JPH0868948A - Secondary imaging type variable magnification finder optical system - Google Patents

Abstract

(57) [Summary] [Purpose] A simple lens configuration with a zoom ratio of about 3 and a viewing angle of 1
To obtain a variable-magnification viewfinder optical system of secondary imaging type of 0 degree or more. An object image formed in the vicinity of a primary image forming surface by an objective lens system having a variable power unit is re-imaged on a secondary image forming surface by a re-imaging lens system, and on the secondary image forming surface. When observing an object image through an eyepiece, the objective lens system has, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power for zooming,
It has a third lens group having a positive refractive power and a fourth lens group having a positive refractive power for correcting an image plane variation due to zooming, and each of the first lens group to the fourth lens group is composed of a single lens. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable-magnification finder optical system of secondary imaging type, and more particularly, by appropriately setting the lens configuration of an objective lens system or a re-imaging lens system having a variable power portion. The present invention relates to a variable-magnification viewfinder optical system of secondary imaging type suitable for a video camera, a silver-salt camera, or the like having a zoom ratio of about 3 and a viewing angle of 20 degrees or more and a predetermined eyepoint length.

[0002]

2. Description of the Related Art Conventionally, in a camera in which a photographing system and a finder optical system are separately configured, when the photographing system is a variable magnification system, the variable magnification finder optical system having a structure in which the finder field magnification changes with the magnification change Above all preferred. Further, since the variable magnification finder optical system is incorporated in the camera, it is preferable that it has a small size and can easily obtain a predetermined variable magnification ratio. The variable-magnification finder optical system is configured with the secondary imaging method,
Of these, the objective lens forming the variable power finder optical system is composed of a multi-lens group, and a predetermined lens group among the multi-lens groups of the objective lens is moved on the optical axis to perform zooming. The real image type variable magnification finder optical system is well known and various proposals have been made.

Since the real image type finder optical system has a structure for observing the real image formed by the objective lens system, a visual field mask and an information object can be provided at the position of the real image, and the outline of the finder visual field and the information object are clear. The viewfinder field does not change even if the position of the observing eye changes slightly.

As a variable-magnification finder optical system of the secondary imaging type, in Japanese Patent Application Laid-Open No. 3-87303, the objective lens system is a first lens group having a positive refractive power, a second lens group having a negative refractive power for zooming, and a variable power lens group. A third lens unit having a positive refracting power and a fourth lens unit having a positive refracting power for compensating an image plane variation caused by doubling, and an object image formed by the objective lens system is erected by the re-imaging lens system. Are re-imaged and the re-imaged object image is observed with an eyepiece lens.

[0005]

In the variable magnification finder optical system of the secondary imaging type, the objective lens system is composed of a plurality of lens groups, and some of these lens groups are moved along the optical axis to change the magnification. In order to obtain a viewing angle of 10 degrees or more at a multiplication ratio of about 3, it is important to properly set the lens configuration of each lens group forming the objective lens system and the re-imaging lens system. If the objective lens system or the re-imaging lens system has an improper lens configuration, the entire lens system becomes large, a predetermined zoom ratio cannot be obtained, and it becomes difficult to observe a good object image over the entire finder field. come.

The present invention simplifies the entire lens system by appropriately setting the lens configuration of the objective lens system, has a variable power ratio of about 3, a viewing angle of 10 degrees or more, and has a good viewfinder image. It is an object of the present invention to provide a variable-magnification finder optical system of secondary imaging type that can be observed in the above.

Further, according to the present invention, the finder image can be satisfactorily observed over the entire field of view of the finder by properly setting the lens configuration of the re-imaging lens system.
It is an object of the present invention to provide a variable magnification finder optical system of the next imaging type.

