JPH01113736A - Real image type finder optical system - Google Patents

Abstract

PURPOSE:To make the visual field of a finder easy to see and to facilitate the positioning adjustment of a visual field frame by arranging a half mirror between a Porro prism and an eyepiece lens and arranging a plate having an information display body like the visual field frame on an optical axis different from the finder optical axis through the half mirror. CONSTITUTION:The finder image is formed on a first image forming face 16 in the vicinity of the incidence face of a Porro prism 15 through an objective lens 11 and a field lens 13 and is inverted to an erect image by the Porro prism 15 and is observed through an eyepiece lens 12. A plate 17 having an information display body 1 like a visual field frame is arranged in a position optically equivalent to the first image forming face 16 by the half mirror 2 and the visual field frame 1 on the plate 17 is observed together with the finder image through the half mirror 2 and an eyepiece lens 18. The objective lens 11 has a power varying lens part consisting of two lenses, and the focal length of the objective lens 11 is changed to change the angle of view controlled by the visual field frame 1 having fixed size.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a real-image finder optical system, and particularly to a photographic finder optical system in which a finder image is observed through a finder optical system provided separately from a photographing system. The present invention relates to a real-image finder optical system with a simple configuration suitable for cameras, video cameras, etc.

(Prior Art) Various finder optical systems for cameras in which a photographing system and a finder optical system are configured separately have been proposed.

As such a finder optical system, for example, the following types are well known.

(a) Reverse Galilean type Albada finder (b) Reverse Galileo, O type daylighting type finder (c) Real image type finder Figure 2 is a schematic diagram of the conventional reverse Galileo type Albada finder optical system.

In the figure, 20 is an information display such as a field frame, 21 is an objective lens with a negative refractive power, 23 is a half mirror surface provided on the lens surface of the objective lens 21, and 22 is an eyepiece lens with a positive refractive power.

The finder optical system shown in the figure has a member on which an information display body 20 such as a field frame is deposited near the eyepiece lens 22, and the observation side lens surface of the objective lens 21 is a half mirror.
The viewfinder field of view and the information display are always observed through the same optical axis.

In the case of the finder optical system shown in Fig. 2, the information display body 20 is fixed when the angle of view changes, such as when the photographing lens is a variable magnification lens such as a zoom lens or a pseudo variable magnification lens that allows cropping photography. , it is necessary to construct a finder optical system that corresponds to changes in the angle of view of the photographic lens by varying the magnification of the objective lens 21.

However, in general, it is difficult to achieve a high zoom ratio using only the objective lens 21, and it is also difficult to position the information display body 20 and the half mirror within the objective lens 21, and furthermore, it is difficult to make adjustments.

FIG. 3 is a schematic diagram of a conventional inverted Galileo type daylight finder optical system. The finder optical system shown in the figure has a half mirror 33 between an objective lens 31 with negative refractive power and an eyepiece 32 with positive refractive power, and an information display body 34 such as a field frame located at a position different from the finder optical axis. The finder field of view and the information display body 34 are observed simultaneously through different optical axes. Note that 36 is a reflecting mirror.

The finder optical system shown in FIG. 3 uses the information display 3
or change the apparent size of the objective lens 31.
It is necessary to change the magnification of the lens to accommodate changes in the angle of view of the photographic lens.

However, even if the apparent size of the information display body 34 is changed, if the angle of view becomes too small, it will be extremely difficult for some observers to see, and even if the angle of view is increased, the finder optical system tends to become complicated, so there is a limit. Ta.

Further, the variable magnification using only the objective lens 31 has the same drawback as the finder optical system shown in FIG. 2, in that it is difficult to achieve a high variable magnification.

FIG. 4 is a schematic diagram of a conventional real-image finder optical system. In the figure, 41 is an objective lens, 42 is a field lens, 43 is an information display such as a field frame, 44 is an eyepiece lens, and 40 is a Porro prism for an erect normal image.

In the figure, the objective lens 41 is an inverted imaging system, and a finder image is formed near the information display body 43, and the finder image is inverted to an erect image via a porro prism 40 and observed with an eyepiece lens 44. ing.

In the case of the finder optical system shown in the figure, since the objective lens 41 is an imaging system, a transparent plate 45 having an information display body 43 such as a field frame is arranged near the imaging position.

When the angle of view changes, such as when the photographing lens is a variable magnification lens such as a zoom lens or a pseudo variable magnification lens that allows cropping photography, the objective lens 41 is configured with a variable magnification lens such as a zoom lens, or the information display By changing the apparent size of the body 43, it is necessary to correspond to changing the magnification of the photographic lens.

