JP2019215411A - Eyepiece optical system, electronic view finder, and imaging apparatus - Google Patents

Abstract

To achieve high magnification while keeping high imaging performance.SOLUTION: An eyepiece optical system 52 comprises a first lens L1 having positive refractive power, a second lens L2 having positive refractive power, a third lens L3 having negative refractive power and a fourth lens L4 having positive refractive power in order from a display surface 51a side to an eye-point EP side. Predetermined conditional expressions (1)-(4) are satisfied.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to an eyepiece optical system, an electronic viewfinder, and an imaging device.

  Patent Literature 1 discloses a triplet-type optical system including three lenses as an example of an eyepiece optical system suitable for an electronic viewfinder. Specifically, in Patent Document 1, in order from the display surface (object) side to the pupil (exit) side, a first lens having a positive refractive power and a first lens having a negative refractive power and An eyepiece optical system is disclosed in which a second lens having a concave surface is arranged and a third lens having a positive refractive power is arranged.

JP 2014-215471 A

  In recent years, an eyepiece optical system such as that described in Patent Document 1 has been required to have higher magnification. As a measure for responding to such a demand, for example, it is conceivable to shorten the focal length of a lens forming the eyepiece optical system. However, simply adjusting the focal length may hinder aberration correction. This is not preferable for maintaining good imaging performance.

  The present disclosure has been made in view of such a point, and an object of the present disclosure is to realize high magnification in an eyepiece optical system while maintaining high imaging performance.

  The present disclosure relates to an eyepiece optical system for observing an enlarged display surface. The eyepiece optical system includes, in order from the display surface side to the pupil side, a first lens having a positive refractive power, a second lens having a positive refractive power, a third lens having a negative refractive power, , A diagonal length of the display surface is H, a focal length of the entire eyepiece optical system is f, and a combined focal point of the first lens and the second lens. When the distance is f12, the focal length of the third lens is f3, and the focal length of the fourth lens is f4, the following conditional expressions (1) to (4) are satisfied.

0.50 <H / f <0.73 (1)
0.48 <f12 / f <0.6 (2)
−0.56 <f3 / f <−0.38 (3)
0.82 <f4 / f <1.15 (4)

  According to the present disclosure, it is possible to realize high magnification while maintaining high imaging performance.

FIG. 1 is a diagram illustrating a schematic configuration of the imaging apparatus. FIG. 2 is a cross-sectional view illustrating a configuration of the eyepiece optical system according to the first embodiment. FIG. 3 is a diagram illustrating spherical aberration, astigmatism, and distortion of the first embodiment. FIG. 4 is a lateral aberration diagram of the first embodiment. FIG. 5 is a diagram corresponding to FIG. 2 showing the diopter changed in the first embodiment. FIG. 6 is a diagram corresponding to FIG. 3 showing the diopter changed in the first embodiment. FIG. 7 is a diagram corresponding to FIG. 4 and showing the diopter changed in the first embodiment. FIG. 8 is a cross-sectional view illustrating a configuration of the eyepiece optical system according to the second embodiment. FIG. 9 is a diagram illustrating spherical aberration, astigmatism, and distortion of the second embodiment. FIG. 10 is a lateral aberration diagram of the second embodiment. FIG. 11 is a diagram corresponding to FIG. 8 and showing the diopter changed in the second embodiment. FIG. 12 is a diagram corresponding to FIG. 9 and showing a diopter changed in the second embodiment. FIG. 13 is a diagram corresponding to FIG. 10 showing the diopter changed in the second embodiment. FIG. 14 is a cross-sectional view illustrating a configuration of the eyepiece optical system according to the third embodiment. FIG. 15 is a diagram illustrating spherical aberration, astigmatism, and distortion of the third embodiment. FIG. 16 is a lateral aberration diagram of the third embodiment. FIG. 17 is a diagram corresponding to FIG. 14 and showing the diopter changed in the third embodiment. FIG. 18 is a diagram corresponding to FIG. 15 showing the diopter changed in the third embodiment. FIG. 19 is a diagram corresponding to FIG. 16 and showing the diopter changed in the third embodiment.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In addition, the following description is an illustration.

