Observation optical system and optical device

Abstract

This invention provides a small-scale observation optical system with good optical performance and an optical device incorporating the observation optical system. The observation optical system comprises two lenses, an objective lens with negative refractive power and an eyepiece with positive refractive power, arranged sequentially from the object side to the viewpoint side. When the paraxial radius of curvature of the viewpoint-side surface of the eyepiece is set to R4 and the paraxial radius of curvature of the viewpoint-side surface of the objective lens is set to R2, the observation optical system satisfies the condition expressed by 1.7 < (R4 - R2) / (R4 + R2) < 4.

Description

Technical Field

[0001] The present invention relates to an observation optical system and optical device. Background Technology

[0002] Previously, optical systems described in Patent Documents 1 to 7 have been known as viewfinders for cameras and the like.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2002-214542

[0004] Patent Document 2: Japanese Patent Application Publication No. 10-282408

[0005] Patent Document 3: Japanese Patent Application Publication No. 7-092387

[0006] Patent Document 4: Japanese Patent Application Publication No. 6-230276

[0007] Patent Document 5: Japanese Patent Application Publication No. 63-071822

[0008] Patent Document 6: Japanese Patent Application Publication No. 61-091618

[0009] Patent Document 7: Japanese Patent Application Publication No. 52-062023

[0010] In recent years, there has been a demand for observation optical systems that are small in size and have good optical performance. Utility Model Content

[0011] This invention provides a small observation optical system with good optical performance and an optical device equipped with the observation optical system.

[0012] The observation optical system of this utility model includes two lenses, an objective lens with negative refractive power and an eyepiece with positive refractive power, arranged sequentially from the object side to the viewpoint side. The observation optical system satisfies the following conditions when: the paraxial radius of curvature of the viewpoint-side surface of the eyepiece is set to R4; the paraxial radius of curvature of the viewpoint-side surface of the objective lens is set to R2; the distance from the intersection of the object-side surface of the objective lens and the optical axis to the intersection of the viewpoint-side surface of the eyepiece and the optical axis is set to Dsum; the focal length of the objective lens is set to f1; the focal length of the eyepiece is set to f2; the average refractive index below the d-line of all lenses included in the observation optical system is set to Nave; and the center thickness of the eyepiece is set to D2.

[0013] 1.7 < (R₄ - R₂) / (R₄ + R₂) < 4 (1)

[0014] 50 <Dsum / (|f1| / f2)<80 (2)

[0015] 1.45 <Nave<1.65 (3)

[0016] 0.1 <D2 / Dsum<0.3 (4)。

[0017] The viewpoint side of the objective lens preferably includes a region in the paraxial region where the concave surface faces the viewpoint side and the negative refractive power weakens as it moves away from the optical axis.

[0018] The viewpoint side of the eyepiece preferably includes a paraxial region with a convex surface facing the viewpoint side and a region where the positive refractive power increases as it moves away from the optical axis.

[0019] The observation optical system preferably satisfies the following condition (1-1), more preferably satisfies the following condition (1-2), and even more preferably satisfies the following condition (1-3).

[0020] 1.8<(R4-R2) / (R4+R2)<3.5 (1-1)

[0021] 1.85 < (R₄ - R₂) / (R₄ + R₂) < 3 (1-2)

[0022] 1.9 < (R₄ - R₂) / (R₄ + R₂) < 2.7 (1-3)

[0023] The observation optical system preferably satisfies the following condition (2-1), more preferably satisfies the following condition (2-2), and even more preferably satisfies the following condition (2-3).

[0024] 55 <Dsum / (|f1| / f2)<78 (2-1)

[0025] 60 <Dsum / (|f1| / f2)<75 (2-2)

[0026] 61.5 <Dsum / (|f1| / f2)<74 (2-3)

[0027] The observation optical system preferably satisfies the following condition (3-1), more preferably satisfies the following condition (3-2), and even more preferably satisfies the following condition (3-3).

[0028] 1.46 <Nave<1.6 (3-1)

[0029] 1.47 <Nave<1.58 (3-2)

[0030] 1.475 <Nave<1.56 (3-3)

[0031] The observation optical system preferably satisfies the following condition (4-1), more preferably satisfies the following condition (4-2), and even more preferably satisfies the following condition (4-3).

[0032] 0.105 <D2 / Dsum<0.26 (4-1)

[0033] 0.11 <D2 / Dsum<0.24 (4-2)

[0034] 0.115 <D2 / Dsum<0.22 (4-3)

[0035] With the refractive index below the d-line of the objective lens set to N1 and the Abbe number of the d-line reference of the objective lens set to ν1, the observation optical system preferably satisfies the conditional expression (5) expressed below.

[0036] 1.8<N1+0.01×v1<2.14 (5).

[0037] With the refractive index below the d-line of the eyepiece set to N2 and the Abbe number of the d-line reference of the eyepiece set to ν2, the observation optical system preferably satisfies the condition (6) expressed below.

[0038] 1.8<N2+0.01×ν2<2.14 (6).

[0039] The observation optical system preferably satisfies the condition (7) expressed below.

[0040] 1 < f2 / Dsum < 2 (7).

[0041] With the air equivalent length along the optical axis from the viewpoint side of the objective lens to the object side of the eyepiece set to D12, the observation optical system preferably satisfies the condition (8) expressed below.

