Observation optics and optical devices

Abstract

To provide an observation optical system which offers good performance and enables observation with a wide apparent field of view, and an optical device having the same.SOLUTION: An observation optical system disclosed herein comprises a display element and an ocular lens located on the eye-point side of the display element. The ocular lens comprises a first negative lens having the greatest negative refractive power among lenses constituting the ocular lens, a first positive lens disposed next to the first negative lens on the display element side, and a second positive lens disposed on the eye-point side of the first negative lens at a position on the most display element side among positive lenses. The ocular lens includes five or more lenses. The observation optical system satisfies predefined conditional expressions.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an observation optical system and an optical device.

Background Art

[0002] Conventionally, as an eyepiece optical system applicable to an observation optical system, lens systems described in Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 below are known.

Prior Art Documents

Patent Documents

[0003] <0000XX2>

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=4X]] There is a demand for an observation optical system that can observe with a wide apparent field of view while preferably correcting various aberrations such as field curvature and chromatic aberration of magnification and having good performance. These required levels are increasing year by year.

[0005] The present disclosure provides an observation optical system that can observe with a wide apparent field of view while having good performance, and an optical device including this observation optical system.

Means for Solving the Problems

[0006] An observation optical system according to one aspect of the present disclosure comprises a display element and an eyepiece positioned on the eye point side of the display element, wherein the eyepiece includes a first negative lens having the strongest negative refractive power among the lenses included in the eyepiece, a first positive lens positioned adjacent to the display element side of the first negative lens, and a second positive lens positioned on the display element side among the positive lenses positioned on the eye point side of the first negative lens, the number of lenses included in the eyepiece is five or more, and when H is the half value of the longest diameter of the display area in the display element, f is the focal length of the eyepiece when the diopter is -1 diopter, TLA is the sum of the air-equivalent distance on the optical axis from the display surface of the display element to the lens surface of the eyepiece closest to the display element and the distance on the optical axis from the lens surface of the eyepiece closest to the display element to the lens surface of the eyepiece closest to the eye point when the diopter is -1 diopter, and Nn1 is the refractive index of the first negative lens with respect to the d line, 0.355 <H / f<0.48 (1) 0.17 <H / TLA<0.285 (2) 1.5 <Nn1<1.7 (3) The conditions (1), (2), and (3) expressed by are satisfied.

[0007] The eyepiece may be configured to contain five or six lenses.

[0008] When the paraxial radius of curvature of the eye-point side surface of the first positive lens is Rpr, and the paraxial radius of curvature of the display element side surface of the first negative lens is Rnf, the observation optical system of the above embodiment is: 0<|(Rnf-Rpr) / (Rnf+Rpr)|<0.6 (4) It is preferable that the condition expressed in equation (4) is satisfied.

[0009] When the focal length of the first positive lens is fp1, the observation optical system in the above embodiment is: 0 <f / fp1<1.8 (5) It is preferable that the condition (5) expressed by is satisfied.

[0010] When the focal length of the first negative lens is fn1, the observation optical system of the above aspect is -1.4 < f / fn1 < -0.3 (6) and preferably satisfies the conditional expression (6) represented by this.

[0011] When the focal length of the second positive lens is fp2, the observation optical system of the above aspect is 0 < f / fp2 < 0.9 (7) and preferably satisfies the conditional expression (7) represented by this.

[0012] When the focal length of the first positive lens is fp1, the observation optical system of the above aspect is 0 < H / fp1 < 0.9 (8) and preferably satisfies the conditional expression (8) represented by this.

[0013] When the focal length of the first negative lens is fn1, the observation optical system of the above aspect is -0.6 < H / fn1 < -0.2 (9) and preferably satisfies the conditional expression (9) represented by this.

[0014] When the focal length of the second positive lens is fp2, the observation optical system of the above aspect is 0 < H / fp2 < 0.4 (10) and preferably satisfies the conditional expression (10) represented by this.

[0015] When the Abbe number of the first negative lens with respect to the d-line is νn1, the observation optical system of the above aspect is 19 < νn1 < 27 (11) and preferably satisfies the conditional expression (11) represented by this.

[0016] When the refractive index with respect to the d-line of the lens having the strongest positive refractive power among the lenses included in the eyepiece lens is Nps, the observation optical system of the above aspect is 1.6 < Nps < 2 (12) and preferably satisfies the conditional expression (12) represented by this.

[0017] If νps is the Abbe number of the lens with the strongest positive refractive power among the lenses included in the eyepiece, then the observation optical system of the above embodiment is: 35 < νps < 55 (13) It is preferable that the conditional expression (13) represented by is satisfied.

[0018] If Nave is the average refractive index of all lenses included in the eyepiece with respect to the d line, then the observation optical system of the above embodiment is: 1.55 <Nave<1.75 (14) It is preferable that the conditional expression (14) represented by is satisfied.

[0019] If the focal length of the lens closest to the eye point of the eyepiece is denoted as fe, then the observation optical system in the above embodiment is: 0 <f / |fe|<0.9 (15) It is preferable that the conditional expression (15) represented by is satisfied.

[0020] If Ref is the paraxial radius of curvature of the display element side surface of the lens closest to the eye point of the eyepiece, and Rer is the paraxial radius of curvature of the eye point side surface of the lens closest to the eye point of the eyepiece, then the observation optical system of the above embodiment is: 0<|(Rer-Ref) / (Rer+Ref)|<3 (16) It is preferable that the conditional expression (16) represented by is satisfied.

[0021] When the diopter is -1 diopter, and the air distance on the optical axis between the lens closest to the eye point and the second lens from the eye point is denoted as dE, then the observation optical system of the above embodiment is: 0.002 <dE / TLA<0.07 (17) It is preferable that the conditional expression (17) represented by is satisfied.

[0022] When the focal length of the lens closest to the display element in the eyepiece is denoted as fo, the observation optical system in the above embodiment is: 0.01 <f / |fo|<1.8 (18) It is preferable that the conditional expression (18) represented by is satisfied.

[0023] If Rof is the paraxial radius of curvature of the display element-side surface of the lens closest to the display element of the eyepiece, and Ror is the paraxial radius of curvature of the eye point-side surface of the lens closest to the display element of the eyepiece, then the observation optical system of the above embodiment is: 0<|(Ror-Rof) / (Ror+Rof)|<10 (19) It is preferable that the condition expressed in equation (19) is satisfied.

[0024] If dO is the air gap on the optical axis between the lens closest to the display element of the eyepiece and the second lens from the display element side of the eyepiece, then the observation optical system of the above embodiment is: 0 <dO / TLA<0.1 (20) It is preferable that the conditional expression (20) represented by is satisfied.

[0025] An optical apparatus according to another aspect of the present disclosure comprises the observation optical system of the above aspect.

[0026] Furthermore, the terms "~consisting of" and "~consisting of" in this specification are intended to include, in addition to the listed components, lenses that have substantially no refractive power, as well as optical elements other than lenses such as apertures, filters, and cover glasses, and lens flanges, lens barrels, etc.

[0027] In this specification, "lens with positive refractive power" and "positive lens" are synonymous. "Lens with negative refractive power" and "negative lens" are synonymous. "Single lens" means a single lens that is not joined together. However, a composite aspherical lens (a lens in which a spherical lens and an aspherical film formed on the spherical lens are integrally constructed and function as a single aspherical lens as a whole) is not considered a joined lens and is treated as a single lens. For lenses including aspherical surfaces, the sign of refractive power, radius of curvature, and surface shape shall be those of the paraxial region unless otherwise specified. The sign of the radius of curvature shall be positive for the radius of curvature of the surface with the convex shape facing the display element, and negative for the radius of curvature of the surface with the convex shape facing the eye point.

