Optical system and imaging apparatus having the same

Abstract

To provide an optical system that is compact and has high optical performance, and an imaging apparatus having the same.SOLUTION: An optical system L0 is composed of a front group La, an aperture stop SP, and a rear group Lb having a positive refractive power as a whole, which are arranged in order from an object side to an image side. The rear group includes a final lens Lp arranged on the most image side and having a positive refractive power. The distance TTL from a lens surface on the object side of a lens arranged on the most object side in the optical system to an image surface, the diameter Φi of an image circle, the average value PNdave of refractive indices for the d-lines of all the positive lenses included in the optical system, the effective diameter Φp on a lens surface on the image side of the final lens, and the air conversion length sk of the distance on the optical axis from the lens surface on the image side of the final lens to the image surface, satisfy predetermined conditional expressions.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] 2. Description of the Related Art In recent years, as imaging elements become smaller and have more pixels, optical systems used in imaging devices are required to be small and have high optical performance.

[0003] Patent Document 1 describes an optical system consisting of a first lens with positive refractive power, a second lens with negative refractive power, a third lens, a fourth lens, a fifth lens, and a sixth lens, arranged in this order from the object side to the image side. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-115174 A Summary of the Invention [Problem to be solved by the invention]

[0005] The optical system described in Patent Document 1 employs a telephoto power arrangement to reduce the overall length, and uses multiple aspherical lenses to correct distortion and curvature of field. However, in the optical system described in Patent Document 1, the Petzval sum of the entire system is large and the angle of incidence of the off-axis light beam is also large, so that when attempting to apply the optical system to an imaging device with a large image sensor, the correction of curvature of field and reduction in peripheral light amount become issues.

[0006] In order to realize an optical system that is compact and has high optical performance, it is important to place a large-diameter lens having positive refractive power closest to the image side and to appropriately set the refractive index and power arrangement of each lens.

[0007] The present invention provides an optical system which is small in size and has high optical performance, and an imaging device having the same. [Means for solving the problem]

[0008] An optical system according to one aspect of the present invention is an optical system comprising, in order from the object side to the image side, a front group, an aperture stop, and a rear group having positive refractive power overall, the rear group including a final lens having positive refractive power and arranged closest to the image side, wherein TTL denotes the distance on the optical axis from the object side lens surface of the lens arranged closest to the object side in the optical system to the image plane, Φi denotes the diameter of the image circle, PNdave denotes the average value of the refractive indexes at the d-line of all positive lenses included in the optical system, Φp denotes the effective diameter of the image side lens surface of the final lens, and sk denotes the air-equivalent length of the distance on the optical axis from the image side lens surface of the final lens to the image plane, 0.5 <TTL / Φi<1.4 1.64 <PNdave<2.00 2.0<Φp / sk<4.0 The present invention is characterized in that the following condition is satisfied: Other objects and features of the present invention will be described in the following embodiments. Effect of the Invention

[0009] According to the present invention, it is possible to provide an optical system that is small in size and has high optical performance, and an imaging device having the same. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of the first embodiment. [Diagram 2] 4A to 4C are aberration diagrams of Example 1 when focusing on an object at infinity. [Diagram 3] FIG. 11 is a cross-sectional view of an optical system according to a second embodiment. [Figure 4] 11A to 11C are aberration diagrams of Example 2 when focusing on an object at infinity. [Diagram 5] FIG. 11 is a cross-sectional view of an optical system according to a third embodiment. [Figure 6] 13A to 13C are aberration diagrams of Example 3 when focusing on an object at infinity. [Figure 7] FIG. 11 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 8] 13A to 13C are aberration diagrams of Example 4 when focusing on an object at infinity. [Figure 9] FIG. 11 is a cross-sectional view of an optical system according to a fifth embodiment. [Figure 10] 13A to 13C are aberration diagrams of Example 5 when focusing on an object at infinity. [Figure 11] FIG. 13 is a cross-sectional view of the optical system of Example 6. [Figure 12] 13A to 13C are aberration diagrams of Example 6 when focusing on an object at infinity. [Figure 13] FIG. 13 is a cross-sectional view of the optical system of Example 7. [Figure 14] 13A to 13C are aberration diagrams of Example 7 when focusing on an object at infinity. [Figure 15] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an optical system and an image pickup apparatus having the same according to the present invention will be described with reference to the accompanying drawings.

[0012] 1, 3, 5, 7, 9, 11, and 13 are cross-sectional views of the optical system L0 of Examples 1 to 7 when focused at infinity. The optical system L0 of each Example is an optical system used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide cameras, and surveillance cameras.

[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 in each embodiment is configured to include a plurality of lenses.

[0014] In each lens cross-sectional view, La denotes a front group, Lb denotes a rear group, and Lp denotes a lens (final lens) with positive refractive power that is arranged closest to the image side among the lenses included in the rear group Lb.

[0015] Also, SP is an aperture stop. IP is an image plane (paraxial), and when the optical system L0 of each embodiment is used as the photographing optical system of a digital still camera or digital video camera, the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is disposed thereon. When the optical system L0 of each embodiment is used as the photographing optical system of a silver halide film camera, a photosensitive surface equivalent to the film surface is disposed on the image plane IP. In this specification, the "front group La" and the "rear group Lb" may be composed of multiple lenses or may be composed of a single lens.

[0016] 2, 4, 6, 8, 10, 12, and 14 are aberration diagrams of the optical systems L0 of Examples 1 to 7 when focused on an object at infinity, respectively.

[0017] In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.56 nm) and g-line (wavelength 435.84 nm). In the astigmatism diagram, dS shows the amount of astigmatism on the sagittal image plane, and dM shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the lateral chromatic aberration diagram, the amount of lateral chromatic aberration for the g-line is shown. ω is the imaging half angle of view (°).

