Optical system and imaging device having the same

Abstract

To provide a compact, light-weight optical system that offers high optical performance by appropriately setting refractive indices and power arrangement of lenses.SOLUTION: An optical system L0 provided herein comprises a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, and a plurality of lenses, arranged continuously in order from the most image side, and satisfies the following conditional expressions: 1.70<PNdave<2.10, -100<(R11+R12) / (R12-R11)<0.60, 2.90<(R21+R22) / (R22-R21)<100, where PNdave represents an average refractive index of materials of all positive lenses included in the optical system for the d-line, R11 represents an object-side paraxial curvature radius of the first lens, R12 represents an image-side paraxial curvature radius of the first lens, R21 represents an object-side paraxial curvature radius of the second lens, and R22 represents an image-side paraxial curvature radius of the second lens.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system, and is suitable for digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, surveillance cameras, and the like.

Background Art

[0002] In recent years, imaging devices have been miniaturized, and imaging elements used in imaging devices have been made higher in pixel count. Along with the miniaturization and higher pixel count of imaging elements, the optical systems used in imaging devices are required to have high optical performance and be small and lightweight. Patent Document 1 discloses an optical system composed of six lenses, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens, which are arranged in order from the object side to the image side, as an optical system that satisfies these requirements. The first lens is a lens with a positive refractive power having a convex surface facing the object side near the optical axis. The second lens is a lens with a negative refractive power having a concave surface facing the image side near the optical axis. The third lens is a lens having a convex surface facing the object side near the optical axis. The fourth lens is a lens having a convex surface facing the image side near the optical axis. The fifth lens is a lens having a convex surface facing the object side near the optical axis. The sixth lens is a lens having a concave surface facing the image side near the optical axis.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to miniaturize the optical system, it is effective to adopt a telephoto-type power arrangement and strengthen the positive refractive power on the object side and the negative refractive power on the image side. However, when the negative refractive power on the image side is strengthened, large distortion occurs, so it becomes difficult to achieve both correction of distortion and field curvature with a limited number of lenses.

[0005] The optical system described in Patent Document 1 corrects distortion and field curvature by using a plurality of aspherical lenses. However, since the Petzval sum of the entire system is large, there is a problem in correcting field curvature when applying it to an imaging device with a large sensor size.

[0006] An object of the present invention is to provide an optical system having high optical performance, small size, and light weight by appropriately setting the refractive index and power arrangement of each lens.

Means for Solving the Problems

[0007] The optical system according to one aspect of the present invention includes a first lens having a positive refractive power, a second lens having a negative refractive power, which are arranged continuously in order from the most image side. Composed of 4 or 5 lenses An optical system, The optical system includes a lens with a positive refractive power arranged closest to the object side, Let the average refractive index of the material of all positive lenses included in the optical system at the d-line be PNdave, the object-side paraxial curvature radius of the first lens be R11, the image-side paraxial curvature radius of the first lens be R12, the object-side paraxial curvature radius of the second lens be R21, and the image-side paraxial curvature radius of the second lens be R22. Let the focal length of the first lens be f1, the focal length of the optical system be f, the distance on the optical axis from the aperture stop with the back focus as the air-equivalent length to the image plane be SPIP, and the distance on the optical axis from the lens surface on the object side of the lens arranged closest to the object side with the back focus as the air-equivalent length to the image plane be TTL When doing so, 1.70 < PNdave < 2.10 -100 < (R11 + R12) / (R12 - R11) < 0.60 2.90 < (R21 + R22) / (R22 - R21) < 100 0.80 < f1 / f < 8.00 0.80 < SPIP / TTL < 0.95 It is characterized by satisfying the conditional expression.

[0008] Other objects and features of the present invention will be described in the following embodiments.

Effects of the Invention

[0009] According to the present invention, it is possible to provide an optical system having high optical performance, small size, and light weight.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the optical system of the present invention and an imaging device having the same will be described with reference to the accompanying drawings. In each figure, the same members are denoted by the same reference numerals, and overlapping descriptions are omitted.

[0012] Figures 1, 3, 5, 7, 9, 11, 13, 15, and 17 are cross-sectional views of the optical systems L0 of Examples 1 to 9, respectively. The optical system L0 of each example is an optical system used in an imaging device such as a digital video camera, a digital still camera, a broadcast camera, a silver halide film camera, or a surveillance camera.

[0013] In each lens cross-sectional view, the left side is the object side and the right side is the image side. The optical system L0 of each example is composed of a plurality of lenses. In each lens cross-sectional view, "Li" (i is a natural number) represents the "i-th lens" when the lenses constituting the optical system L0 are counted in order from the image side to the object side. L1 represents the lens disposed closest to the image side among the lenses included in the optical system L0. L2 represents the lens disposed second from the image side among the lenses included in the optical system L0.

[0014] Also, SP is the aperture stop. IP is the image plane. When the optical system L0 of each example is used as the imaging optical system of a digital still camera or a digital video camera, the imaging plane of a solid-state imaging device (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is disposed. When the optical system L0 of each example is used as the imaging optical system of a silver halide film camera, a photosensitive surface corresponding to the film surface is placed on the image plane IP.

[0015] Also, by moving the entire optical system L0 along the optical axis, focusing is performed from an infinite object point to a closest object point.

[0016] Note that in the optical system L0 of each example, one or a plurality of lenses may be decentered so as to include a component perpendicular to the optical axis during image blur correction, thereby having a function as an anti-shake optical system. Also, a parallel plate having substantially no refractive power, such as a low-pass filter or an infrared cut filter, may be disposed between the lens disposed closest to the image side and the imaging plane.

