JPH0651197A - Real image type finder - Google Patents

Abstract

PURPOSE:To provide a real image type finder optical system which is small in size and applicable to a wide visual field. CONSTITUTION:The real image type finder optical system has an objective group O which has positive refracting power, a condenser group C which has positive refracting power, and an ocular group I which has positive refracting power in order from a subject side. The objective group O consists of a 1st objective group O1 having negative refracting power and a 2nd objective group O2 having positive refracting power; and the 1st objective group O1 consists of a single negative meniscus lens, and the 2nd objective group O2 consists of a cemented lens having positive refracting power. Further, various conditions are satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a real image type finder optical system such as a lens shutter camera and a video camera.

[0002]

2. Description of the Related Art Conventionally, many finder optical systems used in compact cameras and the like are virtual image type such as albada type and inverse Galileo type. Since these optical systems can easily obtain a relatively wide field of view and do not require an erecting prism, the optical system can be downsized. However, the virtual image type finder optical system has drawbacks such as a large lens diameter of a subject side lens and a display of a field frame or the like is difficult to see.

Therefore, in recent years, there has been a demand for a real image type finder optical system which is compatible with the progress of downsizing of cameras and widening of the angle of view of photographing lenses.

[0004]

The real image type finder optical system is for magnifying and observing a subject image formed through an objective lens group and a condenser lens group through an eyepiece lens group. The feature is that the visual field is clearly divided by providing the display frame at the position of the subject image formed by the objective lens group. However, since the subject image is formed once inside the viewfinder, the structure of the viewfinder optical system is complicated and large.

Further, when the real image type finder optical system is small and can observe a wide field of view, the focal length of the objective lens is shortened in order to correspond to a wide angle of view, and the objective lens is formed through the objective lens for further size reduction. It is effective to make the real image as small as possible, but as a result, the refractive power of the objective lens group tends to increase. However, increasing the refracting power of the objective lens group of the real-image finder optical system makes it difficult to maintain a good aberration state because there is a limit in correcting aberrations, and there is a limit to downsizing and widening the field of view. there were.

The present invention, compared to conventional objective lenses,
It is an object of the present invention to provide a real image type finder optical system that is smaller in the number of objective lens groups and that is compatible with a wide field of view.

[0007]

In order to solve the above-mentioned problems, the present invention has, in order from the object side, an objective lens group having a positive refractive power, a condenser lens group having a positive refractive power, and a positive refractive power. And a real image type finder optical system having an eyepiece lens group having a first objective lens group having a negative refractive power and a second objective lens group having a positive refractive power. The objective lens group is composed of a negative meniscus single lens, the second objective lens group is composed of a cemented lens having a positive refractive power, and further, the following conditions are satisfied.

-0.95 <f1 / f2 <-0.5-2.0 <(r2 + r1) / (r2-r1) <-1.4-0.45 <r4 / f2 <-0.30 20 <Ν3 −ν4 <40, where f1: f1 <0, the focal length of the first objective lens group, f2: the focal length of the second objective lens group, r1: the most object side lens of the first objective lens group Radius of curvature of the lens surface on the subject side (in the case of an aspherical surface, the radius of curvature of the apex of that surface), r2: radius of curvature of the lens surface of the image side of the lens closest to the subject in the first objective lens group (note that the aspherical surface) In the case of, the radius of curvature of the apex of the surface), r4: The radius of curvature of the bonding surface of the second objective lens group (in the case of an aspherical surface, the radius of curvature of the apex of the surface), ν3: junction of the second objective lens group Abbe number on the subject side of the lens, ν4: Abbe number on the image side of the cemented lens of the second objective lens group.

[0009]

The real image type finder optical system of the present invention comprises, in order from the subject side, an objective lens group having a positive refracting power as a whole,
The objective lens group includes a first objective lens group having a negative refractive power and a second objective lens group having a positive refractive power, and a condenser lens group having a positive refractive power and an eyepiece lens group having a positive refractive power. Composed.

In order for the real image type finder having such a structure to have a wide field of view, it is necessary to increase the refractive power of the objective lens group. In order to miniaturize the real image type finder optical system, it is effective to limit the number of lenses to be formed and to make the subject image formed by the objective lens group as small as possible. Therefore, by defining the objective lens group by the following conditional expression, it is possible to achieve a small-sized real image type viewfinder with a wide field of view. (1) -0.95 <f1 / f2 <-0.5 (2) -2.0 <(r2 + r1) / (r2-r1) <-1.4 (3) -0.45 <r4 / f2 <−0.30 (4) 20 <ν3 −ν4 <40, where f1: f1 <0, the focal length of the first objective lens group, f2: the focal length of the second objective lens group, r1: the first objective lens group The radius of curvature of the object-side lens surface of the most object-side lens in the lens group (here, the apex curvature radius of that surface in the case of an aspherical surface), r2: the image-side lens of the most object-side lens of the first objective lens group The radius of curvature of the surface (note that, in the case of an aspherical surface, the radius of curvature of the apex of the surface), r4: the radius of curvature of the cemented surface of the second objective lens group (in the case of an aspherical surface, the radius of curvature of the apex of the surface), ν3: Abbe number on the object side of the cemented lens of the second objective lens group, ν4: Abbe number on the image side of the cemented lens of the second objective lens group , It is.