[0018] Next, the characteristic configuration of the optical system L0 in each embodiment will be described.

[0019] The optical system L0 in each embodiment is an optical system that is arranged in order from the object side to the image side, and is composed of a front group La, an aperture stop SP, and a rear group Lb having positive refractive power as a whole. The rear group Lb includes a final lens Lp having positive refractive power and arranged closest to the image side.

[0020] Generally, when a lens is located near the image surface IP, the height of the off-axis light beam incident on the lens increases, and the power to refract the off-axis light beam becomes stronger. In the optical system L0 of each embodiment, the rear group Lb is provided with positive refractive power, and further, a final lens Lp, which is a large-diameter lens with positive refractive power, is located closest to the image side of the rear group Lb, thereby refracting the off-axis light beam appropriately, correcting pincushion distortion and suppressing the angle of incidence of the off-axis light beam on the image surface.

[0021] Furthermore, the optical system L0 of each embodiment satisfies the following conditional expression (1).

[0022] 0.5 <TTL / Φi<1.4 ···(1) Here, TTL is the distance on the optical axis from the object side lens surface of the lens arranged closest to the object in the optical system L0 to the image surface IP (total lens length). In other words, it is the length on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the optical system L0 plus the back focus. Φi is the diameter of the image circle.

[0023] Conditional formula (1) specifies the ratio of the total lens length to the diameter of the image circle. If the upper limit of conditional formula (1) is exceeded, the total lens length will become too long. If the lower limit of conditional formula (1) is exceeded and the diameter of the image circle becomes too large, it will become difficult to simultaneously correct both the curvature of field and the distortion.

[0024] In this specification, the image circle is a circle whose radius is the height from the optical axis of the light beam that reaches the position farthest from the optical axis among the light beams that reach the image plane IP when focusing at infinity. The diameter of the image circle is equivalent to twice the image height of the optical system L0. If the ratio of the image plane illuminance of the off-axis light beam to the on-axis light beam is less than 20%, the off-axis light beam may be considered not to reach the image plane IP. In addition, when the focal length of the optical system L0 is f and the half angle of view (°) is ω, the diameter Φi of the image circle may be expressed as Φi=2×f×tanω.

[0025] When the optical system L0 is a zoom lens, TTL is the distance from the object-side lens surface of the lens placed closest to the object at the wide-angle end to the image plane IP, and Φi is the diameter of the image circle at the wide-angle end.

[0026] Furthermore, the optical system L0 of each embodiment satisfies the following conditional expression (2).

[0027] 1.64 <PNdave<2.00 ···(2) Here, PNdave is the average value (average refractive index) of the refractive indices at the d-line (wavelength 587.56 nm) of all the positive lenses included in the optical system L0.

[0028] Conditional expression (2) specifies the average refractive index of all positive lenses included in optical system L0. If the refractive index is higher than the upper limit of conditional expression (2), the color dispersion increases, making it difficult to correct axial chromatic aberration. If the refractive index is lower than the lower limit of conditional expression (2), the Petzval sum of the entire optical system L0 increases, making it difficult to correct field curvature.

[0029] Furthermore, the optical system L0 of each embodiment satisfies the following conditional expression (3).

[0030] 2.0<Φp / sk<4.0 (3) Here, Φp is the effective diameter of the image-side lens surface of the final lens Lp, and sk is the air-equivalent distance (back focus) on the optical axis from the image-side lens surface of the final lens Lp to the image plane IP.

[0031] Conditional formula (3) specifies the ratio of the effective diameter and the back focus of the lens surface of the final lens Lp on the image side. If the effective diameter of the final lens Lp is large enough to exceed the upper limit of conditional formula (3), the optical system L0 becomes large in the radial direction. If the effective diameter of the final lens Lp is small enough to fall below the lower limit of conditional formula (3), the incidence height of the off-axis light beam incident on the final lens Lp becomes low, and the refraction effect on the off-axis light beam becomes small. This makes it difficult to correct pincushion distortion and suppress the image plane incidence angle.

[0032] In this specification, the effective diameter of a lens is the diameter of a circle whose radius is the height from the optical axis of the light ray passing through the position farthest from the optical axis among the light rays passing through the lens surface. The effective diameter may also be a diameter defined by a circle inscribed in a mechanical member such as a pressing ring or a rivet on the lens surface, or a diameter defined by a circle connecting the outermost periphery of a surface generally formed by polishing or molding when no mechanical member is arranged. In addition, when the optical system L0 is a zoom lens, sk is the back focus of the zoom lens at the wide-angle end, and Φp is the effective diameter of the lens surface on the image side of the final lens Lp at the wide-angle end.

[0033] It is also preferable that the numerical ranges of the conditional expressions (1) to (3) are set to the numerical ranges of the following conditional expressions (1a) to (3a).

[0034] 0.9 <TTL / Φi<1.38 ···(1a) 1.64 <PNdave<1.85 ···(2a) 2.2<Φp / sk<3.5 (3a) It is further preferable that the numerical ranges of the conditional expressions (1) to (3) be the numerical ranges of the following conditional expressions (1b) to (3b).

[0035] 0.95 <TTL / Φi<1.37 ···(1b) 1.641 <PNdave<1.792 ···(2b) 2.4<Φp / sk<3.2 (3b) Next, conditions and configurations that the optical system L0 of each embodiment should preferably satisfy are described. The optical system L0 of each embodiment should preferably satisfy one or more of the following conditional expressions (4) to (14) and configurations.

[0036] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (4), where the focal length of the front group La is fa and the focal length of the optical system L0 is f.

