Observation device and imaging device having the same

Abstract

To provide an observation device having a viewfinder optical system which has a high magnification and a long eye relief and offers superior optical performance.SOLUTION: An observation device is provided, comprising an image display element 1 for displaying an image and a viewfinder optical system L0 for observing the image displayed on an image display surface of the image display element, the viewfinder optical system comprising a first lens L1 having positive refractive power, a second lens L2 having negative refractive power, and a third lens L3 having positive refractive power arranged in order from the image display surface side to the observation side. A refractive index nd1 of the first lens for the d-ray, a refractive index nd2 of the second lens for the d-ray, a focal length f of the viewfinder optical system, an air-equivalent length d12 of an optical axial distance from the image display surface to an image display surface-side surface of the first lens at standard diopter, a focal length f1 of the first lens, and a half a diagonal length H of the image display surface satisfy given conditional expressions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an observation device and an imaging device having the same, which is suitable for observing images displayed on an image display element in an electronic viewfinder used in, for example, a video camera, a still camera, or a broadcast camera. [Background technology]

[0002] Conventionally, observation devices equipped with a viewfinder optical system using multiple lenses have been known for observing images displayed on an image display element such as a liquid crystal panel. To improve visibility, these viewfinder optical systems are required to have a sufficiently large field of view (high magnification), a long eye relief, and good correction of various aberrations.

[0003] Furthermore, with the recent trend toward miniaturization of products with observation devices, such as cameras, it is desirable to satisfy these demands using a relatively small image display element with a diagonal length of 20 mm or less as a finder optical system.

[0004] Known high-magnification viewfinder optical systems are composed of three or more lenses, including a lens with positive refractive power, a lens with negative refractive power, and a lens with positive refractive power, arranged from the image display surface side (object side) toward the observation side.

[0005] It is also known that high-refractive-index materials can be used in the lenses to achieve high magnification in viewfinder optical systems, but high-refractive-index materials are generally expensive, so in order to keep the sales price of the product down, it is necessary to properly consider the lens arrangement and materials.

[0006] Patent Document 1 proposes a finder optical system that consists 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, with the focal lengths of the third and fourth lenses being set appropriately.

[0007] Furthermore, Patent Document 2 proposes a finder optical system that includes a lens with positive refractive power and two lenses with negative refractive power, at least one of which is a Fresnel lens. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-124349 [Patent Document 2] Japanese Patent Publication No. 2020-27113 Summary of the Invention [Problem to be solved by the invention]

[0009] To ensure high magnification and long eye relief in a viewfinder optical system, it is necessary to appropriately set the focal length and refractive index of each lens. Furthermore, in viewfinder optical systems that use a small image display device for magnified viewing, it is also necessary to appropriately set the arrangement of each lens and the ratio of their refractive powers.

[0010] Furthermore, increasing the magnification of a viewfinder optical system means shortening the focal length of the viewfinder optical system. In an optical system with a short focal length, the object-side principal point must be brought closer to the image display surface, and therefore optical performance can generally be improved by making the distance from the image display element to the viewfinder optical system relatively short. Therefore, in order to achieve a viewfinder optical system with high magnification, long eye relief, and good correction of various aberrations, it is important to appropriately set the distance from the image display element to the viewfinder optical system.

[0011] In the finder optical systems disclosed in Patent Documents 1 and 2, the eye relief is not necessarily sufficient, and various aberrations remain to some extent.

[0012] An object of the present invention is to provide an observation device having a finder optical system with high magnification, long eye relief, and high optical performance. [Means for solving the problem]

[0013] An observation device according to one aspect of the present invention is an observation device having an image display element that displays an image, and a finder optical system for observing an image displayed on an image display surface of the image display element, wherein the finder optical system has, arranged in this order from the image display surface side to the observation side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power; the finder optical system is composed of three or four lenses, The first lens Materials The refractive index at the d-line is nd1, and the refractive index of the second lens is Materials Let nd2 be the refractive index at the d-line, f be the focal length of the viewfinder optical system, d12 be the air-equivalent length on the optical axis from the image display surface to the lens surface of the first lens on the image display surface side at standard diopter, f1 be the focal length of the first lens, and H be half the diagonal length of the image display surface. 1.700≦nd1 nd2≦1.700 0.10 <d12 / f<0.37 0.20 <f1 / f<0.83 0.3 686 ≦H / f≦0.60 00 The present invention is characterized in that the following conditional expression is satisfied:

[0014] Other objects and features of the present invention will be described in the following embodiments. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an observation device having a finder optical system with high magnification, long eye relief, and high optical performance. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view of a lens of a finder optical system in the observation device of Example 1. FIG. [Figure 2] 3A to 3C are diagrams showing various aberrations in the finder optical system of the observation device of Example 1. [Figure 3] FIG. 10 is a cross-sectional view of the lenses of a finder optical system in the observation device of Example 2. [Figure 4] 10A to 10C are diagrams showing various aberrations in the finder optical system of the observation device of Example 2. [Figure 5] FIG. 10 is a cross-sectional view of the lenses of a finder optical system in the observation device of Example 3. [Figure 6] 10A to 10C are diagrams showing various aberrations in the finder optical system of the observation device of Example 3. [Figure 7] FIG. 10 is a cross-sectional view of the lenses of a finder optical system in the observation device of Example 4. [Figure 8] 10A to 10C are diagrams showing various aberrations in the finder optical system of the observation device of Example 4. [Figure 9] FIG. 10 is a cross-sectional view of the lenses of a finder optical system in the observation device of Example 5. [Figure 10] 10A to 10C are diagrams showing various aberrations in the finder optical system of the observation device of Example 5. [Figure 11] FIG. 13 is a cross-sectional view of the lenses of a finder optical system in the observation device of Example 6. [Figure 12] 13A to 13C are diagrams showing various aberrations in the finder optical system of the observation device of Example 6. [Figure 13] FIG. 13 is a cross-sectional view of the lenses of a finder optical system in the observation device of Example 7. [Figure 14] 13A to 13C are diagrams showing various aberrations in the finder optical system of the observation device of Example 7. [Figure 15] FIG. 13 is a cross-sectional view of the lenses of a finder optical system in the observation device of Example 8. [Figure 16] 13A to 13C are diagrams showing various aberrations in the finder optical system of the observation device of Example 8. [Figure 17] FIG. 13 is a cross-sectional view of the lenses of a finder optical system in the observation device of Example 9. [Figure 18] 13A to 13C are diagrams showing various aberrations in the finder optical system of the observation device of Example 9. [Figure 19] FIG. 23 is a cross-sectional view of the lenses of the finder optical system of the observation device of Example 10. [Figure 20]16A to 16C are diagrams showing various aberrations in the finder optical system of the observation device of Example 10. [Figure 21] FIG. 20 is a cross-sectional view of the lenses of the finder optical system of the observation device of Example 11. [Figure 22] 16A to 16C are diagrams showing various aberrations in the finder optical system of the observation device of Example 11. [Figure 23] FIG. 23 is a cross-sectional view of the lenses of the finder optical system of the observation device of Example 12. [Figure 24] 16A to 16C are diagrams showing various aberrations in the finder optical system of the observation device of Example 12. [Figure 25] 1 is a schematic diagram illustrating a main part of an imaging device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The viewfinder optical system provided in the observation device according to each embodiment will be described below with reference to the accompanying drawings. The observation device of the present invention has an image display element that displays an image, and a viewfinder optical system for observing the image displayed on the image display surface of the image display element.

[0018] Fig. 1 is a lens cross-sectional view of the finder optical system of Example 1 at a diopter of -1.0 diopter (standard diopter), and Fig. 2 is an aberration diagram of the finder optical system of Example 1 at a diopter of -1.0 diopter.

[0019] Fig. 3 is a lens cross-sectional view of the finder optical system of Example 2 at a diopter of -1.0 diopter (standard diopter), and Fig. 4 is an aberration diagram of the finder optical system of Example 2 at a diopter of -1.0 diopter.

[0020] Fig. 5 is a lens cross-sectional view of the finder optical system of Example 3 at a diopter of -1.0 diopter (standard diopter), and Fig. 6 is an aberration diagram of the finder optical system of Example 3 at a diopter of -1.0 diopter.

[0021] Fig. 7 is a lens cross-sectional view of the finder optical system of Example 4 at a diopter of -1.0 diopter (standard diopter), and Fig. 8 is an aberration diagram of the finder optical system of Example 4 at a diopter of -1.0 diopter.

[0022] Fig. 9 is a lens cross-sectional view of the finder optical system of Example 5 at a diopter of -1.0 diopter (standard diopter), and Fig. 10 is an aberration diagram of the finder optical system of Example 5 at a diopter of -1.0 diopter.

