Display optics, display device, and imaging device

Abstract

This invention provides a display optical system with high magnification, long eye relief, and high optical performance. [Solution] The display optical system enables observation of the image displayed on the display element ID. The display optical system has a first lens 1 with positive refractive power, a second lens 2 with positive refractive power, a third lens 3 with negative refractive power, a fourth lens 4 with positive refractive power, and a fifth lens 5 with positive refractive power, arranged in order from the display element side to the observation side. The first, second, third, fourth, and fifth lenses are each single lenses, not cemented lenses. The focal length f1 of the first lens, the focal length f2 of the second lens, and the refractive index nd2 of the second lens at the d line are 1.700 ≤ nd2 and 0.000.

Description

[Technical Field]

[0001] This invention relates to a display optical system used in display devices such as electronic viewfinders and head-mounted displays. [Background technology]

[0002] Display optical systems for observing images displayed on display elements such as liquid crystal panels require a sufficiently wide field of view (high magnification), long eye relief, and good correction of various aberrations. In such display optical systems, it is preferable to use high-refractive index materials for the lenses constituting the display optical system in order to achieve high magnification, but high-refractive index materials are generally expensive.

[0003] Patent Document 1 discloses a display optical system consisting of 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 which the radii of curvature of the second, third, and fourth lenses are appropriately set. Patent Document 2 also proposes a display optical system consisting of a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power, in which the lenses of the first and third lens groups are meniscus-shaped and the total length of the lenses is appropriately set. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-189750 [Patent Document 2] Japanese Patent Publication No. 2018-28632 [Overview of the project] [Problems that the invention aims to solve]

[0005] To achieve high magnification and ensure sufficient eye relief in a display optical system, it is necessary to appropriately set the focal length and refractive index of each lens. However, increasing the refractive power of each lens to achieve high magnification can make the lens shape difficult to manufacture or drastically increase sensitivity. Furthermore, in display optical systems that magnify images formed on small display elements, it is also necessary to appropriately set the arrangement of each lens and the ratio of their refractive powers.

[0006] The present invention provides a display optical system with high magnification, long eye relief, and high optical performance, as well as a display device and imaging device equipped therewith. [Means for solving the problem]

[0007] One aspect of the present invention is a display optical system that enables observation of an image displayed on a display element. The display optical system has a first lens with positive refractive power, a second lens with positive refractive power, a third lens with negative refractive power, a fourth lens with positive refractive power, and a fifth lens with positive refractive power, arranged in order from the display element side to the observation side. The first, second, third, fourth, and fifth lenses are each single lenses, and the third lens is a meniscus lens with its concave surface facing the display element side. When the focal length of the first lens is f1, the focal length of the second lens is f2, and the refractive index of the second lens at the d line is nd2, 1.700 ≤ nd2 0.000 <f2 / f1≦0.790 It is characterized by satisfying the following conditions. Furthermore, an imaging device and a display device having the above-mentioned display optical system also constitute another aspect of the present invention. [Effects of the Invention]

[0008] The present invention can provide a display optical system that has high magnification, long eye relief, and high optical performance. [Brief explanation of the drawing]