[0037] 0.1 <f / |fa|<1.5 ···(4) Conditional formula (4) prescribes the ratio of the focal length of the front group La to the focal length of the optical system L0. If the upper limit of conditional formula (4) is exceeded and the refractive power of the front group La becomes strong, pincushion distortion becomes large, making it difficult to achieve both field curvature and distortion, which is undesirable. If the lower limit of conditional formula (4) is exceeded and the refractive power of the front group La becomes weak, the optical system becomes closer to a telecentric optical system on the image side, the position of the exit pupil becomes farther from the image plane IP, and the overall lens length becomes longer, which is undesirable. Note that when optical system L0 is a zoom lens, f is the focal length of the zoom lens at the wide-angle end.

[0038] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (5), where fp is the focal length of the final lens Lp.

[0039] 0.6 <fp / f<6.0 ···(5) Conditional formula (5) specifies the ratio of the focal length of the final lens Lp to the focal length of the optical system L0. If the upper limit of conditional formula (5) is exceeded and the refractive power of the final lens Lp becomes weak, it is undesirable because it becomes difficult to correct pincushion distortion and to suppress the image plane incidence angle. If the lower limit of conditional formula (5) is exceeded and the refractive power of the final lens Lp becomes strong, it is undesirable because the optical system approaches a telecentric optical system on the image side and the overall lens length becomes long.

[0040] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (6).

[0041] 0.1 <sk / f<0.7 ···(6) Conditional formula (6) defines the ratio of the back focus to the focal length of the optical system L0. If the back focus is longer than the upper limit of conditional formula (6), the total lens length will be longer, which is not preferable. If the back focus is shorter than the lower limit of conditional formula (6), the effective diameter of the final lens Lp located on the image side will be larger, which is not preferable, as the optical system L0 will be larger in the radial direction.

[0042] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (7), where SPIP is the distance on the optical axis from the aperture stop SP to the image plane IP.

[0043] 0.6 <SPIP / TTL<1.0 ···(7) Conditional formula (7) specifies the ratio between the position of the aperture stop SP and the total lens length of the optical system L0. If the position of the aperture stop SP is on the object side and exceeds the upper limit of conditional formula (7), biased vignetting is likely to occur, and the shape of the blur becomes irregular, which is not preferable. If the position of the aperture stop SP is on the image side and falls below the lower limit of conditional formula (7), the exit pupil approaches the image plane IP, which makes it difficult to suppress the angle of incidence of the off-axis light beam on the image plane, which is not preferable. Note that when the optical system L0 is a zoom lens, SPIP is the distance from the aperture stop SP of the zoom lens to the image plane IP at the wide-angle end.

[0044] In the optical system L0 of each embodiment, it is preferable that the rear group Lb includes at least four lenses, which corrects axial chromatic aberration and lateral chromatic aberration.

[0045] In the optical system L0 of each embodiment, in order to correct lateral chromatic aberration and field curvature, it is preferable that the rear group Lb includes a negative lens Ln (first negative lens) arranged on the object side of the final lens Lp.

[0046] In the optical system L0 of each embodiment, when the paraxial radius of curvature of the object-side lens surface of the negative lens Ln is R1 and the paraxial radius of curvature of the image-side lens surface of the negative lens Ln is R2, it is preferable that the optical system L0 satisfies the following conditional formula (8).

[0047] 0.0<(R1+R2) / (R2-R1)<50.0 (8) Conditional formula (8) defines the shape of the negative lens Ln. If the upper limit of conditional formula (8) is exceeded and the values ​​of R1 and R2 become closer to each other, the refractive power of the negative lens Ln becomes weak, which is undesirable because the correction of lateral chromatic aberration becomes insufficient. If the lower limit of conditional formula (8) is exceeded, the radius of curvature of the lens surface on the image side of the negative lens Ln becomes small, which is undesirable because it becomes difficult to simultaneously correct the curvature of field and the distortion.

[0048] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (9), where the refractive index of the negative lens Ln at the d-line is Ndn and the Abbe number of the negative lens Ln at the d-line is νdn.

[0049] 1.500 <Ndn<4.1945 / νdn+1.520 ···(9) Conditional formula (9) specifies the refractive index of the negative lens Ln. If the refractive index of the negative lens Ln is higher than the upper limit of conditional formula (9), the Petzval sum of the entire optical system L0 becomes large, which is undesirable as it makes it difficult to correct the curvature of field. If the refractive index of the negative lens Ln is lower than the lower limit of conditional formula (9), it becomes impossible to select a material with large dispersion, which is undesirable as it results in insufficient correction of lateral chromatic aberration.

[0050] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (10), where the focal length of the rear group Lb is fb.

[0051] 0.10 <fb / |fa|<10.00 ···(10) Conditional formula (10) prescribes the ratio of the focal length of the front group La to the focal length of the rear group Lb. If the upper limit of conditional formula (10) is exceeded and the positive refractive power of the rear group Lb becomes weak, it becomes difficult to correct pincushion distortion and suppress the image plane incidence angle, which is undesirable. If the lower limit of conditional formula (10) is exceeded and the refractive power of the rear group Lb becomes strong, it becomes close to a telecentric optical system on the image side, and the overall lens length becomes long, which is undesirable.

[0052] In the optical system L0 of each embodiment, the front group La includes a positive lens Lap (first positive lens), and when the refractive index of the positive lens Lap at the d-line is Ndap, it is preferable that the following conditional expression (11) is satisfied.

[0053] 1.60 <Ndap<2.00 ···(11) Conditional expression (11) specifies the refractive index of the positive lens Lap. If the refractive index of the positive lens Lap is higher than the upper limit of conditional expression (11), the color dispersion increases, making it difficult to correct axial chromatic aberration, which is not preferable. If the refractive index of the positive lens Lap is lower than the lower limit of conditional expression (11), the Petzval sum of the entire optical system L0 increases, making it difficult to correct field curvature, which is not preferable.

[0054] In the optical system L0 of each embodiment, the rear group Lb includes a positive lens Lbp (second positive lens), and when the refractive index of the positive lens Lbp at the d-line is Ndbp, it is preferable that the following conditional expression (12) is satisfied.

