Optical system and imaging device

Abstract

To provide an optical system that is small, requires low cost, and has a small image surface incidence angle and a wide angle.SOLUTION: The present invention includes a first unit (L1), a second unit (L2), and a third unit (L3) arranged in this order from an object to an image. The first unit has a first substrate (L11) and a first lens (L12) of a negative power arranged on an image side of the first substrate. The second unit has a second substrate (L21) and a second lens (L22) arranged on an image side of the second substrate. The third unit has a third substrate (L32) and a third lens (L31) arranged on an object side of the third substrate. The power P1 of the first lens on the optical axis, the power P2 of the second lens on the optical axis, and the power P3 of the third lens on the optical axis satisfy a predetermined conditional expression.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system and an imaging device. [Background technology]

[0002] Conventionally, a technique called wafer level optics has been known as a method for manufacturing a small optical system at low cost. Patent Document 1 discloses an optical system made of three lens surfaces manufactured by wafer level optics. Patent Document 2 discloses an optical system made of two lens surfaces. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 9,798,115 [Patent Document 2] International Publication No. 2018 / 220937 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the optical system disclosed in Patent Document 1, the incident angle (image plane incident angle) of the off-axis light beam when it is incident on the image plane is large, so image quality deteriorates due to color mixing and reduced light amount. In the optical system disclosed in Patent Document 2, although the image plane incident angle is small, the overall length is long, which is insufficient for miniaturization, and the reduction of various aberrations is also insufficient.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a small, low-cost optical system and an imaging device that has a small, wide-angle image plane incidence angle. [Means for solving the problem]

[0006] An optical system according to one aspect of the present invention includes a first unit, a second unit, and a third unit arranged in this order from an object side to an image side, the first unit having a first substrate and a first lens having negative power arranged on the image side of the first substrate, the second unit having a second substrate and a second lens arranged on the image side of the second substrate, and the third unit having a third substrate and a third lens arranged on the object side of the third substrate, an aperture stop is disposed on the image side of the first unit; A power P1 on the optical axis of the first lens, a power P2 on the optical axis of the second lens, and a power P3 on the optical axis of the third lens. , the distance on the optical axis from the object side surface of the first unit to the aperture stop is d0, and the radius of curvature on the optical axis of the first lens is R1. satisfies a predetermined conditional expression.

[0007] Other objects and features of the present invention are illustrated in the following examples. Effect of the Invention

[0008] According to the present invention, it is possible to provide a small-sized, low-cost optical system and an imaging device having a small, wide-angle image plane incidence angle. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of an optical system in the first embodiment. [Diagram 2] 4A to 4C are aberration diagrams of the optical system in Example 1. [Diagram 3] FIG. 11 is a cross-sectional view of an optical system in Example 2. [Figure 4] 10A to 10C are aberration diagrams of the optical system in Example 2. [Diagram 5] FIG. 11 is a cross-sectional view of an optical system according to a third embodiment. [Figure 6] 11A to 11C are aberration diagrams of the optical system in Example 3. [Figure 7] FIG. 11 is a cross-sectional view of an optical system in Example 4. [Figure 8] 11A to 11C are aberration diagrams of the optical system in Example 4. [Figure 9] FIG. 13 is a schematic diagram of a main part of an electronic device according to a fifth embodiment. [Figure 10] FIG. 13 is a schematic diagram of a main part of an imaging device according to a sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] The optical system of each embodiment is a small optical system obtained by using a technology called wafer level optics. Such an optical system is called a wafer level lens, and an imaging device using a wafer level lens as an imaging optical system is called a wafer level camera. The optical system of each embodiment is characterized by its small size and low cost, and is therefore suitable for use as an optical system for a camera built into electronic devices such as a mobile phone, a smartphone, and a wearable terminal, or as an objective optical system for an endoscope.

[0012] 1, 3, 5, and 7 are cross-sectional views of optical systems 1a to 1d of Examples 1 to 4, respectively. In each cross-sectional view, the left side is the object side (front) and the right side is the image side (rear). SP is an aperture stop, and IP is an image plane. On the image plane IP, a photosensitive surface corresponding to the imaging surface of a solid-state imaging element such as a CCD sensor or CMOS sensor in an imaging device, or the film surface of a silver halide film camera, is disposed.

[0013] 2, 4, 6, and 8 are aberration diagrams of the optical systems 1a to 1d of Examples 1 to 4, respectively. In the spherical aberration diagrams, Fno is the F-number, and the spherical aberration diagrams show the amount of spherical aberration for the d-line (wavelength 587.6 nm), g-line (wavelength 435.8 nm), C-line (wavelength 656.3 nm), and F-line (wavelength 486.1 nm), respectively. In the astigmatism diagrams, ΔS shows the amount of astigmatism in the sagittal image plane (solid line), and ΔM shows the amount of astigmatism in the meridional image plane (broken line). In the distortion diagrams, the amount of distortion for the d-line is shown. In the lateral chromatic aberration diagrams, the amount of chromatic aberration for the g-line is shown. Y is the image height (maximum image height).

