JPH10104515A - Keplerian variable power finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide Keplerian variable power finder having a finder magnification at the end of minimum magnification larger than 0.5 times, a zooming ratio larger than two, well compensated various aberrations and a low cost in spite of the simple constitution. SOLUTION: In a Keplerian variable power finder having, in order from the object side, a first lens group including a negative lens L1 , a second group including a positive lens L2 , a third lens group including a negative lens L3 and a fourth lens group including a positive lens L4 , an objective lens system having a positive refractive power as a whole and an eyepiece lens system for observing an image by the objective lens system, by moving at least the second lens group of the objective lens system to the direction of the optical axis, the magnification of the finder is changed and the eyepiece lens system is composed of a positive lens L5 and a negative lens L6 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder optical system used for a still camera, a video camera, a TV camera or the like, and more particularly to a Keplerian type variable magnification finder.

[0002]

2. Description of the Related Art A Kepler-type finder constituted by an objective lens having a positive refractive power and an eyepiece having a positive refractive power is provided by:
By arranging a field frame or a reticle near the focal point of the objective lens, the field of view, the division of the field of view, and various displays can be clearly observed. In addition, this Kepler type finder has an entrance pupil inside the finder or on the object side of the finder, so if it is configured as a so-called zoom finder that continuously changes the magnification of the finder, or if the finder is widened However, there is also an advantage that the diameter of the objective lens does not increase, and in particular, a zoom finder is widely used. In particular, as the configuration of the objective lens, in order from the object side, a Kepler-type optic having a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power Japanese Patent Application Laid-Open No. 3-233420 and Japanese Patent Application Laid-Open
242377 are known.

[0003]

In recent years, there has been a tendency for lens shutter cameras to be miniaturized, and accordingly, the finder optical system has also been required to be miniaturized. However, even if the optical system is small, there is a demand that an image obtained by looking through the viewfinder is easy to see when the image is large. Also,
The zoom ratio of lens shutter cameras tends to increase, and accordingly, the zoom ratio of the viewfinder has also increased. Therefore, there is a demand for a small finder having a large image, a large zoom ratio, and a small size. However, in the proposals of JP-A-3-233420 and the like, the finder magnification is as small as about 0.4 at the lowest magnification end. In addition, although each group is composed of one sheet and various aberrations are satisfactorily corrected in spite of being small in size, their zoom ratio is at most about 2 times and has a sufficiently large zoom ratio. Is hard to say. In JP-A-6-242377 having a zoom ratio of 2 times or more, the finder magnification is as low as about 0.3 times at the lowest magnification end.
In addition, none of the groups is composed of one lens. In particular, the second lens group is composed of a plurality of lenses, so that an increase in cost was unavoidable. The present invention has been made in view of the above problems, and has a large finder magnification at the lowest magnification end of 0.5 times or more, a zoom ratio of 2 times or more, and a simple configuration. ,
It is an object of the present invention to provide a low-cost Kepler-type variable magnification finder in which various aberrations are well corrected.

[0004]

Means for Solving the Problems] Therefore, the present invention includes, in order from the object side, a first lens group including a negative lens L _1, a second lens group including a positive lens L _2, a negative lens L ₃ An objective lens system having a positive refractive power as a whole, including a third lens group including a positive lens L ₄ and a fourth lens including a positive lens L ₄ , and an image formed by the objective lens system as a whole having a positive refractive power. In a Kepler-type variable magnification finder having an eyepiece lens system for observing, by moving at least the second lens group of the objective lens system in the optical axis direction, the finder magnification is changed, and the eyepiece lens system is by configuring the positive lens L ₅ and the negative lens L _6, it is obtained by solving the above problems.

In order to increase the finder magnification, the following two methods can be considered. The first technique is to enlarge the image by the objective lens system. In other words, if the image by the objective lens system is large, the image seen by the eye looks large even if the loupe magnification is the same. Here, the loupe magnification refers to an enlargement ratio by only the eyepiece lens system, and is generally defined by the following equation. Loupe magnification = 250 / _{fe In the} above equation, 250 is the clear visual distance 250 (mm),
f _e is the focal length of the entire eyepiece system. The second technique is to increase the loupe magnification. In other words, if the images obtained by the objective lens system have the same size, the image seen by the eye looks large if the loupe magnification is large. In the present invention,
By employing both the first technique and the second technique, it is possible to increase the finder magnification at low cost while achieving downsizing, in particular, shortening the overall length.

