JPH1078547A - Keplerian variable power finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a keplerian variable power finder having twice and more zooming ratio, simple constitution and well conpensated aberrations by fixing a first lens group of an objective lens system, moving a second and a third lenses to the object side while expanding the air gap between them and changing the focal distance. SOLUTION: An objective lens system has a positve refractive power as a whole and is composed of a first to a fourth lens groups in order from the object side. The first lens group, the second lens group, the third lens group and the fourth lens group are composed of a negative lens L1 , a positive lens L2 , a negative lens L2 , a positive lens L4 , respectively. A mirror as a first reflection surface H1 is arranged in the air gap between the negative lens L3 of the third lens group and the positive lens L4 of the fourth lens group By fixing the first lens group, moving the second lens group together with the third lens group to the object side while expanding the air gap between them, power variation from a low power end to the high power end is performed.

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, the zoom ratio of a lens shutter camera has tended to increase, and accordingly, the zoom ratio of a finder has also increased. Therefore, a small viewfinder with a large zoom ratio
Has been requested. However, in the proposal of JP-A-3-233420 and the like, although each group is composed of one sheet and various aberrations are satisfactorily corrected while being small, their zoom ratio is at most about two times. It is hard to say that it has a sufficiently large zoom ratio. Further, in JP-A-6-242377 having a zoom ratio of 2 or more, there is no one in which each group is constituted by one lens.
It is composed of a plurality of lenses, which inevitably increases the cost. The present invention has been made in view of the above problems, and has a zoom ratio of 2 times or more, and is a low-cost Kepler-type variable magnification in which various aberrations are favorably corrected while having a simple configuration. The task is to provide a finder.

[0004]

SUMMARY OF to the invention therefore, in order from the object side, a first lens group including a negative single lens L _1, a second lens group including a positive single lens L _2, a negative and a third lens group including a single lens L ₃ of having an objective lens system having a positive refractive power as a whole, a positive refractive power as a whole,
In a Keplerian type variable magnification finder having an eyepiece system for observing an image by the objective lens system, the first lens group is fixed and the second lens is fixed when changing magnification from a low magnification end to a high magnification end. The object has been achieved by moving both the second lens unit and the third lens unit toward the object side while increasing the air gap between the group and the third lens unit. As described above, in the finder according to the present invention, the first lens group of the objective lens system is fixed, and the air gap between the second lens group and the third lens group is increased.
By moving both the second lens unit and the third lens unit toward the object side, a zoom objective unit that changes the focal length is formed.

In the case of a finder having a zoom ratio of 2 or more,
It is common to use a plurality of lenses in the zooming group to obtain good aberration. 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 main zooming unit is formed of a single lens. Therefore, in a negative / positive / negative Kepler type finder having a zoom ratio of 2 times or more, while each group is constituted by a single lens, the air between the second lens group and the third lens group is obtained in order to obtain good aberrations. distance D ₂₃ is, upon zooming from low magnification end to high magnification end, and configured to increase. That is, the combined magnification β ₂₃ of the second lens unit and the third lens unit at the high magnification end is about 1 when the air gap D ₂₃ is reduced upon zooming from the low magnification end to the high magnification end. whereas it is approximately doubled if the air space D ₂₃ is increased, the resultant magnification beta ₂₃ is able ensure more than twice. That is, the second
Since the magnification after the lens group is large, the power of the first lens group can be increased, which is suitable for miniaturization, and the moving amount of the second lens group is reduced to obtain a required zoom ratio. Can be.

For example, if the third lens group is formed so as to move to the object side up to the intermediate magnification, and to move to the eye point side from the intermediate magnification to the high magnification end, the magnification of the third lens group is increased up to the intermediate magnification. Increases, but thereafter the magnification of the third lens group decreases. In other words, the reduction effect works where a large zoom ratio is required. At this time, in order to secure a required zoom ratio, it is necessary to increase the amount of movement of the second lens group, which results in an increase in size. If the power of the second lens group is increased in order to reduce the movement amount, fluctuations of various aberrations increase, which is not preferable.

Therefore, in the present invention, since the magnification of the third lens group always increases, D _12W : the apex distance between the first lens group and the second lens group at the low magnification end D _23W : the second lens group A vertex distance between the first lens group and the third lens group at a low magnification end D _12T : a vertex distance between the first lens group and the second lens group at a high magnification end D _23T : a height between the second lens group and the third lens group It is preferable that the following conditional expression is satisfied: 1.5 <( _D12W + _D23W ) / ( _D12T + _D23T ) <3.0 (1)

If the lower limit of conditional expression (1) is exceeded, the magnification of the third lens unit at the high magnification end becomes smaller than the magnification at the intermediate magnification, so that the amount of movement of the second lens unit is increased as described above. Inevitably, the overall length is longer, which is against miniaturization.
Conversely, if the upper limit of conditional expression (1) is exceeded, the position of the principal ray passing through the first lens unit at the low magnification end is further away from the optical axis, so that the diameter of the first lens unit increases and the size of the lens increases. Is inevitable.

