Optical system and imaging device

Abstract

To provide an optical system and an imaging device that have a small size and a high optical performance and require less cost.SOLUTION: An optical system (1a) 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 (11) and a first lens (12) with a negative power arranged on an image side of the first substrate. The second unit has a second substrate (21) and a second lens (22) with a positive power arranged on an object side of the second substrate. The third unit has a third substrate (31) and a third lens (32) with a positive power arranged on an object side of the third substrate.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, there has been a demand for compact optical systems suitable for use in medical endoscopes, etc. Furthermore, such optical systems are required to have high optical performance in order to perform accurate diagnoses, treatments, etc. Patent Document 1 discloses a compact lens system for medical endoscopes that is manufactured by a wafer-level process. [Prior art documents] [Patent documents]

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

[0004] However, the lens system disclosed in Patent Document 1 requires a large number of substrates and bonding steps in the wafer level process, which increases costs.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide an optical system and an imaging apparatus that are small in size, low in cost, and have high optical performance. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided an optical system including 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 includes a first substrate and a third unit disposed on the image side of the first substrate. Face and a first lens having a negative power disposed on the object side of the second substrate. Face and a second lens having a positive power disposed on the object side of the third substrate. Face and a third lens having a positive power disposed at the first unit does not have any lens other than the first lens, the second unit does not have any lens other than the second lens, The third unit is before The lens does not include any lens other than the third lens.

[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 an optical system and an imaging device that are small in size, low in cost, and have high optical performance. [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 cross-sectional view of an optical system in Example 5. [Figure 10] 13A to 13C are aberration diagrams of the optical system in Example 5. [Figure 11] FIG. 13 is a cross-sectional view of an optical system in Example 6. [Figure 12] 13A to 13C are aberration diagrams of the optical system in Example 6. [Figure 13] FIG. 13 is a cross-sectional view of an optical system in Example 7. [Figure 14] 13A to 13C are aberration diagrams of the optical system in Example 7. [Figure 15]FIG. 13 is a cross-sectional view of an optical system in Example 8. [Figure 16] 13A to 13C are aberration diagrams of the optical system in Example 8. [Figure 17] FIG. 11 is a cross-sectional view of an optical system as a comparative example. [Figure 18] FIG. 13 is a schematic diagram of a main part of an electronic device according to a fifth embodiment. [Figure 19] 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, 7, 9, 11, 13, and 15 are cross-sectional views of optical systems (wafer-level lenses) 1a, 1b, 1c, 1d, 1e, 1f, 1g, and 1h of Examples 1 to 8, 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, 8, 10, 12, 14, and 16 are aberration diagrams of the optical systems 1a, 1b, 1c, 1d, 1e, 1f, 1g, and 1h of Examples 1 to 8, respectively. Each aberration diagram includes (A) a spherical aberration diagram, (B) an astigmatism diagram, (C) a distortion aberration diagram, and (D) a lateral chromatic aberration diagram. In the spherical aberration diagram, the spherical aberration amounts for the d-line (wavelength 587.6 nm), the g-line (wavelength 435.8 nm), the C-line (wavelength 656.3 nm), and the F-line (wavelength 486.1 nm) are shown, respectively. In the astigmatism diagram, ΔSd and ΔSg indicate the astigmatism amounts in the sagittal image plane for the d-line and the g-line, respectively, and ΔMd and ΔMg indicate the astigmatism amounts in the meridional image plane for the d-line and the g-line, respectively. The distortion diagram shows the amount of distortion for the d-line, and the lateral chromatic aberration diagram shows the amount of chromatic aberration for the g-line, C-line, and F-line.

[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 (front cover glass) 11 and a first lens 12 with negative power arranged on the image side of the first substrate 11. The second unit L2 has a second substrate 21, a second lens 22 with positive power arranged on the object side of the second substrate 21, and an aperture stop SP arranged on the image side of the second substrate 21. The third unit L3 has a third substrate (back cover glass) 31 and a third lens 32 arranged on the object side of the third substrate 31.

[0015] In Examples 1 to 3 and 7, there is a fourth substrate (sensor cover glass) 41 arranged on the image side of the third substrate. In Examples 4 to 6 and 8, the third substrate 31 serves both as a back cover glass and a sensor cover glass.

[0016] The first substrate 11 is a flat substrate, and the first lens 12 is a negative lens (plano-concave lens) with a concave surface facing the image side. The first lens 12 is formed on the image side surface of the first substrate 11 using a wafer level process, and is disposed on the first substrate 11 in close contact with the substrate. The second substrate 21 is a flat substrate, and the second lens 22 is a positive lens (plano-convex lens) with a convex surface facing the object side. The second lens 22 is formed on the object side surface of the second substrate 21 using a wafer level process, and is disposed on the second substrate 21 in close contact with the substrate. The third substrate 31 is a flat substrate, and the third lens 32 is a positive lens (plano-convex lens) with a convex surface facing the object side. The third lens 32 is formed on the object side surface of the third substrate 31 using a wafer level process, and is disposed on the third substrate 31 in close contact with the substrate. The fourth substrate (sensor cover glass) 41 is provided to protect the image sensor (imaging element).