Namely the first method, by arranging the negative lens L ₃ in the third lens unit of the objective lens system, while reducing the amount of movement of the second lens group is a primary variable power group, the objective lens The focal length of the system has been increased. Since the amount of movement of the second lens group is small, the overall length can be shortened. In the second method, the focal length _fe of the eyepiece system is reduced, and thus the magnification of the entire finder system is increased.

However, if the focal length of the eyepiece lens system is simply reduced, the distance between the image plane of the objective lens system and the eyepiece lens system is reduced. Can not be secured. Therefore, the following means is used to secure a space for disposing the reflection means. In other words, if the principal point position of the eyepiece lens system is arranged closer to the object side, the principal point position will increase the space from the image by the objective lens system to the eyepiece lens system more than the lens inside or near the eyepiece lens system. You can take large. Therefore, in order to place a principal point more to the object side, the eyepiece system, in order from the object side, by constituting the positive lens L ₄ and the negative lens L _5, and a space to place the reflecting means ing. In the present invention, the negative lens L ₆ of the eyepiece system is constituted by a meniscus lens having a convex surface facing the object side, and f _123W : a low magnification end from the first lens unit to the third lens unit of the objective lens system. composite focal length at f _e: the focal point of the eyepiece system distance f _3: the focal length of the third lens group of the objective lens system f _5: focal length of the positive lens L ₅ of the eyepiece lens system f _12W: the objective lens system the The combined focal length of the first lens group and the second lens group at the low magnification end, f _12T : the combined focal length of the first lens group and the second lens group of the objective lens system at the high magnification end. _{55 <f 123W / f e <} 1 (1) -6 <f 3 × f 5 / (f 12W × f 12T) <- preferably satisfies 3 (2) the condition.

That is, while moving the principal point to the object side,
To ensure a sufficient distance from the final lens surface of the eyepiece lens system to the eye, that is, the eye relief, the negative lens L ₅
Is desirably a meniscus shape with the convex surface facing the object side. That is, even if the positive lens and the negative lens have the same refractive power, the combined principal point position changes depending on the shape. For meniscus shape of the negative lens L ₅ is a convex surface facing the object side, the principal point is present on the eye point side, as compared to the negative lens in the main point position is in the center and the object side of the negative lens, Easy eye relief.

Further, in order to obtain an appropriate loupe magnification,
It is desirable to be within the range of conditional expression (1). If the focal length of the eyepiece system is increased beyond the lower limit of the conditional expression (1), the effect of increasing the loupe magnification as described above is diminished. On the other hand, when the value exceeds the upper limit of the conditional expression (1), the focal length of the eyepiece system becomes small, so that it becomes difficult to correct the coma.

In order to more effectively increase the finder magnification, it is desirable that the ratio is within the range of conditional expression (2). The third lens group and the fourth lens group of the objective lens system are combined to have a function as a so-called rear converter that changes the focal length of the zoom objective unit formed by the first lens group and the second lens group. . Therefore, beyond the lower limit of condition (2), the focal length f ₃ of the third lens group becomes large, the smaller the role as rear converter, which is not preferable. Conversely, exceeding the upper limit of the conditional expression (2), the focal length f ₅ of the positive lens L ₅ of the eyepiece lens system is exceeded.
Is too small, a negative lens L is required to secure a space for inserting a reflection unit for reflecting a required light beam.
The refractive power of No. ₆ must be increased, and it is difficult to correct coma aberration, which is not preferable.

In the case of a finder having a zoom ratio of 2 or more,
It is common to obtain a good aberration by using a plurality of lenses for the second lens group which is the main zooming group. However, a multiple-sheet configuration is not preferable because the structure becomes complicated and the size becomes large. If the zoom ratio is less than 2, excellent spherical aberration and coma can be obtained even when the second lens group is constituted by a single lens using an aspherical surface only on one surface.

Therefore, in a negative / positive / negative Keplerian finder having a zoom ratio of 2 times or more, when the second lens group is constituted by a single lens having an aspherical surface only on one surface, the following results are obtained. Was done. That is, when spherical aberration is made equal to the case where the second lens group is composed of a plurality of lenses, in a finder using an aspheric surface only for the object side lens surface, coma aberration becomes an outer coma and the eye point side lens surface In viewfinders using only aspherical surfaces, coma tends to be inner coma,
No favorable aberration was obtained in any case.

