JPH11237548A - Variable power finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a real image type finder provided with excellent optical performance over the entire variable power range by making the difference of the position on an optical axis of a telephoto end to the wide angle end of a second group and the distance from the lens surface on the most object side of a first group to the lens surface on the most image surface side of a third group at the wide angle end satisfy a specified condition. SOLUTION: An object lens system 10 is provided with the first group L1 of positive refractive index power, the second group L2 of negative refractive power and the third group L3 of positive refractive power. At the time of varying power from the wide angle end to the telephoto end, the second group L2 is moved with a projected track to an observation side and the third group L3 is moved so as to reduce an air interval with the second group L2 to the object side. At the time of defining the difference of the position on the optical axis of the telephoto end to the wide angle end of the second group L2 as m2 (where it is positive at the time of being provided on the observation side) and the distance from the lens surface on the most object side of the first group L1 to the lens surface to the most image surface side of the third group L3 at the wide angle end as L0 , the condition of -0.5<m2/L0 <0.1 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a real image type variable magnification finder, and more particularly to an external type finder provided separately from a photographing system, which appropriately sets the lens configuration of an objective lens system constituting the finder. The present invention relates to a real image type variable magnification finder suitable for, for example, a still camera or a video camera, which enables a small and excellent finder image to be observed.

[0002]

2. Description of the Related Art Conventionally, in a camera in which a photographing system and a finder system are separately configured, when the photographing system is a variable magnification system, the finder system also includes a variable magnification system. Is configured to change. In general, a variable-magnification finder is required to have a configuration that is small and can easily obtain a predetermined magnification ratio because it is incorporated in a camera.

[0003] The present applicant discloses in Japanese Patent Application Laid-Open No. 8-69032 that an objective lens is divided into three lens groups: a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power. The third lens unit is moved to the object side for zooming, and the image plane variation (diopter variation) accompanying the zooming is corrected by moving the second lens unit. There has been proposed a real image type variable magnification finder in which the changed object image is converted into an erect image via an image inverting member such as a roof prism and the erect image is observed with an eyepiece.

The applicant of the present invention has disclosed Japanese Patent Application Laid-Open No. 61-156018.
In Japanese Unexamined Patent Application Publication No. H11-116616 and the like, the objective lens is composed of three lens groups, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power. The second group is moved to the object side to change the magnification, and the image plane variation accompanying the magnification is corrected by moving the first group, and the object image obtained by changing the magnification variously by the objective lens is used as a Porro prism or the like. A real image type variable magnification finder is proposed in which an erect image is formed through an image reversing member and the erect image is observed with an eyepiece.

[0005]

Problems to be Solved by the Invention JP-A-8-690
In a real image type viewfinder proposed in Japanese Patent Application Laid-Open No. 32, JP-A-61-156018, JP-A-1-116616, etc., a luminous flux from an object image formed on an image forming surface is subsequently transmitted by an objective lens system. The light is guided to an image inverting optical system and an eyepiece lens. In each of these publications, a good finder image is observed by appropriately setting the lens configuration of each lens group.

In a real image type zoom finder, in order to obtain a predetermined zoom ratio while miniaturizing the entire lens system,
In particular, it is necessary to appropriately set the lens configuration of the objective lens. For example, if the lens configuration of the objective lens system is inappropriate, the size of the entire lens system is increased, and the fluctuation of aberration due to zooming is increased. Generally, in order to reduce the size of the entire lens system, it is sufficient to increase the refractive power of each lens unit. However, if the refractive index is simply increased, aberration fluctuations during zooming increase, and it becomes difficult to observe a good finder image.

According to the present invention, by appropriately setting the lens configuration of an objective lens system having a zooming unit, it is possible to easily obtain a predetermined zooming ratio while miniaturizing the entire lens system. It is an object of the present invention to provide a small real image type variable magnification finder capable of observing a good finder image over a magnification range.