[0028] The "focal length" used in the conditional formulas is the paraxial focal length. The values ​​used in the conditional formulas are relative to the d-line. Unless otherwise specified, the "distance on the optical axis" used in the conditional formulas is the geometric distance on the optical axis. The "d-line," "C-line," and "F-line" described herein are emission lines, and the wavelength of the d-line is treated as 587.56 nm (nanometers), the wavelength of the C-line as 656.27 nm (nanometers), and the wavelength of the F-line as 486.13 nm (nanometers). [Effects of the Invention]

[0029] According to this disclosure, it is possible to provide an observation optical system that has good performance and is capable of observation with a wide apparent field of view, and an optical device equipped with this observation optical system. [Brief explanation of the drawing]

[0030] [Figure 1] This is a cross-sectional view corresponding to the observation optical system of Example 1, showing the configuration and light beam of an observation optical system according to one embodiment. [Figure 2] These are aberration diagrams for the observation optical system of Example 1. [Figure 3] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 2. [Figure 4] These are aberration diagrams for the observation optical system of Example 2. [Figure 5] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 3. [Figure 6] These are aberration diagrams for the observation optical system of Example 3. [Figure 7] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 4. [Figure 8] These are aberration diagrams for the observation optical system of Example 4. [Figure 9] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 5. [Figure 10] These are aberration diagrams for the observation optical system of Example 5. [Figure 11] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 6. [Figure 12] These are aberration diagrams for the observation optical system of Example 6. [Figure 13] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 7. [Figure 14] These are aberration diagrams for the observation optical system of Example 7. [Figure 15] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 8. [Figure 16] These are aberration diagrams for the observation optical system of Example 8. [Figure 17] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 9. [Figure 18] These are aberration diagrams for the observation optical system of Example 9. [Figure 19] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 10. [Figure 20] These are aberration diagrams for the observation optical system of Example 10. [Figure 21] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 11. [Figure 22] These are aberration diagrams for the observation optical system of Example 11. [Figure 23] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 12. [Figure 24] These are aberration diagrams for the observation optical system of Example 12. [Figure 25]This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 13. [Figure 26] These are aberration diagrams for the observation optical system of Example 13. [Figure 27] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 14. [Figure 28] These are aberration diagrams for the observation optical system of Example 14. [Figure 29] This is a cross-sectional view showing the configuration and light beam of the observation optical system in Example 15. [Figure 30] These are aberration diagrams for the observation optical system of Example 15. [Figure 31] This is a perspective view of the rear side of an optical device according to one embodiment. [Modes for carrying out the invention]

[0031] The embodiments of this disclosure will be described below with reference to the drawings.

[0032] Figure 1 shows the configuration of the observation optical system 5 and a cross-sectional view of the light beam according to one embodiment of the present disclosure. The example shown in Figure 1 corresponds to Embodiment 1 described later. In Figure 1, the light beam is shown as the on-axis light beam and the off-axis light beam corresponding to the maximum apparent field of view. In Figure 1, the left side is shown as the display element side and the right side as the eye point side. The eye point EP in Figure 1 does not show the shape but rather the position in the optical axis direction.

[0033] The observation optical system 5 comprises a display element 1 and an eyepiece lens 3 positioned on the eye point side of the display element 1. The display element 1 is an element that displays an image. The display element 1 includes a display area 1a on which the image is displayed and a cover member 1b made of an optical material that does not have refractive power. In the example in Figure 1, the display area 1a is located on the surface of the cover member 1b on the display element side. The display element 1 can be configured as an image display panel made of, for example, a liquid crystal display element or an organic electroluminescence (EL) display element. The display element 1 and the eyepiece lens 3 are positioned with a predetermined air gap between them.

[0034] Display element 1 is an example of an object to be observed. The eyepiece 3 is used to observe the image displayed in the display area 1a of the display element 1. In other words, the observation optical system 5 is configured to observe the image displayed on the display element 1 through the eyepiece 3.

[0035] The eyepiece 3 includes a first positive lens, a first negative lens, and a second positive lens. The first negative lens is the lens with the strongest negative refractive power among the lenses included in the eyepiece 3. The first positive lens is a positive lens positioned adjacent to the display element side of the first negative lens. The second positive lens is the positive lens positioned closest to the display element among the positive lenses positioned closer to the eye point than the first negative lens. By arranging the lenses in this manner, with a positive lens, a negative lens, and a positive lens in order from the display element side to the eye point side, it is advantageous to ensure a wide apparent field of view while effectively correcting chromatic aberration and suppressing an increase in the diameter of the optical system.

[0036] As an example, the eyepiece 3 in Figure 1 consists of, in order from the display element side to the eye point side, a lens L1 with positive refractive power, a lens L2 with positive refractive power, a lens L3 with negative refractive power, a lens L4 with positive refractive power, and a lens L5 with positive refractive power. In the example in Figure 1, lens L3 corresponds to the first negative lens, lens L2 corresponds to the first positive lens, and lens L4 corresponds to the second positive lens.

[0037] The eyepiece 3 is configured to contain five or more lenses. By using a lens configuration of five or more lenses, it becomes easier to ensure a wide apparent field of view while effectively correcting chromatic aberration, astigmatism, and distortion.

[0038] The eyepiece 3 may be configured to contain five or six lenses. In this case, it becomes easier to secure a wide apparent field of view while minimizing the number of lenses while effectively correcting chromatic aberration, astigmatism, and distortion.

[0039] Next, preferred and possible configurations for the conditional equations of the observation optical system 5 will be described. In the following explanation of the conditional equations, the same symbols will be used for things with the same definition, and some redundant explanations of symbols will be omitted to avoid redundant explanations.

[0040] When H is the half-value of the longest diameter of the display area 1a in the display element 1, and f is the focal length of the eyepiece lens 3 when the diopter is -1 diopter, it is preferable that the observation optical system 5 satisfies the following condition (1). By ensuring that the corresponding value in condition (1) does not fall below the lower limit, it is possible to suppress the weakening of the refractive power of the eyepiece lens 3, which is advantageous in securing a wide apparent field of view. By ensuring that the corresponding value in condition (1) does not exceed the upper limit, it is advantageous to suppress aberrations such as field curvature while miniaturizing in the radial and optical axis directions. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (1-1), and even more preferable that it satisfies the following condition (1-2). 0.355 <H / f<0.48 (1) 0.36 <H / f<0.475 (1-1) 0.365 <H / f<0.47 (1-2)

[0041] In this specification, "the longest diameter of the display area 1a in the display element 1" with respect to H means twice the distance between the point furthest from the optical axis Z in the radial direction and the optical axis Z in the display area 1a where the centroid coincides with the optical axis Z. For example, if the display area 1a is rectangular, H can be half the length of the diagonal of the display area 1a. Also, for example, if the display area 1a is a perfect circle, H can be the radius of the display area 1a, and if the display area 1a is an ellipse, H can be half the longest diameter (major axis) of the diameter of the display area 1a.

[0042] Furthermore, the display area 1a refers to the area where the image is actually displayed. For example, if the display element 1 has a display section with an aspect ratio of 4:3 in which multiple pixels are arranged, and displays an image with an aspect ratio of 3:2 in a part of the display section, then the display area 1a refers to the area where the image with an aspect ratio of 3:2 is displayed. Therefore, the diameter of the display element 1 and the longest diameter of the display area 1a do not necessarily coincide.

[0043] The observation optical system 5 preferably satisfies the following condition (2). Here, TLA is defined as the sum of the air-equivalent distance on the optical axis from the display surface of the display element 1 to the lens surface of the eyepiece 3 closest to the display element, and the distance on the optical axis from the lens surface of the eyepiece 3 closest to the display element to the lens surface of the eyepiece 3, when the diopter is -1 diopter. By ensuring that the corresponding value of condition (2) does not fall below the lower limit, it is advantageous to shorten the overall length of the observation optical system 5. By ensuring that the corresponding value of condition (2) does not exceed the upper limit, it is advantageous to suppress aberrations such as field curvature. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (2-1), and even more preferable that it satisfies the following condition (2-2). 0.17 <H / TLA<0.285 (2) 0.175 <H / TLA<0.28 (2-1) 0.18 <H / TLA<0.275 (2-2)

[0044] When the refractive index of the first negative lens with respect to the d line is Nn1, it is preferable that the observation optical system 5 satisfies the following condition (3). By ensuring that the corresponding value in condition (3) does not fall below the lower limit, it is possible to suppress the weakening of the refractive power of the first negative lens, which is advantageous for shortening the overall length of the observation optical system 5 in the optical axis direction when trying to secure a wide apparent field of view. By ensuring that the corresponding value in condition (3) does not exceed the upper limit, the refractive power of the first negative lens does not become too strong, which suppresses excessive correction of chromatic aberration. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (3-1), and even more preferable that it satisfies the following condition (3-2). 1.5 <Nn1<1.7 (3) 1.51 <Nn1<1.69 (3-1) 1.52 <Nn1<1.68 (3-2)

[0045] The observation optical system 5 preferably satisfies conditions (1), (2), and (3). More preferably, the observation optical system 5 satisfies conditions (1-1), (1-2), (2-1), (2-2), (3-1), and (3-2) in addition to satisfying conditions (1), (2), and (3).

