Eyepiece lens, viewing optical system, and optical device

Abstract

Provided is an eyepiece lens, an observation optical system, and an optical device, which have good performance and enable observation at a wider field angle. The eyepiece lens includes, in order from an observation object side to a view point side, a positive first lens, a negative second lens, a positive third lens, and a positive fourth lens. All the lenses are single lenses. The second lens has a biconcave shape. An observation object side surface of the fourth lens has a convex shape. When the refractive index at the d line of the third lens is N3, the eyepiece lens satisfies a conditional expression represented by 1.76 < N3 < 2.

Description

Technical Field

[0001] This invention relates to an eyepiece lens, an observation optical system, and an optical device. Background Technology

[0002] Previously, lens systems described in Patent Documents 1 to 4 were known as eyepiece lenses or magnifying lenses.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2013-088632

[0004] Patent Document 2: Japanese Patent Application Publication No. 60-057315

[0005] Patent Document 3: Japanese Patent Application Publication No. 7-234357

[0006] Patent Document 4: Japanese Patent Application Publication No. 8-254660

[0007] In recent years, there has been a demand for eyepiece lenses with good performance and the ability to observe with a wider field of view. Summary of the Invention

[0008] The present invention was made in view of the above circumstances, and its object is to provide an eyepiece lens, observation optical system and optical device with good performance and capable of observation with a wider field of view.

[0009] The eyepiece lens of the present invention includes, from the object side to the viewpoint side, a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, and a fourth lens with positive refractive power. The first lens, the second lens, the third lens, and the fourth lens are all single lenses. The second lens is biconcave, and the object-side surface of the fourth lens is convex. When the refractive index under the d-line of the third lens is set to N3, the following condition (1) is satisfied.

[0010] 1.76 < N3 < 2 (1)

[0011] The eyepiece lens of the present invention is further preferably satisfied with the following condition (1-1).

[0012] 1.8 < N3 < 1.9 (1-1)

[0013] When the focal length of the second lens is set to f2 and the focal length of the fourth lens is set to f4, the eyepiece lens of the present invention preferably satisfies the following condition (2), and more preferably satisfies the following condition (2-1).

[0014] -0.42 < f2 / f4 < -0.2 (2)

[0015] -0.35 < f2 / f4 < -0.21 (2-1)

[0016] When the focal length of the eyepiece lens is set to f and the focal length of the first lens is set to f1, the eyepiece lens of the present invention preferably satisfies the following condition (3), and more preferably satisfies the following condition (3-1).

[0017] 1.2 < f / f1 < 3.5 (3)

[0018] 1.4 < f / f1 < 2.5 (3-1)

[0019] When the focal length of the first lens is set to f1 and the focal length of the fourth lens is set to f4, the eyepiece lens of the present invention preferably satisfies the following condition (4), and more preferably satisfies the following condition (4-1).

[0020] 2.7 < f4 / f1 < 8 (4)

[0021] 3 < f4 / f1 < 5 (4-1)

[0022] When the radius of curvature of the viewpoint side surface of the second lens is set to R2r and the radius of curvature of the object-side surface of the third lens is set to R3f, the eyepiece lens of the present invention preferably satisfies the following condition (5), and more preferably satisfies the following condition (5-1).

[0023] -2.1<(R2r+R3f) / (R2r-R3f)<-0.2 (5)

[0024] -1.75<(R2r+R3f) / (R2r-R3f)<-0.6 (5-1)

[0025] In the eyepiece lens of the present invention, the first lens is preferably biconvex. In the eyepiece lens of the present invention, the viewpoint-side surface of the third lens is preferably convex. In the eyepiece lens of the present invention, the object-side surface of the fourth lens is preferably aspherical. In the eyepiece lens of the present invention, the viewpoint-side surface of the second lens is preferably aspherical.

[0026] The eyepiece lens of the present invention preferably adjusts its diopter by changing the distance between the observed object and the optical axis of the eyepiece lens.

[0027] An observation optical system according to one aspect of the present invention includes a display element and an eyepiece lens of the present invention, and an image of the display element is observed through the eyepiece lens. In this observation optical system, when adjusting the diopter, the eyepiece lens is fixed, and the display element moves by changing the distance between the display element and the eyepiece lens in the optical axis direction.

[0028] Another aspect of the present invention relates to an observation optical system comprising a display element and a lens group including multiple lenses, and an image of the display element is observed via the lens group. In this observation optical system, when adjusting the diopter, the lens group is fixed, and the display element is moved by changing the distance between the display element and the lens group in the optical axis direction. When the refractive index of at least one lens in the lens group below the d line is set to Nx, the following condition (6) is satisfied.

[0029] 1.76 < Nx < 2 (6)

[0030] The observation optical system involved in the other approach described above is further preferably satisfied with the following condition (6-1).

[0031] 1.8 < Nx < 1.9 (6-1)

[0032] In the observation optical system described above, the preferred lens group comprises four lenses, and the lens that satisfies condition (6) is the third lens from the side of the display element among the four lenses.

[0033] One aspect of the present invention relates to an optical device comprising the eyepiece lens of the present invention. Another aspect of the present invention relates to an optical device comprising the observation optical system of the present invention.

[0034] In addition, the term "including" in this specification means 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, and cover glass, and lens flanges, lens barrels, etc.

[0035] In addition, 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. "Single lens" refers to a single lens without any joints. However, compound aspherical lenses (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 joint lenses, but are used as a single lens. Regarding the sign of refractive power, radius of curvature, and surface shape associated with lenses containing aspherical surfaces, unless otherwise specified, they are assumed to be considered in 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 being observed is marked positive, and the radius of curvature of a surface with a convex shape facing the viewpoint is marked negative.

[0036] The "focal length" used in the conditional formula is the paraxial focal length. The values ​​used in the conditional formula are based on the d-line. 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.

[0037] Invention Effects

[0038] According to the present invention, an eyepiece lens, an observation optical system, and an optical device with good performance and capable of observation with a wider field of view can be provided. Attached Figure Description

[0039] Figure 1 Corresponding to the eyepiece lens of Embodiment 1, this is a cross-sectional view showing the structure and beam of the eyepiece lens according to one embodiment.

[0040] Figure 2 These are the spherical aberration diagram, astigmatism diagram, distortion aberration diagram, and magnification chromatic aberration diagram of the eyepiece lens in Example 1.

[0041] Figure 3 This is a lateral aberration diagram of the eyepiece lens in Example 1.

[0042] Figure 4 This is a cross-sectional view showing the structure of the eyepiece lens and the light beam in Embodiment 2.

[0043] Figure 5 These are the spherical aberration diagram, astigmatism diagram, distortion aberration diagram, and magnification chromatic aberration diagram of the eyepiece lens in Example 2.

