Optical system and imaging device

Abstract

To provide an optical system that is compact yet possesses high optical performance. [Solution] The optical system (1a) consists of a first unit (L1), a second unit (L2), and a third unit (L3) arranged in order from the object side to the image side. The first unit has a first substrate (11) and a first lens (12), the second unit has a second substrate (21) and a second lens (22), and the third unit has a third substrate (31) and a third lens (32). At least one of the first lens, the second lens, or the third lens is joined with a fourth lens (4R) to form a bonded lens (4sm), and the power and Abbe number of the fourth lens and the lens (4B) joined to the fourth lens are different from each other.

Description

Technical Field

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

Background Art

[0002] In recent years, as an optical system used in imaging devices such as medical endoscopes and mobile phones, there has been a demand for an optical system that is small and has high optical performance. Patent Documents 1 and 2 disclose wafer-level lenses (wafer-level optics) that are optical systems manufactured by a wafer-level process.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the configuration disclosed in Patent Document 1, it is difficult to realize an optical system having high optical performance because various aberrations cannot be sufficiently reduced. In the configuration disclosed in Patent Document 2, it is difficult to realize a small wafer-level lens because the number of lenses is large.

[0005] Therefore, an object of the present invention is to provide an optical system that is small and has high optical performance.

Means for Solving the Problems

[0006] An optical system as one aspect of the present invention comprises a first unit, a second unit, and a third unit arranged adjacently in order from the object side to the image side, wherein the first unit has a first lens with negative power, the second unit has a second lens with positive power, and the third unit has a third lens with positive power, and the first lens, the second lens, and the third lens are each arranged on a substrate, and at least one of the first lens, the second lens, or the third lens is bonded to a fourth lens, and the power and Abbe number of the fourth lens and the lens bonded to the fourth lens are different from each other.

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

[0008] According to the present invention, it is possible to provide an optical system that is compact yet possesses high optical performance. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of the optical system in Example 1. [Figure 2] This is an aberration diagram of the optical system in Example 1. [Figure 3] This is a cross-sectional view of the optical system in Example 2. [Figure 4] This is an aberration diagram of the optical system in Example 2. [Figure 5] This is a cross-sectional view of the optical system in Example 3. [Figure 6] This is an aberration diagram of the optical system in Example 3. [Figure 7] This is a cross-sectional view of the optical system in Example 4. [Figure 8] This is an aberration diagram of the optical system in Example 4. [Figure 9] This is a cross-sectional view of the optical system in Example 5. [Figure 10] This is an aberration diagram of the optical system in Example 5. [Figure 11]It is a cross-sectional view of the optical system in Example 6. [Figure 12] It is an aberration diagram of the optical system in Example 6. [Figure 13] It is a cross-sectional view of the optical system in Example 7. [Figure 14] It is an aberration diagram of the optical system in Example 7. [Figure 15] It is a cross-sectional view of the optical system in Example 8. [Figure 16] It is an aberration diagram of the optical system in Example 8. [Figure 17] It is a cross-sectional view of the optical system in Example 9. [Figure 18] It is an aberration diagram of the optical system in Example 9. [Figure 19] It is a cross-sectional view of the optical system in Example 10. [Figure 20] It is an aberration diagram of the optical system in Example 10. [Figure 21] It is a schematic diagram of the main part of the electronic device in Example 11. [Figure 22] It is a schematic diagram of the main part of the imaging device in Example 12.

Modes for Carrying Out the Invention

[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-sized optical system obtained by using a technique called wafer-level process. Such an optical system is called a wafer-level lens (wafer-level optics), and an imaging device using the wafer-level lens as an imaging optical system is called a wafer-level camera. Due to the characteristics of being small-sized and low-cost, the optical system of each embodiment is suitable for use as, for example, an optical system of a camera incorporated in an electronic device such as a mobile phone, a smartphone, a wearable terminal, or an objective optical system of an endoscope.

[0012] Figures 1, 3, 5, 7, 9, 11, 13, 15, 17, and 19 are cross-sectional views of the optical systems (wafer-level lenses) 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, and 1j of Examples 1 to 10, 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 the aperture diaphragm, and IP is the image plane. The image plane IP is where the photosensitive surface, corresponding to the imaging surface of a solid-state image sensor such as a CCD sensor or CMOS sensor in an imaging device, or the film surface of a silver halide film camera, is located.

[0013] Figures 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 are aberration diagrams of the optical systems 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, and 1j of Examples 1 to 10, respectively. Each aberration diagram includes (A) a spherical aberration diagram, (B) an astigmatism diagram, (C) a distortion aberration diagram, and (D) a chromatic aberration diagram. In the spherical aberration diagram, 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) are shown, respectively. In the astigmatism diagram, ΔSd represents the amount of astigmatism at the sagittal image plane for the d line, and ΔMd represents the amount of astigmatism at the meridional image plane for the d line. The distortion diagram shows the amount of distortion for the d line. The chromatic aberration diagram shows the amount of chromatic aberration for the g line, C line, and F line. Fno is the F number, and Y is the image height (mm).

[0014] The optical system of each embodiment consists of a first unit L1, a second unit L2, and a third unit L3 arranged in order from the object side to the image side. The first unit L1 has a first substrate 11 and a first lens 12 with negative power (negative refractive power) located on the image side of the first substrate 11. The second unit L2 has a second substrate 21 and a second lens 22 with positive power (positive refractive power) located on either the object side or the image side of the second substrate 21. The third unit L3 has a third substrate 31 and a third lens 32 with positive power located on either the object side or the image side of the third substrate 31. At least one of the first lens 12, the second lens 22, or the third lens 32 is joined with a fourth lens 4R to form a cemented lens 4sm. The power and Abbe number (Abbe number of the materials constituting each lens) of the fourth lens 4R and the lens (fifth lens 4B) joined to the fourth lens 4R are different from each other. The bonded lens 4sm is placed in close contact with one of the substrates: the first substrate 11, the second substrate 21, or the third substrate 31. The first substrate 11 is a planar substrate, and the first lens 12 is a concave lens. The first lens 12 is formed on the image-side surface of the first substrate 11 using a wafer-level process. The image-side surface of the first lens 12 is aspherical. The second substrate 21 is a planar substrate, and the second lens 22 is a convex lens. The second lens 22 is formed on the object-side or image-side surface of the second substrate 21 using a wafer-level process. The surface of the second lens 22 opposite to the second substrate 21 is aspherical. The third substrate 31 is a planar substrate, and the third lens 32 is a convex lens. The third lens 32 is formed on the object-side or image-side surface of the third substrate 31 using a wafer-level process. The surface of the third lens 32 opposite to the third substrate 31 is aspherical.

[0015] The bonded lens 4sm is formed on at least one of the first substrate 11, the second substrate 21, or the third substrate 31 using a wafer-level process. Specifically, first, one lens constituting the bonded lens 4sm (the fourth lens 4R or the fifth lens 4B) is formed on one of the first substrate 11, the second substrate 21, or the third substrate 31. Then, the other lens (the fifth lens 4B or the fourth lens 4R) is formed using a different material by a wafer-level process.

[0016] In at least one lens of the bonded lens 4sm, one surface is in close contact with the substrate and therefore has a planar shape. The remaining two surfaces constituting the bonded lens 4sm are preferably aspherical. Furthermore, when forming lenses on each substrate, it is preferable to form the lens on only one side of the substrate. For example, when forming a lens on a thin substrate, a flat support material can be bonded to one side of the substrate to prevent bending, and then the lens can be formed on the other side to accurately form the lens shape. However, when forming lenses on both sides of the substrate, it is not possible to bond the support material, making it difficult to form a highly accurate lens shape. In addition, when wafer-level optics are used as small imaging devices such as endoscopes and smartphones, it is preferable to use a hard, environmentally resistant material such as glass for the surface closest to the object.

[0017] When forming lenses using wafer-level processes, it is more cost-effective to form the lenses from resin materials. Therefore, if the lens surface is positioned on the object side, it is not possible to achieve a configuration with excellent environmental resistance. Since it is difficult to create a curved surface for glass materials in wafer-level processes, positioning the flat surface of the substrate glass closest to the object side allows for wafer-level optics with excellent environmental resistance.

[0018] In the optical systems of each embodiment, in order to achieve a compact and low-cost optical system, the first unit L1, the second unit L2, and the third unit L3 are manufactured using a wafer-level process. That is, the first unit L1, the second unit L2, and the third unit L3 are manufactured by forming a lens layer made of a curable resin material on a wafer (planar substrate) made of glass material. In each embodiment, the materials of the first substrate 11 and the first lens 12 are different from each other. Similarly, the materials of the second substrate 21 and the second lens 22, and the materials of the third substrate 31 and the third lens 32 are different from each other.

[0019] In the second unit L2 or the third unit L3, an aperture diaphragm SP is formed on the substrate using a similar wafer process. The manufactured first unit L1, second unit L2, third unit L3, and image sensor are arranged at desired intervals, bonded together at the light-effective outer edge, and then cut to produce a large number of wafer-level lenses. The material forming the lens layer can be any curable resin material, such as a thermoplastic resin or an ultraviolet-curable resin. Examples include acrylic resin, silicone resin, and cycloolefin polymer.

