JP5311242B2 - Eyepiece optical system and optical apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact eyepiece optical system having favorable optical performance while securing a high magnification. <P>SOLUTION: The eyepiece optical system EL for observing an image displayed on an image display element Ob includes: aligned in order from the image display element Ob side along an optical axis, a positive first lens L1; a negative second lens L2 having a strong concave surface in the image display element Ob side; and a positive third lens L3 having a strong convex surface in an eye point EP side for achieving both the high magnification and miniaturization. The first lens L1 is cemented and integrated with the image display element Ob for miniaturizing the eyepiece optical system EL while retaining telecentricity and substantially wide luminous flux. <P>COPYRIGHT: (C)2013,JPO&amp;INPIT

Description

  The present invention relates to an eyepiece optical system for observing an image displayed on an image display element, and an optical apparatus including the eyepiece optical system.

  In recent years, an electronic viewfinder that can observe an image displayed on a small image display element at a high magnification using an eyepiece optical system has been proposed (see, for example, Patent Document 1).

JP 2004-48371 A

  However, the eyepiece optical system used in such a viewfinder is required to achieve a reduction in size of the optical system and good optical performance while ensuring a high magnification.

  The present invention has been made in view of such a problem, and an object thereof is to provide an eyepiece optical system having a small size and good optical performance while securing a high magnification, and an optical apparatus including the eyepiece optical system. .

In order to achieve such an object, an eyepiece optical system according to the present invention is an eyepiece optical system for observing an image displayed on an image display element, and is arranged in order from the image display element side along an optical axis. However, it has a first lens that is a positive lens, a second lens that is a negative lens, and a third lens that is a positive lens, and satisfies the following conditional expression.
2.50 <f1 / fe <8.00
0.52 <d12 / fe <0.80
However,
f1: focal length of the first lens,
fe: focal length of the eyepiece optical system,
d12: an interval between the first lens and the second lens.

In the above eyepiece optical system, it is preferable that the following conditional expression is satisfied.
0.00 ≦ d0 / d12 <0.50
However,
d0: an interval between the image display element and the first lens.

  In the eyepiece optical system described above, it is preferable that the image display element and the first lens are cemented and d0 = 0.00.

In the above eyepiece optical system, it is preferable that the following conditional expression is satisfied.
5.00 <f1 / f3 <13.000
4.00 <(− 1) × (f1 / f2) <12.00
However,
f2: focal length of the second lens,
f3: focal length of the third lens.

  In the above eyepiece optical system, it is preferable that at least one of the second lens and the third lens has an aspherical surface.

  In the above eyepiece optical system, it is preferable that at least one of the second lens and the third lens is a plastic lens.

  In the above eyepiece optical system, it is preferable to perform diopter correction by changing the distance between the first lens and the second lens.

  An optical device according to the present invention includes an objective lens, an image sensor that captures an image formed by the objective lens, an image display element that displays the image captured by the image sensor, and the image display element. An eyepiece optical system for observing the image displayed on the screen, and the eyepiece optical system according to the present invention is used as the eyepiece optical system.

  According to the present invention, it is possible to obtain a small and good optical performance while ensuring a high magnification.

It is sectional drawing of the eyepiece optical system which concerns on 1st Example. FIG. 6 is a diagram illustrating various aberrations when the ^diopter is −1 [m ⁻¹ ] in the first example. It is sectional drawing of the eyepiece optical system which concerns on 2nd Example. It is an aberration diagram when the diopter in the second example is -1 [m ^-1 ]. It is sectional drawing of the eyepiece optical system which concerns on 3rd Example. FIG. 11 is a diagram illustrating various aberrations when the ^diopter is −1 [m ⁻¹ ] in the third example. It is sectional drawing of the eyepiece optical system which concerns on 4th Example. FIG. 10 is various aberration diagrams when the ^diopter is −1 [m ⁻¹ ] in the fourth example. It is sectional drawing of a digital single-lens reflex camera.

  Hereinafter, preferred embodiments of the present application will be described with reference to the drawings. A digital single-lens reflex camera CAM provided with an eyepiece optical system EL according to the present application is shown in FIG. The digital single lens reflex camera CAM includes an objective lens OL, an image sensor C such as a CCD or a CMOS, and an electronic viewfinder EVF. The electronic viewfinder EVF includes an image display element Ob such as a liquid crystal display element, and an eyepiece optical system EL for observing an image displayed on the image display element Ob.

