JPWO2017022670A1 - Eyepiece optics and electronic viewfinder - Google Patents

Abstract

An eyepiece optical system (10) for projecting an image displayed on an image display device (15) disposed on an image plane side (22) onto an eye (5) disposed on an exit side (21), the exit side First lens (L1) having a positive refractive power convex toward the exit side from the first to the image side, a second lens (L2) having a positive refractive power, and a third lens having a negative refractive power ( L3) and a fourth meniscus type first meniscus lens having a negative refractive power convex toward the exit side and a fourth meniscus type having a positive refractive power convex toward the exit side. Lens (L4), a fifth lens (L5) having a positive refractive power, and a sixth lens (L6) having a negative refractive power, and having a positive refractive power convex toward the exit side An eyepiece optical system having the second meniscus type second cemented lens (B2).

Description

  The present invention relates to an eyepiece optical system suitable for an electronic viewfinder.

  Japanese Patent Application Laid-Open No. 2012-42844 describes that an electronic viewfinder is provided that can easily ensure image quality even when downsizing, securing an eye point, and securing a viewing angle. This document includes a first lens group that is a single lens having a positive refractive power and a convex surface facing the exit side, and a biconcave having a negative refractive power and a concave surface facing both the display surface side and the exit side. An optical system is disclosed that includes a second lens group that is a single lens and a third lens group that is a biconvex single lens having positive refractive power and having convex surfaces facing both the display surface side and the exit side.

  In an electronic viewfinder for a head-mounted display (HMD), there is a demand for an optical system that is small and can provide a clearer image.

  One aspect of the present invention is an eyepiece optical system that projects an image displayed on an image display device disposed on the image plane side onto an eye disposed on the exit side, and is directed from the exit side to the image plane side. A first lens having a positive refractive power convex to the exit side, a second lens having a positive refractive power, and a third lens having a negative refractive power, which are bonded to the exit side. A first meniscus type cemented lens having a negative refractive power, a fourth lens having a positive meniscus type having a positive refractive power on the exit side, a fifth lens having a positive refractive power, and a negative refractive power. The eyepiece optical system includes a sixth lens and a second meniscus type cemented lens having a positive refractive power convex on the exit side.

  An eyepiece optical system for an electronic viewfinder is required to have a high angle of view. In order to ensure a large angle of view, the lens arrangement is preferably asymmetric. On the other hand, it is preferable that the lens arrangement is symmetrical for aberration correction. Particularly, an eyepiece optical system for HMD is required to have a high angle of view. On the other hand, in the HMD, since the actual distance between the eyes and the screen is short, the positional relationship between the image and the eyes changes when the position of the eyes is slightly shifted. Therefore, if the aberration is not corrected well, the appearance of the image (video) is greatly changed and difficult to see.

  The eyepiece optical system according to the present invention includes a first lens convex to the exit side, a first meniscus cemented lens convex to the exit side, and a meniscus convex to the exit side from the exit side to the image plane side. A type fourth lens and a meniscus type second cemented lens convex on the exit side are arranged. That is, this eyepiece optical system has an asymmetric lens arrangement as a whole, with all the lenses in the four-group configuration being convex on the exit side, that is, in the eye direction. Therefore, it is easy to increase the angle of view. On the other hand, the first cemented lens, the fourth lens, and the second cemented lens are meniscus types having a concave image surface side, and even if they are asymmetrically arranged, they do not increase the diameter of the light beam that passes through the optical system. The surface can be passed. For this reason, this eyepiece optical system has a configuration in which it is easy to ensure aberration correction capability even in an asymmetric arrangement.

  The first cemented lens of the two (two sets) cemented lenses that are the main lenses of the four-group configuration of the eyepiece optical system is a negative meniscus type that is convex on the exit side as a whole. The cemented lens is a positive meniscus type that is convex on the exit side as a whole. Therefore, these cemented lenses are both asymmetrically arranged as a meniscus type convex on the exit side, but their refractive power is negative and reverse (asymmetric), and for rays passing through this eyepiece optical system, Symmetric correction is possible.

  For this reason, as a minimum configuration, the first lens, the first cemented lens, the fourth lens, and the second cemented lens are composed of a small number of lenses such as a total of six lenses. -It is possible to provide an eyepiece optical system with a high angle of view and a good correction of aberrations.

