Optical system and optical device

Abstract

To provide an optical system which offers good imaging performance, and an optical device.SOLUTION: An optical system OL for use in optical devices such as cameras 1 is provided, the system comprising a diffractive optical element Lpf, as well as a first lens group G1, a second lens group G2 configured to move while focusing, and a rear group GR comprising at least one lens group, arranged in order from the object side, the first lens group G1 having positive lenses. The optical system satisfies conditions represented by the following expressions: 0.60<θgFp1<1.00, 0.10<TLpf / TL<0.40, where θgFp1 represents a partial dispersion ratio of a medium of a positive lens with the smallest Abbe number for the d-ray in the first lens group G1, TLpf represents an optical axial distance from a most object-side lens surface of the optical system OL to a diffractive optical surface of the diffractive optical element Lpf when focused at infinity, and TL represents a total length of the optical system OL when focused at infinity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, optical systems that are miniaturized by using diffractive optical elements have been proposed (see, for example, Patent Document 1). However, Patent Document 1 has a problem in that further improvement in optical performance is desired. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-092575 Summary of the Invention

[0004] An optical system according to a first aspect of the present invention has a diffractive optical element and includes, in order from the object side, a first lens group, a second lens group that moves during focusing, and a rear group having at least one lens group, wherein the first lens group has a positive lens and satisfies the following condition: 0.60 < θgFp1 < 1.00 0.10 < TLpf / TL < 0.40 however, θgFp1: partial dispersion ratio of the positive lens medium with the smallest Abbe number for the d-line of the medium in the first lens group TLpf: The distance on the optical axis from the lens surface closest to the object in the optical system to the diffractive optical surface of the diffractive optical element when focused at infinity TL: Total length of the optical system when focused at infinity

[0005] An optical system according to a second aspect of the present invention has an aperture stop and, in order from the object side, a first lens group having a diffractive optical element, a second lens group that moves during focusing, and a rear group having at least one lens group, wherein the diffractive optical element is located closer to the image plane than the largest air gap in the first lens group, and satisfies the following condition: 0.30 < d1 / dG1 < 0.60 0.30 < TLs / TL < 0.70 however, d1: The maximum value of the air gap on the optical axis within the first lens group dG1: the distance on the optical axis from the lens surface in the first lens group closest to the object to the lens surface in the first lens group closest to the image plane TLs: The distance on the optical axis from the lens surface closest to the object to the aperture stop when focusing at infinity TL: Total length of the optical system when focused at infinity [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 2 is a cross-sectional view showing the lens configuration of the optical system according to Example 1 when focused at infinity. [Figure 2] 1A and 1B are diagrams showing various aberrations of the optical system according to Example 1, where FIG. 1A shows the optical system focused at infinity, and FIG. 1B shows the optical system focused at a close distance. [Figure 3] FIG. 10 is a cross-sectional view showing the lens configuration of the optical system according to Example 2 when focused at infinity. [Figure 4] 10A and 10B are diagrams showing various aberrations of the optical system according to Example 2, where FIG. 10A shows the optical system focused at infinity, and FIG. [Figure 5] FIG. 10 is a cross-sectional view showing the lens configuration of the optical system according to Example 3 when focused at infinity. [Figure 6] 10A and 10B are diagrams showing various aberrations of the optical system according to Example 3, where FIG. 10A shows the optical system focused at infinity, and FIG. [Figure 7] FIG. 10 is a cross-sectional view showing the lens configuration of the optical system according to Example 4 when focused at infinity. [Figure 8] 10A and 10B are diagrams showing various aberrations of the optical system according to Example 4, where FIG. 10A shows the optical system focused at infinity, and FIG. [Figure 9] FIG. 11 is a cross-sectional view showing the lens configuration of the optical system according to Example 5 when focused at infinity. [Figure 10] 10A and 10B are diagrams showing various aberrations of the optical system according to Example 5, where FIG. 10A shows the optical system focused at infinity, and FIG. [Figure 11] FIG. 13 is a cross-sectional view showing the lens configuration of the optical system according to Example 6 when focused at infinity. [Figure 12] 10A and 10B are diagrams showing various aberrations of the optical system according to Example 6, where FIG. 10A shows the optical system focused at infinity, and FIG. [Figure 13] FIG. 13 is a cross-sectional view showing the lens configuration of the optical system according to Example 7 when focused at infinity. [Figure 14] 10A and 10B are diagrams showing various aberrations of the optical system according to Example 7, where FIG. 10A shows the optical system focused at infinity, and FIG. [Figure 15] FIG. 13 is a cross-sectional view showing the lens configuration of the optical system according to Example 8 when focused at infinity. [Figure 16] 13A and 13B are diagrams showing various aberrations of the optical system according to Example 8, where FIG. 13A shows the optical system focused at infinity, and FIG. [Figure 17] FIG. 2 is a cross-sectional view of a camera equipped with the optical system. [Figure 18] 4 is a flowchart illustrating a method for manufacturing the optical system. DETAILED DESCRIPTION OF THE INVENTION