[0020] In each embodiment, the first substrate 11, the second substrate 21, and the third substrate 31 are made of glass, and the first lens 12, the second lens 22, and the third lens 32 are made of resin, but the invention is not limited to these. If the refractive indices of the first substrate 11 and the first lens 12 are different, for example, both the first substrate 11 and the first lens 12 may be formed of resin. The same applies to the second unit L2 and the third unit L3. The aperture diaphragm SP can be formed, for example, by depositing a light-shielding film such as chromium using a mask, or by etching after deposition to form the opening. In this case, forming the aperture diaphragm SP on a flat surface such as a substrate is preferable from a manufacturing standpoint because it facilitates control of the mask arrangement in the thickness direction.

[0021] The optical system of each embodiment is an integrated optical system comprising a first unit L1, a second unit L2, and a third unit L3. By bonding the optical system of each embodiment to a fourth substrate (sensor cover glass) 41 or a fifth substrate (sensor cover glass) 51, it functions as an imaging system. A back cover glass (third substrate 31 or fourth substrate 41) is provided on the image-side surface of the optical system of each embodiment. By directly bonding the back cover glass (third substrate 31 or fourth substrate 41) and the sensor cover glass (fourth substrate 41 or fifth substrate 51) via a plane, a stable manufacturing process can be achieved. With this configuration, it is possible to provide a compact optical system with high optical performance while suppressing material and manufacturing costs (i.e., low cost).

[0022] In each embodiment, the configuration includes both a back cover glass (third substrate 31 or fourth substrate 41) and a sensor cover glass (fourth substrate 41 or fifth substrate 51), but the system is not limited to this. For example, it is possible to combine the functions of the sensor cover glass and the back cover glass and configure them as a single substrate. In that case, by directly bonding the sensor cover glass and the wafer-level optical system, the thickness of the substrate can be reduced, making it possible to obtain a miniaturized and high-performance optical system.

[0023] Wafer-level lenses, such as those in each embodiment, are desirable to be as compact as possible. When miniaturizing very wide-angle optical systems with a half-angle of view of 50° or more, as in each embodiment, it is important to minimize the number of lenses and substrates. In the case of a wide-angle wafer-level optics consisting of a small number of lenses, such as four, as in the present invention, various aberrations can be well corrected by placing lenses made of low-dispersion material at a certain distance from the aperture diaphragm. However, there are few low-dispersion materials that are reflowable resins, making it difficult to correct various aberrations (especially chromatic aberration) with a small number of lenses. It is also possible to correct chromatic aberration by adding lenses with different Abbe numbers to existing wafer-level optics. However, in the case of wafer-level optics, it is desirable for the lenses to be held by the substrate, so one side of the lens becomes flat, making it difficult to correct various aberrations such as field curvature and chromatic aberration in a balanced manner.

[0024] Therefore, in the optical systems of each embodiment, chromatic aberration and field curvature are effectively corrected by placing two lenses with different dispersions in close proximity. In particular, by making the surfaces on both sides of one lens spherical (especially aspherical), the light beam at each image height can be corrected independently, thus enabling good correction of various aberrations across the entire image plane.

[0025] In the optical system of each embodiment, when the Abbe numbers of the fourth lens 4R and the fifth lens 4B constituting the cemented lens 4sm are νr and νb, respectively, it is preferable that the following condition (1) is satisfied.

[0026] 8<|νr-νb|<60 ···(1) If the value falls below the lower limit of condition (1), sufficient chromatic aberration correction cannot be obtained. On the other hand, if the value exceeds the upper limit of condition (1), it becomes difficult to select the lens material for forming the lens, which is undesirable because the lens material becomes expensive or the reflow process becomes difficult to control.

[0027] More preferably, the numerical range of condition (1) is set as shown in condition (1a) below.

[0028] 10<|νr-νb|<45 ···(1a) More preferably, the numerical range of condition (1) is set as shown in condition (1b) below.

[0029] 11<|νr-νb|<40 ···(1b) In the optical systems of each embodiment, the aperture diaphragm SP is positioned in the middle portion of the optical system, that is, between the lens closest to the object and the lens closest to the image. This allows for the separation of light beams at each image height incident on the object-side lens and the image-side lens, making it possible to effectively correct chromatic aberration. Specifically, it is preferable to position the aperture diaphragm SP on the second substrate 21 or the third substrate 31. This allows for effective correction of various aberrations and enables the formation of an aperture on a plane, thus enabling the manufacture of the optical system at a low cost.

[0030] Furthermore, in the optical systems of each embodiment, by using the cemented lens 4sm, chromatic aberration, mainly lateral aberration, can be corrected effectively. To correct chromatic aberration effectively, it is preferable to position the cemented lens 4sm at a certain distance from the aperture diaphragm SP. Therefore, when the distance on the optical axis from the cemented surface of the cemented lens 4sm to the aperture diaphragm SP is dsm, and the focal length of the optical system (entire system) is f, it is preferable to satisfy the following condition (2).

[0031] 0.05 <dsm / f<2.50 ···(2) If the upper or lower limit of condition (2) is exceeded, it becomes difficult to adequately correct the chromatic aberration of the optical system.

[0032] More preferably, the numerical range of condition (2) is set as shown in condition (2a) below.

[0033] 0.10 <dsm / f<2.20 ···(2a) More preferably, the numerical range of condition (2) is set as shown in condition (2b) below.

[0034] 0.12 <dsm / f<1.90 ···(2b) Furthermore, in order to correct chromatic aberration and other aberrations in a balanced manner, it is preferable to appropriately set the refractive power at the periphery and the central part of the fourth lens 4R and fifth lens 4B that constitute the cemented lens 4sm. By making the refractive power at the periphery and the central part of at least one of the fourth lens 4R or the fifth lens 4B different, aberrations can be corrected independently in light beams with different image heights, and various aberrations such as chromatic aberration can be effectively corrected. Here, the focal length in the region of 70% of the effective diameter of the fourth lens 4R and the paraxial focal length in the central region of the effective diameter of the fourth lens 4R are denoted as f7r and fr, respectively. Also, the focal length in the region of 70% of the effective diameter of the fifth lens 4B and the paraxial focal length in the central region of the effective diameter of the fifth lens 4B are denoted as f7b and fb, respectively. At this time, it is preferable to satisfy at least one of the following conditional equations (3a) and (3b).

[0035] 0.05<|f7r / fr-1|<20.00 ···(3a) 0.05<|f7b / fb-1|<20.00 ···(3b) Here, the focal length f7r in the region of 70% of the effective diameter of the fourth lens 4R is as follows: That is, it is the value calculated by replacing the object-side radius of curvature r1 used in the calculation of the focal length of the fourth lens 4R with the radius of curvature r7r1 calculated from the region of 70% of the effective diameter of the object-side surface. Also, it is the value calculated by replacing the image-side radius of curvature r2 used in the calculation of the focal length of the fourth lens 4R with the radius of curvature r7r2 calculated from the region of 70% of the effective diameter of the image-side surface. Similarly, the focal length f7b in the region of 70% of the effective diameter of the fifth lens 4B is as follows: That is, it is the value calculated by replacing the object-side radius of curvature b1 used in the calculation of the focal length of the fifth lens 4B with the radius of curvature r7b1 calculated from the region of 70% of the effective diameter of the object-side surface. Furthermore, the value obtained by replacing the image-side radius of curvature b2 used in the calculation of the focal length of the fifth lens 4B with the radius of curvature r7b2 calculated from the region representing 70% of the effective diameter of the image-side surface.

[0036] In the optical system of each embodiment, the aspherical shape is expressed by the following equation (A), where x is the amount of variation from the vertex of the surface in the direction of the optical axis, h is the height from the optical axis in the direction perpendicular to the optical axis, r is the radius of paraxial curvature, k is the cone constant, and Ai (i=4, 6, 8, ...) are the aspherical coefficients of each order.

[0037]

number

[0038] When xh is the displacement in the direction of the optical axis at a height h from the optical axis at a point where 70% of the effective diameter is reached, as calculated from equation (A), the radius of curvature r7 at 70% of the effective diameter can be determined from the following equation (B).

[0039]

number

[0040] The effective ray diameter is defined as twice the distance from the optical axis to the point furthest from the optical axis within the region through which the effective imaging beam can pass on each optical surface. The effective imaging beam refers to the beam excluding stray light and rays that image outside the area where the image is recorded on the image plane IP. For the object-side surface of the optical system in this embodiment, the effective ray diameter coincides with twice the greater of the distance between the point through which the lower or upper line of the off-axis beam passes and the optical axis. In each embodiment, the effective ray diameter may be referred to as the effective diameter, maximum effective diameter, etc. An optical surface refers to a lens surface, both sides of a flat plate, or their bonding surface. The value obtained by dividing the effective ray diameter by 2 is called the effective radius.

[0041] If the refractive power falls below the lower limit of condition (3a) or condition (3b), the change in refractive power between the center and periphery of the lens becomes small, resulting in insufficient correction of aberrations in the off-axis beam. On the other hand, if the refractive power falls above the upper limit of condition (3a) or condition (3b), the change in refractive power between the center and periphery of the lens becomes large, causing a rapid change in curvature at the periphery, making it impossible to reduce field curvature and other issues.

[0042] More preferably, the numerical ranges of conditional expression (3a) and conditional expression (3b) are set as shown in conditional expression (3c) and conditional expression (3d), respectively.

