JP3082707B2 - Zoom finder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom finder, and more particularly to a real image type compact high zoom zoom finder.

[0002]

2. Description of the Related Art In recent years, cameras have been required to have higher functionality and smaller size. One of the advanced functions is to increase the zoom ratio (high zoom ratio). In a camera provided with a finder as a completely independent unit separate from a photographing system, a finder unit that satisfies the two conflicting conditions is required. The most contradictory to the high zoom ratio among the miniaturization is the miniaturization in the full length direction.
The length of the finder objective system is important for reducing the overall length.

[0003]

A conventional example having a positive / negative / positive objective optical system and having a variable magnification ratio of about 3 to 4 is disclosed in Japanese Patent Laid-Open Publication No. Hei.
-173713, JP-A-2-173714, JP-A-2-191908, JP-A-6-102
Although it is proposed in Japanese Patent Publication No. 453, if an attempt is made to further increase the zoom ratio, the overall length of the objective system becomes longer and the compactness is lacking.

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and a zooming system capable of satisfying, at a high level, a contradictory demand for a further high zooming ratio of 5 times or more and compactness. The purpose is to provide a finder.

[0005]

In order to achieve the above object, a variable magnification finder according to a first aspect of the present invention is a real image type variable magnification finder separate from a photographing system.
A first group having a positive refractive power and a second group having a negative refractive power
A four-group objective optical system including a lens group, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, and zooming by moving the second lens group in the optical axis direction. And correcting a diopter change due to zooming at least by moving the third lens unit in the optical axis direction, thereby satisfying the following conditional expression (1). 0.15 ≦ β4W / FLWobj ≦ 0.28 (1) where β4W is the imaging magnification of the fourth unit at the wide-angle end , FLWobj is the focal length of the objective optical system at the wide-angle end , and the unit of β4W / FLWobj is mm ^{− Is} one.

A zoom finder according to a second aspect of the present invention is characterized in that, in the configuration of the first aspect, the following conditional expression (2) is further satisfied. 0.038 ≦ 1 / FL1 ≦ 0.068 (2) where FL1: a positive first lens group focal length , and the unit of 1 / FL1 is mm ⁻¹ .

The variable magnification finder according to a third aspect of the present invention is the variable magnification finder according to the first aspect, wherein, when the maximum effective diameter of the aspheric surface is ymax, an arbitrary height in the vertical direction of the optical axis satisfying 0.7ymax <y <ymax.
The third lens unit has at least one aspherical surface satisfying the following conditional expression (3) with respect to y. -0.07 <φ3 · (N'-N) · (d / dy) {x (y) -x0 (y)} <0… (3) where φ3: refractive power of the third lens unit, N: aspherical surface The refractive index of the object-side medium with respect to d-line, N ': the refractive index of the aspheric surface with respect to the d-line of the image-side medium, x (y): the surface shape of the aspheric surface, x0 (y): the reference spherical shape of the aspheric surface , X (y) and x0 (y) are expressed by the following equations (A) and (B), respectively, and x (y) = (r / ε) · [1-√ {1-ε · (y ² / r ² )}] + ΣAiy ⁱ (where i ≧ 2)… (A) x0 (y) = r # · [1-√ {1- (y ² / r # ² )}]… ( B) In equations (A) and (B), r: reference radius of curvature of aspheric surface, ε: quadratic surface parameter, Ai: coefficient of i-th order aspheric surface, r #: paraxial radius of curvature of aspheric surface {where , 1 / r # = (1 / r) + 2 · A2} , and the unit of φ3 · (N′−N) · (d / dy) {x (y) −x0 (y)} is mm ⁻¹
It is.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a variable magnification finder embodying the present invention will be described with reference to the drawings. 1 to 7
Shows optical configurations and optical paths at the wide-angle end [W], the middle band [M], and the telephoto end [T] corresponding to the first to seventh embodiments, respectively. At the wide-angle end [W] in FIGS.
= 1,2,3, ...) is the i-th surface counted from the object side, Gi (i = 1,
(2, 3) indicates the i-th optical element counted from the object side, and indicates that the surface Si marked with * is a surface composed of an aspherical surface.