[0007] Preferred embodiments will now be described with reference to the drawings.

[0008] [First embodiment] As shown in Fig. 1, the optical system OL according to the first embodiment includes, in order from the object side, a first lens group G1 having a diffractive optical element Lpf, a second lens group G2 that moves during focusing, and a rear group GL having at least one lens group. The first lens group G1 also includes a positive lens (e.g., a positive meniscus lens L11 in the first embodiment shown in Fig. 1) closest to the object side. This configuration allows the optical system OL to be compact yet effectively correct spherical aberration and axial chromatic aberration.

[0009] It is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (1).

[0010] 0.40 < TL / f < 0.65 (1) however, TL: Total length of optical system OL when focused at infinity f: focal length of the entire optical system OL when focused at infinity

[0011] Conditional expression (1) defines the ratio of the overall length of the optical system OL to the focal length of the entire optical system OL. By satisfying conditional expression (1), the optical system OL can be compact yet effectively correct spherical aberration. Exceeding the upper limit of conditional expression (1) is undesirable because spherical aberration will be over-corrected. To ensure the effect of conditional expression (1), it is more preferable to set the upper limit of conditional expression (1) to 0.57, and more preferably 0.55 or 0.53. To ensure the effect of conditional expression (1), it is undesirable because spherical aberration will be under-corrected. To ensure the effect of conditional expression (1), it is more preferable to set the lower limit of conditional expression (1) to 0.41.

[0012] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (3).

[0013] 0.10 < TLpf / TL < 0.40 (3) however, TLpf: The distance on the optical axis from the lens surface closest to the object in the optical system OL to the diffractive optical surface of the diffractive optical element Lpf when focused at infinity TL: Total length of optical system OL when focused at infinity

[0014] Conditional expression (3) defines the ratio of the on-optical axis distance from the lens surface of the optical system OL closest to the object to the diffractive optical surface of the diffractive optical element Lpf to the total length of the optical system OL. By satisfying conditional expression (3), the diffractive optical element Lpf can be easily manufactured while still achieving good correction of chromatic aberration in the optical system OL. Exceeding the upper limit of conditional expression (3) is undesirable because second-order axial chromatic aberration is undercorrected. To ensure the effect of conditional expression (3), it is more desirable to set the upper limit of conditional expression (3) to 0.35. Falling below the lower limit of conditional expression (3) is undesirable because second-order axial chromatic aberration is overcorrected. To ensure the effect of conditional expression (3), it is more desirable to set the lower limit of conditional expression (3) to 0.18.

[0015] [Second embodiment] As shown in Fig. 1, the optical system OL according to the second embodiment has a diffractive optical element Lpf and includes, in order from the object side, a first lens group G1, a second lens group G2 that moves during focusing, and a rear group GR that includes at least one lens group. The first lens group G1 includes a positive lens (for example, a positive meniscus lens L11 in the first embodiment shown in Fig. 1). This configuration allows the optical system OL to be compact yet effectively correct spherical aberration and axial chromatic aberration.