[0008]

The variable magnification finder according to the present invention comprises: (1-1) an object image formed by an objective lens system having a positive refractive power having a variable magnification function in order from the object side through an image inverting optical system. In the variable magnification finder for observing the erect image with an eyepiece system, the objective lens system includes a first group having a positive refractive power, a second group having a negative refractive power, and a second group having a positive refractive power. The zoom lens system has three lens units, three at the time of zooming from the wide-angle end to the telephoto end. The second unit moves with a convex locus toward the observation side, and the third unit moves toward the object side. The air gap with the second lens unit is moved so as to decrease, and the difference between the position of the second lens unit on the optical axis at the telephoto end and the position at the telephoto end with respect to the wide-angle end is m2 (when provided on the observation side, it is positive) the distance between the most object side lens surface of the first group to the lens surface on the most image side of the third group L at the wide-angle end ₀ It is characterized by satisfying the the time _{-0.5 <m2 / L 0 <0.1} ··· (1a) following condition. 5 (1-
2) In a variable magnification finder, an object image formed by an objective lens system having a positive refractive power having a zooming function in order from the object side is converted into an erect image via an image inverting optical system, and the erect image is observed by an eyepiece lens system. The objective lens system has a negative lens group having a negative refractive power and a lens group having a positive refractive power. When zooming from the wide-angle end to the telephoto end, the positive lens group moves to the object side, and each lens The air spacing of the group is reduced, and when the refractive index of the material of the positive lens in the positive lens group is Np, the condition 1.52 <Np <1.9 (1b) is satisfied. It is characterized by:

[0009]

FIG. 1 is a sectional view of a principal part of a variable magnification finder according to the present invention, and FIGS. 2 to 7 are lens sectional views of numerical examples 1 to 6 of the present invention, respectively. 2 to 7 show the viewfinder optical path shown in FIG. 1 in an expanded state. The lens sectional view shows the zoom position at the wide-angle end. 8 to 25 show aberration diagrams at a reference distance of 3 m when the numerical examples 1 to 6 of the present invention are expressed in units of mm.

In FIG. 1, reference numeral 10 denotes a positive refractive power objective lens system having a zooming portion (zooming function), which forms an object image (finder image) on a predetermined surface.

F is a field lens having a reflecting surface, which is formed in a triangular prism shape. The field lens F1 receives the light beam from the objective lens 10 from the incident surface F1, reflects the light beam on the reflecting surface F2, totally reflects the light beam on the reflecting surface F3, and then faces the convex surface to the observation side (E).
It is injected from 4. Reference numeral 4 denotes a finder field frame, which is made up of mechanical or liquid crystal display means.

P is an image reversing optical system, which includes a roof surface 4
It consists of a roof prism having two reflecting surfaces. Le
Is an eyepiece having a positive refractive power. The roof prism P causes the light beam from the field lens F to be incident on the incident surface P1 and totally reflected on the surface P2, and then totally reflected on the roof surface P3, totally reflected on the incident surface P1, and emitted from the surface P2 to obtain an eyepiece. Light is guided to Le.

The object image formed on the finder field frame 4 between the field lens F and the roof prism P by the objective lens system 10 is turned upside down, left and right through the field lens F and the roof prism P and converted into an erect image. I have.
In the present embodiment, the field lens F and the roof prism P constitute one element of the image reversing means. Incidentally, a Porro prism or the like may be used as one element of the image inverting means.

In FIGS. 2 to 7, the field lens F and the roof prism P are shown as two glass blocks whose optical paths are expanded for simplicity. Eyepiece Le with positive refractive power
Observes the object image formed in the finder field frame 4 from the eye point E as an erect object image via the roof prism P. The finder field frame 4 is provided with a frame indicating the finder field range, various kinds of information, and the like.

The objective lens system 10 has a first group L1 composed of a single positive lens with a convex surface facing the observation side, a second group L2 composed of a single negative lens with a concave surface facing the object side, and both lens surfaces. The third lens unit L3 includes a single positive lens having a convex surface. In this way, by configuring each lens group with a single lens, miniaturization and simplification of the entire lens system are achieved.

In this embodiment, zooming is performed by moving the third lens unit L3 to the object side as indicated by an arrow, and the resulting change in image plane fluctuation (finder diopter) is projected by moving the second lens unit L3 toward the observation side as indicated by an arrow. It is corrected by moving while having a locus. The first group is fixed during zooming.

