JPH01255825A - Variable power finder - Google Patents

Abstract

PURPOSE:To obtain a bright and clear finder visual field by switching a first objective lens group to two states of a state that it has been inserted into a finder effective optical path and a state that it has been brought to drawback to the outside of the finder effective optical path, and also, allowing it to satisfy a specific condition. CONSTITUTION:The title finder is constituted of the first objective lens group I and a second objective lens groups II, a condenser lens group III and an eyepiece group IV. A high magnification state is constituted of the fixed objective lens group III, and a low magnification state is constituted by inserting the objective lens group I for variable power being movable and afocal as a whole into the side of an object of the fixed objective lens group II. Also, this finder is allowed to satisfy conditions of ¦psi1¦<0.0001, 0.02<1/f2<0.035, and 0.025<1/fe<0.04. In this regard, psi1: f2: and (fe) denote refracting power of the first objective lens group I, a focal distance of the second objective lens group II, and a focal distance of the eyepiece group IV, respectively. In such a way, a satisfactory finder optical system by which not only a finder visual field image (object) but also a visual field frame, a distance measuring frame, an in-finder display, etc., are very easily visible can be obtained.

Description

[Detailed Description of the Invention] The present invention relates to a finder used in cameras, etc., and more particularly, it is a real-image finder that can provide a bright and clear viewfinder field of view, and is a 35W version. This invention relates to a compact variable magnification finder suitable for mounting on a bifocal switching type camera.

Furthermore, as is well known, real-image type finders are more sensitive to field frames, distance measuring frames, and various The on-screen display etc. can be seen extremely clearly, and
Because it can be configured without the use of a semi-transparent mirror, which is essential for the Albata type and daylight type, a very bright viewfinder field of view can be obtained. This is a great advantage for cameras that require a series of operations to observe the field of view within the viewfinder.

However, as the name suggests, a real image finder is an inverted real image formed by an objective lens system that has positive refractive power as a whole and is observed through an eyepiece system, so some form of image inversion optical system is installed within the finder optical system. A viewfinder field image of an erect normal image can be obtained, which is preferable as a finder for a camera. Therefore, in general, many real-image finders using a Boro prism, which can configure an image reversing optical system in a relatively compact manner, have been proposed as non-TTL finders. Some of them have a variable magnification function for the viewfinder magnification, and some of them have been implemented, but most of them have a variable magnification function.
It is placed and mounted inside a camera body that is considerably larger than the 35mm still camera used for ffIl cine cameras, and the telephoto lens system that has become popular in recent years is built into the body, and the entire body is very large. In the so-called 350-version bifocal switching type camera, which is compactly packaged in 2008, a real-image type finder has not been implemented, despite the above-mentioned advantages in viewfinder performance. The main reasons for this are: (a) It is difficult to maintain the current level of compactness in terms of the overall dimensions of the camera body.

(b) Two points can be considered: the number of lenses is increased compared to the reverse Galilean type, which tends to increase the cost or increase the size.

Therefore, in the present invention, for (a), we first assume that the thickness of the mounted bifocal switching camera body (↑ length in the optical axis direction of the darkest lens) is 3511I11 or less, and the length of the finder in the thickness direction is 30~ The goal was to make it 35 mm or less. Of course, dimensions also occur in other directions, but
We decided to make them as small as possible.Furthermore, in general, if you lower the finder magnification, the effective diameter of the lens will become smaller and the dimensions of the entire system can also be made smaller, but this is essential to the finder design to obtain an easy-to-read finder. Therefore, in the present invention, we pursued compactness under the condition that the finder magnification is 0.45 times or more.Similarly, the variable magnification ratio of the finder magnification is similar to that of recent bifocal switching cameras. In consideration of the high magnification ratio required in

Regarding (b), the aim was to keep the number of lenses that make up the finder optical system to the minimum necessary and to use plastic as much as possible.