Conditional expression (1) defines the balance of the refractive power of the objective lens group. For example, the refractive power distribution of the first objective lens group and the second objective lens group is defined so as to enable good aberration correction when the objective lens group is given a small size and a refractive power corresponding to a wide angle of view. Is. Therefore,
When the refractive power distribution is below the lower limit of the conditional expression (1), the refractive power of the objective lens group becomes small, so that it becomes impossible to deal with a wide angle of view. As a result, in order to deal with a wide angle of view, it is necessary to enlarge the real image formed by the objective lens, which is disadvantageous for downsizing. On the other hand, if the upper limit of conditional expression (1) is exceeded, the refractive power of the objective lens group increases and a wide angle of view can be dealt with, but a good aberration state cannot be obtained. Therefore, it is preferable to satisfy the conditional expression (1).

However, even within the range of the conditional expression (1), it becomes difficult to correct aberrations if the number of constituent objective lens groups is reduced. However, increasing the number of objective lens groups for this purpose is contrary to miniaturization. Therefore, in the present invention, while satisfying the conditional expression (1), the shape of the first objective lens group is defined by the conditional expression (2), and the second objective lens group is defined by the conditional expressions (3) and (4). Conditional expression (1)
Within the range, the number of objective lens groups is minimized to achieve a good aberration state.

As described above, the conditional expression (2) defines the shape of the first objective lens group for maintaining a favorable aberration state within the range of the conditional expression (1) in the refractive power arrangement of the objective lens group. It is a thing. If conditional expression (1) is satisfied and the upper limit of conditional expression (2) is exceeded, negative spherical aberration and astigmatism will occur, and the aberration state of the objective lens group will deteriorate. On the other hand, if the lower limit of conditional expression (2) is exceeded, the distortion of the objective lens group will be largely negative. Therefore, the range of conditional expression (2) is preferable.

Further, the conditional expressions (3) and (4) define the second objective lens group in order to maintain a good aberration state when the refractive power arrangement of the objective lens group is within the range of the conditional expression (1). It is a conditional expression. The first objective lens group in the present invention has a large negative refractive power and is composed of a single lens, so that chromatic aberration occurs. Therefore, the conditional expression (3) is a conditional expression that defines the correction of the chromatic aberration and the coma aberration of the light ray passing through the wide angle of view. If the lower limit of conditional expression (3) is not reached, chromatic aberration cannot be satisfactorily corrected over a wide angle of view, and if the upper limit is exceeded, chromatic aberration can be favorably corrected, but coma tends to increase, which is not desirable. Therefore, the range of conditional expression (3) is preferable.

Further, the second objective lens group is a cemented lens so that the achromatic condition is satisfied in the objective lens group, and the difference in Abbe number between the subject side and the image side medium of this cemented lens is expressed by conditional expression (4). Stipulate in. Within the range of this conditional expression (4), it is possible to reduce the chromatic aberration generated in the objective lens group. Needless to say, the introduction of an aspherical surface in the present invention is advantageous in correcting aberrations. In particular, in the conditional expression, introducing an aspherical surface into the curved surface of the first objective lens group on the object side, the curved surface of the second objective lens group on the object side, and the condenser lens group means that the field curvature generated in the objective lens group. Effective for correcting coma and distortion.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a real image type finder according to the present invention. The objective lens group O is composed of a first objective lens group O _{1 including a} negative meniscus lens ₁ and a second objective lens group O _{2 which} is a cemented lens of a positive lens 2 and a negative meniscus lens 3 in order from the subject side, and is a condenser lens. A condenser lens group C composed of 4 and a real image of a subject formed through the objective lens group O and the condenser lens group C are formed on the field frame 5, and the subject image is formed by the erecting prism 6
Through the eyepiece lens I including the biconvex positive lens 7 and the plane-parallel plate 8 and is magnified and observed at the eye point 9.

However, in FIG. 1, the optical path of the erecting system prism P is replaced with a glass block. The objective lens group forms an inverted image of the subject, and the eyepiece system has a function of enlarging the inverted image formed by the objective lens. However, the observer then observes the inverted image. In order for an observer to observe an erect image, an optical system for converting an inverted image formed by the objective lens group into an erect image is required. Therefore, according to the present invention, an inverted image formed by the objective lens group O is made into an erected image by introducing a reflecting member into the space between the erecting system prism P and the air space between the objective lens group O and the condenser lens group C. Converting. There are a plurality of ways of arranging the reflecting members to be introduced into those spaces, but in the present invention, the following four are shown as examples.