Therefore, the second lens group, which is the main zooming group, is constituted by a single lens having aspherical surfaces on both sides. As a result of repeated studies, both the object side lens surface and the eye point side lens surface are moved away from the optical axis. As the curvature of the aspheric surface decreases, the sum of the two aspheric surfaces is kept almost constant, and the distribution of the two aspheric surfaces is adjusted to an appropriate ratio. It has been found that coma aberrations canceling out, and spherical aberration and coma aberration can be satisfactorily corrected. Therefore, the second lens group is constituted by a single lens, in order to obtain a large zoom ratio, it is preferable that the both surfaces of the positive lens L ₂ in the second lens group an aspherical surface.

The correction of coma depends greatly on the aspherical shape of the positive lens L ₂ in the second lens unit. To obtain good coma, both aspherical surfaces of the positive lens L ₂ are required. It is preferable that the shape of the lens surface satisfies the following conditional expression: 0.2 <| S ₂ / S ₁ | <0.4 (3) Here, S _1: In the aspheric lens surface of the positive lens L ₂ on the object side, the optical axis y = | optical axis direction defined by the following equation at a height (a) | 0.25 × r ₃ S ₂ : Optical axis defined by the following equation (a) at a height of y = | 0.25 × r ₃ | from the optical axis on the aspheric lens surface on the eye point side of the positive lens L _2. Displacement in the direction r ₃ : Paraxial radius of curvature of the aspherical lens surface on the object side of the positive lens L ₂ .

At this time, the shape of the aspherical lens surface is such that the height in the direction perpendicular to the optical axis is y, the amount of displacement of the aspherical surface in the optical axis direction at the height y is S (y), and the reference radius of curvature is R. , The cone coefficient is κ, and the nth order aspherical coefficient is C _n , And the paraxial radius of curvature r is defined as r = 1 / (2C ₂ -1 / R) ‥‥ (b).

If the upper limit of conditional expression (3) is exceeded, the amount of aspherical surface of the lens surface on the eye point side is too large, and the frame becomes an inner frame, which causes flare. Conversely, conditional expression (3)
If the lower limit is exceeded, the aspherical amount of the object-side lens surface increases, resulting in an outer coma, which also makes it impossible to obtain good coma.

In the case of the objective lens system having at least three lens units that move the second lens unit as the main zooming unit as described above, the zooming method for changing the focal length includes:
The following two types are conceivable. The first is the third objective lens system.
In this method, the lens unit is fixed during zooming, and zooming is performed by moving the first lens unit and the second lens unit in the optical axis direction. The second method is a method in which the first lens group of the objective lens system is fixed during zooming, and zooming is performed by moving the second lens group and the third lens group in the optical axis direction.
In the method in which the first and second lens groups are moved, it is possible to suppress the fluctuation of the pupil position and the fluctuation of the astigmatism. Second and third
In the method of moving the lens groups, the same effect as the method of moving the first and second lens groups can be obtained, and since the first lens group can be fixed, the object point of the second lens group is fixed. With benefits.

In the present invention, β _34W is a composite magnification of the third lens unit and the fourth lens unit at the low magnification end, and r _{1 is a} radius of curvature of the object side lens surface of the negative lens L ₁ of the first lens unit. r ₂ : when the paraxial radius of curvature of the lens surface on the eye point side of the negative lens L ₁ of the first lens unit is 1 <β _34W <1.4 (4) −0.4 <(r ₁ + r ₂ ) / (R ₁ −r ₂ ) <0.2 (5) It is preferable to satisfy the following conditional expression.

That is, in order to achieve a reduction in the size of the entire objective lens system, it is desirable that the magnification of the combination of the third lens unit and the fourth lens unit is 1 or more. However, it goes without saying that there is a limit to increasing the magnification. If the magnification is increased, the focal lengths of the first lens group and the second lens group must also be shortened. However, since the required exit pupil diameter must be secured,
The combined aperture ratio between the lens group and the second lens group increases. Therefore, it becomes difficult to correct various aberrations, especially spherical aberration. Therefore, it is desirable that the magnification be within the range of conditional expression (4), and it is desirable that the magnification be within the range of conditional expression (5) for spherical aberration correction.

If the lower limit of conditional expression (4) is exceeded, the effect of the third lens unit will be weakened, and the effect of the rear converter as described above will not be utilized. Conversely, if the upper limit of conditional expression (4) is exceeded, it will be difficult to correct the aberrations in the first and second lens units in order to enlarge them, and it will be difficult to configure each lens unit with a simple lens configuration. Therefore, the size of the objective lens system is rather increased.

