JP3306764B2 - 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 real image type variable magnification finder and a camera using the same, and particularly to an external type finder provided separately from a photographing system, and an objective lens system and an eyepiece constituting the finder. The present invention relates to a real image type zoom finder suitable for, for example, a still camera or a video camera, and a camera using the same, which enable a good finder image to be observed by appropriately setting a lens configuration such as a lens system. .

[0002]

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

[0003] The applicant of the present invention disclosed in Japanese Patent Application Laid-Open Nos. 61-156018 and 1-116616, etc. an objective lens comprised of a plurality of lens groups, and changed the air gap between the lens groups during zooming. The magnification of the object lens is changed by changing the magnification of the objective lens to an erect image through an image inverting member such as a Porro prism, and the erect image is observed with an eyepiece. It proposes a variable magnification finder.

In Japanese Patent Application Laid-Open No. 5-203876, in a zoom finder of this type, the first lens group constituting the objective lens is formed by using two negative lenses and an aspheric surface, and aberration correction of off-axis rays is excellent. And proposes a variable-magnification finder with a wider view angle.

[0005]

In a real image type viewfinder, a condenser lens such as a condenser lens is arranged near a first image forming surface on which an object image is formed by an objective lens system, and is disposed on the first image forming surface. The light flux from the formed object image is guided to a subsequent image inverting optical system or eyepiece.

[0006]

According to the present invention, an object image formed by an objective lens system is formed by appropriately setting a lens configuration such as an objective lens system having a zooming portion and an eyepiece for observing the object image formed by the objective lens system. (1) A real image type that allows a predetermined zoom ratio to be easily obtained without providing a condenser lens such as a condenser lens in the vicinity of the image forming plane, and enables a wide angle of view and a good viewfinder image to be observed over the entire zoom range. A variable magnification finder and a camera using the same are provided.

[0008]

According to a first aspect of the present invention, there is provided a variable magnification finder for converting an object image formed by an objective lens system having a positive refractive power into an erect image through an image inverting optical system, and using the erect image as an eyepiece. A viewfinder for observation with a lens system,
The objective lens system includes, in order from the object side, a positive or negative first lens unit having an aspheric surface, a negative second lens unit, and a positive third lens unit. The zooming is performed by moving the lens on the axis, and the diopter change accompanying the zooming is corrected by the first or second unit, and the second unit includes a single negative lens having a concave surface facing the object side. When the radii of curvature of the object-side and image-side lens surfaces of the negative lens are R2a and R2b, and the focal lengths of the second group and the eyepiece are f2 and fe, respectively, -2.4 <(R2a + R2b) ) / (R2a-R2b) <-0.8-0.9 <f2 / fe <-0.4.

[0009]

1 to 3 are lens sectional views of Numerical Examples 1 to 3, which will be described later, of the present invention.

In the figure, reference numeral 10 denotes an objective lens system having a positive refractive power having a zooming portion, which forms an object image (finder image) on a predetermined surface. P denotes an image reversing optical system, which comprises a triangular prism P1 and a roof prism P2.
The object image formed at the position 4 between the two is inverted upside down, left and right, and converted into an erect image.

In FIG. 1, the triangular prism P1 and the roof prism P2 are shown as two glass blocks whose optical paths are expanded for simplicity. Le denotes an eyepiece having a positive refractive power, and observes the object image formed at the position 4 from the eye point E as an erect object image via the image inverting optical system P.
The position 4 is provided with a frame indicating a finder visual field range, various kinds of information, and the like.

The objective lens system 10 has a positive or negative first lens unit L
The zoom lens includes three lens groups: 1, a second negative lens unit L2, and a third positive lens unit L3.

In this embodiment, zooming is performed by moving the third lens unit to the object side as indicated by an arrow, and a change in the finder diopter accompanying the second lens unit has a locus convex on the image surface side as indicated by an arrow. It is corrected while moving it. The first group is fixed during zooming.

In this embodiment, the first unit L1 comprises a single positive or negative lens, the second unit L2 comprises a single negative lens having a concave surface facing the object side, and the third unit L3 comprises both lens surfaces. Consists of two lenses, a positive lens having a convex surface and a positive lens having a convex surface facing the image plane side (pupil side).