The first to seventh embodiments are real image type zoom finders separate from the photographing system, and include, in order from the object side, a first lens unit Gr1 having a positive refractive power, and a negative refractive power. And a third group Gr2 having a positive refractive power.
3 and a fourth group Gr4 having a negative or positive refractive power. And the second
Zooming is performed by moving the group Gr2 in the optical axis direction, and at least the diopter change due to zooming is corrected by moving the third group Gr3 in the optical axis direction.

The objective optical system according to the first embodiment is
This is a four-group zoom including four zoom groups of positive, negative, positive, and negative. The first group Gr1 includes one biconvex positive lens G1. The second group Gr2 includes a biconcave negative lens G2,
A light shielding plate A, a negative meniscus lens G3 concave to the object side,
Consists of The third group Gr3 includes one biconvex positive lens G4. The fourth unit Gr4 includes one negative objective prism G5 having a concave surface facing the object side.
The eyepiece optical system includes an eyepiece prism G6 having a convex surface facing the object side, and a biconvex positive eyepiece G7.

The objective optical system in the second embodiment is
This is a four-group zoom including four zoom groups of positive, negative, positive, and negative. The first group Gr1 includes one biconvex positive lens G1. The second group Gr2 includes two biconcave negative lenses G
2, G3, and a light-shielding plate A disposed therebetween. The third group Gr3 includes one biconvex positive lens G4. The fourth group Gr4 includes one biconcave negative lens G5. The eyepiece optical system includes an eyepiece prism G6 having a convex surface facing the object side, and a biconvex positive eyepiece G7.

The objective optical system according to the third embodiment has:
This is a four-group zoom including four zoom groups of positive, negative, positive, and negative. The first group Gr1 includes one biconvex positive lens G1. The second group Gr2 includes a negative meniscus lens G2 concave on the image side, a light shielding plate A, and a biconcave negative lens G3. The third group Gr3 includes one biconvex positive lens G4. The fourth unit Gr4 includes one negative objective prism G5 having a concave surface facing the object side. The eyepiece optical system includes an eyepiece prism G6 having a convex surface facing the object side, and a biconvex positive eyepiece G7.

The objective optical system according to the fourth embodiment is
This is a four-group zoom including four zoom groups of positive, negative, positive, and negative. The first group Gr1 includes one biconvex positive lens G1. The second group Gr2 includes two biconcave negative lenses G
2, G3, and a light-shielding plate A disposed therebetween. The third group Gr3 includes one biconvex positive lens G4. The fourth unit Gr4 includes a single negative meniscus lens G5 that is concave on the object side. The eyepiece optical system includes an eyepiece prism G6 having a convex surface facing the object side, and a biconvex positive eyepiece G7.

The objective optical system according to the fifth embodiment comprises:
This is a four-group zoom including four zoom groups of positive, negative, positive, and negative. The first group Gr1 includes one biconvex positive lens G1. The second group Gr2 includes a biconcave negative lens G2,
A light shielding plate A, a negative meniscus lens G3 concave to the object side,
Consists of The third group Gr3 includes one biconvex positive lens G4. The fourth unit Gr4 includes one negative objective prism G5 having a concave surface facing the object side.
The eyepiece optical system includes an eyepiece prism G6 having a convex surface facing the object side, and a biconvex positive eyepiece G7.

The objective optical system according to the sixth embodiment comprises:
This is a four-group zoom including four zoom groups of positive, negative, positive, and negative. The first group Gr1 includes one biconvex positive lens G1. The second group Gr2 includes a negative meniscus lens G2 concave on the image side, a light shielding plate A, and a biconcave negative lens G3. The third group Gr3 includes one biconvex positive lens G4. The fourth unit Gr4 includes one negative objective prism G5 having a concave surface facing the object side. The eyepiece optical system comprises an eyepiece prism G6 having a convex surface facing the object side, an eyepiece prism G7 having a concave surface facing the pupil side, and a biconvex positive eyepiece G8.

The objective optical system according to the seventh embodiment comprises:
This is a four-group zoom including four positive / negative / positive / positive zoom groups. The first group Gr1 includes a single positive meniscus lens G1 that is convex on the object side. The second group Gr2 includes a negative meniscus lens G2 concave on the image side, a light shielding plate A, and a biconcave negative lens G3. The third group Gr3 includes one biconvex positive lens G4. 4th group Gr4
Is a positive meniscus objective prism G5 convex to one image side.
Consists of The eyepiece optical system includes an eyepiece prism G6 consisting of only a plane, an eyepiece prism G7 having a concave surface facing the pupil, and a biconvex positive eyepiece G8.