[0023] Fig. 11 is a lens cross-sectional view of the finder optical system of Example 6 at a diopter of -1.0 diopter (standard diopter), and Fig. 12 is an aberration diagram of the finder optical system of Example 6 at a diopter of -1.0 diopter.

[0024] Fig. 13 is a lens cross-sectional view of the finder optical system of Example 7 at a diopter of -1.0 diopter (standard diopter), and Fig. 14 is an aberration diagram of the finder optical system of Example 7 at a diopter of -1.0 diopter.

[0025] Fig. 15 is a lens cross-sectional view of the finder optical system of Example 8 at a diopter of -1.0 diopter (standard diopter), and Fig. 16 is an aberration diagram of the finder optical system of Example 8 at a diopter of -1.0 diopter.

[0026] Fig. 17 is a lens cross-sectional view of the finder optical system of Example 9 at a diopter of -1.0 diopter (standard diopter), and Fig. 18 is an aberration diagram of the finder optical system of Example 9 at a diopter of -1.0 diopter.

[0027] Fig. 19 is a lens cross-sectional view of the finder optical system of Example 10 at a diopter of -1.0 diopter (standard diopter), and Fig. 20 is an aberration diagram of the finder optical system of Example 10 at a diopter of -1.0 diopter.

[0028] Fig. 21 is a lens cross-sectional view of the finder optical system of Example 11 at a diopter of -1.0 diopter (standard diopter), and Fig. 22 is an aberration diagram of the finder optical system of Example 11 at a diopter of -1.0 diopter.

[0029] Fig. 23 is a lens cross-sectional view of the finder optical system of Example 12 at a diopter of -1.0 diopter (standard diopter), and Fig. 24 is an aberration diagram of the finder optical system of Example 12 at a diopter of -1.0 diopter.

[0030] The finder optical system of each embodiment is used in an observation device such as an electronic viewfinder of an imaging device such as a digital camera or video camera. In each lens cross-sectional view, the left side is the image display surface side (object side) and the right side is the observation side (exit pupil side). In each lens cross-sectional view, L0 is the finder optical system. Li is the ith lens. IP is the image display surface of an image display element 1 made of liquid crystal, organic EL, or the like. 10 is a protective member such as a cover glass for the finder optical system, and EP is the observation surface (eye point) for observation. The eye point EP may be moved in the optical axis direction as long as light rays from the outermost periphery of the image display surface pass through the observer's pupil. The distance from the final lens surface to the eye point is called the eye relief.

[0031] In each aberration diagram, the spherical aberration diagram shows spherical aberration for the d-line (wavelength 587.56 nm). In the astigmatism diagram, S shows the curvature of field for the d-line at the sagittal image plane, and M shows the curvature of field for the d-line at the meridional image plane. The distortion diagram shows the d-line. The chromatic aberration diagram shows chromatic aberration for the F-line (wavelength 486.13 nm), c-line (wavelength 656.27 nm), and g-line (wavelength 435.84 nm) when the d-line (wavelength 587.56 nm) is used as the reference.

[0032] To observe a small display panel with a diagonal length of approximately 20 mm or less over a wide field of view of 30 degrees or more, the viewfinder optical system L0 needs to have a strong positive refractive power. As a result, each lens needs to have either a strong positive or a strong negative refractive power. Furthermore, to increase the eye relief, the viewfinder optical system L0 needs to have a bright F-number. This requires a wide effective light beam range for the eyepiece. As a result, it becomes difficult to correct spherical aberration, field curvature, astigmatism, and chromatic aberration, leading to a degradation of optical performance, especially at the peripheral image height on the object side.

[0033] Therefore, the viewfinder optical system L0 in the observation device of each embodiment has, arranged in order from the image display surface to the observation side, a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, and a third lens L3 with positive refractive power, and has an optimal power arrangement. This realizes a viewfinder optical system L0 with high magnification, long eye relief, and high optical performance. Note that the viewfinder optical system L0 may also have a fourth lens L4 with positive or negative refractive power arranged on the observation side of the third lens L3.

[0034] Specifically, the observation device of each embodiment satisfies the following conditional expressions (1) to (5).

[0035] 1.700≦nd1 (1) nd2≦1.700 (2) 0.10 <d12 / f<0.37 ···(3) 0.20 <f1 / f<0.83 ···(4) 0.33≦H / f≦0.60 (5) Here, nd1 represents the refractive index of the first lens L1 at the d-line. nd2 represents the refractive index of the second lens L2 at the d-line. f represents the focal length of the viewfinder optical system L0. d12 represents the air-equivalent distance on the optical axis from the image display surface IP to the lens surface of the first lens L1 on the image display surface side. f1 represents the focal length of the first lens L1. H represents half the diagonal length of the image display surface IP.