[0042] 0.05 <R2 / D12<1 (8)。

[0043] Another aspect of this utility model relates to an optical device that has the observation optical system described above.

[0044] In addition, the terms "including" and "including" in this specification mean that, in addition to the constituent elements listed, it may also include lenses that do not substantially have refractive power, as well as optical elements other than lenses such as apertures, filters, cover glass and prisms, and lens flanges, lens barrels and imaging elements.

[0045] In this specification, "lens with positive refractive power" and "positive lens" have the same meaning. "Lens with negative refractive power" and "negative lens" have the same meaning. Compound aspherical lenses (i.e., lenses in which a spherical lens and an aspherical film formed on the spherical lens are integrated and function as a single aspherical lens) are not considered as combined lenses, but rather as a single lens. Unless otherwise specified, the sign of the refractive power, radius of curvature, and surface shape associated with lenses containing aspherical surfaces are considered within the paraxial region. Regarding the sign of the radius of curvature, the radius of curvature of a surface with a convex shape facing the object is positive, and the radius of curvature of a surface with a convex shape facing the viewpoint is negative.

[0046] The "focal length" used in the conditional formula is the paraxial focal length. The values ​​used in the conditional formula are those taken with the d-line as a reference at a diopter of -1 diopter. The "d-line," "C-line," and "F-line" described in this specification are bright lines. The wavelength of the d-line is 587.56 nm, the wavelength of the C-line is 656.27 nm, and the wavelength of the F-line is 486.13 nm.

[0047] Utility Model Effect

[0048] According to this utility model, a small observation optical system with good optical performance and an optical device having the observation optical system can be provided. Attached Figure Description

[0049] Figure 1 This is a cross-sectional view of the structure and beam of an observation optical system according to an embodiment of the present invention, corresponding to the observation optical system of Embodiment 1.

[0050] Figure 2 This is a diagram of the aberrations of the observation optical system in Example 1.

[0051] Figure 3 This is a cross-sectional view showing the structure of the observation optical system and the beam of Embodiment 2.

[0052] Figure 4 This is an aberration diagram of the observation optical system in Example 2.

[0053] Figure 5 This is a cross-sectional view showing the structure and beam of the observation optical system of Embodiment 3.

[0054] Figure 6 This is an aberration diagram of the observation optical system in Example 3.

[0055] Figure 7 This is a perspective view of the rear side of an optical device according to one embodiment.

[0056] Symbol Explanation

[0057] 2-On-axis beam, 3-Off-axis beam corresponding to the maximum apparent field of view, 100-Camera, 101-Viewfinder, 102-Camera body, 103-Operation button, 104-Zoom lever, 105-Shutter button, 106-Display, D2-Eyepiece center thickness, Dsum-Distance from the intersection of the object-side surface of the objective lens and the optical axis to the intersection of the viewpoint-side surface of the eyepiece and the optical axis, EP-Viewpoint, L1-Objective lens, L2-Eyepiece, Z-Optical axis. Detailed Implementation

[0058] The embodiments of this utility model will now be described with reference to the accompanying drawings.

[0059] exist Figure 1 The diagram shows a cross-sectional view of the structure and beam of an observation optical system according to one embodiment of the present invention. Figure 1 In the diagram, as beams, there is an on-axis beam 2 and an off-axis beam 3 corresponding to the largest apparent field of view. Figure 1 In the diagram, the left side is designated as the object side and the right side as the viewpoint side. Figure 1 The viewpoint EP shown represents the position along the optical axis, not the shape. Figure 1 The example shown corresponds to Example 1 described later.

[0060] The observation optical system comprises two lenses along the optical axis Z, from the object side to the viewpoint side: an objective lens L1 with negative refractive power and an eyepiece L2 with positive refractive power. This structure, with the negative and positive lenses arranged sequentially from the object side to the viewpoint EP side, facilitates a shorter overall optical length and miniaturization.

[0061] The viewpoint-side surface of objective lens L1 preferably includes a region in the paraxial region where the concave surface faces the viewpoint side and the negative refractive power weakens with distance from the optical axis Z. With this configuration, the increase in aberration can be suppressed, and the optical performance of the peripheral portion can be well maintained.

[0062] The object-side surface of the objective lens L1 is preferably flat. This improves the ease of assembly into the mechanical housing.

[0063] The viewpoint-side surface of eyepiece L2 preferably includes a paraxial region with a convex surface facing the viewpoint side, where the positive refractive power increases with distance from the optical axis Z. With this configuration, the increase in aberration can be suppressed, and the optical performance of the peripheral portion can be well maintained.

[0064] The object-side surface of the eyepiece L2 is preferably flat. This improves the ease of assembly into the mechanical frame.

[0065] Next, preferred and possible structures related to the conditional expressions of the observation optical system of this utility model will be described. In the following descriptions related to the conditional expressions, to avoid redundant explanations, the same notation will be used for parts that are defined the same, thereby omitting repeated explanations of the notation.

[0066] With the paraxial radius of curvature of the viewpoint-side surface of eyepiece L2 set to R4 and the paraxial radius of curvature of the viewpoint-side surface of objective lens L1 set to R2, the observation optical system preferably satisfies the following condition (1). By ensuring that the corresponding value of condition (1) is not below the lower limit, the refractive power of objective lens L1 will not become too weak, which is beneficial for radial miniaturization. By ensuring that the corresponding value of condition (1) is not above the upper limit, the refractive power of eyepiece L2 will not become too weak, which is beneficial for correcting distortion aberrations.