Further, the first to seventh embodiments are configured to satisfy the following conditional expression (1). 0.15 ≦ β4W / FLWobj ≦ 0.28 (1) where β4W is the imaging magnification of the fourth lens unit Gr4 at the wide-angle end [W] , and FLWobj is the focal length of the objective optical system at the wide-angle end [W]. The unit of / FLWobj is mm ^-1 .

The positive / negative / positive objective configuration is conventionally known as a high-magnification and compact viewfinder objective configuration. If the fourth lens unit Gr4 having a high magnification is arranged behind the positive, negative, and positive positions, the overall configuration of the finder objective system is further reduced because the objective configuration is a telephoto type as a whole. This is utilized in the first to seventh embodiments. That is, in the positive / negative / positive / (negative or positive) objective configuration, by setting the imaging magnification of the fourth lens unit Gr4 to a high magnification, the total length of the finder objective system can be further shortened while the zoom ratio is 5 Even if it is more than twice, the compactness is not impaired.

Conditional expression (1) defines a condition range for sufficiently exhibiting the above-described effects and ensuring good aberration performance over the entire zoom range by setting a fourth range with respect to the focal length of the objective system at the wide-angle end [W]. It is represented by the ratio of the imaging magnification of the group Gr4. Conditional expression (1)
If the lower limit is exceeded, the above-mentioned effects will not be sufficiently exerted, and compactness will be lost. If the upper limit of conditional expression (1) is exceeded, the deterioration of the image surface property and the astigmatism particularly in the entire zoom range become remarkable, and it becomes difficult to secure good aberration performance.

Further, the first to seventh embodiments are configured to further satisfy the following conditional expression (2). 0.038 ≦ 1 / FL1 ≦ 0.068 (2) where FL1: the focal length of the first positive lens unit Gr1 , and the unit of 1 / FL1 is mm ⁻¹ .

In the objective configuration in the first to seventh embodiments, the refractive power of the first positive lens unit Gr1 has a great effect on the amount of movement of the second lens unit Gr2, which mainly performs zooming, due to zooming. . In order to shorten the overall length of the objective optical system, it is important to reduce the amount of movement of each group due to zooming. Conditional expression
(2) makes it possible to both reduce the amount of movement of the second group Gr2, which is an essential condition for shortening the overall length of the objective optical system, and to ensure good aberration performance over the entire zoom range. This shows an appropriate setting range of the refractive power of the first lens unit Gr1 for performing the above operation. If conditional expression (2) is satisfied, a compact viewfinder with a short overall length of the objective optical system can be achieved while ensuring good aberration over the entire zoom range. If the lower limit of conditional expression (2) is exceeded, the amount of movement of the second unit Gr2 required for zooming will increase, and the overall length of the objective optical system will increase. If the upper limit of conditional expression (2) is exceeded, aberration fluctuations, particularly due to zooming, will increase, and the position error sensitivity in the optical axis direction with respect to the diopter of the first lens unit Gr1 will also increase.

In the first to seventh embodiments, the maximum effective diameter of the aspherical surface (that is, the maximum height in the direction perpendicular to the optical axis) is ym.
When ax is satisfied, the third lens unit Gr3 has at least one aspheric surface satisfying the following conditional expression (3) for an arbitrary height y in the vertical direction of the optical axis where 0.7ymax <y <ymax. . -0.07 <φ3 · (N′-N) · (d / dy) {x (y) −x0 (y)} <0 (3) where φ3: refractive power of the third group Gr3, N: aspherical surface Where N 'is the refractive index of the aspherical image-side medium for the d-line, x (y) is the aspherical surface shape, and x0 (y) is the aspherical reference spherical shape. X (y) and x0 (y) are expressed by the following equations (A) and (B), respectively, and x (y) = (r / ε) · [1-√ {1-ε · (y ² / r ² )}] + ΣAiy ⁱ (where i ≧ 2)… (A) x0 (y) = r # · [1-√ {1- (y ² / r # ² )}]… (B) In equations (A) and (B), r: reference radius of curvature of aspheric surface, ε: quadratic surface parameter, Ai: coefficient of aspheric surface of order i, r #: paraxial radius of curvature of aspheric surface {here And 1 / r # = (1 / r) + 2 · A2} , and the unit of φ3 · (N′−N) · (d / dy) {x (y) −x0 (y)} is mm ^{− 1}
It is.