[0043] 0.06<|f7r / fr-1|<12.00 ···(3c) 0.06<|f7b / fb-1|<12.00 ···(3d) More preferably, the numerical ranges of conditional expression (3a) and conditional expression (3b) are set as shown in conditional expression (3e) and conditional expression (3f), respectively.

[0044] 0.08<|f7r / fr-1|<6.00 ···(3e) 0.08<|f7b / fb-1|<6.00 ···(3f) Furthermore, in the optical systems of each embodiment, chromatic aberration (especially lateral chromatic aberration) can be effectively corrected by appropriately setting the Abbe number of the cemented lens 4sm material and the focal length in the region of 70% of the effective diameter. Here, let f7r be the focal length of the fourth lens 4R in the region of 70% of the effective diameter, νr be the Abbe number of the fourth lens 4R, f7b be the focal length of the fifth lens 4B in the region of 70% of the effective diameter, νb be the Abbe number of the fifth lens 4B, and f be the focal length of the optical system (entire system). In this case, it is preferable that the following condition (4) is satisfied.

[0045] 0.000<|f / (f7r×νr)+f / (f7b×νb)|<0.050 ···(4) If the upper or lower limit of condition (4) is exceeded, the chromatic aberration occurring in the cemented lens 4sm increases, making it impossible to reduce the overall chromatic aberration of the optical system. Furthermore, the balance between the correction of chromatic aberration and other aberrations is disrupted, making it impossible to reduce other aberrations.

[0046] More preferably, the numerical range of condition (4) is set as shown in condition (4a) below.

[0047] 0.000<|f / (f7r×νr)+f / (f7b×νb)|<0.028 ···(4a) More preferably, the numerical range of conditional expression (4) is set as shown in conditional expression (4b) below.

[0048] 0.000<|f / (f7r×νr)+f / (f7b×νb)|<0.023 ···(4b) Furthermore, by appropriately setting the refractive power of the peripheral portion of the cemented lens 4sm and the refractive power of the peripheral portions of the fourth lens 4R and fifth lens 4B that constitute the cemented lens 4sm, various aberrations, including chromatic aberration, can be effectively corrected. Here, let f7sm be the focal length in the region of 70% of the effective diameter of the cemented lens 4sm, f7r be the focal length in the region of 70% of the effective diameter of the fourth lens 4R, and f7b be the focal length in the region of 70% of the effective diameter of the fifth lens 4B. In this case, it is preferable that at least one of the following conditional equation (5a) or conditional equation (5b) is satisfied.

[0049] 0.1 < |f7sm / f7r| < 6.0 ···(5a) 0.1 < |f7sm / f7b| < 6.0 ···(5b) Here, the focal length f7sm in the region representing 70% of the effective diameter of the cemented lens 4sm is as follows: That is, it is the value calculated by replacing the radii of curvature r1, r2, b1, and b2 of each lens surface used in the calculation of the focal length of the cemented lens 4sm with the radii of curvature r7r1, r7r2, r7b1, and r7b2 calculated from the region representing 70% of the effective diameter of each lens surface. If the value deviates from the upper or lower limit of condition (5a) or condition (5b), excessively strong refractive force will be generated in the peripheral part of the lens, making it difficult to correct various aberrations.

[0050] More preferably, the numerical ranges of conditional expression (5a) and conditional expression (5b) are set as shown in conditional expressions (5c) and (5d), respectively.

[0051] 0.2 < |f7sm / f7r| < 5.0 ···(5c) 0.2 < |f7sm / f7b| < 5.0 ···(5d) More preferably, the numerical ranges of conditional expression (5a) and conditional expression (5b) are set as shown in the following conditional expressions (5e) and (5f), respectively.

[0052] 0.5 < |f7sm / f7r| < 4.0 ···(5e) 0.5 < |f7sm / f7b| < 4.0 ···(5f) Preferably, the optical system of each embodiment satisfies the following condition (6).

[0053] 0.7 <f2 / f<5.0 ···(6) In condition (6), f is the focal length of the entire optical system, and f2 is the focal length of the second unit L2. By satisfying condition (6), it becomes possible to correct spherical aberration to an appropriate value.

[0054] More preferably, the numerical range of condition (6) is set as shown in condition (6a) below.

[0055] 0.9 <f2 / f<4.0 ···(6a) More preferably, the numerical range of condition (6) is set as shown in condition (6c) below.

[0056] 0.9 <f2 / f<2.0 ···(6b) Preferably, the optical system of each embodiment satisfies the following condition (7).

[0057] -4.0 <f3 / f1<-0.3 ···(7) In condition (7), f1 is the focal length of the first unit L1, and f3 is the focal length of the third unit L3. By satisfying condition (7), astigmatism and distortion can be corrected to appropriate values.

[0058] More preferably, the numerical range of condition (7) is set as shown in condition (7a) below.

[0059] -3.5 <f3 / f1<-0.5 ···(7a) More preferably, the numerical range of condition (7) is set as shown in condition (7b) below.

[0060] -3.0 <f3 / f1<-0.7 ···(7b) Furthermore, the optical system of each embodiment is configured to cancel out aberrations between the first unit L1, which has negative power, and the second unit L2, which has positive power, while balancing this with the aberrations generated in the third unit, which is positioned closest to the image. For this reason, it is preferable that the following condition (8) is satisfied.

[0061] 0.3 < (f2 - f1) / f3 < 7.0 ... (8) If the value falls below the lower limit of condition equation (8), the power of the third unit L3 decreases, which disrupts the balance of aberration correction and is undesirable. On the other hand, if the value exceeds the upper limit of condition equation (8), the power of the third unit L3 increases, making it difficult to correct various aberrations. Furthermore, the diameter of the third unit L3 increases, making it difficult to secure the effective width and increasing the difficulty of manufacturing.

[0062] More preferably, the numerical range of condition (8) is set as shown in condition (8a) below.

[0063] 0.5 < (f2 - f1) / f3 < 5.0 ... (8a) More preferably, the numerical range of condition (8) is set as shown in condition (8b) below.

[0064] 0.6 < (f2 - f1) / f3 < 2.0 ... (8b) Furthermore, in the optical system of each embodiment, by appropriately setting the refractive power of the third unit L3, which is positioned closest to the image plane, the incident angle, distortion, and field curvature of the light beam incident on the image plane can be effectively corrected. Therefore, by satisfying the following condition (9), various aberrations can be corrected more effectively.

[0065] 0.5 <f3 / f<4.0 ···(9) More preferably, the numerical range of condition (9) is set as shown in condition (9a) below.

[0066] 0.9 <f3 / f<3.0 ···(9a) More preferably, the numerical range of condition expression (9) is set as shown in condition expression (9b) below.

[0067] 1.1 <f3 / f<2.5 ···(9b) Preferably, the optical system of each embodiment satisfies the following condition (10).

[0068] 0.5 <L / f<3.5 ···(10) In condition (10), L is the distance along the optical axis from the third lens 32 to the image plane IP. By satisfying condition (10), spherical aberration and astigmatism can be corrected to appropriate values.

[0069] More preferably, the numerical range of condition expression (10) is set as shown in condition expression (10a) below.

[0070] 0.8 <L / f<2.6 ···(10a) Furthermore, the optical systems of each embodiment are wide-angle optical systems, and the first unit L1, which is the only one with negative refractive power, plays a significant role in correcting aberrations. In particular, since the off-axis rays are greatly bent by the lens surface facing the air in the first unit L1, it is important to appropriately set the distance between the refractive power of the air-facing surface of the first unit L1 and the aperture. Here, let da1 be the distance along the optical axis from the lens surface facing the air in the lens of the first unit L1 to the aperture diaphragm SP, and let Yim be the maximum image height. At this time, it is preferable that the following condition (11) is satisfied.

[0071] -2.0 <da1×f1 / (f×Yim)<-0.3 ···(11) If the refractive power falls below the lower limit of condition (11), the refractive power of the first unit L1 weakens, making aberration correction in the rear group difficult, and the effective diameter of the first unit L1 increases, making it difficult to miniaturize the optical system. On the other hand, if the refractive power exceeds the upper limit of condition (11), the refractive power of the first unit L1 becomes strong, causing higher-order aberrations to occur and making it impossible to reduce various aberrations such as field curvature.

[0072] More preferably, the numerical range of condition expression (11) is set as shown in condition expression (11a) below.

[0073] -1.5 <da1×f1 / (f×Yim)<-0.6 ···(11a) More preferably, the numerical range of conditional expression (11) is set as shown in conditional expression (11b) below.

[0074] -1.4 <da1×f1 / (f×Yim)<-0.7 ···(11b) In each embodiment, if multiple apertures are arranged in the optical system, the aperture closest to the point where the off-axis rays with an image height of 70% of the maximum image height intersect the optical axis functions as the aperture diaphragm SP.

[0075] The optical systems of each embodiment will be described in detail below. [Examples]

[0076] First, with reference to Figures 1 and 2, the optical system 1a in Example 1 (Numerical Example 1) will be described.

[0077] As shown in Figure 1, the optical system 1a consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a first lens 12 positioned on the image side of the first substrate 11. The first lens 12 is a negative lens with a concave surface facing the image side and is formed on the image side surface of the first substrate 11 using a wafer-level process. The second unit L2 consists of a second substrate 21 and a second lens 22 positioned on its object side and an aperture diaphragm SP positioned on the image side of the second substrate 21. The second lens 22 is a positive lens with a convex surface facing the object side and is formed on the object side surface of the second substrate 21 using a wafer-level process. The third unit L3 consists of a third substrate 31 and a bonded lens 4sm positioned on its object side and a fourth substrate 41 which is a sensor cover glass.