[0067] 1.7 < (R₄ - R₂) / (R₄ + R₂) < 4 (1)

[0068] To obtain better characteristics, it is preferable to set the lower limit of condition (1) to any one of 1.8, 1.85, 1.9, and 1.95. Furthermore, it is preferable to set the upper limit of condition (1) to any one of 3.5, 3, 2.7, and 2.5. For example, the observation optical system preferably satisfies condition (1-1) below, more preferably satisfies condition (1-2) below, more preferably satisfies condition (1-3) below, and more preferably satisfies condition (1-4) below.

[0069] 1.8 < (R⁴ - R²) / (R⁴ + R²) < 3.5 (1-1)

[0070] 1.85 < (R₄ - R₂) / (R₄ + R₂) < 3 (1-2)

[0071] 1.9 < (R₄ - R₂) / (R₄ + R₂) < 2.7 (1-3)

[0072] 1.95<(R4-R2) / (R4+R2)<2.5 (1-4)

[0073] Let Dsum be the distance from the intersection of the object-side surface of objective lens L1 and the optical axis Z to the intersection of the viewpoint-side surface of eyepiece L2 and the optical axis Z, let f1 be the focal length of objective lens L1, and let f2 be the focal length of eyepiece L2. The observation optical system preferably satisfies the following conditional expression (2). Here, the unit of Dsum is mm (millimeters). By ensuring that the corresponding value of conditional expression (2) is not below the lower limit, it is possible to maintain each aberration well while simultaneously expanding the apparent field of view. By ensuring that the corresponding value of conditional expression (2) is not above the upper limit, it is possible to maintain the apparent field of view while simultaneously shortening the overall optical length, thereby facilitating miniaturization. As an example, in... Figure 1 The diagram shows... Figure 1 The observation of Dsum in the optical system and D2 related to the conditional expression described later.

[0074] 50 <Dsum / (|f1| / f2)<80 (2)

[0075] To obtain better characteristics, it is preferable to set the lower limit of condition (2) to any one of 55, 60, 61.5, and 62. Furthermore, it is preferable to set the upper limit of condition (2) to any one of 78, 75, 74, and 73. For example, the observation optical system preferably satisfies condition (2-1), more preferably condition (2-2), more preferably condition (2-3), and more preferably condition (2-4).

[0076] 55 <Dsum / (|f1| / f2)<78 (2-1)

[0077] 60 <Dsum / (|f1| / f2)<75 (2-2)

[0078] 61.5 <Dsum / (|f1| / f2)<74 (2-3)

[0079] 62 <Dsum / (|f1| / f2)<73 (2-4)

[0080] When the average refractive index along the d-line of all lenses included in the observation optical system is set to Nave, the observation optical system preferably satisfies the following condition (3). By ensuring that the corresponding value of condition (3) is not below the lower limit, the increase of Pezvalence can be suppressed, thus facilitating the correction of image plane curvature. By ensuring that the corresponding value of condition (3) is not above the upper limit, it is possible to prevent the materials that can be selected as lens materials from being limited to materials with low Abbe numbers, thus facilitating the correction of chromatic aberration.

[0081] 1.45 <Nave<1.65 (3)

[0082] To obtain better characteristics, it is preferable to set the lower limit of condition (3) to any one of 1.46, 1.47, 1.475, and 1.48. Furthermore, it is preferable to set the upper limit of condition (3) to any one of 1.6, 1.58, 1.56, and 1.54. For example, the observation optical system preferably satisfies condition (3-1), more preferably condition (3-2), more preferably condition (3-3), and more preferably condition (3-4).

[0083] 1.46 <Nave<1.6 (3-1)

[0084] 1.47 <Nave<1.58 (3-2)

[0085] 1.475 <Nave<1.56 (3-3)

[0086] 1.48 <Nave<1.54 (3-4)

[0087] When the center thickness of eyepiece L2 is set to D2, the observation optical system preferably satisfies the following condition (4). By ensuring that the corresponding value of condition (4) is not below the lower limit, the edge thickness of eyepiece L2 (the thickness of the outermost periphery of the lens) is easily ensured, thus becoming advantageous in terms of lens manufacturability. By ensuring that the corresponding value of condition (4) is not above the upper limit, Dsum will not become too small, thus suppressing the steepness of the angle of light incident from objective lens L1 to eyepiece L2 with respect to the optical axis Z, which is beneficial for suppressing aberrations.

[0088] 0.1 <D2 / Dsum<0.3 (4)

[0089] To obtain better characteristics, it is preferable to set the lower limit of condition (4) to any one of 0.105, 0.11, 0.115, and 0.118. Furthermore, it is preferable to set the upper limit of condition (4) to any one of 0.26, 0.24, 0.22, and 0.2. For example, the observation optical system preferably satisfies condition (4-1), more preferably condition (4-2), more preferably condition (4-3), and more preferably condition (4-4).