[0017] In each embodiment, in order to realize a small-sized 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 image side of the second substrate 21 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.

[0018] 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 11, the second substrate 21, and the third substrate 31 are each made of glass, and the first lens 12, the second lens 22, and the third lens 32 are each made of resin, but this is not limited thereto. If the refractive indexes of the first substrate 11 and the first lens 12 are different from each other, for example, both the first substrate 11 and the first lens 12 may be made of resin. This also applies to the second unit L2 and the third unit L3.

[0019] The aperture stop SP can be formed on the second substrate 21 by depositing a light-shielding film such as chromium using a mask, or by forming an opening by etching after deposition. In this case, forming the aperture stop SP on a flat surface such as a substrate makes it easier to control the mask arrangement in the thickness direction, which is preferable in terms of manufacturing.

[0020] The optical system of each embodiment is an optical system in which the first unit L1, the second unit L2, and the third unit L3 are integrated. The optical system of each embodiment is bonded to the fourth substrate (sensor cover glass) 41 to function as an imaging system. By forming the lens surface of the third lens 32 on the object side of the third substrate 31 (back cover glass), it is possible to directly bond the back cover glass and the sensor cover glass. With this configuration, it is possible to provide a small optical system with high optical performance with reduced costs for materials and manufacturing processes (i.e., low cost). In addition, it is preferable to use the third substrate 31 as a sensor cover glass and form the lens surface of the third lens 32 on the object side of the third substrate 31, which results in a lower manufacturing cost.

[0021] It is preferable that the optical system of each embodiment satisfies at least one of the following conditional formula (1a) or (1b).

[0022] 1.00 <f2 / f<1.50 ···(1a) 0.60 <f2 / f<1.60 ···(1b) Here, f is the focal length of the optical system (entire system), and f2 is the focal length of the second lens 22. By satisfying conditional formula (1a) or (1b), it becomes possible to correct spherical aberration to an appropriate value.

[0023] More preferably, the numerical range of conditional formula (1a) or conditional formula (1b) is set as in the following conditional formula (1c).

[0024] 0.75 <f2 / f<1.55 ···(1c) More preferably, the numerical range of conditional formula (1a) or (1b) is set as in the following conditional formula (1d).

[0025] 0.85 <f2 / f<1.52 ···(1d) It is also preferable that the optical system of each embodiment satisfies at least one of the following conditional formula (2a) or (2b).

[0026] -2.50 <f3 / f1<-1.80 ···(2a) -3.50 <f3 / f1<-1.50 ···(2b) Here, f1 is the focal length of the first lens 12, and f3 is the focal length of the third lens 32. By satisfying conditional formula (2a) or (2b), it becomes possible to correct astigmatism and distortion to appropriate values.

[0027] More preferably, the numerical range of conditional formula (2a) or conditional formula (2b) is set as in the following conditional formula (2c).

[0028] -3.20 <f3 / f1<-1.60 ···(2c) More preferably, the numerical range of conditional formula (2a) or conditional formula (2b) is set as in the following conditional formula (2d).

[0029] -3.00 <f3 / f1<-1.65 ···(2d) It is also preferable that the optical system of each embodiment satisfies the following conditional formula (3a) or (3b).

[0030] 0.10 <d / f<0.50 ···(3a) 0.07 <d / f<0.65 ···(3b) Here, d is the distance on the optical axis OA from the aperture stop SP to the object-side surface of the third lens 32. By satisfying conditional formula (3a) or conditional formula (3b), it becomes possible to correct astigmatism and distortion to appropriate values.

[0031] More preferably, the numerical range of conditional formula (3a) or conditional formula (3b) is set as in the following conditional formula (3c).

[0032] 0.10 <d / f<0.62 ···(3c) It is also preferable that the optical system of each embodiment satisfies the following conditional formula (4a) or (4b).

[0033] 1.20 <L / f<2.40 ···(4a) 1.00 <L / f<2.40 ···(4b) Here, L is the distance from the third lens 32 to the image plane IP. By satisfying conditional formula (4a) or conditional formula (4b), it becomes possible to correct spherical aberration and astigmatism to appropriate values.

[0034] More preferably, the numerical range of conditional formula (4a) or conditional formula (4b) is set as in the following conditional formula (4c).

[0035] 1.20 <L / f<2.20 ···(4c) Moreover, the optical system of each embodiment is structured to cancel various aberrations between the first lens L12 and the second lens L22, which are located on the object side of the aperture stop SP, while balancing with the aberrations occurring in the third lens L32, which is located on the image side of the aperture stop SP. For this reason, it is preferable to satisfy the following conditional expression (5).

[0036] 0.30<(f2-f1) / f3<1.60 (5) If the lower limit of conditional expression (5) is exceeded, the power of the third lens L32 becomes small, which causes the balance of aberration correction before and after the aperture stop SP to be lost, which is undesirable. On the other hand, if the upper limit of conditional expression (5) is exceeded, the power of the third lens L32 becomes large, which makes it difficult to correct various aberrations, and at the same time, the diameter of the third lens L32 becomes large, which makes it difficult to ensure the outside effective width, resulting in a configuration that is difficult to manufacture.

[0037] More preferably, the numerical range of conditional expression (5) is set as in the following conditional expression (5a).