[0036] Next, the technical meanings of conditional expressions (1) to (5) will be explained.

[0037] Conditional formula (1) specifies the refractive index of the first lens L1 of the viewfinder optical system L0. To achieve high magnification and long eye relief while adequately correcting various aberrations, such as spherical aberration, field curvature, and astigmatism, it is necessary to use a high-refractive-index material for the lenses. However, high-refractive-index materials are generally very expensive, making it impractical to use high-refractive-index materials for all lenses. Therefore, it is necessary to construct the viewfinder optical system using a minimum amount of high-refractive-index material. Viewfinder optical systems used to magnify and view a small display panel generally increase in diameter because the effective range of the lens's light beam increases with increasing distance from the display panel. However, increasing the diameter of the lens exponentially increases the volume of the lens itself, and the number of molding machines that can be used is limited, significantly increasing costs. Therefore, using a high-refractive-index material for the first lens L1 allows for adequate correction of various aberrations while achieving a high-magnification, long-eye relief viewfinder optical system at relatively low cost. If the lower limit of conditional expression (1) is not reached, the curvature of the first lens L1 becomes too steep, making it difficult to correct various aberrations such as spherical aberration, curvature of field, and astigmatism, which is undesirable.

[0038] It is also preferable that the numerical range of conditional expression (1) be set to the range of the following conditional expression (1a).

[0039] 1.700≦nd1<1.900 (1a) It is more preferable that the numerical range of conditional expression (1) be set to the following conditional expression (1b).

[0040] 1.720 <nd1<1.855 ···(1b) Conditional formula (2) specifies the refractive index of the second lens L2 in the viewfinder optical system L0. As mentioned above, using a high refractive index material in the viewfinder optical system L0 leads to higher costs. Exceeding the upper limit of conditional formula (2) is undesirable because it increases the cost of the viewfinder optical system L0. Furthermore, while the second lens L2 has negative refractive power, the viewfinder optical system L0 as a whole has a strong positive refractive power. Therefore, unless the refractive index of the lens with negative refractive power is reduced, it becomes difficult to correct the Petzval sum. Therefore, exceeding the upper limit of conditional formula (2) is undesirable because it also leads to worsening of field curvature and astigmatism.

[0041] It is also preferable that the numerical range of conditional expression (2) be set to the range of the following conditional expression (2a).

[0042] 1.580 <nd2<1.700 ···(2a) It is more preferable that the numerical range of conditional expression (2) be set to the following conditional expression (2b).

[0043] 1.620 <nd2<1.700 ···(2b) Conditional formula (3) defines the distance on the optical axis from the image display surface IP to the lens surface of the first lens L1 on the image display surface side at standard diopter. Increasing the magnification of the viewfinder optical system L0 means shortening the focal length of the viewfinder optical system L0. In this case, the principal point of the viewfinder optical system L0 must be closer to the image display surface IP, and it is important to shorten the distance from the image display surface IP to the first lens L1 of the viewfinder optical system L0. Exceeding the upper limit of conditional formula (3) undesirably increases the distance from the image display surface IP to the first lens L1 of the viewfinder optical system L0, resulting in worsening of field curvature, distortion, and lateral aberration. Exceeding the lower limit of conditional formula (3) undesirably makes it impossible to ensure the diopter adjustment range of the viewfinder optical system L0 and makes it difficult to hold the first lens L1 of the viewfinder optical system L0.

[0044] It is also preferable that the numerical range of conditional expression (3) is within the range of conditional expression (3a).

[0045] 0.12 <d12 / f<0.37 ···(3a) It is more preferable that the numerical range of conditional expression (3) be set within the range of the following conditional expression (3b).

[0046] 0.15 <d12 / f<0.37 ···(3b) Conditional expression (4) defines the ratio of the focal length of the viewfinder optical system L0 to the focal length of the first lens L1, and is a conditional expression for achieving both high magnification of the viewfinder optical system L0 and correction of various aberrations such as spherical aberration, curvature of field, and astigmatism. Exceeding the upper limit of conditional expression (4) is undesirable because the power of the first lens L1 becomes weak and correction of spherical aberration, curvature of field, astigmatism, and other aberrations becomes insufficient. Falling below the lower limit of conditional expression (4) is undesirable because the power of the first lens L1 becomes too strong, increasing sensitivity and making it more likely that the performance of the viewfinder optical system L0 will deteriorate.