[0055] 1.60 <Ndbp<2.00 ···(12) Conditional expression (12) specifies the refractive index of the positive lens Lbp. If the refractive index of the positive lens Lbp is higher than the upper limit of conditional expression (12), the color dispersion increases, making it difficult to correct axial chromatic aberration, which is not preferable. If the refractive index of the positive lens Lbp is lower than the lower limit of conditional expression (12), the Petzval sum of the entire optical system L0 increases, making it difficult to correct field curvature, which is not preferable.

[0056] In the optical system L0 of each embodiment, the rear group Lb includes a negative lens Lbn (second negative lens), and when the refractive index at the d-line of the negative lens Lbn is Ndbn, it is preferable that the following conditional expression (13) is satisfied.

[0057] 0.00 <Ndbp-Ndbn<0.40 ···(13) Conditional expression (13) specifies the refractive index difference between the positive lens Lbp and the negative lens Lbn. If a material with a large refractive index difference is selected that exceeds the upper limit of conditional expression (13), achromatization becomes difficult and correction of axial chromatic aberration becomes insufficient, which is not preferable. If a material with a small refractive index difference is selected that falls below the lower limit of conditional expression (13), the Petzval sum of the entire optical system L0 becomes large, which makes correction of field curvature difficult, which is not preferable.

[0058] In the optical system L0 of each embodiment, when the largest effective diameter of the lens having the largest effective diameter in the front group La is Φa, it is preferable that the following conditional expression (14) be satisfied:

[0059] 1.0<Φp / Φa<4.0 (14) Conditional formula (14) prescribes the ratio of the effective diameter of the front group La to the effective diameter of the final lens Lp arranged closest to the image side. If the effective diameter of the final lens Lp is greater than the upper limit of conditional formula (14), the optical system L0 becomes large in the radial direction, which is undesirable. If the effective diameter of the final lens Lp is smaller than the lower limit of conditional formula (14), it becomes difficult to correct pincushion distortion and suppress the image plane incidence angle, which is undesirable.

[0060] The optical system L0 in each embodiment is preferably composed of five to eight lenses in order to achieve both high optical performance and compactness.

[0061] It is more preferable that the numerical ranges of the conditional expressions (4) to (14) be within the ranges of the following conditional expressions (4a) to (14a).

[0062] 0.15 <f / |fa|<1.40 ···(4a) 0.7 <fp / f<5.0 ···(5a) 0.2 <sk / f<0.6 ···(6a) 0.70 <SPIP / TTL<0.95 ···(7a) 0.5<(R1+R2) / (R2-R1)<25.0 (8a) 1.510 <Ndn<4.1945 / νdn+1.500 ···(9a) 0.15 <fb / |fa|<8.50 ···(10a) 1.61 <Ndap<1.95 ···(11a) 1.70 <Ndbp<1.95 ···(12a) 0.00 <Ndbp-Ndbn<0.30 ···(13a) 1.2<Φp / Φa<3.0 (14a) It is more preferable that the numerical ranges of the conditional expressions (4) to (14) be within the ranges of the following conditional expressions (4b) to (9b).

[0063] 0.19 <f / |fa|<1.30 ···(4b) 0.9 <fp / f<4.2 ···(5b) 0.3 <sk / f<0.5 ···(6b) 0.76 <SPIP / TTL<0.91 ···(7b) 1.0<(R1+R2) / (R2-R1)<13.0 (8b) 1.520 <Ndn<4.1945 / νdn+1.470 ···(9b) 0.19 <fb / |fa|<7.50 ···(10b) 1.615 <Ndap<1.920 ···(11b) 1.75 <Ndbp<1.91 ···(12b) 0.015 <Ndbp-Ndbn<0.262 ···(13b) 1.5<Φp / Φa<2.7 (14b) In the optical system L0 of each embodiment, an optical member such as a cover glass or an IR cut filter may be disposed between the final lens Lp and the image surface IP. The refractive power of a lens refers to the refractive power in the vicinity of the optical axis (paraxial).

[0064] Next, the optical system L0 of each embodiment will be described in detail.

[0065] The optical system L0 of the first embodiment is composed of, in order from the object side to the image side, a front group La, an aperture stop SP, and a rear group Lb having a positive refractive power overall. The front group La is composed of one positive lens. The rear group Lb is composed of, in order from the object side to the image side, a cemented lens of a positive lens and a negative lens, a negative lens, a positive lens, and a positive lens.

[0066] The optical system L0 of the second embodiment is composed of a front group La, an aperture stop SP, and a rear group Lb having a positive refractive power overall, arranged in that order from the object side to the image side. The front group La is composed of a positive lens and a negative lens, arranged in that order from the object side to the image side. The rear group Lb is composed of a cemented lens of a negative lens and a positive lens, a negative lens, a negative lens, and a positive lens, arranged in that order from the object side to the image side.

[0067] The optical system L0 of the third embodiment is composed of, in order from the object side to the image side, a front group La, an aperture stop SP, and a rear group Lb having a positive refractive power overall. The front group La is composed of one positive lens. The rear group Lb is composed of, in order from the object side to the image side, a cemented lens of a negative lens and a positive lens, a negative lens, a negative lens, and a positive lens.

[0068] The optical system L0 of the fourth embodiment is composed of, in order from the object side to the image side, a front group La, an aperture stop SP, and a rear group Lb having a positive refractive power overall. The front group La is composed of one positive lens. The rear group Lb is composed of, in order from the object side to the image side, a cemented lens of a negative lens and a positive lens, a negative lens, a negative lens, a negative lens, and a positive lens.