[0044] Figure 6 This is a lateral aberration diagram of the eyepiece lens in Example 2.

[0045] Figure 7 This is a cross-sectional view showing the structure of the eyepiece lens and the light beam in Embodiment 3.

[0046] Figure 8 These are the spherical aberration diagram, astigmatism diagram, distortion aberration diagram, and magnification chromatic aberration diagram of the eyepiece lens in Example 3.

[0047] Figure 9 This is a lateral aberration diagram of the eyepiece lens in Example 3.

[0048] Figure 10 This is a cross-sectional view showing the structure of the eyepiece lens and the light beam in Embodiment 4.

[0049] Figure 11 These are the spherical aberration diagram, astigmatism diagram, distortion aberration diagram, and magnification chromatic aberration diagram of the eyepiece lens in Example 4.

[0050] Figure 12 This is a lateral aberration diagram of the eyepiece lens in Example 4.

[0051] Figure 13 This is a cross-sectional view showing the structure of the eyepiece lens and the light beam in Embodiment 5.

[0052] Figure 14These are the spherical aberration diagram, astigmatism diagram, distortion aberration diagram, and magnification chromatic aberration diagram of the eyepiece lens in Example 5.

[0053] Figure 15 This is a lateral aberration diagram of the eyepiece lens in Example 5.

[0054] Figure 16 This is a schematic structural diagram of an optical device according to one embodiment.

[0055] Figure 17 It is a diagram used to illustrate the movement of display elements.

[0056] Symbol Explanation

[0057] 1-Display element, 2-Optical component, 3-Eyepiece lens, 5-Observation optical system, 10-Camera, 20-Lens barrel, 22-Imaging lens, 24-Shutter, 26-Imaging element, 30-Camera body, 32-Rear LCD panel, 34-Viewing window, 36-Diopter adjustment dial, 50-Processor, 60-Observer, A, B-Arrows, EP-Viewpoint, L1-First lens, L2-Second lens, L3-Third lens, L4-Fourth lens, Z1, Z2-Optical axis. Detailed Implementation

[0058] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 The structure of an observation optical system 5 according to an embodiment of the present invention is shown in the figure. Figure 1 The examples shown correspond to Embodiment 1 described later, and also to the first and second embodiments of the invention described below. Figure 1 In this example, display element 1 is set as the observed object. Figure 1 In the diagram, the left side represents the object being observed, and the right side represents the viewpoint. Figure 1 The viewpoint EP does not represent shape, but rather position along the optical axis. Figure 1 The diagram also illustrates the on-axis beam and the beam at the maximum field of view within the range from display element 1 to viewpoint EP.

[0059] First, the observation optical system 5 according to the first embodiment of the present invention will be described. The observation optical system 5 includes a display element 1 and an eyepiece lens 3. The display element 1 is an element for displaying images. The display element 1 can be, for example, a liquid crystal display element or an organic EL (organic electroluminescence) display element. In practice, the display element has a thickness, but... Figure 1 For convenience, the display surface of display element 1 is illustrated using display element 1.

[0060] The observation optical system 5 is configured to observe the image displayed on the display element 1 via the eyepiece lens 3. Figure 1 The image shows an example where a parallel, flat, non-refractive optical component 2 is disposed between the display element 1 and the eyepiece lens 3. The optical component 2 is assumed to be a protective cover glass or various filters, but a structure without the optical component 2 is also possible.

[0061] The eyepiece lens 3 comprises multiple lenses. Figure 1 The eyepiece lens 3, from the object side to the viewpoint side, comprises, in sequence, a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, a third lens L3 with positive refractive power, and a fourth lens L4 with positive refractive power. All four lenses are unjoined single lenses and are arranged with air gaps between them and adjacent lenses on the optical axis. This structure of the eyepiece lens 3 facilitates obtaining a wider field of view.

[0062] When the refractive index along the d-line of the third lens L3 is set to N3, the eyepiece lens 3 is configured to satisfy the following conditional expression (1). By setting it to not be below the lower limit of conditional expression (1), correction of image plane curvature becomes easier. By setting it to not be above the upper limit of conditional expression (1), materials other than low Abbe numbers can be used in the third lens L3, thus chromatic aberration correction becomes easier. Moreover, if the structure is configured to satisfy the following conditional expression (1-1), even better characteristics can be achieved.

[0063] 1.76 < N3 < 2 (1)

[0064] 1.8 < N3 < 1.9 (1-1)

[0065] The preferred structure of the eyepiece lens 3 will now be described. The first lens L1 is preferably biconvex. In this case, it is advantageous to widen the distance between the observed object, i.e., the display element 1, and the eyepiece lens 3. In structures where the distance between the display element 1 and the first lens L1 changes during diopter adjustment, a wider distance between the display element 1 and the eyepiece lens 3 makes it easier to ensure space for diopter adjustment. Furthermore, a wider distance between the display element 1 and the eyepiece lens 3 makes it less likely that dust and scratches on the surface of the display element 1 will be visible. For better observation with a wider field of view, the first lens L1 can also be configured as an aspherical surface having at least one surface.

[0066] The second lens L2 is preferably biconcave. In this case, it is beneficial to maintain the field of view and suppress image plane curvature while increasing the good viewing distance. The viewpoint-side surface of the second lens L2 is preferably aspherical. In this case, it is beneficial to correct axial chromatic aberration while suppressing magnification chromatic aberration. To obtain even better characteristics, the second lens L2 may also be configured such that both the object-side surface and the viewpoint-side surface are aspherical.

[0067] The viewpoint-side surface of the third lens L3 is preferably convex. In this case, it is beneficial to correct spherical aberration. Furthermore, when the viewpoint-side surface of the third lens L3 is made convex and is configured to satisfy condition (1), the correction effect of spherical aberration can be enhanced. The third lens L3 can be biconvex or a meniscus shape with the convex surface facing the viewpoint side.

[0068] The object-side surface of the fourth lens L4 is preferably convex. This helps to suppress astigmatism while obtaining a wide field of view. For example, the fourth lens L4 can be configured in a biconvex shape. The object-side surface of the fourth lens L4 is preferably aspherical. This helps to ensure a wide field of view while correcting coma aberration generated in the peripheral portion of the lens. For even better characteristics, the fourth lens L4 can also be configured with aspherical surfaces on both the object-side and viewpoint-side surfaces.

[0069] When the focal length of the second lens L2 is set to f2 and the focal length of the fourth lens L4 is set to f4, the eyepiece lens 3 preferably satisfies the following condition (2). Condition (2) is a formula related to the preferred range of the ratio of the refractive power of the second lens L2 to the refractive power of the fourth lens L4. By setting it to not be below the lower limit of condition (2), the refractive power of the fourth lens L4 will not become excessive relative to the refractive power of the second lens L2, thus suppressing astigmatism. By setting it to not be above the upper limit of condition (2), the refractive power of the fourth lens L4 will not be insufficient relative to the refractive power of the second lens L2, thus suppressing the radial outward expansion of off-axis rays on the viewpoint side due to the fourth lens L4, thereby suppressing coma in the peripheral field of view. Moreover, if the structure satisfies the following condition (2-1), even better characteristics can be achieved.