[0009] [Figure 1] Cross-sectional view of the display optical system of Example 1. [Figure 2] Aberration diagram of the display optical system in Example 1. [Figure 3] Cross-sectional view of the display optical system of Example 2. [Figure 4] Aberration diagram of the display optical system of Example 2. [Figure 5] Cross-sectional view of the display optical system of Example 3. [Figure 6] Aberration diagram of the display optical system of Example 3. [Figure 7] Cross-sectional view of the display optical system of Example 4. [Figure 8] Aberration diagram of the display optical system of Example 4. [Figure 9] Cross-sectional view of the display optical system of Example 5. [Figure 10] Aberration diagram of the display optical system of Example 5. [Figure 11] Cross-sectional view of the display optical system of Example 6. [Figure 12] Aberration diagram of the display optical system of Example 6. [Figure 13] Cross-sectional view of the display optical system of Example 7. [Figure 14] Aberration diagram of the display optical system of Example 7. [Figure 15] Cross-sectional view of the display optical system of Example 8. [Figure 16] Aberration diagram of the display optical system of Example 8. [Figure 17] Cross-sectional view of the display optical system of Example 9. [Figure 18] Aberration diagram of the display optical system of Example 9. [Figure 19] Cross-sectional view of the display optical system of Example 10. [Figure 20] Aberration diagram of the display optical system of Example 10. [Figure 21] Cross-sectional view of the display optical system of Example 11. [Figure 22] Aberration diagram of the display optical system of Example 11. [Figure 23] Cross-sectional view of the display optical system of Example 12. [Figure 24] Aberration diagram of the display optical system of Example 12. [Figure 25] Diagram showing an imaging device equipped with the display optical systems of Examples 1 to 12. [Figure 26]A diagram showing a display device equipped with the display optical system of Examples 1 to 12. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figures 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, and 23 show the configuration of the display optical system (finder optical system) of Embodiments 1 to 12 at a diopter of -1.0 diopter (standard diopter). Before going into a detailed description of Embodiments 1 to 12, we will first explain matters common to each embodiment.

[0011] The display optical system in each embodiment guides light from the display element ID to the eye point (observation surface or exit pupil) EP on the observation side. In each embodiment, a small display element with a diagonal length of approximately 20 mm or less is used as the display element ID, and the image displayed on the display element ID can be observed with a wide field of view of 30° or more. This display optical system can be used as the optical system of an electronic viewfinder in various imaging devices such as digital still cameras, video cameras, and broadcast cameras, or as the optical system in a display device such as a head-mounted display. The diopter of the display optical system in each embodiment can be adjusted by moving the entire system relative to the display element ID or by moving the display element ID itself.

[0012] To observe the small display element ID described above over a wide field of view, the entire display optical system needs to have strong positive power, which requires each lens to have strong positive or negative refractive power. Furthermore, to ensure sufficient eye relief, the F-number of the display optical system needs to be bright, which requires a wide effective ray range for the eyepiece. As a result, correcting spherical aberration, field curvature, astigmatism, and chromatic aberration becomes difficult, and optical performance may deteriorate, especially at the peripheral image height on the object side.

[0013] Therefore, the display optical system in each embodiment has a first lens 1 with positive refractive power, a second lens 2 with positive refractive power, a third lens 3 with negative refractive power, a fourth lens 4 with positive refractive power, and a fifth lens 5 with positive refractive power, arranged in order from the object side (display element side) to the observation side. The display optical system in Embodiment 12 further has a sixth lens 6 with positive refractive power. Each lens is a single lens that is not joined to any other lens. By setting the optimal refractive power for each lens, a display optical system with high magnification, sufficiently long eye relief, and high optical performance is realized.

[0014] Furthermore, the display optical system in each embodiment satisfies the following conditions: (1) and (2).

[0015] 1.700 ≤ nd2 (1) 0.000 <f2 / f1≦0.790 (2) In equations (1) and (2), nd2 represents the refractive index of the second lens 2 at the d line, f1 represents the focal length of the first lens 1, and f2 represents the focal length of the second lens 2.

[0016] The conditions in equation (1) relate to the refractive index nd2 of the second lens 2. In order to achieve high magnification and long eye relief while effectively correcting various aberrations such as spherical aberration, field curvature, and astigmatism, it is necessary to use high-refractive index materials for the lenses. However, high-refractive index materials are generally expensive, and it is not practical to use them for all lenses. Therefore, it is necessary to construct a display optical system using high-refractive index materials for a minimum number of lenses.

[0017] In a display optical system that magnifies and allows observation of a display image from a small display element, the effective range of the lens generally increases as it moves away from the display element, resulting in a larger lens diameter. As the lens diameter increases, the volume of the lens increases exponentially, which leads to a greater amount of high-refractive-index material being used and makes lens molding more difficult.

[0018] Furthermore, using a high-refractive index material in the second lens 2 rather than the first lens 1 allows for more effective correction of various aberrations. Therefore, by using a high-refractive index material in the second lens 2, it is possible to achieve a display optical system with high magnification and long eye relief while effectively correcting various aberrations. If nd2 falls below the lower limit of equation (1), the curvature of the second lens 2 becomes large, making it difficult to correct various aberrations such as spherical aberration, field curvature, and astigmatism, which is undesirable.