[0046] When the paraxial radius of curvature of the eye-point side surface of the first positive lens is Rpr and the paraxial radius of curvature of the display element side surface of the first negative lens is Rnf, it is preferable that the observation optical system 5 satisfies the following conditional equation (4). By ensuring that the corresponding value of conditional equation (4) does not fall below the lower limit, it is possible to suppress the excessive refraction of off-axis rays at the display element side surface of the first negative lens in relation to the refraction of off-axis rays at the eye-point side surface of the first positive lens, which is advantageous in suppressing excessive correction of chromatic aberration. By ensuring that the corresponding value of conditional equation (4) does not exceed the upper limit, it is possible to suppress the weakening of the refraction of off-axis rays at the display element side surface of the first negative lens in relation to the refraction of off-axis rays at the eye-point side surface of the first positive lens, which is advantageous in suppressing insufficient correction of chromatic aberration. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following conditional equation (4-1), and even more preferable that it satisfies the following conditional equation (4-2). 0<|(Rnf-Rpr) / (Rnf+Rpr)|<0.6 (4) 0.001<|(Rnf-Rpr) / (Rnf+Rpr)|<0.58 (4-1) 0.002<|(Rnf-Rpr) / (Rnf+Rpr)|<0.55 (4-2)

[0047] When the focal length of the first positive lens is fp1, it is preferable that the observation optical system 5 satisfies the following condition (5). By ensuring that the corresponding value of condition (5) does not fall below the lower limit, it is possible to suppress the weakening of the positive refractive power of the first positive lens, which is advantageous in suppressing astigmatism and field curvature. By ensuring that the corresponding value of condition (5) does not exceed the upper limit, it is possible to suppress the weakening of the refractive power of the eyepiece lens 3, which is advantageous in securing a wide apparent field of view. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (5-1), and even more preferable that it satisfies the following condition (5-2). 0 <f / fp1<1.8 (5) 0.05 <f / fp1<1.78 (5-1) 0.1 <f / fp1<1.76 (5-2)

[0048] When the focal length of the first negative lens is fn1, it is preferable that the observation optical system 5 satisfies the following condition (6). By ensuring that the corresponding value in condition (6) does not fall below the lower limit, the refractive power of the first negative lens does not become too strong, thus suppressing excessive correction of chromatic aberration. By ensuring that the corresponding value in condition (6) does not exceed the upper limit, the refractive power of the first negative lens does not become too weak, which is advantageous for shortening the overall length of the observation optical system 5 in the optical axis direction when seeking to secure a wide apparent field of view. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (6-1), and even more preferable that it satisfies the following condition (6-2). -1.4 <f / fn1<-0.3 (6) -1.38 <f / fn1<-0.4 (6-1) -1.35 <f / fn1<-0.5 (6-2)

[0049] When the focal length of the second positive lens is fp2, it is preferable that the observation optical system 5 satisfies the following condition (7). By ensuring that the corresponding value in condition (7) does not fall below the lower limit, it is possible to suppress the weakening of the positive refractive power of the second positive lens, which is advantageous in suppressing astigmatism and spherical aberration. By ensuring that the corresponding value in condition (7) does not exceed the upper limit, it is possible to suppress the weakening of the refractive power of the eyepiece 3, which is advantageous in securing a wide apparent field of view. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (7-1), and even more preferable that it satisfies the following condition (7-2). 0 <f / fp2<0.9 (7) 0.15 <f / fp2<0.85 (7-1) 0.2 <f / fp2<0.8 (7-2)

[0050] When the focal length of the first positive lens is fp1, it is preferable that the observation optical system 5 satisfies the following condition (8). For the lower limit of condition (8), since H>0 and fp1>0, H / fp1>0. By ensuring that the corresponding value of condition (8) does not exceed the upper limit, the refractive power of the first positive lens does not become too strong, thus suppressing excessive correction of astigmatism and field curvature. It is more preferable that the observation optical system 5 satisfies the following condition (8-1). By ensuring that the corresponding value of condition (8-1) does not fall below the lower limit, the height of the off-axis light rays emitted from the display surface of the display element 1 from the optical axis Z does not become too low, which is advantageous in securing a wide apparent field of view. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (8-2). 0 <H / fp1<0.9 (8) 0.02 <H / fp1<0.8 (8-1) 0.04 <H / fp1<0.75 (8-2)

[0051] The observation optical system 5 preferably satisfies the following condition (9). By ensuring that the corresponding value of condition (9) does not fall below the lower limit, the height of the off-axis light rays emitted from the display surface of the display element 1 from the optical axis Z does not become too high, which is advantageous for miniaturizing the lens adjacent to the display surface. Alternatively, by ensuring that the corresponding value of condition (9) does not fall below the lower limit, the refractive power of the first negative lens does not become too strong, which can suppress excessive correction of chromatic aberration. By ensuring that the corresponding value of condition (9) does not exceed the upper limit, the refractive power of the first negative lens does not become too weak, which is advantageous for shortening the overall length of the observation optical system 5 in the optical axis direction when trying to secure a wide apparent field of view. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (9-1), and even more preferable that it satisfies the following condition (9-2). -0.6 <H / fn1<-0.2 (9) -0.55 <H / fn1<-0.25 (9-1) -0.5 <H / fn1<-0.3 (9-2)

[0052] The observation optical system 5 preferably satisfies the following condition (10). For the lower limit of condition (10), since H>0 and fp2>0, H / fp2>0. By ensuring that the corresponding value of condition (10) does not exceed the upper limit, the refractive power of the second positive lens does not become too strong, thus suppressing overcorrection of astigmatism and spherical aberration. The observation optical system 5 more preferably satisfies the following condition (10-1). By ensuring that the corresponding value of condition (10-1) does not fall below the lower limit, the height of the off-axis light rays emitted from the display surface of the display element 1 from the optical axis Z does not become too low, which is advantageous in securing a wide apparent field of view. To obtain even better characteristics, the observation optical system 5 more preferably satisfies the following condition (10-2). 0 <H / fp2<0.4 (10) 0.02 <H / fp2<0.35 (10-1) 0.04 <H / fp2<0.3 (10-2)

[0053] When the Abbe number of the first negative lens with respect to the d line is νn1, it is preferable that the observation optical system 5 satisfies the following condition (11). By ensuring that the corresponding value of condition (11) does not fall below the lower limit, the chromatic dispersion of the first negative lens does not become too large, thus suppressing overcorrection of lateral chromatic aberration. By ensuring that the corresponding value of condition (11) does not exceed the upper limit, the chromatic dispersion of the first negative lens does not become too small, which is advantageous for correcting lateral chromatic aberration. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (11-1), and even more preferable that it satisfies the following condition (11-2). 19 < νn1 < 27 (11) 20 < νn1 < 26 (11-1) 21 < νn1 < 25 (11-2)

[0054] When the refractive index of the lens with the strongest positive refractive power among the lenses included in the eyepiece 3 with respect to the d line is Nps, it is preferable that the observation optical system 5 satisfies the following condition (12). By ensuring that the corresponding value of condition (12) does not fall below the lower limit, it is possible to suppress the refractive power of the lens with the strongest positive refractive power from becoming too weak, which is advantageous for shortening the overall length of the observation optical system 5 in the optical axis direction. By ensuring that the corresponding value of condition (12) does not exceed the upper limit, it is possible to suppress chromatic aberration occurring in the lens with the strongest positive refractive power, which is particularly advantageous for correcting chromatic aberration of magnification. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (12-1), and even more preferable that it satisfies the following condition (12-2). 1.6 <Nps<2 (12) 1.65 <Nps<1.95 (12-1) 1.7 <Nps<1.9 (12-2)