  In the digital single lens reflex camera CAM having such a configuration, light from an object (subject) (not shown) is collected by the objective lens OL and formed on the image sensor C to form an image of the subject. The subject image formed on the image sensor C is captured by the image sensor C, and the subject image captured by the image sensor C is displayed on the image display element Ob. Thereby, the photographer can observe the image of the object (subject) formed by the objective lens OL via the eyepiece optical system EL.

  Further, when a release button (not shown) is pressed by the photographer, the image captured by the image sensor C at this time (that is, the image displayed on the image display element Ob observed through the eyepiece optical system EL corresponds to the image). Image) is recorded in a memory (not shown) as an image of the object (subject). In this way, the photographer can photograph an object (subject) with the digital single-lens reflex camera CAM.

  For example, as shown in FIG. 1, the eyepiece optical system EL includes a first lens L1 that is a positive lens, a second lens L2 that is a negative lens, and a positive lens that are arranged in order from the image display element Ob side along the optical axis. The third lens L3 is a lens, and the first lens L1 is arranged in the vicinity of the image display element Ob. The problem of the present embodiment is to achieve an eyepiece with good aberrations while ensuring a compact eyepiece optical system and an apparent viewing angle of 25 ° or more. In particular, it is intended to achieve both telecentricity and a reduction in the overall length and outer dimensions of the lens.

  When observing a display element such as a liquid crystal, it is important to ensure telecentricity in order to observe light emitted vertically from the display surface. However, in order to ensure telecentricity, it is necessary to arrange a lens system larger than the image display element, which is not suitable for downsizing. Furthermore, when trying to achieve a high-magnification eyepiece optical system in which the diagonal length of the object is around 15 mm and the apparent viewing angle is 20 ° or more, strong positive refractive power is required, and positive distortion is generated. The field of view was deformed into a pincushion type and was easy to give a sense of incongruity.

  In order to improve these aberrations, the eyepiece optical system EL of the present embodiment is integrated in the vicinity of the image display element Ob (or integrated with the image display element Ob) in order to ensure telecentricity while keeping the outer dimensions small. Like) a positive lens (first lens L1) is arranged. Furthermore, a negative lens (second lens L2) is arranged for correcting coma and distortion, and a positive lens (third lens L3) is arranged for correcting coma, distortion, and field curvature. Yes. In addition, the above-described problems are solved by defining conditional expressions described below.

  In the eyepiece optical system EL having such a configuration, when the focal length of the first lens L1 is f1, and the focal length of the eyepiece optical system EL is fe, the condition represented by the following conditional expression (1) is satisfied. It is preferable.

  2.50 <f1 / fe <8.00 (1)

  Conditional expression (1) defines the focal length of the first lens L1 with respect to the focal length of the entire eyepiece optical system EL in order to ensure telecentricity and correct distortion. In particular, if the telecentricity is not maintained, the image around the image display element Ob becomes very difficult to see due to color shift and insufficient light quantity. Further, by arranging a positive lens (first lens L1) in the vicinity of the image display element Ob, the pincushion distortion can be corrected well. When the condition is less than the lower limit value of the conditional expression (1), the distortion is excessively corrected, resulting in barrel distortion. In addition, since it is incident on the second lens L2 at a large angle, it is difficult to correct coma. On the other hand, when the condition exceeds the upper limit value of the conditional expression (1), the correction of the distortion aberration is insufficient and the pincushion type aberration remains. In addition, the lens diameter increases to ensure telecentricity.

  In addition, the effect of this embodiment can be made more reliable by setting the upper limit value of conditional expression (1) to 7.00. Moreover, the effect of this embodiment can be made more reliable by setting the lower limit of conditional expression (1) to 3.00.

  In such an eyepiece optical system EL, it is preferable that the condition represented by the following conditional expression (2) is satisfied when the distance between the first lens L1 and the second lens L2 is d12.

  0.41 <d12 / fe <0.80 (2)

Conditional expression (2) defines the distance between the first lens L1 and the second lens L2 with respect to the focal length of the entire eyepiece optical system EL. When the condition is lower than the lower limit value of the conditional expression (2), the distance between the first lens L1 and the second lens L2 is narrowed and the second lens L2 is increased in size. Further, the light ray incident on the second lens L2 becomes high, and coma aberration occurs. On the other hand, when the condition exceeds the upper limit value of the conditional expression (2), the distance between the first lens L1 and the second lens L2 is widened so that the refractive power of the second lens L2 is sufficient to obtain a sufficient magnification. It becomes too strong and curvature of field occurs.