[0019] The conditions in equation (2) relate to the relationship between the focal length f1 of the first lens 1 and the focal length f2 of the second lens 2. These conditions are necessary to achieve both high magnification and correction of field curvature, astigmatism, and distortion. If f2 / f1 exceeds the upper limit of equation (2), it is undesirable because the power of the second lens 2 is weak, resulting in insufficient correction of field curvature, astigmatism, and distortion. If f2 / f1 falls below the lower limit of equation (2), it is undesirable because the power of the first lens 1 is weak, making it difficult to achieve high magnification.

[0020] Furthermore, it is preferable to set the numerical ranges of equations (1) and (2) as follows.

[0021] 1.700 ≤ nd2 ≤ 1.900 (1a) 0.075 ≤ f2 / f1 ≤ 0.790 (2a) Furthermore, it is preferable to set the numerical ranges of equations (1) and (2) as follows.

[0022] 1.720 ≤ nd2 ≤ 1.855 (1b) 0.080 ≤ f2 / f1 ≤ 0.790 (2b) As mentioned earlier, it is preferable that each lens be a single lens. To avoid increasing the size of the display optical system, it is preferable that it be composed of the minimum number of lenses. For this reason, it is necessary to individually optimize the surface shape of each lens to properly correct spherical aberration and lateral aberration, but using cemented lenses is undesirable because it reduces the actual number of lens surfaces, making aberration correction difficult.

[0023] The display optical system in each embodiment preferably satisfies at least one of the following conditions (3) to (12).

[0024] -2.00 ≤ f2 / f3 ≤ -0.80 (3) -2.00 ≤ f3 / f ≤ -0.40 (4) 0.50 ≤ f² / f ≤ 2.00 (5) 0.80 ≤ f₄ / f ≤ 5.00 (6) 1.50 ≤ f5 / f ≤ 5.00 (7) -1.00≦(R22+R21) / (R22-R21)<0.00 (8) 0.50≦(R32+R31) / (R32-R31)≦3.00 (9) 1.10 ≤ TL / f ≤ 1.90 (10) 0.10 ≤ Db / f ≤ 0.50 (11) 0.32 ≤ H / f ≤ 0.50 (12) In equations (3) to (12), f3 is the focal length of the third lens 3, f4 is the focal length of the fourth lens 4, and f5 is the focal length of the fifth lens 5. Also, R21 is the radius of curvature of the object-side lens surface of the second lens 2, R22 is the radius of curvature of the observation-side lens surface of the second lens 2, R31 is the radius of curvature of the object-side lens surface of the third lens 3, and R32 is the radius of curvature of the observation-side lens surface of the third lens 3. Furthermore, TL is the distance along the optical axis from the lens surface closest to the object in the display optical system (the object-side lens surface of the first lens 1) to the lens surface closest to the observation in the display optical system. Db is the distance along the optical axis from the display surface of the display element ID as the object surface to the lens surface closest to the object in the display optical system, and H is half the diagonal length of the display surface of the display element ID.

[0025] The conditions in equation (3) relate to the relationship between the focal length f2 of the second lens 2 and the focal length f3 of the third lens 3. These conditions are necessary to effectively correct aberrations such as field curvature, astigmatism, and lateral aberration, and to achieve high magnification and long eye relief. If f2 / f3 exceeds the upper limit of equation (3), the negative power of the third lens 3 weakens, increasing the Petzval sum of the display optical system and making it difficult to correct aberrations such as field curvature and astigmatism, which is undesirable. If f2 / f3 falls below the lower limit of equation (3), the power of the second lens 2 is insufficient, making it difficult to correct lateral aberration, which is also undesirable.

[0026] The conditions in equation (4) relate to the relationship between the focal length f3 of the third lens 3 and the focal length f of the entire display optical system. These conditions are necessary to effectively correct aberrations such as field curvature and astigmatism, and to achieve high magnification and long eye relief. If f3 / f exceeds the upper limit of equation (4), the negative power of the third lens 3 weakens, increasing the Petzval sum of the display optical system and making it difficult to correct aberrations such as field curvature and astigmatism, which is undesirable. If f3 / f falls below the lower limit of equation (4), the power of the third lens 3 becomes too strong, resulting in insufficient positive power for the entire display optical system and making it difficult to achieve high magnification, which is also undesirable.

