JP2006195367A - Real image type optical finder and imaging apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a real image type high variable-power optical finder where the whole length of an objective lens is shortened. <P>SOLUTION: The real image type optical finder includes an objective lens system 1 having positive refractive power, image erection optical systems 1a and 2a, and an eyepiece system 2b having positive refractive power. The objective lens system 1 includes, in order from an object side, a 1st lens group G<SB>1</SB>having positive refractive power, a 2nd lens group G<SB>2</SB>having negative refractive power, a 3rd lens group G<SB>3</SB>having negative refractive power and a 4th lens group G<SB>4</SB>having positive refractive power, the power is varied by shifting the 2nd lens group G<SB>2</SB>and the 3rd lens group G<SB>3</SB>, and the following conditional expression is satisfied; 9 mm<f1<13.8 mm (provided that f1 denotes the focal distance of the 1st lens group G<SB>1</SB>). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a real image type optical viewfinder having a high zoom ratio and a short objective lens length, and an image pickup apparatus including the same.

Conventionally, as a finder optical system for a silver salt or digital compact camera, a four-group configuration of positive, negative, negative and positive has been proposed as an objective lens particularly suitable for high zoom ratio (for example, patent document). 1 to 6).
Japanese Unexamined Patent Publication No. 3-153206 Japanese Patent Laid-Open No. 5-93863 JP-A-6-300971 JP-A-7-13076 JP 2001-330785 A Japanese Patent Laid-Open No. 2002-90658

  However, these conventional methods have a problem that the total length of the objective lens is long.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a real image optical finder having a short overall length of the objective lens and a high zoom ratio, and an imaging apparatus including the same. There is.

In order to achieve the above object, a real image type optical finder according to the first invention is a real image having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power. In the optical finder, the objective lens system includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens having a negative refractive power, which are arranged in order from the object side. It includes a lens group and a fourth lens group having a positive refractive power, and is configured to perform zooming by moving the second lens group and the third lens group, and satisfy the following conditional expression: ing.
9mm <f1 <13.8mm
Where f1 is the focal length of the first lens group.

The real image type optical finder according to the second aspect of the present invention is the real image type optical finder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power. The objective lens system includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a positive lens arranged in order from the object side. A fourth lens group having a refractive power, each of the lens groups is composed of a single lens, and zooming is performed by moving the second lens group and the third lens group. It is configured to satisfy the conditional expression.
1.45 <fe / f1 <2
Here, fe is the focal length of the eyepiece lens system, and f1 is the focal length of the first lens group.

The real image type optical finder according to the third aspect of the present invention is a real image type optical finder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power. The system is arranged in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a positive refractive power. And a fourth lens group having a zoom ratio, and changing the magnification by moving the second lens group and the third lens group, and satisfying the following conditional expression.
1.5 <f1 / fw <2.5
Here, f1 is the focal length of the first lens group, and fw is the focal length at the wide angle end of the objective lens.

Moreover, it is preferable that the real image type optical finder according to the present invention satisfies the following conditional expression.
-6.41 <(R8-R 7) / (R8 + R7) <-0.71
Where R7 is the radius of curvature of the object side surface of the fourth lens group, and R8 is the radius of curvature of the image side surface of the fourth lens group.

Moreover, it is preferable that the real image type optical finder according to the present invention satisfies the following conditional expression.
-4.82 <(R4-R3) / (R4 + R3) <-1.97
Here, R3 is the radius of curvature of the object side surface of the second lens group, and R4 is the radius of curvature of the image side surface of the second group.

Moreover, it is preferable that the real image type optical finder according to the present invention satisfies the following conditional expression.
1.47 <R1 / fw <1.98
Where R1 is the radius of curvature of the object-side surface of the first lens group, and fw is the point distance at the wide-angle end of the objective lens system at the wide-angle end.

Moreover, it is preferable that the real image type optical finder according to the present invention satisfies the following conditional expression.
-1.72 <f3 / fw <-1.09
Here, f3 is the focal length of the third lens group, and fw is the focal length at the wide angle end of the objective lens system.

Moreover, it is preferable that the real image type optical finder according to the present invention satisfies the following conditional expression.
1.2 <f1 / (ft / fw) <3.27
Where f1 is the focal length of the first lens group, ft is the focal length at the telephoto end of the objective lens system at the telephoto end, and fw is the focal length at the wide-angle end of the objective lens system.

In the real image type optical finder according to the present invention, it is preferable that the second lens group is composed of a single lens so as to satisfy the following conditional expression.
-1.84 <f2 / (ft / fw) <-0.99
Where f2 is the focal length of the second lens group, ft is the focal length at the telephoto end of the objective lens system, and fw is the focal length at the wide-angle end of the objective lens system at the wide-angle end.

  In the real image type optical viewfinder according to the present invention, it is preferable that a prism having a reflecting surface for erecting an image having positive power on the object side is disposed between the fourth lens group and the intermediate image. .