Accordingly, the object of the present invention is to provide a real image finder that provides a bright and clear viewfinder field of view, and that can be mounted on a compact 35mm version bifocal switching camera and has a finder magnification ratio of 1.8 or more. To provide a finder under the condition that the finder magnification is 0.45 times or more.

Honkori Satomi Woodcutter! First, in the configuration of a real image finder, one of the important points is where in the optical system to place the field frame that determines the imaging position of the real image by the objective lens group, that is, the finder field of view. In the present invention, the finder magnification is 0.4.
5 or more and a variable magnification ratio of 1.8 or more, which means aiming for a finder magnification of 0.81 or more on the high magnification side. - In general, the focal length of the objective lens group is fir
If the focal length of the eyepiece group is fe, then the finder magnification is expressed as r”i fi/' 0, which means that the aforementioned finder magnification of 0.81 times or more, for example, about 1.0 times, is used as a real image finder. In order to obtain , we have to set feζf , −−−−−−−(1). At this time, if the objective lens group is composed of a single lens, a lens back of approximately the same length as the focal length of the objective lens group is required.

On the other hand, a total of four reflecting surfaces are required as an image reversing optical system to obtain an erect viewfinder field image, and this image reversing optical system alone requires a considerable amount of space. Taking these into consideration, in the present invention, the second reflective surface is located approximately at the center of the four reflective surfaces, that is, from the subject side. A condenser lens and a field frame were placed between the third reflective surfaces. This is mentioned above (1
), it means that the limited space between the objective lens group and the eyepiece lens group, that is, the optical path length, is balanced, and the condenser lens is placed on the subject side of the imaging position to be advantageous for compactness. The four reflecting surfaces mentioned above were made of umbrellas and were made into flat mirrors, and the space between them was made of air. This will be explained below.

Generally, a Porro prism whose interior is filled with an optical medium is often used as an image reversal optical system.

The above-mentioned 2. Even when a condenser lens and a field frame are arranged between the third reflective surfaces, for example, the Porro prism can be used as it is on the second reflective surface. An image reversal optical system is also conceivable, which is separated between the third reflective surfaces and composed of two prisms sandwiching a condenser lens and a field frame. However, the physical distance filled with a medium with a higher refractive index than air becomes optically shorter, and both the objective lens group and the eyepiece lens group must be placed in the same space unless their focal lengths are shortened. I can't. On the other hand, if the focal length can be shortened, the overall length of the optical system can also be shortened, which should be advantageous for compact viewfinder optical systems, but in real-image viewfinder optical systems, the objective lens group and eyepiece lens group are each independent. However, aberrations must be corrected to some extent,
Furthermore, the shorter the focal length, the more difficult it becomes to correct aberrations, so there is a limit to the focal lengths of the objective lens group and the eyepiece lens group, depending on the performance required of the finder. Therefore, in a real image magnification finder that can be installed in a compact bifocal switching type camera, which is the object of the present invention, and has a viewfinder magnification of 0.45 or more and a magnification ratio of 1.8 or more, the objective lens group and Since the focal length of the eyepiece lens group is set as short as possible to correct aberrations, when considering an image reversal optical system, it is necessary to reduce the space occupied by the entire finder optical system. It is advantageous to use air between the four reflecting surfaces.

Next, the arrangement of the optical system related to variable magnification will be explained.