  FIG. 1 is a diagram illustrating a schematic configuration of the imaging apparatus 100. An imaging device 100 shown in FIG. 1 includes an imaging lens 1 for imaging an object to obtain an optical image, an imaging device 2 for photoelectrically converting an optical image obtained by the imaging lens 1 and outputting an image signal, The image processing apparatus includes a signal processing unit 3 that performs various kinds of signal processing on an image signal output from the image sensor 2, a driver 4, and an electronic viewfinder 5 for visually recognizing an image.

  The electronic viewfinder 5 has an image display device 51 for displaying an image and an eyepiece optical system 52 for enlarging and observing the image displayed thereon.

  The image display device 51 includes a liquid crystal display element such as a liquid crystal or an EL, and has a substantially rectangular display surface 51a. An image corresponding to the signal output from the signal processing unit 3 is displayed on the display surface 51a.

  The eyepiece optical system 52 is configured as a lens system for magnifying and observing an image displayed on the display surface 51a. Specifically, the eyepiece optical system 52 according to the present embodiment includes, in order from the display surface 51a side to the eye point EP (pupil side) indicating a virtual stop, a first lens L1 having a positive refractive power, and a positive lens L1. A second lens L2 having a refractive power, a third lens L3 having a negative refractive power, and a fourth lens L4 having a positive refractive power are arranged. Further, as shown in FIG. 1, a cover glass C is interposed between the display surface 51a and the first lens L1.

  The first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 each use plastic as a lens material and have at least one aspheric surface.

  Further, as shown in each embodiment described later, the first lens L1, the second lens L2, the third lens L3, and the fourth lens L4 are integrated along the optical axis OA when adjusting the diopter of the eyepiece optical system 52. Move.

  Further, in the eyepiece optical system 52 according to the present embodiment, the diagonal length of the display surface 51a is H, the focal length of the entire eyepiece optical system 52 is f, and the combined focal length of the first lens L1 and the second lens L2 is f12. When the focal length of the third lens L3 is f3 and the focal length of the fourth lens L4 is f4, the following conditional expressions (1) to (4) are satisfied.

0.50 <H / f <0.73 (1)
0.48 <f12 / f <0.6 (2)
−0.56 <f3 / f <−0.38 (3)
0.82 <f4 / f <1.15 (4)

  Conditional expression (1) defines the ratio of the diagonal length H of the display surface 51a to the focal length f of the entire eyepiece optical system 52. If the upper limit of conditional expression (1) is exceeded, the focal length f of the entire system becomes excessively short with respect to the effective diameter which is the size of the pupil. As a result, the F value of the eyepiece optical system 52 becomes unnecessarily low (the lens becomes unnecessarily bright), and it becomes difficult to correct spherical aberration and coma. Conversely, when the value goes below the lower limit of conditional expression (1), the diagonal length H of the display surface 51a becomes excessively short with respect to the focal length f of the entire system. This reduces the size of the image displayed on the display surface 51a, which is not preferable for use as the eyepiece optical system 52.

  Conditional expression (2) defines the ratio of the combined focal length f12 of the first and second lenses L1 and L2 to the focal length f of the entire system. When the value exceeds the upper limit of conditional expression (2), the combined focal length f12 becomes excessively long, so that it is difficult to reduce the size of the eyepiece optical system 52. Conversely, if the lower limit of conditional expression (2) is not reached, the combined focal length will be excessively short, which is disadvantageous for correcting astigmatism.

  Conditional expression (3) is an expression that defines the ratio of the focal length f3 of the third lens L3 to the focal length f of the entire system. If the upper limit of conditional expression (3) is exceeded, the focal length f3 of the third lens L3 will be excessively short, so that the refractive power of the third lens L3 will be unnecessarily large, and spherical aberration and coma will be corrected. Becomes difficult. Conversely, if the lower limit of conditional expression (3) is not reached, the focal length f3 of the third lens L3 becomes excessively long, so that the refractive power of the third lens L3 becomes unnecessarily small, and chromatic aberration is not corrected. It will be difficult.

  Conditional expression (4) is an expression that defines the ratio of the focal length f4 of the fourth lens L4 to the focal length f of the entire system. When the value exceeds the upper limit of conditional expression (4), the focal length f4 of the fourth lens L4 becomes excessively long, so that it becomes difficult to reduce the size of the eyepiece optical system 52. Conversely, if the lower limit of conditional expression (4) is not reached, the focal length f4 of the fourth lens L4 will be excessively short. It becomes difficult to correct aberration.