[0090] 0.105 <D2 / Dsum<0.26 (4-1)

[0091] 0.11 <D2 / Dsum<0.24 (4-2)

[0092] 0.115 <D2 / Dsum<0.22 (4-3)

[0093] 0.118 <D2 / Dsum<0.2 (4-4)

[0094] With the refractive index of objective lens L1 along the d-line set to N1 and the Abbe number of objective lens L1 along the d-line set to ν1, the observation optical system preferably satisfies the following conditional expression (5). By ensuring that the corresponding value of conditional expression (5) is not below the lower limit, materials other than those with low refractive index and low Abbe number can be selected, thus making it easier to correct magnification chromatic aberration. By ensuring that the corresponding value of conditional expression (5) is not above the upper limit, materials other than those with high refractive index and high Abbe number can be selected, thus allowing the selection of materials with low specific gravity, thereby making it easier to reduce weight.

[0095] 1.8 <N1+0.01×ν1<2.14 (5)

[0096] To obtain better characteristics, it is preferable to set the lower limit of condition (5) to any one of 1.85, 1.9, and 1.95. Furthermore, it is preferable to set the upper limit of condition (5) to any one of 2.13, 2.12, and 2.11. For example, the observation optical system preferably satisfies condition (5-1) below, more preferably satisfies condition (5-2) below, and even more preferably satisfies condition (5-3) below.

[0097] 1.85 <N1+0.01×ν1<2.13 (5-1)

[0098] 1.9<N1+0.01×ν1<2.12 (5-2)

[0099] 1.95 <N1+0.01×ν1<2.11 (5-3)

[0100] With the refractive index of eyepiece L2 along the d-line set to N2 and the Abbe number of eyepiece L2 along the d-line reference set to ν2, the observation optical system preferably satisfies the following conditional expression (6). By ensuring that the corresponding value of conditional expression (6) is not below the lower limit, materials other than those with low refractive index and low Abbe number can be selected, thus making it easy to correct magnification chromatic aberration. By ensuring that the corresponding value of conditional expression (6) is not above the upper limit, materials other than those with high refractive index and high Abbe number can be selected, thus allowing the selection of materials with low specific gravity, thereby making it easy to reduce weight.

[0101] 1.8 <N2+0.01×ν2<2.14 (6)

[0102] To obtain better characteristics, it is preferable to set the lower limit of condition (6) to any one of 1.85, 1.9, and 1.95. Furthermore, it is preferable to set the upper limit of condition (6) to any one of 2.13, 2.12, and 2.11. For example, the observation optical system preferably satisfies condition (6-1) below, more preferably satisfies condition (6-2) below, and even more preferably satisfies condition (6-3) below.

[0103] 1.85 <N2+0.01×ν2<2.13 (6-1)

[0104] 1.9 <N2+0.01×ν2<2.12 (6-2)

[0105] 1.95 <N2+0.01×ν2<2.11 (6-3)

[0106] The optical system is preferably designed to satisfy the following condition (7). By ensuring that the corresponding value of condition (7) is not below the lower limit, excessive reduction of viewfinder magnification can be suppressed. By ensuring that the corresponding value of condition (7) is not above the upper limit, Dsum will not become too small, thus making it easier to correct various aberrations.

[0107] 1 <f2 / Dsum<2 (7)

[0108] To obtain better characteristics, it is preferable to set the lower limit of condition (7) to any one of 1.1, 1.2, and 1.3. Furthermore, it is preferable to set the upper limit of condition (7) to any one of 1.8, 1.7, and 1.6. For example, the observation optical system preferably satisfies the following condition (7-1), more preferably satisfies the following condition (7-2), and even more preferably satisfies the following condition (7-3).

[0109] 1.1 < f2 / Dsum < 1.8 (7-1)

[0110] 1.2 <f2 / Dsum<1.7 (7-2)

[0111] 1.3 <f2 / Dsum<1.6 (7-3)

[0112] With the air equivalent length along the optical axis Z from the viewpoint side of objective lens L1 to the object side of eyepiece L2 set to D12, the observation optical system preferably satisfies the following conditional expression (8). By ensuring that the corresponding value of conditional expression (8) is not below the lower limit, the increase in the total optical length can be suppressed. By ensuring that the corresponding value of conditional expression (8) is not above the upper limit, the excessive negative distortion aberration can be suppressed.

[0113] 0.05 <R2 / D12<1 (8)

[0114] To obtain better characteristics, it is preferable to set the lower limit of condition (8) to any one of 0.15, 0.2, and 0.25. Furthermore, it is preferable to set the upper limit of condition (8) to any one of 0.8, 0.6, and 0.5. For example, the observation optical system preferably satisfies the following condition (8-1), more preferably satisfies the following condition (8-2), and even more preferably satisfies the following condition (8-3).

[0115] 0.15 <R2 / D12<0.8 (8-1)

[0116] 0.2 <R2 / D12<0.6 (8-2)

[0117] 0.25 <R2 / D12<0.5 (8-3)

[0118] Including structures related to conditional expressions, the above-mentioned preferred structures and achievable structures can be combined arbitrarily, and preferably selected appropriately according to the required specifications. Figure 1 The example provided is just one illustration; various modifications can be made without departing from the technical spirit of this utility model.

[0119] As an example, a preferred embodiment of the observation optical system of this invention is an observation optical system comprising two lenses, an objective lens L1 with negative refractive power and an eyepiece L2 with positive refractive power, arranged sequentially from the object side to the viewpoint side. The observation optical system satisfies the above-mentioned conditions (1), (2), (3) and (4).