In this embodiment, the objective lens system 10 is composed of three lens groups of first, second and third groups, and each lens group is provided with an aspheric surface of a predetermined shape. By adopting a configuration in which an object image is formed in the finder field frame 4 between the field lens F and the roof prism P, aberration correction is facilitated, and a good object image can be observed.

The objective lens system according to the present invention basically forms a retrofocus type of a front group (first group and second group) having a negative refractive power and a rear group (third group) having a positive refractive power. In addition, the back focus of the objective lens system is sufficiently long.

Further, each embodiment has a field lens and further has an image reversing function. The field lens reflects a chief ray path emitted from the objective lens system, and then causes the lens surface F4 having a positive refractive power to enter the image inverting optical system P for an erect erect image as convergent light or parallel light. Thus, the size of the image reversing optical system can be reduced. Further, the cost can be reduced by simultaneously providing the effects of the image reversing optical system and the field lens with one member. In the present embodiment, the lens surface F4 of the field lens is formed of a spherical surface, but the same effect can be obtained by using an aspheric surface, a toric surface, or the like.

Next, the features of the configuration of the first invention of the above-described configuration (1-1) will be described.

The first invention corresponds to Numerical Embodiments 1 to 6.

In the first invention, a positive lens group is disposed closest to the object side, and the objective lens system is composed of a positive first group, a negative second group, and a positive third group in this order from the object side. Is moved toward the object side from the wide-angle end to the telephoto end to perform zooming, and the second unit corrects diopter change accompanying zooming. In the first invention, the third lens unit is largely moved toward the object side from the wide-angle end to the telephoto end to perform zooming, and the second unit is moved so as to reciprocate from the wide-angle end to the telephoto end. The overall length has been shortened.

Conditional expression (1a) defines the amount of movement of the second lens unit, and is intended to maintain the balance of the total length at the wide-angle end and the telephoto end and to reduce the size of the objective lens system.
If the lower limit is exceeded, the second lens unit moves excessively toward the object side at the telephoto end with respect to the wide-angle end, and the overall length at the telephoto end increases, which is not good. If the upper limit value is exceeded, the total length of the second lens unit at the wide-angle end with respect to the telephoto end becomes longer, and the diameter of the front lens becomes large. In order to achieve a further balance between miniaturization and high performance, it is preferable to set the lower limit of conditional expression (1a) to -0.4. The upper limit is preferably set to 0.05.

In order to obtain good optical performance while further reducing the size of the entire lens system in the first invention, it is preferable to satisfy at least one of the following conditions.

(A-1) Assuming that the focal length of the i-th lens unit of the objective lens system is fi: -0.1 <f2 / f1 <-0.005 (2a) 0.005 <f3 / f1 <0.1 (3a) The following condition must be satisfied.

Conditional expression (2a) represents the second condition of the objective lens system.
The ratio of the refractive power of the first lens group to that of the first lens group is mainly for miniaturization and high performance.

If the lower limit of conditional expression (2a) is exceeded, the first condition
It is not preferable because the refractive power of the group becomes too weak and it becomes difficult to correct the distortion. When the value exceeds the upper limit, the refractive power of the first group becomes too strong, and the lens diameter of the first group increases.
This is not preferable because the overall length of the lens at the telephoto end tends to increase.

In order to further reduce the size and improve the performance, it is preferable to set the lower limit of conditional expression (2a) to -0.08. Further, it is preferable that the upper limit value be -0.01.

Conditional expression (3a) represents the third condition of the objective lens system.
The ratio of the refractive power of the first lens group to that of the first lens group is mainly for miniaturization and high performance.

If the lower limit of conditional expression (3a) is exceeded, the refractive power of the first lens unit will be weak, and if the refractive power of the third lens unit is too strong, it will be difficult to correct distortion, which is not desirable. Also,
When the value exceeds the upper limit, the refractive power of the first lens unit becomes strong, and when the refractive power of the third lens unit becomes too weak, the lens diameter of the first lens unit increases, and the total lens length at the telephoto end tends to increase. Absent.

In order to further reduce the size and improve the performance, it is preferable to set the lower limit of conditional expression (3a) to 0.01. Further, the upper limit is preferably set to 0.08.