[0038] 0.50<(f2-f1) / f3<1.60 (5a) More preferably, the numerical range of conditional expression (5) is set as in the following conditional expression (5b).

[0039] 0.60<(f2-f1) / f3<1.55 (5b) In addition, in the optical systems of the respective embodiments, only the third lens L32 is responsible for aberration correction on the image side of the aperture stop SP. Also, the light rays are largely bent at the outer periphery of the third lens L32 to correct high-order aberrations. For this reason, it is preferable to appropriately set the distance d from the aperture stop SP to the third lens L32 and the power of the third lens L32. Specifically, it is preferable to satisfy the numerical range of the following conditional expression (6).

[0040] 0.03 <d / f3<0.40 ···(6) If the lower limit of conditional expression (6) is exceeded, the power of the third lens L32 becomes small, making it difficult to correct aberrations that occur on the image side of the aperture stop SP. On the other hand, if the upper limit of conditional expression (6) is exceeded, the angle of light rays incident on the outer periphery of the third lens L32 becomes gentle, making it difficult to correct high-order aberrations.

[0041] More preferably, the numerical range of conditional expression (6) is set as in the following conditional expression (6a).

[0042] 0.04 <d / f3<0.35 ···(6a) More preferably, the numerical range of conditional expression (6) is set as in the following conditional expression (6b).

[0043] 0.05 <d / f3<0.34 ···(6b) It is also preferable to satisfy the following condition (7), in order to make it possible to correct various aberrations more satisfactorily.

[0044] 1.50 <f3 / f<3.00 ···(7) More preferably, the numerical range of conditional expression (7) is set as in the following conditional expression (7a).

[0045] 1.60 <f3 / f<2.80 ···(7a) In the manufacturing process of the wafer-level lens of each embodiment, the first lens L12 and the second lens L22 are arranged opposite to each other with an air layer between them. Therefore, when bonding the first unit L1 including the first lens L12 and the second unit L2 including the second lens L22, it is necessary to bond the outer peripheries of the first lens L12 and the second lens L22 to each other. Since the first lens L12 and the second lens L22 are usually made of resin, it is a manufacturing issue to bond the outer peripheries of the resin material with high precision to suppress deformation, etc. In addition, in the optical system of each embodiment, the power of the first lens L12 and the second lens L22 is relatively strong to correct high-order aberrations, so each lens tends to be large and the difference in thickness between the optical axis and the outer periphery tends to be large.

[0046] For this reason, it is preferable that the optical system of each embodiment satisfies the following conditional expression (8).

[0047] 0.60 <Lar / (d1+d2)<2.00 ···(8) Here, Lar is the distance between the first lens L12 and the second substrate L21, d1 is the thickness of the first substrate L11, and d2 is the thickness of the second substrate L21. If the lower limit of conditional expression (8) is not met, the thicknesses of the substrates 1 and 2 become too thick, making it impossible to obtain a compact optical system. On the other hand, if the upper limit of conditional expression (8) is exceeded, the thicknesses of the first substrate L11 and the second substrate L21 become too thin, resulting in a configuration that is difficult to manufacture due to many deformations, etc. Alternatively, if the distance between the first lens L12 and the second lens L22 or the thickness of the second lens L22 becomes large, spherical aberration, astigmatism, etc. increase, which is not preferable.

[0048] More preferably, the numerical range of conditional expression (8) is set as in the following conditional expression (8a).

[0049] 0.75 <Lar / (d1+d2)<1.80 ···(8a) The optical system of each embodiment will be described in detail below. EXAMPLES

[0050] First, an optical system 1a in Example 1 (Numerical Example 1) will be described with reference to FIG. 1 and FIG. 2. As shown in FIG. 1, the optical system 1a includes a first unit L1, a second unit L2, and a third unit L3. The first unit L1 includes a first substrate (front cover glass) 11 and a first lens 12 arranged on the image side thereof. The first lens 12 is a negative lens with a concave surface facing the image side, and the focal length f1 of the first lens 12 is f1=-0.224 mm. The first lens 12 is formed on the image side surface of the first substrate 11 using a wafer level process. The second unit L2 includes a second substrate 21 and a second lens 22 arranged on the object side thereof. The second lens 22 is a positive lens with a convex surface facing the object side, and the focal length f2 of the second lens 22 is f2=0.287 mm. The second lens 22 is formed on the object side surface of the second substrate 21 using a wafer level process. The third unit L3 is composed of a third substrate (back cover glass) 31 and a third lens 32 arranged on the object side thereof. The third lens 32 is a positive lens with a convex surface facing the object side, and the focal length f3 of the third lens 32 is f3 = 0.508 mm. The third lens 32 is formed on the object side surface of the third substrate 31 using a wafer level process.

[0051] In this embodiment, the focal length f of the optical system 1a is f=0.238 mm. The distance d on the optical axis from the aperture stop SP to the third lens 32 is d=0.0657 mm. The distance L from the third lens 32 to the image plane IP is L=0.424 mm. The optical system 1a of this embodiment is designed to focus on an object located 10 mm away from the surface of the first unit L1 closest to the object.