[0055] When νps is the d-line reference Abbe number of the lens with the strongest positive refractive power among the lenses included in the eyepiece 3, it is preferable that the observation optical system 5 satisfies the following condition (13). By ensuring that the corresponding value of condition (13) does not fall below the lower limit, the dispersion of colors occurring in the lens with the strongest positive refractive power can be suppressed, which is particularly advantageous for correcting chromatic aberration of magnification. By ensuring that the corresponding value of condition (13) does not exceed the upper limit, it is possible to prevent the refractive index of the lens with the strongest positive refractive power from becoming too low, thus preventing the refractive power of this lens from becoming too weak, which is advantageous for shortening the overall length of the observation optical system 5 in the optical axis direction. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (13-1), and even more preferable that it satisfies the following condition (13-2). 35 < νps < 55 (13) 38 < νps < 54 (13-1) 40 < ν ps < 53 (13-2)

[0056] When the average refractive index of all lenses included in the eyepiece 3 with respect to the d line is taken as Nave, it is preferable that the observation optical system 5 satisfies the following condition (14). By ensuring that the corresponding value in condition (14) does not fall below the lower limit, it is possible to suppress the Petzval sum from becoming large, which is advantageous for correcting field curvature. By ensuring that the corresponding value in condition (14) does not exceed the upper limit, it is possible to prevent the selection of lens materials from being limited to those with small Abbe numbers, which is advantageous for correcting chromatic aberration. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (14-1), and even more preferable that it satisfies the following condition (14-2). 1.55 <Nave<1.75 (14) 1.56 <Nave<1.7 (14-1) 1.57 <Nave<1.68 (14-2)

[0057] When the focal length of the lens closest to the eye point of the eyepiece 3 is denoted by fe, it is preferable that the observation optical system 5 satisfies the following condition (15). For the lower limit of condition (15), since f>0 and |fe|>0, f / |fe|>0. By ensuring that the corresponding value of condition (15) does not exceed the upper limit, it is possible to suppress the weakening of the refractive power of the eyepiece 3, which is advantageous in securing a wide apparent field of view. It is even more preferable that the observation optical system 5 satisfies the following condition (15-1). By ensuring that the corresponding value of condition (15-1) does not fall below the lower limit, it is possible to suppress the weakening of the refractive power of the lens closest to the eye point of the eyepiece 3, which is advantageous in suppressing astigmatism and spherical aberration. To obtain even better characteristics, it is even more preferable that the observation optical system 5 satisfies the following condition (15-2). 0 <f / |fe|<0.9 (15) 0.001 <f / |fe|<0.85 (15-1) 0.004 <f / |fe|<0.8 (15-2)

[0058] When Ref is the paraxial radius of curvature of the display element side surface of the lens closest to the eye point of the eyepiece 3, and Rer is the paraxial radius of curvature of the eye point side surface of the lens closest to the eye point of the eyepiece 3, it is preferable that the observation optical system 5 satisfies the following conditional equation (16). By ensuring that the corresponding value of conditional equation (16) does not fall below the lower limit, the refraction of off-axis rays at the lens closest to the eye point does not become too strong, thus suppressing excessive correction of field curvature. By ensuring that the corresponding value of conditional equation (16) does not exceed the upper limit, it is possible to suppress the weakening of off-axis rays at the lens closest to the eye point, which is advantageous for correcting field curvature. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following conditional equation (16-1), and even more preferable that it satisfies the following conditional equation (16-2). 0<|(Rer-Ref) / (Rer+Ref)|<3 (16) 0.1<|(Rer-Ref) / (Rer+Ref)|<2.8 (16-1) 0.14<|(Rer-Ref) / (Rer+Ref)|<2.7 (16-2)

[0059] When the diopter is -1 diopter, and the air distance on the optical axis between the lens closest to the eye point of the eyepiece 3 and the second lens from the eye point of the eyepiece 3 is denoted as dE, it is preferable that the observation optical system 5 satisfies the following condition (17). Ensuring that the corresponding value of condition (17) does not fall below the lower limit is advantageous in securing the range of motion when adjusting the diopter. Ensuring that the corresponding value of condition (17) does not exceed the upper limit is advantageous in shortening the overall length of the observation optical system 5 in the optical axis direction. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (17-1), and even more preferable that it satisfies the following condition (17-2). 0.002 <dE / TLA<0.07 (17) 0.003 <dE / TLA<0.068 (17-1) 0.004 <dE / TLA<0.065 (17-2)

[0060] When the focal length of the lens closest to the display element in the eyepiece 3 is denoted as fo, it is preferable that the observation optical system 5 satisfies the following condition (18). By ensuring that the corresponding value in condition (18) does not fall below the lower limit, it is possible to suppress the weakening of the refractive power of the lens closest to the display element in the eyepiece 3, which is advantageous in suppressing astigmatism, spherical aberration, and field curvature. By ensuring that the corresponding value in condition (18) does not exceed the upper limit, it is possible to suppress the weakening of the refractive power of the eyepiece 3, which is advantageous in securing a wide apparent field of view. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (18-1), and even more preferable that it satisfies the following condition (18-2). 0.01 <f / |fo|<1.8 (18) 0.015 <f / |fo|<1.75 (18-1) 0.02 <f / |fo|<1.7 (18-2)

[0061] When Rof is the paraxial radius of curvature of the display element-side surface of the lens closest to the display element of the eyepiece 3, and Ror is the paraxial radius of curvature of the eye point-side surface of the lens closest to the display element of the eyepiece 3, it is preferable that the observation optical system 5 satisfies the following condition (19). By ensuring that the corresponding value of condition (19) does not fall below the lower limit, the refraction of off-axis rays at the lens closest to the display element does not become too strong, thus suppressing excessive correction of field curvature. By ensuring that the corresponding value of condition (19) does not exceed the upper limit, it is possible to suppress the weakening of off-axis rays at the lens closest to the display element, which is advantageous for correcting field curvature. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (19-1), and even more preferable that it satisfies the following condition (19-2). 0<|(Ror-Rof) / (Ror+Rof)|<10 (19) 0.005<|(Ror-Rof) / (Ror+Rof)|<9.9 (19-1) 0.01<|(Ror-Rof) / (Ror+Rof)|<9.8 (19-2)

[0062] When dO is the air gap on the optical axis between the lens of the eyepiece 3 closest to the display element and the second lens of the eyepiece 3 from the display element side, it is preferable that the observation optical system 5 satisfies the following condition (20). Ensuring that the corresponding value of condition (20) does not fall below the lower limit is advantageous in securing the range of motion when adjusting the diopter. Ensuring that the corresponding value of condition (20) does not exceed the upper limit is advantageous in shortening the overall length of the observation optical system 5 in the optical axis direction. To obtain even better characteristics, it is more preferable that the observation optical system 5 satisfies the following condition (20-1), and even more preferable that it satisfies the following condition (20-2). 0 <dO / TLA<0.1 (20) 0.01 <dO / TLA<0.095 (20-1) 0.02 <dO / TLA<0.09 (20-2)

[0063] The eyepiece 3 may be configured to include three or four resin lenses. This configuration is advantageous in that it improves design flexibility and shortens the overall length of the observation optical system 5 in the optical axis direction while correcting astigmatism and field curvature.

[0064] The eyepiece 3 may be configured to include an aspherical lens. Including an aspherical lens is advantageous for good aberration correction.

[0065] The lenses included in eyepiece 3 may all be configured as unjoined single lenses. In this case, the design flexibility is greater compared to when the lenses are joined, which is advantageous for correcting aberrations and for obtaining a wider apparent field of view.

[0066] The preferred and possible configurations described above, including the configurations related to the conditional expressions, can be combined in any way and are preferably selected as appropriate according to the required specifications. It should be noted that the preferred conditional expressions that the observation optical system 5 of this disclosure satisfies are not limited to those described in formula form, but include all conditional expressions obtained by arbitrarily combining lower and upper limits from the preferred, more preferred, and even more preferred conditional expressions.

[0067] As an example, a preferred embodiment of the present disclosure is an observation optical system 5 comprising a display element 1 and an eyepiece 3 positioned on the eye point side of the display element 1, wherein the eyepiece 3 includes a first negative lens having the strongest negative refractive power among the lenses included in the eyepiece 3, a first positive lens positioned adjacent to the display element side of the first negative lens, and a second positive lens positioned on the display element side among the positive lenses positioned on the eye point side of the first negative lens, the number of lenses included in the eyepiece 3 being five or more, and satisfying the above conditional equations (1), (2), and (3).