[0047] It is also preferable that the numerical range of conditional expression (4) be set to the following conditional expression (4a).

[0048] 0.40 <f1 / f<0.82 ···(4a) It is more preferable that the numerical range of conditional expression (4) be set within the range of the following conditional expression (4b).

[0049] 0.45 <f1 / f<0.82 ···(4b) Conditional formula (5) defines the relationship between half the diagonal length of the image display surface IP and the focal length of the viewfinder optical system L0, and is a conditional formula for achieving both a wide angle of view and various aberrations such as spherical aberration, curvature of field, and astigmatism. Exceeding the upper limit of conditional formula (5) is undesirable because the magnification of the viewfinder optical system L0 becomes excessively large, making it difficult to correct various aberrations such as spherical aberration, curvature of field, and astigmatism. Falling below the lower limit of conditional formula (5) is undesirable because it makes it difficult to achieve a wide angle of view.

[0050] It is also preferable that the numerical range of conditional expression (5) be set to the range of the following conditional expression (5a).

[0051] 0.35≦H / f≦0.55 (5a) It is more preferable that the numerical range of conditional expression (5) be within the range of the following conditional expression (5b).

[0052] 0.35≦H / f≦0.48 (5b) In the finder optical system L0 of each embodiment, it is preferable that one or more of the following conditional expressions (6) to (16) be satisfied.

[0053] 2.0 <d3 / d5<7.0 ···(6) -0.90 <f2 / f<-0.10 ···(7) -2.00 <f1 / f2<-0.80 ···(8) -0.20 <f / f12<1.00 ···(9) 0.40 <f3L / f<1.50 ···(10) -0.20≦f3L / f12<1.00 (11) -1.50<(R12+R11) / (R12-R11)<-0.10 ···(12) 0.40<(R22+R21) / (R22-R21)<5.00 (13) -20.00<(R21+R12) / (R21-R12)<-1.50 ···(14) 0.50 <f / TL<0.90 ···(15) -0.20 <f3 / f4<0.30 ···(16) Here, d3 represents the central thickness of the first lens L1, and d5 represents the central thickness of the second lens L2. f2 represents the focal length of the second lens L2. f12 represents the composite focal length of the first lens L1 and the second lens L2. f3L represents the composite focal length of the third lens L3 and all lenses arranged on the observation side of the third lens L3. R11 represents the radius of curvature of the lens surface of the first lens L1 on the image display surface side. R12 represents the radius of curvature of the lens surface of the first lens L1 on the observation side. R21 represents the radius of curvature of the lens surface of the second lens L2 on the image display surface side. R22 represents the radius of curvature of the lens surface of the second lens L2 on the observation side. TL represents the radius of curvature of the lens surface of the first lens L1. Image display surfacef4 represents the focal length of the fourth lens L4.

[0054] The technical meanings of conditional expressions (6) to (16) will be explained below.

[0055] Conditional formula (6) defines the ratio of the center thickness of the first lens L1 to the center thickness of the second lens L2, and is a conditional formula for effectively correcting various aberrations such as field curvature and astigmatism, while ensuring a wide field of view and increasing the eye relief. Exceeding the upper limit of conditional formula (6) is undesirable because the center thickness of the second lens L2 becomes too thin, making molding difficult. Falling below the lower limit of conditional formula (6) is undesirable because the center thickness of the second lens L2 becomes too thick and the principal point on the image display surface side becomes farther away, worsening field curvature and astigmatism.

[0056] Conditional expression (7) defines the focal length of the second lens L2 in the viewfinder optical system L0, and is a conditional expression for achieving both high magnification of the viewfinder optical system L0 and correcting various aberrations such as curvature of field, astigmatism, and chromatic aberration. Exceeding the upper limit of conditional expression (7) is undesirable because the power of the second lens L2 becomes weak and correction of curvature of field and chromatic aberration becomes insufficient. Falling below the lower limit of conditional expression (7) is undesirable because the power of the second lens L2 becomes too strong and curvature of field and astigmatism worsen.

[0057] Conditional expression (8) defines the ratio of the focal lengths of the first lens L1 and the second lens L2 in the viewfinder optical system L0, and is a conditional expression for balancing various aberrations such as spherical aberration, curvature of field, and astigmatism. If the upper limit of conditional expression (8) is exceeded, the power of the first lens L1 becomes too strong, which undesirably worsens spherical aberration. If the lower limit of conditional expression (8) is exceeded, the power of the second lens L2 becomes too strong, which undesirably worsens curvature of field and astigmatism.