[0009] In the present invention, in order the air gap D ₂₃ between the second lens group and the third lens group, to increase at high magnification end, f _2: the focal point of the second lens group distances f _3: 3 Assuming that the focal length of the lens unit is: 2.3 <| f ₃ / f ₂ | <3 (2) It is preferable to satisfy the following conditional expression. Above the upper limit of condition (2), to move in the direction of the air gap D ₂₃ is reduced at high magnification end, small synthetic magnification beta ₂₃ between the second lens group and the third lens group at high magnification end . In addition, since the power of the second lens unit, which is the main zooming unit, is increased, fluctuations of various aberrations are increased, and it becomes difficult to obtain good aberrations. On the other hand, when the lower limit of conditional expression (2) is exceeded, the power of the second lens unit, which is the main zooming unit, becomes small, so that the amount of movement of the second lens unit must be increased, which is contrary to miniaturization. .

At this time, the second lens group is replaced by a single lens L ₂
In constructed, and in order to satisfactorily correct the coma aberration in the spherical aberration and the low magnification end in the high magnification end, to form a positive least one of the lens surfaces of the single lens L ₂ of the second lens group aspherical Is preferred.

Further, in the present invention, the objective lens system includes:
It is preferable that a fourth lens group having a positive refractive power be provided on the eye point side of the third lens group. With this configuration,
The third lens group and the fourth lens group are combined to function as a so-called rear converter for changing the focal length of the zoom objective section formed by the first lens group and the second lens group, and to perform correction by the zoom objective section. It has both the function of correcting the aberrations that cannot be corrected, particularly the distortion, and the function of a field lens for guiding the incident light beam of the finder to an appropriate eye point position.

At this time, in order to achieve a reduction in the size of the _entire system including the fourth lens unit, β _234T : the composite magnification of the second, third and fourth lens _units at the high magnification end; Then, it is preferable to satisfy the following conditional expression: -2.2 <β _234T <−1.2 (3) If the upper limit of conditional expression (3) is exceeded, in order to obtain a large angle of view at the low magnification end, the focal length of the first lens unit must be reduced, and spherical aberration at the high magnification end must be corrected. Becomes difficult. On the other hand, if the lower limit of conditional expression (3) is exceeded, the magnification at the high magnification end is small. Therefore, in order to obtain a large finder magnification, the focal length of the first lens unit must be increased, and the overall length becomes large. turn into.

In order to actually form a finder with such a configuration of the present invention, the finder image must be naturally erected. As a method of erecting,
A device using a relay lens and a device using a reflection unit are known. Among them, the method using a relay lens makes it difficult to achieve both the miniaturization of the entire viewfinder and the correction of aberrations, and inevitably increases the number of components of the optical system.
Therefore, in the case of the present invention aiming at miniaturization of the finder, it is desirable to use a reflecting means.

Therefore, in the present invention, the objective lens system has a fourth lens group having a positive refractive power on the eye point side of the third lens group, and an air gap between the third lens group and the fourth lens group. Has reflecting means, and the eyepiece system,
It is preferable to have at least one reflecting means for reflecting a light beam from the objective lens system and at least one positive lens having an aspherical object-side lens surface. First, as for the reflecting means disposed in the objective lens system, the third lens group and the fourth lens group must have a wide air space in order for the third lens group and the fourth lens group to have the function as the rear converter as described above. Since the combined magnification of the third lens group and the fourth lens group is desirably 1 or more at an interval, the reflection means can be arranged without difficulty.
Moreover, the total length can be shortened by reflection at the objective lens system. The following three reflective surfaces are
It is arranged on the eye point side of the image by the objective lens system, that is, in the eyepiece lens system. That from the image by the object lens system requires only the reflecting surface of the eyepiece system positive lens L ₅ to 3 times, will be referred to as a short optical path length from the image to the eyepiece system positive lens L _5, eyepiece system positive lens L
_Since the refractive power of ₅ can be increased, the loupe magnification can be increased. 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 eyepiece system positive lens L _5.