[0068] In observation optical systems for viewfinders of digital cameras and the like, the increasing pixel count of display elements has recently led to a demand for wider apparent fields of view and higher resolution. However, attempting to obtain a wider apparent field of view increases the amount of various aberrations such as field curvature and chromatic aberration, making it difficult to achieve both a wider apparent field of view and high resolution. Therefore, by adopting the above-described preferred embodiment, it becomes easier to realize an observation optical system that allows observation with a wider apparent field of view while suppressing field curvature and chromatic aberration.

[0069] Next, embodiments of the observation optical system 5 of this disclosure will be described with reference to the drawings. Note that the reference numerals assigned to the components in the cross-sectional views of each embodiment are used independently for each embodiment to avoid increasing the number of digits in the reference numerals and complicating the explanation and drawings. Therefore, even if the same reference numerals are used in the drawings of different embodiments, they do not necessarily represent the same configuration. Furthermore, Examples 1 to 12, 14, and 15 below are embodiments of the present disclosure, while Example 13 is a reference example of the present disclosure.

[0070] [Example 1] The configuration of the observation optical system 5 of Example 1 is shown in Figure 1, and its illustration method and configuration are as described above, so some redundant explanations will be omitted here. The observation optical system 5 of Example 1 comprises a display element 1 and an eyepiece lens 3, in order from the display element side to the eye point side.

[0071] The eyepiece 3 consists of five lenses, L1 to L5, arranged in order from the display element side to the eye point side. During diopter adjustment, the display element 1 and lens L1 move integrally along the optical axis Z, while the other lenses remain fixed. The brackets and horizontal double arrows below the display element 1 and lens L1 in Figure 1 indicate that the display element 1 and lens L1 move integrally along the optical axis Z during diopter adjustment. In this specification, "moving integrally" means moving simultaneously and by the same amount in the same direction.

[0072] Table 1 shows the basic lens data for observation optical system 5 of Example 1, Table 2 shows the specifications and variable interplanar spacing, and Table 3 shows the aspherical coefficient.

[0073] Table 1 is described as follows: The Sn column shows the surface number of each surface, with the surface on which the display area 1a of the display element 1 is located being designated as the first surface, and the number increasing by one as you move toward the eye point. In the optical axis direction, the position of the first surface corresponds to the position of the display surface. The R column shows the radius of curvature of each surface. The D column shows the interplanar spacing on the optical axis between each surface and the surface adjacent to it on the eye point side. The Nd column shows the refractive index of each component with respect to the d line. The νd column shows the Abbe number of each component with respect to the d line.

[0074] Table 1 also lists display element 1 and eye point EP. In the Sn column for the surface corresponding to eye point EP, the surface number and the phrase (EP) are listed. Aspherical surface numbers are marked with an asterisk (*), and the column for the radius of curvature of the aspherical surface lists the value of the paraxial radius of curvature. In Table 1, the sign of the radius of curvature of a surface with a convex shape facing the display element is positive, and the sign of the radius of curvature of a surface with a convex shape facing the eye point is negative. For the variable surface spacing during diopter adjustment, the symbol DD[ ] is used, and the surface number on the display element side of this spacing is written in column D inside the brackets.

[0075] Table 2 shows the focal length f of the eyepiece 3, the apparent field of view across the entire diagonal angle of view, and the variable plane spacing for each diopter. In the diopter column, the unit diopters is denoted as "dpt". In the apparent field of view column, [°] indicates that the unit is degrees. Table 2 also shows the half-value H of the longest diameter of the display area 1a in the display element 1.

[0076] Table 3 shows the aspherical surface numbers in the Sn row, and the aspherical coefficient values ​​for each aspherical surface in the KA and Am rows. In this example, m = 4, 6, 8, 10, 12, 14, 16, 18, and 20. The values ​​of the aspherical coefficients in Table 3, "E ± n" (n: integer), are multiplied by 10. ±n This means "[...]. KA and Am are the aspheric coefficients in the aspheric equation expressed by the following formula. Zd = C × h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2}+ΣAm×hm however, Zd: Aspherical depth (length of the perpendicular line drawn from a point on the aspherical surface at height h to a plane perpendicular to the optical axis Z to which the aspherical surface tangent is located). h: Height (distance from the optical axis Z to the lens surface) C: Reciprocal of the radius of paraxial curvature KA, Am: Aspherical coefficients Therefore, the Σ in aspherical formulas represents the summation with respect to m.

[0077] In the data in each table, degrees are used as the unit for angles and millimeters (mm) as the unit for lengths. However, since optical systems can be used with proportional magnification or reduction, other appropriate units can also be used. Furthermore, the values ​​in the tables below are rounded to a predetermined number of decimal places.

[0078] [Table 1]

[0079] [Table 2]

[0080] [Table 3]

[0081] Figure 2 shows the aberration diagrams for each aspect of the observation optical system 5 of Example 1 at a diopter of -1.00 diopters. From left to right in Figure 2, the diagrams show spherical aberration, astigmatism, distortion, and chromatic aberration. In the spherical aberration diagram, the aberrations along the d, C, and F lines are shown as solid, long dashed, and short dashed lines, respectively. In the astigmatism diagram, the aberration along the d line in the sagittal direction is shown as a solid line, and the aberration along the d line in the tangential direction is shown as a short dashed line. In the distortion diagram, the aberration along the d line is shown as a solid line. In the chromatic aberration diagram, the aberrations along the C and F lines are shown as long dashed and short dashed lines, respectively. The unit "dpt" on the horizontal axis of the spherical aberration and astigmatism diagrams represents diopters. The unit "min" on the horizontal axis of the chromatic aberration diagram represents minutes of angle. In the spherical aberration diagram, the diameter of the eye point EP is shown after "Φ=" in millimeters (mm). In other aberration diagrams, the apparent field of view value at half the field of view is shown after "ω=".

[0082] The symbols, meanings, methods of description, and methods of illustration for each data point in Example 1 described above are the same in the following examples unless otherwise specified, so redundant explanations will be omitted below.

[0083] [Example 2] Figure 3 shows the configuration and light beam of the observation optical system 5 of Example 2. The observation optical system 5 of Example 2 comprises, in order from the display element side to the eye point side, a display element 1, an optical element 2, and an eyepiece lens 3. The optical element 2 is a parallel plate-shaped member with no refractive power, and is intended to be a protective cover glass or various filters.

[0084] The eyepiece 3 consists of, in order from the display element side to the eye point side, a lens L1 with positive refractive power, a lens L2 with negative refractive power, a lens L3 with positive refractive power, a lens L4 with positive refractive power, and a lens L5 with positive refractive power. During diopter adjustment, the display element 1 and the optical member 2 move together along the optical axis Z.

[0085] For the observation optical system 5 of Example 2, the basic lens data is shown in Table 4, the specifications and variable plane spacing in Table 5, the aspherical coefficient in Table 6, and the aberration diagrams for each state when the diopter is -0.97 diopters are shown in Figure 4.

[0086] [Table 4]

[0087] [Table 5]

[0088] [Table 6]

[0089] [Example 3] Figure 5 shows the configuration and light beam of the observation optical system 5 of Example 3. The observation optical system 5 of Example 3 comprises a display element 1 and an eyepiece lens 3, in order from the display element side to the eye point side. The eyepiece lens 3 consists of a lens L1 with positive refractive power, a lens L2 with positive refractive power, a lens L3 with negative refractive power, a lens L4 with positive refractive power, and a lens L5 with positive refractive power, in order from the display element side to the eye point side. When adjusting the diopter, lenses L2, L3, and L4 move integrally along the optical axis Z.

[0090] For the observation optical system 5 of Example 3, the basic lens data is shown in Table 7, the specifications and variable plane spacing in Table 8, the aspherical coefficient in Table 9, and the aberration diagrams for each state when the diopter is -0.96 diopters are shown in Figure 6.