[0014] The optical system of each embodiment is composed of a first unit L1, a second unit L2, and a third unit L3 arranged in this order from the object side to the image side. The first unit L1 has a first substrate L11 and a first lens L12 with negative power arranged on the image side of the first substrate L11. The second unit L2 has a second substrate L21 and a second lens L22 arranged on the image side of the second substrate L21. An aperture stop SP is arranged on the image side of the first unit L1. The third unit L3 has a third substrate L32 and a third lens L31 arranged on the object side of the third substrate L32.

[0015] The first substrate L11 is a flat substrate, and the first lens L12 is a plano-concave lens. The first lens L12 is disposed in close contact with the first substrate L11. The image-side surface of the first lens L12 is an aspheric surface S1. The aspheric surface S1 is configured so that the radius of curvature of the periphery (the outermost periphery of the effective beam diameter) is larger than the radius of curvature of the center (on the optical axis OA).

[0016] The second substrate L21 is a flat substrate, and the second lens L22 is a plano-convex lens. The second lens L22 is disposed in close contact with the second substrate L21. The image-side surface of the second lens L22 is an aspheric surface S2. The aspheric surface S2 is configured so that the radius of curvature of the periphery (the outermost periphery of the effective beam diameter) is larger than the radius of curvature of the center (on the optical axis).

[0017] The third substrate 32 is a flat substrate, and the third lens L31 is a plano-convex lens. The third lens L31 is disposed in close contact with the third substrate L32. The object-side surface of the third lens L31 is an aspheric surface S3. The aspheric surface S3 is configured so that the radius of curvature of the periphery (the outermost periphery of the effective beam diameter) is smaller than the radius of curvature of the center (on the optical axis). The third substrate L32 functions as a cover glass that protects the image sensor (imaging element) and the third lens L31.

[0018] In each embodiment, in order to realize a small and low-cost optical system, the first unit L1, the second unit L2, and the third unit L3 are manufactured by a wafer-level process. That is, the first unit L1, the second unit L2, and the third unit L3 are each manufactured by forming a lens layer made of a curable resin material on a wafer (flat substrate) made of a glass material. In the second unit L2, an aperture stop SP is formed on the object side of the second substrate L21 by a similar wafer process. A large number of wafer-level lenses can be manufactured by arranging the first unit L1, the second unit L2, the third unit L3, and the image sensor manufactured by the wafer-level process at desired intervals, bonding them outside the effective beam diameter, etc., and then cutting them.

[0019] The material forming the lens layer may be a thermoplastic resin or an ultraviolet-curable resin as long as it is a curable resin material. Examples include acrylic resin, silicone resin, and cycloolefin polymer. In each embodiment, the first substrate L11, the second substrate L21, and the third substrate L32 are each made of glass, and the first lens L12, the second lens L22, and the third lens L31 are each made of resin, but this is not limited thereto. If the refractive indexes of the first substrate L11 and the first lens L12 are different from each other, for example, both the first substrate L11 and the first lens L12 may be made of resin. This also applies to the second unit L2 and the third unit L3.

[0020] The aperture stop SP can be formed on the second substrate L21 by depositing a light-shielding film such as chromium using a mask, or by forming an opening by etching after deposition.

[0021] In each embodiment, the cover glass (third substrate L32) is an integrated glass substrate, but is not limited to this. For example, the cover glass may be divided into two pieces, one of which is bonded to the third lens L31 side and the peripheral portion thereof by a wafer process to form a wafer lens portion, and the other may be used as a cover glass for an image sensor to manufacture a sensor portion, and then the wafer lens portion and the sensor portion may be bonded to each other on their respective flat surfaces.

[0022] In each embodiment, in order to achieve a wide-angle, bright, and compact optical system with a simple configuration consisting of three lens surfaces, the power ratio between the first lens L12 arranged on the object side of the aperture stop SP and the second lens L22 and third lens L31 arranged on the image side of the aperture stop SP is appropriately set. Specifically, when the power of the center (on the optical axis) of the first lens L12 is P1, the power of the center (on the optical axis) of the second lens L22 is P2, and the power of the center (on the optical axis) of the third lens L31 is P3, the following conditional formula (1) is satisfied.

[0023] |P1| / |P2+P3|<1 (1) Here, the power P of each lens is given by P = ΔN / R, where NR is the refractive index of the image-side surface of each lens, NF is the refractive index of the object-side surface, ΔN = NR - NF is the refractive index difference between the object-side surface and image-side surface of each lens, and R is the radius of curvature of each lens on the optical axis.

[0024] When the power P1 of the center of the first lens L12 becomes large, the light beam on the image side of the first lens L12 spreads, and the on-axis light beam and the off-axis light beam are not separated by the aperture stop SP. This makes it difficult for the second lens L22 and the third lens L31 to independently correct various aberrations such as spherical aberration and curvature of field. In addition, in each embodiment, since two lenses are arranged on the image side of the aperture stop SP, the role of aberration correction can be shared between the second lens L22 and the third lens L31. As a result, the angle of incidence of off-axis light on the image plane IP can be reduced while correcting various aberrations, making it possible to obtain a high-resolution image.

[0025] In each embodiment, in order to more effectively achieve both reduction in aberrations and size reduction, it is preferable to satisfy the following condition (2).