[0017] Figures 2, 4, 6, 8, 10, 12, 14, 16, and 18 are aberration diagrams of the optical system L0 at infinity focus in Examples 1 to 9, respectively.

[0018] In the spherical aberration diagram, Fno is the F-number, showing the spherical aberration amounts for the d-line (wavelength 587.56 nm) and the g-line (wavelength 435.84 nm). In the astigmatism diagram, dS represents the astigmatism amount on the sagittal image plane, and dM represents the astigmatism amount on the meridional image plane. The distortion aberration diagram shows the distortion aberration amount for the d-line. The longitudinal chromatic aberration diagram shows the longitudinal chromatic aberration amount for the g-line. ω is the imaging semi-field angle (°).

[0019] Next, the characteristic configurations of the optical system L0 in each example will be described.

[0020] The optical system L0 of each example has a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, and a plurality of lenses, which are arranged continuously in order from the most image side.

[0021] Furthermore, when the average refractive index of the material of all the positive lenses included in the optical system L0 at the d-line (wavelength 587.56 nm) is defined as PNdave, the optical system L0 of each example satisfies the following conditional expression (1).

[0022] 1.70 < PNdave < 2.10 ···(1) Conditional expression (1) defines the average refractive index of the positive lenses included in the optical system L0. If the refractive index is higher than the upper limit value of conditional expression (1), the color dispersion becomes large and it is difficult to correct the axial chromatic aberration, which is not preferable. If the refractive index is lower than the lower limit value of conditional expression (1), the Petzval sum of the optical system L0 becomes large and it is difficult to correct the field curvature, which is not preferable.

[0023] Furthermore, when the object-side paraxial curvature radius of the first lens L1 is R11 and the image-side paraxial curvature radius of the first lens L1 is R12, the optical system L0 of each example satisfies the following conditional expression (2).

[0024] -100 < (R11 + R12) / (R12 - R11) < 0.60 ···(2) Conditional expression (2) defines the shape of the first lens L1. If the paraxial curvature radius on the object side of the first lens L1 becomes smaller than the upper limit value of conditional expression (2), the distance between the first lens L1 and the second lens L2 at the peripheral part becomes larger, and the diameter of the first lens L1 becomes larger, which is not preferable. If the difference between the paraxial curvature radius on the object side and the paraxial curvature radius on the image side becomes smaller than the lower limit value of conditional expression (2), the correction of the spiral distortion becomes insufficient, which is not preferable.

[0025] Furthermore, when the paraxial curvature radius on the object side of the second lens L2 is R21 and the paraxial curvature radius on the image side of the second lens L2 is R22, the optical system L0 of each embodiment satisfies the following conditional expression (3).

[0026] 2.90 < (R21 + R22) / (R22 - R21) < 100 ···(3) Conditional expression (3) defines the shape of the second lens L2. If the difference between the paraxial curvature radius on the object side and the paraxial curvature radius on the image side becomes smaller than the upper limit value of conditional expression (3), the correction of the field curvature becomes insufficient, which is not preferable. If the paraxial curvature radius on the image side becomes smaller than the lower limit value of conditional expression (3), the distance between the second lens L2 and the first lens L1 at the peripheral part becomes larger, and the diameter of the first lens L1 becomes larger, which is not preferable.

[0027] It should be noted that it is preferable that the numerical ranges of conditional expressions (1) to (3) are the numerical ranges of the following conditional expressions (1a) to (3a).

[0028] 1.705 < PNdave < 2.000 ···(1a) -50.0 < (R11 + R12) / (R12 - R11) < 0.60 ···(2a) 2.90 < (R21 + R22) / (R22 - R21) < 50.0 ···(3a) Also, it is more preferable that the numerical ranges of conditional expressions (1) to (3) are the numerical ranges of the following conditional expressions (1b) to (3b).

[0029] 1.709 < PNdave < 2.000 ···(1b) -10.0 < (R11 + R12) / (R12 - R11) < 0.6 ···(2b) 2.90 < (R21 + R22) / (R22 - R21) < 45.0 ···(3b) Next, the preferable conditions and configurations satisfied by the optical system L0 of each embodiment will be described. The optical system L0 of each embodiment preferably satisfies one or more of the following conditional expressions (4) to (9) and the following configurations.

[0030] The optical system L0 of each embodiment preferably has a positive refractive power lens Lp arranged on the most object side in order to shorten the overall optical length in a telephoto type power arrangement.

[0031] When the focal length of the lens Lp arranged on the most object side of the optical system L0 of each embodiment is fp and the focal length of the optical system L0 is f, it preferably satisfies the following conditional expression (4).

[0032] 0.55 < fp / f < 2.00 ···(4) The conditional expression (4) defines the ratio between the focal length of the lens Lp and the focal length of the optical system L0. If the refractive power of the lens Lp becomes weak exceeding the upper limit value of the conditional expression (4), it becomes difficult to maintain the telephoto type power arrangement, and the overall optical length becomes large, which is not preferable. If the refractive power of the lens Lp becomes strong below the lower limit value of the conditional expression (4), the distortion of the spool type becomes large, and it becomes difficult to achieve both the field curvature and the distortion, which is not preferable.

[0033] When the focal length of the first lens L1 of the optical system L0 of each embodiment is f1, it preferably satisfies the following conditional expression (5).

[0034] 0.80 < f1 / f < 8.00 ···(5) The conditional expression (5) defines the ratio between the focal length of the first lens L1 and the focal length of the optical system L0. If the refractive power of the first lens L1 becomes weaker exceeding the upper limit value of the conditional expression (5), the correction of the spiral distortion becomes insufficient, and it becomes difficult to achieve both the image plane curvature and the distortion, which is not preferable. If the refractive power of the first lens L1 becomes stronger falling below the lower limit value of the conditional expression (5), it becomes difficult to maintain the telephoto type power arrangement, and the overall optical length becomes large, which is not preferable.