[0058] Conditional formula (9) defines the composite focal length of the first lens L1 and the second lens L2 in the viewfinder optical system L0 and is a conditional formula for correcting curvature of field, astigmatism, and distortion. In the viewfinder optical system L0, both the first lens L1 and the second lens L2 have strong power. On the other hand, the composite focal length of the first lens L1 and the second lens L2 has relatively weak power, which corrects curvature of field, astigmatism, and distortion. Exceeding the upper limit of conditional formula (9) is undesirable because the composite focal length of the first lens L1 and the second lens L2 becomes too positive, resulting in insufficient correction of curvature of field and astigmatism. Failing the lower limit of conditional formula (9) is undesirable because the composite focal length of the first lens L1 and the second lens L2 becomes too negative, making it difficult to achieve a high magnification for the viewfinder optical system L0.

[0059] Conditional expression (10) defines the composite focal length of the third lens L3 and subsequent lenses in the viewfinder optical system L0, and is a conditional expression for achieving both high magnification of the viewfinder optical system L0 and correction of various aberrations such as curvature of field. If the upper limit of conditional expression (10) is exceeded, the composite focal length of the third lens L3 and subsequent lenses will be too weak, making it difficult to increase the magnification of the viewfinder optical system L0, which is undesirable. If the lower limit of conditional expression (10) is exceeded, the composite focal length of the third lens L3 and subsequent lenses will be too strong, making it difficult to correct curvature of field, which is undesirable.

[0060] Conditional expression (11) defines the ratio of the composite focal length of the third lens L3 and subsequent lenses in the viewfinder optical system L0 to the composite focal length of the first lens L1 and second lens L2 in the viewfinder optical system L0. If the upper limit of conditional expression (11) is exceeded, the composite focal length of the first lens L1 and second lens L2 will be too strong relative to the composite focal length of the third lens L3 and subsequent lenses, which is undesirable because correction of field curvature and astigmatism will be insufficient. If the lower limit of conditional expression (11) is exceeded, the composite focal length of the third lens L3 and subsequent lenses will be too strong, which is undesirable because correction of field curvature will be difficult.

[0061] Conditional expression (12) defines the shape of the first lens L1 in the viewfinder optical system L0. If the upper limit of conditional expression (12) is exceeded, the curvature of first lens L1 on the image display element side becomes stronger than the curvature on the observation side, making it difficult to correct curvature of field, which is undesirable. If the lower limit of conditional expression (12) is exceeded, the curvature of first lens L1 on the image display element side becomes too negative, which means that the first lens cannot be given sufficient power, resulting in insufficient correction of spherical aberration, curvature of field, astigmatism, etc., which is undesirable.

[0062] Conditional expression (13) defines the shape of the second lens L2 in the viewfinder optical system L0. If the upper limit of conditional expression (13) is exceeded, the curvature of the second lens L2 on the observation side becomes too positive, which is undesirable because correction of curvature of field and astigmatism becomes insufficient. If the lower limit of conditional expression (13) is exceeded, the curvature of the second lens L2 on the observation side becomes too negative, which is undesirable because lateral aberration worsens.

[0063] Conditional expression (14) defines the shape of the air gap between the first lens L1 and the second lens L2 of the viewfinder optical system L0. If the upper limit of conditional expression (14) is exceeded, the curvature of the first lens L1 on the observation side becomes too weak, which makes it difficult to sufficiently correct spherical aberration and lateral aberration, and therefore it is undesirable. If the lower limit of conditional expression (14) is exceeded, the curvature of the first lens L1 on the observation side and the curvature of the second lens L2 on the image display element side become too close, which makes it difficult to sufficiently correct curvature of field and astigmatism, and therefore it is undesirable.

[0064] Conditional expression (15) defines the thickness of the entire lens system. If the upper limit of conditional expression (15) is exceeded, the lens system becomes too thick, which increases the distance from the image display element 1 to the viewer (EP), making it difficult to increase the magnification of the finder optical system L0, which is undesirable. If the lower limit of conditional expression (15) is exceeded, the curvature of each lens cannot be sufficiently strengthened, making it difficult to increase the magnification of the finder optical system L0, which is undesirable.