FIG. 1 shows the structures of Examples 1 to 4, and the method of converting an inverted image formed by the objective lens group O into an erect image is also the same. The structures of Examples 1 to 4 will be described in order from the object side. The objective lens group O is the first negative meniscus lens 1 having a convex surface facing the object side and an aspheric surface facing the image side.
Objective lens group O ₁ and a positive lens 2 having the image side as a bonding surface
Object side is a second objective lens group O ₂ the image side is laminated a negative meniscus lens 3 aspherical concave cemented surface and. The condenser lens group C is composed of a biconvex lens 4 having an aspherical surface on the object side. Behind it, a field plate 5 in the form of a parallel plate, an erecting prism 6, and an eyepiece lens group I composed of a biconvex positive lens 7 and a parallel plate 8 are formed.

Tables 1 to 4 show the values of specifications of Examples 1 to 4. F and FNO in each table are the combined focal length and F number of the objective lens group O and the condenser lens group C. 2ω and m are the angle of view and magnification of the real image finder. The leftmost number indicates the order from the object side. r is the radius of curvature of the lens surface, d is the lens surface spacing, and n and ν are the refractive index and the Abbe number. Also, (EP) is an eye point. The * on the left side of the number on the left side represents an aspherical surface.

The shape of this aspherical surface is shown by the following aspherical equation. When the height in the vertical direction from the optical axis is indicated by y, the distance along the optical axis direction from the tangent plane of the aspherical apex at y is x. The radius of curvature of the vertex is r, the conic constant is k, and the aspherical coefficient of order n is An. then,
The aspherical shape is represented by the following formula.

[0021]

[Equation 1]

The aspherical surface in the specifications of each embodiment is expressed by the conical constant k and each aspherical surface constant from the above aspherical surface equation.

[0023]

[Table 1] (Values of Specifications of Example 1) f = 8.275 FNO = 4.5 2ω = 55.44 °
m = -O.39 Second surface vertex curvature radius: r = 2.76O conic constant: k = O.8O59 aspheric constants: A2 = O.OOOO A4 = O.OOOO A6 = -1.3OO1 × 1O -4 A8 = 3.O179 × 1O - ⁵ A1O = -4.46O9 × 1O ^-6 Fifth surface vertex radius of curvature: r = -4.773 Cone constant: k = 0.5419 Spherical constant: A2 = O.OOOO A4 = O.OOOO A6 = -2.2668 × 1O ^-5 A8 = 1.9496 × 1O ^-6 A1O = -8.O8O6 × 1O ^-8 6th surface vertex curvature radius: r = 2O.OOO Cone constant: k = -1.OOOO Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = O.OOOO A8 = O.OOOO A1O = O.OOOO 12th surface vertex radius of curvature: r = 17.55OO Cone constant: k = -2.8OOO Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = O.OOOO A8 = -4.3OOO × 1O ^-9 A1O = O.OOOO (conditional value) (1) f1 / f2 = -0.68 (2) (r2 + r1) / (r2-r1) = -1. 62 (3) r4 / f2 = -0.40 (4) v3 -v4 = 29.9

[0024]

[Table 2] (Values of specifications of Example 2) f = 8.282 FNO = 4.3 2ω = 55.44 ° m =-
O.39 Second surface Vertex radius of curvature: r = 2.399 Conical constant: k = O.714O Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = 3.2759 × 1O ^-4 A8 = -4.6616 × 1O ^-5 A1O = 3.728 O × 1O ^-6 Fifth surface Vertex radius of curvature: r = -4.4O1 Cone constant: k = O.387O Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = -3.4244 × 1O ^-5 A8 = 2.7692 × 1O ^-6 A1O = -9.O531 × 1O ^-8 6th surface vertex radius of curvature: r = 2O.OOO Cone constant: k = -1.OOOO Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = O.OOOO A8 = O.OOOO A1O = O.OOOO 12th surface vertex radius of curvature: r = 17.55OO Cone constant: k = -2.8OOO Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = O .OOOO A8 = -4.3OOO × 1O ^-9 A1O = O.OOOO (conditional value) (1) f1 / f2 = -0.63 (2) (r2 + r1) / (r2-r1) = -1.53 (3) r4 / f2 = -0.45 (4) v3 -v4 = 27.3

[0025]