[0091] [Table 7]

[0092] [Table 8]

[0093] [Table 9]

[0094] [Example 4] Figure 7 shows the configuration and light beam of the observation optical system 5 of Example 4. The observation optical system 5 of Example 4 comprises, in order from the display element side to the eye point side, a display element 1, an optical member 2, and an eyepiece lens 3. The eyepiece lens 3 consists of, in order from the display element side to the eye point side, a lens L1 with positive refractive power, a lens L2 with negative refractive power, a lens L3 with positive refractive power, a lens L4 with positive refractive power, and a lens L5 with positive refractive power. When adjusting the diopter, lenses L1, L2, L3, and L4 move integrally along the optical axis Z.

[0095] For the observation optical system 5 of Example 4, the basic lens data is shown in Table 10, the specifications and variable plane spacing in Table 11, the aspherical coefficient in Table 12, and the aberration diagrams for each state when the diopter is -0.99 diopters are shown in Figure 8.

[0096] [Table 10]

[0097] [Table 11]

[0098] [Table 12]

[0099] [Example 5] Figure 9 shows the configuration and light beam of the observation optical system 5 of Example 5. The observation optical system 5 of Example 5 comprises a display element 1 and an eyepiece lens 3, in order from the display element side to the eye point side. The eyepiece lens 3 consists of a lens L1 with negative refractive power, a lens L2 with positive refractive power, a lens L3 with negative refractive power, a lens L4 with positive refractive power, a lens L5 with positive refractive power, and a lens L6 with positive refractive power, in order from the display element side to the eye point side. During diopter adjustment, the display element 1 and lens L1 move integrally along the optical axis Z.

[0100] For the observation optical system 5 of Example 5, the basic lens data is shown in Table 13, the specifications and variable plane spacing in Table 14, the aspherical coefficient in Table 15, and the aberration diagrams for each state when the diopter is -0.97 diopters are shown in Figure 10.

[0101] [Table 13]

[0102] [Table 14]

[0103] [Table 15]

[0104] [Example 6] Figure 11 shows the configuration and light beam of the observation optical system 5 of Example 6. The observation optical system 5 of Example 6 comprises a display element 1 and an eyepiece lens 3, in order from the display element side to the eye point side. The eyepiece lens 3 consists of a lens L1 with negative refractive power, a lens L2 with positive refractive power, a lens L3 with positive refractive power, a lens L4 with negative refractive power, a lens L5 with positive refractive power, and a lens L6 with positive refractive power, in order from the display element side to the eye point side. During diopter adjustment, the display element 1 and lens L1 move integrally along the optical axis Z.

[0105] For the observation optical system 5 of Example 6, the basic lens data is shown in Table 16, the specifications and variable plane spacing in Table 17, the aspherical coefficient in Table 18, and the aberration diagrams for each state when the diopter is -0.99 diopters are shown in Figure 12.

[0106] [Table 16]

[0107] [Table 17]

[0108] [Table 18]

[0109] [Example 7] Figure 13 shows the configuration and light beam of the observation optical system 5 of Example 7. The observation optical system 5 of Example 7 comprises, in order from the display element side to the eye point side, a display element 1, an optical member 2, and an eyepiece lens 3. The eyepiece lens 3 consists of, in order from the display element side to the eye point side, a lens L1 with negative refractive power, a lens L2 with positive refractive power, a lens L3 with negative refractive power, a lens L4 with positive refractive power, a lens L5 with positive refractive power, and a lens L6 with positive refractive power. During diopter adjustment, the display element 1 and the optical member 2 move integrally along the optical axis Z.

[0110] For observation optical system 5 of Example 7, the basic lens data is shown in Table 19, the specifications and variable plane spacing in Table 20, the aspherical coefficient in Table 21, and the aberration diagrams for each state when the diopter is -0.97 diopters are shown in Figure 14.

[0111] [Table 19]

[0112] [Table 20]

[0113] [Table 21]

[0114] [Example 8] Figure 15 shows the configuration and light beam of the observation optical system 5 of Example 8. The observation optical system 5 of Example 8 comprises a display element 1 and an eyepiece lens 3, in order from the display element side to the eye point side. The eyepiece lens 3 consists of a lens L1 with negative refractive power, a lens L2 with positive refractive power, a lens L3 with negative refractive power, a lens L4 with positive refractive power, a lens L5 with positive refractive power, and a lens L6 with positive refractive power, in order from the display element side to the eye point side. During diopter adjustment, lenses L2, L3, L4, and L5 move integrally along the optical axis Z.

[0115] For observation optical system 5 of Example 8, the basic lens data is shown in Table 22, the specifications and variable plane spacing in Table 23, the aspherical coefficient in Table 24, and the aberration diagrams for each state when the diopter is -1.01 diopters are shown in Figure 16.

[0116] [Table 22]

[0117] [Table 23]

[0118] [Table 24]

[0119] [Example 9] Figure 17 shows the configuration and light beam of the observation optical system 5 of Example 9. The observation optical system 5 of Example 9 comprises, in order from the display element side to the eye point side, a display element 1, an optical member 2, and an eyepiece lens 3. The eyepiece lens 3 consists of, in order from the display element side to the eye point side, a lens L1 with negative refractive power, a lens L2 with positive refractive power, a lens L3 with negative refractive power, a lens L4 with positive refractive power, a lens L5 with positive refractive power, and a lens L6 with positive refractive power. When adjusting the diopter, lenses L1, L2, L3, L4, and L5 move integrally along the optical axis Z.

[0120] For observation optical system 5 of Example 9, the basic lens data is shown in Table 25, the specifications and variable plane spacing in Table 26, the aspherical coefficient in Table 27, and the aberration diagrams for each state when the diopter is -0.97 diopters are shown in Figure 18.

[0121] [Table 25]

[0122] [Table 26]

[0123] [Table 27]

[0124] [Example 10] Figure 19 shows the configuration and light beam of the observation optical system 5 of Example 10. The observation optical system 5 of Example 10 comprises, in order from the display element side to the eye point side, a display element 1, an eyepiece lens 3, and an optical member 2. The eyepiece lens 3 consists of, in order from the display element side to the eye point side, a lens L1 with negative refractive power, a lens L2 with positive refractive power, a lens L3 with negative refractive power, a lens L4 with positive refractive power, and a lens L5 with positive refractive power. During diopter adjustment, lenses L2, L3, L4, and L5 move integrally along the optical axis Z.

[0125] For observation optical system 5 of Example 10, the basic lens data is shown in Table 28, the specifications and variable plane spacing in Table 29, the aspherical coefficient in Table 30, and the aberration diagrams for each state when the diopter is -0.97 diopters are shown in Figure 20.

[0126] [Table 28]

[0127] [Table 29]

[0128] [Table 30]

[0129] [Example 11] Figure 21 shows the configuration and light beam of the observation optical system 5 of Example 11. The observation optical system 5 of Example 11 comprises a display element 1 and an eyepiece lens 3, arranged in order from the display element side to the eye point side. The eyepiece lens 3 consists of a lens L1 with negative refractive power, a lens L2 with positive refractive power, a lens L3 with negative refractive power, a lens L4 with positive refractive power, and a lens L5 with positive refractive power, arranged in order from the display element side to the eye point side. During diopter adjustment, the display element 1 and lens L1 move integrally along the optical axis Z.

[0130] For the observation optical system 5 of Example 11, the basic lens data is shown in Table 31, the specifications and variable plane spacing in Table 32, the aspherical coefficient in Table 33, and the aberration diagrams for each state when the diopter is -0.97 diopters are shown in Figure 22.

[0131] [Table 31]

[0132] [Table 32]

[0133] [Table 33]

[0134] [Example 12] Figure 23 shows the configuration and light beam of the observation optical system 5 of Example 12. The observation optical system 5 of Example 12 comprises a display element 1 and an eyepiece lens 3, arranged in order from the display element side to the eye point side. The eyepiece lens 3 consists of a lens L1 with negative refractive power, a lens L2 with positive refractive power, a lens L3 with positive refractive power, a lens L4 with negative refractive power, and a lens L5 with positive refractive power, arranged in order from the display element side to the eye point side. During diopter adjustment, the display element 1 and lens L1 move integrally along the optical axis Z.

[0135] For the observation optical system 5 of Example 12, the basic lens data is shown in Table 34, the specifications and variable plane spacing in Table 35, the aspherical coefficient in Table 36, and the aberration diagrams for each state when the diopter is -0.96 diopters are shown in Figure 24.