(A-2) Each lens group of the objective lens system is composed of a single lens, and has at least three aspheric surfaces as a whole.

It is difficult to reduce the size of the entire lens system if the number of lenses is large. Therefore, in order to reduce the number of lenses, it is preferable that each group is constituted by a single lens, and at least three aspherical surfaces are used in the objective lens system in order to correct aberrations generated at this time. Further, in order to achieve high performance in the entire zoom range, each group must be corrected for aberrations to some extent independently. For that purpose, it is preferable to use an aspheric surface for each group of the objective lens system.

(A-3) A field lens having a reflecting surface is provided between the objective lens system and the image inversion optical system, and the field lens is located at a position of an object image formed by the objective lens system. A lens surface a having a positive refractive power is provided in the vicinity, the radius of curvature of the lens surface a is Rf, the focal length of the eyepiece is fe, and the distance between the position of the object image and the lens surface a is df. 0.2 <fe / Rf <2.0 (4a) -10 <1000 × df / fe <0.5 (5a)

Conditional expression (4a) defines the radius of curvature of the lens surface of the field lens, and provides an appropriate field effect.

If the lower limit of conditional expression (4a) is exceeded, the radius of curvature of the lens surface of the field lens becomes too large, so that the effect as a field lens cannot be obtained and the size of the image reversing optical system is undesirably increased. . Further, it is not preferable to make telecentric only with the objective lens system because the diameter of the lens on the most observation side of the objective lens system increases. In addition, if the radius of curvature of the lens surface of the field lens becomes too small when the upper limit value is exceeded, the balance of the refractive power with the positive lens group that performs zooming is lost, and the refractive power of the positive lens group is reduced. If the total length of the lens is increased and the refractive power distribution is not changed, it becomes difficult to correct the distortion at the wide-angle end, which is not preferable in any case.

In order to more appropriately set the lens surface of the field lens, it is preferable to set the lower limit of conditional expression (4a) to 0.4. The upper limit is preferably set to 1.5.

Conditional expression (5a) is for appropriately setting the distance between the position (focal position) of the object image formed by the objective lens and the lens surface.

If the distance between the lens surface and the image forming surface of the objective lens exceeds the lower limit of conditional expression (5a), the effect as a field lens is impaired and the size of the objective lens system is increased, which is not good. Further, if the distance between the lens surface and the focal position of the objective lens exceeds the upper limit value, the size of the erecting image inverting optical system is unfavorably increased.

In order to properly set the distance between the focal position of the objective lens and the lens surface, it is preferable to set the lower limit of conditional expression (5a) to -5.0. Further, it is preferable to set the upper limit to 0.1.

(A-4) The distance from the lens surface closest to the object in the first group at the wide-angle end of the objective lens system to the lens surface closest to the observation side in the third group is L ₀ , and the objective lens system at the wide-angle end is 1.5 <L ₀ /fw<3.5 (6a) when the focal length of fw is fw.

Conditional expression (6a) defines the total length of the objective lens system at the wide-angle end.

If the lower limit of conditional expression (6a) is exceeded, the total length of the lens at the wide-angle end becomes too small with respect to the focal length at the wide-angle end. On the other hand, exceeding the upper limit value is not preferable because the total length of the lens at the wide-angle end increases with respect to the focal length at the wide-angle end.

In order to properly set the overall length of the objective lens system at the wide-angle end, it is preferable to set the lower limit of conditional expression (6a) to 1.8. Further, the upper limit is preferably set to 2.8.

Next, the features of the configuration of the second aspect of the configuration (1-2) will be described. The second invention corresponds to Numerical Embodiments 4 to 6.

In the second invention, the refractive index of the material of the positive lens of the positive lens group for performing the magnification change is appropriately set. In order to reduce the size of the objective lens system, it is necessary to set a relatively high refractive power to the variable power unit. However, if the positive refractive power is set strong, the Petzval sum of the objective lens system becomes too large in the positive direction and the astigmatic difference increases, or the peripheral diopter increases, which is not good.
If the number of lenses is increased or the refractive power is weakened to correct this, the overall length of the objective lens will increase. Therefore, in the second invention, the Petzval sum is prevented from increasing in the positive direction by setting the refractive index of the material of the positive lens of the positive lens group performing the zooming to be relatively high, and the astigmatic difference is favorably reduced. Correction is possible, realizing high performance and miniaturization.