[0069] The optical system L0 of the fifth embodiment is composed of a front group La, an aperture stop SP, and a rear group Lb having a positive refractive power overall, arranged in that order from the object side to the image side. The front group La is composed of a negative lens and a positive lens, arranged in that order from the object side to the image side. The rear group Lb is composed of a cemented lens of a positive lens and a negative lens, a negative lens, a positive lens, and a positive lens, arranged in that order from the object side to the image side.

[0070] The optical system L0 of the sixth embodiment is composed of a front group La, an aperture stop SP, and a rear group Lb having a positive refractive power overall, arranged in that order from the object side to the image side. The front group La is composed of a cemented lens of a negative lens and a positive lens, arranged in that order from the object side to the image side. The rear group Lb is composed of a cemented lens of a positive lens and a negative lens, a negative lens, a positive lens, and a positive lens, arranged in that order from the object side to the image side.

[0071] The optical system L0 of the seventh embodiment is composed of a front group La, an aperture stop SP, and a rear group Lb having a positive refractive power overall, arranged in that order from the object side to the image side. The front group La is composed of a negative lens and a positive lens, arranged in that order from the object side to the image side. The rear group Lb is composed of a positive lens, a cemented lens of a positive lens and a negative lens, a negative lens, a positive lens, and a positive lens, arranged in that order from the object side to the image side.

[0072] Numerical Examples 1 to 7 corresponding to Examples 1 to 7, respectively, are shown below.

[0073] 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 mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. In addition, nd represents the refractive index of each optical member with respect to the d-line, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material is expressed as νd=(Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the d-line (587.56 nm), F-line (486.13 nm), and C-line (656.27 nm) of the Fraunhofer lines.

[0074] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system of each example is focused on an object at infinity. "Back focus" is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image surface expressed as an air-equivalent length. "Total lens length" is the distance on the optical axis from the foreground (the lens surface closest to the object) of the optical system to the final surface plus the back focus.

[0075] If the optical surface is aspheric, a * symbol is added to the right of the surface number. The aspheric shape is expressed as follows, where X is the displacement from the apex of the surface in the optical axis direction, H is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, K is the conic constant, and A3 to A15 are the aspheric coefficients of each order:

[0076]

number

[0077] In addition, "e±XX" in each aspheric coefficient is "×10± XX " It means.