[0078] The cemented lens 4sm is composed of a third lens 32 (fifth lens 4B) having positive power near the optical axis, and a fourth lens 4R having positive power near the optical axis, arranged in order from the object side to the image side. The third lens 32 and the fourth lens 4R have different Abbe numbers and powers.

[0079] The third lens 32 has positive power in a region representing 70% of the effective diameter. The fourth lens 4R has negative power in a region representing 70% of the effective diameter. The fourth lens 4R is formed on the object-side surface of the third substrate 31 using a wafer-level process. Similarly, the third lens 32 is closely bonded to the object-side surface of the fourth lens 4R using a wafer-level process.

[0080] The optical system 1a in this embodiment is designed to focus on an object located 5 mm from the object-side surface of the first unit L1. Optical system 1a has a half-angle of view of 59.6° and an FNo of 2.8, providing a bright, wide-angle optical system despite its very compact size.

[0081] Figures 2(A) to 2(D) show the aberration diagrams of the optical system 1a in this embodiment. As shown in Figure 2(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in Figure 2(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in Figure 2(C), the distortion of this embodiment is less than 40%. As shown in Figure 2(D), the chromatic aberration of this embodiment is less than 0.01 mm. Thus, the optical system 1a of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the axial to the off-axial beam are well corrected. [Examples]

[0082] Next, with reference to Figures 3 and 4, the optical system 1b in Example 2 (Numerical Example 2) will be described.

[0083] As shown in Figure 3, the optical system 1b consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a first lens 12 positioned on the image side of the first substrate 11. The first lens 12 is a negative lens with a concave surface facing the image side and is formed on the image side surface of the first substrate 11 using a wafer-level process. The second unit L2 consists of a second substrate 21 and a second lens 22 positioned on its object side and an aperture diaphragm SP positioned on the image side of the second substrate 21. The second lens 22 is a positive lens with a convex surface facing the object side and is formed on the object side surface of the second substrate 21 using a wafer-level process. The third unit L3 consists of a third substrate 31 and a bonded lens 4sm positioned on its object side and a fourth substrate 41 which is a sensor cover glass.

[0084] The cemented lens 4sm consists of a third lens 32 (fifth lens 4B) having positive power near the optical axis and a fourth lens 4R having negative power near the optical axis, arranged in order from the object side to the image side. The third lens 32 and the fourth lens 4R have different Abbe numbers and powers.

[0085] The third lens 32 has negative power in a region representing 70% of its effective diameter. The fourth lens 4R has positive power in a region representing 70% of its effective diameter. The fourth lens 4R is formed on the object-side surface of the third substrate 31 using a wafer-level process. Similarly, the third lens 32 is closely bonded to the object-side surface of the fourth lens 4R using a wafer-level process.

[0086] The optical system 1b of this embodiment is designed to focus on an object located 5 mm from the object-side surface of the first unit L1. Optical system 1b has a half-angle of view of 59.0° and an FNo of 2.8, providing a bright, wide-angle optical system despite its very compact size.

[0087] Figures 4(A) to 4(D) show the aberration diagrams for the optical system 1b in this embodiment. As shown in Figure 4(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in Figure 4(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in Figure 4(C), the distortion of this embodiment is less than 40%. As shown in Figure 4(D), the chromatic aberration of this embodiment is less than 0.01 mm.

[0088] Thus, the optical system 1b of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the axial to the off-axial beam are well corrected. [Examples]

[0089] Next, with reference to Figures 5 and 6, the optical system 1c in Example 3 (Numerical Example 3) will be described.

[0090] As shown in Figure 5, the optical system 1c consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a first lens 12 positioned on the image side of the first substrate 11. The first lens 12 is a negative lens with a concave surface facing the image side and is formed on the image side surface of the first substrate 11 using a wafer-level process. The second unit L2 consists of a second substrate 21 and a second lens 22 positioned on its object side and an aperture diaphragm SP positioned on the image side of the second substrate 21. The second lens 22 is a positive lens with a convex surface facing the object side and is formed on the object side surface of the second substrate 21 using a wafer-level process. The third unit L3 consists of a third substrate 31 and a bonded lens 4sm positioned on its object side and a fourth substrate 41 which is a sensor cover glass.

[0091] The cemented lens 4sm is composed of a fourth lens 4R, which has negative power near the optical axis, and a third lens 32 (fifth lens 4B), which has positive power near the optical axis, arranged in order from the object side to the image side. The third lens 32 and the fourth lens 4R have different Abbe numbers and powers.

[0092] The third lens 32 has positive power in a region representing 70% of the effective diameter. The fourth lens 4R has negative power in a region representing 70% of the effective diameter. The third lens 32 is formed on the object-side surface of the third substrate 31 using a wafer-level process. Similarly, the fourth lens 4R is closely bonded to the object-side surface of the third lens 32 using a wafer-level process.

[0093] The optical system 1c in this embodiment is designed to focus on an object located 50 mm from the object-side surface of the first unit L1. The optical system 1c has a half-angle of view of 59.0° and an FNo of 2.9, resulting in a very compact yet bright and wide-angle optical system.

[0094] Figures 6(A) to 6(D) show the aberration diagrams for the optical system 1c in this embodiment. As shown in Figure 6(A), the spherical aberration in this embodiment is less than 0.1 mm. As shown in Figure 6(B), the astigmatism in this embodiment is less than 0.1 mm. As shown in Figure 6(C), the distortion in this embodiment is less than 40%. As shown in Figure 6(D), the chromatic aberration in this embodiment is less than 0.03 mm.

[0095] Thus, the optical system 1c of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the axial to the off-axial beam are well corrected. [Examples]

[0096] Next, with reference to Figures 7 and 8, the optical system 1d in Example 4 (Numerical Example 4) will be described.

[0097] As shown in Figure 7, the optical system 1d consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a cemented lens 4sm positioned on the image side of the first substrate 11. The cemented lens 4sm is composed of, in order from the object side to the image side, a fourth lens 4R having negative power near the optical axis and a first lens 12 (fifth lens 4B) having negative power near the optical axis. The first lens 12 and the fourth lens 4R have different Abbe numbers and powers.

[0098] The first lens 12 has negative power in a region representing 70% of its effective diameter. The fourth lens 4R also has negative power in a region representing 70% of its effective diameter. The fourth lens 4R is formed on the image-side surface of the first substrate 11 using a wafer-level process. Similarly, the first lens 12 is closely bonded to the image-side surface of the fourth lens 4R using a wafer-level process.

[0099] The second unit L2 consists of a second substrate 21, a second lens 22 positioned on the object side, and an aperture diaphragm SP positioned on the image side of the second substrate 21. The second lens 22 is a positive lens with its convex surface facing the object side and is formed on the object-side surface of the second substrate 21 using a wafer-level process. The third unit L3 consists of a third substrate 31, a third lens 32 positioned on the object side, and a fourth substrate 41 which is a sensor cover glass. The third lens 32 is a positive lens with its convex surface facing the object side and is formed on the object-side surface of the third substrate 31 using a wafer-level process.

[0100] The optical system 1d in this embodiment is designed to focus on an object located 5 mm from the object-side surface of the first unit L1. The optical system 1d has a half-angle of view of 59.0° and an FNo of 2.8, resulting in a very compact yet bright and wide-angle optical system.

[0101] Figures 8(A) to 8(D) show the aberration diagrams for the optical system 1d in this embodiment. As shown in Figure 8(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in Figure 8(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in Figure 8(C), the distortion of this embodiment is less than 40%. As shown in Figure 8(D), the chromatic aberration of this embodiment is less than 0.01 mm.

[0102] Thus, the optical system 1d of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the axial to the off-axial beam are well corrected. [Examples]

[0103] Next, with reference to Figures 9 and 10, the optical system 1e in Example 5 (Numerical Example 5) will be described.

[0104] As shown in Figure 9, the optical system 1e consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a first lens 12 positioned on the image side of the first substrate 11. The first lens 12 is a negative lens with a concave surface facing the image side and is formed on the image side surface of the first substrate 11 using a wafer-level process. The second unit L2 consists of a second substrate 21, a second lens 22 positioned on its object side, and an aperture diaphragm SP positioned on the image side of the second substrate 21. The second lens 22 is a positive lens with a convex surface facing the object side and is formed on the object side surface of the second substrate 21 using a wafer-level process. The third unit L3 consists of a third substrate 31, a bonded lens 4sm positioned on its image side, a fourth substrate 41 which is a back cover glass, and a fifth substrate 51 which is a sensor cover glass. The second unit L2 and the third unit L3 are joined via the image-side surface of the second substrate 21 and the object-side surface of the third substrate 31.

[0105] The cemented lens 4sm consists of a third lens 32 (fifth lens 4B) having positive power near the optical axis and a fourth lens 4R having negative power near the optical axis, arranged in order from the object side to the image side. The third lens 32 and the fourth lens 4R have different Abbe numbers and powers.

[0106] The third lens 32 has positive power in a region representing 70% of the effective diameter. The fourth lens 4R has negative power in a region representing 70% of the effective diameter. The third lens 32 is formed on the image-side surface of the third substrate 31 using a wafer-level process. Similarly, the fourth lens 4R is in close contact with the image-side surface of the third lens 32 using a wafer-level process.