However, even if the apparent size of the information display body 43 is changed, if the angle of view becomes too small, it will become extremely difficult for the observer to see, and even if the angle of view is increased, the finder optical system tends to become complicated, so there is a limit. there were.

Further, even if the objective lens 41 is a zoom lens, it is difficult to achieve a high zoom ratio and there is a limit. Also, in order to change the size of the information display body 43, the imaging position of the objective lens 41 is changed to the Porro prism 40.
This has the disadvantage that the finder optical system becomes complicated due to its construction, and that it is difficult to adjust the positioning of the information display body 43, etc.

Further, a plate 4 provided with an information display body 43 such as a field of view frame, etc.
5 needs to be placed outside the Porro prism 40, which not only limits the magnification of the finder, but also has the disadvantage that dust and the like may adhere to the plate 45.

(Problems to be Solved by the Invention) When observing a finder image in a real-image finder optical system, the present invention efficiently uses a plate having an information display such as a field frame on an optical axis different from the finder optical axis. The purpose of the present invention is to provide a real-image finder optical system with a simple configuration that makes it easier to see the viewfinder field of view, facilitates the positioning and adjustment of the field frame, and can easily accommodate changing magnification of the photographic lens. .

(Means for Solving the Problem) In a real-image finder optical system in which a finder image formed on a first imaging plane by an objective lens and a field lens is observed as an erect image through a porro prism with an eyepiece lens, between the Porro prism and the eyepiece;
Alternatively, a half mirror is placed at an arbitrary position in the eyepiece, a plate having an information display such as a field frame is placed on an optical axis different from the viewfinder optical axis through the half mirror, and the plate is illuminated by an illumination means. The information display body on the plate and the finder image can be observed simultaneously through the half mirror.

(Embodiment) FIG. 1 is a schematic diagram of a real image finder optical system showing an embodiment of the present invention. In the figure, 11 is an objective lens;
A field lens 13 is arranged near where a finder image is formed by the objective lens 11. 16 is a first imaging plane formed by the objective lens 11 and field lens 13; 15 is a Porro prism for erecting a normal image; 12 is an eyepiece; 19 is a front eyepiece; 18 is a rear eyepiece;
1 is a pupil position, 1 is an information display such as a field frame, 17 is a plate having an information display such as a field frame, and 2 is a half mirror provided in the eyepiece lens 12.

In this embodiment, a finder image is formed via the objective lens 11 and the field lens 13 on a first image forming surface 16 near the entrance surface of the Porro prism 15. After the finder image is inverted into an erect image using the Porro prism 15, it is observed using the eyepiece lens 12 so that the diopter is adjusted to the pupil position 14.

At the same time, a plate 17 having an information display such as a field frame is placed at a position optically equivalent to the first image forming surface 16 using the half mirror 2, and the field frame 1 on the plate is connected to the half mirror 2 and the eyepiece 18. through the viewfinder image.

Incidentally, the plate 17 is illuminated by external light or illumination means provided at an arbitrary position. For example, the illumination means may be IRED, EL, or the like, or a frosted glass diffuser plate may be disposed at the side of the plate 17 to illuminate with external light.

In this embodiment, the objective lens 11 has a variable magnification lens section composed of at least two lenses. As a result, the focal length of the objective lens 11 changes, so that the angle of view regulated by the field frame l of a constant size changes.

That is, the focal length of the objective lens 11 is F. , eyepiece 1
If the focal length of 2 is Fe, the finder magnification γ is γ=F, /Fe ・−−−−−−−−−−−−−−
--- Expressed as (1), the focal ratio m of the objective lens 11
By increasing i''o, the finder magnification γ can also be increased.

Furthermore, the eyepiece lens 12 has a variable magnification lens composed of at least two lenses, and the information display body 1 such as a field frame on the plate 17 adjusts the field of view based on information on changes in the angle of view of the photographing lens. The size of the frame l is changed.

That is, in conditional expression (1), the focal length R of the objective lens 11
F O is constant and the focal length of the eyepiece 12 jliF,
If it becomes smaller, the finder magnification γ can be increased.

With the above configuration, the angle of view can be changed within a range corresponding to the magnification of the photographic lens by changing the viewfinder magnification only by changing the magnification of the objective lens 11. Further changes in magnification can be accommodated by changing the magnification of the eyepiece lens 12 and changing the visual field frame 1 as necessary for the above-mentioned changes in the angle of view.