In order to achieve the above-mentioned object, in the present invention, the high magnification state is composed of a fixed objective lens group, and the low magnification state is for a generally afocal variable magnification that is movable toward the object side of the fixed objective lens group. It was constructed by inserting an objective lens group. The reason for this will be explained below. In a finder optical system, the position of the pupil (eye point) is the aperture position of the entire optical system, and in the case of a real image finder, the pupil is also located on the side of the objective lens group symmetrically to the image formation position by the objective lens group. There exists a so-called entrance pupil position that is conjugate to . The position of this entrance pupil is fixed in a real-image variable magnification finder optical system in which the eyepiece group is configured (fixed) so that it always maintains a constant moderate diopter and appropriate field of view relative to the field frame even when changing magnification. Since the finder magnification is changed by changing the focal length of the objective lens group, this entrance pupil position is the effective beam diameter of the finder optical system that changes (moves) between high and low magnification states. becomes the minimum,
From this, the object side becomes thicker depending on the required angle of view.Also, since the low magnification state obviously corresponds to a wider field of view and has a larger angle of view, the change in the entrance pupil position due to the above-mentioned magnification change The placement of the finder optical system must be considered in consideration of the effective luminous flux required for the finder.More specifically, the size (aperture) required for the objective window in the finder on the front of the camera body does not change much with zooming. This is preferable, because if there is an extreme difference in size, there is a possibility that harmful light that causes ghosts, flares, etc. may enter if an unnecessarily large window is opened. This is because it occurs.

Considering the above points, in order to prevent the entrance pupil position from being too far from the viewfinder window in low magnification conditions, we first constructed a fixed objective lens group on the high magnification side, and installed a variable magnification lens as a so-called wide converter on the subject side. A focal length lens group was inserted to change the magnification. As a result, it is possible to secure the lens back of the fixed side objective lens group so that the real image of the objective lens group is formed almost at the center of the image reversal optical system in the high magnification state where < fe - fe as described above. It is now possible to configure it with lenses. If we consider constructing a fixed optical system in a low magnification state and inserting a teleconverter as a front converter, the second. Third
In terms of aberration correction, it is difficult to configure an objective lens group with a single lens that has the necessary lens back to form an image between the mirrors.

In addition, regardless of whether the teleconverter or wideconverter is used, configuring the variable magnification lens group to be inserted and retracted as a movable group behind the fixed objective lens group (on the image plane side) is necessary for the eyepiece lens system of the real image finder optical system. It is wise to avoid this method because of its high magnification, which makes it difficult for dust to enter. According to the configuration of the present invention, it is possible to have a sealed structure including the fixed high-magnification objective lens group, the condenser lens group, and the eyepiece lens group, and dust-proof measures can be taken during the process such as only assembling this part in a clean room. If you do
This prevents dust from appearing within the field of view of the viewfinder and making the viewfinder difficult to read.

In order to achieve the above object, it is necessary to satisfy the following conditions in addition to the above configuration.

■l? , l < 0.0001 ■0.02 < 1/f! <0.035■0.02
5 < 1/f, < 0.04, ψ1: refractive power of the first objective lens group.

f2: Focal length of the second objective lens group.

fe: Focal length of the eyepiece group.

shall be.

If the range of the 0 type is exceeded, the change in viewfinder diopter will become large before and after changing the magnification, making it difficult to see the viewfinder field image.

Formula (2) defines the focal length range of the second objective lens group in order to maintain finder magnification and achieve compactness. More specifically, this shows the range that is possible with a compact single-lens configuration with good aberration performance before and after zooming; beyond this upper limit, it becomes difficult to correct aberrations. Therefore, the magnification also decreases. If it falls below the lower limit, the desired compactness cannot be achieved.

Type 0 stipulates the focal length range of the eyepiece group that can correct aberrations even with the eyepiece system alone, so that the field frame, distance measurement frame, in-finder display, etc. can be easily seen when making the entire finder optical system more compact. If the upper limit is exceeded, it becomes difficult to correct the aberrations of both the eyepiece system and the finder field system in a well-balanced manner, while suppressing the occurrence of aberrations in the eyepiece system alone. Moreover, if the lower limit is exceeded, it becomes difficult to downsize and the magnification decreases.

Furthermore, when implementing the present invention, it is desirable to satisfy the following conditions.