  In addition, the effect of this embodiment can be made more reliable by setting the lower limit of conditional expression (2) to 0.45. Furthermore, the effect of this embodiment can be made more reliable by setting the lower limit value of conditional expression (2) to 0.52. Moreover, the effect of this embodiment can be made more reliable by setting the upper limit value of conditional expression (2) to 0.63.

  In such an eyepiece optical system EL, it is preferable that the condition represented by the following conditional expression (3) is satisfied when the distance between the image display element Ob and the first lens L1 is d0.

  0.00 ≦ d0 / d12 <0.50 (3)

  Conditional expression (3) defines the position of the first lens L1 between the image display element Ob and the second lens L2. If the condition exceeds the upper limit value of the conditional expression (3), the distortion aberration is insufficiently corrected and pincushion type aberration remains. On the other hand, the lower limit value of the conditional expression (3) is a condition value when the image display element Ob and the first lens L1 are adjacent to each other.

  In addition, the effect of this embodiment can be made more reliable by setting the upper limit of conditional expression (3) to 0.10.

  In such an eyepiece optical system EL, it is preferable that the image display element Ob and the first lens L1 are cemented and d0 = 0.00. In this way, by integrating the positive lens (first lens L1) with the image display element Ob, distortion is corrected, and the light beam emitted vertically from the image display element Ob is bent in the optical axis direction. The optical system after the second lens L2 can be reduced in size.

  In such an eyepiece optical system EL, it is preferable that the condition represented by the following conditional expression (4) is satisfied when the focal length of the third lens L3 is f3.

  5.00 <f1 / f3 <13.000 (4)

  Conditional expression (4) defines the focal lengths of the first lens L1 and the third lens L3 for correcting distortion. When the condition is lower than the lower limit value of the conditional expression (4), the power of the third lens L3 becomes weak and a sufficient finder magnification cannot be obtained. Further, when the focal length of the first lens L1 is shortened, coma aberration is newly generated. On the other hand, if the condition exceeds the upper limit value of conditional expression (4), negative distortion remains and the field of view is deformed into a barrel shape. In addition, it is difficult to correct spherical aberration.

  In addition, the effect of this embodiment can be made more reliable by setting the lower limit of conditional expression (4) to 7.00. Moreover, the effect of this embodiment can be made more reliable by setting the upper limit of conditional expression (4) to 12.00.

  In such an eyepiece optical system EL, it is preferable that the condition represented by the following conditional expression (5) is satisfied when the focal length of the second lens L2 is f2.

  4.00 <(− 1) × (f1 / f2) <12.00 (5)

  Conditional expression (5) defines the focal lengths of the first lens L1 and the second lens L2 for satisfactorily correcting distortion and coma. When the condition is lower than the lower limit value of the conditional expression (5), if the position of the third lens L3 is the same because the focal length of the second lens L2 is increased, the height of the light incident on the third lens L3 is increased. The eye point is short and difficult to use. Therefore, if the eye point is to be lengthened, it is necessary to shift the third lens L3 backward, and the entire optical system becomes large. In addition, correction of distortion is insufficient. On the other hand, when the condition exceeds the upper limit value of the conditional expression (5), the second lens L2 is increased in size. In addition, the incident angle of the light beam on the third lens L3 increases, and field curvature and spherical aberration occur, making correction difficult.

  In addition, the effect of this embodiment can be made more reliable by setting the lower limit of conditional expression (5) to 5.00. Moreover, the effect of this embodiment can be made more reliable by setting the upper limit of conditional expression (5) to 10.00.

  In such an eyepiece optical system EL, it is preferable that at least one of the second lens L2 and the third lens L3 has an aspherical surface. In particular, coma, astigmatism, and distortion can be improved by forming an aspheric surface on the second lens L2. In addition, by forming an aspheric surface on the third lens L3, distortion, coma, and spherical aberration can be improved.

  In such an eyepiece optical system EL, it is preferable that at least one of the second lens L3 and the third lens L3 is a plastic lens. Thus, by using the second lens L2 and the third lens L3 as plastic lenses, an aspheric surface can be easily formed, which is advantageous for aberration correction. In addition, even if all the lenses are plastic lenses, they have sufficient correction capability.