[0027] The conditions in equation (5) relate to the relationship between the focal length f2 of the second lens 2 and the focal length f of the entire display optical system. These conditions are necessary to achieve both high magnification and correction of aberrations such as field curvature, astigmatism, and lateral aberration. If f2 / f exceeds the upper limit of equation (5), the positive power of the entire display optical system becomes insufficient, making high magnification difficult, which is undesirable. If f2 / f falls below the lower limit of equation (5), the power of the second lens 2 becomes too strong, increasing aberrations such as field curvature, astigmatism, and lateral aberration, which is also undesirable.

[0028] The conditions in equation (6) relate to the relationship between the focal length f4 of the fourth lens 4 and the focal length f of the entire display optical system. These conditions are necessary to balance the sensitivity of the display optical system with the correction of aberrations such as field curvature and astigmatism. If f4 / f exceeds the upper limit of equation (6), the sensitivity of the display optical system increases, making manufacturing more difficult, which is undesirable. If f4 / f falls below the lower limit of equation (6), aberrations such as field curvature and astigmatism increase, which is also undesirable.

[0029] The conditions in equation (7) concern the relationship between the focal length f5 of the fifth lens 5 and the focal length f of the entire display optical system. These conditions are necessary to achieve both the sensitivity of the display optical system and the correction of lateral aberration. If f5 / f exceeds the upper limit of equation (7), the correction of lateral aberration will be insufficient, which is undesirable. If f5 / f falls below the lower limit of equation (7), the sensitivity of the display optical system will become too high, which is also undesirable.

[0030] Equation (8) is a condition relating to the shape of the lens surface of the second lens 2, and is a condition for achieving both high magnification of the display optical system and correction of aberrations such as field curvature and astigmatism. If (R22+R21) / (R22-R21) exceeds the upper limit of equation (8), it becomes difficult to correct aberrations such as field curvature and astigmatism, which is undesirable. If (R22+R21) / (R22-R21) falls below the lower limit of equation (8), it becomes difficult to increase the magnification of the display optical system, which is also undesirable.

[0031] The conditions in equation (9) relate to the shape of the lens surface of the third lens 3, and are necessary to achieve both high magnification of the display optical system and correction of aberrations such as field curvature, astigmatism, and distortion. If (R32+R31) / (R32-R31) exceeds the upper limit of equation (9), it becomes difficult to correct aberrations such as field curvature and astigmatism, which is undesirable. If (R32+R31) / (R32-R31) falls below the lower limit of equation (9), it becomes difficult to correct distortion, which is also undesirable.

[0032] The conditions in equation (10) relate to the relationship between the overall thickness TL of the display optical system and the overall focal length f of the display optical system. These conditions are necessary to achieve both high magnification of the display optical system and correction of aberrations such as spherical aberration and lateral aberration. If TL / f exceeds the upper limit of equation (10), the thickness of the display optical system becomes too large, making high magnification difficult, which is undesirable. If TL / f falls below the lower limit of equation (10), it becomes impossible to set an appropriate curvature for each lens, making correction of aberrations such as spherical aberration and lateral aberration difficult, which is also undesirable.

[0033] The conditions in equation (11) relate to the relationship between the distance Db from the object plane to the lens surface closest to the object at the standard diopter of the display optical system and the focal length f of the entire display optical system. These conditions are for controlling the difficulty of manufacturing the display optical system while effectively correcting field curvature and astigmatism. Diopter adjustment can be performed by moving the display optical system relative to the display surface of the display element ID so as to change the distance Db. If Db / f exceeds the upper limit of equation (11), it is undesirable because Db is too long, making it impossible to effectively correct field curvature and astigmatism. If Db / f falls below the lower limit of equation (11), it is undesirable because the first lens 1 may come into contact with the display element ID when adjusting the diopter of the display optical system or when dropping the imaging device or display device.