[0107] The optical system 1e in this embodiment is designed to focus on an object located 5 mm from the object-side surface of the first unit L1. The optical system 1e has a half-angle of view of 58.6° and an FNo of 2.8, providing a bright, wide-angle optical system despite its very compact size.

[0108] Figures 10(A) to (D) show the aberration diagrams for the optical system 1e in this embodiment. As shown in Figure 10(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in Figure 10(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in Figure 10(C), the distortion of this embodiment is less than 40%. As shown in Figure 10(D), the chromatic aberration of this embodiment is less than 0.01 mm.

[0109] Thus, the optical system 1e of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the axial to the off-axial beam are well corrected. [Examples]

[0110] Next, with reference to Figures 11 and 12, the optical system 1f in Example 6 (Numerical Example 6) will be described.

[0111] As shown in Figure 11, the optical system 1f consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a first lens 12 positioned on the image side of the first substrate 11. The first lens 12 is a negative lens with a concave surface facing the image side and is formed on the image side surface of the first substrate 11 using a wafer-level process. The second unit L2 consists of a second substrate 21 and a second lens 22 positioned on its object side. The second lens 22 is a positive lens with a convex surface facing the object side and is formed on the object side surface of the second substrate 21 using a wafer-level process. The third unit L3 consists of a third substrate 31, a bonded lens 4sm positioned on its image side, an aperture diaphragm SP positioned on the image side of the third substrate 31, a fourth substrate 41 which is a back cover glass, and a fifth substrate 51 which is a sensor cover glass. The second unit L2 and the third unit L3 are joined via the image-side surface of the second substrate 21 and the object-side surface of the third substrate 31.

[0112] The cemented lens 4sm is composed of a fourth lens 4R, which has negative power near the optical axis, and a third lens 32 (fifth lens 4B), which has positive power near the optical axis, arranged in order from the object side to the image side. The third lens 32 and the fourth lens 4R have different Abbe numbers and powers.

[0113] The third lens 32 has positive power in a region representing 70% of the effective diameter. The fourth lens 4R has negative power in a region representing 70% of the effective diameter. The fourth lens 4R is formed on the image-side surface of the third substrate 31 using a wafer-level process. Similarly, the third lens 32 is in close contact with the image-side surface of the fourth lens 4R using a wafer-level process.

[0114] The optical system 1f in this embodiment is designed to focus on an object located 5 mm from the object-side surface of the first unit L1. The optical system 1f has a half-angle of view of 59.0° and an FNo of 2.8, resulting in a very compact yet bright and wide-angle optical system.

[0115] Figures 12(A) to (D) show the aberration diagrams for the optical system 1f in this embodiment. As shown in Figure 12(A), the spherical aberration in this embodiment is less than 0.04 mm. As shown in Figure 12(B), the astigmatism in this embodiment is less than 0.04 mm. As shown in Figure 12(C), the distortion in this embodiment is less than 40%. As shown in Figure 12(D), the chromatic aberration in this embodiment is less than 0.01 mm.

[0116] Thus, the optical system 1f of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the axial to the off-axial beam are well corrected. [Examples]

[0117] Next, with reference to Figures 13 and 14, the optical system 1g in Example 7 (Numerical Example 7) will be described.

[0118] As shown in Figure 13, the optical system 1g consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a cemented lens 4sm positioned on the image side of the first substrate 11. The cemented lens 4sm is composed of a fourth lens 4R having negative power near the optical axis and a first lens 12 (fifth lens 4B) having negative power near the optical axis, in order from the object side to the image side. The first lens 12 and the fourth lens 4R have different Abbe numbers and powers.

[0119] The first lens 12 has positive power in a region representing 70% of the effective diameter. The fourth lens 4R has negative power in a region representing 70% of the effective diameter. The fourth lens 4R is formed on the image-side surface of the first substrate 11 using a wafer-level process. Similarly, the first lens 12 is closely bonded to the image-side surface of the fourth lens 4R using a wafer-level process.

[0120] The second unit L2 consists of a second substrate 21, a second lens 22 positioned on the object side of the substrate 21, and an aperture diaphragm SP positioned on the image side of the substrate 21. The second lens 22 is a positive lens with its convex surface facing the object side and is formed on the object-side surface of the substrate 21 using a wafer-level process. The third unit L3 consists of a third substrate 31, a third lens 32 positioned on its image side, a fourth substrate 41 which is a back cover glass, and a fifth substrate 51 which is a sensor cover glass. The third lens 32 is a positive lens with its convex surface facing the image side and is formed on the image-side surface of the substrate 31 using a wafer-level process. The second and third units are joined via the image-side surface of the second substrate 21 and the object-side surface of the third substrate 31.

[0121] The optical system 1g in this embodiment is designed to focus on an object located 5 mm from the object-side surface of the first unit L1. Optical system 1g has a half-angle of view of 59.0° and an FNo of 2.8, providing a bright, wide-angle optical system despite its very compact size.

[0122] Figures 14(A) to (D) show the aberration diagrams for the optical system 1g in this embodiment. As shown in Figure 14(A), the spherical aberration in this embodiment is less than 0.04 mm. As shown in Figure 14(B), the astigmatism in this embodiment is less than 0.04 mm. As shown in Figure 14(C), the distortion in this embodiment is less than 40%. As shown in Figure 14(D), the chromatic aberration in this embodiment is less than 0.01 mm.

[0123] Thus, the optical system 1g of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the axial to the off-axial beam are well corrected. [Examples]

[0124] Next, with reference to Figures 15 and 16, the optical system 1h in Example 8 (Numerical Example 8) will be described.

[0125] As shown in Figure 15, the optical system 1h consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a first lens 12 positioned on the image side of the first substrate 11. The first lens 12 is a negative lens with its concave surface facing the image side and is formed on the image-side surface of the first substrate 11 using a wafer-level process. The second unit L2 consists of a second substrate 21, a cemented lens 4sm positioned on its object side, and an aperture diaphragm SP positioned on the image side of the second substrate 21.

[0126] The cemented lens 4sm is composed of a second lens 22 (fifth lens 4B) having positive power near the optical axis and a fourth lens 4R having negative power near the optical axis, arranged in order from the object side to the image side. The second lens 22 and the fourth lens 4R have different Abbe numbers and powers.

[0127] The second lens 22 has positive power in a region representing 70% of the effective diameter. The fourth lens 4R has negative power in a region representing 70% of the effective diameter. The fourth lens 4R is formed on the object-side surface of the second substrate 21 using a wafer-level process. Similarly, the second lens 22 is closely bonded to the object-side surface of the fourth lens 4R using a wafer-level process.

[0128] The third unit L3 consists of a third substrate 31, a third lens 32 positioned on its image side, a fourth substrate 41 which is a back cover glass, and a fifth substrate 51 which is a sensor cover glass. The third lens 32 is a positive lens with its convex surface facing the image side, and is formed on the image-side surface of the third substrate 31 using a wafer-level process. The second and third units are joined via the image-side surface of the second substrate 21 and the object-side surface of the third substrate 31.

[0129] The optical system 1h in this embodiment is designed to focus on an object located 5 mm from the object-side surface of the first unit L1. The optical system 1h has a half-angle of view of 58.6° and an FNo of 2.8, resulting in a very compact yet bright and wide-angle optical system.

[0130] Figures 16(A) to (D) show the aberration diagrams for optical system 1h in this embodiment. As shown in Figure 16(A), the spherical aberration in this embodiment is less than 0.04 mm. As shown in Figure 16(B), the astigmatism in this embodiment is less than 0.04 mm. As shown in Figure 16(C), the distortion in this embodiment is less than 40%. As shown in Figure 16(D), the chromatic aberration in this embodiment is less than 0.01 mm.

[0131] Thus, the optical system 1h of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the on-axis to the off-axis beam are well corrected. [Examples]

[0132] Next, with reference to Figures 17 and 18, the optical system 1i in Example 7 (Numerical Example 7) will be described.

[0133] As shown in Figure 17, the optical system 1i consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a cemented lens 4sm positioned on the image side of the first substrate 11.

[0134] The cemented lens 4sm is composed of, in order from the object side to the image side, a fourth lens 4R having positive power near the optical axis and a first lens 12 (fifth lens 4B) having negative power near the optical axis. The first lens 12 and the fourth lens 4R have different Abbe numbers and powers.

[0135] The first lens 12 has negative power in a region representing 70% of its effective diameter. The fourth lens 4R also has negative power in a region representing 70% of its effective diameter. The fourth lens 4R is formed on the image-side surface of the first substrate 11 using a wafer-level process. Similarly, the first lens 12 is closely bonded to the image-side surface of the fourth lens 4R using a wafer-level process.

[0136] The second unit L2 consists of a second substrate 21, a second lens 22 positioned on the image side thereof, and an aperture diaphragm SP positioned on the image side of the second substrate 21. The second lens 22 is a positive lens with its convex surface facing the image side and is formed on the image side surface of the second substrate 21 using a wafer-level process. The third unit L3 consists of a third substrate 31, a third lens 32 positioned on the image side thereof, and a fourth substrate 41 that serves as both a back cover glass and a sensor cover glass. The third lens 32 is a positive lens with its convex surface facing the image side and is formed on the image side surface of the third substrate 31 using a wafer-level process.