[0026] -1.00 <P1 / (P2+P3)<-0.15 ···(2) If the lower limit of conditional expression (2) is exceeded, the power of the first lens L12 becomes large, the distance on the optical axis between the first lens L12 and the aperture stop SP becomes long, and the effective diameter of the light beam of the surface closest to the object becomes large. On the other hand, if the upper limit of conditional expression (2) is exceeded, the combined power of the second lens L22 and the third lens L31 becomes large, and various aberrations such as field curvature increase.

[0027] More preferably, the numerical range of conditional expression (2) is set as shown in the following conditional expression (2a).

[0028] -0.80 <P1 / (P2+P3)<-0.20 ···(2a) More preferably, the numerical range of conditional expression (2) is set as in the following conditional expression (2b).

[0029] -0.75 <P1 / (P2+P3)<-0.25 ···(2b) In the optical system of each embodiment, the second lens L22 and the third lens L31 are arranged close to each other, so that the aberration correction can be distributed to each lens. As a result, the angle of incidence on the image plane IP can be reduced while correcting various aberrations well. Specifically, when the distance on the optical axis from the image side surface of the second lens L22 to the object side surface of the third lens L31 is d3 and the distance on the optical axis from the aperture stop SP to the object side surface of the third lens L31 is ds3, it is preferable to satisfy the following conditional formula (3).

[0030] 0.01 <d3 / ds3<0.40 ···(3) If the lower limit of conditional expression (3) is exceeded, the distance between the second lens L22 and the third lens L31 becomes small, and high positioning accuracy is required, which increases the difficulty of manufacturing. On the other hand, if the upper limit of conditional expression (3) is exceeded, the distance between the second lens L22 and the third lens L31 increases, which changes the role of aberration correction. As a result, the effect of suppressing the angle of incidence on the image plane IP decreases.

[0031] In the optical system of each embodiment, the second lens L22 and the third lens L31 are configured to have a concave air lens at the outer periphery, so that the distance between the second lens L22 and the third lens L31 can be increased for off-axis light beams. As a result, the role of aberration correction can be shared between the axial light beam and the off-axis light beam, so that various aberrations can be easily corrected. Specifically, when the reciprocal of the radius of curvature of the peripheral portion (the outermost portion of the effective beam diameter) of the second lens L22 is PA2 and the reciprocal of the radius of curvature of the peripheral portion (the outermost portion of the effective beam diameter) of the third lens L31 is PA3, it is preferable to satisfy the following conditional formula (4).

[0032] PA3-PA2<0 (4) By satisfying conditional expression (4), it is possible to provide a configuration in which the second lens L22 and the third lens L31 have a concave air lens on their outer peripheries.

[0033] The shape of the aspheric surface in each embodiment is expressed by the following formula (a), where X is the amount of displacement from the surface vertex 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, k is the conic constant, and Ai: (i=4, 6, 8, ...) is the aspheric coefficient of each order.

[0034]

number

[0035] The inclination of the aspheric shape at the height h in the optical axis direction can be calculated from the differentiation of formula (a). The differentiation of formula (a) is expressed by the following formula (b).

[0036]

number

[0037] The local radius of curvature Re at a height h in the optical axis direction can be calculated from the following formula (c) by setting the conic coefficient k in formula (b) and the aspheric coefficient Ai of each order to 0.

[0038]

number

[0039] In the optical system of each embodiment, in order to correct various aberrations more satisfactorily, it is preferable to satisfy the following conditional expression (5), where f is the focal length of the entire optical system.

[0040] 0.8<(PA3-PA2)*f<2.0 (5) If the lower limit of conditional expression (5) is exceeded, the power of the air lens becomes weak, making it difficult to share the role of aberration correction between the on-axis light beam and the off-axis light beam. On the other hand, if the upper limit of conditional expression (5) is exceeded, the radius of curvature of each of the lens surfaces of the second lens L22 and the third lens L31 becomes small, so the amount of aberration generated on the lens surfaces increases, making it difficult to cancel the aberration with the first lens L12.

[0041] In the optical system of each embodiment, by appropriately setting the power of the negative lens in front of the aperture stop SP and the power of the lens group with positive power behind the aperture stop SP while arranging lens surfaces in front of the aperture stop SP, it is possible to achieve size reduction and reduction of various aberrations. For this reason, it is preferable to provide the aperture stop SP in the second unit L2 located immediately behind the first unit L1. More preferably, the aperture stop SP is arranged close to the second substrate L21 (for example, arranged on the second substrate L21). By arranging the aperture stop SP close to the second substrate L21 of the second unit L2, the aperture stop SP can be formed in a wafer process, resulting in an easy-to-manufacture configuration. Note that the aperture stop SP can be easily manufactured whether it is formed on the object side surface of the second substrate L21 facing the air surface or on the image side surface of the second substrate L21 facing the second lens L22.

[0042] In the optical system of each embodiment, the image side surface of the first lens L12 is preferably an aspheric surface S1. Also, in the aspheric surface S1 of the first lens L12, the power of the peripheral portion (the outermost portion of the effective beam diameter) is smaller than the power of the central portion (on the optical axis). This makes it possible to reduce various aberrations. Specifically, when the power ratio of the central portion to the peripheral portion of the first lens L12 is rp1, it is preferable to satisfy the following conditional expression (6).