[0016] It is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (2).

[0017] 0.60 < θgFp1 < 1.00 (2) however, θgFp1: partial dispersion ratio of the positive lens medium in the first lens group G1 that has the smallest Abbe number for the d-line of the medium

[0018] Conditional expression (2) defines the partial dispersion ratio of the medium of the positive lens in the first lens group G1 that has the smallest Abbe number for the d-line of the medium. This configuration allows the optical system OL to be compact yet effectively correct chromatic aberration. Exceeding the upper limit of conditional expression (2) is undesirable because second-order axial chromatic aberration will be over-corrected. To ensure the effect of conditional expression (2), it is more desirable to set the upper limit of conditional expression (2) to 0.75. Falling below the lower limit of conditional expression (2) is undesirable because second-order axial chromatic aberration will be under-corrected. To ensure the effect of conditional expression (2), it is more desirable to set the lower limit of conditional expression (2) to 0.61.

[0019] Here, the partial dispersion ratio θgFp1 is defined by the following formula (a), where the refractive index of the lens medium for the g-line (λ=435.8 nm) is ng, the refractive index for the F-line (λ=486.1 nm) is nF, and the refractive index for the C-line (λ=656.3 nm) is nC.

[0020] θgFp1 = (ng-nF) / (nF-nC) (a)

[0021] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (3).

[0022] 0.10 < TLpf / TL < 0.40 (3) however, TLpf: The distance on the optical axis from the lens surface closest to the object in the optical system OL to the diffractive optical surface of the diffractive optical element Lpf when focused at infinity TL: Total length of optical system OL when focused at infinity

[0023] Conditional expression (3) defines the ratio of the on-optical axial distance from the lens surface of the optical system OL closest to the object to the diffractive optical surface of the diffractive optical element Lpf to the overall length of the optical system OL. By satisfying conditional expression (3), the diffractive optical element Lpf can be easily manufactured while still achieving good correction of chromatic aberration in the optical system OL. Exceeding the upper limit of conditional expression (3) is undesirable because second-order axial chromatic aberration is undercorrected. To ensure the effect of conditional expression (3), it is preferable to set the upper limit of conditional expression (3) to 0.35, and more preferably 0.33. Falling below the lower limit of conditional expression (3) is undesirable because second-order axial chromatic aberration is overcorrected. To ensure the effect of conditional expression (3), it is preferable to set the lower limit of conditional expression (3) to 0.14, and more preferably 0.18.

[0024] In the optical system OL according to this embodiment, the first lens group G1 preferably includes a diffractive optical element Lpf. This configuration allows the optical system OL to be compact yet still effectively correct spherical aberration and axial chromatic aberration.

[0025] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (1).

[0026] 0.40 < TL / f < 0.65 (1) however, TL: Total length of optical system OL when focused at infinity f: focal length of the entire optical system OL when focused at infinity

[0027] Conditional expression (1) defines the ratio of the overall length of the optical system OL to the focal length of the entire optical system OL. By satisfying conditional expression (1), the optical system OL can be compact yet effectively correct spherical aberration. Exceeding the upper limit of conditional expression (1) is undesirable because spherical aberration will be over-corrected. To ensure the effect of conditional expression (1), it is more preferable to set the upper limit of conditional expression (1) to 0.57, and more preferably 0.55 or 0.53. To ensure the effect of conditional expression (1), it is undesirable because spherical aberration will be under-corrected. To ensure the effect of conditional expression (1), it is more preferable to set the lower limit of conditional expression (1) to 0.41.

[0028] [Third embodiment] As shown in Figure 1, the optical system OL according to the third embodiment has an aperture stop S and, in order from the object side, includes a first lens group G1 having a diffractive optical element Lpf, a second lens group G2 that moves during focusing, and a rear group GR having at least one lens group. The diffractive optical element Lpf is located closer to the image plane than the largest air gap in the first lens group G1. This configuration allows the optical system OL to be compact yet effectively correct spherical aberration and axial chromatic aberration.

