JPH04194913A - Variable power finder - Google Patents

Abstract

PURPOSE:To reduce the moving amount of a lens group and to accomplish high variable power ratio by constituting an objective lens of a 1st lens group having negative refracting power, a 2nd lens group having positive refracting power, and a 3rd lens group having the positive refracting power and moving only the 2nd lens group. CONSTITUTION:The objective lens is constituted of the 1st lens group L1 which is negative, the 2nd lens group L2 which is positive and the 3rd lens group L3 which is positive in order from an object side. When the objective lens performs zooming from a wide end W to a telephoto end T, the image surface I of the objective lens temporarily moves to the object side and then it returns to a pupil side. This zooming is performed by moving only the 2nd lens group L2. Thus, the moving amount DELTA of the image surface I is reduced and the variable power ratio is made high.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable magnification finder, and more particularly to a variable magnification finder used in a camera such as a lens shutter camera.

A variable magnification finder consisting of an objective lens, a condenser lens, and an eyepiece in order from the object side is known, for example, as proposed in Japanese Patent Application Laid-open No. 7017/1983.

In this variable magnification finder of JP-A-62-7017,
The objective lens has two groups, a negative lens and a positive lens, and magnification is changed by fixing the negative lens and moving the positive lens.

In other words, the viewfinder magnification can be changed by moving only one lens group, so the zooming mechanism has a simple configuration. Therefore, a low-cost and compact variable magnification finder is realized.

However, since this variable magnification finder is configured to change magnification with one lens group, it is difficult to achieve a high magnification ratio with a small amount of lens movement. There's a problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a variable magnification finder with a simple zooming mechanism, a small amount of lens group movement, and a high variable magnification ratio.

In order to achieve the object described in "A sentence to address the problem," the present invention provides a variable magnification finder consisting of, in order from the object side, an objective lens, a condenser lens, and an eyepiece lens, all of which have positive refractive power. The lens consists of a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, and by moving only the second lens group, the finder magnification can be adjusted. It is characterized by changing.

Figures 1 (W), (M), and (T) schematically show the lens configuration and optical path at the wide end, intermediate focal length state, and telephoto end of the objective lens constituting the variable magnification finder of the present invention. ing.

This objective lens has a negative first lens group (
L+), a positive second lens group (L2), and a positive third lens group (L3). As shown in the figure, when the objective lens zooms from the wide end (W) to the telephoto end (T), the image plane (I) of the objective lens once moves toward the object side and then returns to the pupil side. The second zooming is performed by moving only the second lens group (L2).

The amount by which the image plane (I) moves is represented by Δ in FIG. 1(M). Here, from the third lens group (L3) to the image plane (■)
Assuming that the distance to is D, the following conditional expression (2) holds true.

D= (1-e, φ 1-e2φ1-e2φ2+Ole
2φ, φ2)/φ...■ However, φ: Power of the objective lens φ1: Power of the first lens group (L,) φ2: Power of the second lens group (L e,: Power of the Luns group (Ll) Principal point interval e2 between and second lens group (L2): second lens group (L2) and third lens group (L3)
is the principal point spacing between .

Furthermore, if △””Dw DT:O, then conditional expression (2) holds true.

△=D, -D car DT Dm......■ However, as shown in Fig. 1, D:: Third lens group (L3
) Distance (D) from the principal point position of the third lens group (L3) to the image plane (I) ) D□: Distance (D) from the principal point position of the third lens group (L3) to the image plane (D) at the telephoto end (T).

Therefore, if the relationship between the focal length (fO) of the objective lens and the amount of movement of the image plane (Δ) is expressed in a graph, it will be as shown in Fig. 2. Here, f in the case where the objective lens has a three-group configuration of negative, positive, and positive (the configuration of the objective lens of the present invention).