Conditional expression (5) relates to not only spherical aberration but also distortion. If the upper limit of conditional expression (5) is exceeded, the radius of curvature of the object-side lens surface of the negative lens L1 of the _first lens unit becomes large, and has a large deflection angle with respect to the land light beam, so that it is difficult to correct spherical aberration. Becomes Conversely, if the lower limit of conditional expression (5) is exceeded, the radius of curvature of the object-side lens surface is small, and the deflection angle with respect to the off-axis light beam becomes large, making it difficult to correct distortion.

Under such a configuration of the present invention,
In order to actually constitute a finder, the finder image must be naturally erected. As a method of erecting, a method using a relay lens and a method using a reflection unit are known. Among them, the method using a relay lens makes it difficult to achieve both miniaturization of the entire viewfinder and correction of aberrations, and generally an increase in the number of constituent optical systems is unavoidable. Therefore, in the case of the present invention aiming at miniaturization of the finder, it is desirable to use a reflecting means.

That is, in the present invention, it is preferable that a reflecting means is provided in the air gap between the third lens unit and the fourth lens unit of the objective lens system. This is because, in order for the third lens group and the fourth lens group to have the effect as a rear converter as described above, it is desirable to arrange both lens groups with a wide air gap therebetween. This is because the overall length can be shortened by the arrangement and the reflection at the objective lens system.

In the present invention, it is preferable that another reflecting means is provided between the image formed by the objective lens system and the eyepiece system. That is, three reflecting surfaces are arranged on the eye point side of the image formed by the objective lens system. That requires only three reflecting surfaces from the image to the positive lens L ₅ of the eyepiece system according to the objective lens system is made to the fact that the optical path length from the image to the positive lens L ₅ is short, the focal length f of the eyepiece system _{Since e} can be further reduced, the loupe magnification is increased, which is preferable. Therefore, it is possible to obtain a small finder that is relatively inexpensive, bright, and has a high magnification.
Furthermore, the eyepiece system, in order to obtain a symmetrical coma aberration, it is desirable that the aspherical surface is present one face to the positive lens L ₅ of the eyepiece system.

[0025]

Embodiments of the present invention will be described below. FIGS. 1, 5, 9, and 13 are developed views showing the lens configuration of the first to fourth embodiments of the present invention in the minimum magnification state, the intermediate magnification state, and the maximum magnification state, respectively. In each of the Keplerian variable magnification finder of each embodiment, the objective lens system has a positive refractive power as a whole, and includes first to fourth lens groups in order from the object side. The first lens group is a negative lens L _1, second lens group is a positive lens L ₂ of the bi-aspherical, the third lens group is composed of the negative lens L _3, the fourth lens group is a positive lens It is composed of L _4.
A negative lens L ₃ of the third lens group in the air gap of the positive lens L ₄ in the fourth lens group, the mirror M ₁ is placed as the first reflection surface. In the vicinity of the image plane of the objective lens system, a glass plate A used for displaying a field frame or the like is arranged.

[0026] eyepoint EP side than the image by the objective lens system, second, third and has a fourth reflection surface is disposed in, of which the second reflecting surface is composed by a mirror M ₂ , The third and fourth reflecting surfaces H ₃ and H ₄ are prism P
It is constituted by. The eye point EP side of the prism P, a positive lens L ₅ which object-side lens surface is aspherical, the negative meniscus lens having a convex surface directed toward the object side L ₆
Are arranged in that order. Each positive lens L ₂ , L ₄ , L ₅
Is made of acrylic resin, and each negative lens L ₁ , L ₃ , L ₆
Is made of polycarbonate resin. The prisms P of the first and second embodiments are made of polyolefin resin, and the prisms P of the third and fourth embodiments are made of polyolefin resin.
Is made of MAS resin. In the viewfinders of the first embodiment and the fourth embodiment, the magnification is changed by fixing the first lens group and moving the second lens group and the third lens group in the optical axis direction. In the viewfinders of the example and the third embodiment, zooming is performed by fixing the third lens group and moving the first lens group and the second lens group in the optical axis direction.

Tables 1 to 4 show the first to fourth data, respectively.
The specifications of the embodiment will be described. In [Overall Specifications] of each table, m is a magnification, X is a diopter, 2ω is an angle of view, EP is an eye relief (distance from the last lens surface to the eye point EP), and 2H ′ is a pupil diameter. In [Lens Specifications], the first column No is the number of each lens surface from the object side, the second column r is the radius of curvature of each lens surface, the third column d is the distance between each lens surface, and the fourth column ν Is the Abbe number of each lens, the fifth column n is the refractive index of each lens with respect to d-line (λ = 587.6 nm), and the sixth column is the number of each lens. In the first column, an asterisk (*) represents an aspherical surface, and r of the aspherical lens surface represents a vertex radius of curvature. During [Aspherical Data], aspherical coefficients C _n not indicated are all zero. Table 5 below shows various values related to the conditional expressions (1) to (5) for each example.