■ 0.1 < ra/ r r <0.7■-3,
0< r &/ r s< 0.2 However, rl: radius of curvature of the lens surface on the subject side of the negative lens constituting the first lens group.

r4: radius of curvature of the pupil-side lens surface of the positive lens constituting the first lens group.

r: radius of curvature of the lens surface on the subject side of the positive single lens constituting the second lens group.

rh: radius of curvature of the pupil-side lens surface of the positive single lens constituting the second lens group.

shall be.

If the upper limit of formula 0 is exceeded, distortion deteriorates and the angular magnification of the afocal system cannot be made large enough to achieve the desired finder zoom ratio.

On the other hand, when the lower limit is exceeded, the deterioration of spherical aberration, astigmatism, and 1x lateral chromatic aberration becomes significant.

The 0 type has a second objective lens group that forms an aberration-corrected objective lens system even if it is a single lens in a high magnification state, and is also well balanced with the aberration correction in a shared low magnification state ( It is a condition for obtaining a single ball), and the upper limit and
If the lower limit is outside this range, it becomes difficult to correct distortion and astigmatism in a well-balanced manner in both the high magnification state and the low magnification state.

In particular, when the lower limit is exceeded, the principal point of the objective lens is forward (
At the same focal length, the lens back is shortened and high magnification can be achieved in a compact manner.However, at this time, the real image created by the objective lens has an increased field curvature, and the eyepiece group must be aligned with this image plane. If you try to do so, the aberration performance of the eyepiece system alone will deteriorate significantly, making it difficult to simultaneously view the viewfinder field (subject), field frame, distance measuring frame, infinder display, etc. with good aberration correction. .

Further, in order to achieve the purpose even better, it is desirable to impose the following conditions on the eyepiece group.

■ νde 〉45 ■ ν2<40 ■0.7 <rp /rs <0.95■-0,5<
r m / f , <-0,4@)-0,65<
f N / f , < -0,4 However, shear: Atsube number at the d-line of the positive lens constituting the eyepiece group.

ShinN = Atsube number at the d-line of the negative lens constituting the eyepiece lens group.

rr: radius of curvature of the lens surface on the negative lens side of the positive lens.

rN: radius of curvature of the lens surface on the positive lens side of the negative lens.

r,: radius of curvature of the lens constituting the eyepiece group closest to the pupil.

fN: Focal length of negative lens.

fe: Focal length of the entire eyepiece group.

shall be.

Equations 0 and 0 are conditions for suppressing the occurrence of chromatic aberration in the eyepiece system alone and in the entire finder optical system.

Equation 0 defines the ratio of the radius of curvature of the lens surfaces of the opposing positive lens and negative lens in the eyepiece group, and is a condition for correcting aberrations in a well-balanced manner so that the aberrations occurring on both surfaces cancel each other out. .

Type 0 is the final surface in the eyepiece group (the surface closest to the pupil)
This is a condition that defines the radius of curvature of .When this upper limit is exceeded, astigmatism deteriorates and magnification also decreases. Moreover, when the lower limit is exceeded, distortion and astigmatism deteriorate.

The [phase] formula defines the ratio of the focal length of the negative lens constituting the eyepiece group and the focal length of the entire eyepiece group, and
This is a condition for correcting chromatic aberration in both the eyepiece system and the finder field system in a well-balanced manner while maintaining the viewfinder magnification.

In order to obtain a viewfinder that is easier to see, it is desirable to use at least one aspherical surface in the objective lens group (especially necessary when the objective lens group in a high magnification state is composed of a single lens).

By using an aspheric surface, it is possible to suppress the field curvature of the objective lens group alone to a sufficiently small level. Further, it is desirable to use an aspheric surface whose curvature decreases as it moves away from the optical axis for the condenser lens group. By using an aspheric surface for the condenser lens, it is possible to suppress distortion to a small level. Furthermore, it is desirable to use at least one aspherical surface in the eyepiece lens group.

By using an aspheric surface in the eyepiece group, it is possible to reduce distortion, astigmatism, and 2 spherical aberrations in the eyepiece group alone. Therefore, it is possible to reduce the distortion, astigmatism, and spherical aberration of the eyepiece group alone. It is possible to obtain a good finder optical system in which the display etc. are very easy to see.

