JPH05142627A - Real image type finder - Google Patents

Abstract

PURPOSE:To provide the real-image type finder which secures a large space for providing an erect optical system and also has a margin as to the interval between an object image formed by an objective system and the erect optical system without making the overall angular magnifications of the finder small. CONSTITUTION:This finder is equipped with the objective system, a condenser lens which guides the object image formed by the objective system to the ocular side, the erect optical system which inverts the direction of the object image, and an ocular lens system consisting of lens groups in positive and negative order from the object side in order from the object side, and the most pupil-side surface of the ocular lens system is concave; and conditions shown by inequalities I and II, i.e., -0.7<fE/fEN<0 and 0.5<fE/rE<3.5 are satisfied, where fE is the focal length of the ocular system, fEN is the focal length of the pupil- side negative lens of the ocular system, and rE is the radius of curvature of the most pupil-side concave surface of the ocular system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a real image type viewfinder used in a compact camera or the like, and more particularly to an eyepiece lens system located on the pupil side in the viewfinder.

[0002]

2. Description of the Related Art A real image type finder generally comprises an objective lens system, an erecting optical system such as a prism for inverting an image, and an eyepiece lens system. A conventional real image finder provided in a compact camera generally has an eyepiece lens system composed of only one positive lens.

[0003]

However, as in the above-mentioned conventional real image type finder, the objective lens system is not provided.
If only one positive lens is used, it is necessary to set the focal length of the eyepiece lens system large in order to secure the space for the erecting optics. Especially in the case of wide-angle systems, the angular magnification of the entire viewfinder tends to be small. ..

If the focal length of the objective lens system is reduced to increase the angular magnification, there is no margin in the distance from the object image formed by the objective lens system to the erecting optical system. It is not possible to provide a mechanism or the like for putting in and taking out the field frame corresponding to shooting.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. It is possible to secure a large space for installing an erecting optical system without reducing the angular magnification of the entire finder. It is an object of the present invention to provide a real image type finder in which there is a margin between the object image formed by the objective lens system and the erecting optical system.

[0006]

In order to achieve the above object, a real image type finder according to the present invention comprises an objective lens system and a condenser lens for guiding an object image by the objective lens system to an eyepiece side in order from the object side. , An erecting optical system for reversing the direction of the object image, and an eyepiece lens system composed of a lens group arranged in order from the object side to positive and negative, and the most pupil side surface of the eyepiece lens system is a concave surface. , The focal length of the eyepiece system is fE, the focal length of the negative lens on the pupil side of the eyepiece system is fEN, and the radius of curvature of the most pupil-side concave surface of the eyepiece system is rE. And

[0007]

[Formula 1] -0.7 <fE / fEN <0 0.5 <fE / rE <3.5

[0008]

Embodiments of the present invention will be described below.

As shown in FIG. 1, for example, the real image type finder of the embodiment is represented by an objective lens system including first to twelfth surfaces, and thirteenth and fourteenth surfaces in order from the object side. , A condenser lens for guiding an object image by the objective lens system to the eyepiece side, a prism system as an erecting optical system for reversing the object image developed and shown on the 15th and 16th surfaces, and 17th surface To the twentieth surface, and an eyepiece lens system configured to guide an inverted image to the eye.

By constructing the eyepiece lens system by arranging the positive lens group and the negative lens group in this order from the object side, it is possible to increase the distance from the condenser lens to the eyepiece system without increasing the focal length of the eyepiece lens. Therefore, it is possible to secure a large magnification for each finder system.

In the real image type finder of the embodiment, the focal length of the eyepiece lens system is fE, and the focal length of the negative lens on the pupil side of the eyepiece lens system is fEN, which satisfies the condition of equation (2).

[0012]

[Formula 2] -0.7 <fE / fEN <0 (1)

The condition (1) defines the power distribution of the positive lens group and the negative lens group of the eyepiece lens system. If the upper limit of condition (1) is exceeded, the eyepiece system will not have a positive or negative arrangement from the object side, and if the lower limit is exceeded, a large angular magnification can be secured, but the power of the positive and negative lens units will be excessive. Next to
It becomes difficult to see the field frame, and it becomes difficult to correct aberrations in the eyepiece lens system and the entire finder system.