[0028]

[Table 1] [Overall specifications] m = 0.504 to 1.259 X = -1.00D 2ω = 55 ° to 20.2 ° EP = 12.0 2H ′ = 4.0 [Lens specifications] rdν n 1 -13.9013 1.0000 30.24 1.585180 L _{1 2 * 13.4056 (D 1) 3} * 8.7832 2.8000 57.57 1.491080 L 2 4 * -8.4943 (D 2) 5 -25.5385 1.0000 30.24 1.585180 L 3 6 25.2715 (D 3) 7 * 12.5173 3.0000 57.57 1.491080 L 4 8 -35.8950 6.9780 9 ∞ 1.0000 58.80 1.522160 A10 ∞ 7.8000 11 ∞ 18.6000 50.97 1.525000 P12 ∞ 0.1000 13 * 22.0718 4.0000 57.57 1.491080 L ₅ 14 -18.9403 0.5000 15 8.2403 2.9000 30.24 1.585180 L ₆ 16 6.8958 12.0000 17 Eye point [Aspherical data] No = 2 κ = -0.6022 C ₂ = 0 C ₄ = 1.17980 × 10 ^-4 C ₆ = -7.23700 × 10 ^-5 C ₈ = 8.59290 × 10 ^-6 C ₁₀ = -3.50840 × 10 ^-7 No = 3 κ = -2.1621 C ₂ = 0 C ₄ = 4.49670 × 10 ^-5 C ₆ = -2.71840 × 10 ^-6 C ₈ = -7.75240 × 10 ^-7 C ₁₀ = -6.19640 × 10 ^-8 C ₁₂ = -0.23853 × 10 ^-8 C ₁₄ = 0.38816 × 10 ^-9 C ₁₆ = -0.4 1806 × 10 ^-11 No = 4 κ = 0.6167 C ₂ = 0 C ₄ = 6.46 980 × 10 ^-6 C ₆ = 3.61470 × 10 ^-5 C ₈ = -4.47530 × 10 ^-6 C ₁₀ = 1.03840 × 10 ^-7 No = 7 κ = -2.5000 C ₂ = 0 No = 13 κ = -5.8607 C ₂ = 0 C ₄ = 8.81390 × 10 ^-6 C ₆ = -4.32 120 × 10 ^-7 C ₈ = 1.79050 × 10 ^-9 C ₁₀ = 1.15690 × 10 ^-11 [variable Distances] ratio _{0.504 0.796 1.259 D 1 11.15878 6.18140 2.3452} D 2 1.27227 3.89338 10.0798 D 3 14.30072 16.65700 14.30673

[0029]

[Table 2] [Overall specifications] m = 0.503 to 1.259 X = -1.00D 2ω = 55 ° to 20.2 ° EP = 12.0 2H ′ = 4.0 [Lens specifications] rdν n 1 -13.9013 1.0000 30.24 1.585180 L _{1 2 * 13.4056 (D 1) 3} * 8.7832 2.8000 57.57 1.491080 L 2 4 * -8.4943 (D 2) 5 -25.5385 1.0000 30.24 1.585180 L 3 6 25.2715 14.3007 7 * 12.5173 3.0000 57.57 1.491080 L 4 8 -35.8950 6.9779 9 ∞ 1.0000 58.80 1.522160 A 10 ∞ 7.8000 11 ∞ 18.6000 50.97 1.525000 P 12 ∞ 0.1000 13 * 16.9184 4.0000 57.57 1.491080 L ₅ 14 -21.0490 0.5000 15 10.0000 2.9000 30.24 1.585180 L ₆ 16 8.0 118 12.0000 17 Eye point [Aspherical data] No = 2 κ =- 0.6022 C ₂ = 0 C ₄ = 1.17980 × 10 ^-4 C ₆ = -7.23700 × 10 ^-5 C ₈ = 8.59290 × 10 ^-6 C ₁₀ = -3.50840 × 10 ^-7 No = 3 κ = -2.1621 C ₂ = 0 C ₄ = 4.49670 × 10 ^-5 C ₆ = -2.71840 × 10 ^-6 C ₈ = -7.75240 × 10 ^-7 C ₁₀ = -6.19640 × 10 ^-8 C ₁₂ = -0.23853 × 10 ^-8 C ₁₄ = 0.38816 × 10 ^-9 C ₁₆ = -0.41806 × 10 ^-11 No = 4 κ = 0.6167 C ₂ = 0 C ₄ = 6.46 980 × 10 ^-6 C ₆ = 3.61470 × 10 ^-5 C ₈ = -4.47530 × 10 ^-6 C ₁₀ = 1.03840 × 10 ^-7 No = 7 κ = -2.5000 C ₂ = 0 No = 13 κ = -5.0907 C ₂ = 0 C ₄ = 6.88710 × 10 ^-5 C ₆ = 1.64040 × 10 ^-7 C ₈ = -4.16930 × 10 ^-8 C ₁₀ = 6.57230 × 10 ^-10 [variable interval ratio _{0.503 0.796 1.259 D 1 11.15878 5.75949 2.34452} D 2 1.27227 4.68552 10.08259