[0034] The conditions in equation (12) relate to the relationship between H, half the diagonal length of the display surface of the display element ID, and f, the focal length of the display optical system. These conditions are necessary to achieve both a wide field of view and correction of various aberrations such as spherical aberration, field curvature, and astigmatism. If H / f exceeds the upper limit of equation (12), the magnification of the display optical system becomes excessively large, making it difficult to correct various aberrations such as spherical aberration, field curvature, and astigmatism, which is undesirable. If H / f falls below the lower limit of equation (12), it becomes difficult to achieve a wide field of view, which is also undesirable.

[0035] Furthermore, it is preferable to set the numerical ranges for equations (3) to (12) as follows.

[0036] -1.70 ≤ f2 / f3 ≤ -0.90 (3a) -1.50 ≤ f3 / f ≤ -0.45 (4a) 0.60 ≤ f² / f ≤ 1.50 (5a) 0.80 ≤ f₄ / f ≤ 3.00 (6a) 1.80 ≤ f5 / f ≤ 4.00 (7a) -1.50≦(R22+R21) / (R22-R21)≦-0.45 (8a) 0.70≦(R32+R31) / (R32-R31)≦2.50 (9a) 1.20 ≤ TL / f ≤ 1.80 (10a) 0.15 ≤ Db / f ≤ 0.40 (11a) 0.34 ≤ H / f ≤ 0.50 (12a) Furthermore, it is even preferable to set the numerical ranges of equations (3) to (12) as follows.

[0037] -1.60 ≤ f2 / f3 ≤ -1.00 (3b) -1.20 ≤ f3 / f ≤ -0.50 (4b) 0.70 ≤ f² / f ≤ 1.30 (5b) 0.90 ≤ f₄ / f ≤ 2.70 (6b) 2.00 ≤ f5 / f ≤ 3.50 (7b) -1.20≦(R22+R21) / (R22-R21)≦-0.50 (8b) 0.80≦(R32+R31) / (R32-R31)≦1.90 (9b) 1.25 ≤ TL / f ≤ 1.70 (10b) 0.15 ≤ Db / f ≤ 0.35 (11b) 0.34 ≤ H / f ≤ 0.45 (12b) Furthermore, it is preferable that the second lens 2 is a biconvex lens. Since the second lens 2 is the lens that requires the strongest power in the display optical system, making it a biconvex lens allows the power to be distributed to both sides, thereby reducing sensitivity.

[0038] Furthermore, it is preferable that the third lens 3 is a meniscus lens with its concave surface facing the object. This is because if the observation-side surface of the third lens 3 is concave, the difference in thickness between the center and periphery of the third lens 3 becomes too large, making it difficult to manufacture the third lens 3.

[0039] Furthermore, it is preferable that the fifth lens 5 is a meniscus lens with its convex surface facing the observation side. This is because using a meniscus lens for the fifth lens 5 can reduce sensitivity. If the fifth lens 5 is a biconvex lens, sensitivity increases, which makes it more difficult to manufacture the display optical system, and is therefore undesirable.

[0040] Furthermore, it is preferable that the curved shape of the object-side lens surface of the first lens 1 has an inflection point (inflection curve). An inflection point is the point where the convex shape switches to a concave shape, that is, the sign of the curvature changes. This is because, as a display optical system, a relatively strong positive power is required at the image height near the center, while having less power at the image height in the peripheral area allows for better correction of various aberrations such as field curvature.

[0041] Next, as a detailed explanation of Examples 1 to 12, Tables 1 to 12 show the numerical values ​​corresponding to each of Examples 1 to 12.