[0120] Next, embodiments of the observation optical system of this utility model will be described with reference to the accompanying drawings. Furthermore, to avoid complicating the description and drawings due to the increased number of reference numerals, the reference numerals used to label the constituent elements of the observation optical system in the cross-sectional views of each embodiment are used independently for each embodiment. Therefore, even if the same reference numerals are used in the drawings of different embodiments, the structures are not necessarily the same.

[0121] [Example 1]

[0122] The structure of the observation optical system and the cross-sectional view of the beam in Example 1 are shown in the figure. Figure 1 The illustrated method and structure are as described above, therefore some repetitive descriptions are omitted here. The observation optical system of Embodiment 1 includes two lenses, from the object side to the viewpoint side: an objective lens L1 with negative refractive power and an eyepiece L2 with positive refractive power. The viewpoint-side surface of the objective lens L1 is an aspherical surface including a region in the paraxial region where the concave surface faces the viewpoint side and the negative refractive power weakens with distance from the optical axis Z. The object-side surface of the objective lens L1 is a plane. The viewpoint-side surface of the eyepiece L2 is an aspherical surface including a region in the paraxial region where the convex surface faces the viewpoint side and the positive refractive power strengthens with distance from the optical axis Z. The object-side surface of the eyepiece L2 is a plane.

[0123] Regarding the observation optical system of Example 1, the basic lens data are shown in Table 1, and the aspherical coefficients are shown in Table 2.

[0124] The basic lens data is presented in the table below. The Sn column shows the surface numbering, with the surface closest to the object side designated as surface 1, increasing by one number each time it faces the viewpoint side. The R column shows the radius of curvature of each surface. The D column shows the surface spacing along the optical axis between each surface and its adjacent surface on the viewpoint side. The Nd column shows the refractive index of each component relative to the d-line. The νd column shows the Abbe number of each component based on the d-line reference. The ER column shows the effective radius of each lens surface.

[0125] In the table of basic lens data, the radius of curvature of the convex facet facing the object is marked positive, and the radius of curvature of the convex facet facing the viewpoint is marked negative. The bottom column of column D shows the distance between the viewpoint EP and the face closest to the viewpoint. Furthermore, the angle of view at a diopter of -1 diopter is shown outside the columns of the table of basic lens data. This angle of view corresponds to the apparent field of view.

[0126] In the basic lens data, aspherical surfaces are marked with an asterisk (*), and the paraxial radius of curvature is recorded in the radius of curvature column. In Table 2, the surface number of the aspherical surface is shown in row Sn, and the aspherical coefficient values ​​for each aspherical surface are shown in rows KA and Am (m = 4, 6, 8, 10). The aspherical coefficient value “E±n” (n: integer) represents “×10”. ±n KA and Am are the aspheric coefficients in the aspheric formula expressed below.

[0127] Zd=C×h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2 )+∑Am×h m

[0128] in,

[0129] Zd: Aspherical depth (the length of the perpendicular line from a point on the aspherical surface at height h to a plane tangent to the vertex of the aspherical surface and perpendicular to the optical axis Z).

[0130] h: Height (distance from the optical axis Z to the lens surface)

[0131] C: The reciprocal of the paraxial radius of curvature

[0132] KA, Am: Aspheric coefficients

[0133] In aspherical form, ∑ represents the summation related to m.

[0134] In the data in each table, "degree" is used as the unit of angle and "mm" (millimeters) is used as the unit of length. Optical systems can use both magnified and reduced scales, so other appropriate units can also be used. Furthermore, the values ​​are rounded to a specified number of decimal places in the tables shown below.

[0135] [Table 1]

[0136] Example 1

[0137] Sn R D Nd νd ER 1 ∞ 2.5516 1.49100 57.58 7.24 *2 6.7051 19.0000 5.50 3 ∞ 3.2984 1.49100 57.58 4.66 *4 -17.7477 7.0000 4.78

[0138] Viewing angle (degrees): 25.3

[0139] [Table 2]

[0140] Example 1

[0141]

[0142]

[0143] exist Figure 2 The diagram shows aberrations of the observation optical system of Example 1 at a refractive power of -1 diopter. Figure 2 In the diagram, from left to right, spherical aberration, astigmatism, distortion aberration, and chromatic aberration are represented sequentially. In the spherical aberration diagram, aberrations below the d-line, C-line, and F-line are represented by solid lines, long dashed lines, and short dashed lines, respectively. In the astigmatism diagram, aberrations below the d-line in the sagittal direction are shown as solid lines, and aberrations below the d-line in the meridional direction are shown as short dashed lines. In the distortion aberration diagram, aberrations below the d-line are shown as solid lines. In the chromatic aberration diagram, aberrations below the C-line and F-line are represented by long dashed lines and short dashed lines, respectively. The unit dpt on the horizontal axis of the spherical aberration and astigmatism diagrams represents diopter. The unit min on the horizontal axis of the chromatic aberration diagram represents the angular quantity. In the spherical aberration diagram, the diameter of the viewpoint EP is shown after “Φ=" with units set to mm (millimeters). In other aberration diagrams, the apparent field of view at half the field of view is shown after “ω=".