[0029] Furthermore, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (4).

[0030] 0.30 < d1 / dG1 < 0.60 (4) however, d1: the maximum value of the air gap on the optical axis within the first lens group G1 dG1: the distance on the optical axis from the lens surface of the first lens group G1 closest to the object to the lens surface of the first lens group G1 closest to the image plane

[0031] Conditional expression (4) defines the ratio of the maximum value of the air gap on the optical axis within the first lens group G1 to the axial distance from the lens surface closest to the object to the lens surface closest to the image plane in the first lens group G1. By satisfying conditional expression (4), it is possible to achieve both good spherical aberration correction and weight reduction in the optical system OL. Below the lower limit of conditional expression (4), it is not preferable to make the optical system OL lighter. To ensure the effect of conditional expression (4), it is more preferable to set the lower limit of conditional expression (4) to 0.305. Exceeding the upper limit of conditional expression (4) is also not preferable, as it makes it difficult to correct aberrations. To ensure the effect of conditional expression (4), it is more preferable to set the upper limit of conditional expression (4) to 0.58, and more preferably 0.56.

[0032] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (5).

[0033] 0.30 < TLs / TL < 0.70 (5) however, TLs: The distance on the optical axis from the lens surface closest to the object in the optical system OL to the aperture stop S when focusing at infinity TL: Total length of optical system OL when focused at infinity

[0034] Conditional expression (5) defines the ratio of the on-optical-axis distance from the lens surface closest to the object of the optical system OL to the aperture stop S when the optical system OL is focused at infinity to the total length of the optical system OL when focused at infinity. By satisfying conditional expression (5), the lateral chromatic aberration and curvature of field of the optical system OL can be effectively corrected. Below the lower limit of conditional expression (5), the curvature of field is overcorrected and the lateral chromatic aberration becomes difficult to correct, which is undesirable. To ensure the effect of conditional expression (5), it is preferable to set the lower limit of conditional expression (5) to 0.35, and more preferably 0.38. Above the upper limit of conditional expression (5), it is undesirable to undercorrect the curvature of field and the lateral chromatic aberration becomes difficult to correct, which is undesirable. To ensure the effect of conditional expression (5), it is preferable to set the upper limit of conditional expression (5) to 0.68, and more preferably 0.65.

[0035] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (1).

[0036] 0.40 < TL / f < 0.65 (1) however, TL: Total length of optical system OL when focused at infinity f: focal length of the entire optical system OL when focused at infinity

[0037] Conditional expression (1) defines the ratio of the overall length of the optical system OL to the focal length of the entire optical system OL. By satisfying conditional expression (1), the optical system OL can be compact yet effectively correct spherical aberration. Exceeding the upper limit of conditional expression (1) is undesirable because spherical aberration will be over-corrected. To ensure the effect of conditional expression (1), it is more preferable to set the upper limit of conditional expression (1) to 0.57, and more preferably 0.55 or 0.53. To ensure the effect of conditional expression (1), it is undesirable because spherical aberration will be under-corrected. To ensure the effect of conditional expression (1), it is more preferable to set the lower limit of conditional expression (1) to 0.41.

[0038] The following description is common to the first to third embodiments described above.

[0039] In the optical system OL according to this embodiment, it is desirable that the diffractive optical element Lpf be positioned closer to the object than the negative lens component closest to the object. By configuring the optical system OL in this way, it is possible to effectively correct axial chromatic aberration while keeping the optical system OL compact.

[0040] In the optical system OL according to this embodiment, it is desirable that the first lens group G1 has two positive lenses arranged on the object side of the diffractive optical element Lpf. This configuration makes it possible to effectively correct spherical aberration while keeping the optical system OL compact.

[0041] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (6).