In the real image type optical finder according to the present invention, it is preferable that the first lens group, the second lens group, the third lens group, and the fourth lens group are all composed of one lens. Yes.
In the real image type optical finder according to the present invention, the object side surface of the prism is preferably a convex surface.
An imaging apparatus according to the present invention includes any one of the above-described real image type optical viewfinders and an imaging optical system having an optical axis different from that of the viewfinder.

  According to the present invention, it is possible to provide a real image optical viewfinder having a high zoom ratio and a short objective lens length, and an image pickup apparatus including the same.

Prior to the description of the embodiments, the effects of the present invention will be described in detail.
According to the present invention, in the real image type optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective lens system is A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, which are arranged in order. And changing the magnification by moving the second lens group and the third lens group, and satisfying the following conditional expression (1).
9mm <f1 <13.8mm (1)
Where f1 is the focal length of the first lens group.
The positive / negative / negative positive four-group configuration is suitable for high zooming, and has been widely used in high zoom zoom lenses. Since the lens arrangement is symmetric as a whole, it is suitable for correcting off-axis aberrations. Further, considering that the pupil diameter of the observer is about 4 mm, the objective lens length can be designed short by satisfying conditional expression (1). That is, if the lower limit of conditional expression (1) is not reached, the focal length of the entire objective lens system is shortened. As a result, the observation magnification is reduced and it is difficult to secure a space for arranging the image erecting optical system. Alternatively, since aberrations occurring in the first lens group are corrected by subsequent lenses, it is difficult to achieve the original purpose of shortening the overall length. If the upper limit is exceeded, the focal length of the entire objective lens system becomes long, and as a result, the objective lens length becomes long. Alternatively, if the focal length is shortened and aberrations are corrected well with the subsequent lenses, the number of lenses increases, resulting in a long focal length, and a space for arranging the image erecting optical system. It becomes difficult to secure.

Further, according to the present invention, in the real image optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective systems are sequentially arranged from the object side. A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, arranged, Each lens group is composed of one lens, and is configured to satisfy the following conditional expression (2) by performing zooming by moving the second group and the third group.
1.45 <fe / f1 <2 (2)
Here, fe is the focal length of the eyepiece lens system, and f1 is the focal length of the first lens group.
The positive / negative / negative positive four-group configuration is suitable for high zooming, and has been widely used in high zoom zoom lenses. Since the lens arrangement is symmetric as a whole, it is suitable for correcting off-axis aberrations. Furthermore, the objective lens length can be designed to be short by disposing an image erecting optical system, taking into consideration easy magnification, and satisfying conditional expression (2). That is, if the lower limit of conditional expression (2) is not reached, the focal length of the entire objective lens system is shortened. As a result, the observation magnification is reduced, and it is difficult to secure a space for arranging the image erecting optical system. Alternatively, since aberrations occurring in the first lens group are corrected by subsequent lenses, it is difficult to achieve the original purpose of shortening the overall length. If the upper limit is exceeded, the focal length of the entire objective lens system becomes long, and as a result, the objective lens length becomes long. Or, if the focal length is shortened and aberrations are corrected well with subsequent lenses, the number of lenses increases, resulting in a long focal length, or a space where an image erecting optical system is disposed. It will be difficult to secure.

According to the present invention, in the real image optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective lens system is A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power arranged in order. In addition, zooming is performed by moving the second lens group and the third lens group, and the following conditional expression (3) is satisfied.
1.5 <f1 / fw <2.54 (3)
Here, f1 is the focal length of the first lens group, and fw is the focal length at the wide angle end of the objective lens.
If the lower limit of conditional expression (3) is not reached, the power of the first lens group becomes strong, and the aberration fluctuation at the time of zooming becomes large. In addition, the effect on the diopter for the mounting error of the first lens group becomes strong. In addition, the back focus of the objective lens system becomes short, and it becomes difficult to put a prism in the objective lens system. If the upper limit of conditional expression (3) is exceeded, the distortion disparity due to zooming becomes large.
Furthermore, it is preferable that conditional expression (3) satisfies the following conditional expression.
1.88 <f1 / fw <2.51
1.92 <f1 / fw <2.30
1.98 <f1 / fw <2.30

According to the present invention, in the real image optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective lens system is A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power arranged in order. In addition, zooming is performed by moving the second lens group and the third lens group, and the following conditional expression (4) is satisfied.
-6.41 <(R8-R7) / (R8 + R7) <-0.71 (4)
However, R7 is the radius of curvature of the object side surface of the fourth lens group, and R8 is the radius of curvature of the image side surface of the fourth lens group.
If the above conditional expression (4) is not satisfied, the balance between the amount of spherical aberration and coma generated on the R7 and R8 surfaces in the telephoto state is lost, which is not desirable.

According to the present invention, in the real image optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective lens system is A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power arranged in order. In addition, zooming is performed by moving the second lens group and the third lens group, and the following conditional expression (5) is satisfied.
-4.82 <(R4-R3) / (R4 + R3) <-1.97 (5)
Here, R3 is the radius of curvature of the object side surface of the second lens group, and R4 is the radius of curvature of the image side surface of the second lens group.
If the upper limit of conditional expression (5) is exceeded, it will be difficult to correct spherical aberration at the telephoto end. If the lower limit is not reached, the fluctuation of astigmatism increases.