[0144] Unless otherwise specified, the symbols, meanings, recording methods, and illustration methods related to Embodiment 1 described above are the same in the following embodiments, and therefore repeated descriptions are omitted below.

[0145] [Example 2]

[0146] exist Figure 3 The diagram shows the structure and cross-sectional view of the observation optical system of Embodiment 2. The observation optical system of Embodiment 2 comprises two lenses, from the object side to the viewpoint side: an objective lens L1 with negative refractive power and an eyepiece L2 with positive refractive power. The viewpoint-side surface of the objective lens L1 is an aspherical surface including a region in the paraxial region where the concave surface faces the viewpoint side and the negative refractive power weakens with distance from the optical axis Z. The object-side surface of the objective lens L1 is a plane. The viewpoint-side surface of the eyepiece L2 is an aspherical surface including a region in the paraxial region where the convex surface faces the viewpoint side and the positive refractive power strengthens with distance from the optical axis Z. The object-side surface of the eyepiece L2 is a plane.

[0147] Regarding the observation optical system of Example 2, the basic lens data are shown in Table 3, the aspherical coefficients are shown in Table 4, and the aberrations at a diopter of -1 are illustrated in Table 5. Figure 4 .

[0148] [Table 3]

[0149] Example 2

[0150] Sn R D Nd νd ER 1 ∞ 1.4000 1.49100 57.58 6.96 *2 6.0159 19.0000 5.40 3 ∞ 4.4516 1.49100 57.58 5.13 *4 -17.4140 7.0000 5.09

[0151] Viewing angle (degrees): 25.7

[0152] [Table 4]

[0153] Example 2

[0154] Sn 2 4 KA 2.4143586E-01 1.6405367E+00 A4 1.4546993E-04 0.0000000E+00 A6 3.1264952E-06 0.0000000E+00 A8 -2.4383249E-07 0.0000000E+00 A10 5.1861288E-09 0.0000000E+00

[0155] [Example 3]

[0156] exist Figure 5 The diagram shows the structure and cross-sectional view of the observation optical system of Embodiment 3. The observation optical system of Embodiment 3 comprises two lenses, from the object side to the viewpoint side: an objective lens L1 with negative refractive power and an eyepiece L2 with positive refractive power. The viewpoint-side surface of the objective lens L1 is an aspherical surface including a region in the paraxial region where the concave surface faces the viewpoint side and the negative refractive power weakens with distance from the optical axis Z. The object-side surface of the objective lens L1 is a plane. The viewpoint-side surface of the eyepiece L2 is an aspherical surface including a region in the paraxial region where the convex surface faces the viewpoint side and the positive refractive power strengthens with distance from the optical axis Z. The object-side surface of the eyepiece L2 is a plane.

[0157] Regarding the observation optical system of Example 3, the basic lens data are shown in Table 5, the aspherical coefficients are shown in Table 6, and the aberrations at a diopter of -1 are illustrated in Table 6. Figure 6 .

[0158] [Table 5]

[0159] Example 3

[0160] Sn R D Nd νd ER 1 ∞ 2.3703 1.53480 55.73 7.23 *2 7.2804 19.5177 5.65 3 ∞ 2.9616 1.53480 55.73 4.66 *4 -19.4394 7.0000 4.76

[0161] Viewpoint (degrees): 25.1

[0162] [Table 6]

[0163] Example 3

[0164] Sn 2 4 KA -3.6789161E-01 1.3046748E+00 A4 -5.5068452E-05 0.0000000E+00 A6 2.2321132E-05 0.0000000E+00 A8 -6.3997811E-07 0.0000000E+00 A10 7.6204201E-09 0.0000000E+00

[0165] Table 7 shows the corresponding values ​​of conditional equations (1) to (8) for the observation optical systems of Examples 1 to 3. The values ​​shown in Table 7 are based on the d-line.

[0166] [Table 7]

[0167] Formula number Conditional expression Example 1 Example 2 Example 3 (1) (R4-R2) / (R4+R2) 2.4339 2.0556 2.1975 (2) Dsum / (|f1| / f2) 65.7752 71.9371 66.3507 (3) Nave 1.49100 1.49100 1.53480 (4) D2 / Dsum 0.1327 0.1791 0.1192 (5) N1+0.01×ν1 2.06680 2.06680 2.09210 (6) N2+0.01×ν2 2.06680 2.06680 2.09210 (7) f2 / Dsum 1.4546 1.4271 1.4628 (8) R2 / D12 0.3529 0.3166 0.3730

[0168] In the observation optical systems of Examples 1 to 3, although they are small in size, various aberrations are well corrected, thereby achieving high optical performance.

[0169] Next, the optical device of the observation optical system according to the embodiments of the present invention will be described. Figure 7 This is a perspective view showing the schematic structure of the rear side of a camera 100, which is an optical device according to one embodiment of the present invention. As an example, the camera 100 is a digital camera. The camera 100 has a viewfinder 101 according to one embodiment of the present invention 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 the present invention.

[0170] The camera 100 has operation buttons 103 for various settings, a zoom lever 104 for zooming, and a display screen 106 for displaying images and various settings on the back of the camera body 102. A shutter button 105 is located on the top surface of the camera body 102. Furthermore, the camera 100 has an imaging lens (not shown) on the front surface of the camera body 102, and an imaging element (not shown) inside the camera body 102 for capturing images of the subject formed by the imaging lens. The user observes the subject image through the viewfinder 101 from the rear side.