Conditional expression (1b) defines the material of the lens of the positive lens group, and is used for favorably correcting astigmatism.

If the value exceeds the lower limit of the condition (1b), the Petzval sum increases positively, and it becomes difficult to correct astigmatism. If the value exceeds the upper limit, astigmatism can be satisfactorily corrected, but the Abbe number of the lens material becomes small, and the balance of chromatic aberration deteriorates.

For better correction of astigmatism,
It is preferable to let the lower limit value in conditional expression (1b) to be 1.56.

In the second aspect of the present invention, in order to obtain good optical performance while further reducing the size of the entire lens system, it is preferable to satisfy at least one of the following conditions.

(A-1) The objective lens system has three lens groups: a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power. That is.

In the second invention, zooming is performed in the third lens unit and diopter change is performed in the second lens unit. However, if the refractive power of the third lens unit is increased for miniaturization, distortion is caused particularly at the wide-angle end. Since the aberration is deteriorated, it is preferable to dispose the first lens unit having a relatively low refractive power to correct the distortion and further reduce the size.

(A-2) The positive lens group has an aspheric surface in which the positive refractive power becomes weaker from the center of the optical axis to the periphery, and the focal lengths of the negative lens group and the positive lens group are respectively fn. , FP, -2.0 <fn / fP <-0.5 (2b).

Since the positive lens unit is a zooming unit, it is difficult to obtain high optical performance over the entire zooming range, especially if aberration correction is not performed independently. For this reason, it is preferable to use an aspheric surface whose positive refractive power becomes weaker from the center of the optical axis to the periphery, whereby various aberrations generated in the lens unit having a positive refractive power can be satisfactorily corrected. In order to obtain higher optical performance, it is preferable that both lens surfaces have aspherical lenses.

If the lower limit value of conditional expression (2b) is exceeded, it is not preferable that the refractive power of the third lens unit becomes too weak, because the total optical length at the telephoto end increases. On the other hand, if the value exceeds the upper limit, the refractive power of the third lens unit becomes too strong, and it becomes difficult to correct distortion particularly at the wide-angle end, which is not preferable.

In order to set a more appropriate refractive power, it is preferable to set the lower limit of conditional expression (2b) to -1.5. Further, the upper limit is preferably set to -1.0.

(A-3) A field lens having a reflecting surface is provided between the objective lens system and the image inverting optical system, and the field lens is located at a position of an object image formed by the objective lens system. A lens surface a having a positive refractive power with a convex surface facing the observation side in the vicinity thereof;
Is the radius of curvature of Rf, the focal length of the eyepiece is fe,
When the distance between the position of the object image and the lens surface a is df, 0.2 <fe / Rf <2.0 (3b) −0.5 <1000 × df / fe <0.5 · .. (4b) The following condition must be satisfied.

Here, the technical meanings of the conditional expressions (3b) and (4b) are the same as the conditional expressions (4a) and (5a) of the first invention.

(A-4) Each lens group of the objective lens system is composed of a single lens, and each lens group has at least one aspheric surface.

In order to achieve high performance in the entire zoom range while miniaturizing, each group must be corrected for aberrations to some extent independently. For this purpose, each group of the objective lens system must have an aspheric surface. Preferably, it is used.

Furthermore, in the above invention, it is preferable that the field lens has two reflecting surfaces. For example, if a field lens is provided with a curvature on the exit surface of the triangular prism, the optical path of the objective lens system is bent to reduce the size of the camera, etc., and to increase the cost by integrating the field lens and the triangular prism. Not preferred.

In the first and second aspects of the present invention, the observation surface having the refractive power of the field lens and the image forming surface of the objective lens system are set substantially equal. It is preferable to provide finder information on the lens surface on the side. With such a configuration, for example, a distance measurement mark or the like can be visually recognized by being superimposed on the object image, and finder information can be displayed at relatively low cost.