[0043] 1.05<|rp1|<10.00 (6) Here, the power ratio rp1 of the central portion to the peripheral portion of the first lens L12 is calculated by the following formula (7).

[0044] rp1 = R1e / R1 (7) In equation (7), R1 is the radius of curvature of the center of the aspheric surface S1 on the image side of the first lens L12, and R1e is the radius of curvature of the peripheral portion of the aspheric surface S1 on the image side of the first lens L12, and are calculated in the same manner as in equations (a), (b), and (c) described above.

[0045] If the lower limit of conditional expression (6) is exceeded, the aspheric effect of the first lens L12 becomes small, making it difficult to reduce various aberrations (field curvature and distortion) for off-axis light. On the other hand, if the upper limit of conditional expression (6) is exceeded, the power of the center of the first lens L12 becomes strong, the effective diameter of the light beam on the surface closest to the object becomes large, and the optical system becomes large.

[0046] More preferably, the numerical range of conditional expression (6) is set as in the following conditional expression (6a).

[0047] 1.15<|rp1|<8.00 (6a) More preferably, the numerical range of conditional expression (6) is set as in the following conditional expression (6b).

[0048] 1.15<|rp1|<6.00 (6b) In addition, in the optical system of each embodiment, the image side surface of the second lens L22 and the object side surface of the third lens L31 are both aspheric, and in combination with the aspheric surface of the first lens L12, the aberrations of the on-axis light beam and the off-axis light beam are corrected in a well-balanced manner. Here, the ratio (power ratio) of the total power of the central portions of the second lens L22 and the third lens L31 to the total power of the peripheral portions of the second lens L22 and the third lens L31 is rp23. In this case, by satisfying the following conditional expression (7), various aberrations can be corrected well. 1.00<|rp23|<10.00 ···(7) In conditional formula (7), the power ratio rp23 is given by the following formula (8a) when the power of the center of the second lens L22 is P2, the power of the peripheral portion is P2e, and the power of the center of the third lens L31 is P3, and the power of the peripheral portion is P3e.

[0049] rp23=(P2+P3) / (P2e+P3e) ···(8a) Here, the power P (P2, P3) is given by the following equation (8b), where the refractive index of the image-side surface of each lens is NR, the refractive index of the object-side surface is NF, and the radius of curvature of the center is R.

[0050] P = (NR - NF) / R (8b) Similarly, the power Pe (P2e, P3e) is given by the following equation (8c), where the refractive index of the image-side surface of each lens is NR, the refractive index of the object-side surface is NF, and the radius of curvature of the peripheral portion is Re.

[0051] Pe = (NR - NF) / Re (8c) If the lower limit of conditional expression (7) is exceeded, the aspheric effect of the second lens L22 and the third lens L31 becomes small, making it difficult to reduce various aberrations (field curvature and distortion) for off-axis light. On the other hand, if the upper limit of conditional expression (7) is exceeded, the power of the center of the second lens L22 or the third lens L31 becomes strong, making it difficult to correct spherical aberration for the axial light beam, or the lens curvature becomes large, making manufacturing more difficult, which is not preferable.

[0052] More preferably, the numerical range of conditional expression (7) is set as in the following conditional expression (7a).

[0053] 1.05<|rp23|<6.00 (7a) More preferably, the numerical range of conditional expression (7) is set as in the following conditional expression (7b).

[0054] 1.05<|rp23|<4.00 (7b) Furthermore, when the power ratio of the center to the peripheral portion of the second lens L22 is rp2 and the power ratio of the center to the peripheral portion of the third lens L31 is rp3, it is preferable that either one of the power ratios rp2 or rp3 satisfies the following conditional expressions (9a) and (9b).

[0055] 0.01<|rp2|<1.00 (9a) 0.01<|rp3|<1.00 (9b) By satisfying either conditional expression (9a) or (9b), one of the second lens L22 and the third lens L31 can be made an aspheric surface with a strong power in the peripheral portion, and the other can be made an aspheric surface with a weak power in the peripheral portion. As a result, the role of correcting aberrations of on-axis light beams and off-axis light beams can be shared between the central portion and the peripheral portion of the second lens L22 or the third lens L31, and various aberrations can be corrected well.

[0056] If the lower limits of both conditional expressions (9a) and (9b) are exceeded, the power at the center becomes too weak, making it difficult to correct spherical aberration of the on-axis light beam, etc. On the other hand, if the upper limits of both conditional expressions (9a) and (9b) are exceeded, it becomes impossible to separate the roles of aberration correction between the on-axis light beam and the off-axis light beam, making it difficult to correct various aberrations.

[0057] It is more preferable that the numerical ranges of the conditional expressions (9a) and (9b) are the numerical ranges of the following conditional expressions (9c) and (9d), respectively.

[0058] 0.04<|rp2|<0.80 (9c) 0.04<|rp3|<0.80 (9d) In the optical system of each embodiment, when the distance on the optical axis from the object-side surface of the first unit L1 to the aperture stop SP is d0 and the radius of curvature of the center of the first lens L12 is R1, it is preferable to satisfy the following conditional expression (10).