The relationship between fo and Δ is represented by A, and the relationship between fo and Δ in the case of a negative-positive two-group configuration (for example, the objective lens configuration of JP-A-62-7017) is represented by B. In addition, for the objective lens with three negative and positive groups and the objective lens with two negative and positive groups, the focal length (fo) of the objective lens is 7 to 13 mm, and the focal length of the eyepiece lens used at the same time (f[ ) is standardized as 16.8mm.

Comparing A and B in FIG. 2, it can be seen that A has a smaller movement amount (Δ) of the image plane (I) than B, and is more effective because it allows a larger magnification ratio.

The conditions for (A) in the case of the three-group configuration of negative, positive and positive in FIG. 2 are as shown below.

e+u=9mm e2II=1mm e+r=1mm e2r=9mm ψ1-~0.047619047 φ2 = 0.078345346 φ3= 0.057583784 However, eIw: 1121st group (L) at wide end (W)
, ) and the second lens group (L2) e211: The second lens group (L2) at the wide end (W)
2) and the third lens group (L3): principal point distance e, T: principal point distance e2T between the 1121st group (L,) and the second lens group (L2) at the telephoto end (T): telephoto end ( Second lens group (L2) in T)
principal point interval φ3 between and the third lens group (L3): power of the third lens group (L3).

In the case of the negative, positive, and positive three lens group configuration (A) as in the present invention, the 1121st lens group (Ll) and the third lens group (L3) are fixed, so the following conditional expression (2) holds true.

e+w→e2W"e+v+f'!2T"eq ""
``■ However, e: is the principal point interval between the 1121st lens group (Ll) and the third lens group (L3).

The conditions for (B) in the case of the negative-positive two-group configuration are as shown below.

φ1--0.104828483 φ2 = 0.22996541 esv=2mm However, 08th lens = principal point distance between the 1121st lens group and the second lens group at the telephoto end.

In this way, under certain common conditions, the three negative, positive and positive
When comparing an objective lens with a group configuration and an objective lens with a two-group configuration of negative and positive, the maximum value of the amount of movement of the image plane (I) is -0.24 mm for A and -0.42 mm for 1B.

Converting this to the amount of diopter change, since the focal length (f') of the eyepiece is the same, the amount of image plane movement for 1 diopter is fE2/1000 = 16.82/1
000=0.28224mm. Therefore, the diopter change amount of A is 0.85 diopter, and the diopter change amount of B' is 1.49 diopter. Under this condition, A
In B, it falls within 1 diopter, but in B, it falls within 1 diopter.
It exceeds pter. Here, if A and B are matched with respect to the amount of movement of the image plane (I), then A can have a larger zoom ratio.

In Figure 2, in the case of a three-group configuration (negative, positive, positive) (A), the telephoto end (T
) and the wide end (W), the configuration must satisfy the above conditional expression (2) and the following conditional expressions (2) to (2).

φ−−φ1+φ2+φ3−e+uφ, φ2−e, □φ1
φ3-e2. φ, φ3−e2oφ2φ3→e+we2w
φ1φ2φ3・・・・・・■ φ1−φ1+φ2+φ3−erTφ1φ2−e1■φ1
φ3-e2□φ, φ3-e2rφ2φ3+elTe2
□φ, φ2φ3...■ Du=I)v ・・・・・・■ However, φll: Power of the objective lens at the wide end (W) φd: Power of the objective lens at the telephoto end (T) It is.

Also, the camera body size (thickness) is 20 to 60 =
11-mm is common, and assuming that the length occupied by the finder objective lens is half the body size, e,
It is desirable to set the range of 10<ea<30.

In Fig. 2, conditions A (fo-7 to 13 mm, fp
"16.8m"+e211"eJanymm), en
= 10 mm, and the power distribution when eq = 30 mm is as follows from conditional expressions (■ to ■).

When er+ = 10mm, φ, -11. /21.000 ψ2 * 1 / 12.764 φ3-=1/17.366 When e, = 30mm, φ+ −-1/78.000 φ2 * 1/44.635 φ3-1/10.836 It is.