[0052] As shown in FIG. 2(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in FIG. 2(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in FIG. 2(C), the distortion of this embodiment is less than 40%. As shown in FIG. 2(D), the lateral chromatic aberration of this embodiment is less than 0.01 mm. Thus, the optical system 1a of this embodiment has appropriate aberrations. EXAMPLES

[0053] Next, an optical system 1b in Example 2 (Numerical Example 2) will be described with reference to FIG. 3 and FIG. 4. As shown in FIG. 3, the basic configuration of the optical system 1b in this example is the same as that of the optical system 1a in Example 1. The focal length f1 of the first lens 12 is f1=-0.230 mm. The focal length f2 of the second lens 22 is f2=0.283 mm. The focal length f3 of the third lens 32 is f3=0.455 mm. The focal length f of the optical system 1b is f=0.235 mm. The distance d from the aperture stop SP to the third lens 32 is d=0.0865 mm. The distance L from the third lens 32 to the image plane IP is L=0.424 mm. The optical system 1b in this example is designed to focus on an object at a position 10 mm from the surface of the first unit L1 closest to the object.

[0054] As shown in FIG. 4(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in FIG. 4(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in FIG. 4(C), the distortion of this embodiment is less than 40%. As shown in FIG. 4(D), the lateral chromatic aberration of this embodiment is less than 0.01 mm. Thus, the optical system 1b of this embodiment has appropriate aberrations. EXAMPLES

[0055] Next, an optical system 1c in Example 3 (Numerical Example 3) will be described with reference to Figs. 5, 6, and 17. As shown in Fig. 5, the basic configuration of the optical system 1c in this example is similar to that of the optical system 1a in Example 1. The focal length f1 of the first lens 12 is f1 = -0.255 mm. The focal length f2 of the second lens 22 is f2 = 0.372 mm. The focal length f3 of the third lens 32 is f3 = 0.539 mm.

[0056] Here, an optical system (wafer level lens) 20 as a comparative example will be described with reference to FIG. 17. FIG. 17 is a cross-sectional view of the optical system 20 as a comparative example. The optical system 20 is composed of a first unit L10, a second unit L20, and a third unit L30. The first unit L10 has a first substrate 211 and a first lens 212 arranged on the image side thereof. The first lens 212 is a negative lens with a concave surface facing the image side. The second unit L20 has a second substrate 221 and a second lens 222 arranged on the object side thereof. The second lens 222 is a positive lens with a convex surface facing the object side. The second unit L20 also has a third substrate 231 and a third lens 232 arranged on the image side thereof. The third lens 232 is a positive lens with a convex surface facing the image side. The second unit L20 also has an aperture stop SP between the second substrate 221 and the third substrate 231. The third unit L30 has a fourth substrate (back cover glass) 261 and a fifth substrate (sensor cover glass) 241.

[0057] On the other hand, the optical system 1c of this embodiment reduces the number of substrates by using the third substrate 31 required for forming the third lens 32 as a back cover glass. Thus, according to this embodiment, by forming the final lens of the optical system 1c on the object side, it is possible to provide a small optical system with high optical performance and reduced costs for materials and manufacturing processes.

[0058] The focal length f of the optical system 1c is f=0.284 mm. The distance d from the aperture stop SP to the third lens 32 is d=0.0379 mm. The distance L from the third lens 32 to the image plane IP is L=0.624 mm. The optical system 1c of this embodiment is designed to focus on an object located 10 mm away from the surface of the first unit L1 closest to the object.

[0059] As shown in FIG. 6(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in FIG. 6(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in FIG. 6(C), the distortion of this embodiment is less than 40%. As shown in FIG. 6(D), the lateral chromatic aberration of this embodiment is less than 0.01 mm. Thus, the optical system 1c of this embodiment has appropriate aberrations. EXAMPLES

[0060] Next, an optical system 1d in Example 4 (Numerical Example 4) will be described with reference to FIG. 7 and FIG. 8. As shown in FIG. 7, the basic configuration of the optical system 1d in this example is the same as that of the optical system 1a in Example 1. In the optical system 1d in this example, the third substrate 31 is used as a sensor cover glass, and the lens surface of the third lens 32 is formed on the object side of the third substrate 31, so that the third substrate 31 serves both as a sensor cover glass and a back cover glass. The optical system 1d in this example has a half angle of view of 59° and an FNo of 2.8, and is a bright and wide-angle optical system that is very small in size. The optical system 1d in this example is designed to focus on an object at a position 5 mm away from the surface of the first unit L1 that is closest to the object.

[0061] As shown in FIG. 8(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in FIG. 8(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in FIG. 8(C), the distortion of this embodiment is less than 40%. As shown in FIG. 8(D), the lateral chromatic aberration of this embodiment is less than 0.01 mm. Thus, the optical system 1d of this embodiment has appropriate aberrations. EXAMPLES

[0062] Next, an optical system 1e in Example 5 (Numerical Example 5) will be described with reference to FIG. 9 and FIG. 10. As shown in FIG. 9, the basic configuration of the optical system 1e in this example is the same as that of the optical system 1d in Example 4. In the optical system 1e in this example, the third substrate 31 is used as a sensor cover glass, and the lens surface of the third lens 32 is formed on the object side of the third substrate 31, so that the third substrate 31 serves both as a sensor cover glass and a back cover glass. The optical system 1e in this example has a half angle of view of 57° and an FNo of 2.8, and is a bright and wide-angle optical system while being very small in size. The optical system 1e in this example is designed to focus on an object at a position 5 mm away from the surface of the first unit L1 closest to the object side.