[0059] 0.50 <d0 / R1<4.00 ···(10) If the lower limit of condition (10) is exceeded, the power of the first lens L12 will be strong or the distance to the aperture stop SP will be small, making it difficult to reduce various aberrations. On the other hand, if the upper limit of condition (10) is exceeded, the effective diameter of the light beam at the surface closest to the object will be large, resulting in a large optical system.

[0060] More preferably, the numerical range of conditional expression (10) is set as in the following conditional expression (10a).

[0061] 0.70 <d0 / R1<2.00 ···(10a) In each embodiment, the first lens L12, the second lens L22, and the third lens L31 are each made of a curable resin, so that they can be easily manufactured. In addition, in the wafer level optics, wiring is installed by soldering or the like after the wafer level lens and the image sensor are joined, so a resin that can withstand a certain degree of high temperature is preferable. In addition, when the optical system of each embodiment is used as an imaging optical system, it is preferable to use a material with low birefringence. From the above, it is preferable to select a material with a refractive index of about 1.5 as the resin material used for the wafer level lens.

[0062] In each embodiment, when the refractive index of the first lens L12 at the d-line is N1, it is preferable to satisfy the following conditional expression (11).

[0063] 1.40 <N1<1.65 ···(11) More preferably, the numerical range of conditional expression (11) is set as in the following conditional expression (11a).

[0064] 1.45 <N1<1.63 ···(11a) In each embodiment, when the refractive index at the d-line of the lens having the greater absolute value of the power at the center between the second lens L22 and the third lens L31 is N23, it is preferable to satisfy the following conditional expression (12).

[0065] 1.40 <N23<1.65 ···(12) More preferably, the numerical range of conditional expression (12) is set as in the following conditional expression (12a).

[0066] 1.45 <N23<1.63 ···(12a) If the lower limit of each of the conditional expressions (11) and (12) is exceeded, the curvature of each lens increases, making it difficult to manufacture and correct the curvature of field. On the other hand, if the upper limit of each of the conditional expressions (11) and (12) is exceeded, the dispersion of the material increases, making it impossible to tolerate an increase in chromatic aberration and increasing birefringence, which is undesirable.

[0067] The optical system of each embodiment has a configuration in which a first lens L12 with negative power is disposed closer to the object side than the aperture stop SP, and a second lens L22 and a third lens L31 with positive power are disposed closer to the image side than the aperture stop SP to cancel out aberrations. Therefore, by using low-dispersion materials for both the first lens L12 and the second lens L22, axial chromatic aberration and lateral chromatic aberration can be corrected satisfactorily.

[0068] In each embodiment, when the Abbe number of the first lens L12 with respect to the d-line is ν1, it is preferable to satisfy the following conditional expression (13).

[0069] 40<ν1<80 (13) More preferably, the numerical range of conditional expression (13) is set as in the following conditional expression (13a).

[0070] 45<ν1<70 (13a) In each embodiment, when the Abbe number based on the d-line of the lens having the greater absolute value of power at the center out of the second lens L22 and the third lens L31 is ν23, it is preferable to satisfy the following conditional expression (14).

[0071] 40<ν23<80 (14) More preferably, the numerical range of conditional expression (14) is set as in the following conditional expression (14a).

[0072] 45<ν23<70 (14a) If the lower limit of each of the conditional expressions (13) and (14) is exceeded, it becomes difficult to correct chromatic aberration, whereas if the upper limit of each of the conditional expressions (13) and (14) is exceeded, the refractive index becomes low, the curvature of field increases, and the material becomes expensive, which is undesirable.

[0073] In each embodiment, the Abbe number ν23 of the lens having the greater absolute value of the power at the center between the second lens L22 and the third lens L31 is closer to the Abbe number ν1 of the first lens L12, which is preferable for good balance in chromatic aberration correction. Specifically, it is preferable to satisfy the following conditional expression (15).

[0074] 0≦|ν1−ν23|<15 (15) The Abbe number ν is expressed by the following formula, where nd, nF, and nC are the refractive indices at the Fraunhofer lines d-line (wavelength 587.6 nm), F-line (wavelength 486.1 nm), and C-line (wavelength 656.3 nm).

[0075] ν=(nd-1) / (nF-nC) The optical system of each embodiment will be described in detail below. EXAMPLES

[0076] First, an optical system 1a in Example 1 (Numerical Example 1) will be described with reference to FIG. 1. The optical system 1a in this example has a first unit L1, a second unit L2, and a third unit L3 arranged in this order from the object side to the image side. The first unit L1 has a first substrate (flat substrate) L11, and a first lens (plano-concave lens) L12 with negative power arranged on the image side of the first substrate L11. The second unit L2 has a second substrate (flat substrate) L21, a second lens (plano-convex lens) L22 arranged on the image side of the second substrate L21, and an aperture stop SP arranged on the object side of the second substrate L21. The third unit L3 has a third substrate (flat substrate) L32, and a third lens L31 arranged on the object side of the third substrate L32.

[0077] The optical system 1a of this embodiment has a half angle of view of 59°, an F-number of 2.9, and an image height of 0.28 mm, and is a small yet bright wide-angle optical system. When miniaturizing a wide-angle optical system with a half angle of view of 50° or more, as in this embodiment, it is necessary to reduce the effective diameter of the light beam at the surface closest to the object while shortening the overall length and controlling various aberrations. If the effective diameter of the light beam at the surface closest to the object becomes large, the size of one optical system becomes large, and the number of optical systems that can be produced from one wafer becomes small, resulting in a high-cost manufacturing method.

