JPH04204911A - Real image type variable power finder optical system - Google Patents

Abstract

PURPOSE:To provide a higher variable power ratio, higher magnification and smaller size by satisfying specific relations between the respective lens groups of a 1st group having a negative refractive index, a 2nd group having a positive refractive index and a 3rd group having a lens prism as well as the focal lengths of the lenses and the focal length of an eyepiece lens. CONSTITUTION:The conditions 0.055(1/mm)<1/fe<0.090(1/mm), -0.08<f1/f2<-2.00, -0.100(1/mm)<1/f1<-0.050(1/mm), 0.085(1mm)<1/ f2<0.150(1/mm), 0.5<f21/f22<2.0, 2.0<fp/fe<10.0 are satisfied when the focal lengths of the 1st group I, the 2nd group II are respectively designated as f1, f2; the focal lengths of two elements of the positive lenses of the 2nd group II respectively as f21(mm), f22(mm); the focal length of the lens prism III of the 3rd group is designated as fp, and the focal length of the eyepiece lens as f2. The variable power from a wide angle end to a telephoto end is executed by moving the 1st group I to an object side and the 2nd group II to an image plane side respectively on the optical axis. The size of the system is reduced in spite of the high variable power ratio and the high magnification with this constitution.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a real-image variable magnification finder optical system, and in particular to an appropriate lens configuration of an external variable magnification finder optical system provided separately from a photographing system. The present invention relates to a small-sized real-image variable magnification finder optical system suitable for, for example, still cameras and video cameras, which enables good viewfinder image observation by setting the settings.

(Prior art) Conventionally, in cameras where the photographing system and finder system are configured separately, when the photographing system is a variable magnification system, it is necessary to use a variable magnification finder, which has a configuration in which the viewfinder field magnification changes as the magnification changes. It is preferable.

Further, since the variable magnification finder is to be incorporated into the camera, it is preferable that the variable magnification finder is small and has a structure that allows a predetermined variable magnification ratio to be easily obtained.

The variable magnification finder optical system is constructed using a secondary imaging method, and the objective lens constituting the variable magnification finder optical system is composed of multiple lens groups. The real image variable magnification finder optical system, which changes magnification by moving the lens group along the optical axis, is well known.
Various proposals have been made so far.

The present applicant has previously published, for example, JP-A-62-7017, JP-A-64-65519, and JP-A-64-65520.
Publication No. 1-11616, and Japanese Patent Application No. 1983
No. 315338, etc., proposes a variable magnification finder optical system that has high optical performance and satisfactorily corrects aberration fluctuations associated with variable magnification.

FIG. 11 is a sectional view of a lens of a real image variable magnification finder optical system previously proposed by the present applicant in Japanese Patent Application No. 63-315338. In the figure, the objective lens 110 has two lens groups, a front lens group with negative refractive power and a rear lens group (2) with positive refractive power, in order from the object side.6 111 is a prism reflection for erecting a normal image. The body 112 is a field lens.

In the figure, magnification is changed by moving the lens group (2) of the objective lens 110 on the optical axis as shown by the arrow in the figure, and the finder image formed near the field lens 112 by the objective lens 110 is displayed at the eyepiece. A viewfinder image of an erect normal image is observed by magnifying it with a lens 120.

(Problems to be Solved by the Invention) The present invention further improves the real image type variable magnification finder shown in FIG. To provide a real image type variable magnification finder optical system which has a relatively short overall lens length and small size while having a variable magnification ratio and high magnification, and has high optical performance with good correction of various aberrations.

(Means for Solving the Problems) The real image variable magnification finder optical system of the present invention includes, in order from the object side, a first group with negative refractive power, a second group with positive refractive power, and a second group with positive refractive power. an objective lens having three lens groups; a field mask disposed near the object image formed by the objective lens; and an eyepiece lens for observing the object image formed near the field mask; In a real image variable magnification finder optical system that performs magnification by moving the first group and the second group on the optical axis, the first group includes at least one negative lens or at least one positive lens and at least one positive lens. and the second group includes at least two negative lenses.
The third group includes a lens prism integrally configured with a positive refractive surface and at least two reflective surfaces, and the eyepiece includes an optical member having at least two reflective surfaces and at least one reflective surface. the focal lengths of the first group and the second group are fl (mm) and f2 (mm), respectively.
), the focal lengths of the two positive lenses of the second group are each f2
1 (mm), f22 (mm), the focal length of the lens prism fp, and the focal length fe of the eyepiece, 0.055 (1/mm) <l/fe< 0.090 (
1/mm) -(1)-O, o8 < fl/f2
<-2,oo ・-(2)-0,10
0(1/mm) <]/f1<-0,050(1/mm
) ---(3)0.085(+/+nm) <]/
f2< 0.150 (1/mm) --・<4')0
．． 5 <f21/f22 <2.0
...(5) 2.0 < fp/fe < 10.0
=16).