  In such an eyepiece optical system EL, it is preferable to perform diopter correction by changing the distance between the first lens L1 and the second lens L2. In this way, by changing the distance between the first lens L1 and the second lens L2 along the optical axis, diopter correction can be performed without causing a decrease in optical performance.

  Thus, according to the present embodiment, it is possible to obtain an eyepiece optical system EL that is small and has good optical performance while securing a high magnification, and an optical device (digital single-lens reflex camera CAM) including the eyepiece optical system EL. .

(First embodiment)
Embodiments of the present application will be described below with reference to the accompanying drawings. First, a first embodiment of the present application will be described with reference to FIGS. FIG. 1 is a cross-sectional view when the diopter of the eyepiece optical system EL according to the first example is −1 [m ⁻¹ ]. The eyepiece optical system EL according to the first example includes a first lens L1, which is a positive lens, a second lens L2, which is a negative lens, and a positive lens, which are arranged in order from the image display element Ob side along the optical axis. The first lens L1 is disposed adjacent to the image display element Ob.

The first lens L1 is a positive lens that is joined and integrated with the image display element Ob by a frame member (not shown) in order to reduce the size of the eyepiece optical system EL while ensuring telecentricity and a sufficiently wide light flux. . The second lens L2 is a negative lens (meniscus lens) having a strong concave surface on the image display element Ob side, and the lens surface on the image display element Ob side of the second lens L2 is an aspherical surface. The third lens L3 is a positive lens (convex lens) having a strong convex surface on the eye point EP side in order to achieve both high magnification and downsizing, and the lens surface on the eye point EP side of the third lens L3 is an aspherical surface. ing.

  The first lens L1 is a glass lens, and the second lens L2 and the third lens L3 are plastic lenses. Further, at the time of diopter correction, the image display element Ob and the first lens L1 are fixed, and the second lens L2 and the third lens L3 move integrally along the optical axis, so that the first lens L1 and The distance from the second lens L2 changes.

Tables 1 to 4 are shown below. These are values of specifications of the eyepiece optical system EL according to the first to fourth examples (when the diopter is -1 [m ^-1 ]), respectively. It is a table. In [Overall specifications] in each table, f1 to f3 are the focal lengths of the first to third lenses L1 to L3, h is the object height, and TL is located closest to the eye point EP from the image display element Ob. The distance to the lens surface on the eye point EP side of the lens is indicated by fe, and the focal length of the entire eyepiece optical system EL is indicated. In [Lens Specifications], the numerical value on the left side of the table indicates the order (surface number) of the optical surface from the observation image (display element surface), and the curvature radius of the lens surface, the lens surface interval, An Abbe number with respect to d-line (wavelength λ = 587.6 nm) and a refractive index with respect to d-line (wavelength λ = 587.6 nm) are shown. Note that * attached to the right of the surface number indicates that the lens surface is an aspherical surface. The curvature radius “0” indicates a plane, and the refractive index of air (nd = 1.0000) is omitted.

Further, the aspheric coefficient shown in [Aspherical data] has an x-axis as the optical axis direction, a y-axis as a direction perpendicular to the optical axis, a kinematic constant as k, When the aspherical coefficient of 10) is An and the paraxial radius of curvature shown in [Lens Specifications] is r, it is expressed by the following equation (6). In each example, the secondary aspherical coefficient A2 is 0, and the description is omitted.
In [Aspherical data], “En” indicates “× 10 ⁻ⁿ ”.

x = (y ² / r) / [1+ {1-κ × (y ² / r ² )} ^1/2 }]
+ A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ + A10 × y ¹⁰ (6)

  The focal length, radius of curvature, and other length units listed in all the following specifications are generally “mm”, but the optical system can be optically equivalent even when proportionally enlarged or reduced. Since performance is obtained, it is not limited to this. In addition, the same reference numerals as in the present embodiment are used in the specification values of the second to fourth embodiments described later.

  Table 1 below shows specifications in the first embodiment. The surface numbers 1 to 6 in Table 1 correspond to the surfaces 1 to 6 in FIG. In the first embodiment, the third and sixth lens surfaces are aspherical.