[0070] -0.42 < f2 / f4 < -0.2 (2)

[0071] -0.35 < f2 / f4 < -0.21 (2-1)

[0072] When the focal length of the eyepiece lens 3 is set to f and the focal length of the first lens L1 is set to f1, the eyepiece lens 3 preferably satisfies the following condition (3). By setting it to not be below the lower limit of condition (3), the refractive power of the first lens L1 will not be insufficient, thus making the correction of distortion aberrations easier. By setting it to not be above the upper limit of condition (3), the refractive power of the first lens L1 will not become excessive, thus making it easier to suppress the angle of the principal ray of the maximum field of view emitted from the first lens L1 towards the viewpoint side relative to the optical axis Z1 to not become large, thereby facilitating the correction of magnification chromatic aberration. Moreover, if the structure satisfies the following condition (3-1), even better characteristics can be achieved.

[0073] 1.2 < f / f1 < 3.5 (3)

[0074] 1.4 < f / f1 < 2.5 (3-1)

[0075] When the focal length of the first lens L1 is set to f1 and the focal length of the fourth lens L4 is set to f4, the eyepiece lens 3 preferably satisfies the following condition (4). The eyepiece lens 3 is configured with refractive power of positive, negative, positive, and positive sequentially from the object being observed. Thus, it can be roughly shown that the light rays from the display element 1 toward the viewpoint side of the peripheral field of view decrease in height between the first lens L1 and the second lens L2, and increase in height when passing through the second lens L2 and the third lens L3. On the other hand, in order to obtain a wide field of view, it is preferable to ensure a certain height of light rays in the fourth lens L4. By setting it to not be below the lower limit of condition (4), the refractive power of the first lens L1 is not insufficient relative to the refractive power of the fourth lens L4, so the angle of the light rays from the first lens L1 toward the viewpoint side of the peripheral field of view with respect to the optical axis Z1 does not become excessively small. Taking into account the rise and fall of the light height and the assurance of the light height in the fourth lens L4, the angle of the light rays passing through the peripheral side of the field of view of the second lens L2 and the third lens L3 relative to the optical axis Z1 will not become excessively small, thus suppressing the undercorrection of chromatic aberration. By setting it to not exceed the upper limit of condition (4), the refractive power of the first lens L1 relative to the refractive power of the fourth lens L4 will not become excessive, thus the angle of the off-axis principal ray emitted from the first lens L1 towards the viewpoint side relative to the optical axis Z1 will not become excessively large. Taking into account the rise and fall of the light height and the assurance of the light height in the fourth lens L4, the angle of the light rays passing through the peripheral side of the field of view of the second lens L2 and the third lens L3 relative to the optical axis Z1 will not become excessively large, thus suppressing the overcorrection of chromatic aberration.

[0076] That is, by satisfying condition (4), it is beneficial to correct magnification color difference. Moreover, if the structure is designed to satisfy the following condition (4-1), it can achieve even better characteristics.

[0077] 2.7 < f4 / f1 < 8 (4)

[0078] 3 < f4 / f1 < 5 (4-1)

[0079] When the radius of curvature of the viewpoint-side surface of the second lens L2 is set to R2r, and the radius of curvature of the object-side surface of the third lens L3 is set to R3f, the eyepiece lens 3 preferably satisfies the following conditional expression (5). Conditional expression (5) is an expression that defines the shape factor of the air lens formed between the second lens L2 and the third lens L3. By setting it to not be below the lower limit of conditional expression (5), overcorrection of spherical aberration in the air lens can be suppressed. By setting it to not be above the upper limit of conditional expression (5), undercorrection of spherical aberration in the air lens can be suppressed. If spherical aberration is undercorrected in the air lens and other lens surfaces are used to correct the spherical aberration, chromatic aberration will occur. However, by setting it to not be above the upper limit of conditional expression (5), this undesirable situation can be prevented. Moreover, if the structure satisfies the following conditional expression (5-1), even better characteristics can be achieved.

[0080] -2.1<(R2r+R3f) / (R2r-R3f)<-0.2 (5)

[0081] -1.75<(R2r+R3f) / (R2r-R3f)<-0.6 (5-1)

[0082] The preferred and possible structures described above can be combined in any way. For example, an eyepiece lens 3 in a preferred embodiment of the above structure includes, from the object side to the viewpoint side, a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, a third lens L3 with positive refractive power, and a fourth lens L4 with positive refractive power. All lenses are single lenses, the second lens L2 is biconcave, and the object-side surface of the fourth lens L4 is convex, and condition (1) is satisfied.

[0083] Recently, in viewfinder eyepieces for digital cameras and other devices, the increasing pixel count of liquid crystal display elements has led to a demand for wider field of view and higher resolution. However, achieving a wider field of view results in significant aberrations such as astigmatism and chromatic aberration at the periphery of the field of view, making it difficult to achieve the same result as high resolution. Therefore, by employing the preferred embodiment described above, aberrations such as astigmatism and chromatic aberration can be suppressed, resulting in an eyepiece lens that allows for observation with a wider field of view.

[0084] The eyepiece lens 3 is preferably configured to allow for diopter adjustment. The eyepiece lens 3 can be configured to allow diopter adjustment by changing the distance between the display element 1 and the eyepiece lens 3 along the optical axis. In this case, the amount of change in the air gap during diopter adjustment can be reduced.

[0085] exist Figure 1 In the example, when adjusting the diopter, the eyepiece lens 3 is fixed, and the display element 1 moves by changing the distance between the display element 1 and the eyepiece lens 3 in the optical axis direction. Figure 1 The double arrows below display element 1 indicate that display element 1 moves along the optical axis Z1 of eyepiece lens 3 during diopter adjustment. In this case, the reduction in good viewing distance can be suppressed during diopter adjustment. Furthermore, the phrase "eyepiece lens 3 is fixed" means that when the observation optical system is mounted on the device, eyepiece lens 3 is fixed relative to the device. In this case, the distance between display element 1 and eyepiece lens 3 changes along the optical axis during diopter adjustment, but the distance between eyepiece lens 3 and viewpoint EP remains approximately constant. Even with diopter adjustment, the reduction in good viewing distance is small, thus allowing for good observation.

[0086] Next, the observation optical system 5 according to the second embodiment of the present invention will be described. In the following description of the second embodiment, some descriptions of the same structure as in the first embodiment will be omitted. The observation optical system 5 according to the second embodiment includes a display element 1 and a lens group including multiple lenses, and is configured to observe the image displayed on the display element 1 via the lens group.