(Example) Figures 1 to 5 are numerical examples 1 to 5 of the present invention, which will be described later.
5 and 5 to 10 are aberration diagrams of numerical examples 1 to 5 of the present invention, respectively, which will be described later. Figure 1 (A
) shows the case at high magnification (wide-angle end), and (B) shows the case at low magnification (telephoto end). In the aberration diagrams, (A) shows the case at high magnification (wide-angle end), (B) shows the case at medium magnification (middle part), and (C) shows the case at low magnification (telephoto end).

In the figure, 1 is an objective lens, which has three lens groups: a first group with negative refractive power, a second group m with positive refractive power, and a third group m with positive refractive power. .

Reference numeral 40 denotes a field mask representing the field of view range, and is placed near the point where the objective lens 1 forms an image. The field mask 40 has an information display such as a field frame printed or vapor-deposited on the surface facing the objective lens 1 so that it can be observed together with a finder image during observation. 2 is an eyepiece lens having positive refractive power as a whole.

In this embodiment, the first lens group has one negative lens 11 (the first
, 4 and 5) or one positive lens 10 and one negative lens 11 (FIGS. 2 and 3).

The second group m has two positive lenses 21 and 22. The third group m includes a lens prism 31 integrally comprising a positive refractive surface and at least two reflective surfaces, or the lens prism 31 and one positive lens 32. The eyepiece lens 2 includes an optical member 41 having two reflective surfaces and a positive lens 42 having both lens surfaces convex. Further, at least one lens surface of the positive lens 42 is provided with an aspherical surface.

In FIGS. 1 to 4, the optical member 41 is composed of a lens prism integrally formed with a converging or diverging refractive surface and two reflecting surfaces, and in FIG. 5, the optical member 41 is composed of two reflecting mirrors. . In the lens cross-sectional view, the lens prism 31 and the optical member 41 are shown as expanded glass blocks for simplicity.

In this embodiment, the lens prism 31 of the third group m of the objective lens 1 and the optical member 41 of the eyepiece lens 2 constitute an image inversion optical system for obtaining a finder image for an erect normal image.

In this embodiment, the objective lens 1 is
A finder image is formed on the imaging surface near the field mask 40, and the finder image of the erect image magnified by the eyepiece 2 is observed from an eye point (not shown) together with the field frame and an information display provided in its vicinity. ing.

When changing the magnification from the wide-angle end (high magnification) to the telephoto end (low magnification), move the first group toward the object side and the second group m toward the image plane on the optical axis as shown in the arrows shown in the figure. It's being moved.

As described above, the image reversal optical system in this embodiment includes the lens prism 31 having a refractive surface and at least two reflective surfaces, and the optical member 4 having at least two reflective surfaces.
1, it is possible to obtain an erect finder image and to downsize the entire variable magnification finder optical system.

Furthermore, in this embodiment, the two reflecting surfaces of the lens prism 31 and/or the two reflecting surfaces of the optical member 41 may be constructed of roof reflecting surfaces, which further reduces the size of the entire variable magnification finder optical system. It is possible to aim for

Next, the technical meaning of each of the above-mentioned conditional expressions will be explained.

Conditional expression (1) relates to the refractive power of the eyepiece lens 2, and if the refractive power exceeds the upper limit and becomes too strong, it becomes difficult to perform good aberration correction with a simple configuration. Furthermore, if the lower limit is exceeded and the refractive power becomes too weak, the finder magnification will decrease and the entire finder optical system will become larger, which is not good.