[0030]

[Table 3] [General Data] m = 0.508~0.893 X = -1.00D 2ω = 54.7 ° ~29.0 ° EP = 12.0 2H '= 8.0 r d ν n 1 -10.2693 1.0000 30.24 1.585180 L 1 2 * 17.7496 (D _{1) 3 * 7.9334 3.4650 57.57 1.491080} L 2 4 * -7.2651 (D 2) 5 17.6678 1.0000 30.24 1.585180 L 3 6 9.2991 12.6785 7 * 10.4096 3.0000 57.57 1.491080 L 4 8 -21.4859 1.1359 9 ∞ 1.0000 58.80 1.522160 A 10 ∞ 7.8000 11 ∞ 18.6000 33.59 1.571100 P 12 ∞ 0.1000 13 * 10.7899 3.6000 57.57 1.491080 L 5 14 -23.4729 0.5000 15 12.0000 1.9000 30.24 1.585180 L 6 16 7.8978 12.0000 15 eyepoint [aspherical data] No = 2 κ = -12.3843 C 2 = 0 C ₄ = -2.77320 × 10 ^-5 C ₆ = 1.78890 × 10 ^-5 C ₈ = -2.99910 × 10 ^-6 C ₁₀ = 1.87590 × 10 ^-7 No = 3 κ = -5.8798 C ₂ = 0 C ₄ = 2.35 140 × 10 ^-4 C ₆ = 1.86890 × 10 ^-4 C ₈ = -5.64460 × 10 ^-5 C ₁₀ = 7.20110 × 10 ^-6 C ₁₂ = -0.40422 × 10 ^-6 C ₁₄ = -0.19716 × 10 ^-8 C ₁₆ = 0.82776 × 10 ^-9 No = 4 κ _{3.8100 C 2 = 0 C 4 =} 9.82700 × 10 -4 C 6 = 1.54570 × 10 -4 C 8 = -1.62210 × 10 -5 C 10 = 1.10500 × 10 -6 No = 7 κ = -2.5000 C 2 = 0 No = 13 κ = -1.2349 C ₂ = 0 C ₄ = 6.00690 × 10 ^-5 C ₆ = 6.23930 × 10 ^-7 C ₈ = -5.73290 × 10 ^-8 C ₁₀ = 8.28450 × 10 ^-10 [Variable interval] Magnification 0.508 0.684 0.893 D ₁ 6.87908 4.00615 2.05170 D ₂ 1.13450 3.27814 5.83971

[0031]