[0078] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 6.260 0.86 1.72916 54.7 4.80 2 10.445 0.67 4.58 3 (Aperture) ∞ 0.90 4.47 4 6.769 1.21 1.90043 37.4 4.14 5 -17.277 0.50 1.74077 27.8 3.80 6 5.222 1.38 3.35 7* -17.501 0.71 1.63560 23.9 4.36 8* -102.984 1.65 5.27 9* -6.645 1.30 1.63560 23.9 7.43 10* -6.698 0.36 8.53 11* 5.559 1.95 1.53500 56.0 12.13 12* 7.159 (variable) 12.62 Image plane ∞ Aspheric Data Side 7 K = 0.00000e+00 A 4=-1.07563e-02 A 6=-1.05029e-02 A 8=-6.35129e-04 A 3= 4.83637e-03 A 5= 1.12736e-02 A 7= 4.29894e-03 Side 8 K = 0.00000e+00 A 4= 7.30840e-03 A 6=-4.56636e-04 A 8=-9.60399e-05 A 3=-2.56213e-03 A 5=-4.86845e-03 A 7= 7.05515e-04 9th page K = 1.46022e+00 A 4= 3.50415e-02 A 6= 2.52119e-04 A 8=-1.67257e-04 A10= 2.35759e-06 A 3=-1.55185e-02 A 5=-1.27191e-02 A 7= 8.24290e-04 Side 10 K =-1.25577e+00 A 4= 1.62098e-02 A 6= 1.87296e-03 A 8= 5.42303e-06 A10=-2.12988e-08 A 3=-3.98973e-03 A 5=-8.68766e-03 A 7=-1.76229e-04 Page 11 K =-1.44696e+01 A 4= 7.50341e-03 A 6= 1.22100e-03 A 8=-8.39694e-05 A10=-4.58570e-07 A 3= 3.44333e-03 A 5=-6.75667e-03 A 7= 1.70998e-04 A 9= 1.04779e-05 Side 12 K =-1.20114e+01 A 4=-8.25372e-03 A 6=-4.77190e-03 A 8=-2.89053e-04 A10=-1.08364e-06 A 3= 2.30350e-03 A 5= 7.76429e-03 A 7= 1.58451e-03 A 9= 2.76387e-05 Various data Focal length 13.82 F-number: 2.88 Half angle of view (°) 29.72 Image height 7.89 Lens length 16.32 BF 4.83 d12 4.83 Single lens data Lens starting surface focal length 1 1 19.72 2 4 5.53 3 5 -5.36 4 7 -33.28 5 9 154.89 6 11 32.60 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 8.535 1.78 1.72916 54.7 8.35 2 54.576 1.59 7.97 3 1116.973 0.50 1.76182 26.5 6.96 4 15.804 1.18 6.63 5(Aperture) ∞ 1.00 6.34 6 -16.891 0.50 1.63980 34.5 6.09 7 5.764 2.04 1.90043 37.4 5.98 8 -19.006 0.33 6.27 9* 9.018 0.55 1.61550 25.8 6.74 10* 6.674 2.94 7.04 11* -4.712 1.80 1.67070 19.3 7.95 12* -6.144 0.16 9.79 13* 8.031 1.93 1.53110 56.0 12.23 14* 10.796 (variable) 13.08 Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-1.84389e-03 A 6=-1.16302e-04 A 8= 4.41572e-06 A10= 1.25231e-07 A12=-7.95831e-09 Side 10 K = 0.00000e+00 A 4=-1.02522e-03 A 6=-1.31968e-04 A 8= 8.52375e-06 A10=-9.50218e-08 A12=-2.02084e-09 Page 11 K = 0.00000e+00 A 4= 5.16315e-03 A 6=-3.54315e-04 A 8= 2.68121e-05 A10=-1.19044e-06 A12= 2.36728e-08 Side 12 K = 0.00000e+00 A 4= 1.70854e-03 A 6=-8.20838e-05 A 8= 4.87853e-06 A10=-1.77527e-07 A12= 2.49283e-09 Page 13 K =-9.97557e+00 A 4=-1.35719e-03 A 6= 1.42774e-05 A 8= 8.19110e-07 A10=-4.84714e-08 A12= 9.59127e-10 A14=-6.48919e-12 Side 14 K =-2.08501e+01 A 4=-9.41503e-04 A 6=-1.72682e-05 A 8= 1.41035e-06 A10=-4.48295e-08 A12= 6.50318e-10 A14=-3.78611e-12 Various data Focal length 17.20 F-number 2.06 Half angle of view(°) 24.65 Image height 7.89 Lens length 21.52 BF 5.22 d14 5.22 Single lens data Lens starting surface focal length 1 1 13.65 2 3 -21.05 3 6 -6.66 4 7 5.11 5 9 -45.81 6 11 -60.86 7 13 47.55 [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 4.707 1.13 1.61800 63.4 5.68 2 9.145 1.07 4.97 3 (Aperture) ∞ 0.88 3.73 4 -13.939 0.40 1.60342 38.0 3.47 5 4.094 1.49 1.85150 40.8 3.37 6 -10.702 0.16 3.89 7* -20.317 0.92 1.63560 23.9 4.05 8* 16.176 2.24 4.80 9* -2.684 1.11 1.67070 19.3 5.38 10* -4.213 0.07 7.49 11 144.002 2.21 1.90366 31.3 11.56 12 -15.708 (variable) 12.19 Image plane ∞ Aspheric Data Side 7 K = 0.00000e+00 A 4=-4.18307e-03 A 6= 1.49689e-03 A 8=-8.47348e-04 A10= 2.67501e-04 A12=-3.97751e-05 A14= 2.16051e-06 Side 8 K = 0.00000e+00 A 4=-2.16772e-03 A 6= 5.73321e-04 A 8=-1.35772e-04 A10= 2.41817e-05 A12=-1.37987e-06 A14=-9.50059e-09 9th page K =-4.70448e+00 A 4=-2.76003e-02 A 6= 5.61591e-03 A 8=-1.38408e-03 A10= 2.30576e-04 A12=-2.32076e-05 A14= 9.79590e-07 Side 10 K = 0.00000e+00 A 4= 1.27980e-03 A 6= 5.55638e-05 A 8=-5.37022e-06 A10= 9.26509e-07 A12=-6.95746e-08 A14= 2.53834e-09 Various data Focal length 12.64 F-number: 2.91 Half angle of view (°) 31.97 Image height 7.89 Lens length 15.87 BF 4.19 d12 4.19 Single lens data Lens starting surface focal length 1 1 14.30 2 4 -5.20 3 5 3.65 4 7 -14.03 5 9 -15.58 6 11 15.78 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 4.508 1.10 1.69680 55.5 5.41 2 10.717 1.00 4.80 3 (Aperture) ∞ 1.02 3.90 4 -13.463 0.40 1.69895 30.1 3.43 5 4.776 1.39 1.83481 42.7 3.91 6 -9.237 0.16 4.36 7* -16.299 0.43 1.53110 55.9 4.46 8* -187.887 1.34 4.77 9 -2.854 0.86 1.92286 20.9 4.91 10 -4.834 0.42 6.52 11* -4.029 0.55 1.53110 55.9 6.64 12* -5.433 0.15 8.35 13 132.002 2.50 2.00100 29.1 12.25 14 -13.257 (variable) 12.81 Image plane ∞ Aspheric Data Side 7 K = 0.00000e+00 A 4=-8.03294e-03 A 6= 6.42603e-04 A 8=-1.71864e-05 A10=-2.18210e-05 A12= 5.95829e-06 A14=-3.26994e-07 Side 8 K = 0.00000e+00 A 4=-9.37478e-03 A 6= 5.54245e-04 A 8=-6.69460e-05 A10=-6.99311e-06 A12= 1.91513e-06 A14=-4.31530e-08 Page 11 K = 0.00000e+00 A 4= 2.04929e-03 A 6= 2.43258e-04 A 8=-7.52984e-05 A10= 7.10962e-06 A12=-4.53349e-07 A14= 1.70146e-08 Side 12 K = 0.00000e+00 A 4= 2.56257e-03 A 6= 2.07946e-04 A 8=-4.35551e-05 A10= 3.28693e-06 A12=-1.10371e-07 A14= 1.45867e-09 Various data Focal length 12.94 F-number 2.80 Half angle of view (°) 31.36 Image height 7.89 Lens length 15.50 BF 4.19 d14 4.19 Single lens data Lens