According to the present invention, in the real image optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective lens system is A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power arranged in order. In addition, zooming is performed by moving the second lens group and the third lens group, and the following conditional expression (6) is satisfied.
1.47 <R1 / fw <1.98 (6)
Where R1 is the radius of curvature of the object side surface of the first lens group, and fw is the focal length at the wide-angle end of the objective lens system.
If the lower limit of conditional expression (6) is not reached, distortion at the wide-angle end will increase in the negative direction. If the upper limit is exceeded, spherical aberration and coma at the telephoto end will increase.

According to the present invention, in the real image optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective lens system is A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power arranged in order. In addition, zooming is performed by moving the second lens group and the third lens group, and the following conditional expression (7) is satisfied.
-1.72 <f3 / fw <-1.09 (7)
Here, f3 is the focal length of the third lens group, and fw is the focal length at the wide angle end of the objective lens system.
If the upper limit of conditional expression (7) is exceeded, the lens will become decentered in terms of optical performance, making it difficult to handle the movable group. If the lower limit is not reached, the amount of movement of the second lens group and the third lens group increases, making it difficult to reduce the size.

According to the present invention, in the real image optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective lens system is A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power arranged in order. In addition, zooming is performed by moving the second lens group and the third lens group, and the following conditional expression (8) is satisfied.
1.2 <f1 / (ft / fw) <3.27 (8)
Here, f1 is the focal length of the first lens group, ft is the focal length at the telephoto end of the objective lens system, and fw is the focal length at the wide-angle end of the objective lens system.
If the lower limit of the conditional expression (8) is not reached, the power of the first lens group becomes too strong, and the diopter is not easy to handle due to misalignment during mounting, making it difficult to handle in manufacturing. Moreover, if it exceeds an upper limit, size reduction will become difficult.

According to the present invention, in the real image optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective lens system is A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power arranged in order. In addition, the second lens group is composed of one lens, and is configured to satisfy the following conditional expression (9) by performing zooming by moving the second lens group and the third lens group. .
-1.84 <f2 / (ft / fw) <-0.99 (9)
Where f2 is the focal length of the first lens group, ft is the focal length at the telephoto end of the objective lens system, and fw is the focal length at the wide-angle end of the objective lens system.
If the lower limit of conditional expression (9) is not reached, the power of the second lens group becomes weak, and the amount of movement of the second lens group and the third lens group during zooming increases, making it difficult to reduce the size. If the upper limit is exceeded, the power of the second lens group becomes strong, which is advantageous for downsizing, but it is difficult to maintain good aberrations.

According to the present invention, in the real image optical viewfinder having an objective lens system having a positive refractive power, an image erecting optical system, and an eyepiece system having a positive refractive power, the objective lens system is A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power arranged in order. In addition, zooming is performed by moving the second lens group and the third lens group, and a prism having a positive power on the object side and an image erecting reflecting surface is arranged between the fourth lens group and the intermediate image. Has been.
By placing an image erecting reflecting surface between the fourth lens group and the intermediate image, it can be mounted on a thin camera, which is a recent trend, while maintaining a high zoom ratio. Further, in the positive / negative / negative positive lens configuration, the positive power of the fourth lens group is increased. Therefore, it is good for aberration correction to make the incident surface of the prism between the fourth lens group and the intermediate image convex and disperse the positive power of the fourth lens group.

Further, according to the present invention, preferably, the first lens group having a positive refractive power, the second lens group having a negative refractive power, the third lens group having a negative refractive power, and the first lens group having a positive refractive power. Each of the four lens groups is composed of one lens.
By satisfying the above conditional expressions (1) to (9) and constituting each lens group with one lens, the objective lens optical system has the necessary optical performance, is advantageous for shortening the overall length, and is compact. can do. Optical performance can be derived effectively by using an aspherical surface.

Hereinafter, the present invention will be described in detail based on the illustrated embodiments.
Example 1
FIG. 1 is a cross-sectional view along the optical axis showing the configuration of a real image type optical viewfinder according to the present embodiment, where (a) shows a wide angle, (b) shows an intermediate state, and (c) shows a telephoto state. Yes.

The optical system of the present embodiment is composed of an objective lens system 1 and an eyepiece lens system 2 as shown in FIGS. Objective lens system 1 includes a first lens group G ₁ consisting of a single double-convex positive lens, a second lens group G ₂ consisting of a single double-concave negative lens, a piece having a concave surface on the object side a third lens group G ₃ consisting of a negative lens, a fourth lens group G ₄ consisting of a single double-convex positive lens, and is composed of a double reflected possible prisms 1a. The second lens group G ₂ and the third lens group G ₃ is adapted to be moved along the optical axis Lc independently. The eyepiece lens system 2 is composed of a prism 2a capable of reflecting twice and a single biconvex positive lens 2b. The image erecting optical system includes a prism 1 a in the objective lens system 1 and a prism 2 a in the eyepiece lens system 2.

