Optical system and image pickup apparatus having the same

Abstract

The present disclosure relates to an optical system and an image pickup apparatus having the optical system. The optical system includes a plurality of lenses and an aperture. The plurality of lenses consist in order from an object side to an image side of a first lens having positive refractive power, a second lens having positive refractive power, a third lens having negative refractive power, a fourth lens, a fifth lens, and a sixth lens. The aperture is located between the first lens and the second lens. A predetermined condition is satisfied.

Description

Technical Field

[0001] This invention relates to optical systems and is suitable for use in digital video cameras, digital cameras, broadcast cameras, film-based cameras, surveillance cameras, etc. Background Technology

[0002] In recent years, image pickup devices have been made smaller, and the optical systems used in image pickup devices (imaging optics) have been required to have short total lens lengths and high optical performance.

[0003] As an optical system to meet these needs, Japanese Patent Publication No. (“JP”) 2020-24337 discloses an optical system consisting of six lenses.

[0004] In attempts to shorten the total lens length of an optical system, various aberrations such as spherical aberration and field curvature may increase, and optical performance may deteriorate. When the aperture stop (aperture) is positioned closer to the imaging plane due to the shortening of the total lens length, shading is likely to occur because the light beam is incident obliquely on the periphery of the image sensor in an image-collecting device such as a digital camera, which includes the image sensor (oblique incidence). Shading can be suppressed by placing the aperture stop closer to the object than the center of the optical system, but because the lens configuration is asymmetrical with respect to the aperture stop of the optical system, it becomes difficult to satisfactorily correct various aberrations, and the number of lenses tends to increase. In the optical system disclosed in JP 2020-24337, both the reduction of the total lens length and high optical performance are insufficient.

[0005] In order to reduce the overall lens length and improve performance while suppressing oblique incidence on the periphery of the image sensor, it is important to properly set the lens configuration of the optical system (such as material, number and shape), in addition to the sign of the refractive power of each lens. Summary of the Invention

[0006] The present invention provides an optical system with a short total lens length and excellent optical performance, while suppressing oblique incidence around the image sensor.

[0007] An optical system according to one aspect of the present invention has a plurality of lenses and an aperture. The plurality of lenses, from the object side to the image side, are sequentially composed of a first lens with positive refractive power, a second lens with positive refractive power, a third lens, a fourth lens, a fifth lens, and a sixth lens with negative refractive power. The aperture is located between the first and second lenses. The following conditional expression is satisfied:

[0008] 0.5 <SPIP / TTL<1.0

[0009] 1.65 <PNdave<2.00

[0010] Where SPIP is the distance from the aperture to the image plane on the optical axis at the back focal length, expressed in terms of air equivalent length; TTL is the distance from the lens surface on the object side of the first lens to the image plane on the optical axis at the back focal length, expressed in terms of air equivalent length; and PNdave is the average refractive index of all materials of the positive lens included in the optical system with respect to the d-line. An image pickup device having the above-described optical system also constitutes another aspect of the present invention.

[0011] Other features of the invention will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0012] Figure 1 It is a cross-sectional view of the optical system based on Example 1.

[0013] Figure 2 It is an aberration diagram based on the optical system in Example 1.

[0014] Figure 3 It is a cross-sectional view of the optical system based on Example 2.

[0015] Figure 4 It is an aberration diagram based on the optical system in Example 2.

[0016] Figure 5 It is a cross-sectional view of the optical system based on Example 3.

[0017] Figure 6 It is an aberration diagram based on the optical system in Example 3.

[0018] Figure 7 This is a schematic diagram of an image pickup device. Detailed Implementation

[0019] A description of embodiments of the present invention will now be given with reference to the accompanying drawings.

[0020] Figure 1 , Figure 3 and Figure 5 These are lens cross-sectional views of the optical systems according to Examples 1 to 3 at infinity in a focused state.

[0021] According to the various examples, the optical system L0 is an optical system used in image acquisition devices such as digital video cameras, digital cameras, broadcast cameras, film-based cameras, and surveillance cameras.

[0022] In each lens cross-sectional view, the left side is the object side (magnification side), and the right side is the image side (reduction side). The optical system L0 according to the various examples includes multiple lenses.