[0087] exist Figure 1 In the image, eyepiece lens 3 is shown as an example of a lens group.

[0088] In the observation optical system 5 according to the second embodiment, when adjusting the diopter, the lens group is fixed, and the display element 1 is moved by changing the distance between the display element 1 and the lens group in the optical axis direction. Moreover, it is configured such that when the refractive index below the d line of at least one lens in the lens group is set to Nx, the following conditional expression (6) is satisfied. In addition, the meaning and effect of "the lens group is fixed" are the same as the meaning and effect of "the eyepiece lens 3 is fixed" as described in the first embodiment. By setting it to not be below the lower limit of conditional expression (6), the correction of image plane curvature becomes easier. By setting it to not be above the upper limit of conditional expression (6), materials other than low Abbe number can also be used in the lens, thus the correction of chromatic aberration becomes easier. Moreover, if the structure is set to satisfy the following conditional expression (6-1), even better characteristics can be achieved.

[0089] 1.76 < Nx < 2 (6)

[0090] 1.8 < Nx < 1.9 (6-1)

[0091] Condition (6) represents the range of higher refractive indices. Lenses with high refractive indices that satisfy condition (6) have the advantage of being beneficial for correcting image plane curvature. Generally, the higher the refractive index of a lens, the stronger its refractive power becomes; the stronger the refractive power, the greater the aberration variation when the light passing through the lens changes. Therefore, in the observation optical system according to the second embodiment, the display element is moved while the eyepiece lens 3 is fixed during diopter adjustment. According to this structure, the variation in the height of the light passing through the lens during diopter adjustment can be reduced. That is, when diopter adjustment is performed, the lens group is fixed while the display element 1 is moved, and condition (6) is satisfied, thereby enabling the use of lenses with high refractive indices while suppressing aberration variation during diopter adjustment.

[0092] like Figure 1 As shown, the lens group can also be configured with four lenses. In this case, the lens that satisfies condition (6) is preferably the third lens from the display element 1 side among the four lenses constituting the lens group. When the lens group is configured with four lenses and has a wide field of view, the light height in the third lens from the display element 1 side tends to increase. Therefore, the third lens from the display element 1 side satisfies condition (6), thereby significantly reducing aberrations during diopter adjustment. This effect is particularly pronounced when the lens group consists of a positive lens, a negative lens, a positive lens, and a positive lens in sequence from the object being observed.

[0093] The preferred and possible structures described in the above embodiments can be combined arbitrarily in each embodiment, and are preferably adopted selectively according to the required specifications. Furthermore, when the lens group of the observation optical system 5 in the second embodiment includes a positive lens, a negative lens, a positive lens, and a positive lens in sequence from the observation object side, the lens group can selectively adopt the structure of the eyepiece lens 3 and the preferred structure of the eyepiece lens 3 described in the first embodiment.

[0094] Next, a numerical embodiment of the eyepiece lens of the present invention will be described.

[0095] [Example 1]

[0096] The structure and beam of the eyepiece lens 3 in Example 1 are as follows: Figure 1As shown, the illustrated method and structure are as described above, therefore, repeated descriptions are omitted here. The eyepiece lens 3 of Embodiment 1, from the object side to the viewpoint side, sequentially includes a first lens L1 in a biconvex shape in the paraxial region, a second lens L2 in a biconcave shape in the paraxial region, a third lens L3 in a biconvex shape in the paraxial region, and a fourth lens L4 in a biconvex shape in the paraxial region. All four lenses, from the first lens L1 to the fourth lens L4, are single lenses. The first lens L1, the second lens L2, and the fourth lens L4 are aspherical lenses. During diopter adjustment, the eyepiece lens 3 is fixed, and the display element 1 moves along the optical axis. This changes the distance between the display element 1 and the eyepiece lens 3 along the optical axis. The above is a summary of the eyepiece lens 3 of Embodiment 1.

[0097] The basic lens data of the eyepiece lens 3 of Embodiment 1 are shown in Table 1. Table 1 also shows the display element 1, optical component 2, and viewpoint EP. In Table 1, in the Sn column, the surface of the display element 1 is indicated by OBJ, and the surface numbering is shown as the object-side surface of the optical component 2 is set as the first surface, with the numbering increasing sequentially towards the viewpoint side. The surface corresponding to the viewpoint EP is indicated by EP. The radius of curvature of each surface is shown in the R column, and the surface spacing on the optical axis of each surface and its adjacent surface on the viewpoint side is shown in the D column. The refractive index along the d-line of each component is shown in the Nd column, and the Abbe number of the d-line reference of each component is shown in the νd column.

[0098] In Table 1, the sign of the radius of curvature of the convex surface facing the object being observed is set to positive, and the sign of the radius of curvature of the convex surface facing the viewpoint is set to negative. In Table 1, the variable surface interval during diopter adjustment is represented by DD[2].

[0099] Table 2 shows the focal length f and field of view values ​​at half angle of view for eyepiece lens 3. The (°) column for field of view indicates the unit is degrees. Table 2 also shows the values ​​for a diopter of -1.00 diopters. Table 3 shows the values ​​for the variable surface spacing at each diopter.

[0100] Table 4 shows the aspherical coefficients of the aspherical lenses included in eyepiece lens 3. In the basic lens data, the aspherical surface number is marked with an asterisk (*), and the paraxial radius of curvature is recorded in the radius of curvature column. In Table 4, the surface number of the aspherical surface is shown in the Sn column, and the aspherical coefficient values ​​for each aspherical surface are shown in the KA and Am (m = 3, 4, 5, ... 16) columns.

[0101] The numerical values ​​of the aspheric coefficients in Table 4, “E±n” (n: an integer), represent “×10”. ±n KA and Am are the aspheric coefficients in the aspheric formula expressed by the following equation.

[0102] Zd=C×h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2}+∑Am×h m

[0103] in,

[0104] Zd: Aspherical depth (the length of the perpendicular line from a point on the aspherical surface at height h down to a plane perpendicular to the optical axis that connects to the vertex of the aspherical surface).

[0105] h: Height (distance from the optical axis to the lens surface)

[0106] C: The reciprocal of the paraxial radius of curvature

[0107] KA, Am: Aspheric coefficients

[0108] In aspherical form, ∑ represents the summation related to m.

[0109] In the data in each table, angles are measured in degrees, lengths in millimeters, and diopters in diopters. However, optical systems can be used in both magnified and reduced scales, so other appropriate units may also be used. Furthermore, the values ​​in the tables shown below are rounded to the specified number of decimal places.