[0042] 0.05 < -fr / f < 2.50 (6) however, fr: focal length of rear group GR when focused at infinity f: focal length of the entire optical system OL when focused at infinity

[0043] Conditional expression (6) defines the ratio of the focal length of the rear group GR to the focal length of the entire optical system OL when focusing at infinity. By satisfying conditional expression (6), the optical system OL can be compact yet effectively correct spherical aberration. Exceeding the upper limit of conditional expression (6) is undesirable because the refractive power of the second lens group G2 becomes too strong, making it difficult to correct spherical aberration when focusing at close distances. To ensure the effectiveness of conditional expression (6), it is preferable to set the upper limit of conditional expression (6) to 1.00, or even 0.50. Falling below the lower limit of conditional expression (6) is undesirable because the refractive power of the rear group GR becomes too strong, making it difficult to correct axial chromatic aberration. To ensure the effectiveness of conditional expression (6), it is undesirable to set the lower limit of conditional expression (6) to 0.06, or even 0.20.

[0044] In the optical system OL according to this embodiment, it is desirable that the first lens group G1 has positive refractive power. By configuring the optical system OL in this way, it is possible to make the optical system OL compact while still effectively correcting spherical aberration.

[0045] Furthermore, in the optical system OL according to this embodiment, it is desirable that the diffractive optical element Lpf has two diffractive element elements made of different optical materials, and that these two diffractive element elements are cemented together, with a diffractive optical surface formed on the cemented surface of the diffractive element elements. In the following description, the two diffractive element elements of the diffractive optical element Lpf that are cemented together and have a diffractive optical surface formed on the cemented surface are referred to as a phase Fresnel element (PF element Epf). With this configuration, the optical system OL can effectively correct axial chromatic aberration over a wide wavelength range using the diffractive optical element Lpf, and can suppress diffraction flare of unwanted orders over a wide wavelength range that occurs in the diffractive optical element Lpf.

[0046] Here, it is desirable that the diffractive optical element Lpf has a lens component, and one of two diffractive element elements (PF element Epf) is cemented to the object-side lens surface or the image-plane-side lens surface of this lens component. This configuration makes it easy to manufacture the diffractive optical element Lpf. It is also desirable that the lens component constituting the diffractive optical element Lpf has a meniscus shape. This configuration can reduce spherical aberration generated by the diffractive optical element Lpf.

[0047] Furthermore, it is desirable that one of the two diffractive element components (PF element Epf) of the diffractive optical element Lpf be in contact with air. By configuring it in this way, the weight of the diffractive optical element Lpf can be reduced.

[0048] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (7).

[0049] 12.0 < νdp1 < 32.0 (7) however, νdp1: Abbe number of the positive lens in the first lens group G1 that has the smallest Abbe number for the d-line of the medium

[0050] Conditional expression (7) defines the minimum Abbe number of the medium of the positive lens in the first lens group G1. By satisfying conditional expression (7), the optical system OL can be made compact while still achieving good correction of chromatic aberration. Exceeding the upper limit of conditional expression (7) undesirably results in overcorrection of first-order axial chromatic aberration. To ensure the effectiveness of conditional expression (7), it is preferable to set the upper limit of conditional expression (7) to 30.0, and more preferably 28.0. Falling below the lower limit of conditional expression (7) undesirably results in undercorrection of first-order axial chromatic aberration. To ensure the effectiveness of conditional expression (7), it is preferable to set the lower limit of conditional expression (7) to 15.0, and more preferably 17.0.

[0051] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (8).

[0052] 0.10 < d1 / TL < 0.31 (8) however, d1: the maximum value of the air gap on the optical axis within the first lens group G1 TL: Total length of optical system OL when focused at infinity

[0053] Conditional expression (8) defines the ratio of the maximum value of the air gap on the optical axis within the first lens group G1 to the total length of the optical system OL when focused at infinity. By satisfying conditional expression (8), the weight of the optical system OL can be reduced while still achieving good correction of spherical aberration. Exceeding the upper limit of conditional expression (8) undesirably results in undercorrection of spherical aberration. To ensure the effectiveness of conditional expression (8), it is more desirable to set the upper limit of conditional expression (8) to 0.30, or even 0.25. Falling below the lower limit of conditional expression (8) undesirably results in overcorrection of spherical aberration. To ensure the effectiveness of conditional expression (8), it is more desirable to set the lower limit of conditional expression (8) to 0.12.