[0035] For the optical system L0 of each embodiment, when the distance (air equivalent length) on the optical axis from the lens surface on the image side of the first lens L1 to the image plane is sk, it is preferable to satisfy the following conditional expression (6).

[0036] 0.20 < sk / f < 0.50 ···(6) The conditional expression (6) defines the ratio between the back focus and the focal length of the optical system L0. If the back focus is long exceeding the upper limit value of the conditional expression (6), the overall optical length becomes large, which is not preferable. If the back focus is short falling below the lower limit value of the conditional expression (6), the shadow of foreign matter attached to the lens is likely to be reflected in the photograph, which is not preferable.

[0037] For the optical system L0 of each embodiment, it is preferable to satisfy the following conditional expression (7). Let the distance on the optical axis from the aperture stop SP with the back focus as the air equivalent length to the image plane IP (paraxial) be SPIP, and the distance on the optical axis from the lens surface on the object side of the lens arranged most on the object side with the back focus as the air equivalent length to the image plane IP (paraxial) be TTL.

[0038] 0.60 < SPIP / TTL < 0.95 ···(7) The conditional expression (7) defines the ratio between the position of the aperture stop SP and the overall optical length. If the position of the aperture stop SP is on the object side exceeding the upper limit value of the conditional expression (7), the deviation of vignetting is likely to occur, and the shape of the blur becomes abnormal, which is not preferable. If the position of the aperture stop SP is on the image side falling below the lower limit value of the conditional expression (7), the angle of the off-axis light rays incident on the image plane IP becomes large, and shading by the imaging device is likely to occur, which is not preferable.

[0039] For the optical system L0 of each embodiment, it is preferable to arrange the aperture stop SP adjacent to the image side of the lens that is arranged closest to the object side in order to reduce the angle of off-axis light incident on the image plane IP and reduce shading by the imaging device.

[0040] For the optical system L0 of each embodiment, when the imaging semi-field angle (°) is ω, it is preferable to satisfy the following conditional expression (8). The semi-field angle may be defined as the semi-field angle of light that forms an image at the end of the image circle of the optical system L0, or may be defined as the semi-field angle of light that forms an image at the maximum image height of the image sensor of the imaging device to which the optical system L0 is mounted.

[0041] 1.40 < TTL / ftanω < 3.20 ···(8) Conditional expression (8) defines the overall optical length of the optical system L0. If it exceeds the upper limit value of conditional expression (8), it is not preferable because the overall optical length increases. If the overall optical length becomes short by falling below the lower limit value of conditional expression (8), the telephoto-type power arrangement becomes strong, and it becomes difficult to achieve both image plane curvature and distortion correction, so it is not preferable.

[0042] For the optical system L0 of each embodiment, when the refractive index of the second lens L2 at the d-line is Nd2 and the Abbe number is νd2, it is preferable to satisfy the following conditional expression (9).

[0043] Nd2 < 4.19450 / νd2 + 1.52010 ···(9) Conditional expression (9) defines the refractive index of the lens L2. If the refractive index of the negative lens L2 becomes large by exceeding the upper limit value of conditional expression (9), the Petzval sum of the optical system L0 becomes large, and it becomes difficult to correct the image plane curvature, so it is not preferable.

[0044] Note that it is preferable to set the numerical ranges of conditional expressions (4) to (9) as the numerical ranges of the following conditional expressions (4a) to (9a).

[0045] 0.55 < fp / f < 1.50 ···(4a) 0.80 < f1 / f < 4.00 ···(5a) 0.23 < sk / f < 0.40 ···(6a) 0.70 < SPIP / TTL < 0.90 ···(7a) 1.9 < TTL / (f×tanω) < 3.1 ···(8a) Nd2 < 4.19450 / νd2 + 1.48010 ···(9a) Furthermore, it is more preferable that the numerical ranges of conditional expressions (4) to (9) are the numerical ranges of the following conditional expressions (4b) to (9b).

[0046] 0.79 < fp / f < 1.35 ···(4b) 0.85 < f1 / f < 1.90 ···(5b) 0.25 < sk / f < 0.39 ···(6b) 0.80 < SPIP / TTL < 0.90 ···(7b) 1.9 < TTL / (f×tanω) < 2.5 ···(8b) Nd2 < 4.19450 / νd2 + 1.45710 ···(9b) In order to achieve both high optical performance and miniaturization, the optical system L0 of each embodiment preferably has three or more lenses with positive refractive power and two or more lenses with negative refractive power, and the total number of lenses included in the optical system L0 is preferably composed of eight or fewer lenses.

[0047] For each embodiment, the optical system L0 preferably has an aspherical lens made of a resin material on the image side of the aperture stop in order to correct field curvature.

[0048] Note that a cover glass, an IR cut filter, etc. are not regarded as lenses, and a cover glass, an IR cut filter, etc. may be arranged on the object side of the lens Lp of the optical system L0 of each embodiment or between the first lens L1 and the image plane. Also, the refractive power of a lens represents the refractive power in the vicinity of the optical axis (paraxial). Here, the vicinity of the optical axis refers to the paraxial region. In the case of an aspherical lens, the concave and convex surfaces in the vicinity of the optical axis are defined by the sign of the paraxial curvature radius. Similarly, the positive and negative of the refractive power are also calculated from the paraxial curvature radius.

[0049] Next, the optical system L0 of each embodiment will be described in detail.