starting surface focal length 1 1 10.41 2 4 -5.00 3 5 3.95 4 7 -33.63 5 9 -9.55 6 11 -33.93 7 13 12.14 [Numerical Example 5] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 -11.704 0.29 1.59270 35.3 5.34 2 4.905 0.08 4.65 3 5.130 1.22 1.91082 35.2 4.63 4 -29.778 0.32 4.26 5(Aperture) ∞ 0.92 4.17 6 5.703 1.26 1.87070 40.7 3.92 7 -8.099 0.18 1.76182 26.5 3.61 8 5.381 0.68 3.38 9* -21.874 0.63 1.53500 56.0 3.81 10* -135.199 1.97 4.63 11* -5.817 1.59 1.53500 56.0 8.06 12* -5.050 0.18 8.94 13* 6.415 1.77 1.53500 56.0 11.65 14* 8.812 (variable) 12.22 Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-2.23331e-02 A 6=-1.37107e-02 A 8=-4.99539e-04 A 3= 1.02926e-02 A 5= 2.10970e-02 A 7= 4.33469e-03 Side 10 K = 0.00000e+00 A 4=-1.34981e-02 A 6=-8.17785e-03 A 8=-2.49052e-04 A 3= 1.01369e-02 A 5= 1.34718e-02 A 7= 2.44157e-03 Page 11 K =-3.44235e+01 A 4=-1.31612e-02 A 6=-6.61143e-03 A 8=-1.37858e-04 A10= 6.72689e-07 A 3= 3.65090e-04 A 5= 1.47395e-02 A 7= 1.44729e-03 Side 12 K =-3.08794e+00 A 4=-4.69366e-02 A 6=-9.52789e-03 A 8=-1.71551e-04 A10= 7.65261e-07 A 3= 4.54234e-02 A 5= 2.71741e-02 A 7= 1.88545e-03 Page 13 K =-4.72297e+01 A 4=-3.62984e-02 A 6=-3.40402e-03 A 8=-8.43606e-05 A10=-2.63594e-07 A 3= 5.57242e-02 A 5= 1.28857e-02 A 7= 6.48527e-04 A 9= 6.89276e-06 Side 14 K =-1.98741e+01 A 4=-2.10859e-02 A 6=-5.43361e-03 A 8=-2.11629e-04 A10=-6.17168e-07 A 3= 1.69037e-02 A 5= 1.31038e-02 A 7= 1.38770e-03 A 9= 1.76760e-05 Various data Focal length 10.39 F-number: 2.55 Half angle of view (°) 37.20 Image height 7.89 Lens length 15.65 BF 4.54 d14 4.54 Single lens data Lens starting surface focal length 1 1 -5.79 2 3 4.89 3 6 4.01 4 7 -4.22 5 9 -48.87 6 11 41.54 7 13 35.08 [Numerical Example 6] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 -9.182 0.26 1.59270 35.3 5.05 2 7.573 1.16 1.91082 35.2 4.55 3 -15.973 0.36 4.19 4(Aperture) ∞ 0.95 3.70 5 5.201 1.28 1.87070 40.7 3.52 6 -11.975 0.18 1.76182 26.5 3.23 7 4.561 0.76 3.42 8* -85.757 0.61 1.53500 56.0 3.99 9* -3646.869 1.98 4.79 10* -4.133 1.32 1.53500 56.0 8.03 11* -3.726 0.08 8.68 12* 6.434 1.79 1.53500 56.0 11.47 13* 8.046 (variable) 11.95 Image plane ∞ Aspheric Data Side 8 K = 0.00000e+00 A 4=-2.15591e-02 A 6=-1.45344e-02 A 8=-6.45412e-04 A 3= 7.31285e-03 A 5= 2.05408e-02 A 7= 4.98873e-03 Page 9 K = 0.00000e+00 A 4=-1.38627e-02 A 6=-7.94143e-03 A 8=-2.15749e-04 A 3= 6.84598e-03 A 5= 1.26489e-02 A 7= 2.30518e-03 Page 10 K =-1.83110e+01 A 4=-1.28739e-02 A 6=-6.60464e-03 A 8=-1.38472e-04 A10 = 5.89377e-07 A 3=-4.50600e-03 A 5= 1.51074e-02 A 7= 1.45049e-03 Page 11 K =-4.49148e+00 A 4=-4.78510e-02 A 6=-9.42635e-03 A 8=-1.74438e-04 A10 = 6.95369e-07 A 3= 3.87383e-02 A 5= 2.75181e-02 A 7= 1.89210e-03 Page 12 K =-5.38183e+01 A 4=-3.59530e-02 A 6=-3.36121e-03 A 8=-8.55245e-05 A10=-2.45687e-07 A 3= 5.16366e-02 A 5= 1.29027e-02 A 7= 6.49569e-04 A 9= 6.80215e-06 Page 13 K =-2.25124e+01 A 4=-2.20658e-02 A 6=-5.43967e-03 A 8=-2.11458e-04 A10=-6.20841e-07 A 3= 1.55469e-02 A 5= 1.34176e-02 A 7= 1.38383e-03 A 9= 1.77223e-05 Various data Focal length 10.39 F-number: 2.86 Half angle of view (°) 37.20 Image height 7.89 Lens length 15.55 BF 4.83 d13 4.83 Single lens data Lens starting surface focal length 1 1 -6.96 2 2 5.78 3 5 4.31 4 6 -4.31 5 8 -164.16 6 10 33.15 7 12 43.30 [Numerical Example 7] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* -3586.364 0.50 1.58313 59.4 4.98 2* 3.305 0.40 4.07 3 6.805 1.15 1.72916 54.7 3.97 4 -20.438 0.41 3.51 5(Aperture) ∞ 0.92 3.45 6 6.513 1.36 1.75500 52.3 4.01 7 -6.331 0.11 4.25 8 -8.195 1.51 1.65844 50.9 4.27 9 -3.404 0.50 1.73800 32.3 4.52 10 13.112 1.15 5.05 11* -10.477 0.56 1.53500 56.0 5.24 12* -12.314 0.82 6.05 13* -4.165 1.53 1.53500 56.0 7.58 14* -4.049 0.18 8.44 15* 4.151 1.87 1.53500 56.0 12.30 16* 4.590 (variable) 12.86 Image plane ∞ Aspheric Data Front page K = 0.00000e+00 A 4=-1.58804e-02 A 6= 2.24199e-03 A 8= 1.83096e-04 A 3=-3.16093e-03 A 5= 4.71244e-03 A 7=-1.32163e-03 2nd side K = 4.72161e-01 A 4=-1.76482e-02 A 6= 1.39866e-03 A 8=-9.37739e-05 A 3=-5.29217e-03 A 5= 3.59190e-03 A 7=-4.59994e-04 Page 11 K = 0.00000e+00 A 4=-1.05979e-02 A 6=-2.78920e-04 A 8= 1.32419e-04 A10=-5.02271e-06 Side 12 K = 0.00000e+00 A 4=-5.08433e-03 A 6=-3.11798e-04 A 8= 1.12668e-04 A10=-4.13907e-06 Page 13 K =-1.22936e+01 A 4= 9.88450e-03 A 6= 2.44515e-03 A 8= 8.11852e-05 A10=-7.20367e-07 A 3=-8.89814e-03 A 5=-5.23719e-03 A 7=-6.59829e-04 Page 14 K =-1.34110e+00 A 4=-1.16917e-04 A 6=-1.54999e-03 A 8=-3.18547e-05 A10=-6.97583e-08 A 3=-3.16936e-03 A 5= 3.22415e-03 A 7= 3.73888e-04 Page 15 K =-1.12242e+00 A 4=-2.35753e-02 A 6=-4.14295e-03 A 8=-1.53627e-04 A10=-4.33086e-07 A 3= 4.45348e-03 A 5= 1.17935e-02 A 7= 1.01655e-03 A 9= 1.26550e-05 Page 16 K =-6.08828e-01 A 4=-1.82200e-02 A 6=-1.43596e-03 A 8=-3.10115e-05 A10=-5.37345e-08 A 3= 5.03772e-03 A 5= 6.01578e-03 A 7= 2.59656e-04 A 9= 2.01631e-06 Various data Focal length 8.79 F-number: 2.88 Half angle of view (°) 41.92 Image height 7.89 Lens length 17.05 BF 4.07 d16 4.07 Single lens data Lens starting surface focal length 1 1 -5.66 2 3 7.13 3 6 4.46 4 8 7.86 5 9 -3.62 6 11 -147.00 7 13 48.53 8 15 32.60 Various values ​​in each numerical example are summarized in Table 1 below.