Refractive index n2 and Abbe number ν2 of the second lens constituting the first cemented lens, refractive index n3 and Abbe number ν3 of the third lens, and refraction of the fifth lens constituting the second cemented lens It is desirable that the refractive index n5 and Abbe number ν5 and the refractive index n6 and Abbe number ν6 of the sixth lens satisfy the following conditions.
0 <| n2-n3 | <0.2 (A)
15 <| ν2-ν3 | <55 (B)
0.1 <| n5-n6 | <0.5 (C)
0 <| ν5-ν6 | <30 (D)
The refractive index and Abbe number are the values of the d-line. Further, the upper limit of the condition (A) is more preferably 0.1, the lower limit of the condition B is more preferably 20, the upper limit is more preferably 40, and the upper limit of the condition D is more preferably 20.

  As shown in these conditions, it is desirable that the first cemented lens is a combination of lenses having a refractive index close to each other and an Abbe number larger than 15, preferably 20 or more different. It is desirable that the second cemented lens is a combination of lenses having an Abbe number smaller than 30, preferably close to 20 or less and having a different refractive index. Correction of chromatic aberration of magnification in addition to axial chromatic aberration is facilitated by correcting chromatic aberration using a combination of lenses having a close refractive index and a different Abbe number and a combination of lenses having a close Abbe number and a different refractive index. It is also possible to achromatic the eye position when it moves relative to the optical axis.

  In addition to the two cemented lenses, the eyepiece optical system includes a first lens on the exit side (eyeball side) and a fourth lens positioned between the two cemented lenses. These lenses can employ plastic lenses, and aberration correction capability can be improved by making at least one of these surfaces aspherical. For example, by matching the astigmatism in the sagittal direction and the tangential direction as much as possible in the image height direction, it is possible to suppress the fluctuation of the image when the eye position is shifted, and to provide an electronic viewfinder that allows easy viewing of the image.

  The first lens on the most exit side may be a meniscus type convex on the exit side. By making all the lens groups constituting the eyepiece optical system into a meniscus type convex toward the exit side, a more compact eyepiece optical system can be provided.

  In one form of the most compact arrangement of the eyepiece optical system, the first cemented lens is arranged with a minimum air space on the optical axis from the first lens, and the curvature of the surface on the exit side of the fourth lens is as follows. When the absolute value of the radius is larger than the absolute value of the radius of curvature of the image-side surface of the first cemented lens, the fourth lens is arranged so that the periphery has a minimum air space with respect to the first cemented lens. The second cemented lens is arranged with a minimum air space on the optical axis from the fourth lens.

  Another aspect of the present invention is an electronic viewfinder having the above eyepiece optical system and an image display device arranged on the image plane side. It is possible to provide a compact electronic viewfinder that displays large and clear images. Another different aspect of the present invention is a head mounted display having the electronic viewfinder described above.

The figure which shows the outline | summary of the head mounted display containing an eyepiece optical system. FIG. 2A shows lens data, FIG. 2A shows data for each lens, and FIG. 2B shows data for an aspheric surface. The figure which shows the various aberrations of an eyepiece optical system. The figure which shows the magnification chromatic aberration of an eyepiece optical system.

BEST MODE FOR CARRYING OUT THE INVENTION

  FIG. 1 shows an example of a head mounted display (HMD) provided with an eyepiece optical system. The HMD 1 includes an electronic viewfinder 7 set in front of the user's 2 eye 5. The electronic viewfinder 7 includes an eyepiece optical system 10 and an image display device 15 disposed on the opposite side of the eye 5 with respect to the eyepiece optical system 10. An example of the image display device 15 is a liquid crystal panel (LCD), an organic EL, or the like. The eyepiece optical system 10 projects (images) an image displayed on the image display device 15 disposed on the image plane side 22 onto the eye 5 on the exit side 21, and the user 2 passes the eye 5 to form a diagonal length. An image displayed on a small image display device (display panel) 15 having a size of 6 mm to several tens of mm (18 mm in this example) can be enlarged and observed in each field of view of 30 degrees or more.