[0110] [Table 1]

[0111] Example 1

[0112] Sn R D Nd νd 0BJ 4.3000 1 1.2000 1.51680 64.20 2 DD[2] *3 26.7692 6.0184 1.80625 40.91 *4 -11.2207 1.5242 *5 -9.2753 2.8278 1.63351 23.63 *6 13.4282 0.6266 7 159.9161 6.9234 1.81600 46.62 8 -19.0122 0.1000 *9 20.3593 2.7869 1.53389 55.98 *10 -343.2501 15.0000 EP

[0113] [Table 2]

[0114] Example 1

[0115] f 17.26 Field of view [°] 20.0

[0116] [Table 3]

[0117] Example 1

[0118] diopter -1.00 -4.34 2.38 DD[2] 2.54 1.50 3.53

[0119] [Table 4]

[0120] Example 1

[0121] Sn 3 4 5 KA 4.9935872E+00 3.8199961E-02 8.0451835E-01 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -2.7277890E-05 3.5295147E-04 -3.5720032E-05 A5 -5.3616103E-05 -2.1502831E-05 3.0066606E-06 A6 2.3681929E-06 -6.4628496E-06 1.4965371E-05 A7 6.7209627E-06 5.0061587E-07 -1.9259134E-05 A8 -1.8558929E-06 1.0252973E-07 6.0736819E-06 A9 9.2622228E-08 -7.1880255E-08 -7.0096873E-07 A10 1.6690221E-08 1.1899949E-08 1.2109115E-08 A11 -1.0057805E-09 1.5491352E-10 3.7118192E-09 A12 -1.4917926E-10 -8.5827144E-11 -1.3059819E-10 A13 1.5948818E-11 -1.4190084E-11 -5.6934547E-11 A14 -1.8480537E-12 2.2409452E-12 1.0087840E-11 A15 2.3595380E-13 -4.7457710E-14 -7.1918503E-13 A16 -1.0016961E-14 -2.1322474E-15 1.9135841E-14

[0122] Sn 6 9 10 KA 8.2849014E-01 -1.4018990E+00 -2.0530490E+00 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -9.8774485E-04 -2.3385262E-06 1.3224120E-04 A5 -1.6972500E-05 -9.7612011E-06 -2.4067242E-05 A6 2.0098254E-05 2.5061220E-07 2.7870350E-06 A7 -4.3835331E-08 -2.9586751E-07 2.5444448E-07 A8 -2.1850591E-07 3.7999481E-08 1.9431758E-07 A9 8.9099305E-10 -1.4470868E-08 1.3163759E-08 A10 1.8158070E-09 2.0186526E-09 1.2223128E-09 A11 -1.5588733E-10 6.9870008E-12 -8.4148159E-11 A12 1.7140595E-11 -7.9249125E-12 -8.4751535E-12 A13 -1.7279251E-12 -8.6440174E-13 1.4567577E-12 A14 1.0597039E-13 1.3882954E-13 -1.5511273E-13 A15 -4.7925822E-15 -5.9535273E-15 9.7451727E-15 A16 1.2479308E-16 8.2245050E-17 -2.3225557E-16

[0123] exist Figure 2 and Figure 3The diagram shows the aberrations of the eyepiece lens 3 in Example 1, with a diopter of -1.00 diopter. Figure 2 From left to right, the diagrams represent spherical aberration, astigmatism, distortion aberration, and chromatic aberration. 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 represented by solid lines, and aberrations below the d-line in the meridional direction are represented by short dashed lines. In the distortion aberration diagram, aberrations below the d-line are represented by 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 horizontal axis of the spherical aberration and astigmatism diagrams, in units of dpt, represents diopter. Φ in the spherical aberration diagram represents the diameter of the viewpoint EP when the unit is set to mm (millimeters), while ω in other aberration diagrams represents the field of view at half the angle of view.

[0124] exist Figure 3 In the diagram, for each field of view, the lateral aberrations in the meridional direction are shown on the left, and the lateral aberrations in the sagittal direction are shown on the right. Figure 3 In the diagram, the aberrations under the d-line, C-line, and F-line are represented by solid lines, long dashed lines, and short dashed lines, respectively. Figure 3 ω represents the field of view angle at half-angle.

[0125] Unless otherwise specified, the notation, meaning, recording method and diagrammatic method of the data related to Embodiment 1 above are the same in the following embodiments, so repeated descriptions are omitted below.

[0126] [Example 2]

[0127] The structure and beam of the eyepiece lens 3 in Embodiment 2 are shown below. Figure 4 The eyepiece lens 3 of Embodiment 2 has the same general structure as the eyepiece lens 3 of Embodiment 1. When adjusting the diopter, the eyepiece lens 3 can be fixed while the display element 1 is moved. Regarding the eyepiece lens 3 of Embodiment 2, basic lens data are shown in Table 5, specifications are shown in Table 6, variable surface spacing is shown in Table 7, aspherical coefficients are shown in Table 8, and various aberrations are illustrated in Table 9. Figure 5 and Figure 6 middle.

[0128] [Table 5]

[0129] Example 2

[0130] Sn R D Nd vd 0BJ 4.3000 1 1.2000 1.51680 64.20 2 DD[2] *3 26.1752 6.8567 1.80625 40.91 *4 -12.1315 1.5178 *5 -9.1743 3.1994 1.63351 23.63 *6 13.2021 0.5047 7 51.7168 6.8800 1.88300 40.76 8 -22.1180 0.1000 *9 21.9472 2.8172 1.53389 55.98 *10 -137.7660 15.0000 EP

[0131] [Table 6]

[0132] Example 2

[0133] f 17.26 Field of view [°] 20.0

[0134] [Table 7]

[0135] Example 2

[0136] DD[2] 2.14 1.13 3.16 Diopter [dpt] -1.00 -4.28 2.47

[0137] [Table 8]

[0138] Example 2

[0139]

[0140] Sn 6 9 10 KA 8.2583543E-01 -1.2549999E+00 4.9999994E+00 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -8.6864018E-04 1.3571531E-05 1.4068921E-04 A5 -7.9690361E-06 -1.5833431E-05 -2.3678460E-05 A6 1.7485751E-05 5.9878632E-07 3.7625922E-06 A7 -4.2919349E-07 -5.0203553E-08 -2.4446807E-07 A8 -1.4421513E-07 -3.4681666E-08 -9.5672622E-08 A9 4.0804777E-09 -4.8003244E-10 6.0170226E-09 A10 4.9438188E-10 -5.2580900E-10 1.1692362E-09 A11 -3.9576193E-12 4.0348688E-10 -1.5420817E-10 A12 1.1617354E-12 -5.3403712E-11 2.8286823E-11 A13 -4.5374623E-13 2.7851874E-12 -4.7819597E-12 A14 5.1540574E-14 -6.0158642E-14 3.9490439E-13 A15 -3.8643575E-15 7.0995468E-16 -1.5655177E-14 A16 1.2406578E-16 -1.9048785E-17 2.5255761E-16

[0141] [Example 3]

[0142] The structure of the eyepiece lens 3 and the light beam of Example 3 are shown below. Figure 7 The eyepiece lens 3 of Embodiment 3 has the same general structure as the eyepiece lens 3 of Embodiment 1, except that the third lens L3 is a positive meniscus lens with its convex surface facing the viewpoint. When adjusting the diopter, the eyepiece lens 3 can be fixed while the display element 1 is moved. Regarding the eyepiece lens 3 of Embodiment 3, basic lens data are shown in Table 9, specifications are shown in Table 10, variable surface spacing is shown in Table 11, aspherical coefficients are shown in Table 12, and various aberrations are illustrated in Table 12. Figure 8 and Figure 9 middle.