[0008]

The secondary image-forming variable magnification finder optical system of the present invention is a re-imaging lens that reconstructs an object image formed in the vicinity of the primary image forming surface by an objective lens system having a variable magnification portion. When the image is re-imaged on the secondary image plane by the system and the object image on the secondary image plane is observed through the eyepiece lens, the objective lens system has the first refractive power first from the object side. A first lens unit, a second lens unit having a negative refractive power for zooming, a third lens unit having a positive refractive power that corrects an image plane variation due to zooming, and a fourth lens unit having a positive refractive power, The fourth group is characterized in that each is composed of a single lens.

[0009]

1 is a lens cross-sectional view of a variable-power finder optical system of a secondary imaging type according to Numerical Embodiment 1 which will be described later. In the figure, reference numeral 1 denotes an objective lens system having a variable power portion, a first lens group 11 having a positive refractive power, and a second lens group 1 having a negative refractive power for zooming.
2. The third lens unit 13 has a positive refractive power that corrects the image plane variation due to zooming, and the fourth lens unit 14 has a fixed positive refractive power. The first group 11 is composed of a positive lens having both convex lens surfaces, the second group 12 is composed of a negative lens having both concave lens surfaces, and the third group 13 is composed of a positive lens having both convex lens surfaces. The group 14 is composed of a positive lens having a convex surface directed toward the object side.

In this embodiment, each of the first to fourth groups is composed of a single lens made of a plastic material. This simplifies the entire lens system. The zooming from the wide-angle end to the telephoto end is performed by moving the second group 12 monotonously toward the image plane side and moving the third group 13 toward the object side while having a convex locus, as indicated by the arrow. As a result, a predetermined zoom ratio is effectively obtained.

Reference numeral 15 denotes a primary image plane, on which an object image (finder image) is formed by the objective lens 1. Reference numeral 2 denotes a re-imaging lens system, which serves as an erect normal image obtained by inverting the object image formed on the primary imaging surface 15 upside down and left and right.
Re-imaged.

The re-imaging lens system 2 includes an erector lens 16
And a field lens 17. The erector lens 16 is composed of a meniscus-shaped negative lens LFN having a convex surface facing the object side and a positive lens LFP having convex surfaces on both lens surfaces, and two lenses made of different materials, whereby chromatic aberration is satisfactorily corrected.

The field lens 17 is composed of a single positive lens whose convex surface faces the object side. The field lens 17 is provided in the vicinity of the secondary image forming surface 18, whereby the light flux from the erector lens 16 is condensed and efficiently guided to the eyepiece lens 19 described later. The field lens 17 is composed of a lens having the same shape and made of the same material as the fourth group 14 of the objective lens system 1, thereby reducing the cost. The eyepiece lens 19 observes the object image of an erect normal image formed on the secondary imaging surface 18. The eyepiece lens 19 is composed of a single positive lens whose both lens surfaces are convex.

In this embodiment, the eyepiece lens 19 is moved along the optical axis to adjust the diopter. 20 is the observer's pupil position (eye point).

In this embodiment, a light beam from a subject (not shown) is formed as an inverted object image (aerial image) on the primary image forming surface 15 by the objective lens system 1. And the primary image plane 1
The light beam based on the object image formed in 5 is relayed by the erector lens 16 and the field lens 17 of the re-imaging lens system 2 to re-image the object image of an erect normal image on the secondary imaging surface 18. There is. Then, the light flux based on the object image formed on the secondary image forming surface 18 is guided to the eyepiece lens 19. As a result, the object image formed on the secondary image plane 18 is observed from the pupil position 20 via the eyepiece lens 19.

The secondary image-forming variable-magnification viewfinder optical system aimed at by the present invention has been achieved by the above-mentioned construction. However, while further downsizing the entire lens system, a good viewfinder image is obtained over the entire viewfinder field. To observe, at least one of the following conditions should be satisfied.

(1-1) When the focal length at the wide-angle end of the objective lens system is f0 and the focal length of the i-th group is fi, 1.2 <| f2 / f0 | <1.7 (... 1) 0.4 <f3 / f4 <0.6 (2) The condition is satisfied.