[0023] According to the various examples, the optical system L0 includes, from the object side to the image side, a first lens L1 with positive refractive power, an aperture stop (aperture) SP, a second lens L2 with positive refractive power, a third lens L3 with negative refractive power, a fourth lens L4, a fifth lens L5, and a sixth lens L6.

[0024] In each lens cross-sectional diagram, "Li" (where i is a natural number) represents the "i-th lens" when counting the lenses in the optical system L0 sequentially from the object side to the image side. SP represents the aperture stop that determines (limits) the open F-number (Fno) of the beam. IP represents the image plane, on which the imaging plane of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is placed when the optical system L0 according to the various examples is used as an imaging optical system for a digital video camera or digital camera. When the optical system L0 according to the various examples is used as an imaging optical system for a film-based camera, the photosensitive plane corresponding to the film plane is placed on the image plane IP.

[0025] Focusing is performed from an object point at infinity to an object point closer to it by moving the entire optical system L0 along the optical axis.

[0026] According to the various examples, the optical system L0 can be used as an image-stabilizing optical system by eccentricating one or more lenses to include a component orthogonal to the optical axis during image stabilization. A parallel plate, which has essentially no refractive force, such as a low-pass filter or an infrared cutoff filter, can be deployed between the lens closest to the image plane and the imaging plane.

[0027] Figure 2 , Figure 4 and Figure 6 It is an aberration diagram of the optical system L0 at infinity in the focusing state according to Examples 1 to 3.

[0028] In the spherical aberration diagram, Fno represents the F-number and indicates the amount of spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, dS represents the amount of astigmatism on the sagittal image plane, and dM represents the amount of astigmatism on the meridional image plane. The distortion diagram illustrates the distortion for the d-line. The chromatic aberration diagram illustrates the amount of chromatic aberration for the g-line. ω represents the half-angle of the imaging (°), which is the angle of view calculated paraxially.

[0029] The characteristic configurations of the optical system L0 according to the various examples will now be described.

[0030] According to the various examples, the optical system L0 includes, from the object side to the image side, a first lens L1 with positive refractive power, an aperture stop SP, a second lens L2 with positive refractive power, a third lens L3 with negative refractive power, a fourth lens L4, a fifth lens L5, and a sixth lens L6.

[0031] The optical system L0 in each example satisfies the following conditional expressions (1) and (2):

[0032] 0.5 <SPIP / TTL<1.0...(1)

[0033] 1.65 <PNdave<2.00...(2)

[0034] SPIP is the distance along the optical axis from the aperture stop SP to the image plane IP when expressed in air equivalent length at the back focal length. TTL is the total lens length (the distance along the optical axis from the object-side lens surface of the first lens L1 to the image plane IP when expressed in air equivalent length at the back focal length). PNdave is the average refractive index of all materials of the positive lens included in the optical system L0 for the d-line.

[0035] Conditional expression (1) relates to the ratio of the distance along the optical axis from the aperture stop SP to the image plane IP to the total lens length when the back focal length is expressed in terms of air equivalent length. When this ratio is below the lower limit in conditional expression (1), the aperture stop SP is positioned close to the image plane IP, and therefore the angle of incidence of the off-axis beam on the image plane IP becomes larger. This is not preferred because shadows appear around the image sensor. When this ratio is above the upper limit in conditional expression (1), the aperture stop SP is positioned closer to the object than the first lens L1. In this case, the lens configuration of the optical system becomes asymmetrical relative to the aperture stop SP and therefore becomes difficult to satisfactorily correct for various aberrations. Furthermore, the diameter of the lens closer to the image plane IP tends to be larger, making it difficult to reduce the size of the lens.

[0036] Conditional expression (2) relates to the average refractive index of all materials of the positive lens included in the optical system L0 with respect to the d-line. If the average refractive index of the positive lens material is less than the lower limit in conditional expression (2), then the Petzval Sum tends to be large and field curvature becomes difficult to correct. As the average refractive index of the positive lens material increases, field curvature becomes easier to correct, but in general, the dispersion of materials with high refractive indices tends to be greater than that of materials with low refractive indices. Therefore, if the average refractive index of the positive lens material is higher than the upper limit in conditional expression (2), then longitudinal chromatic aberration becomes difficult to correct.