[0137] The optical system 1i in this embodiment is designed to focus on an object located 5 mm from the object-side surface of the first unit L1. The optical system 1i has a half-angle of view of 59.1° and an FNo of 2.9, providing a bright, wide-angle optical system despite its very compact size.

[0138] Figures 18(A) to (D) show the aberration diagrams for the optical system 1i in this embodiment. As shown in Figure 18(A), the spherical aberration in this embodiment is less than 0.04 mm. As shown in Figure 18(B), the astigmatism in this embodiment is less than 0.04 mm. As shown in Figure 18(C), the distortion in this embodiment is less than 40%. As shown in Figure 18(D), the chromatic aberration in this embodiment is less than 0.01 mm.

[0139] Thus, the optical system 1i of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the axial to the off-axial beam are well corrected. [Examples]

[0140] Next, with reference to Figures 19 and 20, the optical system 1j in Example 10 (Numerical Example 10) will be described.

[0141] As shown in Figure 19, the optical system 1j consists of a first unit L1, a second unit L2, and a third unit L3. The first unit L1 consists of a first substrate (front cover glass) 11 and a first lens 12 positioned on the image side of the first substrate 11. The first lens 12 is a negative lens with its concave surface facing the image side and is formed on the image-side surface of the first substrate 11 using a wafer-level process. The second unit L2 consists of a second substrate 21, a cemented lens 4sm positioned on its image side, and an aperture diaphragm SP positioned on the image side of the second substrate 21.

[0142] The cemented lens 4sm is composed of a second lens 22 (fifth lens 4B) having positive power near the optical axis and a fourth lens 4R having negative power near the optical axis, arranged in order from the object side to the image side. The second lens 22 and the fourth lens 4R have different Abbe numbers and powers.

[0143] The second lens 22 has positive power in a region of 70% of the effective diameter. The fourth lens 4R has negative power in a region of 70% of the effective diameter. The second lens 22 is formed on the image-side surface of the second substrate 21 using a wafer-level process. Similarly, the fourth lens 4R is closely bonded to the image-side surface of the second lens 22 using a wafer-level process. The third unit L3 consists of a third substrate 31, a third lens 32 positioned on its image side, and a fourth substrate 41 that serves as both a back cover glass and a sensor cover glass. The third lens 32 is a positive lens with its convex surface facing the image side, and is formed on the image-side surface of the third substrate 31 using a wafer-level process.

[0144] The optical system 1j in this embodiment is designed to focus on an object located 5 mm from the object-side surface of the first unit L1. The optical system 1j has a half-angle of view of 59.0° and an FNo of 2.9, resulting in a very compact yet bright and wide-angle optical system.

[0145] Figures 20(A) to (D) show the aberration diagrams for the optical system 1j in this embodiment. As shown in Figure 20(A), the spherical aberration of this embodiment is less than 0.04 mm. As shown in Figure 20(B), the astigmatism of this embodiment is less than 0.04 mm. As shown in Figure 20(C), the distortion of this embodiment is less than 40%. As shown in Figure 20(D), the chromatic aberration of this embodiment is less than 0.01 mm.

[0146] Thus, the optical system 1j of this embodiment, by having a cemented lens 4sm, is a compact, bright, and wide-angle optical system in which aberrations from the axial to the off-axial beam are well corrected.

[0147] The following shows numerical examples 1 to 10 corresponding to each of the examples 1 to 10. In each numerical example, r is the radius of curvature of the i-th surface from the object side (mm), d is the interplanar spacing between the i-th and (i+1)-th axes from the object side (mm), and nd and νd are the refractive index and Abbe number of the i-th optical element with respect to the d line, respectively. The Abbe number νd of a certain material is given by Nd, NF, and NC, respectively, when the refractive indices at the Fraunhofer lines d line (587.6 nm), F line (486.1 nm), and C line (656.3 nm) are Nd, NF, and NC. νd = (Nd-1) / (NF-NC) It is represented as follows.

[0148] The focal length f (mm) is the value when the lens is focused on an object at infinity. BF is the back focus, which is the distance from the last surface of the optical system to the image plane. The total length of the lens is the distance from the first surface to the image plane. Aspherical surfaces are indicated by adding the sign * after the surface number. The aspherical shape is expressed by the aforementioned formula (A). The notation "e±Z" is "10 ±Z It means "...".

[0149] In each numerical example, "aperture" refers to the aperture diaphragm SP. The effective diameter indicates the maximum light beam diameter when the light beam contributing to image formation passes through each surface.