Accordingly, even when changing the magnification, the appearance of the upper field of view frame 1
This makes it possible to propose a finder optical system with a large zoom ratio without any change in size.

Further, the angle of view of the photographing lens used at this time may be changed by a switching multifocal lens, a zoom lens, or a pseudo variable magnification camera capable of photographing by trimming.

Further, as described above, the finder optical system may utilize both the variable power of the objective lens 11 and the variable power of the eyepiece lens 12, or may utilize either one of them, as necessary.

In this embodiment, the focal length of the eyepiece 18 behind the half mirror 2, that is, the lens for observing the information display such as the field frame 1, or when the eyepiece is a variable magnification lens system, the shortest The focal length at the time of focus is fe,
When the distance between the member in front of the half mirror 2 and the eyepiece lens 18 behind the half mirror 2 is 1, fe/3 < 1 < fe =
It is good to satisfy (2).

If the upper limit of conditional expression (2) is exceeded, the image forming surface of the eyepiece lens,
That is, the imaging position of the objective lens is outside the Porro prism 15 (
(on the eyepiece lens side), making it impossible to arrange the plate 17 having an information display such as a field frame at a point through the half mirror 2, and in addition, the viewfinder magnification becomes too large and the finder optical system becomes large. It's not appropriate.

Furthermore, if the lower limit of conditional expression (2) is exceeded, the half mirror 2 cannot be introduced, which is not appropriate.

As described in detail above, in this embodiment, when the objective lens 11 is to be given a variable power effect, it is composed of a plurality of lenses so that the imaging plane 16 of the objective lens 11 is constant throughout the entire variable power range. It consists of

Further, when giving the eyepiece lens 12 a variable power effect, the power is changed by the rear eyepiece lens 18 behind the half mirror 2.

In order to increase the finder magnification of the entire system, by decreasing the focal length fe of the eyepiece 18 according to the above equation (1), the coordinates on the imaging plane 16 observed at the same exit angle θ' will become smaller. In other words, the angle of incidence θ is also made looser, and a telephoto angle of view can be observed.

Accordingly, if the field frame 1 on the plate 17 is also made smaller, the upper field frame 1 will appear to be the same even with large changes in the field of view, making it possible to observe with a high variable magnification finder using the same field of view frame. .

Note that the field frame 1 may be changed continuously by mechanical means, or may be changed stepwise electrically using a liquid crystal or the like.

In the embodiment shown in FIG. 1, the primary image forming surface 16 of the finder image formed by the objective lens 11 is located on the incident surface side of the Porro prism 15. It may be located inside the prism 15. In this case, the plate 17 having the information display body 1 such as a field frame may be set at a position optically equivalent to the imaging plane inside the Porro prism 15 with respect to the eyepiece 18.

This makes the finder optical system advantageous for arbitrary magnifications, high magnifications, etc., and in addition, it is possible to provide a finder optical system with an easy-to-see viewfinder field of view without adhesion of dust or the like near the imaging plane.

Further, in this embodiment, a plate 17 having an information display such as a field frame is placed in the eyepiece 12 via a half mirror, but it is not placed between the Porro prism 15 and the eyepiece 12. I don't mind.

FIG. 5 is a schematic diagram of the Porro prism of FIG. 1 which inverts the finder image into an erect image.

In the same figure, the Porro prism 50 has three Porro prisms.
When configured as a set of three right-angled isosceles triangular prisms 51゜52.53, the third isosceles triangular prism 53
and the third isosceles triangular prism 5
It may be configured to have an imaging plane of the objective lens, ie, a surface equivalent to an information display such as a field frame, near the entrance plane of No. 3.

FIGS. 6(A) to 6(E) show an example of the developed viewfinder optical system according to the present invention. In the same figure, the first
Elements that are the same as those shown in the figures are numbered the same.

In the figure, the Porro prism is shown in the first position. It is composed of a second prism, and the exit side surface of the second prism is given refractive power. Further, the primary imaging plane is arranged within the Porro prism, that is, between the first prism and the second prism.

Figures 6 (8), (B), and (C) are schematic diagrams of the optical system showing variable power by the objective lens when the objective lens has a variable power lens, respectively, and Figures 6 (D) and (E) 1 is a schematic diagram of an optical system showing magnification change by the eyepieces when each eyepiece has a variable power lens.

7(A), 7(B), and 7(C) are schematic diagrams showing the optical path state of the optical system representing magnification change by the rear eyepiece behind the half mirror 2 in the present embodiment shown in FIG. 1, respectively. be.

Next, a numerical example of the present invention shown in FIG. 6 will be described.