Conditional expression (1) relates to the negative refracting power of the second lens group for zooming which constitutes the objective lens system, and mainly the size reduction of the objective lens system, and a zooming ratio of about 3 and a predetermined zooming ratio. This is for effectively obtaining the multiplication ratio.

If the lower limit of conditional expression (1) is exceeded and the negative refractive power of the second lens unit becomes too strong, a predetermined zoom ratio can be secured with a short amount of movement, but aberration fluctuations associated with zooming can be ensured. Especially, it becomes difficult to satisfactorily correct the fluctuation of the field curvature. If the upper limit is exceeded and the refractive power of the second lens unit becomes too weak, the amount of movement for ensuring a predetermined zoom ratio increases, and the overall objective lens system becomes large, which is not desirable.

Conditional expression (2) relates to the ratio of the refracting powers of the third group and the fourth group for compensating the image plane variation due to the magnification variation forming the objective lens system, and mainly relates to the spherical aberration associated with the magnification variation. This is to satisfactorily correct the fluctuation.

If the lower limit of conditional expression (2) is exceeded and the refractive power of the third lens unit becomes too strong as compared with the fourth lens unit, it becomes difficult to correct spherical aberration associated with zooming. On the contrary, if the refracting power of the third lens unit is too weak as compared with that of the fourth lens unit, the amount of movement of the third lens unit due to zooming increases and the overall size of the objective lens system increases.

(1-2) The re-imaging lens system has an erector lens and a field lens for re-imaging the object image formed on the primary image plane as an erect image, and the erector lens is It is composed of a negative lens LFN and a positive lens LFP, and when the Abbe number of the material of the negative lens LFN is ν _LFN , ν _LFN <35 (3) is satisfied.

Conditional expression (3) is used to satisfactorily correct chromatic aberration by using an appropriate dispersion material for the negative refractive power lens which constitutes the erector lens when the entire optical system is made of a plastic material. is there. Conditional expression (3)
If it is out of the range, it becomes difficult to satisfactorily correct the axial chromatic aberration and the lateral chromatic aberration of the entire finder optical system.

(1-3) The re-imaging lens system has an erector lens and a field lens for re-imaging the object image formed on the primary imaging surface as an erect normal image. When the distance from the lens surface on the observation side to the secondary imaging surface is DL and the focal length of the eyepiece lens is fe, 0.2 <DL / fe <0.4 (4) is satisfied. It is to be.

Field lens 17 of re-imaging lens system 2
Is a secondary imaging plane 1 in order to efficiently collect the light flux from the erector lens 16 and guide it to the eyepiece lens 19 side.
It is better to place it in the vicinity of 8. However, the secondary image plane 1
When it is too close to 8, dust adhering to the lens surface of the field lens 17 is observed together with the finder image, which is not good.

Therefore, in the present invention, by setting each element so as to satisfy the conditional expression (4), the finder image is satisfactorily observed while effectively utilizing the luminous flux.
If the distance DL exceeds the lower limit value of the conditional expression (4) and becomes too short, dust adhering to the field lens becomes conspicuous when observing the finder image, which is not preferable. On the other hand, if the distance DL exceeds the upper limit and the distance DL becomes too long, the condensing property of the light flux as the field lens is deteriorated and the lens outer diameter is increased, which is not preferable.

(1-4) At least one lens surface of the first group of the objective lens system is preferably an aspherical surface having a shape in which the positive refracting power becomes stronger from the lens center to the lens periphery. According to this, it is possible to satisfactorily correct the distortion at the wide-angle end.

(1-5) At least one lens surface of the second lens group of the objective lens system is preferably an aspherical surface whose negative refractive power becomes weaker from the lens center to the lens periphery. According to this, it is possible to satisfactorily correct the fluctuations of the distortion aberration and the astigmatism due to the magnification change.

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are respectively from the object side of the i-th lens. The refractive index of glass and the Abbe number. Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

The aspherical shape has an X axis in the optical axis direction, an H axis in the direction perpendicular to the optical axis, a positive light traveling direction, and R as a paraxial radius of curvature,
When K, B, C, D and E are aspherical coefficients respectively

[0031]

[Equation 1] It is expressed by the formula. Further, "D-0X" means "10 ^-X ".