Conditional expression (2) relates to the ratio of the focal lengths of the first group and the second group m, which constitute one element of the objective lens 1, and if the positive refractive power of the second group II becomes too strong by exceeding the upper limit, It becomes difficult to suppress variations in aberrations caused by zooming.

Furthermore, if the lower limit is exceeded and the refractive power of the second group m becomes too weak, the amount of movement of the second group m to ensure a predetermined variable power ratio increases, which is not good.

Conditional expression (3) concerns the refractive power of the first group (■) of the objective lens 1. When the upper limit is exceeded and the negative refractive power of the first group 1 becomes weaker, the total length of the lens on the low magnification side becomes longer. . Furthermore, if the lower limit value is exceeded and the negative refractive power of the first lens group becomes too strong, it becomes difficult to properly correct aberrations with a simple lens configuration, which is not good.

Conditional expression (4) relates to the refractive power of the second group m of the objective lens 1, and if the refractive power of the second group exceeds the upper limit and becomes too strong, it will be difficult to properly correct aberrations with a simple lens configuration. It's coming. Furthermore, if the lower limit is exceeded and the refractive power of the second group becomes too weak, the amount of movement of the second group m to ensure a predetermined variable power ratio increases, which is not good.

Conditional expression (5) concerns the ratio of the focal lengths of the two positive lenses 21.22 constituting the second group m of the objective lens 1. If the upper limit or lower limit is exceeded, the two positive lenses 21.22 This is not a good idea because the refractive power of one of the lenses becomes too strong, which significantly increases the amount of word count difference generated by that lens, making it difficult to properly correct aberrations.

Conditional expression (6) relates to the ratio of the focal lengths of the lens prism 31 of the third group m of the objective lens 1 and the eyepiece lens 2, and when the upper limit is exceeded, the combination of the first group ■ and the second group m of the objective lens 1 The focal length must be shortened, which makes it difficult to satisfactorily correct various aberrations with a simple lens configuration.

Furthermore, if the lower limit is exceeded and the refractive power of the lens prism 31 becomes too strong, it becomes difficult to correct various aberrations in a well-balanced manner. Furthermore, the combined focal length of the first group I and the second group m becomes too long, which increases the overall length of the objective lens 1, which is not good.

In this embodiment, the lens surface on the eyepiece side of the positive lens 42 of the eyepiece lens 2 is made aspherical to improve the optical performance of the entire finder screen.

The real image type variable magnification finder optical system which is the object of the present invention can be achieved by satisfying the above conditions.
It is desirable to introduce an aspherical surface into at least one lens surface of the second group m.

In addition, if an aspherical surface is introduced into at least one lens surface of the first group of the objective lens 1, the aspherical surface of the first group I and the aspherical surface of the second group m will cause spherical aberration, curvature of field aberration, and distortion. This is good because aberrations (distortion) can be corrected in a well-balanced manner. Also, if the first lens group of the objective lens 1 is constructed using not only a single negative lens but one positive lens and one negative lens, the effect is similar to that of introducing an aspheric surface into the first lens group. In addition, spherical aberration, curvature of field, and distortion can be corrected in a well-balanced manner.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
i represents the i-th lens thickness and air gap from the object side, and its unit is mm.

Ni and vi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side. γ is the angular magnification.

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 apex of the lens and the X-axis as the origin, and R as the paraxial radius of curvature of the lens surface. , B, and C are aspheric coefficients. Furthermore, Table 1 shows the relationship between each of the above-mentioned conditional expressions and the word values in the numerical examples.

Numerical Example 1 1γ1-1.00~0.35 ω-9,80~25
．． 70R11-ω Dll-1,0N 6-1.5
2300 Jiro 58.8R12-00012-1,6 Second surface aspheric coefficient 82・-IXIO-' Numerical example 2 1γl -1,00~0,35 ω-9,80~2
6.7゜RI3-oo D13-1.0
N 7-1.52300 v 7-58.6R14-
oo D14-1.6 Numerical Example 3 1 γl -1,00~ 0.35 ωmaro
9.80-26.7'RI3-oo D13
-1.0 N 7-1.52300 v 7-58
．． 6R14=oo 014-1.6 Numerical Example 4 1γ1・1.00~0.35 ω・9.80~26
．． 7'R11-oo D]l= 1.0 N
6-1.52300 v 6-58.6R12-CX
) 012-1.8 Numerical Example 5 1γ1-0.82~0.30 ω・12.0°~3
2.3゜R]]1=oo Dll-0,7N 6
-1.52300 v 6-58.6 (Table-1) (Effects of the invention) According to the present invention, each lens configuration of the real image variable magnification finder optical system is appropriately configured as described above, and each conditional expression is satisfied. To achieve a real image type variable magnification finder optical system which has a high variable magnification ratio and a high magnification, has a relatively short overall lens length, is compact, and has a simple configuration, and has high optical performance that satisfactorily corrects the difference in the number of words. I can do it.