[0063] As shown in FIG. 10(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in FIG. 10(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in FIG. 10(C), the distortion of this embodiment is less than 40%. As shown in FIG. 10(D), the lateral chromatic aberration of this embodiment is less than 0.01 mm. Thus, the optical system 1e of this embodiment has appropriate aberration. In addition, the optical system 1e of this embodiment has a short distance Lar between the first lens and the second substrate, making it an optical system with high manufacturing stability. EXAMPLES

[0064] Next, an optical system 1f in Example 6 (Numerical Example 6) will be described with reference to FIG. 11 and FIG. 12. As shown in FIG. 11, the basic configuration of the optical system 1f in this example is the same as that of the optical system 1d in Example 4. In the optical system 1f in this example, the third substrate 31 is used as a sensor cover glass, and the lens surface of the third lens 32 is formed on the object side of the third substrate 31, and the third substrate 31 is configured to serve as both the sensor cover glass and the back cover glass. The optical system 1f in this example is an optical system with a half angle of view of 61° and an FNo of 2.8, and is very small, yet has a bright and wide-angle optical system. The optical system 1f in this example is designed to focus on an object at a position 5 mm away from the surface of the first unit L1 that is closest to the object.

[0065] As shown in FIG. 12(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in FIG. 12(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in FIG. 12(C), the distortion of this embodiment is less than 40%. As shown in FIG. 12(D), the lateral chromatic aberration of this embodiment is less than 0.01 mm. Thus, the optical system 1f of this embodiment has appropriate aberrations. EXAMPLES

[0066] Next, an optical system 1g in Example 7 (Numerical Example 7) will be described with reference to Figs. 13 and 14. As shown in Fig. 13, the basic configuration of the optical system 1g in this example is the same as that of the optical system 1a in Example 1. The optical system 1g in this example has an image height of 0.82 mm, a half angle of view of 59°, and an FNo of 2.8, and is a bright, wide-angle optical system while being very small in size. The optical system 1g in this example is designed to focus on an object located 50 mm away from the surface of the first unit L1 closest to the object.

[0067] As shown in FIG. 14(A), the spherical aberration of this embodiment is less than 0.1 mm. As shown in FIG. 14(B), the astigmatism of this embodiment is less than 0.1 mm. As shown in FIG. 14(C), the distortion of this embodiment is less than 40%. As shown in FIG. 14(D), the lateral chromatic aberration of this embodiment is less than 0.03 mm. Thus, the optical system 1g of this embodiment has appropriate aberrations. EXAMPLES

[0068] Next, an optical system 1h in Example 8 (Numerical Example 8) will be described with reference to FIG. 15 and FIG. 16. As shown in FIG. 15, the basic configuration of the optical system 1h in this example is the same as that of the optical system 1d in Example 4. Meanwhile, in the above-mentioned Examples 1 to 7, the aperture stop SP is provided on the image side of the second substrate L21, but in the optical system 1h in this example, the aperture stop SP is provided on the object side surface of the second substrate L21. The optical system 1h in this example is an optical system with a half angle of view of 60° and an FNo of 2.9, and thus a bright and wide-angle optical system is obtained while being very small in size. The optical system 1h in this example is designed to focus on an object at a position 5 mm away from the surface of the first unit L1 that is closest to the object side.

[0069] As shown in FIG. 16(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in FIG. 16(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in FIG. 16(C), the distortion of this embodiment is less than 40%. As shown in FIG. 16(D), the lateral chromatic aberration of this embodiment is less than 0.01 mm. Thus, the optical system 1h of this embodiment has appropriate aberrations.

[0070] Numerical Examples 1 to 8 corresponding to Examples 1 to 8, respectively, are shown below. In each numerical example, r is the radius of curvature (mm) of the i-th surface from the object side, d is the surface distance (mm) on the axis between the i-th and (i+1)-th surfaces from the object side, and nd and vd are the refractive index and Abbe number for the d-line of the i-th optical member, respectively. The Abbe number vd of a certain material is given by Nd, NF, and NC, respectively, when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively, νd=(Nd-1) / (NF-NC) It is expressed as:

[0071] The focal length f (mm) is the value when focused on an object at infinity. BF is the back focus, which is the distance from the final surface of the optical system to the image surface. The total lens length is the distance from the first surface to the image surface. Aspheric surfaces are represented by adding the sign * after the surface number. The aspheric shape is expressed by the following formula, where X is the displacement from the apex 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, K is the conic constant, and Ai (i=4, 6, 8, ...) are the aspheric coefficients.

[0072]

number

[0073] The display of "e±Z" is "10 ±Z " means.