(Table 1)
[Overall specifications]
f1 = 153.7755
f2 = -19.2339
f3 = 13.6538
h = 6.3
TL = 22.6
fe = 22.59
[Lens specifications]
Surface number Curvature radius Surface spacing Abbe number Refractive index Element surface 0 0.00
1 0 1.21 35.31 1.59270
2 -91.1429 13.64
3 * -8.3313 2.46 23.26 1.63980
4 -28.7686 1.22
5 25.3244 4.06 55.91 1.53110
6 * -9.5966 17.00
[Aspherical data]
3rd surface κ = -0.78767, A4 = -4.1624E-04, A6 = -7.6701E-06, A8 = 4.9487E-08, A10 = 0.0000E + 00
6th surface κ = 1.13318, A4 = 2.1110E-04, A6 = -7.1482E-07, A8 = 3.7871E-08, A10 = 0.00000E + 00

FIG. 2 is a diagram of various aberrations when the diopter of the eyepiece optical system EL according to Example 1 is −1 [m ⁻¹ ]. In FIG. 2, each aberration diagram shows spherical aberration, astigmatism, coma aberration, and distortion aberration in order from the left. In each aberration diagram, Y1 indicates the incident height of the light beam to the erect system, and Y0 indicates the height of the image display element. In each aberration diagram, “min” of coma aberration indicates “minute” in angular units, d is aberration for d-line (λ = 587.6 nm), and g is aberration for g-line (λ = 435.8 nm), respectively. Show. In each aberration diagram, the unit of the horizontal axis of spherical aberration and astigmatism is “m ⁻¹ ”, which is indicated by “D” in the figure. The diopter unit “m ⁻¹ ” will be described. The diopter X [m ⁻¹ ] is 1 / X [m (meter)] from the eye point on the optical axis. ] (The sign is positive when the image is closer to the viewer than the eyepiece (optical system)). The description of the aberration diagrams is the same in the other examples.

  From the respective aberration diagrams, it can be seen that in the first example, various aberrations are corrected well and the imaging performance is excellent. As a result, by mounting the eyepiece optical system EL of the first embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

(Second embodiment)
Hereinafter, a second embodiment of the present application will be described with reference to FIGS. FIG. 3 is a cross-sectional view of the eyepiece optical system EL according to the second example when the diopter is −1 [m ⁻¹ ]. The eyepiece optical system EL of the second example has the same configuration as that of the eyepiece optical system EL of the first example except for part of the shapes of the second lens L2 and the third lens L3. The same reference numerals as in the case of the embodiment are attached and detailed description is omitted. The second lens L2 of the second embodiment is a negative lens (concave lens) having a strong concave surface on the image display element Ob side, and the lens surface on the image display element Ob side of the second lens L2 is an aspherical surface. The third lens L3 of the second example is a positive lens (convex lens) having a strong convex surface on the image display element Ob side in order to achieve both high magnification and downsizing, and the lens surfaces on both sides of the third lens L3 are not. It is a spherical surface.

  Table 2 below shows specifications in the second embodiment. The surface numbers 1 to 6 in Table 2 correspond to the surfaces 1 to 6 in FIG. In the second embodiment, the third, fifth and sixth lens surfaces are formed in an aspherical shape.

(Table 2)
[Overall specifications]
f1 = 74.4508
f2 = -8.0912
f3 = 9.0291
h = 6.3
TL = 22.58
fe = 24.79
[Lens specifications]
Surface number Curvature radius Surface spacing Abbe number Refractive index Element surface 0 0.00
1 0 1.37 29.51 1.71736
2 -53.4081 12.97
3 * -5.7090 1.61 30.33 1.58276
4 29.9013 1.66
5 * 7.1199 4.97 55.91 1.54410
6 * -11.9469 17.00
[Aspherical data]
3rd surface κ = 0.27017, A4 = 1.8938E-03, A6 = -6.1539E-05, A8 = 1.0328E-06, A10 = 0.0000E + 00
5th surface κ = -2.20658, A4 = -3.4935E-04, A6 = 9.8856E-06, A8 = -8.1919E-08, A10 = 0.00000E + 00
6th surface κ = -12.5206, A4 = 6.2189E-04, A6 = 1.0942E-05, A8 = -6.6859E-08, A10 = 0.00000E + 00