In the optical system of the present embodiment, zooming is performed by moving the second lens group G ₂ and the third lens group G ₃ on the optical axis Lc. Further, in the optical system of the present embodiment, the prism 1a, is formed by the objective lens system the first lens group G ₁ in _1, the second lens group G _2, the third lens group G ₃ and the fourth lens group G ₄ The inverted image is reflected twice to form an intermediate image, and an erect image is obtained by the prism 2a via the biconvex positive lens 2b in the eyepiece lens system 2.
Aspheric surface is, the image side surface of the biconvex positive lens in the first lens group G _1, the image-side surface of the second lens group biconcave negative lens of G _2, the object side of the negative lens of the third lens group G ₃ , The two surfaces of the biconvex positive lens of the fourth lens group G ₄ , and the object-side surface of the eyepiece lens system 2.

In the following numerical data, R is the paraxial radius of curvature of each lens surface or prism surface, D is the thickness on the optical axis of each lens or prism, or the air spacing between them, and N is the refractive index of each lens or prism. Vd is the Abbe number of each lens or prism, K is the conic coefficient, and A ₄ , A ₆ , A ₈ and A ₁₀ are the aspheric coefficients.
The aspheric shape is expressed by the following expression using each aspheric coefficient. However, the coordinate in the optical axis direction is Z, the coordinate in the direction perpendicular to the optical axis is Y, and r is the radius of curvature at the aspherical vertex.
Z = (Y ² / r) / [1+ {1− (1 + K) · (Y / r) ² } ^1/2 ] + A ₄ Y ⁴ + A ₆ Y ⁶
+ A ₈ Y ⁸ + A ₁₀ Y ¹⁰
In the aspheric coefficient, for example, A ₄ : 6.33E-04 of the aspheric surface 2 can be displayed as 6.33 × 10 ^−4, but in this numerical data, all are displayed in the former format. .
The description regarding the numerical data is commonly used for the numerical data of each embodiment of the present invention.

Hereinafter, numerical data of lenses constituting the real image type optical viewfinder according to the present embodiment will be shown.
Wide-angle end Medium telephoto end Viewfinder magnification 0.29 0.60 1.26
Half angle of view (ω) 19.24 8.92 4.23

FIG. 2 is an aberration diagram of the optical system of the real-image optical finder according to the present embodiment, where (a) shows a state at the wide-angle end, (b) shows an intermediate state, and (c) shows a state at the telephoto end. Yes.
Example 2
FIG. 3 is a cross-sectional view along the optical axis showing the configuration of the real image type optical finder according to the present embodiment, where (a) shows a wide angle, (b) shows an intermediate state, and (c) shows a telephoto state. Yes.

The optical system of the present embodiment is composed of an objective lens system 1 and an eyepiece lens system 2 as shown in FIGS. Objective lens system 1 includes a first lens group G ₁ consisting of a single double-convex positive lens, a second lens group G ₂ consisting of a single double-concave negative lens, a piece having a concave surface on the object side a third lens group G ₃ consisting of a negative lens, a fourth lens group G ₄ consisting of a single double-convex positive lens, and is composed of a double reflected possible prisms 1a. The second lens group G ₂ and the third lens group G ₃ is adapted to be moved along the optical axis Lc independently. The eyepiece lens system 2 is composed of a prism 2a capable of reflecting twice and a single biconvex positive lens 2b. The image erecting optical system includes a prism 1 a in the objective lens system 1 and a prism 2 a in the eyepiece lens system 2.

In the optical system of the present embodiment, zooming is performed by moving the second lens group G ₂ and the third lens group G ₃ on the optical axis Lc. Further, in the optical system of the present embodiment, the prism 1a, is formed by the objective lens system the first lens group G ₁ in _1, the second lens group G _2, the third lens group G ₃ and the fourth lens group G ₄ The inverted image is reflected twice to form an intermediate image, and an erect image is obtained by the prism 2a via the biconvex positive lens 2b in the eyepiece lens system 2.
Aspheric surface is, the image side surface of the biconvex positive lens in the first lens group G _1, the image-side surface of the second lens group biconcave negative lens of G _2, the object side of the negative lens of the third lens group G ₃ 6 surfaces, and both surfaces of the biconvex positive lens of the fourth lens group G ₄ and the object side surface of the eyepiece lens system 2.

Hereinafter, numerical data of lenses constituting the real image type optical viewfinder according to the present embodiment will be shown.
Wide-angle end Medium Telephoto end Magnification 0.29 0.50 0.87
Half angle of view (ω) 19.30 10.77 6.17

  FIG. 4 is an aberration diagram of the optical system of the real-image optical finder according to the present embodiment, where (a) shows a state at the wide-angle end, (b) shows an intermediate state, and (c) shows a state at the telephoto end. Yes.

Example 3
FIG. 5 is a cross-sectional view along the optical axis showing the configuration of the real image type optical viewfinder according to the present embodiment, where (a) shows a wide angle, (b) shows an intermediate state, and (c) shows a telephoto state. Yes.