The respective powers at focal lengths of e, -1, Omm, and ep-30mm are expressed as follows.

When ep = 10mm, L　””　-21,000 fp=12.764 f3=17.366 When ep = 30mm, L=-78,000 f2=44.635 f3=10.836 It is.

However, f,: the first lens group (L
, ): Focal length f2 of the second lens group (L
2) Focal length f3: the third lens group (L
3) is the focal length.

In the present invention, the objective lens is configured with three negative, positive and positive groups in order to increase the variable magnification ratio as described above, and also because it has a negative and positive two group configuration (Japanese Unexamined Patent Application Publication No. 62-7017, etc.). This is also to distribute the positive power of the two lens groups and improve aberration performance.

Therefore, the distribution ratio of the second lens group (l f2/f31 )
It is preferable that the following conditional expression (2) be satisfied.

0,7<l f2/f31<4. , 2...
・・・・When the lower limit of the conditional expression ■ is exceeded, e becomes shorter,
Actual lens placement becomes difficult. If the upper limit of conditional expression (2) is exceeded, e becomes long and becomes inappropriate as a finder. For example, it becomes impossible to achieve compactness.

Therefore, as long as it is within the range of conditional expression (2), e will be an appropriate value and appropriate aberration performance will be obtained.

In a variable magnification finder consisting of, in order from the object side, an objective lens, a condenser lens, and an eyepiece, all of which have positive refractive power, the objective lens includes a first lens group that has negative refractive power, a first lens group that has positive refractive power, and a first lens group that has positive refractive power. The image formed by the objective lens is transferred to the above-mentioned variable magnification finder, which is composed of two lens groups and a third lens group having positive refractive power, and changes the finder magnification by moving only the second lens group. By providing an inverting optical system for inverting the object and making the incident surface of the inverting optical system the lens surface, the inverting optical system can also be used as the third lens group, thereby making it possible to make the variable magnification finder compact. .

Furthermore, the inversion optical system is divided into two parts, an object-side unit and a pupil-side unit, so that the image formed by the objective lens is formed near the division point of the unit, and the entrance surface of the pupil-side unit is formed by the lens. If the pupil-side unit is configured to double as the condenser lens by making it a surface, compactness can be achieved more effectively.

Further, in a variable magnification finder consisting of, in order from the object side, an objective lens, a condenser lens, and an eyepiece, all of which have positive refractive power, the objective lens includes a first lens group that has negative refractive power, a first lens group that has positive refractive power, and a first lens group that has positive refractive power. An image is formed by the objective lens on the above-mentioned variable magnification finder, which is composed of a second lens group with a positive refractive power and a third lens group with a positive refractive power, and whose viewfinder magnification is changed by moving only the second lens group. By providing an inverting optical system that inverts the image and making the incident surface of the inverting optical system the lens surface, even if the inverting optical system is also used as the condenser lens, the variable magnification finder can be used as a condenser lens. can.

Nuj [Example- Examples of the variable magnification finder according to the present invention will be shown below.

However, in each example, r: (i・1, 2, 3.,
,,) is the radius of curvature of the i-th surface counting from the object side, dl
(i・1,2゜3, , ,) indicates the i-th axial surface spacing counting from the object side, and N: (i4.2.3. , ,
, ), ν, (i-1, 2, 3, , , ) is the refractive index for the d-line of the i-th lens counting from the object side.

Indicates the Atsube number. Further, 2ω indicates the angle of view.

Width in the conditional expression (■) and l in the conditional expression (■) in each example
f2/fal, f2 and f3 are shown together.

In each example, a surface with a radius of curvature marked with * indicates that it is an aspherical surface, and is defined by the following equation representing the shape of the aspherical surface. Note that the more general surface shape expressed by the following equation starts from a rotational quadratic surface and uses the optical axis, which is obtained by adding a deformation term (aspherical term) to this, as the axis of rotational symmetry.