[0037] The optical system L0 according to the various examples with the above configuration achieves a short total lens length and excellent optical performance, while suppressing oblique incidence around the image sensor.

[0038] The numerical ranges of conditional expressions (1) and (2) can be replaced by the numerical ranges of the following conditional expressions (1a) and (2a):

[0039] 0.6 <SPIP / TTL<0.9...(1a)

[0040] 1.65 <PNdave<1.90...(2a)

[0041] The numerical ranges of conditional expressions (1) and (2) can be replaced by the numerical ranges of the following conditional expressions (1b) and (2b):

[0042] 0.7 <SPIP / TTL<0.9...(1b)

[0043] 1.70 <PNdave<1.80...(2b)

[0044] The conditions that the optical system L0 can satisfy according to the various examples will now be described.

[0045] According to the various examples, the optical system L0 can satisfy one or more of the following conditional expressions (3) to (10):

[0046] 0.80 <f1 / f<2.00...(3)

[0047] 0.30 <f2 / f<0.80...(4)

[0048] -0.70 <f3 / f<-0.25...(5)

[0049] 0.20 <BF / TTL<0.40...(6)

[0050] 1.5<(L1R2+L1R1) / (L1R2-L1R1)<4.0...(7)

[0051] 15 <Nνdave<30...(8)

[0052] 0.90 <TTL / f<1.40...(9)

[0053] Here, fl is the focal length of the first lens L1. f is the focal length of the optical system L0. f2 is the focal length of the second lens L2. f3 is the focal length of the third lens L3. BF is the back focal length of the optical system L0, and is expressed as the equivalent air length of the distance along the optical axis from the image-side lens surface of the sixth lens L6 to the image plane IP. L1R2 is the radius of curvature of the image-side lens surface of the first lens L1. L1R1 is the radius of curvature of the object-side lens surface of the first lens L1. Nνdave is the average Abbe number for the d-line of all materials included in the negative lens in the optical system L0.

[0054] The conditional expression (3) relates to the ratio of the focal length of the first lens L1 to the focal length of the optical system L0. If this ratio is lower than the lower limit in the conditional expression (3), the refractive power of the first lens L1 becomes stronger, and it becomes difficult to adequately correct various aberrations such as spherical aberration. On the other hand, if this ratio is higher than the upper limit in the conditional expression (3), the refractive power of the first lens L1 becomes weaker, and it becomes difficult to adequately shorten the total lens length.

[0055] Conditional expression (4) relates to the ratio of the focal length of the second lens L2 to the focal length of the optical system L0. If this ratio is lower than the lower limit in conditional expression (4), the refractive power of the second lens L2 becomes stronger and it becomes difficult to adequately correct various aberrations such as spherical aberration. On the other hand, if this ratio is higher than the upper limit in conditional expression (4), the refractive power of the second lens L2 becomes weaker and it becomes difficult to adequately shorten the total lens length.

[0056] Conditional expression (5) relates to the ratio of the focal length of the third lens L3 to the focal length of the optical system L0. If this ratio is below the lower limit in conditional expression (5), the refractive power of the third lens L3 becomes weaker and it becomes difficult to sufficiently shorten the total lens length. On the other hand, if this ratio is above the upper limit in conditional expression (5), the refractive power of the third lens L3 becomes stronger and it becomes difficult to sufficiently correct various aberrations such as spherical aberration.

[0057] The conditional expression (6) relates to the ratio of the back focal length to the total lens length of the optical system L0. If this ratio is below the lower limit in the conditional expression (6), the back focal length becomes too short, the angle of incidence of the off-axis beam on the image plane IP becomes large, and shadows appear. Alternatively, it becomes difficult to reduce the size of the lens because the lens diameter increases in order to suppress shadows. On the other hand, if this ratio is above the upper limit in the conditional expression (6), the back focal length becomes too long and the total lens length increases.

[0058] The conditional expression (7) relates to the shape of the first lens L1. Since the first lens L1 has positive refractive power, satisfying the conditional expression (7) means that the first lens L1 has a meniscus shape that bulges out on the object side. By satisfying the conditional expression (7), various aberrations such as spherical aberration can be satisfactorily corrected.