  By satisfying all of the conditional expressions (1) to (4), it is possible to increase the magnification of the eyepiece optical system 52 while maintaining high imaging performance.

  That is, when a general triplet type eyepiece optical system is used, in order from the display surface side to the pupil side, a lens having a positive refractive power, a lens having a negative refractive power, and a lens having a positive refractive power And will be arranged. In this case, in order to increase the magnification of the eyepiece optical system, for example, among the three lenses, it is conceivable to shorten the focal length of a lens (a lens having a positive refractive power) arranged near the display surface. . However, with such a configuration, it becomes difficult to correct aberrations, and there is a possibility that there is a problem in maintaining good imaging performance.

  Thus, the inventors of the present application have conducted intensive studies and as a result, have paid attention to the fact that a portion which has been constituted by one lens until now is constituted by two lenses. These two lenses are nothing but the first lens L1 and the second lens L2 described above. In such a configuration, by satisfying all of the conditional expressions (1) to (4), it is possible to realize a high magnification without deteriorating the imaging performance. Thus, the eyepiece optical system 52 according to the present embodiment provides good imaging performance despite high magnification, especially when applied to the electronic viewfinder 5 and the imaging apparatus 100 including the same. It is possible to do.

  Specifically, in the case of the conventional product, the loupe magnification is about 7 to 14, whereas in the case of the eyepiece optical system 52 according to the present disclosure, the loupe magnification is 13 to 18.

  The first lens L1 has a concave lens surface on one side, and is arranged with the concave shape facing the display surface 51a. With such a configuration, it is advantageous in realizing good imaging performance despite high magnification.

  The first lens L1 has a convex lens surface on the other side. On the other hand, the second lens L2 also has at least one surface having a convex shape. The first lens L1 and the second lens L2 are arranged in a posture in which the respective convex shapes face each other. With such a configuration, it is advantageous in realizing good imaging performance despite high magnification.

  In addition, the third lens L3 has a concave shape on at least one lens surface, and is arranged with the concave shape facing the eye point EP. With such a configuration, it is advantageous in realizing good imaging performance despite high magnification.

  Hereinafter, Examples 1 to 3 of the present disclosure will be described in detail based on numerical data and drawings.

  In the following numerical data and drawings, ri indicates the radius of curvature of the i-th lens surface in order from the display surface 51a side, and di indicates the i-th lens surface and the (i + 1) -th lens surface. (The center thickness of the lens or the air gap). Also, ni indicates the refractive index of the i-th lens in order from the display surface 51a side, and νi indicates the Abbe number of the i-th lens.

  In each numerical data, an asterisk “*” attached to the right of the surface number indicates that the lens surface has an aspherical shape. This aspherical shape has a z axis in the direction of the optical axis OA, a y axis in a direction perpendicular to the optical axis OA, a positive radius of paraxial curvature with the traveling direction of light being positive, a conic coefficient of K, and a fourth order. Let A be the aspherical coefficient of A, B be the 6th-order aspherical coefficient, C be the 8th-order aspherical coefficient, D be the 10th-order aspherical coefficient, and E be the 12th-order aspherical coefficient. It is defined by an expression.

The display of "E-0X" means "10- ^X ".

  In each of the following embodiments, the size of the image circle is φ6.

<Example 1>
First, a first embodiment of the present disclosure will be described.

-Basic configuration (Example 1)-
The basic configuration of the eyepiece optical system 52 according to the first embodiment is shown in FIG. 2, and the spherical aberration, astigmatism, distortion, and lateral aberration when this configuration is employed are shown in FIGS. ing. 2 to 4 show a state in which the diopter of the eyepiece optical system 52 is set to -4 diopters.