F (X, Y, Z) = X - f (Y, Z) - 〇 However, f (Y, Z) = C, Φ2/ [1 + (1 - εC22Φ2
)I/2]+AΦ2→BΦ4+CΦ6]DΦB+EΦ1
2 Here, Φ2-Y2+Z2 In the plane perpendicular to the axis, x, y in mutually orthogonal coordinate axes.

Z coordinate value C[]: curvature in aspherical term ε: Quadratic surface parameter A, B, C, D, E: Aspheric coefficients.

<Example 1> 2ω = 49.6' ~ 28,7° 1 Xiangshu moxibustion] Ljjl old 1 tae grip rate Lgbe 1rl
34.05 r3* 13.60 d+ 5.788~12.469~18.675rs
11.94 r7 8.13 dl 2.400 N41.4914 ν45
7.82r8 00 d8 0.630 r9 otsd928.800 Ns 1.4914 ν5
57.82rlL1 c.

die 0.794 rl+ 1.6.13 r3: A-0, B=-8,501X 10-5.
C=1179 X 1 leaf 6°D=-1,488X10
-8. E=O r+2: A20, B knee 1.047X10',
C-7,799X10-7゜D=1.194X10
-9. E=0 article (l f2/ f31 = 1.22 f2 = 22.001 f3 = 18.099 eq = 23 <Example 2> 2ω = 49.6° ~ 28.7° 4) 1L certificate plate publication - breast digging rate L2pe1r+ 1
7.17 d+ 1.200 N+ 1.584 ν, 3
1.0r210.69 d220.373~12.240~2.401r334
．． 61 ds2.5QON21.4914 ν257.82r
4 -26.21 d40.631~8.764~1'8.603r59.
64 ds 19.875 N31.584'L/33
1. OF2 (X) de O,200 r716.00 d720.175 N41.584 ν431. O
F2 00 688.230 r12* -32,24 Fence 1 starvation r+s: A"O, B: 1.033X 10-',
C4,292X 10-5゜D=-6,474X 10
E20 article f2/ f31 = 1.18 f2 = 30.771 f3 = 26.138 ep = 21.364 Figures 3 and 5 show lens configurations corresponding to Examples 1 and 2 above. and a diagram showing the optical path at each of the wide end (w), intermediate focal length state (M), and telephoto end (T).

In each embodiment, the lens that moves during zooming is
It is the second lens (L2) in the objective lens (Lo), and its movement from the wide end (w) to the telephoto end (T) is indicated by arrows (ml) and (m2) in each figure, respectively.

Embodiment 1 includes, in order from the object side, a first lens (r, +) consisting of a biconcave negative lens, a second lens (L2) consisting of a biconvex positive lens, and a third lens consisting of a biconvex positive lens. (L3) and an objective lens (LO) composed of.

A condenser lens (L
c), a field frame (FR) provided on the pupil (Ep) side of the condenser lens (LC), a Porro prism (PR) provided as a nine-inversion optical system, and one biconvex positive lens. It consists of an eyepiece lens (L,).

Note that the object side surface of the second lens (L2) and the eyepiece lens (L
The surface on the pupil (Ep) side of E) is an aspherical surface.

In the second embodiment, in order from the object side, the first lens (L+) is made of a negative meniscus lens that is concave on the pupil (Ep) side, the second lens (L2) is made of a biconvex positive lens, and the second lens is also used as an inversion optical system. Consisting of an object side unit of a Porro prism, an objective lens (r, o) consisting of a third lens (L3), which is a plano-convex lens convex to the object side, and a pupil side unit of a Porro prism, which also serves as a 7-inversion optical system. It consists of a condenser lens (Lc), which is a plano-convex lens convex to the object side, and an eyepiece lens (LE), which is a five-sided positive lens. Note that the surface of the eyepiece (LE) on the pupil (Ep) side is an aspherical surface.