In the numerical examples, Ri is the radius of curvature of the i-th lens surface from the object side, Di is the thickness and air gap of the i-th lens from the object side, and Ni and νi are the i-th lens surface from the object side, respectively.
These are the refractive index and Atsube number of the glass of the th lens.

The aspherical shape has the X axis in the optical axis direction, the Y axis in the direction perpendicular to the optical axis, the direction of light propagation as positive, the intersection of the vertex of the lens and the X axis as the origin, and R as the paraxial curvature of the lens surface. Radius, aI *
R2+ R3+ R41aS *b+, b2. b:+,
When b< is the aspherical coefficient, + a4Y8 + a5Y
IO + b, Y3 + b2Y5 + b3Y'
+b4Y9.

Note that the R4 and R6 surfaces are aspherical.

Also, for example, the designation rD-03J means "NO-3".

Knee) 1.1 1:Pa・1 Numerical Example RI=-16,38D I-1,5N 1-1.49
171 v 1-57.4R2-31,8702-variable R3-18,52D 3-3.5 N 2-1.4
9171 Z/ 2-57.4*R4--16,45D
4-Variable R5-47,88D 5-2.0 N 3-1.4
9171 v 3=57.4*86--93.72 0
6-1.0 R11-48,16Dll-5,0N 6-1.491
71shiB-57,4R12--24,64012-0,
1 R13-24,44013-3,0N 7-1.491
71 v 7-57.4RI4-1107.28 01
4-Variable R15--26,75015-1,5N 8-
1.49171shi8-57.4R16-30,4201
6 to 14.0 R17- (Eye point) R4 surface Aspheric coefficient at-0,0a2-4.9870-05a3--3.3
19D-07a4 = 3.091D-09aP, -2
, 4200-10R6 surface Aspherical coefficient at o, oa2=8.425D-05a3=2.45
7D-07a4-1.2120-088s = -1,6
37D-10 (Effects of the Invention) According to the present invention, when observing a finder image in a real-image type finder optical system, by configuring each element as described above, the viewfinder field of view is easy to see, and information such as the field frame etc. A real-image finder optical system that allows for easy positioning and adjustment of the display, and can also handle high variable magnification of the photographic lens.Furthermore, even with large changes in the angle of view of the photographic lens, the upper field of view remains apparently the same. can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a real image finder optical system showing an embodiment of the present invention, Figs. 2 to 4 are schematic diagrams of a conventional finder optical system, Fig. 5 is a schematic diagram of a Porro prism, and Fig. Figures (A) to (E) are schematic diagrams when the finder optical system of the present invention is developed, and Figures 6 (A), (B),
((:) is a schematic diagram of the optical system showing magnification change by the objective lens, Figures 6 (D) and (E) are schematic diagrams of the optical system showing magnification change by the eyepiece lens, and Figure 7 ( A),
(B) and (tl:) are schematic diagrams each showing magnification change by the eyepiece of the finder optical system according to the present invention. In the figure, 1 is a field frame, 2 is a half mirror, 111 is an objective lens, 12 is an eyepiece lens, 13 is a field lens, 14
is the pupil position, 15 is the Porro prism, 16 is the first imaging plane, 1
7 is a plate, and 18 is an eyepiece. Patent applicant: Canon Co., Ltd. No. 1 Illustration 2 Illustration 3 Akira Kuchi 4 Illustration 5 Illustration

Claims (4)

[Claims] (1) In a real-image finder optical system in which a finder image formed on a first imaging plane by an objective lens and a field lens is observed as an erect image through a Porro prism with an eyepiece, the Porro prism and the eyepiece A half mirror is placed between the eyepiece or at any position in the eyepiece, and a plate having an information display such as a field frame is placed on an optical axis different from the viewfinder optical axis through the half mirror, A real-image finder optical system, characterized in that the information display body on the plate illuminated by the illumination means and the finder image can be observed simultaneously through the half mirror. (2) The real image finder optical system according to claim 1, wherein the objective lens has a variable magnification lens group composed of at least two lenses. (3) The eyepiece has a variable magnification lens section composed of at least two lenses, and the information display on the plate is composed of a variable information display whose size changes. A real image finder optical system according to claim 1. (4) The half mirror is arranged in the eyepiece, and the focal length of the rear eyepiece on the observation side of the half mirror, or when the eyepiece has a variable magnification lens, When the focal length at the shortest focus is fe and the shortest air gap in the direction of the finder optical axis in the space in which the half mirror is arranged is 1, fe/3<1<fe. A real image finder optical system according to claim 1.