[0059] The conditional expression (8) relates to the average Abbe number of all materials included in the negative lens in the optical system L0 for the d-line. If the average Abbe number is below the lower limit in the conditional expression (8), then the dispersion becomes large and it becomes difficult to correct longitudinal and lateral chromatic aberrations. Moreover, in general, the refractive index of materials with large dispersion tends to be higher than that of materials with small dispersion. Therefore, the average refractive index of the negative lens becomes high, the Purzval and other properties tend to be large, and it becomes difficult to correct field curvature, etc. On the other hand, if the average Abbe number is above the upper limit in the conditional expression (8), then the dispersion becomes too small and it becomes difficult to correct longitudinal and lateral chromatic aberrations.

[0060] The conditional expression (9) relates to the ratio of the focal length of the optical system L0 to the total lens length. If this ratio is below the lower limit in the conditional expression (9), then the total lens length becomes too short and becomes difficult to adequately correct various aberrations such as spherical aberration. On the other hand, if this ratio is above the upper limit in the conditional expression (9), then the total lens length becomes too long.

[0061] The numerical ranges of conditional expressions (3) to (9) can be replaced by the numerical ranges of the following conditional expressions (3a) to (9a):

[0062] 0.80 <f1 / f<1.80...(3a)

[0063] 0.30 <f2 / f<0.70...(4a)

[0064] -0.60 <f3 / f<-0.25...(5a)

[0065] 0.25 <BF / TTL<0.38...(6a)

[0066] 2.0<(L1R2+L1R1) / (L1R2-L1R1)<3.5...(7a)

[0067] 15 <Nνdave<25...(8a)

[0068] 1.00 <TTL / f<1.30...(9a)

[0069] The numerical ranges of conditional expressions (3) to (9) can be replaced by the numerical ranges of the following conditional expressions (3b) to (9b):

[0070] 0.80 <f1 / f<1.60...(3b)

[0071] 0.30 <f2 / f<0.65...(4b)

[0072] -0.55 <f3 / f<-0.30...(5b)

[0073] 0.28 <BF / TTL<0.35...(6b)

[0074] 2.5<(L1R2+L1R1) / (L1R2-L1R1)<3.5...(7b)

[0075] 18 <Nνdave<25...(8b)

[0076] 1.10 <TTL / f<1.30..(9b)

[0077] The configurations that the optical system L0 can satisfy according to the various examples will now be described.

[0078] The optical system L0 may include two or more negative lenses. This configuration facilitates the correction of field curvature, as well as longitudinal and lateral chromatic aberration.

[0079] The fourth lens L4 may include a region with negative refractive power near the optical axis. The fourth lens L4 may include aspherical surfaces on both sides, with the object-side lens surface of the fourth lens L4 being a concave surface near the optical axis, and the image-side lens surface of the fourth lens L4 being a convex surface near the optical axis. This configuration facilitates field curvature correction.

[0080] The fifth lens L5 may include a region with positive refractive power near the optical axis. The fifth lens L5 may include aspherical surfaces on both sides, including a region on the object side of the fifth lens L5 that is a concave surface near the optical axis, and a region on the image side of the fifth lens L5 that is a convex surface near the optical axis. This configuration facilitates field curvature correction.

[0081] The sixth lens L6 may include a region with positive refractive power near the optical axis. The sixth lens L6 may include aspherical surfaces on both sides, including a region on the object side of the sixth lens L6 that is a convex surface near the optical axis, and a region on the image side of the sixth lens L6 that is a concave surface near the optical axis. This configuration facilitates field curvature correction.

[0082] The paraxial region is located near the optical axis, and in the case of aspherical lenses, the concave and convex surfaces near the optical axis are defined by the sign of the paraxial radius of curvature. The sign of the refractive force is also calculated from the paraxial radius of curvature.

[0083] The optical system L0 according to the various examples will now be described in detail.