[0050] The optical system L0 of Embodiment 1 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, an aperture stop SP, and a sixth lens L6, which are arranged in order from the image side to the object side. The first lens L1 has a positive refractive power. The second lens L2 has a negative refractive power near the optical axis. The third lens L3 has a negative refractive power near the optical axis. The fourth lens L4 has a positive refractive power. The fifth lens L5 has a negative refractive power. The sixth lens L6 has a positive refractive power. The sixth lens L6 is the lens Lp. The second lens L2 has aspherical surfaces formed on both sides. The surface on the object side faces the concave surface toward the object side near the optical axis, and the surface on the image side faces the convex surface toward the image side near the optical axis. The third lens L3 has aspherical surfaces formed on both sides. The surface on the object side faces the concave surface toward the object side near the optical axis, and the surface on the image side faces the concave surface toward the image side near the optical axis.

[0051] The optical system L0 of Embodiment 2 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, an aperture stop SP, and a sixth lens L6, which are arranged in order from the image side to the object side. The first lens L1 has a positive refractive power. The second lens L2 has a negative refractive power near the optical axis. The third lens L3 has a negative refractive power near the optical axis. The fourth lens L4 has a positive refractive power. The fifth lens L5 has a negative refractive power. The sixth lens L6 has a positive refractive power. The sixth lens L6 is the lens Lp. The second lens L2 has aspherical surfaces formed on both sides. The surface on the object side faces the concave surface toward the object side near the optical axis, and the surface on the image side faces the convex surface toward the image side near the optical axis. The third lens L3 has aspherical surfaces formed on both sides. The surface on the object side faces the concave surface toward the object side near the optical axis, and the surface on the image side faces the concave surface toward the image side near the optical axis.

[0052] The optical system L0 of Example 3 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, an aperture stop SP, and a sixth lens L6, which are arranged in order from the image side to the object side. The first lens L1 has a positive refractive power. The second lens L2 has a negative refractive power near the optical axis. The third lens L3 has a negative refractive power near the optical axis. The fourth lens L4 has a positive refractive power. The fifth lens L5 has a negative refractive power. The sixth lens L6 has a positive refractive power. The sixth lens L6 is the lens Lp. The second lens L2 has aspherical surfaces formed on both sides. The surface on the object side faces concave toward the object side near the optical axis, and the surface on the image side faces convex toward the image side near the optical axis. The third lens L3 has aspherical surfaces formed on both sides. The surface on the object side faces concave toward the object side near the optical axis, and the surface on the image side faces concave toward the image side near the optical axis.

[0053] The optical system L0 of Example 4 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, an aperture stop SP, and a sixth lens L6, which are arranged in order from the image side to the object side. The first lens L1 has a positive refractive power. The second lens L2 has a negative refractive power near the optical axis. The third lens L3 has a negative refractive power near the optical axis. The fourth lens L4 has a positive refractive power. The fifth lens L5 has a negative refractive power. The sixth lens has a positive refractive power. The sixth lens L6 is the lens Lp. The second lens L2 has aspherical surfaces formed on both sides. The surface on the object side faces concave toward the object side near the optical axis, and the surface on the image side faces convex toward the image side near the optical axis. The third lens L3 has aspherical surfaces formed on both sides. The surface on the object side faces concave toward the object side near the optical axis, and the surface on the image side faces concave toward the image side near the optical axis.

[0054] The optical system L0 of Example 5 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, an aperture stop SP, and a seventh lens L7, which are arranged in order from the image side to the object side. The first lens L1 has a positive refractive power. The second lens L2 has a negative refractive power near the optical axis. The third lens L3 has a negative refractive power. The fourth lens L4 has a negative refractive power near the optical axis. The fifth lens L5 has a positive refractive power. The sixth lens L6 has a negative refractive power. The seventh lens has a positive refractive power. The seventh lens L7 is the lens Lp. The second lens L2 has aspherical surfaces formed on both sides, the surface on the object side faces the object side with a concave surface near the optical axis, and the surface on the image side faces the image side with a convex surface near the optical axis. The fourth lens L4 has aspherical surfaces formed on both sides, the surface on the object side faces the object side with a concave surface near the optical axis, and the surface on the image side faces the image side with a convex surface near the optical axis.

[0055] The optical system L0 of Example 6 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, an aperture stop SP, and a seventh lens L7, which are arranged in order from the image side to the object side. The first lens L1 has a positive refractive power. The second lens L2 has a negative refractive power near the optical axis. The third lens L3 has a negative refractive power. The fourth lens L4 has a positive refractive power near the optical axis. The fifth lens L5 has a positive refractive power. The sixth lens L6 has a negative refractive power. The seventh lens L7 has a positive refractive power. The seventh lens L7 is the lens Lp. The second lens L2 has aspherical surfaces formed on both sides, the surface on the object side faces the object side with a concave surface near the optical axis, and the surface on the image side faces the image side with a convex surface near the optical axis. The fourth lens L4 has aspherical surfaces formed on both sides, the surface on the object side faces the object side with a concave surface near the optical axis, and the surface on the image side faces the image side with a convex surface near the optical axis.

[0056] The optical system L0 of Example 7 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, an aperture stop SP, and a seventh lens L7, which are arranged in order from the image side to the object side. The first lens L1 has a positive refractive power. The second lens L2 has a negative refractive power near the optical axis. The third lens L3 has a negative refractive power. The fourth lens L4 has a negative refractive power near the optical axis. The fifth lens L5 has a positive refractive power. The sixth lens L6 has a negative refractive power. The seventh lens L7 has a positive refractive power. The seventh lens L7 is the lens Lp. The second lens L2 has aspherical surfaces formed on both sides. The surface on the object side faces concave towards the object side near the optical axis, and the surface on the image side faces convex towards the image side near the optical axis. The fourth lens L4 has aspherical surfaces formed on both sides. The surface on the object side faces concave towards the object side near the optical axis, and the surface on the image side faces concave towards the image side near the optical axis.