[0136] [Table 34]

[0137] [Table 35]

[0138] [Table 36]

[0139] [Example 13] Figure 25 shows the configuration and light beam of the observation optical system 5 of Example 13. The observation optical system 5 of Example 13 comprises, in order from the display element side to the eye point side, a display element 1, an optical member 2, and an eyepiece lens 3. The eyepiece lens 3 consists of, in order from the display element side to the eye point side, a lens L1 with positive refractive power, a lens L2 with negative refractive power, a lens L3 with positive refractive power, a lens L4 with positive refractive power, and a lens L5 with negative refractive power. During diopter adjustment, the display element 1 and the optical member 2 move integrally along the optical axis Z.

[0140] For observation optical system 5 of Example 13, the basic lens data is shown in Table 37, the specifications and variable plane spacing in Table 38, the aspherical coefficient in Table 39, and the aberration diagrams for each state when the diopter is -0.99 diopters are shown in Figure 26.

[0141] [Table 37]

[0142] [Table 38]

[0143] [Table 39]

[0144] [Example 14] Figure 27 shows the configuration and light beam of the observation optical system 5 of Example 14. The observation optical system 5 of Example 14 comprises a display element 1 and an eyepiece lens 3, in order from the display element side to the eye point side. The eyepiece lens 3 consists of a lens L1 with negative refractive power, a lens L2 with positive refractive power, a lens L3 with negative refractive power, a lens L4 with positive refractive power, and a lens L5 with positive refractive power, in order from the display element side to the eye point side. When adjusting the diopter, lenses L2, L3, and L4 move integrally along the optical axis Z.

[0145] For the observation optical system 5 of Example 14, the basic lens data is shown in Table 40, the specifications and variable plane spacing in Table 41, the aspherical coefficient in Table 42, and the aberration diagrams for each state when the diopter is -0.99 diopters are shown in Figure 28.

[0146] [Table 40]

[0147] [Table 41]

[0148] [Table 42]

[0149] [Example 15] Figure 29 shows the configuration and light beam of the observation optical system 5 of Example 15. The observation optical system 5 of Example 15 comprises, in order from the display element side to the eye point side, a display element 1, an optical member 2, and an eyepiece lens 3. The eyepiece lens 3 consists of, in order from the display element side to the eye point side, a lens L1 with positive refractive power, a lens L2 with negative refractive power, a lens L3 with positive refractive power, a lens L4 with positive refractive power, and a lens L5 with negative refractive power. When adjusting the diopter, lenses L1, L2, L3, and L4 move integrally along the optical axis Z.

[0150] For the observation optical system 5 of Example 15, the basic lens data is shown in Table 43, the specifications and variable plane spacing in Table 44, the aspherical coefficient in Table 45, and the aberration diagrams for each state when the diopter is -0.99 diopters are shown in Figure 30.

[0151] [Table 43]

[0152] [Table 44]

[0153] [Table 45]

[0154] Tables 46 to 48 show the corresponding values ​​for conditional equations (1) to (20) of the observation optical system 5 in Examples 1 to 15. The values ​​shown in Tables 46 to 48 are based on the d-line. The corresponding values ​​for the examples shown in Tables 46 to 48 may be used as the upper or lower limit of the conditional equation to set a preferred range for the conditional equation.

[0155] [Table 46]

[0156] [Table 47]

[0157] [Table 48]

[0158] The observation optical system 5 in Examples 1 to 15 has a wide apparent field of view, with an apparent field of view of 40 degrees or more across the entire diagonal angle of view when the diopter is -1 diopter. Furthermore, despite its compact configuration, the observation optical system 5 in Examples 1 to 15 achieves high optical performance with excellent correction of various aberrations.

[0159] Next, an optical device equipped with an observation optical system according to an embodiment of this disclosure will be described. Figure 31 is a perspective view showing a schematic configuration of the rear side of a camera 100, which is an optical device according to one embodiment of this disclosure. The camera 100 is a digital camera, for example. The camera 100 includes a viewfinder 101 and a diopter adjustment dial 107 for adjusting the diopter, located on the upper part of the camera body 102. The viewfinder 101 is an example of an observation optical device and includes an observation optical system according to one embodiment of this disclosure.

[0160] The camera 100 includes an operation button 103 for performing various settings, a zoom lever 104 for zooming, and a monitor 106 for displaying images and various setting screens on the back surface of the camera body 102, and includes a shutter button 105 on the upper surface of the camera body 102. Further, the camera 100 includes an imaging lens (not shown) on the front surface of the camera body 102, and includes an imaging element (not shown) for imaging a subject image formed by the imaging lens inside the camera body 102. The user observes the subject image by looking through the viewfinder 101 from the back side.

[0161] As described above, the technology of the present disclosure has been described with reference to the embodiments and examples. However, the technology of the present disclosure is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, the interval between surfaces, the refractive index, the Abbe number, the aspherical coefficient, etc. of each lens are not limited to the values shown in the above numerical examples, and other values can be taken. Further, the optical device according to the embodiment of the present disclosure is not limited to the above examples, and the present disclosure can also be applied to a film camera, a video camera, a head-mounted display, and the like. [[ID=**6**]]

[0162] Regarding the above embodiments and examples, the following additional claims are further disclosed. [Additional Claim 1] Comprising a display element and an eyepiece lens disposed on the eye point side of the display element, The eyepiece lens includes a first negative lens having the strongest negative refractive power among the lenses included in the eyepiece lens, a first positive lens disposed adjacent to the display element side of the first negative lens, and a second positive lens disposed closest to the display element side among the positive lenses disposed on the eye point side of the first negative lens, The number of lenses included in the eyepiece lens is 5 or more, Let the half value of the longest diameter of the display area in the display element be H, Let the focal length of the eyepiece lens in a state where the diopter is -1 diopter be f, When the diopter is in a state of -1 diopter, the air-equivalent distance on the optical axis from the display surface of the display element to the lens surface closest to the display element of the eyepiece lens, and the distance on the optical axis from the lens surface closest to the display element of the eyepiece lens to the lens surface closest to the eye point of the eyepiece lens, the sum of which is defined as TLA. When the refractive index of the first negative lens with respect to the d-line is Nn1, 0.355 < H / f < 0.48 (1) 0.17 < H / TLA < 0.285 (2) 1.5 < Nn1 < 1.7 (3) An observation optical system that satisfies the conditional expressions (1), (2), and (3) represented by the above. [Additional item 2] The observation optical system according to claim 1, wherein the number of lenses included in the eyepiece lens is 5 or 6. [Additional item 3] When the paraxial curvature radius of the surface on the eye point side of the first positive lens is Rpr, When the paraxial curvature radius of the surface on the display element side of the first negative lens is Rnf, 0 < |(Rnf - Rpr) / (Rnf + Rpr)| < 0.6 (4) The observation optical system according to claim 1 or 2, which satisfies the conditional expression (4) represented by the above. [Additional item 4] When the focal length of the first positive lens is fp1, 0 < f / fp1 < 1.8 (5) The observation optical system according to any one of claims 1 to 3, which satisfies the conditional expression (5) represented by the above. [Additional item 5] When the focal length of the first negative lens is fn1, -1.4 < f / fn1 < -0.3 (6) The observation optical system according to any one of claims 1 to 4, which satisfies the conditional expression (6) represented by the above. [Additional item 6] When the focal length of the second positive lens is fp2, 0 < f / fp2 < 0.9 (7) The observation optical system according to any one of claims 1 to 5, which satisfies the conditional expression (7) represented by the above. [Additional note 7] If the focal length of the first positive lens is fp1, 0 <H / fp1<0.9 (8) An observation optical system according to any one of the appendix items 1 to 6 that satisfies the conditional expression (8) represented by . [Additional note 8] If the focal length of the first negative lens is fn1, -0.6 <H / fn1<-0.2 (9) An observation optical system according to any one of the appendix items 1 to 7 that satisfies the conditional expression (9) represented by . [Additional note 9] If the focal length of the second positive lens is fp2, 0 <H / fp2<0.4 (10) An observation optical system according to any one of the appendix items 1 to 8 that satisfies the conditional expression (10) represented by . [Additional Note 10] If the Abbe number of the first negative lens with respect to the d line is denoted as νn1, 19 < νn1 < 27 (11) An observation optical system according to any one of the appendix items 1 to 9 that satisfies the conditional expression (11) represented by . [Additional Note 11] If Nps is the refractive index of the lens with respect to the d line among the lenses included in the eyepiece, which has the strongest positive refractive power, then 1.6 <Nps<2 (12) An observation optical system according to any one of the appendix items 1 to 10 that satisfies the conditional expression (12) represented by . [Additional Note 12] If νps is the Abbe number relative to the d line of the lens with the strongest positive refractive power among the lenses included in the eyepiece, 35 < νps < 55 (13) An observation optical system according to any one of the appendix items 1 to 11 that satisfies the conditional expression (13) represented by . [Additional Note 13] If Nave is the average value of the refractive index of all lenses included in the eyepiece with respect to the d line, 1.55 <Nave<1.75 (14) The observation optical system according to any one of claims 1 to 12 that satisfies the conditional expression (14) represented by [Claim 14] When the focal length of the lens on the most eye point side of the eyepiece lens is fe, 0 < f / |fe| < 0.9 (15) The observation optical system according to any one of claims 1 to 13 that satisfies the conditional expression (15) represented by [Claim 15] When the paraxial curvature radius of the surface on the display element side of the lens on the most eye point side of the eyepiece lens is Ref, When the paraxial curvature radius of the surface on the eye point side of the lens on the most eye point side of the eyepiece lens is Rer, 0 < |(Rer - Ref) / (Rer + Ref)| < 3 (16) The observation optical system according to any one of claims 1 to 14 that satisfies the conditional expression (16) represented by [Claim 16] When the air interval on the optical axis between the lens on the most eye point side of the eyepiece lens and the second lens from the eye point side of the eyepiece lens in the state where the diopter is -1 diopter is dE, 0.002 < dE / TLA < 0.07 (17) The observation optical system according to any one of claims 1 to 15 that satisfies the conditional expression (17) represented by [Claim 17] When the focal length of the lens on the most display element side of the eyepiece lens is fo, 0.01 < f / |fo| < 1.8 (18) The observation optical system according to any one of claims 1 to 16 that satisfies the conditional expression (18) represented by [Claim 18] When the paraxial curvature radius of the surface on the display element side of the lens on the most display element side of the eyepiece lens is Rof, When the paraxial curvature radius of the surface on the eye point side of the lens on the most display element side of the eyepiece lens is Ror, 0 < |(Ror - Rof) / (Ror + Rof)| < 10 (19) An observation optical system according to any one of the appendix items 1 to 17 that satisfies the conditional expression (19) represented by . [Additional Note 19] If dO is the air gap on the optical axis between the lens closest to the display element of the eyepiece and the second lens from the display element side of the eyepiece, 0 <dO / TLA<0.1 (20) An observation optical system according to any one of the appendix items 1 to 18 that satisfies the conditional expression (20) represented by . [Additional Note 20] An optical apparatus equipped with an observation optical system as described in any one of the appendices 1 to 19. [Explanation of symbols]