In the structures of the first to seventh embodiments, since the third positive lens unit Gr3 has a strong refractive power, the third lens unit G3
The amount of aberration generated at r3 is large. The use of at least one aspherical surface for the third lens unit Gr3 is effective in correcting aberrations more favorably. Conditional expression (3) indicates the range of the aspherical shape for sufficiently exhibiting this effect, and by satisfying conditional expression (3), aberrations (especially, image surface properties and spherical aberration) over the entire zoom range are obtained. Is satisfactorily corrected. If the lower limit of conditional expression (3) is exceeded, the aberration will be overcorrected, and in particular, the image quality will deteriorate. If the upper limit of conditional expression (3) is exceeded, the effect of the aspheric surface will act in the direction of reversely correcting the aberration, and the aberration will be worsened.

Next, a description will be given of a desirable configuration which effectively works in achieving the good aberration correction and compactness in each of the above-mentioned types of objective configurations. Desirable configuration 1
Nos. 3 are configurations that exhibit an effective action in aberration correction. Desirable configuration 4 is a configuration that exhibits an effective action for cutting harmful light and ensuring good mie.
Desirable configuration 5 is a configuration that exerts an effective action particularly with respect to compactness in the radial direction.

<< Preferred Configuration 1 >> In the second to seventh embodiments, the positive third lens unit Gr3 has at least the following conditional expression:
Includes a positive biconvex lens satisfying (4). Nd3 ≧ 1.6 (4) where Nd3 is the refractive index of the lens glass for d-line.

In this type of objective configuration, the third lens group G
Since r3 has a strong positive refractive power, the Petzval sum deteriorates, and the image surface property in the entire zoom region is likely to deteriorate.
As in the second to seventh embodiments, a positive biconvex lens made of a glass material having a high refractive index that satisfies conditional expression (4) is replaced with a third group Gr3.
When at least one image is used, the Petzval sum in the entire finder system is improved, and particularly, the image surface property in the entire zoom range is favorably corrected.

<< Preferred Configuration 2 >> In the sixth embodiment, the positive first lens unit Gr1 is a single lens made of a low dispersion glass type satisfying the following conditional expression (5). νd> 65 (5) where νd: Abbe number at d-line.

The objective optical system forms a real image of the image formed by the first group Gr1 on the objective image plane with the total image forming magnification of the second group Gr2 to the fourth group Gr4. The zooming is performed in the second group G
This is performed by changing the total imaging magnification of the second to fourth lens units Gr2 to Gr4. Chromatic aberration of the image formed by the first group Gr1 (that is, chromatic aberration generated in the first group Gr1)
Is enlarged in the same way by the scaling, so that there is a difference as much as the scaling. This disparity contributes to the chromatic aberration disparity due to zooming. In other words, in a zoom finder, the larger the zoom ratio, the
Since the difference in chromatic aberration between [W] and the telephoto end [T] increases, it becomes difficult to satisfactorily correct chromatic aberration over the entire zoom range.

If the chromatic aberration of the first lens unit Gr1 is large, the difference between the first lens unit and the first lens unit Gr1 is large.
If the amount of chromatic aberration of 1 is reduced, the chromatic aberration difference due to zooming is also reduced. In the sixth embodiment,
In order to reduce the amount of chromatic aberration generated by the first group Gr1, the positive first group Gr1 is constituted by a single lens made of a low dispersion glass type satisfying conditional expression (5). Thus the first
By suppressing the chromatic aberration generated in the group Gr1, the chromatic aberration difference due to zooming can be satisfactorily corrected. The first positive lens unit Gr1 may have a chromatic aberration correction configuration including two positive and negative lenses including a positive lens and a negative lens made of a highly dispersed glass material than the positive lens. In this case, the same effect as described above is obtained. Is obtained.