[0084] According to various examples, the optical system L0, from the object side to the image side, includes a first lens L1, an aperture stop SP, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6. The first lens L1 has positive refractive power. The second lens L2 has positive refractive power. The third lens L3 has negative refractive power. The fourth lens L4 has negative refractive power near the optical axis. The fifth lens L5 has positive refractive power near the optical axis. The sixth lens L6 has positive refractive power near the optical axis. In the fourth lens L4, aspherical surfaces are formed on both surfaces. The object-side surface of the fourth lens L4 is a concave surface near the optical axis, and the image-side lens surface of the fourth lens L4 is a convex surface near the optical axis. In the fifth lens L5, aspherical surfaces are formed on both surfaces. The object-side surface of the fifth lens L5 is a concave surface near the optical axis, and the image-side lens surface of the fifth lens L5 is a convex surface near the optical axis. In the sixth lens L6, aspherical surfaces are formed on both surfaces. The object-side surface of the sixth lens L6 is a convex surface near the optical axis, and the image-side lens surface of the sixth lens L6 is a concave surface near the optical axis.

[0085] The following examples will illustrate numerical examples 1 to 3, respectively, corresponding to Examples 1 to 3.

[0086] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance along the optical axis) between the m-th surface and the (m+1)-th surface, where m is the surface number measured from the light incident side. nd represents the refractive index of each optical element with respect to the d-line, and νd represents the Abbe number of the optical element. The Abbe number νd of a certain material is calculated as follows:

[0087] νd=(Nd-1) / (NF-NC)

[0088] Nd, NF, and NC are the refractive indices of the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) in the Fraunhofer lines.

[0089] In the various numerical examples, d, focal length (mm), F-number, and half angle of view (°) are values ​​when the optical system of each example is focused on an object at infinity. "Back focal length (BF)" is the distance along the optical axis from the last lens surface (the lens surface closest to the image plane) to the paraxial image plane, expressed in air equivalent length. "Total lens length" is the length obtained by adding the back focal length to the distance along the optical axis from the lens surface closest to the object to the last surface.

[0090] The entrance pupil position is expressed as the distance from the lens surface closest to the object (first surface) to the entrance pupil. The exit pupil position is expressed as the distance from the lens surface closest to the image plane (last lens surface) to the exit pupil. The front principal point position is expressed as the distance from the first lens surface to the front principal point. The rear principal point position is expressed as the distance from the last lens surface to the rear principal point. Each of these values ​​is a paraxial quantity and is positively assigned in the direction from the object side to the image side.

[0091] If the optical surface is aspherical, then an asterisk * is appended to the right of the surface number. Aspherical shapes are expressed as follows:

[0092] 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

[0093] Where x is the displacement from the surface vertex along the optical axis, h is the height from the optical axis in the direction orthogonal to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, A12, and A14 are aspheric coefficients of the corresponding orders. Furthermore, "e±XX" in each aspheric coefficient means "×10" ±XX ".

[0094] [Numerical Example 1]

[0095] Unit: mm

[0096] Surface data

[0097]

[0098] Aspherical data

[0099] Surface 7

[0100] K=0.00000e+000 A 4=-1.17343e-002 A 6=6.62086e-004 A 8=7.11821e-005 A10=-1.57795e-005 A12=1.24628e-007

[0101] Surface 8

[0102] K=0.00000e+000 A 4=-9.33591e-003 A 6=9.10480e-004 A 8=-5.56359e-005 A10=1.86493e-006 A12=-2.51762e-008

[0103] 9th surface

[0104] K=0.00000e+000 A 4=8.82669e-003 A 6=-7.18264e-004 A 8=3.71234e-005 A10=-8.01992e-007 A12=8.77474e-010

[0105] Surface 10

[0106] K=0.00000e+000 A 4=3.92160e-003 A 6=9.31874e-005 A 8=-8.10394e-006 A10=2.91020e-007 A12=-2.38551e-009

[0107] Surface 11

[0108] K=0.00000e+000 A 4=-7.49451e-003 A 6=3.07261e-004 A 8=-5.64465e-006 A10=9.78774e-010 A12=1.44863e-009 A14=-1.61988e-011

[0109] Surface 12

[0110] K=0.00000e+000 A 4=-6.85204e-003 A 6=2.82220e-004 A 8=-1.01045e-005 A10=2.47381e-007 A12=-3.28540e-009 A14=1.78261e-011

[0111]

[0112] Single lens data

[0113]

[0114] [Numerical Example 2]

[0115] Unit: mm

[0116] Surface data

[0117]

[0118]

[0119] Aspherical data

[0120] Surface 8

[0121] K=0.00000e+000 A 4=-4.26820e-003 A 6=1.77770e-003 A 8=-2.26805e-004 A10=1.42590e-005 A12=-3.72229e-007