[0015]

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 composed of a lens L ₁ having a negative refractive power, the second lens group is composed of a lens L ₂ having a positive refractive power, a third lens group lens L ₃ having a negative refractive power in the configuration, the fourth lens unit includes a lens L ₄ having a positive refractive power. 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 first mirror as a reflecting surface H ₁ is arranged. In the vicinity of the image plane of the objective lens system, a parallel plate A of glass used for displaying a field frame or the like is arranged.

On the eye point EP side of the image formed by the objective lens system, second, third and fourth reflecting surfaces H ₂ , H ₃ and H ₄ are arranged. Of these, the second reflecting surface H ₂ is constituted by a mirror, and the third and fourth reflecting surfaces H ₃ and H ₄ are constituted by a prism P. This is the eye point EP side of the prism P, the eyepiece lens L ₅ is arranged object-side lens surface is an aspherical surface. Each of the positive lenses L ₂ , L ₄ , L ₅ and the prism P is made of an acrylic resin, and each of the negative lenses L ₁ , L ₃ is made of a polycarbonate resin. In the viewfinder of each embodiment, the first lens group is fixed, and the air gap between the second lens group and the third lens group is increased, and both the second lens group and the third lens group are on the object side. By moving, the magnification is changed from the low magnification end to the high magnification end.

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 (*) indicates an aspherical surface, and for an aspherical lens surface, r indicates a vertex radius of curvature. The shape of the aspherical surface is a shape represented by the following equation. Here, y: height from the optical axis X: distance in the optical axis direction from the tangent plane to the aspheric surface r: vertex radius of curvature κ: conical coefficient C _n : n-th order aspherical coefficient The conic coefficient κ and the aspheric coefficient C _n are shown in [Aspheric data]. During [Aspherical Data], aspherical coefficients C _n not indicated are all zero. Table 5 below shows various values associated with the conditional expressions (1) to (3) for each example.

[0019]

[Table 1] [Overall specifications] m = 0.450-1.125 X = -1.OOD 2ω = 56.5 ° -20.8 ° EP = 15.0 2H ′ = 4.0 [Lens specifications] Nord ν n 1 -15.5788 1.0000 30.24 1.585180 _{L 1 2 * 15.1272 (D 1} ) 3 * 8.9329 2.6000 57.57 1.491080 L 2 4 * -7.6236 (D 2) 5 48.4787 1.0000 30.24 1.585180 L 3 6 9.8203 (D 3) 7 * 11.8661 2.7000 57.57 1.491080 L 4 8 -28.8226 3.6941 9 ∞ 1.0000 58.80 1.522160 A 10 8.3 8.3900 11 ∞ 15.2400 33.59 1.571100 P 12 ∞ 1.0000 13 * 20.3196 3.0000 57.57 1.491080 L ₅ 14 -20.3618 15.0000 15 Eyepoint [Aspherical data] No = 2 κ = -2.8735 C ₂ = 0 C ₄ = -1.48300 × 10 ^-4 C ₆ = 2.73550 × 10 ^-5 C ₈ = -1.55920 × 10 ^-6 C ₁₀ = 2.86620 × 10 ^-8 No = 3 κ = -2.6547 C ₂ = 0 C ₄ = -4.05220 × 10 ^-4 C ₆ = -5.37000 × 10 ^-5 C ₈ = -1.28690 × 10 ^-7 C ₁₀ = -6.12470 × 10 ^-8 C ₁₂ = -0.12190 × 10 ^-7 C ₁₄ = -0.81511 × 10 ^-9 C ₁₆ ^{= 0.51698 × 10 -11 No = 4} κ = 0.6589 C 2 = 0 ^{_{4 = -1.33460 × 10 -4 C 6}} = -6.42370 × 10 -5 C 8 = 3.72580 × 10 -6 C 10 = -3.99010 × 10 -7 No = 7 κ = -2.5000 C 2 = 0 No = 13 κ = -3.3287 C ₂ = 0 [variable interval ratio _{0.450 0.636 1.125 D 1 11.98431 7.88953 2.38530} D 2 0.91953 1.50549 5.28746 D 3 14.36497 17.87379 19.59605

[0020]