[0057] The optical system L0 of Example 8 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, an aperture stop SP, and a seventh lens L7, which are arranged in order from the image side to the object side. The first lens L1 has a positive refractive power. The second lens L2 has a negative refractive power near the optical axis. The third lens L3 has a negative refractive power. The fourth lens L4 has a positive refractive power near the optical axis. The fifth lens L5 has a positive refractive power. The sixth lens L6 has a negative refractive power. The seventh lens L7 has a positive refractive power. The seventh lens L7 is the lens Lp. The second lens L2 has aspherical surfaces formed on both sides. The surface on the object side faces concave towards the object side near the optical axis, and the surface on the image side faces convex towards the image side near the optical axis. The fourth lens L4 has aspherical surfaces formed on both sides. The surface on the object side faces concave towards the object side near the optical axis, and the surface on the image side faces convex towards the image side near the optical axis.

[0058] The optical system L0 of Example 9 is composed of a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, an aperture stop SP, and a seventh lens L7, which are arranged in order from the image side to the object side. The first lens L1 has a positive refractive power. The second lens L2 has a negative refractive power near the optical axis. The third lens L3 has a negative refractive power. The fourth lens L4 has a positive refractive power near the optical axis. The fifth lens L5 has a positive refractive power. The sixth lens L6 has a negative refractive power. The seventh lens L7 has a positive refractive power. The seventh lens L7 is the lens Lp. The second lens L2 has aspherical surfaces formed on both sides. The surface on the object side faces concave towards the object side near the optical axis, and the surface on the image side faces convex towards the image side near the optical axis. The fourth lens L4 has aspherical surfaces formed on both sides. The surface on the object side faces concave towards the object side near the optical axis, and the surface on the image side faces convex towards the image side near the optical axis.

[0059] Numerical Examples 1 to 9 corresponding to Examples 1 to 9 are shown below.

[0060] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance on the optical axis) between the m-th surface and the (m + 1)-th surface. Here, m is the number of the surface counted from the light incident side. Also, nd represents the refractive index with respect to the d-line of each optical member, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material is given by νd=(Nd - 1) / (NF - NC) and is represented by.

[0061] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values when the optical system L0 of each example is focused on an infinitely distant object. "Back focus" is the distance on the optical axis from the final lens surface (the lens surface closest to the image side) to the paraxial image plane, expressed in terms of the air-equivalent length. "Overall lens length" is the length obtained by adding the back focus to the distance on the optical axis from the frontmost surface (the lens surface closest to the object side) to the final surface of the optical system L0.

[0062] When the optical surface is an aspherical surface, an asterisk (*) is attached to the right side of the surface number. The aspherical shape is expressed as follows when X is the displacement amount from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial curvature radius, k is the conic constant, and A4, A6, A8, A10, A12, and A14 are the aspherical coefficients of each order: x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 +A14×h 14 Here, "e±XX" in each aspherical coefficient means "×10± XX ".