The optical system of the present embodiment is composed of an objective lens system 1 and an eyepiece lens system 2 as shown in FIGS. Objective lens system 1 includes a first lens group G ₁ consisting of a single double-convex positive lens, a second lens group G ₂ consisting of a single double-concave negative lens, the made from a single double-concave negative lens a third lens group G _3, and the fourth lens group G ₄ consisting of a single double-convex positive lens, and is composed of a double reflected possible prisms 1a. The second lens group G ₂ and the third lens group G ₃ is adapted to be moved along the optical axis Lc independently. The eyepiece lens system 2 is composed of a prism 2a capable of reflecting twice and a single biconvex positive lens 2b. The image erecting optical system includes a prism 1 a in the objective lens system 1 and a prism 2 a in the eyepiece lens system 2.

In the optical system of the present embodiment, zooming is performed by moving the second lens group G ₂ and the third lens group G ₃ on the optical axis Lc. Further, in the optical system of the present embodiment, the prism 1a, is formed by the objective lens system the first lens group G ₁ in _1, the second lens group G _2, the third lens group G ₃ and the fourth lens group G ₄ The inverted image is reflected twice to form an intermediate image, and an erect image is obtained by the prism 2a via the biconvex positive lens 2b in the eyepiece lens system 2.
Aspheric surface is, the image side surface of the biconvex positive lens in the first lens group G _1, the image-side surface of the second lens group biconcave negative lens of G _2, the object side of the negative lens of the third lens group G ₃ 6 surfaces, and both surfaces of the biconvex positive lens of the fourth lens group G ₄ and the object side surface of the eyepiece lens system 2.
Note that the object-side surface of the biconvex positive lens in the fourth lens group G _4, and aspherical surface is provided to the positive power of the lens periphery is weakened.

Hereinafter, numerical data of lenses constituting the real image type optical viewfinder according to the present embodiment will be shown.
Wide angle end Medium telephoto end Magnification 0.29 0.60 0.87
Half angle of view (ω) 19.21 8.90 4.25

  FIG. 6 is an aberration diagram of the optical system of the real-image optical finder according to the present embodiment, where (a) shows the state at the wide-angle end, (b) shows the middle, and (c) shows the state at the telephoto end. Yes.

Example 4
FIG. 7 is a cross-sectional view along the optical axis showing the configuration of the real image type optical viewfinder according to the present embodiment, where (a) shows a wide angle, (b) shows an intermediate state, and (c) shows a telephoto state. Yes.

The optical system of the present embodiment is configured by an objective lens system 1 and an eyepiece lens system 2 as shown in FIGS. Objective lens system 1 includes a first lens group G ₁ consisting of a single double-convex positive lens, a second lens group G ₂ consisting of a single double-concave negative lens, a piece having a concave surface on the object side a third lens group G ₃ consisting of a negative meniscus lens, a fourth lens group G ₄ consisting of a single double-convex positive lens, and is composed of a double reflected possible prisms 1a. The second lens group G ₂ and the third lens group G ₃ is adapted to be moved along the optical axis Lc independently. The eyepiece lens system 2 is composed of a prism 2a capable of reflecting twice and a single biconvex positive lens 2b. The image erecting optical system includes a prism 1 a in the objective lens system 1 and a prism 2 a in the eyepiece lens system 2.

In the optical system of the present embodiment, zooming is performed by moving the second lens group G ₂ and the third lens group G ₃ on the optical axis Lc. Further, in the optical system of the present embodiment, the prism 1a, is formed by the objective lens system the first lens group G ₁ in _1, the second lens group G _2, the third lens group G ₃ and the fourth lens group G ₄ The inverted image is reflected twice to form an intermediate image, and an erect image is obtained by the prism 2a via the biconvex positive lens 2b in the eyepiece lens system 2.
Aspheric surface is, the image side surface of the biconvex positive lens in the first lens group G _1, the image-side surface of the second lens group biconcave negative lens of G _2, the object side of the negative lens of the third lens group G ₃ 6 surfaces, and both surfaces of the biconvex positive lens of the fourth lens group G ₄ and the object side surface of the eyepiece lens system 2. Further, the peripheral portion of the lens of the image side surface of the biconcave negative lens in the second lens group G _2, abutting surfaces of the lens frame (not shown) is provided.
When the objective lens system 1 has a positive, negative, negative, and positive four-group configuration as in the present embodiment, there is no necessity of bringing the second lens group G ₂ and the third lens group G ₃ having negative power close to each other. Therefore, by providing the abutting surface of the lens frame on the image side surface of the negative lens in the second lens group G _2, it can be more narrow the distance between the first lens group G ₁ and the second lens group G _2.

Hereinafter, numerical data of lenses constituting the real image type optical viewfinder according to the present embodiment will be shown.
Wide angle end Medium telephoto end Magnification 0.29 0.60 1.27
Half angle of view (ω) 18.98 8.91 4.24

  FIG. 8 is an aberration diagram of the optical system of the real-image optical finder according to the present embodiment, where (a) shows the state at the wide-angle end, (b) shows the middle, and (c) shows the state at the telephoto end. Yes.