FIG. 4 is a diagram illustrating various aberrations when the diopter of the eyepiece optical system EL according to Example 2 is −1 [m ⁻¹ ]. From the respective aberration diagrams, it can be seen that in the second example, various aberrations are satisfactorily corrected and the imaging performance is excellent. As a result, by mounting the eyepiece optical system EL of the second embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

(Third embodiment)
Hereinafter, the third embodiment of the present application will be described with reference to FIGS. FIG. 5 is a cross-sectional view when the diopter of the eyepiece optical system EL according to the third example is −1 [m ⁻¹ ]. The eyepiece optical system EL of the third example has the same configuration as the eyepiece optical system EL of the first example except for a part of the configuration of the first lens L1, and each part has the same configuration as the case of the first example. The same reference numerals are assigned and detailed description is omitted. The first lens L1 of the third example is a positive lens disposed in the vicinity of the image display element Ob in order to reduce the size of the eyepiece optical system EL while ensuring telecentricity and a sufficiently wide light beam.

  Table 3 below shows specifications in the third embodiment. The surface numbers 1 to 6 in Table 3 correspond to the surfaces 1 to 6 in FIG. In the third embodiment, the lens surfaces of the third surface and the sixth surface are formed in an aspheric shape.

(Table 3)
[Overall specifications]
f1 = 152.1553
f2 = -25.8256
f3 = 13.6709
h = 6.3
TL = 24.1
fe = 22.24
[Lens specifications]
Surface number Curvature radius Surface spacing Abbe number Refractive index Element surface 0 1.19
1 0 2.20 55.91 1.53110
2 -80.8097 13.95
3 * -15.4973 1.84 23.26 1.63980
4 -261.1676 0.60
5 14.8020 4.32 55.91 1.53110
6 * -12.8083 17.00
[Aspherical data]
3rd surface κ = -0.50322, A4 = -2.4856E-04, A6 = -1.9770E-08, A8 = 5.5301E-08, A10 = 0.0000E + 00
6th surface κ = 0.70400, A4 = 4.5294E-05, A6 = 2.1781E-06, A8 = -5.8682E-09, A10 = 0.00000E + 00

FIG. 6 is a diagram of various aberrations when the diopter of the eyepiece optical system EL according to Example 3 is −1 [m ⁻¹ ]. From the respective aberration diagrams, it can be seen that in the third example, various aberrations are satisfactorily corrected and the imaging performance is excellent. As a result, by mounting the eyepiece optical system EL of the third embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

(Fourth embodiment)
Hereinafter, a fourth embodiment of the present application will be described with reference to FIGS. FIG. 7 is a cross-sectional view when the diopter of the eyepiece optical system EL according to the fourth example is −1 [m ⁻¹ ]. The eyepiece optical system EL according to the fourth example includes a first lens L1, which is a positive lens, a second lens L2, which is a negative lens, and a positive lens, which are arranged in order from the image display element Ob side along the optical axis. The third lens L3 includes a third lens L3 and a fourth lens L4 that is a positive lens. The first lens L1 is disposed adjacent to the image display element Ob.

  The first lens L1 is a positive lens that is joined and integrated with the image display element Ob by a frame member (not shown) in order to reduce the size of the eyepiece optical system EL while ensuring telecentricity and a sufficiently wide light flux. . The second lens L2 is a negative lens (concave lens) having a strong concave surface on the image display element Ob side, and the lens surface on the image display element Ob side of the second lens L2 is an aspherical surface. The third lens L3 is a positive lens (convex lens) having a strong convex surface on the eye point EP side in order to achieve both high magnification and downsizing, and the lens surface on the eye point EP side of the third lens L3 is an aspherical surface. ing. The fourth lens L4 is a positive lens (convex lens) having a strong convex surface on the image display element Ob side.

  The first lens L1 is a glass lens, and the second to fourth lenses L2 to L4 are plastic lenses. In addition, when the diopter is corrected, the image display element Ob and the first lens L1 are fixed, and the second to fourth lenses L2 to L4 move integrally along the optical axis, so that the first lens L1 and The distance from the second lens L2 changes.

  Table 4 below shows specifications in the fourth embodiment. The surface numbers 1 to 8 in Table 4 correspond to the surfaces 1 to 8 in FIG. In the fourth embodiment, the third and sixth lens surfaces are aspherical.