[0079] [Table 1]

[0080] [Imaging device] Next, an embodiment of a digital still camera 10 (imaging device) using the optical system L0 of the present invention as an imaging optical system will be described with reference to Fig. 15. In Fig. 15, 13 is a camera body, and 11 is an imaging optical system constituted by any of the optical systems L0 described in the first to seventh embodiments. 12 is a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built into the camera body 13 and receives an optical image formed by the imaging optical system 11 and photoelectrically converts it. The camera body 13 may be a so-called single-lens reflex camera having a quick-turn mirror, or may be a so-called mirrorless camera having no quick-turn mirror.

[0081] In this way, by applying the optical system L0 of the present invention to an imaging device such as a digital still camera, it is possible to obtain an imaging device with a small lens.

[0082] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0083] L0 optical system La front group SP aperture stop Lb rear group Lp final lens

Claims

1. An optical system comprising, in order from the object side to the image side, a front group, an aperture stop, and a rear group having positive refractive power as a whole, the front group is composed of one positive lens, the rear group includes a final lens having positive refractive power that is located closest to the image side in the rear group, Let TTL be the distance on the optical axis from the object side lens surface of the lens arranged closest to the object in the optical system to the image plane, Φi be the diameter of the image circle, PNdave be the average value of the refractive index at the d-line of the materials of all the positive lenses included in the optical system, Φp be the effective diameter of the image side lens surface of the final lens, sk be the air-equivalent length on the optical axis from the image side lens surface of the final lens to the image plane, fp be the focal length of the final lens, and f be the focal length of the optical system. 0.5<TTL / Φi<1.4 1.64<PNdave<2.00 2.0<Φp / sk<4.0 0.6<fp / f<6.0 An optical system characterized in that the following condition is satisfied:

2. Let fa be the focal length of the front group and f be the focal length of the optical system. 0.1<f / |fa|<1.5 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the focal length of the optical system is f, 0.1<sk / f<0.7 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the distance on the optical axis from the aperture stop to the image plane is defined as SPIP, 0.6<SPIP / TTL<1.0 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. 5. The optical system according to claim 1, wherein the rear group includes at least four lenses.

6. 6. The optical system according to claim 1, wherein the rear group includes a first negative lens arranged on the object side of the final lens.

7. When the paraxial radius of curvature of the object side lens surface of the first negative lens is R1 and the paraxial radius of curvature of the image side lens surface of the first negative lens is R2, 0.0<(R1+R2) / (R2-R1)<50.0 7. The optical system according to claim 6, wherein the following condition is satisfied:

8. When the refractive index of the material of the first negative lens at the d line is Ndn and the Abbe number of the first negative lens at the d line is νdn, 1.500<Ndn<4.1945 / νdn+1.520 8. The optical system according to claim 6, wherein the following condition is satisfied:

9. When the focal length of the front group is fa and the focal length of the rear group is fb, 0.10<fb / |fa|<10.00 9. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the refractive index at d line of the material of the positive lens constituting the front group is Ndap, 1.60<Ndap<2.00 10. The optical system according to claim 1, wherein the following condition is satisfied:

11. the rear group includes a second positive lens, When the refractive index of the material of the second positive lens at the d line is Ndbp, 1.60<Ndbp<2.00 11. The optical system according to claim 1, wherein the following condition is satisfied:

12. the rear group includes a second negative lens, When the refractive index at the d-line of the material of the second negative lens is Ndbn, 0.0<Ndbp−Ndbn<0.4 12. The optical system according to claim 11, wherein the following condition is satisfied:

13. Let Φa be the largest effective diameter of the lens having the largest effective diameter in the front group, 1.0<Φp / Φa<4.0 13. The optical system according to claim 1, wherein the following condition is satisfied:

14. 14. The optical system according to claim 1, wherein the optical system is composed of five to eight lenses.

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

Images