Example 5
FIG. 9 is a cross-sectional view along the optical axis showing the configuration of the real image type optical finder according to the present embodiment, where (a) shows a wide angle, (b) shows an intermediate state, and (c) shows a telephoto state. Yes.

The optical system of the present embodiment is configured by an objective lens system 1 and an eyepiece lens system 2 as shown in FIGS. The objective lens system 1 includes a first lens group G ₁ composed of a single biconvex positive lens, a second lens group G ₂ composed of a single negative lens having a biconcave shape on the optical axis, and both a third lens group G ₃ consisting of a biconcave negative lens, a fourth lens group G ₄ consisting of a single double-convex positive lens, and is composed of a double reflected possible prisms 1a. The second lens group G ₂ and the third lens group G ₃ is adapted to be moved along the optical axis Lc independently. The eyepiece lens system 2 is composed of a prism 2a capable of reflecting twice and a single biconvex positive lens 2b. The image erecting optical system includes a prism 1 a in the objective lens system 1 and a prism 2 a in the eyepiece lens system 2.

In the optical system of the present embodiment, zooming is performed by moving the second lens group G ₂ and the third lens group G ₃ on the optical axis Lc. Further, in the optical system of the present embodiment, the prism 1a, is formed by the objective lens system the first lens group G ₁ in _1, the second lens group G _2, the third lens group G ₃ and the fourth lens group G ₄ The inverted image is reflected twice to form an intermediate image, and an erect image is obtained by the prism 2a via the biconvex positive lens 2b in the eyepiece lens system 2.
Aspheric surface is, the image side surface of the biconvex positive lens in the first lens group G _1, the image-side surface of the second lens group biconcave negative lens of G _2, the object side of the negative lens of the third lens group G ₃ 6 surfaces, and both surfaces of the biconvex positive lens of the fourth lens group G ₄ and the object side surface of the eyepiece lens system 2.
Note that the image side surface of the negative lens in the second lens group G _2, aspherical as positive power gradually becomes stronger toward the peripheral portion is formed from the lens center, the fourth lens group G ₄ An aspherical surface is provided on the object side surface of the biconvex positive lens so that the positive power at the lens periphery is weakened.

Hereinafter, numerical data of lenses constituting the real image type optical viewfinder according to the present embodiment will be shown.
Wide angle end Medium telephoto end Magnification 0.89 0.60 1.27
Half angle of view (ω) 19.11 8.93 4.22

  FIG. 10 is an aberration diagram of the optical system of the real-image optical finder according to the present embodiment, where (a) shows the state at the wide-angle end, (b) shows the middle, and (c) shows the state at the telephoto end. Yes.

Example 6
FIG. 11 is a cross-sectional view along the optical axis showing the configuration of the real image type optical viewfinder according to the present embodiment, where (a) shows a wide angle, (b) shows an intermediate state, and (c) shows a telephoto state. Yes.

The optical system of the present embodiment includes an objective lens system 1 and an eyepiece lens system 2 as shown in FIGS. Objective lens system 1 includes a first lens group G ₁ consisting of a single double-convex positive lens, a second lens group G ₂ consisting of a single double-concave negative lens, a piece having a concave surface on the object side a third lens group G ₃ consisting of a negative lens, a fourth lens group G ₄ consisting of a single double-convex positive lens, and is composed of a double reflected possible prisms 1a. The second lens group G ₂ and the third lens group G ₃ is adapted to be moved along the optical axis Lc independently. The eyepiece lens system 2 is composed of a prism 2a capable of reflecting twice and a single biconvex positive lens 2b. The image erecting optical system includes a prism 1 a in the objective lens system 1 and a prism 2 a in the eyepiece lens system 2.

In the optical system of the present embodiment, zooming is performed by moving the second lens group G ₂ and the third lens group G ₃ on the optical axis Lc. Further, in the optical system of the present embodiment, the prism 1a, is formed by the objective lens system the first lens group G ₁ in _1, the second lens group G _2, the third lens group G ₃ and the fourth lens group G ₄ The inverted image is reflected twice to form an intermediate image, and an erect image is obtained by the prism 2a via the biconvex positive lens 2b in the eyepiece lens system 2.
Aspheric surface is, the image side surface of the biconvex positive lens in the first lens group G _1, the image-side surface of the second lens group biconcave negative lens of G _2, the object side of the negative lens of the third lens group G ₃ 6 surfaces, and both surfaces of the biconvex positive lens of the fourth lens group G ₄ and the object side surface of the eyepiece lens system 2.

Hereinafter, numerical data of lenses constituting the real image type optical viewfinder according to the present embodiment will be shown.
Wide angle end Medium telephoto end Magnification 0.29 0.75 1.89
Half angle of view (ω) 19.18 7.33 2.92

  FIG. 12 is an inspected view of the optical system of the real image type optical finder according to the present embodiment, where (a) shows the wide-angle end, (b) shows the middle, and (c) shows the state at the telephoto end. ing.