Hereinafter, Numerical Examples 1 to 6 of the present invention will be described. In Numerical Examples 1 to 6, 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 in order from the object side, and Ni and νi are the numbers in order from the object side. The refractive index and Abbe number of the glass of the i-th lens.

The aspherical surface has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive light traveling direction, and an origin at the intersection of the vertex of the lens and the X axis, and R as a paraxial radius of curvature of the lens surface. , K,
When B, C, and D are aspheric coefficients, respectively,

[0065]

(Equation 1) It is represented by the following formula. "D-0x" is 10
^-X means

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

[0067]

[Outside 1]

[0068]

[Outside 2]

[0069]

[Outside 3]

[0070]

[Outside 4]

[0071]

[Outside 5]

[0072]

[Outside 6]

[0073]

[Table 1]

[0074]

As described above, according to the present invention, by appropriately setting the lens configuration of the objective lens system having a zooming unit, it is possible to reduce the size of the entire lens system while maintaining a predetermined zooming ratio. It is possible to achieve a compact real image type variable magnification finder that can be easily obtained and that allows a favorable finder image to be observed over the entire magnification range.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a variable magnification finder according to the present invention.

FIG. 2 is a lens sectional view of a numerical example 1 of a variable magnification finder according to the present invention;

FIG. 3 is a sectional view of a zoom lens according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a zoom lens according to a third embodiment of the present invention.

FIG. 5 is a lens sectional view of a numerical example 4 of the variable magnification finder according to the present invention;

FIG. 6 is a lens cross-sectional view of Numerical Example 5 of the variable magnification finder according to the present invention.

FIG. 7 is a sectional view of a zoom lens according to a sixth embodiment of the present invention.

FIG. 8 is an aberration diagram at a wide-angle end at a reference distance of 3 m in Numerical Example 1 of the variable magnification finder according to the present invention;

FIG. 9 is an intermediate aberration diagram at a reference distance of 3 m in Numerical Example 1 of the variable magnification finder according to the present invention;

FIG. 10 is an aberration diagram at a telephoto end at a reference distance of 3 m in Numerical Example 1 of the variable magnification finder according to the present invention;

FIG. 11 is an aberration diagram at a wide-angle end at a reference distance of 3 m in Numerical Example 2 of the variable magnification finder according to the present invention;

FIG. 12 is an intermediate aberration diagram at a reference distance of 3 m in Numerical Example 2 of the variable magnification finder according to the present invention.

FIG. 13 is an aberration diagram at a telephoto end at a reference distance of 3 m in Numerical Example 2 of the variable magnification finder according to the present invention;

FIG. 14 is an aberration diagram at a wide-angle end of a reference distance of 3 m in Numerical Example 3 of the variable magnification finder according to the present invention;

FIG. 15 is an intermediate aberration diagram at a reference distance of 3 m in Numerical Example 3 of the variable magnification finder according to the present invention;

FIG. 16 is an aberration diagram at a telephoto end at a reference distance of 3 m in Numerical Example 3 of the variable magnification finder according to the present invention;

FIG. 17 is an aberration diagram at a wide-angle end at a reference distance of 3 m in Numerical Example 4 of the variable magnification finder according to the present invention;

FIG. 18 is an intermediate aberration diagram at a reference distance of 3 m in Numerical Example 4 of the variable magnification finder according to the present invention.

FIG. 19 is an aberration diagram at a telephoto end at a reference distance of 3 m in Numerical Example 4 of the variable magnification finder according to the present invention;

FIG. 20 is an aberration diagram at a wide-angle end at a reference distance of 3 m in Numerical Example 5 of the variable magnification finder according to the present invention;

FIG. 21 is an intermediate aberration diagram at a reference distance of 3 m in Numerical Example 5 of the variable magnification finder according to the present invention;

FIG. 22 is an aberration diagram at a telephoto end at a reference distance of 3 m in Numerical Example 5 of the variable magnification finder according to the present invention;

FIG. 23 is an aberration diagram at a wide-angle end at a reference distance of 3 m in Numerical Example 6 of the variable magnification finder according to the present invention;

FIG. 24 is an intermediate aberration diagram at a reference distance of 3 m in Numerical Example 6 of the variable magnification finder according to the present invention;