[0063] [Numerical Example 1] Unit: mm Surface Data Surface Number r d nd νd 1 12.364 3.19 1.61800 63.4 2 24.210 2.94 3 (Aperture) ∞ 2.27 4 -50.169 0.69 1.60342 38.0 5 10.139 4.02 1.85150 40.8 6 -33.783 0.40 7* -34.470 1.33 1.63560 23.9 8 * 70.659 5.80 9 * -6.950 3.08 1.67070 19.3 10 * -11.164 0.20 11 478.184 6.09 1.90366 31.3 12 -37.541 11.50 Image plane ∞ Aspherical data The 7th surface K = 0.00000e+000 A 4=-1.02966e-004 A 6= 1.45749e-005 A 8=-1.39350e-006 A10= 6.80905e-008 A12=-1.49610e-009 A14= 1.14433e-011 The 8th surface K = 0.00000e+000 A 4= 6.02186e-006 A 6= 6.43923e-006 A 8=-3.91077e-007 A10= 1.43765e-008 A12=-2.09793e-010 A14= 8.50376e-013 The 9th surface K =-4.41191e+000 A 4=-1.47362e-003 A 6= 4.29446e-005 A 8=-1.68194e-006 A10= 4.49993e-008 A12=-7.25078e-010 A14= 4.77511e-012 The 10th surface K = 0.00000e+000 A 4= 8.83309e-005 A 6= 9.25372e-008 A 8=-7.24772e-010 A10= 1.08868e-010 A12=-1.57886e-012 A14= 9.00701e-015 Focal length 33.13 F number 2.91 Half field angle (°) 33.15 Image height 21.64 Overall lens length 41.51 BF 11.50 [Numerical Example 2] Unit: mm Surface data Surface number r d nd νd 1 13.651 2.98 1.61800 63.4 2 26.798 2.88 3 (Aperture) ∞ 2.70 4 -29.679 0.70 1.60342 38.0 5 11.727 4.28 1.85150 40.8 6 -23.783 0.40 7* -31.235 3.85 1.63560 23.9 8* 326.362 6.92 9* -8.020 3.77 1.67070 19.3 10* -12.457 0.20 11 73.939 4.84 1.90366 31.3 12 -254.677 10.00 Image plane ∞ Aspherical data The 7th surface K = 0.00000e+000 A 4=-1.34864e-004 A 6= 4.33017e-006 A 8=-2.94984e-007 A10= 1.08664e-008 A12=-1.73525e-010 A14= 8.43785e-013 The 8th surface K = 0.00000e+000 A 4=-5.66667e-005 A 6= 1.20119e-006 A 8=-1.06066e-009 A10=-5.01855e-010 A12= 1.73403e-011 A14=-1.38734e-013 The 9th surface K = -4.34585e+000 A4 = -1.00898e-003 A6 = 2.14842e-005 A8 = -5.92000e-007 A10 = 1.13215e-008 A12 = -1.30734e-010 A14 = 6.25651e-013 The 10th surface K = 0.00000e+000 A4 = 1.96956e-005 A6 = 7.34785e-007 A8 = -1.11185e-008 A10 = 1.57907e-010 A12 = -1.19765e-012 A14 = 3.83183e-015 Focal length 34.60 F-number 2.91 Half angle of view (°) 32.02 Image height 21.64 Overall lens length 43.50 BF 10.00 [Numerical Example 3] Unit: mm Surface data Surface number r d nd νd 1 13.201 3.04 1.61800 63.4 2 26.031 2.89 3 (aperture) ∞ 2.44 4 -33.911 0.74 1.60342 38.0 5 9.811 4.21 1.85150 40.8 6 -33.263 0.40 7* -90.919 3.00 1.63560 23.9 8* 60.811 5.38 9* -8.390 4.00 1.67070 19.3 10* -17.176 0.20 11 -211.111 6.30 1.90366 31.3 12 -29.226 10.89 Image plane ∞ Aspherical data The 7th surface K = 0.00000e+000 A 4=-1.60984e-004 A 6= 7.75621e-006 A 8=-6.51995e-007 A10= 2.77714e-008 A12=-5.32718e-010 A14= 3.58464e-012 The 8th surface K = 0.00000e+000 A 4=-6.81171e-005 A 6= 1.56038e-006 A 8=-2.02001e-008 A10=-6.01290e-010 A12= 4.31469e-011 A14=-4.65533e-013 The 9th surface K =-7.11991e+000 A 4=-1.50408e-003 A 6= 4.55541e-005 A 8=-1.63651e-006 A10= 3.84552e-008 A12=-5.40978e-010 A14= 3.19370e-012 The 10th surface K = 0.00000e+000 A 4= 5.39631e-006 A 6=-1.49270e-007 A 8= 4.42673e-009 A10=-5.89346e-011 A12= 4.11714e-013 A14=-1.05328e-015 Focal length 34.39 F-number 2.91 Half field angle (°) 32.17 Image height 21.64 Overall lens length 43.50 BF 10.89 [Numerical Example 4] Unit: mm Surface data Surface number r d nd νd 1 12.361 3.46 1.43875 94.7 2 28.265 2.82 3 (Diaphragm) ∞ 2.59 4 -25.271 0.71 1.60342 38.0 5 9.882 4.60 1.89190 37.1 6 -21.765 0.40 7* -41.047 2.81 1.63560 23.9 8* 37.020 7.59 9* -7.504 2.10 1.67070 19.3 10* -11.582 0.20 11 335.485 7.11 1.80000 29.8 12 -38.684 10.10 Image plane ∞ Aspherical data The 7th surface K = 0.00000e+000 A 4=-3.16322e-004 A 6= 2.09879e-006 A 8= 5.06534e-008 A10=-6.29589e-009 A12= 2.24698e-010 A14=-2.68222e-012 The 8th surface K = 0.00000e+000 A 4=-2.09731e-004 A 6= 1.97459e-006 A 8= 4.26758e-008 A10=-2.19133e-009 A12= 4.51796e-011 A14=-2.96237e-013 The 9th surface K =-5.19215e+000 A 4=-1.35545e-003 A 6= 3.94317e-005 A 8=-1.22569e-006 A10= 2.46402e-008 A12=-2.90244e-010 A14= 1.42214e-012 The 10th surface K = 0.00000e+000, A4 = 9.26493e-005, A6 = 6.49815e-007, A8 = -1.78983e-008 A10 = 3.22776e-010, A12 = -2.73407e-012, A14 = 1.10539e-014 Focal length: 35.00 F-number: 2.91 Half field angle (°): 31.72 Image height: 21.64 Overall lens length: 44.50 BF: 10.10 [Numerical Example 5] Unit: mm Surface data Surface number, r, d, nd, νd 1, 12.361, 3.01, 1.69680, 55.5 2, 29.386, 2.75 3 (aperture stop), ∞, 2.80 4, -36.916, 1.10, 1.69895, 30.1 5, 13.095, 3.81, 1.83481, 42.7 6, -25.327, 0.43 7*, -44.694, 1.18, 1.53110, 55.9 8*, -515.202, 3.67 9, -7.827, 2.36, 1.92286, 20.9 10, -13.255, 1.14 11*, -11.047, 1.50, 1.53110, 55.9 12*, -14.897, 0.40 13, 361.960, 6.85, 2.00100, 29.1 14, -36.352, 11.50 Image plane: ∞ Aspherical data The 7th surface K = 0.00000e+000 A 4=-3.89614e-004 A 6= 4.14518e-006 A 8=-1.47444e-008 A10=-2.48975e-009 A12= 9.04155e-011 A14=-6.59935e-013 The 8th surface K = 0.00000e+000 A 4=-4.54696e-004 A 6= 3.57521e-006 