[Table 2] [Overall specifications] m = 0.455-1.137 X = -1.00D 2ω = 55.1 ° -21.0 ° EP = 15.0 2H ′ = 4.0 [Lens specifications] Nord ν n 1 -26.9599 1.0000 30.24 1.585180 L ₁ 2 * 11.2349 (D ₁ ) 3 * 7.9065 2.9000 57.57 1.491080 L ₂ 4 -11.1076 (D ₂ ) 5 14.4166 1.0000 30.24 1.585 180 L ₃ 6 6.9057 (D ₃ ) 7 * 13.8863 3.0000 57.57 1.491080 L ₄ 8 -29.2272 3.8399 9 ∞ 1.0000 58.80 1.522160 A10 ∞ 8.3900 11 ∞ 15.2400 33.59 1.571100 P12 ∞ 1.0000 13 * 20.3196 3.0000 57.57 1.491080 L ₅ 14 -20.3618 15.0000 15 Eyepoint [Aspherical surface data] No = 2 κ = -0.2397 C ₂ = 0 C ₄ ＝ -3.15870 × 10 ^-6 C ₆ = -1.16350 × 10 ^-5 C ₈ = 1.71080 × 10 ^-6 C ₁₀ = -5.18390 × 10 ^-8 No = 3 κ = -1.2752 C ₂ = 0 C ₄ = -6.08760 × 10 ^-5 C ₆ = 1.61720 × 10 ^-6 C ₈ = -5.08850 × 10 ^-7 C ₁₀ = 6.49 250 × 10 ^-9 C ₁₂ = 0.20560 × 10 ^-9 C ₁₄ = 0.75033 × 10 ^-10 C ₁₆ = -0.12207 × 10 ^{-10 No = 7 κ = -2.5000 C} 2 = 0 _{o = 13 κ = -3.3287 C 2} = 0 [ Variable Interval ratio _{0.455 0.719 1.137 D 1 15.68203 9.63273 4.68338} D 2 0.40601 1.30287 4.69696 D 3 16.47599 21.62843 23.18369

[0021]

[Table 3] [Overall specifications] m = 0.450-1.350 X = -1.00D 2ω = 57.6 ° -17.5 ° EP = 15.0 2H ′ = 4.0 [Lens specifications] rdν n 1 -16.3344 1.0000 30.24 1.585180 L₁ 2 * 15.2434 (D₁) 3 * 8.9953 3.4000 57.57 1.491080 L_Two 4 * -8.3508 (D_Two) 5 678.5465 1.0000 30.24 1.585180 L_Three 6 * 13.5492 (D_Three) 7 * 11.6282 3.3000 57.57 1.491080 L_Four 8 -48.7385 1.4069 9 ∞ 1.0000 58.80 1.522160 A 10 ∞ 8.3900 11 ∞ 15.2400 33.59 1.571100 P12 ∞ 1.0000 13 * 20.3196 3.0000 57.57 1.491080 L_Five 14 -20.3618 15.0000 15 Eye point [Aspherical surface data] No = 2 κ = 0.4865 C_Two= 0 C_Four= -6.29090 × 10^-6  C₆= 5.44060 x 10^-7 C₈= 1.26030 × 10^-7 C_Ten= -6.40290 × 10^-9 No = 3 κ = -2.0127 C_Two= 0 C_Four= -7.64130 × 10^-Five C₆= -2.52810 x 10^-Five C₈= 3.59710 × 10^-7 C_Ten= 1.06520 × 10^-8 C₁₂= -0.34876 × 10^-8 C₁₄= -0.27628 × 10^-9 C₁₆= 0.10165 x 10^-Ten No = 4 κ = -3.0000 C_Two= 0 C_Four= -7.42100 × 10^-Four C₆= -1.11410 × 10^-Five C₈＝ 9.50190 × 10^-7 C_Ten= -9.08130 × 10^-8 No = 6 κ = 9.5522 C_Two= 0C_Four= -3.443740 x 10^-Four C₆= -1.21120 × 10^-Five C₈= 1.29170 × 10^-6 C_Ten= -1.23400 x 10^-7 No = 7 κ = -2.5000 C_Two= 0 No = 13 κ = -3.3287 C_Two= 0 [Variable interval] Magnification 0.450 0.779 1.350 D₁ 15.02375 8.07125 2.54996 D_Two 1.03605 1.66367 5.92033 D_Three 15.98090 22.30579 23.57041

[0022]