  The eyepiece optical system 10 has a design in which an aperture (eye point, virtual aperture) 11 is arranged on the exit side 21. The eyepiece optical system 10 includes a first lens L1 having a positive refractive power convex toward the exit side 21 from the exit side 21 where the eye 5 is disposed toward the image plane side 22 where the image display device 15 is disposed. And a second lens L2 having a positive refractive power and a third lens L3 having a negative refractive power, the first meniscus type having a negative refractive power convex on the exit side 21. A cemented lens B1, a meniscus fourth lens L4 having a positive refractive power convex on the exit side 21, a fifth lens L5 having a positive refractive power, and a sixth lens L6 having a negative refractive power are pasted. The combined lenses have a meniscus type second cemented lens B2 having a convex positive refractive power on the exit side 21, and are composed of six lenses L1 to L6 as a whole.

  More specifically, the first lens L1 is a positive meniscus lens convex on the exit side 21, the second lens L2 is a positive meniscus lens convex on the exit side 21, and the third lens. L3 is a negative meniscus lens convex on the exit side, the fourth lens L4 is a positive meniscus lens convex on the exit side 21, and the fifth lens L5 is a biconvex positive lens. The sixth lens L6 is a biconcave negative lens. The first cemented lens B1 including the second lens L2 and the third lens L3 is arranged with a minimum air distance d2 (0.2 mm in this example) on the optical axis 20 from the first lens L1. Yes. In the fourth lens L4, the absolute value of the curvature radius r6 of the surface S6 on the exit side 21 is larger than the absolute value of the curvature radius r5 of the surface S5 on the image surface side 22 of the first cemented lens B1, and the fourth lens L4. The peripheral portion of the fourth lens L4 is close to the peripheral portion of the first cemented lens B1, and the peripheral portion of the fourth lens L4 is the minimum air space, for example, 0.2 to 0.5 mm with respect to the peripheral portion of the first cemented lens B1. It is arranged to be about. Further, the second cemented lens B2 is disposed with a minimum air distance d8 on the optical axis 20 from the fourth lens L4.

  FIG. 2A shows data of each lens constituting the eyepiece optical system 10. The radius of curvature (r) is the radius of curvature (mm) of each lens (each lens surface S) arranged in order from the exit side 21, the distance d is the distance (mm) between the lens surfaces, and the effective diameter Re is the distance of each lens surface. The effective diameter (mm), the refractive index n is the refractive index (d line) of each lens, the Abbe number ν is the Abbe number (d line) of each lens, and inf is a plane. FIG. 2A shows the focal length (mm) of each lens and the focal length (mm) of each cemented lens. D10 indicates the distance (back focus) between the eyepiece optical system 10 and the image display device 15.

The surface S2 on the image plane side 22 of the first lens L1, the surface S3 on the exit side 21 of the first cemented lens B1, the surface S7 on the image plane side 22 of the fourth lens L4, and the second cemented lens. The surface S8 on the exit side 21 of B2 is an aspherical surface. The aspherical surface has coefficients K, C1, and C2 in FIG. 2B, where X is the coordinate in the optical axis direction, Y is the coordinate perpendicular to the optical axis, the light traveling direction is positive, and R is the paraxial radius of curvature. , C3, C4 and C5 are represented by the following formula (1). “En” means “10 to the power of n”.
X = (1 / R) Y ² / [1+ {1− (1 + K) (1 / R) ² Y ² } ^1/2 ]
+ C1Y ⁴ + C2Y ⁶ + C3Y ⁸ + C4Y ¹⁰ + C5Y ¹² (1)

  FIG. 3 shows spherical aberration, astigmatism, and distortion of the eyepiece optical system 10. The aspherical aberration indicates a wavelength of 465 nm (solid line), a wavelength of 532 nm (broken line), and a wavelength of 635 nm (dashed line). Astigmatism indicates a tangential ray T and a sagittal ray S. FIG. 4 shows the chromatic aberration of magnification of the eyepiece optical system 10 for each of tangential rays and sagittal rays.

  As a whole, the eyepiece optical system 10 includes a first lens L1 having a positive power, a first cemented lens B1 having a negative power, a fourth lens L4 having a positive power, and a positive lens. This is a lens system having a combination of positive, negative, positive and positive powers, in which a second cemented lens B2 having the same power is disposed. A lens system having a positive / negative / positive combination from the exit side 21 toward the image plane side 22 tends to make the rays on the image plane side 22 telecentric. Therefore, it is suitable for inputting and processing an image displayed on the image display device 15 such as LED or organic EL.