In this embodiment, the objective lens system 10 is composed of three lens groups of first, second and third groups, and the first group is provided with an aspheric surface having a predetermined shape. Is formed at the position 4 between the triangular prism P1 and the roof prism P2, thereby facilitating aberration correction and enabling excellent object image observation. By moving the third lens unit to the object side to perform zooming, a predetermined zooming ratio is effectively obtained. And the second
The group consists of a single negative lens with the concave surface facing the object side, the radii of curvature of the lens surfaces on the object side and the image plane side of the negative lens are R2a and R2b, respectively, Where f2 and fe are respectively -2.4 <(R2a + R2b) / (R2a-R2b) <-0.8 {(1) -0.9 <f2 / fe <-0.4} ( 2) The following conditions are satisfied. Conditional expression (1) relates to the lens shape of the negative lens of the second group, and is mainly for favorably correcting spherical aberration. If the curvature of the concave surface on the object side is increased beyond the lower limit value of the conditional expression (1), it becomes difficult to correct spherical aberration. Not so good. Conditional expression (2) relates to the ratio between the refractive power of the second group and the refractive power of the eyepiece, and is intended to reduce the size of the entire objective lens system while mainly ensuring a predetermined zoom ratio. When the value exceeds the upper limit or the lower limit of conditional expression (2), it becomes difficult to reduce the size of the objective lens system while favorably correcting aberrations.

In the present invention, at least one of the following conditions must be satisfied in order to obtain a high optical performance over the entire zoom range and the entire finder visual field while further increasing the angle of view at the wide-angle end. good.

(1-1) The first group is composed of a single lens, and the aspheric surface is provided on a lens surface on the object side of the single lens, and the aspheric surface extends from the center of the lens toward the periphery of the lens. It has a shape in which the refractive power changes in the positive direction.

As a result, the negative distortion on the wide-angle side when mainly widening the angle of view is favorably corrected. In Numerical Example 3 described later, the lens surface of the first group on the object side is concave, but this surface has a shape in which negative refractive power becomes weaker from the center of the lens to the periphery of the lens. At this time, the concave surface may have a positive refractive power around the lens.

[0019]

[0020]

[0021]

(1-2) The third lens unit has an aspheric surface whose positive refractive power becomes weaker from the center of the lens toward the periphery of the lens. The effective diameter is to be larger than the effective size of the object image by the objective lens system.

By setting the effective diameter of the lens surface on the image plane side of the third lens unit in this way, the light beam emitted from the third lens unit is made substantially telecentric, and conventionally arranged near the first image forming surface. The condenser lens can be removed. Further, by using the aspherical surface having the above-described shape for the third lens unit, the burden of correcting aberrations of the third lens unit can be reduced when a finder having a wide angle of view whose diagonal visual field at the wide angle end exceeds 60 degrees is obtained. Thus, on-axis and off-axis aberrations are corrected in a well-balanced manner.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass. The aspheric surface shape is when the X axis is in the optical axis direction, the H axis is perpendicular to the optical axis, the traveling direction of light is positive, R is the paraxial radius of curvature, and A, B, C, and D are aspheric coefficients.

[0025]

(Equation 1) It is represented by the following expression. Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples. "D-0X"
Means "10- ^X ".

<Numerical Example 1> f = 307.05 to 722.86 R 1 = ∞ D 1 = 3.0 N 1 = 1.49171 ν 1 = 57.4 R 2 = 20.04 D 2 = Variable R 3 = -4.35 D 3 = 1.3 N 2 = 1.50137 ν 2 = 56.4 R 4 = -21.75 D 4 = Variable R 5 = 11.50 D 5 = 2.8 N 3 = 1.49171 ν 3 = 57.4 R 6 = -12.47 D 6 = 1.59 R 7 = ∞ D 7 = 4.2 N 4 = 1.49171 ν 4 = 57.4 R 8 = -7.94 D 8 = Variable R 9 = ∞ D 9 = 14.5 N 5 = 1.57090 ν 5 = 33.8 R10 = ∞ D10 = 1.23 R11 = ∞ D11 = 24.00 N 6 = 1.57090 ν 6 = 33.8 R12 = ∞ D12 = 0.2 R13 = 27.63 D13 = 2.5 N 7 = 1.49171 ν 7 = 57.4 R14 = -12.28 D14 = 15.0 R15 = Eye point

[0027]