<< Preferred Configuration 3 >> In the first to seventh embodiments, the second lens unit Gr2 is composed of two negative lenses whose strongly concave surfaces face each other. The second lens unit Gr2 that moves for zooming has a strong negative refractive power in order to suppress the amount of movement. Therefore, it is effective to form the second group Gr2 with two negative lenses whose surfaces having strong negative refractive power face each other in order to ensure good aberration performance. Thus, the second group Gr
With the configuration 2, excellent aberration performance over the entire zoom range
(Especially, distortion and coma) are ensured. This configuration works particularly effectively as the zoom ratio becomes higher.

<< Preferred Configuration 4 >> In the first to seventh embodiments, a light beam regulating member (light shielding plate A) for cutting harmful light is provided between two negative lenses constituting the second group Gr2. Are located. In the viewfinder, it is desirable that the luminous flux incident on the pupil be well controlled over the entire zoom range in order to secure a stable mie. In order to control the light satisfactorily, it is necessary to dispose a light beam restricting member that blocks harmful light at an objective aperture position conjugate with the finder pupil position.

In the objective configuration of this type, the first lens unit Gr1 is provided by a condenser surface placed near the objective image surface.
It is necessary to adjust so as to balance the size of the effective diameter between the third lens unit Gr3 and the third lens unit Gr3. If the refractive power of the condenser surface is made too strong, the effective diameter of the third lens unit Gr3 decreases, but the effective diameter of the first lens unit Gr1 increases. If the refractive power of the condenser surface is made too weak, the effective diameter of the third lens unit Gr3 becomes large. When the refractive power of the condenser surface is adjusted so as to balance the effective diameters of the first lens unit Gr1 and the third lens unit Gr3, the stop position of the objective system conjugate with the finder pupil position becomes close to the second lens unit Gr2. When a light beam regulating member that blocks harmful light is disposed in the second group Gr2, a light beam incident on the pupil is favorably regulated over the entire zoom range, so that a good finder mier can be secured. And
When the second group Gr2 is composed of two negative lenses, 2
By arranging the light flux regulating member between the negative lenses, harmful light can be effectively blocked.

<< Preferred Configuration 5 >> In the first, fourth, and fifth embodiments, the last surface (S2) of the positive first lens unit Gr1 and the negative second lens unit Gr1
With respect to the front surface (S3) of the group Gr2, the maximum effective diameter of the rear surface (S2) of the first group Gr1 (that is, the maximum height in the optical axis vertical direction).
Is defined as Ymax, the following conditional expression (6) is satisfied at the wide-angle end [W] for an arbitrary height Y in the vertical direction of the optical axis where 0.7Ymax <Y <Ymax. 0 <[C01 / {1 + √ (1-ε1 · C01 ² · Y ² )}-C02 / {1 + √ (1-ε2 · C02 ² · Y ² )}] · Y ² + Σ {(A1 i −A2i) · Y ⁱ } + t <0.8 (where i = 2 to 16) (6) where C01: the reference curvature of the last surface (S2) of the first group Gr1, C02: the second curvature The reference curvature of the forefront (S3) of the group Gr2, ε1: the parameter of the secondary surface of the last surface (S2) of the first group Gr1, ε2: the parameter of the secondary surface of the forefront (S3) of the second group Gr2, t: the last surface (S2) of the first lens unit Gr1 and the second lens unit at the wide-angle end [W]
A1i: i-th order aspherical surface coefficient of the last surface (S2) of the first group Gr1, A2i: i-th order aspherical surface coefficient of the last surface (S3) of the second group Gr2 This is an aspheric coefficient.

The surface shape of each surface (S2, S3) is rotationally symmetric about the optical axis, and is defined by the following equations (C) to (E). Expressions (C) to (E) are substantially the same as expression (A) representing the aspheric surface shape x (y) described above. F (X, Y, Z) = Xf (Y, Z) = 0… (C) f (Y, Z) = C0Φ ² / [1+ (1-εC0 ² Φ ² ) ^1/2 ] + ΣAiΦ ⁱ ( Here, i = 2 to 16.)… (D) Φ ² = Y ² + Z ² … (E) where X, Y, Z: X, Y, Z coordinate values of the local coordinate system of each surface , C0: surface vertex curvature (= 1 / r), ε: parameter of a quadratic surface, A2 to A16: aspherical coefficients from second to 16th order.