Below, Examples 1 to 8 according to the present invention are listed in the table, respectively,
This will be explained with a block diagram of the hour wheel. The aspherical surfaces in the examples are all defined by the following equations, where (x, y, z) is any point on the aspherical surface.

However, X: Displacement from the aspherical apex in the direction parallel to the optical axis of the aspherical surface Φ: Distance from the aspherical apex in the direction perpendicular to the aspherical optical axis (=FV+x) C0: Curvature ε at the aspherical apex : Quadratic surface parameter Ai: i-th order aspherical curvature.

Note that all the aspheric surfaces used in this example are Ai=O
consists only of ε, but as is well known, ε is expanded into the coefficient At,
are replaceable and do not impair the generality of the present invention, and
All the lenses in this example have a total of 6 lenses from 61 to G6, and are made of PMMA (Nd=1.4914, νd=5
7.82), PC(Nd=1.584.νd=3
1.0) describes a finder optical system composed of lenses made entirely of plastic materials, but this is the result of pursuing compactness and cost reduction, which are the objectives of the present invention. Needless to say, the present invention is not limited to this embodiment.

Of course, if conditions permit, objective lens group, condenser lens group,
The number of lenses in any of the eyepiece groups may be increased, and the lenses may be made of glass material.

Furthermore, in this embodiment, G5 constituting the eyepiece group
By changing the air spacing of +Ga, it is possible to obtain a variable magnification finder optical system having a diopter adjustment mechanism that has a sufficient adjustment range without substantially changing the finder magnification. At this time, G may be fixed and 66 moved, or G6 may be fixed and G moved. As an example showing the effect of diopter tone, in the optical system of Example 1,
The following table shows the relationship between the interval between G and G6, the central diopter of the viewfinder field of view, and the finder magnification when G is fixed and G is moved.

From this table, it can be seen that the finder has a wide diopter adjustment range from about -4.4 dayopters to +2.5 dayopters.

As a result, it is possible to provide a viewfinder that is preferable even when considering variations and individual differences in visual acuity of users (photographers).

Furthermore, in this example, the field frame position is set at a distance of 1.5 mm from the Ga (condenser lens), but this is mainly due to the presence of dirt, dust, etc. on the lens surface of 64. This was done in consideration of preventing the viewfinder field of view from becoming difficult to see due to the diopter matching the viewfinder, and to provide a space for arranging members for infinder display. If sufficient consideration is given, such as by applying an antistatic coating to the lens surface where dirt and dust tend to adhere, or by controlling the environment during the assembly process, and by reducing the amount of dirt and dust adhering to the lens surface to a negligible level, the above-mentioned The field frame, etc. may be formed directly on the lens surface of the condenser lens by scribing, printing, vapor deposition, etc. Regarding the distance of 1.5 mm,
For example, in Example I, the diopter of the side surface of the pupil of G4 is shifted by about 1.7 diopters to the plus side (in the direction in which the image moves away) compared to the position of the field frame, and it can be said that there is a sufficient effect. G.

It is clear that a sealed structure from to at least GS is particularly effective in preventing the infiltration of dust from the above-mentioned dust problem. In that case, if the assembly process is well controlled, it can be used as a finder without any problems. An example of the sealed structure is shown in Figure 6. Figure 6 shows the structure to which each mirror is fixed when the four mirrors of the image reversal optical system are glass mirrors. The front view (b), left side view (a), and right side view (c) are shown simultaneously. As mentioned above, the second. Third mirror (M2
) (M3) In order to arrange the condenser lens G4 and field frame between them, the structure is divided into two parts (upper and lower parts in the figure), and these structures (hereinafter referred to as "mirror holders") Considering that it is formed by plastic molding, which can be mass-produced with high precision and at low cost, the first mirror part (m3) and the fourth mirror part, which minimizes the division of the molding mold, are used. One part (m4), the second mirror part (at), and the third mirror part (m-) are connected as bare parts, and the two parts (2a) (2b
) The mirror holder configuration shown in FIG. 6 is optimal. However, this is the case of the image reversing optical system of the so-called Porro prism ■ type shown in Fig. 2, and the first to fourth reflecting surfaces of the so-called Porro prism I type shown in Fig. 7 are used. When it is composed of four mirrors, the first and second reflecting surfaces and the third and fourth reflecting surfaces shown in FIG. It is better to do so.