A 8=-5.74335e-008 A10=-7.97906e-010 A12= 2.90616e-011 A14=-8.70907e-014 The 11th surface K = 0.00000e+000 A 4= 9.93948e-005 A 6= 1.56916e-006 A 8=-6.45991e-008 A10= 8.11199e-010 A12=-6.87945e-012 A14= 3.43386e-014 The 12th surface K = 0.00000e+000 A 4= 1.24290e-004 A 6= 1.34138e-006 A 8=-3.73663e-008 A10= 3.75035e-010 A12=-1.67485e-012 A14= 2.94387e-015 Focal length 35.49 F number 2.80 Half field angle (°) 31.36 Image height 21.64 Overall lens length 42.50 BF 11.50 [Numerical Example 6] Unit: mm Surface data Surface number r d nd νd 1 12.175 2.99 1.69680 55.5 2 32.507 3.78 3 (Diaphragm) ∞ 2.49 4 -103.585 1.10 1.69895 30.1 5 9.895 2.58 1.83481 42.7 6 -73.085 0.40 7* -60.538 1.10 1.53110 55.9 8* -202.964 1.77 9 -10.427 4.51 1.92286 20.9 10 -17.032 1.74 11* -13.129 1.50 1.53110 55.9 12* -26.262 0.40 13 58.652 7.61 2.00100 29.1 14 -202.025 9.00 Image plane ∞ Aspherical data The 7th surface K = 0.00000e+000 A 4=-4.27512e-005 A 6= 4.52994e-006 A 8= 1.98759e-007 A10=-1.52654e-008 A12= 6.70645e-010 A14=-9.38008e-012 The 8th surface K = 0.00000e+000 A 4=-8.84659e-005 A 6= 4.96683e-006 A 8= 1.40348e-007 A10=-6.35911e-009 A12= 2.67567e-010 A14=-2.00325e-012 The 11th surface K = 0.00000e+000 A 4=-4.97904e-004 A 6= 9.86601e-007 A 8= 3.57478e-008 A10=-1.42763e-009 A12= 1.32323e-011 A14= 5.54661e-014 Page 12 K = 0.00000e+000 A 4=-3.28690e-004 A 6= 3.26388e-006 A 8=-1.52971e-008 A10=-6.47841e-011 A12= 2.19990e-012 A14=-1.23384e-014 Focal length 34.88 F-number 2.80 Half angle of view (°) 21.39 Image height 13.66 Overall lens length 40.98 BF 9.00 [Numerical Example 7] Unit: mm Surface data Surface number r d nd νd 1 12.516 2.45 2.00100 29.1 2 29.514 2.57 3 (Aperture) ∞ 2.21 4 56.644 1.10 1.96300 24.1 5 5.927 4.00 1.72916 54.7 6 -62.601 0.40 7* -43.848 1.10 1.53110 55.9 8* 64.119 3.18 9 -7.672 4.45 1.94594 18.0 10 -10.932 0.40 11* -26.173 1.50 1.53110 55.9 12* -52.347 0.40 13 61.126 4.12 2.00069 25.5 14 -61.126 13.10 Image plane ∞ Aspherical surface data The 7th surface K = 0.00000e+000 A 4= 6.20693e-005 A 6= 8.19347e-006 A 8=-6.06272e-007 A10= 4.15714e-008 A12=-1.38766e-009 A14= 1.89686e-011 The 8th surface K = 0.00000e+000 A 4= 3.04001e-005 A 6= 5.79722e-006 A 8=-3.32536e-007 A10= 1.87865e-008 A12=-4.96337e-010 A14= 4.81005e-012 The 11th surface K = 0.00000e+000 A 4=-3.01320e-004 A 6=-1.39174e-007 A 8= 3.50464e-008 A10=-1.06628e-009 A12= 1.12362e-011 A14=-3.69959e-014 The 12th surface K = 0.00000e+000 A 4=-2.47472e-004 A 6= 7.98220e-007 A 8= 4.54547e-009 A10=-2.59575e-010 A12= 2.66091e-012 A14=-9.42725e-015 Focal length 34.76 F number 2.80 Half field angle (°) 21.45 Image height 13.66 Overall lens length 40.98 BF 13.10 [Numerical Example 8] Unit: mm Surface data Surface number r d nd νd 1 13.766 2.79 1.69680 55.5 2 34.764 2.64 3 (Diaphragm) ∞ 3.78 4 -32.448 1.10 1.69895 30.1 5 10.903 5.49 1.83481 42.7 6 -21.399 0.72 7* -27.309 1.10 1.53110 55.9 8* -148.417 3.87 9 -8.780 1.70 1.73800 32.3 10 -23.659 1.10 11* -76.516 2.01 1.53110 55.9 12* -80.440 0.40 13 359.385 7.79 2.00100 29.1 14 -38.414 10.00 Image plane ∞ Aspherical data The 7th surface K = 0.00000e+000 A 4=-5.60903e-004 A 6= 9.60410e-006 A 8=-1.15871e-007 A10= 2.61583e-010 A12= 2.85854e-011 A14=-2.47992e-013 The 8th surface K = 0.00000e+000 A 4=-6.11260e-004 A 6= 9.86206e-006 A 8=-1.58943e-007 A10= 1.94628e-009 A12=-1.12356e-011 A14= 7.12536e-014 The 11th surface K = 0.00000e+000 A 4=-1.04540e-004 A 6=-1.85115e-006 A 8= 2.32791e-008 A10=-2.00953e-010 A12= 5.29048e-013 A14= 1.26639e-015 Page 12 K = 0.00000e+000 A4=-1.81722e-005 A6=-1.26945e-006 A8= 1.37153e-008 A10=-9.20735e-011 A12= 3.55152e-013 A14=-5.45787e-016 Focal length 37.37 F-number 2.80 Half field angle (°) 30.07 Image height 21.64 Overall lens length 44.50 BF 10.00 [Numerical Example 9] Unit: mm Surface data Surface number r d nd νd 1 16.840 3.53 1.69680 55.5 2 44.066 2.91 3 (Aperture) ∞ 5.61 4 -37.515 1.17 1.69895 30.1 5 15.004 8.83 1.83481 42.7 6 -22.795 1.05 7* -39.594 1.22 1.53110 55.9 8* 118.252 3.23 9 -10.937 1.10 1.92286 20.9 10 -16.525 0.84 11* -50.759 2.84 1.53110 55.9 12* -99.100 0.40 13 -39.836 5.96 1.95278 18.6 14 -26.557 14.80 Image plane ∞ Aspherical data The 7th surface K = 0.00000e+000 A 4=-6.04132e-004 A 6= 8.13921e-006 A 8=-8.37679e-008 A10= 2.77490e-010 A12= 7.03383e-012 A14=-5.45325e-014 The 8th side K = 0.00000e+000 A 4=-6.72264e-004 A 6= 7.83183e-006 A 8=-9.25804e-008 A10= 5.36563e-010 A12= 1.76231e-012 A14=-1.86736e-014 The 11th side K = 0.00000e+000 A 4=-1.88796e-004 A 6=-2.28010e-006 A 8= 3.22885e-008 A10=-3.71707e-010 A12= 2.29235e-012 A14=-4.11221e-015 The 12th side K = 0.00000e+000 A 4=-8.75801e-005 A 6=-8.46350e-007 A 8= 1.18038e-008 A10=-7.36711e-011 A12= 2.66163e-013 A14=-4.09408e-016 Focal length 46.55 F number 2.80 Half field angle (°) 24.93 Image height 21.64 Overall lens length 53.50 BF 14.80 The various values in each numerical example are summarized in Table 1 below.