[0078] Furthermore, when the wafer level optics is used in a small imaging device such as an endoscope or a smartphone, it is preferable that the surface closest to the object side is made of a hard, environmentally resistant material such as a glass material. Since it is difficult to make the surface of a glass material curved in the wafer process, it is preferable that the surface closest to the object side (the third substrate L32) is a flat glass surface.

[0079] In the optical system 1b of this embodiment, the angle at which the chief ray of the most off-axis light beam strikes the image plane IP is as small as 18.2 degrees in air, so a high-resolution image can be obtained. As shown in Fig. 2, in the optical system 1a of this embodiment, although it is a small, bright, wide-angle optical system, various aberrations such as chromatic aberration are well corrected from the on-axis to the off-axis light beam (periphery of the screen). EXAMPLES

[0080] Next, the optical system 1b in Example 2 (Numerical Example 2) will be described with reference to Fig. 3. The basic configuration of the optical system 1b in this example is similar to that of the optical system 1a in Example 1. Meanwhile, in the optical system 1b in this example, the thickness (thickness in the optical axis direction) of the first substrate L11 of the first unit L1, the thickness of the second substrate L21 of the second unit L2, and the thickness of the cover glass 50 are each thicker than those of the optical system 1a in Example 1. For this reason, the optical system 1b in this example is configured to be less susceptible to cracks or deformations during transportation in the wafer process, and is easily manufactured.

[0081] The optical system 1b of this embodiment has a half angle of view of 59°, an F-number of 2.9, and an image height of 0.28 mm, making it a small, bright, wide-angle optical system. In addition, the angle at which the chief ray of the most off-axis light beam of the optical system 1b of this embodiment is incident on the image surface IP is small at 16.0° in air, so that a high-resolution image can be obtained. As shown in FIG. 4, in the optical system 1b of this embodiment, although it is a small, bright, wide-angle optical system, various aberrations are well corrected from the on-axis to off-axis light beams. EXAMPLES

[0082] Next, an optical system 1c in Example 3 (Numerical Example 3) will be described with reference to Fig. 5. In the optical system 1c of this example, the aperture stop SP of the second unit L2 is disposed on the image side of the second substrate L21 of the second unit L2. In the optical system 1c of this example, the power P3 of the center of the third lens L31 is stronger than the power P2 of the center of the second lens L22.

[0083] The optical system of this embodiment has a half angle of view of 59°, an F-number of 2.89, and an image height of 0.28 mm, making it a small, bright, wide-angle optical system. In addition, the angle at which the chief ray of the most off-axis light beam of the optical system 1d of this embodiment is incident on the image surface IP is small at 20.0° in air, so that a high-resolution image can be obtained. As shown in FIG. 6, in the optical system 1c of this embodiment, although it is a small, bright, wide-angle optical system, various aberrations are well corrected from the on-axis to off-axis light beams. EXAMPLES

[0084] Next, an optical system 1d in Example 4 (Numerical Example 4) will be described with reference to Fig. 7. In the optical system 1d of this example, the aperture stop SP of the second unit L2 is disposed on the image side of the second substrate L21 of the second unit L2, similar to Example 3. In the optical system 1d of this example, the power P3 of the center of the third lens L31 is stronger than the power P2 of the center of the second lens L22.

[0085] The optical system 1d of this embodiment has a half angle of view of 59°, an F-number of 2.9, and an image height of 0.28 mm, making it a small, bright, wide-angle optical system. In addition, the angle at which the chief ray of the most off-axis light beam of the optical system 1d of this embodiment is incident on the image surface IP is small at 17.9° in air, so that a high-resolution image can be obtained. As shown in FIG. 8, in the optical system 1d of this embodiment, although it is a small, bright, wide-angle optical system, various aberrations are well corrected from the on-axis to off-axis light beams.

[0086] Numerical Examples 1 to 4 corresponding to Examples 1 to 4, respectively, are shown below. In each numerical example, m indicates the number of the surface or optical element counted from the light incident side. For example, Rm is the radius of curvature (mm) of the mth optical surface (mth surface). Dm is the axial distance (mm) between the mth surface and the (m+1)th surface. Nd is the refractive index of the material of the optical element for the d-line. νd is the Abbe number of the material of the optical element for the d-line. "E±XX" means "×10 ±XX " f is the focal length, Fno is the effective F-number, ω is the half angle of view (degrees), BF is the back focus, which is the distance from the final surface of the optical system to the image plane.