[0150] (Numerical Example 1) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.54 2 ∞ 0.045 1.52290 50.3 0.40 3* 0.0814 0.120 0.23 4* 0.1350 0.095 1.52290 50.3 0.21 5 ∞ 0.100 1.51680 64.2 0.18 6 (aperture) ∞ 0.034 0.13 7* 0.2293 0.110 1.52290 50.3 0.21 8* 0.5376 0.045 1.63000 24.0 0.23 9 ∞ 0.100 1.51680 64.2 0.29 10 ∞ 0.300 1.51680 64.2 0.35 11 ∞ 0.020 0.55 Image plane ∞ Aspherical data 3rd page K =-9.05286e+00 ,A4= 1.11029e+03 ,A6=-2.41067e+05 ,A8= 3.64355e+07 , A10=-3.27768e+09 ,A12= 1.57316e+11 ,A14=-3.06672e+12 Side 4 K =-5.17841e+00 ,A4= 1.83640e+02 ,A6=-7.86697e+03 ,A8=-1.19106e+06 , A10= 3.60178e+08 ,A12=-3.52832e+10 ,A14= 1.23061e+12 Side 7 K =-4.42195e+01 ,A4= 2.95388e+02 ,A6=-5.30900e+04 ,A8= 5.75919e+06 , A10=-3.27378e+08 ,A12= 7.32429e+09 ,A14=-4.91577e+07 Side 8 K = 1.07888e+00 ,A4=-4.20373e+02 ,A6= 2.28647e+04 ,A8=-1.94505e+06 , A10= 6.62151e+07 ,A12=-2.71527e+03 Focal length 0.217 F-number 2.83 Half-angle 59.63 Image height 0.280 Lens length 1.070 BF 0.020 (Numerical Example 2) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.58 2 ∞ 0.045 1.52290 50.3 0.44 3* 0.0879 0.120 0.25 4* 0.1377 0.133 1.52290 50.3 0.24 5 ∞ 0.100 1.51680 64.2 0.19 6 (aperture) ∞ 0.038 0.13 7* 0.2782 0.045 1.63000 24.0 0.23 8* -0.6263 0.093 1.52290 50.3 0.28 9 ∞ 0.100 1.51680 64.2 0.30 10 ∞ 0.300 1.51680 64.2 0.36 11 ∞ 0.020 0.55 Image plane ∞ Aspherical data 3rd page K =-9.01617e+00 ,A4= 8.79331e+02 ,A6=-1.58823e+05 ,A8= 1.94562e+07 , A10=-1.41225e+09 ,A12= 5.48116e+10 ,A14=-8.68538e+11 Side 4 K =-3.18868e+00 ,A4= 1.20671e+02 ,A6=-1.02991e+04 ,A8= 1.06647e+06 , A10=-5.74328e+07 ,A12= 6.27744e+08 ,A14= 3.38861e+10 Side 7 K =-3.76673e+01 ,A4= 2.48626e+02 ,A6=-3.49626e+04 ,A8= 2.98260e+06 , A10=-1.84831e+08 ,A12= 9.36625e+09 ,A14=-2.68131e+11 Side 8 K =-9.70734e+22 ,A4= 7.33875e+02 ,A6=-5.76856e+04 ,A8= 4.40940e+05 , A10= 1.84269e+08 ,A12=-9.29382e+09 ,A14= 1.19839e+11 Focal length 0.224 F-number 2.83 Half-angle 58.99 Image height 0.280 Lens length 1.093 BF 0.020 (Numerical Example 3) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.240 1.51680 64.2 2.26 2 ∞ 0.200 1.52290 50.3 1.93 3* 0.2609 0.350 1.12 4* 0.3186 0.363 1.52290 50.3 0.84 5 ∞ 0.300 1.51680 64.2 0.69 6 (aperture) ∞ 0.147 0.28 7* 0.5939 0.050 1.63000 24.0 0.91 8* 0.3208 0.424 1.52290 50.3 1.08 9 ∞ 0.300 1.51680 64.2 1.14 10 ∞ 0.300 1.51680 64.2 1.39 11 ∞ 0.020 1.64 Image plane ∞ Aspherical data 3rd page K =-1.73945e+00 ,A4= 2.55076e+00 ,A6=-1.55852e+01 ,A8= 5.63286e+01 , A10=-2.01179e+02 ,A12= 4.31905e+02 ,A14=-3.57624e+02 Side 4 K =-3.19350e+00 ,A4= 8.26777e+00 ,A6=-8.19479e+01 ,A8= 7.54371e+02 , A10=-5.09583e+03 ,A12= 1.78101e+04 ,A14=-2.44071e+04 Side 7 K =-2.31968e+01 ,A4= 6.57776e+00 ,A6=-9.94286e+01 ,A8= 7.52174e+02 , A10=-2.79487e+03 ,A12= 4.36910e+03 ,A14=-1.41223e+03 Side 8 K =-1.07182e+00 ,A4= 7.01018e+00 ,A6=-1.29129e+02 ,A8= 7.83284e+02 , A10=-2.07389e+03 ,A12= 1.99522e+03 ,A14= 5.96501e+01 Focal length 0.584 F-number 2.88 Half-angle 58.99 Image height 0.820 Lens length: 2.695 BF 0.020 (Numerical Example 4) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.66 2 ∞ 0.045 1.52290 50.3 0.52 3* 1.1110 0.035 1.63000 24.0 0.31 4* 0.1177 0.130 0.28 5* 0.1338 0.119 1.52290 50.3 0.21 6 ∞ 0.100 1.51680 64.2 0.17 7 (aperture) ∞ 0.053 0.11 8* 0.2364 0.068 1.52290 50.3 0.26 9 ∞ 0.100 1.51680 64.2 0.29 10 ∞ 0.300 1.51680 64.2 0.35 11 ∞ 0.020 0.56 Image plane ∞ Aspherical data 3rd page K = 4.34938e+01 ,A4=-3.46661e+01 ,A6= 9.70226e+04 ,A8=-1.33543e+07 , A10= 8.47604e+08 ,A12=-2.52180e+10 ,A14= 2.77359e+11 Side 4 K =-1.91555e+01 ,A4= 6.74896e+02 ,A6=-8.57074e+04 ,A8= 7.38633e+06 , A10=-3.82658e+08 ,A12= 1.08650e+10 ,A14=-1.33472e+11 5th page K =-7.65600e+00 ,A4= 3.32416e+02 ,A6=-4.71671e+04 ,A8= 6.29776e+06 , A10=-5.92395e+08 ,A12= 3.21338e+10 ,A14=-7.47792e+11 Side 8 K =-7.54882e+01 ,A4= 2.56483e+02 ,A6=-5.59008e+04 ,A8= 7.18290e+06 , A10=-5.22184e+08 ,A12= 1.97653e+10 ,A14=-3.01523e+11 Focal length 0.224 F-number 2.83 Half-angle 59.00 Image height 0.280 Lens length 1.070 BF 0.020 (Numerical Example 5) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.65 2 ∞ 0.025 1.51100 57.0 0.51 3* 0.0976 0.117 0.30 4* 0.1719 0.087 1.59000 31.0 0.27 5 ∞ 0.100 1.51680 64.2 0.24 6 (aperture) ∞ 0.100 1.51680 64.2 0.13 7 ∞ 0.090 1.51100 57.0 0.13 8* -0.1320 0.030 1.63000 24.0 0.17 9* -0.1789 0.080 0.22 10 ∞ 0.100 1.51680 64.2 0.32 11 ∞ 0.300 1.51680 64.2 0.38 12 ∞ 0.021 0.55 Image plane ∞ Aspherical data 3rd page K =-1.52850e+00 ,A4= 7.05541e+01 ,A6=-4.76384e+02 ,A8=-3.59197e+04 , A10= 2.57289e+06 ,A12=-5.55384e+07 Side 4 K =-9.72216e-01 ,A4=-1.23157e+01 ,A6= 2.66694e+03 ,A8=-2.62236e+05 , A10= 1.27756e+07 ,A12=-2.54287e+08 Side 8 K = 9.48682e-01 ,A4=-1.60743e+02 ,A6=-1.79558e+04 ,A8=-2.14381e+06 , A10= 4.38554e+08 ,A12=-3.64264e+10 9th page K = 1.16667e+00 ,A4= 3.95314e+01 ,A6=-1.02951e+04 ,A8= 1.83106e+06 , A10=-1.35474e+08 ,A12= 4.97126e+09 Focal length 0.228 F-number 2.80 Half-angle 58.60 Image height 0.280 Lens length 1.149 BF 0.021 (Numerical Example 6) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.63 2 ∞ 0.025 1.52290 50.3 0.50 3* 0.0953 0.116 0.31 4* 0.1641 0.089 1.59000 31.0 0.28 5 ∞ 0.102 1.51680 64.2 0.25 6 ∞ 0.102 1.51680 64.2 0.15 7 (aperture) ∞ 0.030 1.63300 23.3 0.13 8* 0.0901 0.110 1.69000 35.0 0.20 9* -0.3208 0.048 0.23 10 ∞ 0.100 1.51680 64.2 0.30 11 ∞ 0.300 1.51680 64.2 0.36 12 ∞ 0.020 0.55 Image plane ∞ Aspherical data 3rd page K =-2.51230e+00 ,A4= 1.50191e+02 ,A6=-5.41471e+03 ,A8= 8.59473e+04 , A10= 2.08109e+06 ,A12=-6.15035e+07 Side 4 K =-2.57106e+00 ,A4= 3.13721e+01 ,A6= 5.22013e+02 ,A8=-1.34901e+05 , A10= 7.80377e+06 ,A12=-1.52685e+08 Side 8 K =-3.18691e-01 ,A4=-1.97315e+02 ,A6=-1.82279e+03 ,A8=-1.67855e+06 , A10= 2.82214e+08 ,A12=-2.05717e+10 9th page K = 5.11486e+00 ,A4= 5.54827e+01 ,A6=-2.90091e+03 ,A8= 5.31654e+05 , A10=-3.70522e+07 ,A12= 1.24796e+09 Focal length 0.220 F-number 2.79 Half-angle 59.00 Image height 0.280 Lens length 1.143 BF 0.020 (Numerical Example 7) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.66 2 ∞ 0.041 1.52290 50.3 0.52 3* 0.2465 0.050 1.63000 24.0 0.32 4* 0.1028 0.080 0.29 5* 0.1425 0.064 1.59000 31.0 0.23 6 ∞ 0.102 1.51680 64.2 0.19 7 (aperture) ∞ 0.102 1.51680 64.2 0.10 8 ∞ 0.070 1.52290 50.3 0.21 9* -0.1428 0.009 0.24 10 ∞ 0.100 1.51680 64.2 0.30 11 ∞ 0.254 1.51680 64.2 0.37 12 ∞ 0.020 0.55 Image plane ∞ Aspherical data 3rd page K =-4.61324e-02 ,A4= 3.75925e+02 ,A6=-1.37514e+04 ,A8= 5.67395e+05 , A10=-3.42776e+07 ,A12= 5.79769e+08 Side 4 K =-2.18853e+00 ,A4= 2.16476e+02 ,A6=-1.68891e+04 ,A8= 3.81220e+05 , A10= 8.71747e+05 ,A12=-1.48286e+08 5th page K =-9.42320e+00 ,A4= 2.98735e+02 ,A6=-4.17697e+04 ,A8= 3.28692e+06 , A10=-1.67034e+08 ,A12= 3.76355e+09 9th page K = 8.35618e-02 ,A4= 1.00261e+02 ,A6=-5.63149e+03 ,A8= 1.08499e+06 , A10=-6.72626e+07 ,A12= 1.96066e+09 Focal length 0.188 F-number 2.80 Half-angle 59.00 Image height 0.280 Lens length: 0.993 BF 0.020 (Numerical Example 8) Unit: mm Surface data Surface number r d nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.65 2 ∞ 0.037 1.51100 57.0 0.51 3* 0.1023 0.102 0.32 4* 0.1921 0.089 1.59000 31.0 0.27 5* -0.2114 0.040 1.51100 57.0 0.24 6 ∞ 0.102 1.51680 64.2 0.16 7 (Aperture stop) ∞ 0.102 1.51680 64.2 0.11 8 ∞ 0.070 1.51100 57.0 0.21 9* -0.1525 0.009 0.24 10 ∞ 0.100 1.51680 64.2 0.30 11 ∞ 0.300 1.51680 64.2 0.36 12 ∞ 0.020 0.55 Image plane ∞ Aspherical data The 3rd surface K = -1.91221e+00, A4 = 5.30807e+01, A6 = -1.86119e+03, A8 = -6.78150e+04, A10 = 5.22275e+06, A12 = -7.90975e+07 The 4th surface K = -7.86472e+00, A4 = 7.69781e+01, A6 = -5.49069e+03, A8 = 9.12301e+03, A10 = 1.44189e+07, A12 = -3.17442e+08 The 5th surface K =-1.42474e+01 ,A4=-8.94822e+01 ,A6=-1.80683e+04 ,A8= 4.54821e+06 , A10=-3.29958e+08 ,A12= 9.43633e+09 9th page K = 2.85911e-01 ,A4= 8.39157e+01 ,A6=-5.66271e+03 ,A8= 1.14875e+06 ,A10=-7.76388e+07 ,A12= 2.37854e+09 Focal length 0.192 F-number 2.80 Half-angle 58.60 Image height 0.280 Lens length 1.072 BF 0.020 (Numerical Example 9) Unit: mm Surface data Face number rd nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.63 2 ∞ 0.045 1.52000 47.0 0.49 3* -0.9279 0.098 1.63000 24.0 0.31 4* 0.2679 0.063 0.24 5 ∞ 0.100 1.51680 64.2 0.19 6 (aperture) ∞ 0.052 1.52000 47.0 0.10 7* -0.4292 0.030 0.15 8 ∞ 0.100 1.51680 64.2 0.21 9 ∞ 0.137 1.52000 47.0 0.29 10* -0.1556 0.078 0.34 11 ∞ 0.400 1.51680 64.2 0.43 12 ∞ 0.020 0.57 Image plane ∞ Aspherical data The third surface K = 8.92526e+00 ,A4= 3.22132e+02 ,A6=-2.77789e+04 ,A8= 2.38806e+06 , A10=-1.15657e+08 ,A12= 2.23681e+09 The fourth surface K =-4.68602e+01 ,A4= 2.95948e+02 ,A6=-3.70873e+04 ,A8= 2.68637e+06 , A10=-9.25452e+07 ,A12= 1.17487e+09 The seventh surface K = 1.64987e+01 ,A4= 9.83713e+00 ,A6= 2.85516e+04 ,A8=-1.48153e+07 , A10= 3.03313e+09 ,A12=-2.24996e+11 The tenth surface K =-5.25306e+00 ,A4=-8.76883e+01 ,A6= 2.41107e+03 ,A8= 1.26015e+04 , A10=-2.77019e+06 ,A12= 5.18753e+07 Focal length 0.226 F number 2.94 Half angle of view 59.09 Image height 0.280 Overall length of the lens 1.224 BF 0.020 (Numerical Example 10) Unit: mm Surface data Surface number r d nd νd Effective diameter 1 ∞ 0.100 1.51680 64.2 0.48 2 ∞ 0.045 1.52000 47.0 0.34 3* 0.2043 0.055 0.24 4 ∞ 0.100 1.51680 64.2 0.18 5 (aperture) ∞ 0.110 1.52000 47.0 0.09 6* -0.0745 0.026 1.63000 24.0 0.12 7* -0.2280 0.030 0.19 8 ∞ 0.100 1.51680 64.2 0.25 9 ∞ 0.103 1.52000 47.0 0.31 10* -0.1605 0.059 0.34 11 ∞ 0.400 1.51680 64.2 0.40 12 ∞ 0.020 0.56 Image plane ∞ Aspherical data 3rd page K =-1.31797e+01 ,A4= 5.73914e+01 ,A6=-8.07855e+03 ,A8= 7.23834e+05 , A10=-3.51063e+07 ,A12= 6.96366e+08 Side 6 K =-2.24008e+01 ,A4=-7.63948e+03 ,A6= 3.57919e+06 ,A8=-1.23628e+09 , A10= 2.00857e+11 ,A12=-1.25481e+13 Side 7 K = 1.43707e+00 ,A4=-4.26973e+02 ,A6= 1.00968e+05 ,A8=-1.75134e+07 , A10= 1.60540e+09 ,A12=-5.79159e+10 Side 10 K =-7.97099e+00 ,A4=-1.15794e+02 ,A6= 8.82572e+03 ,A8=-3.21692e+05 , A10= 6.43005e+06 ,A12=-5.52479e+07 Focal length 0.205 F-number 2.95 Half-angle 59.00 Image height 0.280 Lens length 1.149 BF 0.020 Tables 1 and 2 show the numerical values ​​related to the aforementioned conditional equations (1) to (11) in each numerical example.