[0122] 9th surface

[0123] K=0.00000e+000 A 4=-1.10581e-002 A 6=2.37005e-003 A 8=-2.13564e-004 A10=9.92956e-006 A12=-1.98013e-007

[0124] Surface 10

[0125] K=0.00000e+000 A 4=-2.65169e-003 A 6=3.87732e-004 A 8=-3.29307e-005 A10=1.51180e-006 A12=-2.70444e-008

[0126] Surface 11

[0127] K=0.00000e+000 A 4=1.51347e-003 A 6=-3.58082e-004 A 8=3.04816e-005 A10=-1.03923e-006 A12=1.28063e-008

[0128] Surface 12

[0129] K=0.00000e+000 A 4=-7.34033e-003 A 6=2.53991e-005 A 8=1.97107e-005 A10=-1.02262e-006 A12=2.13649e-008 A14=-1.76667e-010

[0130] Surface 13

[0131] K=0.00000e+000 A 4=-6.88663e-003 A 6=1.95188e-004 A 8=-4.24138e-006 A10=3.40242e-008 A12=7.17160e-010 A14=-1.74573e-011

[0132]

[0133] Single lens data

[0134]

[0135]

[0136] [Numerical Example 3]

[0137] Unit: mm

[0138] Surface data

[0139]

[0140] Aspherical data

[0141] Surface 8

[0142] K=0.00000e+000 A 4=-1.16579e-002 A 6=9.23400e-004 A 8=-1.96407e-004 A10=3.26667e-005 A12=-5.02605e-006

[0143] 9th surface

[0144] K=0.00000e+000 A 4=-1.19318e-002 A 6=7.01526e-004 A 8=7.06491e-005 A10=-1.24604e-005 A12=5.15017e-007

[0145] Surface 10

[0146] K=0.00000e+000 A 4=-2.01834e-004 A 6=-1.54371e-004 A 8=3.25581e-005 A10=-1.09711e-006 A12=-2.61832e-009

[0147] Surface 11

[0148] K=0.00000e+000 A 4=1.50168e-003 A 6=-3.40868e-005 A 8=-1.74033e-005 A10=1.74869e-006 A12=-4.27577e-008

[0149] Surface 12

[0150] K=0.00000e+000 A 4=-6.28654e-003 A 6=7.04829e-005 A 8=1.06047e-005 A10=-5.31978e-007 A12=9.95925e-009 A14=-6.85704e-011

[0151] Surface 13

[0152] K=0.00000e+000 A 4=-6.57786e-003 A 6=2.21104e-004 A 8=-7.14307e-006 A10=1.69631e-007 A12=-2.34045e-009 A14=1.30153e-011

[0153]

[0154] Single lens data

[0155]

[0156] Table 1 below illustrates the various values ​​in the numerical examples.

[0157] numerical values Example 1 Example 2 Example 3 SPIP 13.741 12.915 12.360 TTL 15.351 16.225 14.450 PNdave 1.705 1.767 1.727 f1 14.598 19.607 13.262 f 13.000 12.610 12.610 f2 6.753 5.002 7.586 f3 -5.828 -4.050 -6.558 BF 5.111 4.815 4.193 L1R2 12.606 16.892 8.926 L1R1 6.172 8.823 4.861 Nvdave 23.88 20.09 19.49 conditional expression Example 1 Example 2 Example 3 (1)SPIP / TTL 0.895 0.796 0.855 (2)PNdave 1.705 1.767 1.727 (3)f1 / f 1.123 1.555 1.052 (4)f2 / f 0.519 0.397 0.602 (5)f3 / f -0.448 -0.321 -0.520 (6)BF / TTL 0.333 0.297 0.290 (7)(L1R2+L1R1) / (L1R2-L1R1) 2.919 3.187 3.391 (8)Nv dave 23.88 20.09 19.49 (9)TTL / f 1.181 1.287 1.146

[0158] Image pickup device

[0159] Now for reference Figure 7 Examples of digital cameras (image pickup devices) 10 using optical systems L0 as imaging optical systems, according to various examples, will be described. Figure 7In this designation, reference numeral 13 denotes the camera body, and reference numeral 11 denotes an imaging optical system comprising any of the optical systems L0 described in Examples 1 to 3. Reference numeral 12 denotes a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor, which is built into the camera body 13 and receives the optical image formed by the imaging optical system 11 and performs photoelectric conversion. The camera body 13 can be a so-called single-lens reflex camera with a quick-turn mirror, or a so-called mirrorless camera without a quick-turn mirror.