[0087] (Numerical Example 1) f=0.190 Fno= 2.9 2ω=118° Surface number RD Nd νd Effective diameter 1 ∞ 0.100 1.5168 64.2 0.65 2 ∞ 0.015 1.5100 57.5 0.52 3(Aspherical surface) 0.3713 0.192 0.46 4 (Aperture) ∞ 0.005 0.08 5 ∞ 0.100 1.5168 64.2 0.08 6 ∞ 0.212 1.5100 57.5 0.20 7(Aspherical surface)-0.1297 0.019 0.33 8 (Aspherical surface) 1.4709 0.020 1.5300 56.0 0.46 9 ∞ 0.400 1.5168 64.2 0.46 10 ∞ 0.58 BF = 0.02 Aspheric coefficients 3rd page 7th page 8th page K -1.53475E-01 -4.57347E-01 -3.06926E+05 A4 -5.12770E+01 -5.03263E+00 -3.85649E+01 A6 1.59616E+03 2.77817E+03 1.40993E+03 A8 -3.84752E+04 -8.84526E+04 -1.19111E+04 A10 5.45644E+05 3.05037E+06 0.00000E+00 A12 -3.17073E+06 7.53366E+06 0.00000E+00 (Numerical Example 2) f=0.270 Fno= 2.9 2ω=118° Surface number RD Nd νd Effective diameter 1 ∞ 0.200 1.5168 64.2 0.70 2 ∞ 0.015 1.5100 57.5 0.43 3(Aspherical surface) 0.2471 0.201 0.33 4 (Aperture) ∞ 0.000 1.5900 31.0 0.13 5 ∞ 0.200 1.5168 64.2 0.13 6 ∞ 0.099 1.5100 57.5 0.33 7(Aspherical surface)-0.1737 0.015 0.34 8 (Aspherical) 2.1865 0.031 1.5100 57.5 0.40 9 ∞ 0.700 1.5168 64.2 0.40 10 ∞ 0.59 BF = 0.02 Aspheric coefficients 3rd page 7th page 8th page K -2.70061E-01 -8.02146E-01 -1.00565E+05 A4 -3.66399E+01 1.67753E+01 2.52967E+01 A6 3.70783E+03 2.89776E+01 -7.80701E+02 A8 -2.31286E+05 -4.22271E+04 1.48780E+04 A10 6.66197E+06 1.87184E+06 -1.32383E+05 A12 -7.18648E+07 -2.87542E+07 0.00000E+00 (Numerical Example 3) f=0.204 Fno= 2.89 2ω=118° Surface number RD Nd νd Effective diameter 1 ∞ 0.200 1.5168 64.2 0.70 2 ∞ 0.015 1.5100 57.5 0.43 3(Aspherical surface) 0.3575 0.054 0.37 4 ∞ 0.200 1.5168 64.2 0.30 5(Aperture) ∞ 0.200 1.5100 57.5 0.09 6(Aspherical surface)-1.4001 0.050 0.26 7 (Aspherical surface) 0.1368 0.063 1.5300 56.0 0.40 8 ∞ 0.400 1.5168 64.2 0.41 9 ∞ 0.58 BF = 0.02 Aspheric coefficients 3rd page 6th page 7th page K 2.06682E+00 -2.56116E+06 -3.99423E+00 A4 -6.59715E+01 -3.05178E+02 -5.21606E+01 A6 2.36697E+03 2.18324E+04 1.28637E+03 A8 -8.54718E+04 -1.20470E+06 -9.95378E+03 A10 1.86501E+06 4.51753E+07 0.00000E+00 A12 -2.03631E+07 -7.75518E+08 0.00000E+00 (Numerical Example 4) f=0.275 Fno= 2.9 2ω=118° Surface number RD Nd νd Effective diameter 1 ∞ 0.200 1.5168 64.2 0.70 2∞ 0.011 1.5101 57.5 0.43 3(Aspherical surface) 0.3348 0.081 0.36 4 ∞ 0.200 1.5168 64.2 0.29 5(Aperture) ∞ 0.200 1.5100 57.5 0.12 6(Aspherical surface)-2.9979 0.040 0.27 7 (Aspherical) 0.1707 0.059 1.5300 56.0 0.38 8 ∞ 0.600 1.5168 64.2 0.38 9 ∞ 0.58 BF = 0.02 Aspheric coefficients 3rd page 6th page 7th page K 2.11585E+00 -1.19183E+12 -7.69448E+00 A4 -3.98680E+01 -2.13502E+02 -5.56017E+00 A6 3.62107E+03 1.92912E+04 1.69983E+02 A8 -2.51358E+05 -1.36845E+06 -1.94080E+03 A10 7.64948E+06 5.50551E+07 0.00000E+00 A12 -9.40829E+07 -9.21969E+08 0.00000E+00 Table 1 shows the relationship between the numerical values ​​of the above-mentioned conditional expressions (1) to (15) and each numerical example.

[0088] [Table 1]

[0089] In the first to fourth embodiments, the imaging optical system has been described. The optical system in each embodiment is suitable for use as a built-in camera in electronic devices such as mobile phones, smartphones, and wearable devices, and as an objective optical system in an endoscope. EXAMPLES

[0090] Next, an electronic device according to a fifth embodiment of the present invention will be described with reference to FIG. 9. FIG. 9 is a schematic diagram of a main part of an electronic device (smartphone 70) according to this embodiment. The smartphone 70 has an imaging device 71 as a front camera module. The imaging device 71 has an optical system 72 corresponding to any one of the optical systems according to the first to fourth embodiments described above, and an imaging element 73 that receives an image formed by the optical system 72. In this way, by applying the optical system according to each of the embodiments described above to an imaging device such as a smartphone, it is possible to realize an imaging device that is small in size yet has high optical performance. EXAMPLES

[0091] Next, an imaging device according to a sixth embodiment of the present invention will be described with reference to FIG. 10. FIG. 10 is a schematic diagram of a main part of an imaging device 100 according to this embodiment. The imaging device 100 is used in a small endoscope, and has a camera head 120 and an electric cable 150. The camera head 120 has a lens housing 121 mounting the optical system according to any one of the first to sixth embodiments, an image sensor (imaging element) 122, and a ceramic substrate 123. The wiring of the electric cable 150 is connected to the image sensor 122 via the ceramic substrate 123. In this way, by applying the optical system according to each of the above-mentioned embodiments to an imaging device for an endoscope, it is possible to realize an imaging device that is small in size yet has high optical performance.