4 and 6 are aberration diagrams corresponding to Examples 1 and 2, respectively, where (W) is the wide end, (M) is the intermediate focal length state, and (T) is the aberration for the d-line at the tele end. It shows. Further, a broken line (DM) and a solid line (DS) represent astigmatism on the meridional plane and the sagittal plane, respectively.

As explained above, according to the variable magnification finder of the present invention, the variable magnification finder consists of, in order from the object side, an objective lens, a condenser lens, and an eyepiece lens, all of which have positive refractive power. The objective lens consists of a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, and by moving only the second lens group, the finder Since it is characterized by changing the magnification, it is possible to realize a variable magnification finder with a simple zooming mechanism, a small amount of movement of the lens group, and a high variable magnification ratio.

Furthermore, aberration performance can be improved by providing a configuration that satisfies conditional expression (2).

In addition, by using an inverting optical system that also serves as the third lens group and condenser lens, the finder can be made compact.

Furthermore, the inversion optical system is divided into two parts, an object-side unit and a pupil-side unit, so that the image formed by the objective lens is formed near the division point of the unit, and the entrance surface of the pupil-side unit is formed by the lens. If the pupil-side unit is configured to double as the condenser lens by forming a surface, the finder can be made more compact.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the lens configuration and optical path of an objective lens constituting a variable magnification finder of the present invention at a wide end, an intermediate focal length state, and a telephoto end. FIG. 2 is a graph showing the relationship between the focal length of the objective lens and the amount of movement of the image formed by the objective lens in the present invention. FIG. 3 is a diagram showing the lens configuration and optical path corresponding to Example 1 of the present invention at the wide end, intermediate focal length state, and telephoto end, and FIG. 4 is an aberration diagram corresponding thereto. FIG. 5 shows the lens configuration and optical path corresponding to Example 2 of the present invention at the wide end. FIG. 6 is a diagram showing each of the intermediate focal length state and the telephoto end, and FIG. 6 is an aberration diagram corresponding thereto. Applicant Minolta Camera Co., Ltd.

Claims (1)

[Scope of Claims] (1) A variable magnification finder consisting of, in order from the object side, an objective lens, a condenser lens, and an eyepiece, all of which have positive refractive power, wherein the objective lens is a first lens having negative refractive power. A variable magnification finder comprising a second lens group having a positive refractive power and a third lens group having a positive refractive power, the finder magnification being changed by moving only the second lens group. . (2) The variable magnification finder according to claim 1, further satisfying the following condition; 0.7<|f_2/f_3|<4.2, where f_2: the objective lens Focal length f_3 of the second lens group included: Focal length of the third lens group constituting the objective lens. (3) In a variable magnification finder consisting of, in order from the object side, an objective lens, a condenser lens, and an eyepiece, all of which have positive refractive power, the objective lens includes a first lens group that has negative refractive power, and a first lens group that has positive refractive power. and a third lens group having positive refractive power, the finder magnification is changed by moving only the second lens group, and the image formed by the objective lens is inverted. A variable magnification finder comprising an optical system, wherein the inverting optical system is also used as a third lens group of the objective lens by making the entrance surface of the inverting optical system a lens surface. (4) The inversion optical system is divided into two parts, an object side unit and a pupil side unit, so that the image formed by the objective lens is formed near the division point of the unit, and the entrance plane of the pupil side unit is 4. The variable magnification finder according to claim 3, wherein the pupil side unit is also used as the condenser lens by forming a lens surface. (5) In a variable magnification finder consisting of, in order from the object side, an objective lens, a condenser lens, and an eyepiece, all of which have positive refractive power, the objective lens includes a first lens group that has negative refractive power, and a first lens group that has positive refractive power. and a third lens group having positive refractive power, the finder magnification is changed by moving only the second lens group, and the image formed by the objective lens is inverted. 1. A variable magnification finder comprising an optical system, the inverting optical system serving also as the condenser lens by making the entrance surface of the inverting optical system a lens surface.