Further, the positive lens group of the eyepiece lens system is one positive lens, the negative lens group is a negative meniscus lens with the concave surface facing the pupil side, and the radius of curvature of the concave surface of the negative meniscus lens is rE. It is desirable that the condition of Expression 3 be satisfied.

[0015]

[Equation 3] 0.5 <fE / rE <3.5 (2)

By using a negative meniscus lens for the negative lens group of the eyepiece lens system, the power of the eyepiece lens system is increased and the angular magnification of the entire viewfinder system is increased while ensuring a large distance between the condenser lens and the eyepiece lens system. It can be greatly secured.

The condition (2) defines the shape of the negative lens on the pupil side of the eyepiece system. If the upper limit is exceeded, it will be difficult to correct astigmatism, and if the lower limit is exceeded, the radius of curvature of the concave surface will be too small. The distance from the eyepiece to the pupil becomes smaller. Since the distance from the eyepiece lens system to the pupil changes depending on the usage situation, it is necessary to secure a large distance.

Further, by moving the positive lens group in the eyepiece system, the diopter can be adjusted without changing the distance between the eyepiece and the pupil.

Some recent compact cameras use a wider-angle photographic lens and are capable of panoramic photography with the upper ¼ and lower ¼ of the screen cut. This type of camera is In order to match the field of view of the finder with the shooting range, the camera has a field frame inserted in the optical path of the viewfinder in accordance with the shooting range of panoramic shooting. This field frame for panoramic photography is inserted in the space between the condenser lens and the erecting optical system, so it is necessary to secure a large space for enabling panoramic photography.

Therefore, in order to insert a field-of-view frame for panoramic photography, the distance between the condenser lens and the erecting optical system is LE, and the air conversion distance from the condenser lens to the eyepiece lens system is fBE. It is desirable to meet the conditions.

[0021]

[Formula 4] 0.15 <LE / fE <0.5 (3) 0.9 <fBE / fE <1.3 (4)

Condition (3) defines the distance between the condenser lens and the erecting optical system. If the lower limit is exceeded, sufficient space cannot be secured, and if the upper limit is exceeded, the total length of the eyepiece lens system is too large. Become.

The condition (4) defines the distance from the condenser lens to the eyepiece system, and when the value goes below the lower limit, the space for the erecting optical system is insufficient to satisfy the condition (3) at the same time, and the upper limit is set. If it exceeds, the total length of the eyepiece lens system becomes large and it becomes difficult to correct the aberration of the eyepiece lens system.

Although the prism system is used as the erecting optical system in the embodiment, a plurality of mirrors may be combined together.

[0025]

[Embodiment 1] FIG. 1 is a lens diagram of a real image type finder of Embodiment 1 at a high magnification, and FIG. 2 is a chromatic aberration, a chromatic aberration of magnification, and an astigmatism (S: Sagittal, M: meridional), and distortion. 3 and 4 are a lens diagram and various aberration diagrams of Example 1 at a low magnification.

Specific numerical configurations of Example 1 are as shown in Tables 1 to 3. The symbols in the tables and figures are EP
Is the distance from the pole of the final lens to the eye point (eye relief), r is the radius of curvature of each lens surface, d is the lens thickness or lens interval (the unit is mm), n is the d-line refractive index of each lens, ν is the Abbe number of the d line of each lens, and E. R
Is the eye ring.

The lens of Example 1 includes the third, fourth, fifth, sixth and fifth lenses.
The 7, 10, 11, 13, and 18 surfaces are aspherical surfaces. An aspherical surface has a distance X from the tangent plane of the aspherical vertex of a coordinate point on the aspherical surface having a height Y from the optical axis, and a curvature (1
/ R) is C, the conical coefficient is K, and the fourth-order, sixth-order, and eighth-order aspherical coefficients are A4, A6, and A8.

[0028]

[Formula 5]

Table 2 shows the conical coefficient and aspherical surface coefficient of each aspherical surface.
It is as shown in. The radius of curvature of the aspherical surface in Table 1 is the radius of curvature of the aspherical vertex. Also, the magnification M,
The half angle of view ω and the intervals d2, d6 and d10 are shown in Table 3 as the magnification changes.
It changes as shown in.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Embodiment 2] FIG. 5 is a lens diagram of the real image type finder of Embodiment 2 at a high magnification, and FIG. 6 is a diagram showing various aberrations thereof. Also,
7 and 8 are a lens diagram and various aberration diagrams of Example 2 at low magnification.