FIG. 25 is an aberration diagram at a telephoto end at a reference distance of 3 m in Numerical Example 6 of the variable magnification finder according to the present invention;

[Explanation of symbols]

 Reference Signs List 10 Objective lens system F Field lens P Image reversal optical system Le Eyepiece lens system L1 First group L2 Second group L3 Third group E Eye point d D line FF line C C line ΔS Sagittal image plane ΔM Meridional image plane

Claims (10)

[Claims] An object image formed by an objective lens system having a positive refractive power having a zooming function in order from an object side is converted into an erect image via an image inverting optical system, and the erect image is observed by an eyepiece lens system. In the double viewfinder, the objective lens system includes three lens groups, a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power. During zooming, the second unit moves with a convex trajectory toward the observation side, and the third unit moves toward the object side such that the air gap with the second unit decreases. The difference between the position of the second unit on the optical axis at the telephoto end and the position at the telephoto end with respect to the wide-angle end is m2 (where positive when provided on the observation side). satisfy the -0.5 <m2 / L ₀ <0.1 condition: when the distance to the lens surface on the most image side of the third group was L ₀ Zoom finder, it characterized in that the. 2. When the focal length of the i-th lens unit of the objective lens system is fi, a condition of -0.1 <f2 / f1 <-0.005 0.005 <f3 / f1 <0.1 is satisfied. The variable magnification finder according to claim 1, wherein: 3. The variable magnification finder according to claim 1, wherein each lens group of said objective lens system comprises a single lens, and has at least three aspheric surfaces as a whole. 4. A field lens having a reflection surface is provided between the objective lens system and the image inverting optical system, and the field lens is located near a position of an object image formed by the objective lens system. , The radius of curvature of the lens surface a is Rf, the focal length of the eyepiece is fe, the position of the object image and the lens surface a are
2. The variable magnification finder according to claim 1, wherein a condition of 0.2 <fe / Rf <2.0-10 <1000.times.df / fe <0.5 is satisfied, where df is the distance between the zoom lens and the camera. 5. A first lens at a wide-angle end of the objective lens system.
When the distance from the lens surface closest to the object side of the group to the lens surface closest to the observation side of the third group is L ₀ , and the focal length of the objective lens system at the wide-angle end is fw 1.5 <L ₀ / fw <3 The zoom finder according to claim 1, wherein the following condition is satisfied. 6. An object image formed by an objective lens system having a positive refractive power having a zooming function in order from the object side to form an erect image via an image inverting optical system, and the erect image is observed by an eyepiece lens system. In the magnification finder, the objective lens system has a negative lens group having a negative refractive power and a lens group having a positive refractive power. When the magnification is changed from the wide-angle end to the telephoto end, the positive lens group moves toward the object side. The distance between the air in each lens group is reduced, and when the refractive index of the material of the positive lens in the positive lens group is Np, the condition 1.52 <Np <1.9 is satisfied. Variable magnification finder. 7. The objective lens system according to claim 1, wherein the objective lens system has a first refractive power.
7. The zoom lens according to claim 6, further comprising three lens groups: a first lens group, a second lens group having a negative refractive power, and a third lens group having a positive refractive power.
Variable magnification finder. 8. The positive lens group has an aspherical surface in which positive refractive power decreases from the optical axis center to the periphery.
The focal lengths of the negative lens unit and the positive lens unit are fn and f, respectively.
7. The variable magnification finder according to claim 6, wherein, when P is satisfied, a condition of -2.0 <fn / fP <-0.5 is satisfied. 9. A field lens having a reflecting surface is provided between the objective lens system and the image inverting optical system, and the field lens is observed near a position of an object image formed by the objective lens system. It has a lens surface a having a positive refractive power with the convex surface directed to the side, the radius of curvature of the lens surface a is Rf, the focal length of the eyepiece is fe, the position of the object image and the lens surface a are 7. The variable magnification finder according to claim 6, wherein a condition of 0.2 <fe / Rf <2.0-0.5 <1000.times.df / fe <0.5 is satisfied when an interval of df is df. 10. The variable magnification finder according to claim 6, wherein each lens group of said objective lens system comprises a single lens, and each lens group has at least one aspheric surface.