[Table 4] [General Data] m = 0.508~0.893 X = -1.00D 2ω = 54.7 ° ~28.9 ° EP = 12.0 2H '= 8.0 r d ν n 1 -10.2693 1.0000 30.24 1.585180 L 1 2 * 17.7496 (D _{1) 3 * 7.9334 3.4650 57.57 1.491080} L 2 4 -7.2651 (D 2) 5 17.6678 1.0000 30.24 1.585180 L 3 6 9.2991 (D 3) 7 * 10.4096 3.0000 57.57 1.491080 L 4 8 -21.4860 1.1359 9 ∞ 1.0000 58.80 1.522160 A 10 ∞ 7.8000 11 ∞ 18.6000 33.59 1.571100 P 12 ∞ 0.1000 13 * 12.3906 3.6000 57.57 1.491080 L ₅ 14 -23.2020 0.5000 15 11.0000 2.3000 30.24 1.585 180 L ₆ 16 7.8978 12.0000 15 Eye point [Aspherical data] No = 2 κ = -12.3843 C ₂ = 0 C ₄ = -2.77320 × 10 ^-5 C ₆ = 1.78890 × 10 ^-5 C ₈ = -2.99910 × 10 ^-6 C ₁₀ = 1.87590 × 10 ^-7 No = 3 κ = -5.8798 C ₂ = 0 C ₄ = 2.35140 × 10 ^-4 C ₆ = 1.86890 × 10 ^-4 C ₈ = -5.64460 × 10 ^-5 C ₁₀ = 7.20110 × 10 ^-6 C ₁₂ = -0.40422 × 10 ^-6 C ₁₄ = -0.19716 × 10 ^-8 C ₁₆ = 0.82776 × 10 ^-9 No = 4 κ _{= 3.8100 C 2 = 0 C 4} = 9.82700 × 10 -4 C 6 = 1.54570 × 10 -4 C 8 = -1.62210 × 10 -5 C 10 = 1.10500 × 10 -06 No = 7 κ = -2.5000 C 2 = 0 No = 13 κ = -1.4940 C ₂ = 0 C ₄ = 3.86830 × 10 ^-5 C ₆ = 7.83290 × 10 ^-7 C ₈ = -5.15100 × 10 ^-8 C ₁₀ = 7.13470 × 10 ^-10 [Variable interval] Magnification 0.508 _{0.684 0.893 D 1 6.87908 4.22846 2.08685 D} 2 1.13449 2.43070 5.64693 D 3 12.67853 14.03294 12.95832

[0032]

Table 5 Example No. 1 2 3 4 (1) f _123W / _fe 0.898 0.898 0.613 0.613 f _123W 17.519 17.519 11.826 11.826 _fe 19.5 19.5 19.3 19.3 (2) f ₃ × f ₅ / (f _12W × f _{12T ) -3.492 -3.236 -4.663 -5.117 f 3 -21.55} -21.55 -35.097 -35.097 f 5 21.446 19.786 15.592 17.015 f 12W 7.276 7.276 8.174 8.174 f 12T 18.187 18.11 14.357 14.278 (3) | S 2 / S 1 | 0.306 0.306 0.262 0.262 S ₁ -0.014 -0.014 -0.017 -0.017 S ₂ 0.004 0.004 0.004 0.004 (4) β _34W 1.347 1.347 1.198 1.198 (5) (r ₁ + r ₂ ) / (r ₁ -r ₂ ) 0.018 0.018 -0.267 -0.267 r ₁ -13.901 -13.901 -10.269 -10.269 r ₂ 13.406 13.406 17.750 17.750

FIGS. 2, 3 and 4 show the spherical aberration, astigmatism, distortion, lateral aberration and lateral chromatic aberration of the first embodiment in the minimum magnification state, the intermediate magnification state and the maximum magnification state, respectively. 6 to 8, 10 to 12, and 14 to 1
FIG. 6 shows various aberration diagrams of the second, third, and fourth examples, respectively. In each aberration diagram, H indicates an incident height, and ω indicates a half angle of view. In the astigmatism diagram, a solid line indicates a sagittal image plane, and a dotted line indicates a meridional image plane. As is clear from the aberration diagrams, it is understood that each of the examples has a required lens configuration and satisfies the respective conditional expressions, thereby having excellent imaging performance.

[0034]

As described above, according to the present invention, a Kepler type finder having a small negative / positive / negative configuration having a large zoom ratio, a good aberration, and a finder magnification of 0.5 times or more. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a developed view showing a configuration of a first embodiment.

FIG. 2 is an aberration diagram of the first embodiment in a minimum magnification state.

FIG. 3 is an aberration diagram of the first embodiment in an intermediate magnification state.

FIG. 4 is an aberration diagram of the first embodiment in a maximum magnification state.

FIG. 5 is a development view showing the configuration of the second embodiment, in which the reflection surface is omitted.

FIG. 6 is an aberration diagram in the lowest magnification state of the second embodiment.

FIG. 7 is an aberration diagram of the second embodiment in an intermediate magnification state.

FIG. 8 is an aberration diagram of the second embodiment in a maximum magnification state.

FIG. 9 is a developed view showing the configuration of the third embodiment, in which the reflecting surface is omitted.

FIG. 10 is an aberration diagram of the third embodiment in the lowest magnification state.

FIG. 11 is an aberration diagram of the third embodiment in an intermediate magnification state.

FIG. 12 is an aberration diagram of the third embodiment in a maximum magnification state.

FIG. 13 is a development view showing the configuration of the fourth embodiment, in which the reflection surface is omitted.