Conditional expression numerical value

As the image erecting optical system in the real image type optical finder according to the present invention, for example, as shown in FIG. 13, the prism 1a is configured as a roof reflecting prism and the prism 2a is configured as a pentaprism. The invention is not limited to this, and any material that can erect an image, such as a Porro prism, may be used.
The real image type optical finder according to the present invention configured as described above is a compact camera such as a 35 mm film camera and an APS film compatible camera, a digital camera using an electronic image sensor such as a CCD or CMOS sensor, and a video movie. It can use for various imaging devices. The specific application example is shown below.

  14 to 16 are views showing an embodiment of a digital camera 40 incorporating the real image type optical viewfinder of the present invention. FIG. 14 is a perspective view of the appearance of the digital camera 40 as viewed from the front, and FIG. FIG. 16 is a schematic perspective plan view showing the internal configuration of the digital camera 40. FIG. However, FIGS. 14 and 16 show a state in which the photographing optical system 41 is not retracted. In this example, the digital camera 40 includes an optical system 41 having a photographing optical path 42, a finder optical system 43 having a finder optical path 44, a shutter button 45, a flash 46, a liquid crystal display monitor 47, and a focal length change button. 61, a setting change switch 62, and the like. When the photographing optical system 41 is retracted, the photographing optical system 41, the finder optical system 43, and the flash 46 are covered with the cover 60 by sliding the cover 60. When the cover 60 is opened and the camera 40 is set to the photographing state, the photographing optical system 41 is brought into the non-collapsed state of FIG. Photographing is performed through the optical system 41.

  An object image formed by the photographing optical system 41 is formed on the imaging surface of the CCD 49 via a low-pass filter LF having an IR cut coat and a cover glass CG. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera via the processing means 51. Further, the processing means 51 is connected to a recording means 52 so that a photographed electronic image can be recorded. The recording means 52 may be provided separately from the processing means 51, or may be configured to perform recording and writing electronically using a floppy disk, memory card, MO, or the like. Further, instead of the CCD 49, it may be configured as a silver salt camera in which a silver salt film is arranged.

  Further, on the finder optical path 44, for example, a finder objective optical system configured by the first lens group G1, the second lens group G2, the third lens group G3, the fourth lens group G4, and the prism 1a of the first embodiment. A system 53 is arranged. In the finder objective optical system 53, the focal length changes in conjunction with the zoom lens of the photographing optical system 41, and the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4. The formed reverse image is reflected twice by the prism 1a which is an image erecting optical system to form an intermediate image. On the image side of the prism 1a, an eyepiece optical system 59 including a prism 2a for obtaining an erect image and a positive lens 2b for guiding the obtained erect image to the eyeball E of the observer is disposed. A cover member 50 is disposed on the exit side of the eyepiece optical system 59.

The finder optical system 43 having the finder optical path 44 may use any real image type optical finder of each of the above embodiments when the photographic optical system 41 is a zoom lens. When the photographing optical system 41 is a single-focus optical system, the objective optical system of the finder optical system 43 can be a single-focus objective optical system capable of observing the photographing range.
The digital camera 40 configured as described above can achieve high performance and downsizing since the photographing optical system 41 has high performance and is small and can be retracted.

It is sectional drawing in alignment with the optical axis which shows the structure of the optical system of the real image type optical finder based on 1st Example of this invention, (a) is a wide angle end, (b) is an intermediate | middle, (c) is a telephoto end. Each state is shown. FIG. 4 is an aberration diagram of the optical system of the real-image optical finder according to the first example of the present invention, where (a) shows a state at the wide angle end, (b) shows an intermediate state, and (c) shows a state at the telephoto end. It is sectional drawing in alignment with the optical axis which shows the structure of the optical system of the real image type optical finder based on 2nd Example of this invention, (a) is a wide angle end, (b) is a middle, (c) is a telephoto end. Each state is shown. It is an aberration diagram of the optical system of the real image type optical finder according to the second example of the present invention, where (a) shows a state at the wide angle end, (b) shows an intermediate state, and (c) shows a state at a telephoto end. It is sectional drawing which follows the optical axis which shows the structure of the optical system of the real image type optical finder based on 3rd Example of this invention, (a) is a wide angle end, (b) is a middle, (c) is a telephoto end. Each state is shown. It is an aberration diagram of the optical system of the real image type optical finder according to the third example of the present invention, where (a) shows a state at the wide angle end, (b) shows an intermediate state, and (c) shows a state at a telephoto end. It is sectional drawing in alignment with the optical axis which shows the structure of the optical system of the real image type optical finder based on 4th Example of this invention, (a) is a wide angle end, (b) is a middle, (c) is a telephoto end. Each state is shown. It is an aberration diagram of the optical system of the real image type optical finder according to the fourth example of the present invention, where (a) shows a state at the wide angle end, (b) shows an intermediate state, and (c) shows a state at a telephoto end. It is sectional drawing which follows the optical axis which shows the structure of the optical system of the real image type optical finder based on 5th Example of this invention, (a) is a wide angle end, (b) is an intermediate | middle, (c) is a telephoto end. Each state is shown. It is an aberration diagram of the optical system of the real image type optical finder according to the fifth example of the present invention, where (a) shows a state at a wide angle end, (b) shows an intermediate state, and (c) shows a state at a telephoto end. It is sectional drawing which follows the optical axis which shows the structure of the optical system of the real image type optical finder based on 6th Example of this invention, (a) is a wide angle end, (b) is a middle, (c) is a telephoto end. Each state is shown. It is an aberration diagram of the optical system of the real image type optical finder according to the sixth example of the present invention, where (a) shows a state at the wide angle end, (b) shows an intermediate state, and (c) shows a state at a telephoto end. It is sectional drawing which follows the optical axis which shows the structure of the optical system of the real image type optical finder of this invention which comprised the prism 1a as a roof reflecting prism, and comprised the prism 2a as a pentaprism. It is the perspective view which looked at the external appearance of the digital camera incorporating the real image type optical viewfinder of the present invention from the front. It is the front view which looked at the external appearance of the digital camera shown in FIG. 14 from back. FIG. 15 is a schematic perspective plan view showing an internal configuration of the digital camera shown in FIG. 14.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Objective lens part 2 Eyepiece optical system 1a, 2a Prism 2b Positive lens G ₁ 1st lens group G ₂ 2nd lens group G ₃ 3rd lens group G ₄ 4th lens group Lc Optical axis