  The eyepiece optical system 10 used in the electronic viewfinder 7 needs to have a strong positive refractive power in order to enlarge and observe a small screen at a high angle of view of 30 degrees or more. In the eyepiece optical system 10, the lens group constituting the eyepiece optical system 10, that is, the first lens L1, the first cemented lens B1, the fourth lens L4, and the second cemented lens B2, are all contained in the eye. 5 is a meniscus type that is convex in the emission direction 21 directed to 5 and concave on the image plane side 22. In particular, even in the first cemented lens B1 having a negative power, the meniscus type whose convex surface faces the direction of the eye 5 (the emission direction) 21 contributes to widening the angle of view although the power is negative. I am doing so. For this reason, although this is a combination of a small number of lenses, this eyepiece optical system 10 can obtain a maximum field angle of 34.3 degrees.

Numerical values indicating the main performance of the eyepiece optical system 10 are as follows.
Focal length 29.9mm
F number 7.4
Maximum angle of view 34.3 degrees Image circle φ18mm
Back focus 11.66mm

  In general, in order to correct various aberrations, a lens system having symmetrical lens arrangements on the exit side 21 and the image side 22 is desirable. On the other hand, the eyepiece optical system 10 has a meniscus type in which all the lens groups are convex toward the emission direction 21, and has an asymmetric lens arrangement. Therefore, the eyepiece optical system 10 has a lens arrangement that is generally considered difficult to correct various aberrations. Furthermore, in the present eyepiece optical system 10, all the lens groups L 1, B 1, L 4 and B 2 are unified into a meniscus type that is convex on the exit side 21. Contributes to increasing the angle of view.

  Furthermore, unifying all the lens groups L1, B1, L4, and B2 into a meniscus type that is convex on the exit side 21 increases the asymmetry, but the light rays alternately pass through the convex and concave surfaces. Therefore, in the eyepiece optical system 10, the diameter of the light beam passing through the eyepiece optical system 10 passes through a large number of lens surfaces, and aberration correction can be performed using a large number of lens surfaces while having a compact design. It has the merit of being able to. Therefore, although the lens arrangement is asymmetric, the eyepiece optical system 10 that is compact and has high aberration correction capability can be realized.

  Further, the eyepiece optical system 10 includes a first cemented lens B1 having a negative power and a second cemented lens B2 having a positive power. These two (two sets) cemented lenses B1 and B2 are main lenses having a four-group configuration, and in particular, are lenses that contribute to correction of chromatic aberration. These cemented lenses B1 and B2 are arranged asymmetrically as a meniscus type convex on the exit side 21, that is, the convex surfaces of both lenses B1 and B2 are directed toward the exit side 21, while the refractive power is negative and positive. Let it be asymmetric. By the arrangement of the cemented lenses B1 and B2, it is possible to realize a symmetric correction with respect to the light beam passing through the eyepiece optical system 10. Therefore, it is possible to provide an eyepiece optical system 10 having a small size and a high angle of view that is configured with a small number of sheets and in which aberrations are favorably corrected.

Further, the refractive index n2 and Abbe number ν2 of the second lens L2 constituting the first cemented lens B1, and the refractive index n3 and Abbe number ν3 of the third lens L3 constitute the second cemented lens B2. Differences between the refractive index n5 and Abbe number ν5 of the fifth lens L5 and the refractive index n6 and Abbe number ν6 of the sixth lens L6 are set as follows.
| N2-n3 | = 0.01 (Condition (A))
| Ν2-ν3 | = 26.91 (Condition (B))
| N5-n6 | = 0.16 (Condition (C))
| Ν5-ν6 | = 10.61 (Condition (D))

  Therefore, the first cemented lens B1 and the second cemented lens B2 satisfy the conditions (A) to (D). In other words, the first cemented lens B1 is composed of a combination of lenses having a close refractive index and different Abbe numbers, and the second cemented lens B2 is composed of a combination of lenses having a close Abbe number and different refractive indexes. Therefore, the first cemented lens B1 and the second cemented lens B2 are asymmetrical in arrangement and different in type (asymmetrical type), and as a result, have a symmetrical correction capability. be able to. In this way, by combining the different types of cemented lenses B1 and B2 in a small lens configuration of six groups of four groups, it is possible to satisfactorily correct lateral chromatic aberration in addition to axial chromatic aberration, and the results are shown in FIG. This is as shown in the aberration diagram of FIG.

  In the electronic viewfinder 7, if the aberration is not corrected well for a pupil diameter larger than the pupil diameter (2 to 3 mm in a bright environment) (φ12 mm in this example), an image (video) is displayed when the pupil is decentered. ) Is greatly changed, or the light beam is kicked, which makes it difficult to see.