Now, in the embodiment shown in FIG. 6, the springs (3), (4), (5
) to create a sealed structure that prevents dirt from entering after assembly is completed by pressing the parts tightly together at three locations. Of course, there are two mirror holder parts (2a) (2b)
The method of adhering and fixing is not limited to this, and screwing, adhesion, fitting, etc. are also possible. In addition, A in the figure
The parts indicated by A" and B, B" are the first mirror (
This is a presser part for a temporary spring (not shown) that tightly attaches and fixes the fourth mirror (M1) and the fourth mirror (M4) to the mirror holder.

Furthermore, although not shown, as another example, the shape is almost the same as that shown in Fig. 6, but the glass mirror, which is a separate part, is not used, and the mirror part is integrated with the surrounding sealing structure during plastic molding. (in other words, the hole for installing the glass mirror in Figure 6 has been removed, creating a 45° wall surface for the mirror), and then only the area required as a reflective surface is vapor-deposited and fixed to form a sealed structure. This example reduces the number of parts.

This is very effective in maintaining the angular accuracy of the mirror surface.

Central diopter visual field W -1,027ψ, = -0,0000
644T O,9961/ f z =0.030
5 field of view frame -1,0241/fe =0.03
33 viewfinder magnification I', 0.509 ra
/r, =0.3221r't O,958r6/r
s = -0,7615 viewfinder magnification ratio 188
2 r , / r , = 0.8687 r s /
f, = 0.439O f, / f, = -0,4764 central diopter visual field W -1,005ψ+ = -o, oooo
o16T 1.004 1/ f t -0,03
04 field of view frame -1,0001/fe =0.03
36-finder magnification r' -0,509r4/r+
=0.2615", 0.970 rh/rs =
-0,7542 viewfinder magnification ratio 1.906
r p/ r N=0.8611r */ f ,=
0.4433 f N/ f −= 0.4840 Central diopter visual field W −1,001ψ1−O T −1,0011/ f , = 0.0333 Field of view frame −1,0011/ fe = 0.0341 Fine magnification L7w O, 459r4/r1=0.
1964 r't O, 899 rags = -0,
5692 viewfinder magnification ratio 1.959 r P
/ r N = 0.8602 r m / f , = 0.
4496 f , / f , = −0,4954 Central diopter visual field W −1,0019,=0 T −1,0011/ f t =0.0304 Field of view frame −1,0011/ fe =0.0336
Finder magnification r'w O, 508r4/r+ =
0.2500ry O,970rb/rs =
0.7977 fine magnification ratio 1.909 r
, Ha1=0.8602r a/f −-0,442
6 f N / f −= 0.4833 central diopter visual field W −1,001ψ, = −0,00000
02T −1,0011/ f , =0.0312
Field of view frame -1,0011/fe =0.0336
Finder magnification r'w O, 485r4/r, -0
,2466I't O,949rb/rs=
0.8632 magnification ratio 1.957
rP/rN=0.8602r! l/f −=
0.4426f N/f −= 0.483
3 central diopter visual field W -1,0029, -〇T -1,0021/f! =0.0312 field frame -1,0011/fe =0.0336 viewfinder magnification r, 10.483 r4/r1 =0
．． 2950rr O,953this = 0
．． 5273 viewfinder magnification ratio 1.973 r
P/r N=0.8602r l/f −= 0.
4426 r, /fe=-0,4833 Example 7 Central diopter visual field W -1,000ψ, = -0,0000
603T −0,9711/ f , =0.030
5 field of view frame -1,0011/fe =0.03
45 fine finder magnification r'w O, 49Or</r+
-0,4817r't 0.990rh
/rs = 0.7615 fine magnification ratio
2.019 r p/ r N=0.7917 r m
/ f −= 0.4402 r , / f , == −0,5775 central diopter visual field W −1,0309′l= −0,0000
631T -1,0001/f! =0.030
5 field of view frame -1,0301/ fe =0.03
46-finder magnification rsm O, 47Or-/r+
=0.5855rt O,995ri/rs =
0.7615 Finder magnification ratio 2.115
rP/rN=0.7500rm/f,=
0.4731 f , 4 / f , = -0,5794 Figure 1 is a developed diagram of the basic configuration of the variable magnification finder according to the present invention, and shows the case of wide (Wide) and the case of tele (Tels). ing. Here, (1)(n) is the first
．． The second objective lens group (■) is the condenser lens group, (
(2) is an eyepiece lens group, and between the second objective lens group (n) and the condenser lens group (III) is the first eyepiece lens group. Although a second reflecting mirror is interposed, it is not shown in FIG.