  Here, FIG. 3 shows spherical aberration, astigmatism, and distortion in order from the left side of the paper surface. In each case, the C line (wavelength 656.2725 nm), the e line (wavelength 546.0740 nm), and the F line ( It shows the aberration with respect to a wavelength of 486.1327 nm. In FIG. 3, the vertical axis of the spherical aberration (horizontal axis is “Diopter”) indicates the ratio of the incident height normalized by the maximum height, and the astigmatism (horizontal axis is “Diopter”) and distortion The vertical axis (the horizontal axis is “%”) indicates the half angle of view (°). In particular, in the spherical aberration, the aberration in the sagittal direction is described as “S”, while the aberration in the tangential (meridional) direction is described as “T”.

  4 shows lateral aberration in the tangential direction, while the right figure in FIG. 4 shows lateral aberration in the sagittal direction. Specifically, FIG. 4 shows the magnitude of the aberration with respect to the C-line, the e-line, and the F-line on both the left and right sides, and the image height ratios are 1.00, 0.80, 0.60, The lateral aberration is shown at 0.40 and 0.00.

  In the eyepiece optical system 52 shown in FIG. 2, in order from the display surface 51a side to the eye point EP side, a first lens L1 having a positive refractive power, a second lens L2 having a positive refractive power, and a negative refractive power And a fourth lens L4 having a positive refractive power.

  Here, the first lens L1 to the fourth lens L4 according to Example 1 are designed based on numerical data shown in Tables 1 to 4. In Table 4, the values of the back focus and the total length of the lens are both based on air.

  Further, as described above, the first lens L1 to the fourth lens L4 move integrally along the optical axis OA when adjusting the diopter of the eyepiece optical system 52. Thereby, the diopter of the eyepiece optical system 52 according to the first embodiment can be changed in the range of −4 to +2 diopters. As an example, FIGS. 5 to 7 show a configuration in which the diopter of the eyepiece optical system 52 is set to +2 diopters and the magnitude of aberration in the configuration. See Table 3 for the surface spacing at this time.

  Then, as shown in Tables 13 and 14, the eyepiece optical system 52 according to Example 1 satisfies all of the conditional expressions (1) to (4). Thereby, it is possible to realize a high magnification while maintaining high imaging performance.

  -Numerical example (Example 1)-

<Example 2>
Next, a second embodiment of the present disclosure will be described. The description of the same parts as those in the first embodiment will be omitted.

-Basic configuration (Example 2)-
The basic configuration of the eyepiece optical system 52 according to the second embodiment is shown in FIG. 8, and the spherical aberration, astigmatism, distortion, and lateral aberration when this configuration is adopted are shown in FIGS. ing. 8 to 10 show a state in which the diopter of the eyepiece optical system 52 is set to -4 diopters.

  The eyepiece optical system 52 shown in FIG. 8 includes, in order from the display surface 51a side to the eye point EP side, a first lens L1 having a positive refractive power, a second lens L2 having a positive refractive power, and a negative refractive power. And a fourth lens L4 having a positive refractive power.

  Here, the first lens L1 to the fourth lens L4 according to Example 2 are designed based on numerical data shown in Tables 5 to 8. In Table 8, the values of the back focus and the total length of the lens are both based on air.

  In addition, the first lens L1 to the fourth lens L4 according to the example 2 are gradually reduced in diameter from the display surface 51a to the eye point EP.

  As in the first embodiment, the first lens L1 to the fourth lens L4 move integrally along the optical axis OA when adjusting the diopter of the eyepiece optical system 52. Thereby, the diopter of the eyepiece optical system 52 according to the second embodiment can be changed in the range of −4 to +2 diopters. As an example, FIGS. 11 to 13 show a configuration in which the diopter of the eyepiece optical system 52 is set to 2 diopters and the magnitude of aberration in the configuration. See Table 7 for the surface spacing at this time.

  As shown in Tables 13 and 14, the eyepiece optical system 52 according to the second embodiment satisfies all of the conditional expressions (1) to (4) as in the first embodiment. Thereby, it is possible to realize a high magnification while maintaining high imaging performance.

  -Numerical Example (Example 2)-

<Example 3>
Next, a third embodiment of the present disclosure will be described. The description of the same parts as those of the first and second embodiments will be omitted.

-Basic configuration (Example 3)-
The basic configuration of the eyepiece optical system 52 according to the third embodiment is shown in FIG. 14, and the spherical aberration, astigmatism, distortion, and lateral aberration when this configuration is adopted are shown in FIGS. ing. 14 to 16 show a state in which the diopter of the eyepiece optical system 52 is set to -4 diopters.