Numerical Example 1 β = 0.38 to 1.03 2ω = (viewing angle) 20.8 ° R 1 = aspherical D 1 = 3.50 N 1 = 1.49171 ν 1 = 57.4 R 2 = -66.63 D 2 = variable R 3 = Aspherical D 3 = 1.35 N 2 = 1.49171 ν 2 = 57.4 R 4 = Aspherical D 4 = Variable R 5 = 25.80 D 5 = 5.70 N 3 = 1.49171 ν 3 = 57.4 R 6 = Aspherical D 6 = Variable R 7 = 16.40 D 7 = 4.20 N 4 = 1.49171 ν 4 = 57.4 R 8 = -2102.91 D 8 = 31.14 R 9 = 18.13 D 9 = 1.00 N 5 = 1.58306 ν 5 = 30.2 R10 = 10.83 D10 = 0.65 R11 = 13.27 D11 = 3.45 N 6 = 1.49171 ν 6 = 57.4 R12 = aspherical D12 = 38.38 R13 = 16.40 D13 = 4.20 N 7 = 1.49171 ν 7 = 57.4 R14 = -2102.91 D14 = 33.87 R15 = aspherical D15 = 4.60 N 8 = 1.49171 ν 8 = 57.4 R16 = -37.76 D16 = 22.50 R17 = Eye point

[0033]

[Table 1] Numerical Example 2 β = 0.34 to 0.90 2ω = (viewing angle) 20 ° R 1 = aspherical surface D 1 = 3.70 N 1 = 1.49171 ν 1 = 57.4 R 2 = −78.93 D 2 = variable R 3 = aspherical surface D 3 = 1.30 N 2 = 1.49171 ν 2 = 57.4 R 4 = Aspheric D 4 = Variable R 5 = 21.08 D 5 = 5.80 N 3 = 1.49171 ν 3 = 57.4 R 6 = Aspheric D 6 = Variable R 7 = 15.60 D 7 = 4.00 N 4 = 1.49171 ν 4 = 57.4 R 8 = -2000.00 D 8 = 41.12 R 9 = 24.61 D 9 = 1.00 N 5 = 1.58306 ν 5 = 30.2 R10 = 10.93 D10 = 0.60 R11 = 12.06 D11 = 3.30 N 6 = 1.49171 ν 6 = 57.4 R12 = aspherical D12 = 33.79 R13 = 15.60 D13 = 4.00 N 7 = 1.49171 ν 7 = 57.4 R14 = -2000.00 D14 = 32.33 R15 = aspherical D15 = 4.60 N 8 = 1.49171 ν 8 = 57.4 R16 = -22.05 D16 = 22.50 R17 = Eye point

[0034]

[Table 2] Numerical Example 3 β = 0.38 to 1.02 2ω = (viewing angle) 20.8 ° R 1 = aspherical surface D 1 = 3.60 N 1 = 1.49171 ν 1 = 57.4 R 2 = -65.72 D 2 = variable R 3 = aspherical surface D 3 = 1.35 N 2 = 1.49171 ν 2 = 57.4 R 4 = Aspheric D 4 = Variable R 5 = 26.99 D 5 = 5.60 N 3 = 1.49171 ν 3 = 57.4 R 6 = Aspheric D 6 = Variable R 7 = 16.22 D 7 = 4.15 N 4 = 1.49171 ν 4 = 57.4 R 8 = -2080.00 D 8 = 40.50 R 9 = 24.41 D 9 = 1.00 N 5 = 1.58306 ν 5 = 30.2 R10 = 9.38 D10 = 0.62 R11 = 10.39 D11 = 3.43 N 6 = 1.49171 ν 6 = 57.4 R12 = aspherical D12 = 36.25 R13 = 16.22 D13 = 4.16 N 7 = 1.49171 ν 7 = 57.4 R14 = -2080.00 D14 = 32.99 R15 = aspherical D15 = 4.60 N 8 = 1.49171 ν 8 = 57.4 R16 = -27.46 D16 = 22.50 R17 = Eye point

[0035]

[Table 3]

[0036]

As described above, according to the present invention, by appropriately setting the lens configuration of the objective lens system, the entire lens system can be simplified, the zoom ratio is about 3, and the viewing angle is 10.
It is possible to achieve a variable-magnification finder optical system of the secondary image formation type which has a degree of rotation or more and can observe a finder image satisfactorily.