[Brief explanation of the drawing]

FIGS. 1 to 5 are cross-sectional views of lenses of numerical examples 1 to 5 of the present invention, FIGS. 6 to 10 are word count difference diagrams of numerical examples 1 to 5 of the present invention, and FIG. FIG. 2 is a cross-sectional view of a lens of a conventional real image variable magnification finder optical system. In Figure 1, (A) shows the case at high magnification, (B) shows the case at low magnification, and in the aberration diagram, (A) shows the case at high magnification, (B) shows the case at medium magnification, and (C) shows the case at medium magnification. Shows when the magnification is low. In the figure, 1 is the objective lens, ■ is the first group, ■ is the second group, ■ is the third group, 2 is the eyepiece, 10, 21° 22.32.4
2 is a positive lens, 11 is a negative lens, 31 is a lens prism, 40 is a field mask, and 41 is an optical member. Patent applicant: Canon Co., Ltd. 2nd illustration 3, length, 4th illustration, 5 concave, Fig. 6 (A) Spherical aberration Astigmatism Distortion (5A) Fig. 6 ([3) - JOZoo - 2,00Zoo -10,0010,
00 Spherical aberration Astigmatism Distortion aberration (X
) Section 6 (C) Spherical aberration Astigmatism Distortion aberration (λ) Fig. 7 (A) Pupil Φ3.6 =9.8” ω=
9.8' Spherical aberration Astigmatism Distortion aberration (X) 9g 7 wards (3) Spherical aberration Astigmatism Distortion yield (X)
7th r:gi<C> -Zoo Zoo -200Zoo -10,0
010,00 Spherical aberration Astigmatism Distortion (%) Figure 8 (A) Spherical aberration Astigmatism Distortion (x)
Figure 8 (3) Spherical aberration Astigmatism Distortion aberration (%)
Figure 8 (C) Figure 9 (A) Pupil. 3,4 ω = 9.88 = 98° Spherical aberration Astigmatism Distortion (%) Fig. 9 (3) Fig. 9 (C) Fig. 10 (A) Fig. 10 (B) Fig. 10 ( C)

Claims (2)

[Claims] (1) Formed by an objective lens having three lens groups, in order from the object side: a first group with negative refractive power, a second group with positive refractive power, and a third group with positive refractive power; a field mask disposed near the object image formed in the field mask, and an eyepiece lens for observing the object image formed near the field mask,
In a real image variable magnification finder optical system that performs magnification by moving the first group and the second group on the optical axis, the first group includes at least one negative lens or at least one positive lens and at least one positive lens. a negative lens;
The group has at least two positive lenses, the third group has a lens prism integrally configured with a positive refractive surface and at least two reflective surfaces, and the eyepiece has an optical lens having at least two reflective surfaces. member and at least one positive lens, and the focal lengths of the first group and the second group are each f1 (mm
), f2 (mm), the focal lengths of the two positive lenses of the second group are f21 (mm) and f22 (mm), respectively, the focal length of the lens prism is fp, the focal length of the eyepiece is f
When e is 0.055 (1/mm) < 1/fe < 0.090 (1/
mm) -0.08<f1/f2<-2.00 -0.100(1/mm)<1/f1<-0.050(
1/mm) 0.085 (1/mm) < 1/f2 < 0.1
50 (1/mm) 0.5<f21/f22<2.0 A real image variable magnification finder optical system characterized by satisfying the following condition: 2.0<fp/fe<10.0. (2) The real image variable magnification finder optical system according to claim 1, wherein the third group has at least one positive lens, and the positive lens of the eyepiece has an aspherical surface. .