In the objective configuration having the first positive lens unit Gr1,
Since the second group Gr2 has a strong negative refractive power, the light flux with the first group Gr1 has a strong inclination particularly at the wide-angle end [W]. When the light beam has a strong inclination, the first group Gr
If the distance between the last surface of the first lens unit 1 and the front surface of the second lens unit Gr2 increases, the effective diameter of the first lens unit Gr1 increases. This tendency becomes more remarkable as the viewfinder-compatible angle of view becomes wider. Since the first group Gr1 is a positive lens,
When the effective diameter of the group Gr1 increases, the core thickness increases in order to secure the effective diameter, and the overall length of the objective system also increases.

In order to keep the effective diameter of the first lens unit Gr1 small, the distance between the last surface of the first lens unit Gr1 and the frontmost surface of the second lens unit Gr2 should be as small as possible at the wide-angle end [W] where the effective diameter is the largest. What is necessary is just to make it narrow. Conditional expression (6) expresses this by a mathematical expression. The last surface of the first group Gr1 and the second group G
If conditional expression (6) is satisfied with respect to the forefront of r2,
The effective diameter of the group Gr1 can be reduced, which is particularly advantageous for a wide angle of view. When the value exceeds the upper limit of the conditional expression (6), the diameter of the first lens group increases remarkably, particularly in a viewfinder compatible with wide angles.

<< Example of Finder Configuration >> Next, an example of the configuration of a variable magnification finder embodying the present invention will be described. FIG.
Is a configuration example of a finder including two eyepiece prisms. The objective optical system used in this zoom finder is a four-unit zoom consisting of four positive, negative, positive, and negative zoom groups. The first group Gr1 is a single biconvex positive lens G
Consists of one. The second group Gr2 includes two biconcave negative lenses G2 and G3, and a light shielding plate A disposed therebetween. The third group Gr3 includes one biconvex positive lens G4. The fourth group Gr4 includes one biconcave negative lens G5. Further, the eyepiece optical system has a first eyepiece prism PE1 having a roof reflection surface SD and a second eyepiece prism arranged such that the entrance surface is located at a small interval (S) from the exit surface of the first eyepiece prism PE1. It consists of a two-eye prism PE2 and a biconvex positive eyepiece LE. Note that a plane mirror M1 is disposed between the objective optical system and the eyepiece optical system, where I is an objective image plane, and EP is a pupil.

FIG. 30 shows an example of a finder configuration in which the fourth group Gr4 and the objective prism are integrated. The objective optical system used in this zoom finder is a four-unit zoom consisting of four positive, negative, positive, and negative zoom groups. First
The group Gr1 includes one biconvex positive lens G1. The second group Gr2 includes a negative meniscus lens G2 concave on the image (I) side, a light shielding plate A, and a biconcave negative lens G3. The third group Gr3 includes one biconvex positive lens G4.
Consists of The fourth lens unit Gr4 includes a negative meniscus objective prism PO concave on the object side, and the objective prism PO has a roof reflection surface SD. The eyepiece optical system is composed of an eyepiece prism PE consisting only of a plane and a biconvex positive eyepiece LE. Here, I is an objective image plane, and EP is a pupil.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a variable magnification finder embodying the present invention will be described more specifically with reference to construction data, aberration diagrams, and the like. Examples 1 to 7 given here as examples are examples respectively corresponding to the above-described first to seventh embodiments, and FIGS. 1 to 7 showing the first to seventh embodiments, The optical configuration and optical path of the corresponding Examples 1 to 7 are shown.

Table 1, Table 5, Table 9, Table 13, Table 17, Table 2
1, Table 25 shows the construction data of Examples 1 to 7. In the construction data,
Si (i = 1,2,3, ...) constituting the system, group, and lens (optical element)
Is the i-th surface counted from the object side, the curvature radius of the surface Si, the i-th axial upper surface distance counted from the object side, and the refractive index (Nd ),
Shows the Abbe number (νd). The surface Si marked with * indicates that the surface is constituted by an aspheric surface, and is defined by the above formula (A) representing the surface shape of the aspheric surface.