[0163] 1. Display respects 1a Display area 1b Cover member 2 Optical components 3 Eyepiece 5. Observation Optical System 100 Cameras 101 Finder 102 Camera Body 103 Operation Buttons 104 Zoom Lever 105 Shutter button 106 Monitors 107 Diopter adjustment dial EP Eye Point H is half the diameter of the longest part of the display area. L1 Lens L2 lens L3 lens L4 lens L5 lens L6 lens Z optical axis

Claims

1. The system comprises a display element and an eyepiece positioned on the eye point side of the display element, The eyepiece includes a first negative lens having the strongest negative refractive power among the lenses included in the eyepiece, a first positive lens positioned adjacent to the display element side of the first negative lens, and a second positive lens positioned furthest towards the display element among the positive lenses positioned closer to the eye point than the first negative lens. The number of lenses included in the eyepiece is five or more. H is half the longest diameter of the display area in the display element. The focal length of the eyepiece when the diopter is -1 diopter is f, When the diopter is -1 diopter, the sum of the air-equivalent distance along the optical axis from the display surface of the display element to the lens surface of the eyepiece closest to the display element, and the distance along the optical axis from the lens surface of the eyepiece closest to the display element to the lens surface of the eyepiece closest to the eye point, is defined as TLA. The refractive index of the first negative lens with respect to the d line is Nn1, The Abbe number of the lens with the strongest positive refractive power among the lenses included in the eyepiece is νps, relative to the d line. The average refractive index of all lenses included in the eyepiece with respect to the d line is defined as Nave. When the air gap on the optical axis between the lens closest to the display element of the eyepiece and the second lens from the display element side of the eyepiece is denoted as dO, 0.355<H / f<0.48 (1) 0.17<H / TLA<0.285 (2) 1.5<Nn1<1.7 (3) 46.22 ≤ νps < 55 (13-3) 1.59628 ≤ Nave < 1.75 (14-3) 0.02<dO / TLA<0.1 (20-3) An observation optical system that satisfies the conditions (1), (2), (3), (13-3), (14-3), and (20-3) represented by .

2. The observation optical system according to claim 1, wherein the number of lenses included in the eyepiece is five or six.

3. The paraxial radius of curvature of the eye point side surface of the first positive lens is Rpr, When Rnf is the paraxial radius of curvature of the display element side surface of the first negative lens, 0<|(Rnf-Rpr) / (Rnf+Rpr)|<0.6 (4) The observation optical system according to claim 1 that satisfies the conditional expression (4) represented by .

4. When the focal length of the first positive lens is denoted as fp1, 0<f / fp1<1.8 (5) The observation optical system according to claim 1 that satisfies the conditional expression (5) represented by .

5. When the focal length of the first negative lens is fn1, -1.4<f / fn1<-0.3 (6) The observation optical system according to claim 1 that satisfies the conditional expression (6) represented by .

6. If the focal length of the second positive lens is fp2, 0<f / fp2<0.9 (7) The observation optical system according to claim 1 that satisfies the conditional expression (7) represented by .

7. When the focal length of the first positive lens is denoted as fp1, 0<H / fp1<0.9 (8) The observation optical system according to claim 1 that satisfies the conditional expression (8) represented by .

8. When the focal length of the first negative lens is fn1, -0.6<H / fn1<-0.2 (9) The observation optical system according to claim 1 that satisfies the conditional expression (9) represented by .

9. If the focal length of the second positive lens is fp2, 0<H / fp2<0.4 (10) The observation optical system according to claim 1 that satisfies the conditional expression (10) represented by .

10. When the Abbe number of the first negative lens with respect to the d line is denoted as νn1, 19<νn1<27 (11) The observation optical system according to claim 1 that satisfies the conditional expression (11) represented by .

11. If Nps is the refractive index of the lens with respect to the d line among the lenses included in the eyepiece, 1.6<Nps<2 (12) The observation optical system according to claim 1 that satisfies the conditional expression (12) represented by .

12. If the focal length of the lens closest to the eye point of the aforementioned eyepiece is denoted as fe, 0<f / |fe|<0.9 (15) The observation optical system according to claim 1 that satisfies the conditional expression (15) represented by .

13. The paraxial radius of curvature of the display element side of the lens closest to the eye point of the aforementioned eyepiece is Ref. If Rer is the paraxial radius of curvature of the eyepiece lens closest to the eye point, 0<|(Rer-Ref) / (Rer+Ref)|<3 (16) The observation optical system according to claim 1 that satisfies the conditional expression (16) represented by .

14. When the diopter is -1 diopter, if dE is the air distance on the optical axis between the lens closest to the eye point of the eyepiece and the second lens from the eye point of the eyepiece, 0.002<dE / TLA<0.07 (17) The observation optical system according to claim 1 that satisfies the conditional expression (17) represented by .

15. If the focal length of the lens closest to the display element in the eyepiece is denoted as fo, 0.01<f / |fo|<1.8 (18) The observation optical system according to claim 1, satisfying the conditional expression (18) represented by .

16. The paraxial radius of curvature of the display element side surface of the lens closest to the display element in the aforementioned eyepiece is defined as Rof. If R is the paraxial radius of curvature of the eyepiece lens closest to the display element, on the eye point side, 0<|(Ror-Rof) / (Ror+Rof)|<10 (19) The observation optical system according to claim 1 that satisfies the conditional expression (19) represented by .

17. An optical apparatus comprising an observation optical system according to any one of claims 1 to 16.

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