[0065] Conditional expression (16) defines the ratio of the focal lengths of the third lens L3 and the fourth lens L4, and is a conditional expression for effectively correcting curvature of field and astigmatism and reducing error sensitivity. Exceeding the upper limit of conditional expression (16) undesirably increases the error sensitivity of the viewfinder optical system L0. Falling below the lower limit of conditional expression (16) undesirably worsens curvature of field and astigmatism.

[0066] It is more preferable that the numerical ranges of the conditional expressions (6) to (16) be within the ranges of the following conditional expressions (6a) to (16a).

[0067] 2.5 <d3 / d5<6.0 ···(6a) -0.90 <f2 / f<-0.20 ···(7a) -1.90 <f1 / f2<-0.80 ···(8a) -0.10 <f / f12<0.90 ···(9a) 0.40 <f3L / f<1.40 ···(10a) -0.10≦f3L / f12<1.00 (11a) -1.40<(R12+R11) / (R12-R11)<-0.10 ···(12a) 0.40<(R22+R21) / (R22-R21)<4.00 (13a) -17.00<(R21+R12) / (R21-R12)<-1.50 (14a) 0.55 <f / TL<0.90 ···(15a) -0.20 <f3 / f4<0.20 ···(16a) It is more preferable that the numerical ranges of the conditional expressions (6) to (16) be within the ranges of the following conditional expressions (6b) to (16b).

[0068] 2.5 <d3 / d5<5.7 ···(6b) -0.80 <f2 / f<-0.30 ···(7b) -1.90 <f1 / f2<-0.85 ···(8b) -0.10 <f / f12<0.80 ···(9b) 0.40 <f3L / f<1.30 ···(10b) -0.10 <f3L / f12<0.85 ···(11b) -1.35<(R12+R11) / (R12-R11)<-0.10 (12b) 0.50<(R22+R21) / (R22-R21)<3.00 (13b) -15.00<(R21+R12) / (R21-R12)<-1.50 (14b) 0.60 <f / TL<0.85 ···(15b) -0.15 <f3 / f4<0.15 ···(16b) Next, Numerical Examples 1 to 12 corresponding to Examples 1 to 12 are shown in Tables 1 to 12. In each Numerical Example, "ri" indicates the paraxial radius of curvature of the ith surface, in order from the image display surface IP to the observation side EP. For example, r1 and r2 are surfaces of the image display element, and r1 is the image display surface. The last surface is the observation surface EP. di indicates the on-axis surface spacing between the ith surface and the (i+1)th surface, in order from the image display surface IP. Furthermore, ndi indicates the refractive index of the ith material at the d-line (wavelength = 578.6 nm), and νdi indicates the Abbe number of the ith material at the d-line. ω indicates the apparent field of view (half angle of view (°)) at standard diopter.

[0069] In addition, the units of length used for numerical data are [mm] unless otherwise specified. However, since the finder optical system L0 provides the same optical performance whether proportionally enlarged or reduced, the units are not limited to [mm] and other appropriate units can be used.

[0070] In the numerical data, surfaces with a subscript "*" in the radius of curvature column are aspheric. An aspheric shape is expressed as follows: x is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, r is the paraxial radius of curvature at the vertex of the lens surface, K is the conic constant, and A4, A6, A8, A10, and A12 are the aspheric coefficients of each order. 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 ] In the aspherical coefficients, "Ei" represents an exponential expression with the base 10, that is, "10-i."

[0071] The various values ​​in each numerical example are summarized in Table 13. [Imaging device] Next, an embodiment of an imaging device using an observation device having the finder optical system L0 shown in each example will be described with reference to Fig. 25. Fig. 25 is a schematic diagram of the main parts of an imaging device equipped with the observation device of each example. An object image formed by an imaging optical system 101 is converted into an electrical signal by an imaging element 102, which is a photoelectric conversion element. A CCD sensor, a CMOS sensor, or the like is used as the imaging element 102.

[0072] An output signal from the imaging element 102 is processed in an image processing circuit 103 to form an image. The formed image is recorded on a recording medium 104 such as a semiconductor memory, magnetic tape, or optical disk. The image formed in the image processing circuit 103 is displayed on a finder optical system unit (observation device) 105. The observation device 105 includes an image display element 1051 and a finder optical system 1052 of each embodiment. The image display element 1051 is configured from a liquid crystal display element LCD, an organic EL, or the like.

[0073] In this way, by applying an observation device having the finder optical system of the present invention to an imaging device such as a digital camera or video camera, it is possible to obtain an imaging device that has a wide viewing angle, is small in size, and has high optical performance.