Table 2, Table 6, Table 10, Table 14, Table 18, Table 22, Table 26 show data that changes during zooming in the first to seventh embodiments. Γ is the viewfinder magnification, ω
(°) is half angle of view, DIOPT is diopter, D1, D
2, D3 is the group interval on the axis that changes during zooming. Table 3, Table 7, Table 11, Table 15, Table 19, Table 2
3, Table 27 shows aspherical surface data of Examples 1 to 7. Table 4, Table 8, Table 12, Table 16, Table 20, Table 24, and Table 28 show values corresponding to the conditional expressions of Examples 1 to 7.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

[Table 6]

[0048]

[Table 7]

[0049]

[Table 8]

[0050]

[Table 9]

[0051]

[Table 10]

[0052]

[Table 11]

[0053]

[Table 12]

[0054]

[Table 13]

[0055]

[Table 14]

[0056]

[Table 15]

[0057]

[Table 16]

[0058]

[Table 17]

[0059]

[Table 18]

[0060]

[Table 19]

[0061]

[Table 20]

[0062]

[Table 21]

[0063]

[Table 22]

[0064]

[Table 23]

[0065]

[Table 24]

[0066]

[Table 25]

[0067]

[Table 26]

[0068]

[Table 27]

[0069]

[Table 28]

FIGS. 8 to 10, FIGS. 11 to 13, and FIGS.
FIGS. 16, 17 to 19, 20 to 22, 23 to 25, and 26 to 28 are aberration diagrams corresponding to the first to seventh embodiments, respectively. FIG. 14, FIG.
7, FIG. 20, FIG. 23, and FIG. 26 show the wide-angle end [W] of each embodiment.
9, FIG. 12, FIG. 15, FIG. 18, FIG. 21, FIG. 24, and FIG. 27 show aberrations in the middle band [M] of each embodiment.
0, FIG. 13, FIG. 16, FIG. 19, FIG. 22, FIG. 25, FIG.
Indicates aberrations at the telephoto end [T] in each embodiment.

In the aberration diagrams of spherical aberration and axial chromatic aberration,
The solid line (e) represents the aberration with respect to the e-line, the dashed line (g) represents the aberration with respect to the g-line, and the dashed line (C) represents the aberration with respect to the C-line in diopters (Diopt.).
f. is the incident height (mm) of the light beam on the most object side surface (S1). In the aberration diagrams of astigmatism, distortion, and chromatic aberration of magnification, Y ′ on the vertical axis is a radian value of the angle of incidence on the pupil (that is, the angle of emergence from the final surface of the finder). In the astigmatism aberration diagram, the solid line (mer-e) is the aberration for the e-line on the meridional surface, and the dashed line (sag-e) is the aberration for the e-line on the sagittal surface, expressed in diopters (Diopt.). I have. In the aberration diagram of the lateral chromatic aberration, the solid line (g) represents the aberration with respect to the g-line, and the broken line (C) represents the aberration with respect to the C-line in the unit of angle (Min.).

[0072]

As described above, according to the present invention, it is possible to achieve a higher zoom ratio and a more compact zoom ratio of 5 times or more.
A variable magnification finder capable of satisfying conflicting requirements at a high level can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical configuration and an optical path according to a first embodiment (Example 1).

FIG. 2 is a diagram showing an optical configuration and an optical path according to a second embodiment (Example 2).

FIG. 3 is a diagram showing an optical configuration and an optical path according to a third embodiment (Example 3).

FIG. 4 is a diagram showing an optical configuration and an optical path according to a fourth embodiment (Example 4).

FIG. 5 is a diagram showing an optical configuration and an optical path according to a fifth embodiment (Example 5).

FIG. 6 is a diagram showing an optical configuration and an optical path according to a sixth embodiment (Example 6).

FIG. 7 is a diagram showing an optical configuration and an optical path according to a seventh embodiment (Example 7).

FIG. 8 is an aberration diagram at a wide-angle end [W] of the first embodiment.

FIG. 9 is an aberration diagram at a middle band [M] of the first embodiment.

FIG. 10 is an aberration diagram at a telephoto end [T] in the first embodiment.

FIG. 11 is an aberration diagram at a wide-angle end [W] of the second embodiment.