In addition, the condenser lens group (III) and the eyepiece lens group (
Although 3rd and 4th reflecting mirrors are also interposed between IV),
Not shown. In addition, (1) is a condenser lens group (
It shows the field of view frame placed behind I[[).

FIG. 2 shows the three-dimensional arrangement of the Porro prism ■ type when the variable magnification finder is disposed within the camera body for Wide and Tele. Here, the first. Second. Third. Fourth reflection mirror (M3
) (Mg) (M3) (M3) is also shown. Third
The figure shows the wide (W) position when placed inside the camera body.
+de), a vertical cross-section of the tele (Tele) state. Here, (6) represents the finder-objective center.

Next, in FIG. 4, the lenses 63 to G are shown together with the mirror holder.
The three-view diagrams (a), (b), and (C) show optical path diagrams for both wide and tele when placed in the camera body with a sealed structure between the two.

Magnification is changed by putting the first objective lens group (1) into the optical path for wide mode and removing it from the optical path for tele mode, but the specific switching structure is explained in the fifth section.
As shown in the figure. That is, in this embodiment, the first objective lens group (1
) The holder (7
) is rotatable around the fulcrum (8), and the wide (Wtd
The position of the holder is changed for e) and tele (Tele).

FIG. 6 is as described above. Next, FIG. 7(A) shows the basic structure of the Porro prism ■ type in three dimensions, and FIG. 7(B) shows its equivalent structure. (Ilsl
) is the first reflective surface + (ffi3 is the second reflective surface).

(ms*) is the third reflective surface, and (ms4) is the fourth reflective surface.

FIG. 8(A) shows each aberration in the wide mode of Example 1, and FIG. 8(B) shows the same aberrations in the wide mode of Example 1
(C) shows the aberrations of the eyepiece system of Example 1. 9 to 15 show aberration diagrams of Examples 2 to 8, respectively.

However, FIGS. 9 to 15 only show astigmatism and distortion at the d-line for Wide and Tele, and do not show the eyepiece system. In FIGS. 8 to 15, the solid line (S) indicates astigmatism on the sagittal plane, and the dotted line (T) indicates astigmatism on the tangential plane.