[0092] According to each embodiment, it is possible to provide a small-sized, low-cost optical system and an imaging device having a small, wide-angle image plane incidence angle.

[0093] 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. [Explanation of symbols]

[0094] 1a~1d Optical system L1 1st unit L11 First board L12 1st lens L2 2nd unit L21 Second board L22 2nd lens L31 3rd lens L32 3rd board

Claims

1. The optical system comprises a first unit, a second unit, and a third unit, which are arranged in this order from the object side to the image side, the first unit includes a first substrate and a first lens having a negative power arranged on an image side of the first substrate; the second unit includes a second substrate and a second lens disposed on an image side of the second substrate; the third unit includes a third substrate and a third lens disposed on an object side of the third substrate; an aperture stop is disposed on the image side of the first unit; When the power of the first lens on the optical axis is P1, the power of the second lens on the optical axis is P2, the power of the third lens on the optical axis is P3, the distance on the optical axis from the object side surface of the first unit to the aperture stop is d0, and the radius of curvature of the first lens on the optical axis is R1, |P1| / |P2+P3|<1 0.50<d0 / R1<4.00 An optical system characterized in that the following condition is satisfied:

2. -1.00<P1 / (P2+P3)<-0.15 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. 3. The optical system according to claim 1, wherein the aperture stop is disposed on the second substrate.

4. When the distance on the optical axis from the image side surface of the second lens to the object side surface of the third lens is d3, and the distance on the optical axis from the aperture stop to the object side surface of the third lens is ds3, 0.01<d3 / ds3<0.40 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the reciprocal of the radius of curvature of the outermost periphery of the effective diameter of the light beam of the second lens is PA2, and the reciprocal of the radius of curvature of the outermost periphery of the effective diameter of the light beam of the third lens is PA3, PA3-PA2<0 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the focal length of the entire optical system is f, 0.8<(PA3-PA2)*f<2.0 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. When the power ratio on the optical axis to the outermost periphery of the effective beam diameter of the first lens is rp1, 1.05<|rp1|<10.00 7. The optical system according to claim 1, wherein the following condition is satisfied:

8. A lens system comprising a first unit, a second unit, and a third unit arranged in this order from the object side to the image side, the first unit includes a first substrate and a first lens having a negative power arranged on an image side of the first substrate; the second unit includes a second substrate and a second lens disposed on an image side of the second substrate; the third unit includes a third substrate and a third lens disposed on an object side of the third substrate; When the power of the first lens on the optical axis is P1, the power of the second lens on the optical axis is P2, the power of the third lens on the optical axis is P3, and the power ratio of the first lens on the optical axis to the outermost peripheral part of the effective beam diameter is rp1, |P1| / |P2+P3|<1 1.05<|rp1|<10.00 An optical system characterized in that the following condition is satisfied:

9. When the power ratio of the sum of the powers on the optical axis of the second lens and the third lens to the sum of the powers of the outermost peripheral parts of the effective diameter of the light beam of the second lens and the third lens is rp23, 1.00<|rp23|<10.00 9. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the power ratio on the optical axis to the outermost periphery of the effective beam diameter of the second lens is rp2, 0.01<|rp2|<1.00 10. The optical system according to claim 1, wherein the following condition is satisfied:

11. When the power ratio on the optical axis to the outermost periphery of the effective beam diameter of the third lens is rp3, 0.01<|rp3|<1.00 11. The optical system according to claim 1, wherein the following condition is satisfied:

12. When the refractive index of the first lens at the d line is N1, 1.40<N1<1.65 12. The optical system according to claim 1, wherein the following condition is satisfied:

13. When the refractive index at the d line of the lens having the larger absolute value of the power on the optical axis between the second lens and the third lens is N23, 1.40<N23<1.65 13. The optical system according to claim 1, wherein the following condition is satisfied:

14. When the Abbe number of the first lens based on the d-line is ν1, 40<v1<80 14. The optical system according to claim 1, wherein the following condition is satisfied:

15. When the Abbe number based on the d line of the lens having the larger absolute value of the power on the optical axis between the second lens and the third lens is ν23, 40<v23<80 15. The optical system according to claim 1, wherein the following condition is satisfied:

16. The optical system according to claim 1 , wherein the first substrate and the first lens have mutually different refractive indices.

17. The optical system according to claim 1 , wherein the second substrate and the second lens have mutually different refractive indices.

18. 18. The optical system according to claim 1, wherein the third substrate and the third lens have mutually different refractive indices.

19. 19. An imaging apparatus comprising: an optical system according to claim 1; and an imaging element that receives an image formed by the optical system.

Images