[0042] In each numerical example, the focal length f (mm) is the focal length of the entire display optical system, and the display diagonal length (mm) is the diagonal length (2H) of the display surface of the display element ID. ω is the half-angle of view (°) of the display optical system, and 2ω is the full angle of view (field of view) (°). The surface number i indicates the order of the surfaces when counted from the object side. The first surface is the display surface of the display element ID, and the second surface is the observation side surface of the cover glass of the display element ID. r is the radius of curvature (mm) of each surface, d is the lens thickness or distance (air gap) (mm) on the optical axis between the i-th surface and the (i+1)-th surface, and nd is the refractive index at the d-line of the material of the optical component having each surface. νd is the Abbe number based on the d-line of the material of the optical component having each surface. The Abbe number νd is given by Nd, NF, and NC, respectively, when the refractive indices at the Fraunhofer lines d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the material are Nd, NF, and NC. νd = (Nd - 1) / (NF - NC) It is represented by

[0043] The "*" attached to the surface number means that the surface has an aspherical shape. The aspherical shape is represented by the following formula when x is the displacement amount from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction orthogonal to the optical axis, the light traveling direction is positive, r is the paraxial curvature radius, K is the conic constant, and A4, A6, A8, A10, A12 are the aspherical coefficients. "E±M" of the conic constant and the aspherical coefficients means ×10 means

[0044] x = (h 2 / r) / [1 + {1 - (1 + K)(h / r) 2} 1 / 2 + A4×h 4 + A6×h 6 + A8×h 8 + A10×h 10 + A...×h 12 In addition, each numerical example shows the visibility adjusted by moving the entire display optical system with respect to the display element ID or moving the display element ID itself to change the distance between the second surface and the third surface (the object-side lens surface of the first lens 1), and the focal length of each lens.

[0045] The values corresponding to the above-mentioned conditional expressions (1) to (12) in Numerical Examples 1 to 12 are summarized and shown in Table 13.

[0046] Figures 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24 respectively show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) at the standard visibility of the display optical systems of Numerical Examples 1 to 12. In the spherical aberration figure, the solid line indicates the spherical aberration for the d line, and the two-dot chain line indicates the spherical aberration for the F line. In the astigmatism figure, the solid line S indicates the sagittal image plane, and the broken line M indicates the meridional image plane. The distortion figure shows the distortion at the d line. The chromatic aberration figure shows the longitudinal chromatic aberration at the F line.

[0047] Table 1

[0048] Table 2

[0049] Table 3

[0050] Table 4

[0051] Table 5

[0052] Table 6

[0053] Table 7

[0054] Table 8

[0055] Table 9

[0056] Table 10

[0057] Table 11

[0058] [Table 12]

[0059] [Table 13]

[0060] [Imaging device] Figure 25 shows imaging devices such as digital cameras and video cameras that use the display optical system of each embodiment as a viewfinder optical system. The subject image formed by the imaging optical system 101 is converted into an electrical signal by the image sensor 102, which is a photoelectric conversion element. As a result, the image sensor 102 captures the subject via the imaging optical system 101. A CCD sensor or a CMOS sensor can be used as the image sensor 102.

[0061] The output signal from the image sensor 102 is processed by the image processing circuit 103 to generate an image. The generated image is recorded on a recording medium 104 such as a semiconductor memory, magnetic tape, or optical disc. The image generated by the image processing circuit 103 is also displayed on the display element 1051 (ID) in the electronic viewfinder unit 105. The display element 1051 is composed of liquid crystal display elements (LCD) or organic EL elements, etc.

[0062] The electronic viewfinder unit 105 is provided with the viewfinder optical system 1052 of each embodiment. The observer 106 can observe the image displayed on the display element 1051 through the viewfinder optical system 1052.

[0063] By using the display optical system of each embodiment as a viewfinder optical system, an imaging device can be obtained that has an electronic viewfinder unit 105 that is compact, has a wide field of view, and can perform good image observation.

[0064] [Display device] Figure 26 shows a head-mounted display (HMD) as an image display device using the display optical system of each embodiment. The HMD is mounted on the observer's head (in front of the eyes) by mounting gear (not shown).

[0065] The HMD comprises display elements RID and LID for the right and left eyes, a right-eye display optical system ROS that allows the viewer's right eye to observe the image displayed on the right-eye display element RID, and a left-eye display optical system LOS that allows the viewer's left eye to observe the image displayed on the left-eye display element LID. Each display element displays an image input from an external computer or other device.