[Table 1] <Numerical Example 2> f = 260.08 R 1 = -90.26 D 1 = 1.5 N 1 = 1.49171 ν 1 = 57.4 R 2 = -77.54 D 2 = Variable R 3 = -4.28 D 3 = 1.3 N 2 = 1.50137 ν 2 = 56.4 R 4 = 777.55 D 4 = Variable R 5 = 11.30 D 5 = 2.8 N 3 = 1.49171 ν 3 = 57.4 R 6 = -11.81 D 6 = 1.16 R 7 = 216.97 D 7 = 4.2 N 4 = 1.49171 ν 4 = 57.4 R 8 = -8.02 D 8 = Variable R 9 = ∞ D 9 = 14.5 N 5 = 1.57090 ν 5 = 33.8 R10 = ∞ D10 = 1.23 R11 = ∞ D11 = 24.00 N 6 = 1.57090 ν 6 = 33.8 R12 = ∞ D12 = 0.2 R13 = 27.63 D13 = 2.5 N 7 = 1.49171 ν 7 = 57.4 R14 = -12.28 D14 = 15.0 R15 = Eye point

[0028]

[Table 2] <Numerical Example 3> f = 308.58 R 1 = -17.81 D 1 = 1.5 N 1 = 1.49171 ν 1 = 57.4 R 2 = 15.90 D 2 = Variable R 3 = -4.12 D 3 = 1.3 N 2 = 1.50137 ν 2 = 56.4 R 4 = -11.09 D 4 = Variable R 5 = 12.41 D 5 = 2.8 N 3 = 1.49171 ν 3 = 57.4 R 6 = -13.30 D 6 = 1.24 R 7 = -334.88 D 7 = 4.2 N 4 = 1.49171 ν 4 = 57.4 R 8 = -8.14 D 8 = Variable R 9 = ∞ D 9 = 14.5 N 5 = 1.57090 ν 5 = 33.8 R10 = ∞ D10 = 1.23 R11 = ∞ D11 = 24.00 N 6 = 1.57090 ν 6 = 33.8 R12 = ∞ D12 = 0.2 R13 = 27.63 D13 = 2.5 N 7 = 1.49171 ν 7 = 57.4 R14 = -12.28 D14 = 15.0 R15 = Eye point

[0029]

[Table 3]

[0030]

As described above, according to the present invention, the objective lens system having the variable power unit and the eyepiece lens for observing an object image by the objective lens system are appropriately set, thereby achieving the objective lens system. Viewfinder that can easily obtain a predetermined zoom ratio, has a wide angle of view, and is excellent over the entire zoom range without providing a condenser lens such as a condenser lens near the first image forming plane where an object image is formed by the zoom lens. A real image type zoom finder capable of observing an image and a camera using the same can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 4 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 5 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 6 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

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

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

FIG. 9 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

[Explanation of symbols]

 Reference Signs List 10 Objective lens system P Image inverting optical system Le Eyepiece lens system L1 First group L2 Second group L3 Third group E Eye point d d line g g line ΔS Sagittal image plane ΔM Meridional image plane

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03B 13/00-13/28 G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25 / 04

Claims (4)

(57) [Claims] 1. A finder for converting an object image formed by an objective lens system having a positive refractive power into an erect image via an image inverting optical system, and observing the erect image by an eyepiece lens system.
The objective lens system includes , in order from the object side , a positive or negative first lens unit having an aspheric surface, a negative second lens unit, and a positive third lens unit. Zooming is performed by moving on the axis, and the diopter change accompanying the zooming is corrected by the first group or the second group , and the second group is a single lens having a concave surface facing the object side.
Of the object side and the image plane side of the negative lens.
The curvature radii of the lens surfaces are R2a and R2b, respectively,
When the focal lengths of the eyepieces are f2 and fe, respectively, the condition of -2.4 <(R2a + R2b) / (R2a-R2b) < -0.8-0.9 <f2 / fe <-0.4 is satisfied. Variable magnification finder characterized by doing. 2. The first group comprises a single lens, wherein the aspheric surface is provided on a lens surface on the object side of the single lens, and the aspheric surface has a refractive power from the center of the lens toward the periphery of the lens. 2. The variable magnification finder according to claim 1, wherein the finder has a shape that changes in a positive direction. 3. The third unit has an aspheric surface having a shape in which positive refractive power becomes weaker from the center of the lens toward the periphery of the lens. The effective diameter of the lens surface on the image plane side of the third unit is 2. The variable magnification finder according to claim 1, wherein the magnification is larger than an effective size of an object image by the objective lens system. 4. A camera in which a photographing system and a finder system are formed separately, wherein the finder system is provided.
A camera, characterized in that the camera is the variable magnification finder according to any one of (1) to ( 3 ).