[0171] The above description illustrates the technology of this utility model through various embodiments and examples. However, the technology of this utility model is not limited to the above embodiments and examples and can be modified in various ways. For example, the radius of curvature, interplanar spacing, refractive index, Abbe number, and aspherical coefficient of each lens are not limited to the values ​​shown in the above embodiments and other values ​​can be used.

[0172] Furthermore, the optical device involved in the embodiments of this utility model is not limited to the above-described structure, and can also be applied to film cameras, video cameras, and head-mounted displays, etc.

[0173] The following notes further disclose the above implementation methods and embodiments.

[0174] [Postscript 1]

[0175] An observation optical system comprises, from the object side to the viewpoint side, two lenses: an objective lens with negative refractive power and an eyepiece with positive refractive power.

[0176] The paraxial radius of curvature of the surface on the viewpoint side of the eyepiece is set to R4.

[0177] The paraxial radius of curvature of the viewpoint side surface of the objective lens is set to R2.

[0178] The distance from the intersection of the object-side surface of the objective lens and the optical axis to the intersection of the viewpoint-side surface of the eyepiece and the optical axis is denoted as Dsum.

[0179] Set the focal length of the objective lens to f1.

[0180] Set the focal length of the eyepiece to f2.

[0181] Let Nave be the average refractive index below the d-line of all lenses included in the observation optical system.

[0182] When the center thickness of the eyepiece is set to D2...

[0183] The observation optical system satisfies the following conditional expressions (1), (2), (3) and (4).

[0184] 1.7 < (R₄ - R₂) / (R₄ + R₂) < 4 (1)

[0185] 50 <Dsum / (f1 / f2)<80 (2)

[0186] 1.45 <Nave<1.65 (3)

[0187] 0.1 < D2 / Dsum < 0.3 (4).

[0188] [Postscript 2]

[0189] According to the observation optical system described in Appendix 1, wherein,

[0190] The viewpoint-side surface of the objective lens includes a region in the paraxial region where the concave surface faces the viewpoint side and the negative refractive power weakens as it moves away from the optical axis.

[0191] [Postscript 3]

[0192] According to the observation optical system described in Appendix 1 or 2, wherein,

[0193] The viewpoint side of the eyepiece includes a paraxial region with a convex surface facing the viewpoint side and a region where the positive refractive power increases as it moves away from the optical axis.

[0194] [Postscript 4]

[0195] The observation optical system according to any one of Appendices 1 to 3 satisfies the conditional expression (1-1) expressed below.

[0196] 1.8<(R4-R2) / (R4+R2)<3.5 (1-1).

[0197] [Postscript 5]

[0198] The observation optical system according to any one of Appendices 1 to 3 satisfies the conditional equations (1-2) expressed below.

[0199] 1.85<(R4-R2) / (R4+R2)<3 (1-2).

[0200] [Postscript 6]

[0201] The observation optical system according to any one of Appendices 1 to 3 satisfies the conditional expressions (1-3) expressed below.

[0202] 1.9<(R4-R2) / (R4+R2)<2.7 (1-3).

[0203] [Postscript 7]

[0204] The observation optical system according to any one of Appendices 1 to 6 satisfies the conditional expression (2-1) expressed below.

[0205] 55 <Dsum / (|f1| / f2)<78 (2-1)。

[0206] [Postscript 8]

[0207] The observation optical system according to any one of Appendices 1 to 6 satisfies the conditional expression (2-2) expressed below.

[0208] 60 <Dsum / (|f1| / f2)<75 (2-2)。

[0209] [Postscript 9]

[0210] The observation optical system according to any one of Appendices 1 to 6 satisfies the conditional expression (2-3) expressed below.

[0211] 61.5 <Dsum / (|f1| / f2)<74 (2-3)。

[0212] [Postscript 10]

[0213] The observation optical system according to any one of Appendices 1 to 9 satisfies the conditional expression (3-1) expressed below.

[0214] 1.46 <Nave<1.6 (3-1)。

[0215] [Postscript 11]

[0216] The observation optical system according to any one of Appendices 1 to 9 satisfies the conditional expression (3-2) expressed below.

[0217] 1.47 <Nave<1.58 (3-2)。

[0218] [Postscript 12]

[0219] The observation optical system according to any one of Appendices 1 to 9 satisfies the conditional expression (3-3) expressed below.

[0220] 1.475 <Nave<1.56 (3-3)。

[0221] [Postscript 13]

[0222] The observation optical system according to any one of Appendices 1 to 12 satisfies the conditional expression (4-1) expressed below.

[0223] 0.105 <D2 / Dsum<0.26(4-1)。

[0224] [Postscript 14]

[0225] The observation optical system according to any one of Appendices 1 to 12 satisfies the conditional expression (4-2) expressed below.

[0226] 0.11 <D2 / Dsum<0.24 (4-2)。

[0227] [Postscript 15]

[0228] The observation optical system according to any one of Appendices 1 to 12 satisfies the conditional expression (4-3) expressed below.

[0229] 0.115 <D2 / Dsum<0.22 (4-3)。

[0230] [Postscript 16]

[0231] The observation optical system according to any one of Appendices 1 to 15, wherein,

[0232] With the refractive index below the d-line of the objective lens set to N1 and the Abbe number of the d-line reference of the objective lens set to ν1, the observation optical system satisfies the conditional expression (5) expressed below.