  The eyepiece optical system 52 shown in FIG. 14 includes, in order from the display surface 51a side to the eye point EP side, a first lens L1 having a positive refractive power, a second lens L2 having a positive refractive power, and a negative refractive power. And a fourth lens L4 having a positive refractive power.

  Here, the first lens L1 to the fourth lens L4 according to Example 3 are designed based on numerical data shown in Tables 9 to 12. In Table 12, the values of the back focus and the total length of the lens are both based on air.

  In the first and second embodiments, the cover glass C is interposed between the display surface 51a and the first lens L1, as described above. In the third embodiment, the display surface 51a and the first lens Apart from the first cover glass C1 interposed between the fourth lens L4 and the eye point EP, a second cover glass C2 is interposed between the fourth lens L4 and the eye point EP.

  As in the first and second embodiments, the first lens L1 to the fourth lens L4 move integrally along the optical axis OA when adjusting the diopter of the eyepiece optical system 52. Thus, the diopter of the eyepiece optical system 52 according to the third embodiment can be changed in the range of -4 to +3 diopters. As an example, FIGS. 17 to 19 show a configuration in which the diopter of the eyepiece optical system 52 is set to 3 diopters, and magnitudes of aberrations in the configuration. See Table 11 for the surface spacing at this time.

  Then, as shown in Tables 13 and 14, the eyepiece optical system 52 according to the third embodiment satisfies all of the conditional expressions (1) to (4) as in the first and second embodiments. Thereby, it is possible to realize a high magnification while maintaining high imaging performance.

  -Numerical example (Example 3)-

<Numerical data related to conditional expressions (1) to (4)>
Hereinafter, numerical data related to conditional expressions (1) to (4) are shown in Tables 13 and 14.

  In Tables 13 and 14, f1 indicates the focal length of the first lens L1, f2 indicates the focal length of the second lens L2, and f23 indicates the combined focal length of the second lens L2 and the third lens L3. The distance f34 indicates the combined focal length of the third lens L3 and the fourth lens L4.

  As described above, the first to third embodiments all satisfy the conditional expressions (1) to (4).

100 Imaging device 5 Electronic viewfinder 51a Display surface 52 Eyepiece optical system L1 First lens L2 Second lens L3 Third lens L4 Fourth lens EP Eye point (pupil)
OA optical axis

Claims (8)

An eyepiece optical system for magnifying and observing a display surface,
In order from the display surface side to the pupil side, a first lens having a positive refractive power, a second lens having a positive refractive power, a third lens having a negative refractive power, and a third lens having a positive refractive power. And four lenses are arranged,
The diagonal length of the display surface is H, the focal length of the entire eyepiece optical system is f, the combined focal length of the first lens and the second lens is f12, the focal length of the third lens is f3, An eyepiece optical system characterized by satisfying the following conditional expressions (1) to (4) when the focal length of the four lenses is f4.
0.50 <H / f <0.73 (1)
0.48 <f12 / f <0.6 (2)
−0.56 <f3 / f <−0.38 (3)
0.82 <f4 / f <1.15 (4) In the eyepiece optical system according to claim 1,
The eyepiece optical system, wherein at least one of the first lens, the second lens, the third lens, and the fourth lens has an aspherical shape. An eyepiece optical system according to claim 1 or 2,
The eyepiece optical system, wherein the first lens, the second lens, the third lens, and the fourth lens move integrally along an optical axis when adjusting diopter. In the eyepiece optical system according to any one of claims 1 to 3,
The eyepiece optical system, wherein the first lens has a concave shape on at least one side, and is arranged with the concave shape facing the display surface. In the eyepiece optical system according to any one of claims 1 to 4,
The eyepiece optical system, wherein both the first lens and the second lens have a convex shape on at least one side, and are arranged in a posture in which the convex shapes face each other. The eyepiece optical system according to any one of claims 1 to 5,
The eyepiece optical system, wherein the third lens has a concave shape on at least one side, and is arranged with the concave shape facing the pupil. An electronic viewfinder comprising the eyepiece optical system according to claim 1. An imaging apparatus comprising the electronic viewfinder according to claim 7.