FIG. 12 is an aberration diagram at a middle band [M] of the second embodiment.

FIG. 13 is an aberration diagram at a telephoto end [T] in the second embodiment.

FIG. 14 is an aberration diagram at a wide-angle end [W] of the third embodiment.

FIG. 15 is an aberration diagram at a middle band [M] of the third embodiment.

FIG. 16 is an aberration diagram at a telephoto end [T] in the third embodiment.

FIG. 17 is an aberration diagram at a wide-angle end [W] of the fourth embodiment.

FIG. 18 is an aberration diagram for a middle band [M] in the fourth embodiment.

FIG. 19 is an aberration diagram at a telephoto end [T] in the fourth embodiment.

FIG. 20 is an aberration diagram at a wide-angle end [W] of the fifth embodiment.

FIG. 21 is an aberration diagram at a middle band [M] of the fifth embodiment.

FIG. 22 is an aberration diagram at a telephoto end [T] in Example 5.

FIG. 23 is an aberration diagram at a wide-angle end [W] of the sixth embodiment.

FIG. 24 is an aberration diagram at a middle band [M] of the sixth embodiment.

FIG. 25 is an aberration diagram at a telephoto end [T] according to the sixth embodiment.

FIG. 26 is an aberration diagram at a wide-angle end [W] of the seventh embodiment.

FIG. 27 is an aberration diagram at a middle band [M] of the seventh embodiment.

FIG. 28 is an aberration diagram at a telephoto end [T] in the seventh embodiment.

FIG. 29 is an optical configuration diagram showing in cross section an example of a positive / negative / positive / negative type variable magnification finder including two eyepiece prisms.

FIG. 30 shows a positive / negative lens in which the fourth unit and the objective prism are integrated.
FIG. 3 is an optical configuration diagram showing an example of the configuration of a negative / positive / negative type variable magnification finder in cross section.

[Explanation of symbols]

 Gr1 First group Gr2 Second group Gr3 Third group Gr4 Fourth group I Objective image plane EP Pupil

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 25/00-25/04

Claims (3)

(57) [Claims] 1. A real image type variable magnification finder separate from an imaging system, comprising, in order from an object side, a first group having a positive refractive power, a second group having a negative refractive power, A third group having refractive power;
An objective optical system having a four-group configuration including a fourth group having a negative refracting power; performing zooming by moving the second group in the optical axis direction; and moving at least the third group in the optical axis direction. Is a variable magnification finder that satisfies the following conditional expression (1): 0.15 ≦ β4W / FLWobj ≦ 0.28 (1) where β4W is the second magnification at the wide-angle end. Four groups of imaging magnifications, FLWobj: focal length of the objective optical system at the wide-angle end , and the unit of β4W / FLWobj is mm ⁻¹ . 2. The zoom finder according to claim 1, further satisfying the following conditional expression (2): 0.038 ≦ 1 / FL1 ≦ 0.068 (2) where FL1: positive first lens unit Where the unit of 1 / FL1 is mm ⁻¹ . 3. When the maximum effective diameter of the aspherical surface is ymax,
2. The third group has at least one aspherical surface satisfying the following conditional expression (3) for an arbitrary height y in the vertical direction of the optical axis where 0.7ymax <y <ymax. -0.07 <φ3 · (N'-N) · (d / dy) {x (y) -x0 (y)} <0 (3) where φ3 is the refractive power of the third lens unit , N: refractive index of the aspherical object-side medium for d-line, N ′: refractive index of the aspherical image-side medium for d-line, x (y): surface shape of the aspherical surface, x0 (y): aspherical surface X (y) and x0 (y) are expressed by the following equations (A) and (B), respectively, and x (y) = (r / ε) · [1-√ {1- ε · (y ² / r ² )}] + ΣAiy ⁱ (where i ≧ 2)… (A) x0 (y) = r # · [1-√ {1- (y ² / r # ² )}]… (B) In equations (A) and (B), r: reference radius of curvature of the aspheric surface, ε: quadratic surface parameter, Ai: i-th order aspherical coefficient, r #: near aspherical surface The axial radius of curvature {where 1 / r # = (1 / r) + 2 · A2} , and φ3 · (N′−N) · (d / dy) {x (y) −x0 (y)} Is in mm ^-1
It is.