparent portion, but the portion may be made of air instead of glass.

[Brief explanation of drawings]

Figure 1 shows the finder optical system of a conventional camera using a zoom lens, Figure 2 shows an inverted Galilean off-finder optical system used in a conventional lens shutter camera, and Figures 3a and b show an embodiment of the present invention. FIG. 3 is a cross-sectional view of the optical system taken in directions perpendicular to each other. 301, 302, 303, 304... Lens system up to the afocal portion, 305... Luminous flux splitter, 308... Luminous flux splitter, 309... Concave lens, 310... Convex lens, 311a, 311b...
...Reflector, 312...Field frame.

Claims (1)

[Claims] 1. In an optical device whose photographing optical system is a zoom lens having a portion where the light beam from the on-axis is almost afocal, the light beam from an on-axis object is directed to the afocal portion and is perpendicular to the optical axis up to the afocal portion of the zoom lens. A photographing system is constructed by providing a beam splitter 1 that splits the beam in different directions, bending a part of the incident beam by the beam splitter 1, and installing a lens system after the afocal portion of the zoom lens in the beam. , at least one concave lens is provided in the light beam passing through the beam splitter 1 in the same direction as the optical axis up to the afocal part of the zoom lens, and a composite lens of the lens system up to the afocal part of the zoom lens and the concave lens. The system is an objective lens, and at least one convex lens is provided behind the concave lens, and the convex lens is an eyepiece, so that a beam of light with an F number brighter than the F number necessary for photographing passes up to the afocal part of the zoom lens. The lens diameter is made large so that the light flux with an F number brighter than the F number required for photography passes through the outside of the semi-transparent part of the light flux splitter 1, and between the light flux splitter 1 and the concave lens,
A mirror is provided that bends the light flux passing outside the semi-transparent part so as to be perpendicular to the optical axis up to the afocal part of the zoom lens, and the light flux from the mirror is arranged between the light flux splitter 1, the concave lens, and the mirror. A beam splitter 2 is provided that bends a part of the zoom lens in the same direction as the optical axis up to the afocal portion of the zoom lens, and an image of the beam passing through the semi-transparent part of the beam splitter 1 and an image of the light flux passing outside the semi-transparent part are provided. An inverted Galilean type finder capable of focusing, characterized in that it is possible to see the match with the image.