Specific numerical configurations of the second embodiment are as shown in Tables 4 to 6. The lens of Example 2 includes the third and third lenses.
The surfaces 4, 5, 6, 7, 10, 11, 13, 13 are aspherical surfaces. Table 5 shows the conical coefficient and aspherical surface coefficient of each aspherical surface. Magnification M, half angle of view ω, intervals d2, d6, d1
0 changes as shown in Table 6 with the magnification change.

[0035]

[Table 4]

[0036]

[Table 5]

[0037]

[Table 6]

[0038]

[Third Embodiment] FIG. 9 is a lens diagram of a real image type finder of a third embodiment at a high magnification, and FIG. 10 is a diagram of various aberrations thereof. 11 and 12 are a lens diagram and various aberration diagrams of Example 3 at a low magnification.

Specific numerical configurations of the second embodiment are as shown in Tables 7 to 9. The lens of Example 3 includes the third and third lenses.
The surfaces 4, 8, 9, 12, 13, 15, and 20 are aspherical surfaces. The conical coefficient and aspherical surface coefficient of each aspherical surface are as shown in Table 8. Magnification M, half angle of view ω, intervals d2, d8, d12
Changes with zooming as shown in Table 9.

[0040]

[Table 7]

[0041]

[Table 8]

[0042]

[Table 9]

Table 10 shows the relationship between each embodiment and the conditional expressions described above.

[0044]

[Table 10]

[0045]

As described above, according to the present invention, it is possible to reduce the angular magnification of the entire finder without reducing the angular magnification.
It is possible to secure a large space for installing the erecting optical system, secure a large distance between the object image formed by the objective lens system and the erecting optical system, and insert a field frame or the like compatible with panoramic photography. Become.

[Brief description of drawings]

FIG. 1 is a lens diagram of a real image type finder of Example 1 at a high magnification.

FIG. 2 is a diagram of various types of aberration of the finder of Example 1 at high magnification.

FIG. 3 is a lens diagram of the real image type finder of Example 1 at a low magnification.

FIG. 4 is a diagram of various types of aberration of the finder of Example 1 when the magnification is low.

FIG. 5 is a lens diagram of the real image type finder of Example 2 at a high magnification.

FIG. 6 is a diagram of various types of aberration of the finder of Example 2 at high magnification.

FIG. 7 is a lens diagram of a real image type finder of Example 2 at a low magnification.

FIG. 8 is a diagram of various types of aberration of the finder of Example 2 when the magnification is low.

FIG. 9 is a lens diagram of the real image type finder of Example 3 at a high magnification.

FIG. 10 is a diagram of various types of aberration of the finder of Example 3 at high magnification.

FIG. 11 is a lens diagram of a real image type finder of Example 3 at a low magnification.

FIG. 12 is a diagram of various types of aberration of the finder of Example 3 when the magnification is low.

Claims (4)

[Claims] 1. An objective lens system in order from the object side, a condenser lens for guiding an object image by the objective lens system to an eyepiece side, an erecting optical system for reversing the direction of the object image, and positive and negative from the object side. An eyepiece lens system composed of lens groups arranged in this order, wherein the surface of the eyepiece lens system closest to the pupil side is a concave surface, and the following condition is satisfied. -0.7 <fE / fEN <0 0.5 <fE / rE <3.5 fE: Focal length of eyepiece system fEN: Focal length of negative lens on pupil side of eyepiece system rE: Most of eyepiece system Radius of curvature of the concave surface on the pupil side 2. The eyepiece lens system is configured by arranging two lenses, in order from the object side, a positive lens and a negative meniscus lens having a concave surface facing the pupil side. The real image type viewfinder described in 1. 3. The real image finder according to claim 1, wherein the eyepiece lens system adjusts diopter by moving the positive lens group in the eyepiece lens system. 4. An objective lens system in order from the object side, a condenser lens for guiding an object image by the objective lens system to an eyepiece side, an erecting optical system for inverting the direction of the object image, and positive and negative from the object side. A real image type viewfinder characterized by satisfying the following conditions, and an eyepiece system configured to guide an inverted image to the eye. 0.15 <LE / fE <0.5 0.9 <fBE / fE <1.3 LE: Distance between condenser lens and erecting optical system fBE: Air conversion distance from condenser lens to eyepiece lens system