[0066] By using the display optical systems of each embodiment as the right-eye and left-eye display optical systems ROS and LOS, it is possible to realize a compact HMD that allows for good image observation with a wide field of view. The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of symbols]

[0067] 1. First lens 2. Second lens 3. Third lens 4. Fourth lens 5. Fifth lens ID display element EP Eye Point

Claims

1. A display optical system that enables observation of an image displayed on a display element, Arranged in order from the display element side to the observation side, The first lens has positive refractive power, A second lens with positive refractive power, A third lens with negative refractive power, A fourth lens with positive refractive power, It has a fifth lens with positive refractive power, The first, second, third, fourth, and fifth lenses are each single lenses. The third lens is a meniscus lens with its concave surface facing the display element. When the focal length of the first lens is f1, the focal length of the second lens is f2, and the refractive index of the second lens at the d line is nd2, 1.700 ≤ nd² 0.000<f2 / f1≦0.790 A display optical system characterized by satisfying the following conditions.

2. When the focal length of the third lens is f3, -2.00 ≤ f² / f³ ≤ -0.80 The display optical system according to claim 1, characterized in that it satisfies the following conditions.

3. When the focal length of the third lens is f3 and the focal length of the display optical system is f, -2.00 ≤ f³ / f ≤ -0.40 The display optical system according to claim 1 or 2, characterized in that it satisfies the following conditions.

4. When the focal length of the display optical system is f, 0.50 ≤ f² / f ≤ 2.00 A display optical system according to any one of claims 1 to 3, characterized in that it satisfies the following conditions.

5. When the focal length of the fourth lens is f4 and the focal length of the display optical system is f, 0.80 ≤ f₄ / f ≤ 5.00 A display optical system according to any one of claims 1 to 4, characterized in that it satisfies the following conditions.

6. When the focal length of the fifth lens is f5 and the focal length of the display optical system is f, 1.50 ≤ f5 / f ≤ 5.00 A display optical system according to any one of claims 1 to 5, characterized in that it satisfies the following conditions.

7. When the radius of curvature of the lens surface on the display element side of the second lens is R21, and the radius of curvature of the lens surface on the observation side of the second lens is R22, -1.00≦(R22+R21) / (R22-R21)<0.00 A display optical system according to any one of claims 1 to 6, characterized in that it satisfies the following conditions.

8. When the radius of curvature of the lens surface on the display element side of the third lens is R31, and the radius of curvature of the lens surface on the observation side of the third lens is R32, 0.50≦(R32+R31) / (R32-R31)≦3.00 A display optical system according to any one of claims 1 to 7, characterized in that it satisfies the following conditions.

9. The display optical system according to any one of claims 1 to 8, characterized in that the second lens is a biconvex lens.

10. The display optical system according to any one of claims 1 to 9, characterized in that the fifth lens is a meniscus lens with a convex surface facing the observation side.

11. The display optical system according to any one of claims 1 to 10, characterized in that the lens surface of the first lens on the display element side is a curved surface having an inflection point.

12. When TL is the distance along the optical axis from the lens surface closest to the display element of the display optical system to the lens surface closest to the observation side of the display optical system, and f is the focal length of the display optical system, 1.10 ≤ TL / f ≤ 1.90 A display optical system according to any one of claims 1 to 11, characterized in that it satisfies the following conditions.

13. When Db is the distance along the optical axis from the display surface of the display element to the lens surface of the display optical system closest to the display element, and f is the focal length of the display optical system, 0.10 ≤ Db / f ≤ 0.50 A display optical system according to any one of claims 1 to 12, characterized in that it satisfies the following conditions.

14. The display optical system according to claim 13, characterized in that diopter adjustment is performed by moving the display optical system relative to the display surface so as to change the distance Db.

15. When H is half the diagonal length of the display surface of the display element, and f is the focal length of the display optical system, 0.32 ≤ H / f ≤ 0.50 A display optical system according to any one of claims 1 to 14, characterized in that it satisfies the following conditions.

16. An image sensor that captures an image of a subject via an imaging optical system, A display element that displays an image generated using the signal from the image sensor, An imaging apparatus characterized by having a display optical system according to any one of claims 1 to 15.

17. The display element that displays the input image, A display device characterized by having a display optical system according to any one of claims 1 to 15.

Images