[0143] [Table 9]

[0144] Example 3

[0145] Sn R D Nd νd 0BJ 4.3000 1 1.2000 1.51680 64.20 2 DD[2] *3 23.6587 7.4016 1.80625 40.91 *4 -10.3654 0.7476 *5 -10.2251 2.7407 1.63351 23.63 *6 15.7731 1.5328 7 -152.9384 5.2879 1.81600 46.62 8 -19.2861 0.1000 *9 267.4061 3.3457 1.53389 55.98 *10 -24.8594 15.0000 EP

[0146] [Table 10]

[0147] Example 3

[0148] f 17.26 Field of view [°] 20.0

[0149] [Table 11]

[0150] Example 3

[0151] DD[2] 2.38 1.35 3.38 diopter -1.00 -4.32 2.41

[0152] [Table 12]

[0153] Example 3

[0154] Sn 3 4 5 KA 4.4683342E+00 1.6189781E-01 8.3877736E-01 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -1.3795537E-04 -5.7389511E-05 -6.2392711E-04 A5 -4.5842164E-05 5.4398073E-05 7.4247929E-05 A6 9.9941484E-06 -5.1084421E-06 5.9104873E-05 A7 6.9698261E-07 -5.8859275E-07 -3.0329764E-05 A8 -2.0047163E-07 -5.8452792E-08 7.1042150E-06 A9 -1.1533947E-07 2.6546747E-08 -7.8071018E-07 A10 3.4508576E-08 2.7470713E-09 1.1469817E-08 A11 -4.9648787E-09 -9.1388158E-10 4.0914319E-09 A12 7.7487629E-10 4.3742443E-11 5.2577719E-10 A13 -1.0903136E-10 3.5650140E-12 -2.3437399E-10 A14 8.7069847E-12 -6.3757263E-13 2.87158163E-11 A15 3.1523622E-13 5.3124964E-14 -1.6258964E-12 A16 3.3712262E-15 -1.8918958E-15 3.6283202E-14

[0155] Sn 6 9 10 KA 8.0434545E-01 -4.9999996E+00 -5.0000035E+00 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -6.7507052E-04 3.1045092E-05 3.6311209E-05 A5 6.8443793E-06 1.4863482E-06 -2.0726470E-05 A6 1.4718815E-05 -2.4903191E-06 5.7141803E-06 A7 8.3709634E-09 5.9682217E-07 -6.4320660E-07 A8 -3.4986133E-07 -8.5543998E-08 1.0587754E-08 A9 2.1567730E-08 5.3923922E-09 1.1218294E-09 A10 1.7353220E-09 -1.3744368E-11 3.5076736E-10 A11 -1.7674002E-10 2.0678566E-12 -1.0470377E-10 A12 -2.7732892E-12 -9.9884060E-12 1.6226641E-11 A13 1.2354162E-12 2.3564796E-12 -1.5892578E-12 A14 -1.1546900E-13 -2.3248036E-13 1.2360574E-13 A15 5.7250711E-15 1.0850798E-14 -7.3182074E-15 A16 -1.1075637E-16 -2.0515474E-16 1.9708453E-16

[0156] [Example 4]

[0157] The structure and beam of the eyepiece lens 3 in Example 4 are shown below. Figure 10 The eyepiece lens 3 of Embodiment 4 has the same general structure as the eyepiece lens 3 of Embodiment 1. When adjusting the diopter, the eyepiece lens 3 can be fixed while the display element 1 is moved. Regarding the eyepiece lens 3 of Embodiment 4, basic lens data are shown in Table 13, specifications are shown in Table 14, variable surface spacing is shown in Table 15, aspherical coefficients are shown in Table 16, and various aberrations are illustrated in Table 17. Figure 11 and Figure 12 middle.

[0158] [Table 13]

[0159] Example 4

[0160] Sn R D Nd νd 0BJ 4.3000 1 1.2000 1.51680 64.20 2 DD[2] *3 27.3629 6.4273 1.80625 40.91 *4 -11.4855 1.4960 *5 -9.0268 3.1013 1.63351 23.63 *6 13.2176 0.4635 7 54.7824 7.2865 1.83481 42.74 8 -20.8317 0.1000 *9 20.5809 2.7498 1.53389 55.98 *10 -351.5611 15.0000 EP

[0161] [Table 14]

[0162] Example 4

[0163] f 17.26 Field of view [°] 20.1

[0164] [Table 15]

[0165] Example 4

[0166] DD[2] 2.23 1.24 3.27 diopter -1.00 -4.21 2.52

[0167] [Table 16]

[0168] Example 4

[0169] Sn 3 4 5 KA 4.9647805E+00 -6.4903463E-02 7.5661589E-01 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -2.4746006E-05 2.5491393E-04 -2.1982416E-04 A5 -6.8121552E-05 -2.3245455E-05 9.3144970E-05 A6 1.9999740E-05 -2.7758426E-07 -3.0016752E-05 A7 -4.6756700E-06 -1.8110376E-06 6.7322934E-07 A8 2.2129632E-06 6.8666155E-07 7.8236736E-07 A9 -7.5256501E-07 -1.6031332E-07 5.7899262E-08 A10 1.1607928E-07 1.9627430E-08 -2.8607797E-08 A11 -5.5793643E-09 -3.9066524E-10 6.9403490E-10 A12 -5.6200494E-10 -2.0483069E-11 1.8006294E-10 A13 9.8809679E-11 -2.2624531E-11 2.4504925E-12 A14 -7.8340390E-12 2.9996960E-12 -1.5297958E-12 A15 4.4862985E-13 -9.0002332E-14 3.3919611E-14 A16 -1.3038114E-14 -1.0550708E-15 1.3402065E-15