[0064]

Table 1

[0065] Imaging device Next, an embodiment of a digital still camera (imaging device) 10 using the optical system L0 of each embodiment as an imaging optical system will be described with reference to FIG. 19. In FIG. 19, reference numeral 13 denotes a camera body, and reference numeral 11 denotes a photographing optical system constituted by any one of the optical systems L0 described in Embodiments 1 to 9. Reference numeral 12 denotes a solid-state imaging device (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built in the camera body 13 and receives and photoelectrically converts the optical image formed by the photographing optical system 11. The camera body 13 may be a so-called single-lens reflex camera having a quick-return mirror or a so-called mirrorless camera not having a quick-return mirror.

[0066] By applying the optical system L0 of each embodiment to an imaging device such as a digital still camera in this way, an imaging device with a small lens can be obtained.

[0067] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to these embodiments, and various combinations, modifications, and changes are possible within the scope of the gist thereof.

Description of reference numerals

[0068] L1 First lens L2 Second lens

Claims

1. An optical system including, in order from the object side, a first lens with a positive refractive power, a second lens with a negative refractive power, and four or five lenses, wherein the optical system includes a lens with a positive refractive power disposed on the most object side, when the average refractive index of the materials of all positive lenses included in the optical system at the d-line is PNdaverage, the paraxial curvature radius on the object side of the first lens is R11, the paraxial curvature radius on the image side of the first lens is R12, the paraxial curvature radius on the object side of the second lens is R21, the paraxial curvature radius on the image side of the second lens is R22, the focal length of the first lens is f1, the focal length of the optical system is f, the back focus is the distance on the optical axis from the aperture stop with the air-equivalent length to the image plane is SPIP, and the distance on the optical axis from the lens surface on the object side of the lens disposed on the most object side with the air-equivalent length of the back focus to the image plane is TTL, 1.70 < PNdaverage < 2.10 -100 < (R11 + R12) / (R12 - R11) < 0.60 2.90 < (R21 + R22) / (R22 - R21) < 100 0.80 < f1 / f < 8.00 0.80 < SPIP / TTL < 0.95 An optical system characterized by satisfying the following conditional expressions.

2. when the focal length of the lens with a positive refractive power disposed on the most object side is fp and the focal length of the optical system is f, 0.55 < fp / f < 2.00 The optical system according to claim 1, characterized by satisfying the following conditional expression.

3. when the focal length of the first lens is f1 and the focal length of the optical system is f, 0.80 < f1 / f < 8.00 The optical system according to claim 1 or 2, characterized by satisfying the following conditional expression.

4. The optical system according to any one of claims 1 to 3, further comprising a diaphragm disposed adjacent to the image side of the lens disposed closest to the object side.

5. When the distance on the optical axis from the lens surface on the object side of the lens disposed closest to the object side with the back focus as the air equivalent length to the image surface is TTL, the focal length of the optical system is f, and the imaging semi-angle (°) is ω, 1.40 < TTL / (f × tan ω) < 3.20 The optical system according to any one of claims 1 to 4, characterized in that it satisfies the conditional expression.

6. When the refractive index of the second lens at the d-line is Nd2 and the Abbe number of the second lens at the d-line is νd2, Nd2 < 4.19450 / νd2 + 1.52010 The optical system according to any one of claims 1 to 5, characterized in that it satisfies the conditional expression.

7. The optical system has three or more lenses with positive refractive power and two or more lenses with negative refractive power, The optical system according to any one of claims 1 to 6, characterized in that the total number of lenses included in the optical system is eight or less.

8. The optical system according to any one of claims 1 to 7, characterized in that it includes an aspherical lens made of a resin material disposed on the image side of the diaphragm.

9. The optical system according to any one of claims 1 to 8, characterized in that it is composed of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the diaphragm, and the sixth lens arranged in order from the image side to the object side.

10. The optical system according to any one of claims 1 to 9, characterized in that it is composed of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the diaphragm, and the seventh lens arranged in order from the image side to the object side.

11. An imaging device comprising: an optical system according to any one of claims 1 to 10; and an imaging element that receives an image formed by the optical system.

Images