[0074] (Numerical Example 1) Unit: mm Surface Data Surface number rd nd νd 1 ∞ 0.10 1.51680 64.2 2 ∞ 0.01 1.51000 57.5 3* 0.114 0.17 4* 0.158 0.10 1.55000 44.0 5 ∞ 0.20 1.51680 64.2 6 (Aperture) ∞ 0.07 7* 0.259 0.05 1.51000 57.5 8 ∞ 0.10 1.51680 64.2 9 ∞ 0.30 1.51680 64.2 10∞0.02 Image plane ∞ Aspheric Data 3rd page K=-1.40126e+000, A4= 1.74465e+001, A6=-6.09448e+001, A8= 2.54898e+003, A10= 1.11764e+005, A12=-4.94130e+006 Side 4 K=-2.45619e-001, A4=-2.46995e+001, A6=-3.75404e+002, A8=-7.60321e+003, A10=9.46804e+005, A12=-5.15469e+007 Side 7 K=-1.67841e+001, A4= 3.69380e+001, A6=-1.45726e+003, A8= 3.14333e+004, A10=-4.22638e+004, A12=-7.51083e+006 Focal length 0.24 F-number: 2.88 Half angle of view 59.0 Image height 0.28 Lens length 1.12 BF 0.02 Object distance 10.0 (Numerical Example 2) Unit: mm Surface Data Surface number rd nd νd 1 ∞ 0.10 1.51680 64.2 2 ∞ 0.01 1.51000 57.5 3* 0.118 0.14 4* 0.160 0.10 1.56318 39.6 5 ∞ 0.10 1.51680 64.2 6 (Aperture) ∞ 0.09 7* 0.232 0.06 1.51000 57.5 8 ∞ 0.10 1.51680 64.2 9 ∞ 0.30 1.51680 64.2 10∞0.02 Image plane ∞ Aspheric Data 3rd page K=-8.11341e-001, A4=-1.78031e+001, A6= 1.00708e+003, A8= 3.94833e+003, A10=-2.85870e+006, A12= 5.07388e+007 Side 4 K=-5.24295e+000, A4= 1.20898e+002, A6=-4.98544e+003, A8= 1.15921e+005, A10=-3.00410e+006, A12= 3.92272e+007 Side 7 K=-1.80560e+001, A4= 4.34353e+001, A6=-1.72697e+003, A8=-5.87235e+004, A10=7.12574e+006, A12=-1.59311e+008 Focal length 0.24 F-number: 2.88 Half angle of view 59.0 Image height 0.28 Lens length 1.02 BF 0.02 Object distance 10.0 (Numerical Example 3) Unit: mm Surface Data Surface number rd nd νd 1 ∞ 0.20 1.51680 64.2 2 ∞ 0.01 1.51000 57.5 3* 0.130 0.18 4* 0.205 0.13 1.55000 44.0 5 ∞ 0.20 1.51680 64.2 6 (Aperture) ∞ 0.04 7* 0.286 0.06 1.53000 56.0 8 ∞ 0.20 1.51680 64.2 9 ∞ 0.40 1.51680 64.2 10∞0.02 Image plane ∞ Aspheric Data 3rd page K=-1.16949e+000, A4= 2.17835e+001, A6= 5.85940e+002, A8= 1.97923e+004, A10=-1.54923e+006, A12= 3.88932e+007 Side 4 K= 2.34627e-001, A4=-8.16279e+000, A6=-5.63709e+002, A8= 1.06071e+004, A10=3.25696e+005, A12=-2.41692e+007 Side 7 K=-3.76746e+001, A4= 1.01499e+002, A6=-8.41613e+003, A8= 7.54769e+003, A10=4.76035e+007, A12=-2.17281e+009 Focal length 0.28 F-number: 2.88 Half angle of view: 54.0 Image height 0.28 Lens length 1.43 BF 0.02 Object distance 10.0 (Numerical Example 4) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.62 2∞ 0.045 1.52290 50.3 0.48 3* 0.0846 0.120 0.28 4* 0.1231 0.141 1.52290 50.3 0.25 5 ∞ 0.100 1.51680 64.2 0.19 6 (Aperture) ∞ 0.054 0.12 7* 0.2286 0.072 1.52290 50.3 0.27 8 ∞ 0.400 1.51680 64.2 0.30 9 ∞ 0.020 0.55 Image plane ∞ Aspheric Data 3rd page K =-6.21168e+00, A4= 6.25636e+02, A6=-8.47952e+04, A8= 7.80586e+06, A10=-4.40616e+08, A12= 1.38205e+10, A14=-1.84957e+11 Side 4 K =-4.15041e+00, A4= 2.01549e+02, A6=-1.89467e+04, A8= 1.87535e+06, A10=-1.38040e+08, A12= 5.97522e+09, A14=-1.13123e+11 Side 7 K =-5.85227e+01, A4= 2.60048e+02, A6=-5.58127e+04, A8= 7.10305e+06, A10=-5.13511e+08, A12= 1.94389e+10, A14=-2.98356e+11 Focal length 0.217 F-number: 2.83 Half angle of view 59.0 Image height 0.28 Lens length 1.05 BF 0.020 Object distance 5.0 (Numerical Example 5) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.62 2 ∞ 0.045 1.52290 50.3 0.49 3* 0.1087 0.081 0.29 4* 0.1272 0.130 1.52290 50.3 0.27 5 ∞ 0.100 