[0233] 1.8<N1+0.01×ν1<2.14 (5).

[0234] [Postscript 17]

[0235] The observation optical system according to any one of Appendices 1 to 16, wherein,

[0236] With the refractive index below the d-line of the eyepiece set to N2 and the Abbe number of the d-line reference of the eyepiece set to ν2, the observation optical system satisfies the conditional expression (6) expressed below.

[0237] 1.8<N2+0.01×ν2<2.14 (6).

[0238] [Postscript 18]

[0239] The observation optical system according to any one of Appendices 1 to 17 satisfies the conditional expression (7) expressed below.

[0240] 1 < f2 / Dsum < 2 (7).

[0241] [Postscript 19]

[0242] The observation optical system according to any one of Appendices 1 to 18, wherein,

[0243] With the air equivalent length along the optical axis from the viewpoint side of the objective lens to the object side of the eyepiece set to D12, the observation optical system satisfies the conditional expression (8) expressed below.

[0244] 0.05 <R2 / D12<1 (8)。

[0245] [Postscript 20]

[0246] An optical device comprising an observation optical system as described in any one of Appendices 1 to 19.

Claims

1. An observation optical system comprising, from the object side to the viewpoint side, two lenses in sequence: an objective lens with negative refractive power and an eyepiece with positive refractive power, characterized in that, The paraxial radius of curvature of the surface on the viewpoint side of the eyepiece is set to R4. The paraxial radius of curvature of the viewpoint side surface of the objective lens is set to R2. The distance from the intersection of the object-side surface of the objective lens and the optical axis to the intersection of the viewpoint-side surface of the eyepiece and the optical axis is denoted as Dsum. Set the focal length of the objective lens to f1. Set the focal length of the eyepiece to f2. Let Nave be the average refractive index below the d-line of all lenses included in the observation optical system. When the center thickness of the eyepiece is set to D2... The observation optical system satisfies the following conditional expressions (1), (2), (3) and (4). 1.7 < (R₄ - R₂) / (R₄ + R₂) < 4 (1) 50 <Dsum / (|f1| / f2)<80 (2) 1.45 <Nave<1.65 (3) 0.1 <D2 / Dsum<0.3 (4)。 2. The observation optical system according to claim 1, wherein, The viewpoint-side surface of the objective lens includes a region in the paraxial region where the concave surface faces the viewpoint side and the negative refractive power weakens as it moves away from the optical axis.

3. The observation optical system according to claim 1 or 2, wherein, The viewpoint side of the eyepiece includes a paraxial region with a convex surface facing the viewpoint side and a region where the positive refractive power increases as it moves away from the optical axis.

4. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (1-1) expressed below. 1.8<(R4-R2) / (R4+R2)<3.5 (1-1).

5. The observation optical system according to claim 1 or 2, which satisfies the conditional expressions (1-2) expressed below. 1.85<(R4-R2) / (R4+R2)<3 (1-2).

6. The observation optical system according to claim 1 or 2, which satisfies the conditional expressions (1-3) expressed below. 1.9<(R4-R2) / (R4+R2)<2.7 (1-3).

7. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (2-1) expressed below. 55 <Dsum / (|f1| / f2)<78 (2-1)。 8. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (2-2) expressed below. 60 <Dsum / (|f1| / f2)<75 (2-2)。 9. The observation optical system according to claim 1 or 2, which satisfies the conditional expressions (2-3) expressed below. 61.5 <Dsum / (|f1| / f2)<74 (2-3)。 10. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (3-1) expressed below. 1.46 <Nave<1.6 (3-1)。 11. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (3-2) expressed below. 1.47 <Nave<1.58 (3-2)。 12. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (3-3) expressed below. 1.475 <Nave<1.56 (3-3)。 13. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (4-1) expressed below. 0.105 <D2 / Dsum<0.26 (4-1)。 14. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (4-2) expressed below. 0.11 <D2 / Dsum<0.24 (4-2)。 15. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (4-3) expressed below. 0.115<D2 / Dsum<0.22 (4-3).

16. The observation optical system according to claim 1 or 2, wherein, With the refractive index below the d-line of the objective lens set to N1 and the Abbe number of the d-line reference of the objective lens set to ν1, the observation optical system satisfies the conditional expression (5) expressed below. 1.8 <N1+0.01×ν1<2.14 (5)。 17. The observation optical system according to claim 1 or 2, wherein, With the refractive index below the d-line of the eyepiece set to N2 and the Abbe number of the d-line reference of the eyepiece set to v2, the observation optical system satisfies the conditional expression (6) expressed below. 1.8 <N2+0.01×ν2<2.14 (6)。 18. The observation optical system according to claim 1 or 2, which satisfies the conditional expression (7) expressed below. 1 <f2 / Dsum<2 (7)。 19. The observation optical system according to claim 1 or 2, wherein, With the air equivalent length along the optical axis from the viewpoint side of the objective lens to the object side of the eyepiece set to D12, the observation optical system satisfies the conditional expression (8) expressed below. 0.05 <R2 / D12<1 (8)。 20. An optical device, characterized in that, The observation optical system comprising any one of claims 1 to 19.

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