(Table 4)
[Overall specifications]
f1 = 114.9020
f2 = -11.8799
f3 = 15.7392
f4 = 27.5572
h = 6.3
TL = 24.07
fe = 23.76
[Lens specifications]
Surface number Curvature radius Surface spacing Abbe number Refractive index Element surface 0 0.00
1 0 1.27 60.66 1.60311
2 -69.2988 14.37
3 * -7.3996 1.10 30.33 1.58276
4 113.4125 0.60
5 36.1090 3.49 55.91 1.53110
6 * -10.5120 0.60
7 16.1118 2.64 55.91 1.53110
8 -150.6600 17.00
[Aspherical data]
3rd surface κ = -0.12321, A4 = 0.54536E-04, A6 = -0.39673E-05, A8 = 0.14810E-06, A10 = 0.0000E + 00
6th surface κ = 1.36687, A4 = 0.27848E-03, A6 = -0.79828E-06, A8 = 0.54046E-07, A10 = 0.00000E + 00

FIG. 8 is a diagram of various aberrations when the diopter of the eyepiece optical system EL according to Example 4 is −1 [m ⁻¹ ]. From the respective aberration diagrams, it can be seen that in the fourth example, various aberrations are corrected satisfactorily and the imaging performance is excellent. As a result, by mounting the eyepiece optical system EL of the fourth embodiment, excellent optical performance can be secured even in the digital single-lens reflex camera CAM.

  Table 5 below shows the values corresponding to the conditional expressions in the respective examples.

(Table 5)
First Example Second Example Third Example Fourth Example Conditional Expression (1) 6.516 3.003 6.842 4.836
Conditional expression (2) 0.578 0.523 0.627 0.605
Conditional expression (3) 0.000 0.000 0.085 0.000
Conditional expression (4) 11.242 8.246 11.130 7.300
Conditional expression (5) 7.995 9.201 5.892 9.672

  Thus, it can be seen that each of the above-described conditional expressions is satisfied in each embodiment. As described above, according to each embodiment, an eyepiece optical system EL and an optical device (digital single-lens reflex camera CAM) having good optical performance can be realized.

  In the above-described embodiment, when diopter correction is performed, the image display element Ob and the first lens L1 are fixed, and the other lenses are configured to move integrally along the optical axis. The present invention is not limited to this, and the image display element Ob and the first lens L1 may be moved integrally, and the interval between the first lens L1 and the second lens L2 may be changed. .

  In the above-described embodiment, the digital single-lens reflex camera CAM provided with the eyepiece optical system EL has been described as an example. However, the present invention is not limited to this. For example, a video camera or the like may be used. The present invention can be applied to any optical device provided with an eyepiece optical system for observing a displayed image.

CAM digital SLR camera (optical device)
OL objective lens C imaging device Ob image display device EL eyepiece optical system EP eye point L1 first lens L2 second lens L3 third lens L4 fourth lens

Claims (8)

An eyepiece optical system for observing an image displayed on an image display element,
A first lens that is a positive lens, a second lens that is a negative lens, and a third lens that is a positive lens, arranged in order from the image display element side along the optical axis;
An eyepiece optical system characterized by satisfying the following conditional expression:
2.50 <f1 / fe <8.00
0.52 <d12 / fe <0.80
However,
f1: focal length of the first lens,
fe: focal length of the eyepiece optical system,
d12: an interval between the first lens and the second lens. The eyepiece optical system according to claim 1, wherein the following conditional expression is satisfied.
0.00 ≦ d0 / d12 <0.50
However,
d0: an interval between the image display element and the first lens. The image display element and the first lens are bonded,
The eyepiece optical system according to claim 2, wherein d0 = 0.00. The eyepiece optical system according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
5.00 <f1 / f3 <13.000
4.00 <(− 1) × (f1 / f2) <12.00
However,
f2: focal length of the second lens,
f3: focal length of the third lens.   5. The eyepiece optical system according to claim 1, wherein at least one of the second lens and the third lens has an aspherical surface.   The eyepiece optical system according to any one of claims 1 to 5, wherein at least one of the second lens and the third lens is a plastic lens.   The eyepiece optical system according to claim 1, wherein diopter correction is performed by changing an interval between the first lens and the second lens. An objective lens, an image sensor that captures an image formed by the objective lens, an image display element that displays the image captured by the image sensor, and the image displayed on the image display element With an eyepiece optical system,
An optical apparatus, wherein the eyepiece optical system is the eyepiece optical system according to any one of claims 1 to 7 .

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