[0170] Sn 6 9 10 KA 8.2097765E-01 -1.4189909E+00 5.0000060E+00 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -9.4980779E-04 -3.4807568E-05 1.0353437E-04 A5 1.5576842E-06 1.0261225E-06 -1.2875147E-05 A6 1.9261702E-05 -1.1602396E-06 2.5803458E-06 A7 -1.0281660E-06 -1.9182715E-07 -3.5884364E-07 A8 -8.1558228E-08 3.0370104E-09 -8.0569883E-08 A9 7.8013586E-10 -6.4572807E-09 1.0594388E-08 A10 1.9575477E-09 1.6253398E-09 -5.7679738E-11 A11 -5.4145540E-10 -5.8015869E-11 8.1416603E-11 A12 9.6644665E-11 -1.6949313E-12 -1.7460723E-11 A13 -1.0470339E-11 -4.6875621E-13 1.2310920E-12 A14 7.0786225E-13 5.6321833E-14 -5.2085001E-14 A15 -2.9009717E-14 -1.5225887E-15 1.3666863E-15 A16 5.5278941E-16 -1.4402002E-18 -5.0684939E-18

[0171] [Example 5]

[0172] The structure and beam of the eyepiece lens 3 in Example 5 are shown below. Figure 13 The eyepiece lens 3 of Embodiment 5 has the same general structure as the eyepiece lens 3 of Embodiment 1, except that the third lens L3 is a positive meniscus lens with its convex surface facing the viewpoint. When adjusting the diopter, the eyepiece lens 3 can be fixed while the display element 1 is moved. Regarding the eyepiece lens 3 of Embodiment 5, basic lens data are shown in Table 17, specifications are shown in Table 18, variable surface spacing is shown in Table 19, aspherical coefficients are shown in Table 20, and various aberrations are illustrated in Table 20. Figure 14 and Figure 15 middle.

[0173] [Table 17]

[0174] Example 5

[0175] Sn R D Nd νd 0BJ 4.3000 1 1.2000 1.51680 64.20 2 DD[2] *3 24.5996 7.5834 1.80625 40.91 *4 -10.6388 0.9159 *5 -9.8566 2.6840 1.63351 23.63 *6 16.9770 1.4557 7 -112.6371 4.2354 1.81600 46.62 8 -21.1494 0.1000 *9 101.2847 4.4218 1.53389 55.98 *10 -19.9279 15.0000 EP

[0176] [Table 18]

[0177] Example 5

[0178] f 17.27 Field of view [°] 20.0

[0179] [Table 19]

[0180] Example 5

[0181] DD[2] 2.08 1.06 3.09 diopter -1.00 -4.30 2.44

[0182] [Table 20]

[0183] Example 5

[0184] Sn 3 4 5 KA 4.9834627E+00 4.3528264E-03 7.6844744E-01 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -1.9491252E-04 6.9581659E-05 -3.4615024E-04 A5 6.2844543E-06 2.1640819E-05 4.3750488E-05 A6 -3.0616930E-06 -7.6402543E-06 2.0973802E-06 A7 2.4081035E-06 -9.9625-158E-08 -2.4428281E-06 A8 -7.4224346E-07 1.5824227E-07 7.3260920E-07 A9 6.4084291E-08 -1.3127977E-08 1.5344379E-08 A10 3.6273309E-09 1.6972794E-09 -3.0272910E-08 A11 -7.9982224E-10 -2.0931977E-10 4.7321112E-09 A12 7.5764911E-11 -5.4777005E-12 -4.1583192E-10 A13 -1.0730424E-11 1.8024549E-12 2.6582890E-11 A14 5.5241935E-13 -2.0032333E-13 -5.5950561E-13 A15 3.9016344E-14 2.9861523E-14 -6.2343373E-14 A16 -3.0626384E-15 -1.5127443E-15 3.1801071E-15

[0185] Sn 6 9 10 KA 8.0624492E-01 -5.0000000E+00 -2.1661296E-00 A3 0.0000000E+00 0.0000000E+00 0.0000000E+00 A4 -6.5038830E-04 -1.5441400E-05 1.3588062E-05 A5 2.3225331E-06 9.9881793E-06 -9.5302818E-06 A6 1.2066133E-05 -1.0920572E-06 3.1868888E-06 A7 9.0379350E-07 -6.6239108E-07 -3.0993196E-07 A8 -4.9440353E-07 1.7672210E-07 -4.6554632E-08 A9 4.1975087E-08 -1.9260761E-08 1.0613657E-08 A10 6.1595738E-11 9.2465983E-10 -5.0068601E-10 A11 -2.2495955E-10 -1.0443664E-11 -3.6709582E-11 A12 1.6495354E-11 1.3311962E-12 3.5684361E-12 A13 1.9257944E-13 -4.3665399E-13 2.2438496E-13 A14 -1.2597486E-13 6.1513858E-14 -2.8184227E-14 A15 8.0431754E-15 -4.0187981E-15 1.7288094E-16 A16 -1.6176541E-16 8.9751290E-17 2.9638000E-17

[0186] Table 21 shows the corresponding values ​​of conditional expressions (1) to (6) for the eyepiece lens 3 of Examples 1 to 5. In the conditional expression (6) column, the symbol of the lens that satisfies conditional expression (6) is indicated by putting parentheses below the corresponding value.

[0187] [Table 21]

[0188]

[0189] As can be seen from the data described above, the field of view of the eyepiece lens 3 in Examples 1 to 5 at half angle is more than 17 degrees, which has a wide field of view and the aberrations are well corrected, thus achieving high optical performance.

[0190] Next, an optical device equipped with the observation optical system 5 according to an embodiment of the present invention will be described. Figure 16 The diagram shows a schematic structural diagram of an optical device, namely a camera 10, according to an embodiment of the present invention. As an example, the camera 10 is a digital camera. The camera 10 includes a camera body 30.

[0191] A lens barrel 20 is detachably mounted on the front surface of the camera body 30. The lens barrel 20 contains an imaging lens 22. The imaging lens 22 actually comprises multiple lenses and an aperture stop, but... Figure 16 The diagram is conceptual. Inside the camera body 30, on the extension of the optical axis Z2 of the imaging lens 22, are arranged the shutter 24 and the imaging element 26.

[0192] Furthermore, a display element 1 and an eyepiece lens 3 are disposed inside the camera body 30. The eyepiece lens 3 actually comprises multiple lenses, but... Figure 16The diagram is conceptual. The display element 1 has a display surface that is substantially perpendicular to the optical axis Z1 of the eyepiece lens 3 on the surface opposite to it. The display element 1 and the eyepiece lens 3 constitute the observation optical system 5 of the present invention. The observation optical system 5, together with the viewing window 34 disposed on the back of the camera body 30, constitutes an electronic viewfinder. The display element 1 and the viewing window 34 are disposed on the extension line of the optical axis Z1, separated by the eyepiece lens 3.