Claims (13)

In a real image optical viewfinder having an objective lens system having positive refractive power, an image erecting optical system, and an eyepiece system having positive refractive power, the objective lens systems are arranged in order from the object side. A first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, A real image type optical finder which satisfies the following conditional expression for changing magnification by moving a second lens group and the third lens group.
9mm <f1 <13.8mm
Where f1 is the focal length of the first lens group. In a real image optical viewfinder having an objective lens system having positive refractive power, an image erecting optical system, and an eyepiece system having positive refractive power, the objective lens systems are arranged in order from the object side. A first lens group having a refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, A real image type optical viewfinder characterized in that the lens group is composed of a single lens and satisfies the following conditional expression for changing the magnification by moving the second lens group and the third lens group.
1.45 <fe / f1 <2
Here, fe is the focal length of the eyepiece lens system, and f1 is the focal length of the first lens group. In a real image optical viewfinder having an objective lens system having positive refractive power, an image erecting optical system, and an eyepiece system having positive refractive power, the objective lens systems are arranged in order from the object side. A first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, A real image type optical viewfinder characterized by satisfying the following conditional expression for zooming by moving the second lens group and the third lens group.
1.5 <f1 / fw <2.54
Here, f1 is the focal length of the first lens group, and fw is the focal length of the objective lens at the wide angle end. The real image type optical finder according to claim 1, wherein the following conditional expression is satisfied.
-6.41 <(R8-R7) / (R8 + R7) <-0.71
However, R7 is the radius of curvature of the object side surface of the fourth lens group, and R8 is the radius of curvature of the image side surface of the fourth lens group. The real image type optical finder according to claim 1, wherein the following conditional expression is satisfied.
-4.82 <(R4-R3) / (R4 + R3) <-1.97
Here, R3 is the radius of curvature of the object side surface of the second lens group, and R4 is the radius of curvature of the image side surface of the second lens group. The real image type optical finder according to claim 1, wherein the following conditional expression is satisfied.
1.47 <R1 / fw <1.98
Where R1 is the radius of curvature of the object side surface of the first lens group, and fw is the focal length at the wide-angle end of the objective lens system. The real image type optical finder according to claim 1, wherein the following conditional expression is satisfied.
-1.72 <f3 / fw <-1.09
Here, f3 is the focal length of the third lens group, and fw is the focal length at the wide angle end of the objective lens system. The real image type optical finder according to claim 1, wherein the following conditional expression is satisfied.
1.2 <f1 / (ft / fw) <3.27
Where f1 is the focal length of the first lens group, ft is the focal length at the telephoto end of the telephoto end objective lens system, and fw is the focal length at the wide-angle end of the objective lens system. The real image type optical finder according to claim 1, wherein the following conditional expression is satisfied.
-1.84 <f2 / (ft / fw) <-0.99
Where f2 is the focal length of the second lens group, ft is the focal length at the telephoto end of the objective lens system at the telephoto end, and fw is the focal length at the wide-angle end of the objective lens system.   10. The real image according to claim 1, wherein each of the first lens group, the second lens group, the third lens group, and the fourth lens group includes one lens. Type optical viewfinder.   11. The prism according to claim 1, wherein a prism having a positive power on the object side and a reflecting surface for erecting the image is disposed between the fourth lens group and the intermediate image. The real image type optical viewfinder according to claim 1. The real image type optical finder according to claim 11, wherein the prism has a convex object-side surface. An imaging apparatus comprising: the real-image optical finder according to claim 1; and an imaging optical system having an optical axis different from that of the finder.