FIG. 14 is an aberration diagram of the fourth embodiment in the lowest magnification state.

FIG. 15 is an aberration diagram of the fourth embodiment in an intermediate magnification state.

FIG. 16 is an aberration diagram of the fourth embodiment in a maximum magnification state.

[Explanation of symbols]

L ₁ … the negative lens in the first lens group L ₂ … the positive lens in the second lens group L ₃ … the negative lens in the third lens group L ₄ … the positive lens in the fourth lens group L ₅ … the positive lens in the eyepiece system L ₆ … the eyepiece lens negative lens in system A ... glass plate M _1, M ₂ ... mirror H _3, H ₄ ... reflective surface P ... prism EP ... eyepoint

Claims (6)

[Claims] _{1. A first} lens including a negative lens L1 in order from the object side.
A lens group, a fourth comprising a second lens group including a positive lens L _2, a third lens group including a negative lens L _3, the positive lens L ₄
A Kepler-type variable magnification having an objective lens system having a lens and having an overall positive refractive power, and an eyepiece system having an overall positive refractive power and observing an image formed by the objective lens system. in the viewfinder, by moving at least the second lens group of the objective lens system in the optical axis direction, changing the magnification of the finder, in that the eyepiece system was composed of a positive lens L ₅ and the negative lens L ₆ Characterized Kepler type zoom finder. 2. The Kepler-type zoom finder according to claim 1, wherein said negative lens L ₆ of said eyepiece system is constituted by a meniscus lens having a convex surface facing the object side, and satisfies the following conditional expression. . _{0.55 <f 123W / f e <} 1 (1) -6 <f 3 × f 5 / (f 12W × f 12T) <- 3 (2) where, f _123W: said first lens group of the objective system composite focal length at low magnification end up to the third lens group from f _e: the eyepiece focal length f ₃ of the focal length of the third lens group of the objective lens system f _5: the positive lens of the eyepiece system the focal length f _12W of L _5: composite focal length at low magnification end of the objective lens system the first lens group and the second lens group f _12T: said first lens group of the objective system and the second lens group Is the composite focal length at the high magnification end. Wherein the second lens group of the objective lens system is composed of only the positive lens L _2, both lens surfaces of the positive lens L ₂ is formed in an aspherical shape, and that satisfies the following condition The Kepler-type variable magnification finder according to claim 1, wherein: 0.2 <| S ₂ / S ₁ | <0.4 (3) where y is the height in the direction perpendicular to the optical axis, and S (y) is the amount of displacement of the aspheric surface at the height y in the optical axis direction. The paraxial radius of curvature is r,
Assuming that the conic coefficient is κ and the nth order aspheric coefficient is C _n , The R = 1 / (1 / r -2C 2) becomes equation, when expressed the shape of each aspherical lens surface of the positive lens L _2, S _1: aspheric lens surface on the object side of the positive lens L ₂ S (y) at a height of y = | 0.25 × r ₃ |
Value S _2: the y = with respect to the aspherical lens surface of the positive lens L ₂ of the eye point side | 0.25 × r ₃ | above at a height S (y) value r _3: the positive lens L ₂ This is the paraxial radius of curvature of the aspheric lens surface on the object side. 4. The zooming from a low magnification end to a high magnification end by fixing the third lens group of the objective lens system and moving the first lens group and the second lens group in the optical axis direction. 4. The Keplerian type variable magnification finder according to claim 1, wherein the finder is performed. 5. The variable magnification from the low magnification end to the high magnification end by fixing the first lens group of the objective lens system and moving the second lens group and the third lens group in the optical axis direction. 4. The Keplerian type variable magnification finder according to claim 1, wherein the finder is performed. 6. An object lens system further comprising a reflecting means in an air gap between the third lens group and the fourth lens group, and another reflecting means provided between an image formed by the objective lens system and the eyepiece system. The Keplerian variable magnification finder according to claim 1, wherein the Kepler-type variable magnification finder has the following conditional expression. 1 <β _34W <1.4 (4) −0.4 <(r ₁ + r ₂ ) / (r ₁ −r ₂ ) <0.2 (5) where β _{34W is} the third lens of the objective lens system. Group and fourth
Composite magnification at the low magnification end with the lens group r ₁ : radius of curvature of the object side lens surface of the negative lens L ₁ of the first lens group of the objective lens system r ₂ : negative of the first lens group of the objective lens system it is a paraxial radius of curvature of the eye point side lens surface of the lens L _1.