[Table 4] [Overall specifications] m = 0.355-0.888 X = -1.00D 2ω = 66.4 ° -26.7 ° EP = 15.0 2H ′ = 4.0 [Lens specifications] rd v n 1 40.9199 1.0000 30.24 1.585180 L ₁ 2 _{* 6.7935 (D 1) 3 *} 8.4089 2.9000 57.57 1.491080 L 2 4 * -11.4801 (D 2) 5 15.1064 1.0000 30.24 1.585180 L 3 6 * 7.5339 (D 3) 7 * 13.8519 3.0000 57.57 1.491080 L 4 8 -23.8545 4.8232 9 ∞ 1.0000 58.80 1.522160 A10 8.3 8.3900 11 ∞ 15.2400 33.59 1.571100 P12 ∞ 1.0000 13 * 20.3196 3.0000 57.57 1.491080 L ₅ 14 -20.3618 15.0000 15 Eyepoint [Aspherical surface data] No = 2 κ = 0.6376 C ₂ = 0 C ₄ =- 3.00350 × 10 ^-6 C ₆ = 1.16010 × 10 ^-5 C ₈ = -7.39010 × 10 ^-7 C ₁₀ = 1.45850 × 10 ^-8 No = 3 κ = -0.9362 C ₂ = 0 C ₄ = 3.01460 × 10 ^-5 C ₆ = -1.81910 × 10 ⁻⁵ C ₈ = −1.39020 × 10 ⁻⁷ C ₁₀ = 4.84820 × 10 ⁻⁸ C ₁₂ = −0.65461 × 10 ⁻⁸ C ₁₄ = −0.87973 × 10 ⁻⁹ C ₁₆ = 0.88788 × 10 ^{− 10 No = 4 κ = 0.3652 C} 2 = 0 C 4 _{^{-1.06030 × 10 -4 C 6 = -2.39470}} × 10 -5 C 8 = 1.41230 × 10 -7 C 10 = -1.09140 × 10 -7 No = 6 κ = 2.0080 C 2 = 0 No = 7 κ = -2.5000 C _{2 = 0 No = 13 κ =} -3.3287 C 2 = 0 [ variable interval ratio _{0.355 0.562 0.888 D 1 18.32615 11.90344 6.44245} D 2 1.00086 1.03713 3.67788 D 3 11.07766 17.46409 20.28434

[0023]

[Table 5] Example No. 1 2 3 4 (1) (D _12w + D _23W ) / (D _12T + D _23T ) 1.682 1.715 1.896 1.910 D _12W 11.984 15.682 15.024 18.326 D _23W 0.920 0.406 1.036 1.001 D _12T 2.385 4.683 2.550 6.442 D _23T 5.287 4.697 5.920 3.678 (2) | f ₃ / f ₂ | 2.406 2.406 2.508 2.601 f ₂ 8.833 9.903 9.427 10.382 f ₃ -21.248 -23.822 -23.639 -27.000 (3) β _234T -1.833 -1.788 -2.140 -1.332

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.

[0025]

As described above, according to the present invention, it is possible to obtain a compact Kepler-type finder having a large zoom ratio, good aberration, and a small negative / positive / negative configuration.

[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 eyepiece A… the glass parallel plate H ₁ ~ H ₄ ... Reflection surface P ... Prism EP ... Eye point

Claims (5)

[Claims] In order from 1. A object side, a third lens group including a first lens group including a negative single lens L _1, a second lens group including a positive single lens L _2, a negative single lens L ₃ And an eyepiece system for observing an image formed by the objective lens system having a positive refractive power as a whole and an eyepiece system for observing an image formed by the objective lens system. In the above, at the time of zooming from a low magnification end to a high magnification end, the first lens group is fixed, and the air gap between the second lens group and the third lens group is enlarged, while the second lens group is A Kepler-type zoom finder, wherein both the third lens group and the third lens group are moved to the object side. 2. The method according to claim 1, wherein the following conditional expression is satisfied:
The Keplerian variable magnification finder according to claim 1. _{1.5 <(D 12W + D 23W} ) / (D 12T + D 23T) <3.0 (1) where, D _12W: said first lens group vertex distance D _23W at low magnification end of the second lens group : A vertex distance between the second lens group and the third lens group at a low magnification end D _12T : a vertex distance between the first lens group and the second lens group at a high magnification end D _23T : the second lens group A vertex distance between the lens and the third lens unit at the high magnification end. Wherein said positive at least one of the lens surfaces of the single lens L ₂ of the second lens group is formed aspherical, characterized in that and the following conditional expression is satisfied, according to claim 1 or 2, wherein Kepler type zoom finder. 2.3 <| f ₃ / f ₂ | <3 (2) where f _{2 is} a focal length of the second lens group, and f ₃ is a focal length of the third lens group. 4. The objective lens system has a fourth lens group having a positive refractive power on the eye point side of the third lens group, and satisfies the following conditional expression. 4. The Keplerian variable magnification finder according to 1, 2, or 3. −2.2 <β _234T <−1.2 (3) where β _234T is a composite magnification at the high magnification end of the second, third, and fourth lens groups. 5. The objective lens system further comprises a fourth lens group having a positive refractive power on the eye point side of the third lens group, wherein an air gap between the third lens group and the fourth lens group is provided. The ocular lens system includes a reflecting unit configured to reflect a light beam from the objective lens system and at least one positive lens having an aspherical object-side lens surface. 5. The Kepler-type variable magnification finder according to 1, 2, 3, or 4.