Further, by appropriately setting the lens configuration of the re-imaging lens system, it is possible to achieve a variable-magnification finder optical system of the secondary imaging type capable of observing the finder image satisfactorily over the entire field of view of the finder. it can.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is an aberration diagram at the wide-angle end according to Numerical Example 1 of the present invention.

FIG. 3 is an intermediate aberration diagram of Numerical example 1 of the present invention.

FIG. 4 is an aberration diagram at a telephoto end according to Numerical Example 1 of the present invention.

FIG. 5 is an aberration diagram at the wide-angle end according to Numerical Example 2 of the present invention.

FIG. 6 is an intermediate aberration diagram of Numerical example 2 of the present invention.

FIG. 7 is an aberration diagram at a telephoto end according to Numerical Example 2 of the present invention.

FIG. 8 is an aberration diagram at a wide-angle end according to Numerical Example 3 of the present invention.

FIG. 9 is an intermediate aberration diagram of Numerical Example 3 of the present invention.

FIG. 10 is an aberration diagram at a telephoto end according to Numerical Example 3 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Objective lens system 2 Re-imaging lens system 11 1st group 12 2nd group 13 3rd group 14 4th group 15 Primary imaging surface 16 Erector lens 17 Field lens 18 Secondary imaging surface 19 Eyepiece 20 Eyepoint d d line g g line ΔS sagittal image plane ΔM meridional image plane

Claims (6)

[Claims] 1. An object image formed in the vicinity of a primary imaging plane by an objective lens system having a variable power unit is re-imaged by a re-imaging lens system.
When re-imaging on the next image forming surface and observing the object image on the secondary image forming surface through the eyepiece lens, the objective lens system sequentially moves from the object side to the first lens group having a positive refractive power, Second of negative refracting power for double
The optical system includes a group, a third group having a positive refractive power that corrects an image plane variation due to zooming, and a fourth group having a positive refractive power, and each of the first to fourth groups is composed of a single lens. A variable-magnification viewfinder optical system of the secondary imaging type characterized in that 2. When the focal length at the wide-angle end of the objective lens system is f0 and the focal length of the i-th group is fi, 1.2 <| f2 / f0 | <1.7 0.4 <f3 / f4 The variable magnification viewfinder optical system of the secondary imaging type according to claim 1, wherein the condition <0.6 is satisfied. 3. The re-imaging lens system includes an erector lens and a field lens for re-imaging an object image formed on the primary image plane as an erect normal image, and the erector lens is a negative lens LFN. And a positive lens LFP, wherein when the Abbe number of the material of the negative lens LFN is ν _LFN , ν _LFN <35 is satisfied. Viewfinder optical system. 4. The re-imaging lens system has an erector lens and a field lens for re-imaging an object image formed on the primary imaging surface as an erect normal image, and the field lens on the observation side of the field lens. 2. When the distance from the lens surface to the secondary image formation surface is DL and the focal length of the eyepiece lens is fe, the condition 0.2 <DL / fe <0.4 is satisfied. Second-order imaging type variable magnification finder optical system. 5. The quadratic imaging system according to claim 1, wherein the single lens of the fourth group of the objective lens system and the field lens are made of the same material and have the same shape. Variable finder optical system. 6. The secondary image formation according to claim 1, 2, 3, 4 or 5, wherein the material of each lens constituting the eyepiece lens as the objective lens system and the reimaging lens system is plastic. Variable magnification viewfinder optical system.