[Table 3] (Specification values of Example 3) f = 7.187 FNO = 4.3 2ω = 66.58 ° m =-
O.34 Second surface Vertex radius of curvature: r = 2.241 Conical constant: k = O.378O Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = 1.411O × 1O ^-3 A8 = -2.215O × 1O ^-4 A1O = 2.6554 × 1O ^-5 5th surface Vertex curvature radius: r = -4.423 Conical constant: k = O.2564 Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = -8.O2O7 × 1O ^-5 A8 = 7.4192 × 1O ^-6 A1O = -2.8619 × 1O ^-7 6th surface vertex curvature radius: r = 2O.OOO conical constant: k = -1.OOOO aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = O.OOOO A8 = O.OOOO A1O = O.OOOO 12th surface vertex radius of curvature: r = 17.55OO Cone constant: k = -2.8OOO Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = O .OOOO A8 = -4.3OOO × 1O ^-9 A1O = O.OOOO (value corresponding to the condition) (1) f1 / f2 = -0.55 (2) (r2 + r1) / (r2-r1) = -1.43 (3) r4 / f2 = -0.38 (4) ν3 -ν4 = 27.3

[0026]

[Table 4] (Values of specifications of Example 4) f = 9.5 O1 FNO = 4.4 2 ω = 55.44 ° m =-
O.45 Second surface Vertex radius of curvature: r = 3.O33 Conical constant: k = O.9939 Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = -3.7379 × 1O ^-4 A8 = 6.8O39 × 1O ^-5 A1O = -8.O27O × 1O ^-6 fifth surface vertex curvature radius: r = -4.992 conic constant: k = O.4568 aspheric constants: A2 = O.OOOO A4 = O.OOOO A6 = -1.8561 × 1O - ⁵ A8 = 1.7789 × 1O ^-6 A1O = -6.74O5 × 1O ^-8 6th surface vertex curvature radius: r = 2O.OOO Cone constant: k = -1.OOOO Aspherical constant: A2 = O.OOOO A4 = O .OOOO A6 = O.OOOO A8 = O.OOOO A1O = O.OOOO 12th surface vertex curvature radius: r = 17.55OO Cone constant: k = -2.8OOO Aspherical constant: A2 = O.OOOO A4 = O.OOOO A6 = O.OOOO A8 = -4.3OOO × 1O ^-9 A1O = O.OOOO (Value corresponding to the condition) (1) f1 / f2 = -0.81 (2) (r2 + r1) / (r2-r1) =- 1.92 (3) r4 / f2 = -0.37 (4)? 3-? 4 = 27.3 Aberration diagrams in each example are shown in FIGS. In each aberration diagram, d is d line (λ = 587.6 nm) and F is F line (λ = 48 nm).
It is an aberration diagram due to (6.2 nm). In the astigmatism diagram, the dotted line is the meridional image plane, and the solid line is the sagittal image plane. The minutes in the coma aberration diagram are minutes in degrees, minutes and seconds.

It is needless to say that the real image type finder of the present invention is well corrected for each aberration, although the number of lenses constituting the objective lens is reduced as much as possible for downsizing.

[0028]

According to the present invention, the objective lens group is small,
A real image type finder optical system in which various aberrations are well corrected in a wide field of view can be achieved.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram showing Examples 1 to 4 of the present invention.

FIG. 2 is a diagram of various types of aberration of the first embodiment of the present invention.

FIG. 3 is a diagram of various types of aberration of the second embodiment of the present invention.

FIG. 4 is a diagram of various types of aberration of the third embodiment of the present invention.

FIG. 5 is a diagram of various types of aberration of the fourth embodiment of the present invention.

[Simple explanation of the sign]

 O ... Objective lens C ... Condenser lens P ... Erecting prism I ... Eyepiece E.P ... Eye point

Claims (1)

[Claims] 1. An objective lens group comprising, in order from a subject side, an objective lens group having a positive refractive power, a condenser lens group having a positive refractive power, and an eyepiece lens group having a positive refractive power. Is a first objective lens group having a negative refractive power and a second objective lens group having a positive refractive power, the first objective lens group is a negative meniscus single lens, and the second objective lens group is a positive lens. A real image type viewfinder optical system characterized by comprising a cemented lens having a refracting power of, and further satisfying the following conditions. -0.95 <f1 / f2 <-0.5-2.0 <(r2 + r1) / (r2-r1) <-1.4-0.45 <r4 / f2 <-0.30 20 <ν3- ν4 <40, where f1: f1 <0, the focal length of the first objective lens group, f2: the focal length of the second objective lens group, r1: the subject-side lens of the lens closest to the subject in the first objective lens group The radius of curvature of the surface (in the case of an aspherical surface, the radius of curvature of the apex of the surface), r2: the radius of curvature of the image-side lens surface of the most object-side lens in the first objective lens group (in the case of an aspherical surface, Vertex radius of the surface), r4: radius of curvature of the cemented surface of the second objective lens group (note that the vertex radius of curvature of the surface in the case of an aspherical surface), v3: subject in the cemented lens of the second objective lens group Side Abbe number, ν4: Abbe number on the image side of the cemented lens of the second objective lens group.