[0074] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

[0075] [Numerical Example 1]

[0076] [Table 1]

[0077] [Numerical Example 2]

[0078] [Table 2]

[0079] [Numerical Example 3]

[0080] [Table 3]

[0081] [Numerical Example 4]

[0082] [Table 4]

[0083] [Numerical Example 5]

[0084] [Table 5]

[0085] [Numerical Example 6]

[0086] [Table 6]

[0087] [Numerical Example 7]

[0088] [Table 7]

[0089] [Numerical Example 8]

[0090] [Table 8]

[0091] [Numerical Example 9]

[0092] [Table 9]

[0093] [Numerical Example 10]

[0094] [Table 10]

[0095] [Numerical Example 11]

[0096] [Table 11]

[0097] [Numerical Example 12]

[0098] [Table 12]

[0099] [Table 13] [Explanation of symbols]

[0100] 1. Image display element L0 viewfinder optical system L1 First lens L2 Second lens L3 Third lens

Claims

1. An observation device having an image display element for displaying an image and a finder optical system for observing an image displayed on an image display surface of the image display element, the finder optical system has, arranged in order from the image display surface side to the observation side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power; the finder optical system is composed of three or four lenses, Let nd1 be the refractive index of the material of the first lens at the d-line, nd2 be the refractive index of the material of the second lens at the d-line, f be the focal length of the viewfinder optical system, d12 be the air-equivalent length on the optical axis from the image display surface to the lens surface of the first lens on the image display surface side at standard diopter, f1 be the focal length of the first lens, and H be half the diagonal length of the image display surface. 1.700≦nd1 nd2≦1.700 0.10<d12 / f<0.37 0.20<f1 / f<0.83 0.3686≦H / f≦0.6000 An observation device characterized in that the following conditional expression is satisfied:

2. When the center thickness of the first lens is d3 and the center thickness of the second lens is d5, 2.0<d3 / d5<7.0 2. The observation apparatus according to claim 1, wherein the following condition is satisfied:

3. When the focal length of the second lens is f2, -0.90<f2 / f<-0.10 3. The observation apparatus according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the second lens is f2, -2.00<f1 / f2<-0.80 4. The observation device according to claim 1, wherein the following condition is satisfied:

5. When the composite focal length of the first lens and the second lens is f12, -0.20<f / f12<1.00 5. The observation device according to claim 1, wherein the following condition is satisfied:

6. When the composite focal length of the third lens and all lenses arranged on the observation side of the third lens is f3L, 0.40<f3L / f<1.50 6. The observation apparatus according to claim 1, wherein the following condition is satisfied:

7. When the composite focal length of the third lens and all lenses arranged on the observation side of the third lens is f3L, and the composite focal length of the first lens and the second lens is f12, -0.20≦f3L / f12<1.00 7. The observation apparatus according to claim 1, wherein the following condition is satisfied:

8. When the radius of curvature of the lens surface of the first lens on the image display surface side is R11 and the radius of curvature of the lens surface of the first lens on the observation side is R12, -1.50<(R12+R11) / (R12-R11)<-0.10 8. The observation device according to claim 1, wherein the following condition is satisfied:

9. When the radius of curvature of the lens surface of the second lens on the image display surface side is R21 and the radius of curvature of the lens surface of the second lens on the observation side is R22, 0.40<(R22+R21) / (R22-R21)<5.00 9. The observation device according to claim 1, wherein the following condition is satisfied:

10. When the radius of curvature of the lens surface of the first lens on the observation side is R12 and the radius of curvature of the lens surface of the second lens on the image display surface side is R21, -20.00<(R21+R12) / (R21-R12)<-1.50 10. The observation device according to claim 1, wherein the following condition is satisfied:

11. When the vertex distance from the vertex of the lens surface of the first lens on the image display surface side to the vertex of the lens surface of the lens closest to the observation side is defined as TL, 0.50<f / TL<0.90 11. The observation device according to claim 1, wherein the following condition is satisfied:

12. the viewfinder optical system further includes a fourth lens having a positive refractive power and disposed on the observation side of the third lens, When the focal length of the third lens is f3 and the focal length of the fourth lens is f4, -0.20<f3 / f4<0.30 12. The observation apparatus according to claim 1, wherein the following condition is satisfied:

13. 13. An imaging apparatus comprising: an imaging element; an imaging optical system that forms an object image on the imaging element; and the observation device according to claim 1 that is used to observe an image displayed on the image display element that displays the object image.

Images