[0054] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (9).

[0055] 0.20 < f1 / f < 0.50 (9) however, f1: focal length of the first lens group G1 f: focal length of the entire optical system OL when focused at infinity

[0056] Conditional expression (9) defines the ratio of the focal length of the first lens group G1 to the focal length of the entire optical system OL when focused at infinity. By satisfying conditional expression (9), spherical aberration can be effectively corrected while keeping the optical system OL compact. Exceeding the upper limit of conditional expression (9) undesirably results in overcorrection of spherical aberration. To ensure the effectiveness of conditional expression (9), it is preferable to set the upper limit of conditional expression (9) to 0.45, and more preferably 0.40. To ensure the effectiveness of conditional expression (9), it is preferable to set the upper limit of conditional expression (9) below the lower limit of conditional expression (9) undesirably results in undercorrection of spherical aberration. To ensure the effectiveness of conditional expression (9), it is preferable to set the lower limit of conditional expression (9) to 0.23, and more preferably 0.25.

[0057] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (10).

[0058] 0.15 < -f2 / f < 0.40 (10) however, f2: Focal length of the second lens group G2 f: focal length of the entire optical system OL when focused at infinity

[0059] Conditional expression (10) defines the ratio of the focal length of the second lens group G2 to the focal length of the entire optical system OL when focusing at infinity. By satisfying conditional expression (10), spherical aberration can be effectively corrected when focusing at close distances while keeping the optical system OL compact. Exceeding the upper limit of conditional expression (10) is undesirable because the refractive power of the rear group GR increases, resulting in over-correction of axial chromatic aberration. To ensure the effectiveness of conditional expression (10), it is preferable to set the upper limit of conditional expression (10) to 0.37, or even 0.33. Falling below the lower limit of conditional expression (10) is undesirable because spherical aberration when focusing at close distances is over-corrected. To ensure the effectiveness of conditional expression (10), it is undesirable to set the lower limit of conditional expression (10) to 0.17, or even 0.20.

[0060] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (11).

[0061] 0.10 < dpf / TL < 0.31 (11) however, dpf: Air gap on the optical axis between the diffractive optical element Lpf and the lens located adjacent to it on the object side TL: Total length of optical system OL when focused at infinity

[0062] Conditional expression (11) defines the ratio of the air gap on the optical axis between the diffractive optical element Lpf and the lens disposed adjacent to the object side to the total length of the optical system OL when focused at infinity. By satisfying conditional expression (11), the diffractive optical element Lpf can be easily manufactured while effectively correcting chromatic aberration of the optical system OL. Exceeding the upper limit of conditional expression (11) is undesirable because second-order axial chromatic aberration is undercorrected. To ensure the effect of conditional expression (11), it is preferable to set the upper limit of conditional expression (11) to 0.30, or even 0.25. Falling below the lower limit of conditional expression (11) is undesirable because second-order axial chromatic aberration is overcorrected. To ensure the effect of conditional expression (11), it is more preferable to set the lower limit of conditional expression (11) to 0.12.

[0063] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (12).

[0064] 8.0 < fpf / f < 22.0 (12) however, fpf: focal length of the diffractive optical surface of the diffractive optical element Lpf f: focal length of the entire optical system OL when focused at infinity

[0065] Conditional expression (12) defines the ratio of the focal length of the diffractive optical surface of the diffractive optical element Lpf to the focal length of the entire optical system OL when focused at infinity. By satisfying conditional expression (12), chromatic aberration can be effectively corrected while the optical system OL is compact. Exceeding the upper limit of conditional expression (12) is undesirable because second-order axial chromatic aberration is undercorrected. To ensure the effectiveness of conditional expression (12), it is preferable to set the upper limit of conditional expression (12) to 20.0, more preferably 19.0 or 18.0. Falling below the lower limit of conditional expression (12) is undesirable because second-order axial chromatic aberration is overcorrected. To ensure the effectiveness of conditional expression (12), it is undesirable to set the lower limit of conditional expression (12) to 9.0, more preferably 10.0 or 11.0.