[Brief explanation of the drawing]

The first part is an optical path diagram showing the basic configuration of the variable magnification finder according to the present invention, and the second part is a perspective view showing the basic arrangement of a Porro prism ■ type when it is placed inside the camera body. FIG. 3 is a longitudinal sectional view of the same. FIG. 4 is an optical path diagram in both wide and telephoto modes for a variable magnification finder embodying the present invention, FIG. 5 is a vertical cross-sectional view showing the variable magnification method, and FIG. 6 is a diagram showing the mirror holder. FIG. 7 is a perspective view showing the basic structure of the Porro prism type I. FIGS. 8, 9, 10, and 11. FIG. 12, FIG. 13, FIG. 14, and FIG. 15 are aberration diagrams of Examples 1 to 1, respectively. (I)...-first objective lens group. c n > - second objective lens group. (■) - Condenser lens group. (M+) to (M4) to first to fourth reflecting mirrors. (IVL-m-eyepiece group.

Claims (1)

[Scope of Claims] (1) An objective lens group having positive refractive power as a whole, consisting of, in order from the subject side, a substantially afocal first objective lens group and a second objective lens group having positive refractive power; A condenser lens group having a positive refractive power as a whole, an eyepiece group having a positive refractive power as a whole, and a first lens, a second lens, The real-image finder comprises third and fourth reflecting mirrors, and observes a subject image formed near the condenser lens group by the objective lens group as an erect viewfinder field image by the eyepiece group. The first objective lens group is configured to be able to be retracted out of the effective optical path of the finder optical system, and the first objective lens group can be inserted into the finder effective optical path and retracted outside the finder effective optical path. A variable magnification finder configured to be able to change finder magnification by switching between two states, and satisfying the following conditions: |ψ_1|<0.0001 0.02<1/ f_2<0.035 0.025<1/f_e<0.04 where ψ_1: refractive power of the first objective lens group f_2: focal length of the second objective lens group f_e: focal length of the eyepiece lens group. (2) The first lens group constituting the objective lens group is a negative lens (G_1) and a positive lens (G_2) in order from the subject side.
Similarly, the second lens group consists of a positive single lens (G_3), the condenser lens group consists of a positive single lens (G_4), and the eyepiece lens group consists of a negative single lens (G_4) in order from the subject side. The lens (G_5) and the positive lens (G_6) are composed of two lenses, and have a total lens configuration of 6 lenses in 4 groups, and satisfy the following conditions. Variable magnification finder; 0.1<r_4/r_1<0.7 -3.0<r_6/r_5<-0.2 However, r_1: Radius of curvature r_4 of the lens surface on the subject side of G_1
: radius of curvature of the lens surface on the pupil side of G_2 r_5: radius of curvature of the lens surface on the subject side of G_3 r_6: radius of curvature of the lens surface on the pupil side of G_3. (3) The variable magnification according to claim 1, wherein the eyepiece lens group is composed of a total of two lenses, one positive lens and one negative lens, and satisfies the following conditions. Finder; ν_P>45 ν_N<40 0.7<r_P/r_N<0.95 -0.5<r_B/f_e<-0.4 -0.65<f_N/f_e<-0.4 However, ν_P: Positive Abbe number ν_N of lens at d-line
: Abbe number r_P of the negative lens at the d-line: Radius of curvature of the lens surface on the negative lens side of the positive lens r_N: Radius of curvature of the lens surface on the positive lens side of the negative lens r_B: The closest to the pupil of the lenses constituting the eyepiece group Radius of curvature f_N: Focal length of negative lens f_e: Focal length of the entire eyepiece group. (4) The eyepiece lens group is configured such that at least one lens thereof is movable on the optical axis in parallel with the optical axis, thereby making it possible to adjust the diopter. Variable magnification finder as described. (5) The variable magnification finder according to claim 2, wherein at least (G_3) to (G_5) are constructed in a sealed structure. (6) The variable magnification finder according to claim 1, wherein the objective lens group has at least one aspherical surface. (7) The variable magnification finder according to claim 1, wherein the condenser lens group has at least one aspherical surface whose curvature decreases as the distance from the optical axis increases. (8) The variable magnification finder according to claim 1, wherein the eyepiece lens group has at least one aspherical surface. (9) The variable magnification finder according to claim 2, wherein all lenses are formed by molding using a plastic material.