[0151] [Table 1]

[0152] [Table 2] [Examples]

[0153] Next, with reference to Figure 21, the electronic device in Embodiment 11 of the present invention will be described. Figure 21 is a schematic diagram of the main parts of the electronic device (smartphone 70) of 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 of the optical systems of Embodiments 1 to 10 described above, and an image sensor 73 that receives the image formed by the optical system 72. In this way, by applying the optical systems of 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 yet has high optical performance. [Examples]

[0154] Next, with reference to Figure 22, the imaging device in Embodiment 12 of the present invention will be described. Figure 22 is a schematic diagram of the main parts of the imaging device 100 of this embodiment. The imaging device 100 is used in a small endoscope and has a camera head 120 and an electrical cable 150. The camera head 120 has a lens housing 121 equipped with an optical system of any of Embodiments 1 to 10, an image sensor (image element) 122, and a ceramic substrate 123. The wiring of the electrical cable 150 is connected to the image sensor 122 via the ceramic substrate 123. In this way, by applying the optical systems of each of the above embodiments to the imaging device of an endoscope, it is possible to realize an imaging device that is small yet has high optical performance.

[0155] According to each embodiment, it is possible to provide an optical system and imaging device that are compact yet have high optical performance.

[0156] Although 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 its essence. [Explanation of Symbols]

[0157] 1a~1j Optical system 11. First circuit board 12. First lens 21 Second board 22. Second lens 31 Third board 32 Third Lens L1 Unit 1 L2 Unit 2 L3 Unit 3 4R (4th lens) 4B Fifth lens (lens that is bonded to the fourth lens) 4SM cemented lens

Claims

1. It consists of a first unit, a second unit, and a third unit, which are arranged adjacent to each other in order from the object side to the image side. The first unit has a first lens with negative power, The second unit has a second lens with positive power, The third unit has a positive power third lens, The first lens, the second lens, and the third lens are each arranged on a substrate. At least one of the first lens, the second lens, or the third lens is joined with the fourth lens. An optical system characterized in that the power and Abbe number of the fourth lens and the lens joined to the fourth lens are different from each other.

2. When the Abbe number of the fourth lens is νr and the Abbe number of the lens joined to the fourth lens is νb, 8<|νr−νb|<60 The optical system according to claim 1, characterized in that it satisfies the following condition.

3. When dsm is the distance along the optical axis from the cementing surface of the cemented lens to the aperture diaphragm, and f is the focal length of the optical system, 0.05<dsm / f<2.50 The optical system according to claim 1 or 2, characterized in that it satisfies the following conditional expression.

4. The optical system according to claim 1, characterized in that the second unit or the third unit has an aperture diaphragm.

5. When the focal length in the region of 70% of the effective diameter of the fourth lens is f7r, the paraxial focal length in the central region of the effective diameter of the fourth lens is fr, the focal length in the region of 70% of the effective diameter of the lens joined to the fourth lens is f7b, and the paraxial focal length in the central region of the effective diameter of the lens joined to the fourth lens is fb, 0.05<|f7r / fr-1|<20.00 0.05<|f7b / fb-1|<20.00 The optical system according to any one of claims 1 to 4, characterized in that it satisfies at least one of the following conditional expressions.

6. When the focal length of the fourth lens in the region of 70% of its effective diameter is f7r, the Abbe number of the fourth lens is νr, the focal length of the lens joined to the fourth lens in the region of 70% of its effective diameter is f7b, the Abbe number of the lens joined to the fourth lens is νb, and the focal length of the optical system is f, 0.000<|f / (f7r×νr)+f / (f7b×νb)|<0.050 The optical system according to any one of claims 1 to 5, characterized in that it satisfies the following conditional expression.

7. When the focal length in the region of 70% of the effective diameter of the cemented lens is f7sm, the focal length in the region of 70% of the effective diameter of the fourth lens is f7r, and the focal length in the region of 70% of the effective diameter of the lens cemented to the fourth lens is f7b, 0.1<|f7sm / f7r|<6.0 0.1<|f7sm / f7b|<6.0 The optical system according to any one of claims 1 to 6, characterized in that it satisfies at least one of the following conditional expressions.

8. When the focal length of the second unit is f2 and the focal length of the optical system is f, 0.7<f2 / f<5.0 The optical system according to any one of claims 1 to 7, characterized in that it satisfies the following conditional expression.

9. When the focal length of the first unit is f1 and the focal length of the third unit is f3, -4.0<f3 / f1<-0.3 The optical system according to any one of claims 1 to 8, characterized in that it satisfies the following conditional expression.

10. When the focal length of the first unit is f1, the focal length of the second unit is f2, and the focal length of the third unit is f3, 0.3<(f2-f1) / f3<7.0 The optical system according to any one of claims 1 to 9, characterized in that it satisfies the following conditional expression.

11. When the focal length of the third unit is f3 and the focal length of the optical system is f, 0.5<f3 / f<4.0 The optical system according to any one of claims 1 to 10, characterized in that it satisfies the following conditional expression.

12. When L is the distance along the optical axis from the image-side surface of the third lens to the image plane, 0.5<L / f<3.5 The optical system according to any one of claims 1 to 11, characterized in that it satisfies the following conditional expression.

13. When the distance from the lens surface facing the air to the aperture diaphragm in the first unit's lens is da1, the focal length of the first unit is f1, the focal length of the optical system is f, and the maximum image height is Yim, -2.0 < da1 × f1 / (f × Yim) < -0.3 The optical system according to any one of claims 1 to 12, characterized in that it satisfies the following conditional expression.

14. The optical system according to any one of claims 1 to 13, characterized in that no lens is formed on one surface of the substrate on which the first lens is arranged.

15. The optical system according to any one of claims 1 to 14, characterized in that no lens is formed on one surface of the substrate on which the second lens is arranged.

16. The optical system according to any one of claims 1 to 15, characterized in that no lens is formed on one surface of the substrate on which the third lens is arranged.

17. The optical system according to any one of claims 1 to 16, characterized in that the materials of the first lens and the substrate on which the first lens is arranged are different from each other.

18. The optical system according to any one of claims 1 to 17, characterized in that the materials of the second lens and the substrate on which the second lens is arranged are different from each other.

19. The optical system according to any one of claims 1 to 18, characterized in that the materials of the third lens and the substrate on which the third lens is arranged are different from each other.

20. An imaging device characterized by having an optical system according to any one of claims 1 to 19 and an image sensor that receives an image formed by the optical system.

Images