[0066] In the optical system OL according to this embodiment, it is preferable that the first lens group G1 has one or two positive lenses on the object side of the largest air gap on the optical axis within the first lens group G1. If one positive lens is included, it is more preferable that the positive lens has an aspherical surface. This configuration makes it possible to effectively correct spherical aberration while keeping the optical system OL compact.

[0067] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (13).

[0068] dL1L2 / TL < 0.080 (13) however, dL1L2: the distance on the optical axis from the lens surface closest to the object in the optical system OL to the lens surface closest to the image plane in the lens group located closer to the object than the largest air gap in the first lens group G1 TL: Total length of optical system OL when focused at infinity

[0069] Conditional expression (13) defines the ratio of the distance on the optical axis from the lens surface of optical system OL closest to the object to the lens surface closest to the image plane of the lens group located closer to the object than the largest air gap in first lens group G1 to the total length of optical system OL when focused at infinity. By satisfying conditional expression (13), optical system OL can be made compact while still providing good correction for spherical aberration. In order to ensure the effect of conditional expression (13), it is more desirable to set the upper limit of conditional expression (13) to 0.075.

[0070] Furthermore, it is desirable that the optical system OL according to this embodiment has an aperture stop S on the object side of the second lens group G2. By configuring it in this way, it is possible to maintain good curvature of field of the optical system OL at close distances.

[0071] Furthermore, it is desirable that the optical system OL according to this embodiment has an aperture stop S on the image plane side of the second lens group G2. By configuring it in this way, it is possible to maintain good spherical aberration of the optical system OL at close distances.

[0072] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (14).

[0073] θgFp1 + 0.00316×νdp1 > 0.706 (14) however, θgFp1: partial dispersion ratio of the positive lens medium in the first lens group G1 that has the smallest Abbe number for the d-line of the medium νdp1: Abbe number of the positive lens in the first lens group G1 that has the smallest Abbe number for the d-line of the medium

[0074] Conditional expression (14) defines the relationship between the partial dispersion ratio and the Abbe number of the positive lens medium having the smallest Abbe number at the d-line of the positive lens medium included in the first lens group G1. By satisfying conditional expression (14), the axial chromatic aberration and lateral chromatic aberration of the optical system OL can be corrected well. In order to ensure the effect of conditional expression (14), it is more desirable to set the lower limit of conditional expression (14) to 0.708, and more preferably to 0.710, 0.712, 0.714, or 0.716.

[0075] In the optical system OL according to this embodiment, it is desirable that the lens located on the object side of the largest air gap on the optical axis in the first lens group G1 consists of a single positive lens. By configuring it in this way, the weight of the entire optical system OL can be reduced.

[0076] In addition, in the optical system OL according to this embodiment, it is desirable that the second lens group G2 have negative refractive power. This configuration allows the weight of the second lens group G2, which is the focusing group, to be reduced. It also makes it easier to increase the image plane sensitivity of the optical system OL, achieving both good close-range performance and a short overall length.

[0077] In the optical system OL according to this embodiment, it is desirable that the rear group GR include a lens group that moves during focusing. This configuration makes it possible to suppress fluctuations in axial chromatic aberration when the optical system OL is focused at infinity and when it is focused at close distances.

[0078] In the optical system OL according to this embodiment, the rear group GR preferably comprises, in order from the object side, a third lens group G3, a fourth lens group G4 that moves during focusing, and a fifth lens group G5. This configuration makes it possible to suppress fluctuations in axial chromatic aberration when the optical system OL is focused at infinity and when it is focused at close distances.

[0079] Moreover, it is desirable that the optical system OL according to this embodiment satisfies the following conditional expression (15).