1.51680 64.2 0.23 6 (Aperture) ∞ 0.037 0.13 7* 0.2355 0.070 1.52290 50.3 0.25 8 ∞ 0.436 1.51680 64.2 0.28 9 ∞ 0.020 0.54 Image plane ∞ Aspheric Data 3rd page K =-7.43588e+00, A4= 4.87017e+02, A6=-6.30018e+04, A8= 5.88716e+06, A10=-3.17706e+08, A12= 8.90173e+09, A14=-9.27729e+10 Side 4 K =-1.29842e+00, A4= 3.07945e+01, A6=-2.42278e+03, A8= 4.47425e+05, A10=-3.15142e+07, A12= 1.04795e+09, A14=-1.02518e+10 Side 7 K =-4.78137e+01, A4= 2.30855e+02, A6=-4.83783e+04, A8= 6.29551e+06, A10=-4.66358e+08, A12= 1.79953e+10, A14=-2.79997e+11 Focal length 0.277 F-number: 2.79 Half angle of view: 57.0 Image height 0.28 Lens length 1.02 BF 0.02 Object distance 5.0 (Numerical Example 6) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.65 2 ∞ 0.045 1.51500 54.0 0.51 3* 0.1149 0.140 0.31 4* 0.1755 0.096 1.51500 54.0 0.23 5 ∞ 0.100 1.51680 64.2 0.19 6 (Aperture) ∞ 0.098 0.12 7* 0.1943 0.105 1.51500 54.0 0.38 8 ∞ 0.414 1.51680 64.2 0.40 9 ∞ 0.020 0.55 Image plane ∞ Aspheric Data 3rd page K =-8.38246e+00, A4= 4.47212e+02, A6=-4.82082e+04, A8= 3.54964e+06, A10=-1.58303e+08, A12= 3.76729e+09, A14=-3.72323e+10 Side 4 K =-1.35880e+00, A4= 1.56995e+02, A6=-4.30232e+04, A8= 6.73782e+06, A10=-5.77854e+08, A12= 2.48373e+10, A14=-4.33446e+11 Side 7 K =-2.10248e+01, A4= 1.20066e+02, A6=-1.10557e+04, A8= 6.07621e+05, A10=-1.93372e+07, A12= 3.27476e+08, A14=-2.27986e+09 Focal length 0.226 F-number: 2.84 Half angle of view 61.1 Image height 0.28 Lens length 1.12 BF 0.02 Object distance 5.0 (Numerical Example 7) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 ∞ 0.240 1.51680 64.2 2.35 2 ∞ 0.176 1.52290 50.3 2.02 3* 0.2457 0.341 1.20 4* 0.2957 0.418 1.52290 50.3 0.91 5 ∞ 0.300 1.51680 64.2 0.74 6 (Aperture) ∞ 0.122 0.27 7* 0.7245 0.135 1.52290 50.3 0.83 8 ∞ 0.300 1.51680 64.2 0.88 9 ∞ 0.553 1.51680 64.2 1.14 10 ∞ 0.020 1.62 Image plane ∞ Aspheric Data 3rd page K =-1.82995e+00, A4= 1.95941e+00, A6=-9.41015e+00, A8= 1.22664e+01, A10=-1.03796e+01, A12= 2.50580e+01, A14=-1.99537e+01 Side 4 K =-2.78973e+00, A4= 7.70474e+00, A6=-7.05350e+01, A8= 6.41973e+02, A10=-4.32391e+03, A12= 1.49156e+04, A14=-1.96470e+04 Side 7 K =-4.43879e+01, A4= 3.13426e+00, A6=-4.10059e+01, A8= 3.38398e+02, A10=-1.58008e+03, A12= 3.73365e+03, A14=-3.53936e+03 Focal length 0.565 F-number: 2.75 Half angle of view 59.0 Image height 0.82 Lens length 2.60 BF 0.020 Object distance 50.0 (Numerical Example 8) Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.59 2∞ 0.045 1.52290 50.3 0.45 3* 0.0984 0.125 0.27 4* 0.1397 0.138 1.52290 50.3 0.19 5(Aperture) ∞ 0.100 1.51680 64.2 0.11 6 ∞ 0.033 0.19 7* 0.2093 0.071 1.52290 50.3 0.28 8 ∞ 0.400 1.51680 64.2 0.30 9 ∞ 0.020 0.55 Image plane ∞ Aspheric Data 3rd page K =-1.23301e+01, A4= 7.56038e+02, A6=-1.22104e+05, A8= 1.32431e+07, A10=-8.55926e+08, A12= 2.91280e+10, A14=-4.02217e+11 Side 4 K =-3.52848e+00, A4= 1.55637e+02, A6=-1.82661e+04, A8= 3.72846e+06, A10=-6.48173e+08, A12= 5.88096e+10, A14=-2.17851e+12 Side 7 K =-4.99166e+01, A4= 2.46197e+02, A6=-4.89127e+04, A8= 5.57700e+06, A10=-3.64668e+08, A12= 1.25259e+10, A14=-1.75004e+11 Focal length 0.215 F-number: 2.91 Half angle of view: 59.7 Image height 0.28 Lens length 1.03 BF 0.020 Object distance 5.0 Table 1 shows the values ​​for the above-mentioned conditional expressions (1) to (8) in each of the numerical examples.