  In the present eyepiece optical system 10, as a lens group, the ability to correct various aberrations is improved by allowing light rays to alternately pass through a convex surface and a concave surface, and two types of cemented lenses B1 and B1 of different types are included in the four groups. By incorporating B2, the number of lens surfaces useful for correction is increased with a compact configuration, and the correction capability of chromatic aberration is also improved. In addition, the configuration of two cemented lenses can greatly improve the decentering sensitivity, particularly the on-axis aberration and the lateral chromatic aberration at the time of decentering, compared to the configuration of one triplet. Therefore, in this eyepiece optical system (eyepiece lens system) 10, various aberrations including achromaticity when the position of the eye 5 is moved with respect to the optical axis 20 can be corrected, and the eccentricity sensitivity is improved. it can.

  Further, in this eyepiece optical system 10, a four-group system is configured by combining two sets of cemented lenses B1 and B2 and single plate lenses L1 and L4. The lenses L1 and L4 are plastic lenses. realizable. For this reason, it is easy to make one surface of the lenses L1 and L4 an aspheric surface, and various aberrations can be corrected more easily by introducing an aspheric surface. In this respect, the eccentricity sensitivity can be greatly improved.

  Thus, in the eyepiece optical system 10, a lens system having a high angle of view and a high aberration correction capability is realized by combining a convex meniscus type lens group on the exit side 21. Furthermore, by combining a convex meniscus lens on the exit side 21, it is possible to arrange each lens group close to each other, and it is possible to make the whole compact, and the electronic viewfinder 7 suitable for the HMD 1 can be provided. Can be provided.

  The first lens L1 on the most exit side 21 employs a convex meniscus lens on the exit side 21, but when it is better to provide a larger positive power, the first lens L1 on the most exit side 21 is used. It is also possible to employ a biconvex positive lens as the lens L1 or to replace the first lens L1 on the most exit side 21 with a plurality of positive power lenses. Further, although an example in which the electronic viewfinder 7 is applied to the HMD 1 has been described, the electronic viewfinder 7 can be incorporated in an imaging apparatus such as a camera, and a compact and high performance camera with a viewfinder can be provided. .

Claims (8)

An eyepiece optical system for projecting an image displayed on an image display device arranged on the image plane side to an eye arranged on the exit side,
A first lens having positive refractive power convex toward the exit side from the exit side toward the image plane side;
A lens in which a second lens having a positive refractive power and a third lens having a negative refractive power are bonded to each other, and a meniscus type first cemented lens having a negative refractive power convex on the exit side;
A meniscus type fourth lens having positive refractive power convex on the exit side;
An eyepiece comprising a fifth lens having a positive refractive power and a sixth lens having a negative refractive power, each having a meniscus type second cemented lens having a positive refractive power convex on the exit side. Optical system. In claim 1,
An eyepiece optical system including the first lens, the first cemented lens, the fourth lens, and the second cemented lens. In claim 1 or 2,
The refractive index n2 and Abbe number ν2 of the second lens, the refractive index n3 and Abbe number ν3 of the third lens, the refractive index n5 and Abbe number ν5 of the fifth lens, and the sixth lens An eyepiece optical system in which the refractive index n6 and Abbe number ν6 satisfy the following conditions.
0 <| n2-n3 | <0.2
15 <| ν2-ν3 | <55
0.1 <| n5-n6 | <0.5
0 <| ν5-ν6 | <30   4. The eyepiece optical system according to claim 1, wherein at least one surface of the first lens and at least one surface of the third lens are aspherical surfaces.   5. The eyepiece optical system according to claim 1, wherein the first lens is a meniscus type convex on the exit side. In any one of Claims 1 thru | or 5, a said 1st junction lens is arrange | positioned at a minimum air space | interval on the said 1st lens and an optical axis,
In the fourth lens, the absolute value of the radius of curvature of the exit side surface is larger than the absolute value of the radius of curvature of the image side surface of the first cemented lens, and the periphery is relative to the first cemented lens. Arranged to have minimum air spacing,
The eyepiece optical system, wherein the second cemented lens is disposed with a minimum air space on the optical axis from the fourth lens. The eyepiece optical system according to any one of claims 1 to 6,
An electronic viewfinder having an image display device arranged on the image plane side.   A head mounted display having the electronic viewfinder according to claim 7.

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