[0193] The display element 1 is configured to be movable via a drive mechanism (not shown) disposed inside the camera body 30. Figure 16 In the middle, the direction parallel to the optical axis Z1 of the eyepiece lens 3 is defined as the Z direction, and the direction parallel to the optical axis Z1 of the eyepiece lens 3 is defined as the Z direction. Figure 16 The direction perpendicular to the paper's surface is defined as the X direction, and the direction perpendicular to both the Z and X directions is defined as the Y direction. For example... Figure 16 As indicated by arrow A, display element 1 can move linearly in a direction parallel to the Z-direction. Furthermore, as... Figure 16 As indicated by arrow B, display element 1 can rotate about an axis passing through the center of display element 1 and parallel to the X direction. For ease of understanding, in Figure 17 In the 3D diagram, arrows A and B are marked to indicate the direction of linear movement and rotational movement of display element 1, respectively. During the linear movement and rotational movement of display element 1, eyepiece lens 3 is also fixed relative to camera body 30. Through the linear movement and / or rotational movement of display element 1, the relative positional relationship between display element 1 and eyepiece lens 3 changes, thereby enabling diopter adjustment.

[0194] The camera body 30 has a diopter adjustment dial 36 for adjusting the diopter by moving the display element 1 linearly and / or rotating it, and a rear LCD panel 32 for displaying images. Furthermore, the camera body 30 has a processor 50 inside for image processing, various arithmetic operations, and control of the various components.

[0195] In camera 10, the image of the subject captured by imaging lens 22 is imaged onto the imaging surface of imaging element 26. Imaging element 26 outputs an image representing the image of the subject to processor 50. Processor 50 performs image processing on the image. The image processed is displayed on rear liquid crystal panel 32 and display element 1.

[0196] Observer 60 observes the image displayed on display element 1 through viewing window 34 and eyepiece lens 3. Observer 60 adjusts the refractive power of display element 1 by linearly moving and / or rotating diopter adjustment dial 36 according to their visual acuity. Thus, observer 60 can observe the image displayed on display element 1 in the best possible condition.

[0197] The camera 10 is configured to not only move the display element 1 linearly along the optical axis Z1, but also rotate about an axis parallel to the X direction. Therefore, for example, even if the observer 60 is not in focus on a portion of the display element 1 in the Y direction when peering through the viewing window 34, the observer 60 can rotate and adjust the display element 1 to make it easier to observe. Furthermore, even when the observer 60 is wearing glasses with different upper and lower refractive powers (such as diopter glasses), the display element 1 can be rotated and adjusted to make it easier to observe.

[0198] The present invention has been described above with examples of embodiments and examples, but the technology of the present invention is not limited to the above embodiments and examples, and various modifications are possible. 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 numerical embodiments, and other values ​​may be used. Furthermore, the optical devices involved in the embodiments of the present invention are not limited to the above examples, and the present invention can also be applied to film cameras, video cameras, and head-mounted displays, etc.

Claims

1. An eyepiece lens, comprising, from the object-observation side to the viewpoint side, a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, and a fourth lens with positive refractive power, in sequence. The first lens, the second lens, the third lens, and the fourth lens are all single lenses. The first lens is a biconvex lens. The second lens is biconcave. The viewpoint side surface of the third lens is convex. The fourth lens is biconvex. When the focal length of the second lens is set to f2, When the focal length of the fourth lens is set to f4, it satisfies the condition that... -0.300≤f2 / f4<-0.2 (2a) The conditional expression (2a) is represented. When the radius of curvature of the surface on the viewpoint side of the second lens is set to R2r, When the radius of curvature of the object-side surface of the third lens is set to R3f, it satisfies the condition... -2.1<(R2r+R3f) / (R2r-R3f)<-0.2 (5) The conditional expression (5) is represented. When the focal length of the first lens is set to f1, the following condition is met: 2.7 < f4 / f1 < 8 (4) The conditional expression (4) is represented.

2. The eyepiece lens according to claim 1, which satisfies the following conditions: 3 < f4 / f1 < 5 (4-1) The conditional expression is (4-1).

3. An eyepiece lens, comprising, from the object side to the viewpoint side, a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, and a fourth lens with positive refractive power, in sequence. The first lens, the second lens, the third lens, and the fourth lens are all single lenses. The first lens is a biconvex lens. The second lens is biconcave. The viewpoint side surface of the third lens is convex. The fourth lens is biconvex. When the focal length of the second lens is set to f2, When the focal length of the fourth lens is set to f4, it satisfies the condition that... -0.300≤f2 / f4<-0.2 (2a) The conditional expression (2a) is represented. When the radius of curvature of the surface on the viewpoint side of the second lens is set to R2r, When the radius of curvature of the object-side surface of the third lens is set to R3f, it satisfies the condition... -1.75<(R2r+R3f) / (R2r-R3f)<-0.6 (5-1) The conditional expression is (5-1).

4. The eyepiece lens according to any one of claims 1 to 3, wherein, When the refractive index along the d-line of the third lens is set to N3, the following condition is met: 1.76＜N3＜2 （1） The conditional expression (1) is represented.

5. The eyepiece lens according to any one of claims 1 to 3, wherein, When the focal length of the eyepiece lens is set to f, When the focal length of the first lens is set to f1, it satisfies the following condition: 1.2 < f / f1 < 3.5 (3) The conditional expression (3) is represented.

6. The eyepiece lens according to any one of claims 1 to 3, wherein, The surface of the fourth lens on the object-side is aspherical.

7. The eyepiece lens according to any one of claims 1 to 3, wherein, The viewpoint side surface of the second lens is aspherical.

8. The eyepiece lens according to any one of claims 1 to 3, wherein, The diopter is adjusted by observing the change in the distance between the object and the eyepiece lens along the optical axis.

9. The eyepiece lens according to claim 4, which satisfies the following condition: 1.8＜N3＜1.9 （1-1） The conditional expression is (1-1).

10. The eyepiece lens according to any one of claims 1 to 3, wherein it satisfies the condition of being composed of... -0.300≤f2 / f4<-0.21 (2-1a) The conditional expression is (2-1a).

11. The eyepiece lens according to claim 5, wherein it satisfies the following conditions: 1.4 < f / f1 < 2.5 (3-1) The conditional expression is (3-1).

12. The eyepiece lens according to any one of claims 1 to 3, wherein, When the refractive index along the d-line of at least one of the first, second, third, and fourth lenses is set to Nx, the following condition is satisfied: 1.76 < Nx < 2 (6) The conditional expression (6) is represented.

13. An observation optical system comprising: Display elements; and The eyepiece lens according to any one of claims 1 to 12, The image of the display element is observed through the eyepiece lens. In the observation optical system, When adjusting the diopter, the eyepiece lens is fixed, and the display element moves by changing the distance between the display element and the eyepiece lens in the optical axis direction.

14. An optical device comprising an eyepiece lens according to any one of claims 1 to 12.

15. An optical device comprising the observation optical system of claim 13.

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