[0075] [Table 1]

[0076] The optical system of each embodiment is suitable for use as an imaging optical system used in a built-in camera of electronic devices such as a mobile phone, a smartphone, or a wearable terminal, or as an objective optical system of an endoscope. EXAMPLES

[0077] Next, an electronic device according to a ninth embodiment of the present invention will be described with reference to FIG. 18. FIG. 18 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 eighth 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

[0078] Next, an imaging device according to a tenth embodiment of the present invention will be described with reference to FIG. 19. FIG. 19 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 eighth 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, an imaging device that is small in size yet has high optical performance can be realized.

[0079] According to each embodiment, it is possible to provide an optical system and an imaging device that are small in size, low in cost, and have high optical performance.

[0080] 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]

[0081] 1a~1h Optical system 11 First board 12 First lens 21 Second board 22 Second lens 31 Third board 32 Third lens L1 1st unit L2 2nd unit L3 3rd Unit

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 that is disposed on an image side surface of the first substrate; the second unit includes a second substrate and a second lens having a positive power that is disposed on an object side surface of the second substrate; the third unit includes a third substrate and a third lens having a positive power that is disposed on an object side surface of the third substrate; An optical system, characterized in that the first unit does not have any lens other than the first lens, the second unit does not have any lens other than the second lens, and the third unit does not have any lens other than the third lens.

2. The optical system according to claim 1 , wherein the second unit has an aperture stop.

3. The optical system according to claim 2 , wherein the aperture stop is disposed on the second substrate.

4. When the distance on the optical axis from the aperture stop to the third lens is d and the focal length of the optical system is f, 0.10<d / f<0.50 4. The optical system according to claim 2, wherein the following condition is satisfied:

5. When the distance on the optical axis from the aperture stop to the third lens is d and the focal length of the optical system is f, 0.07<d / f<0.65 4. The optical system according to claim 2, wherein the following condition is satisfied:

6. An optical system including 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 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 an aperture stop, a second substrate, and a second lens having a positive power that is disposed on the object side of the second substrate; the third unit includes a third substrate and a third lens having a positive power that is disposed on the object side of the third substrate; the first unit does not have any lens other than the first lens, the second unit does not have any lens other than the second lens, and the third unit does not have any lens other than the third lens; When the distance on the optical axis from the aperture stop to the third lens is d and the focal length of the optical system is f, 0.07<d / f<0.65 An optical system characterized in that the following condition is satisfied:

7. When the distance on the optical axis from the aperture stop to the third lens is d and the focal length of the third lens is f3, 0.03<d / f3<0.40 7. The optical system according to claim 2, wherein the following condition is satisfied:

8. When the focal length of the second lens is f2 and the focal length of the optical system is f, 1.00<f2 / f<1.50 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. When the focal length of the second lens is f2 and the focal length of the optical system is f, 0.60<f2 / f<1.60 8. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the focal length of the first lens is f1 and the focal length of the third lens is f3, -2.50<f3 / f1<-1.80 10. The optical system according to claim 1, wherein the following condition is satisfied:

11. 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 having a positive power that is disposed on the object side of the second substrate; the third unit includes a third substrate and a third lens having a positive power that is disposed on the object side of the third substrate; the first unit does not have any lens other than the first lens, the second unit does not have any lens other than the second lens, and the third unit does not have any lens other than the third lens; When the focal length of the first lens is f1 and the focal length of the third lens is f3, -2.50<f3 / f1<-1.80 An optical system characterized in that the following condition is satisfied:

12. When the focal length of the first lens is f1 and the focal length of the third lens is f3, -3.50<f3 / f1<-1.50 10. The optical system according to claim 1, wherein the following condition is satisfied:

13. When the distance from the third lens to the image plane is L and the focal length of the optical system is f, 1.20<L / f<2.40 13. The optical system according to claim 1, wherein the following condition is satisfied:

14. When the distance from the third lens to the image plane is L and the focal length of the optical system is f, 1.00<L / f<2.40 13. The optical system according to claim 1, wherein the following condition is satisfied:

15. When the focal length of the first lens is f1, the focal length of the second lens is f2, and the focal length of the third lens is f3, 0.30<(f2-f1) / f3<1.60 15. The optical system according to claim 1, wherein the following condition is satisfied:

16. When the focal length of the third lens is f3 and the focal length of the optical system is f, 1.50<f3 / f<3.00 16. The optical system according to claim 1, wherein the following condition is satisfied:

17. When the thickness of the first substrate is d1, the thickness of the second substrate is d2, and the distance from the image side surface of the first lens to the object side surface of the second substrate is Lar, 0.60<Lar / (d1+d2)<2.00 17. The optical system according to claim 1, wherein the following condition is satisfied:

18. 18. The optical system according to claim 1, wherein the refractive index of the first substrate and the refractive index of the first lens are different from each other.

19. 19. The optical system according to claim 1, wherein the refractive index of the second substrate and the refractive index of the second lens are different from each other.

20. 20. The optical system according to claim 1, wherein the refractive index of the third substrate and the refractive index of the third lens are different from each other.

21. 21. An imaging device comprising: the optical system according to claim 1; and an imaging element that receives light from the optical system.

Images