[0160] By applying the optical system according to the invention to an image pickup device such as a digital camera in this manner, an image pickup device with short lens length and excellent optical performance can be obtained while suppressing oblique incidence around the image sensor.

[0161] The optical systems described in the examples above can be applied not only to image-capturing devices such as digital cameras, but also to various optical devices such as telescopes.

[0162] While the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to cover all such modifications and equivalent structures and functions.

Claims

1. An optical system having a plurality of lenses and an aperture, wherein the plurality of lenses consist of, in order from an object side to an image side, a first lens having positive refractive power, a second lens having positive refractive power, a third lens having negative refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having positive refractive power, wherein wherein a lens surface on the object side of the first lens is convex, wherein a lens surface on the image side of the first lens is concave, wherein a lens surface on the object side of the second lens is convex, wherein a lens surface on the image side of the second lens is convex, wherein a lens surface on the object side of the third lens is concave, wherein a lens surface on the image side of the third lens is concave, wherein the fourth lens includes a region having negative refractive power in the vicinity of an optical axis, wherein a lens surface on the object side of the fourth lens in the region is concave, wherein a lens surface on the image side of the fourth lens in the region is convex, wherein the fifth lens includes a region having positive refractive power in the vicinity of an optical axis, wherein an aspherical surface is formed on both sides of the fifth lens, wherein a lens surface on the object side of the fifth lens in the region is concave, wherein a lens surface on the image side of the fifth lens in the region is convex, wherein the sixth lens includes a region having positive refractive power in the vicinity of an optical axis, wherein an aspherical surface is formed on both sides of the sixth lens, wherein a lens surface on the object side of the sixth lens in the region is convex, wherein a lens surface on the image side of the sixth lens in the region is concave, wherein the aperture is located between the first lens and the second lens, and wherein the following conditional expressions are satisfied: 0.5 < SPIP / TTL < 1.0 1.65 < PNdave < 2.00 wherein SPIP is a distance on the optical axis from the aperture to the image plane when the back focal length is expressed by an air equivalent length, TTL is a distance on the optical axis from a lens surface on the object side of the first lens to the image plane when the back focal length is expressed by an air equivalent length, and PNdave is an average of refractive indexes for a d-line of all materials of positive lenses included in the optical system.

2. The optical system of claim 1, wherein, the following conditional expression is satisfied: 0.80 < f1 / f < 2.00 wherein f1 is a focal length of the first lens, and f is a focal length of the optical system.

3. The optical system of claim 1, wherein, the following conditional expression is satisfied: 0.30 < f2 / f < 0.80 wherein f2 is a focal length of the second lens, and f is a focal length of the optical system.

4. The optical system of claim 1, wherein, the following conditional expression is satisfied: -0.70 < f3 / f < -0.25 wherein f3 is a focal length of the third lens, and f is a focal length of the optical system.

5. The optical system of claim 1, wherein, the following conditional expression is satisfied: 0.20 < BF / TTL < 0.40 wherein BF is an air equivalent length of a distance on the optical axis from a lens surface on the image side of the sixth lens to the image plane.

6. The optical system of claim 1, wherein, the following conditional expression is satisfied: 1.5 < (L1R2+L1R1) / (L1R2-L1R1) < 4.0 wherein L1R1 is a radius of curvature of a lens surface on the object side of the first lens, and L1R2 is a radius of curvature of a lens surface on the image side of the first lens.

7. The optical system of claim 1, wherein, The optical system includes two or more negative lenses, and satisfies the following conditional expression: 15 < Nvdave < 30 where Nvdave is an average value of Abbe numbers for a d-line of all materials of the negative lenses included in the optical system.

8. The optical system of claim 1, wherein, satisfies the following conditional expression: 0.90 < TTL / f < 1.40 where f is a focal length of the optical system.

9. An image pickup apparatus comprising: the optical system according to any one of claims 1 to 8; and an image sensor configured to receive an image formed by the optical system.

Images