[0080] ndp1 < 1.810 (15) however, ndp1: refractive index at the d-line of the positive lens medium in the first lens group G1 that has the smallest Abbe number at the d-line of the medium

[0081] Conditional expression (15) defines the refractive index of the positive lens medium in the first lens group G1 that has the smallest Abbe number for the d-line. By satisfying conditional expression (15), the Petzval sum of the optical system OL can be set to an appropriate value, thereby achieving both a compact and lightweight optical system OL and satisfactory correction of field curvature. Exceeding the upper limit of conditional expression (15) is undesirable because it is not possible to achieve both satisfactory correction of field curvature and coma. To ensure the effect of conditional expression (15), it is more desirable to set the upper limit of conditional expression (15) to 1.800.

[0082] It should be noted that the conditions and configurations described above each exert the effects described above, and are not limited to those that satisfy all of the conditions and configurations; the effects described above can be obtained by satisfying any one of the conditions or configurations, or a combination of any one of the conditions or configurations.

[0083] Next, a camera, which is an optical device equipped with the optical system OL according to this embodiment, will be described with reference to FIG. 17. This camera 1 is a so-called mirrorless camera with interchangeable lenses that includes the optical system OL according to this embodiment as a photographing lens 2. In this camera 1, light from an object (subject) (not shown) is collected by the photographing lens 2 and forms a subject image on the imaging surface of the imaging unit 3 via an OLPF (Optical low pass filter) (not shown). The subject image is then photoelectrically converted by a photoelectric conversion element provided in the imaging unit 3 to generate an image of the subject. This image is displayed on an EVF (Electronic View Finder) 4 provided in the camera 1. This allows the photographer to observe the subject through the EVF 4.

[0084] Furthermore, when the photographer presses a release button (not shown), an image photoelectrically converted by the imaging unit 3 is stored in a memory (not shown). In this way, the photographer can photograph a subject using this camera 1. Note that although an example of a mirrorless camera has been described in this embodiment, the same effects as those of the camera 1 can be achieved even when the optical system OL according to this embodiment is mounted on a single-lens reflex camera that has a quick-return mirror in the camera body and observes a subject through a viewfinder optical system.

[0085] The following contents can be appropriately adopted within the scope that does not impair the optical performance.

[0086] In this embodiment, an optical system OL having a three-group or five-group configuration is shown, but the above-described configuration conditions can also be applied to other group configurations, such as four-group, six-group, or seven-group configurations. Furthermore, a configuration in which a lens or lens group is added closest to the object, or a configuration in which a lens or lens group is added closest to the image plane, may also be used. Specifically, a configuration in which a lens group whose position relative to the image plane is fixed during zooming or focusing is added closest to the image plane, may be considered. Furthermore, a lens group refers to a portion having at least one lens separated by an air gap that changes during zooming or focusing. Furthermore, a lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

[0087] Alternatively, a single or multiple lens groups, or a partial lens group, may be moved in the optical axis direction to function as a focusing lens group that focuses from an object at infinity to an object at close range. In this case, the focusing lens group can be used for autofocusing and is suitable for driving a motor (such as an ultrasonic motor) for autofocusing. In particular, it is preferable to use at least a portion of the second lens group G2 as a focusing lens group, with the remaining lenses fixed in position relative to the image plane during focusing. Considering the load on the motor, it is preferable for the focusing lens group to be composed of a single lens.

[0088] Alternatively, a lens group or a partial lens group may be moved so as to have a displacement component perpendicular to the optical axis, or rotated (oscillated) in a plane including the optical axis to serve as an image stabilization lens group that corrects image blur caused by camera shake. In particular, it is preferable to use at least a portion of the third lens group G3 as an image stabilization lens group.

[0089] The lens surface may be spherical, flat, or aspherical. A spherical or flat lens surface is preferable because it facilitates lens processing and assembly adjustment and prevents degradation of optical performance due to errors in processing and assembly adjustment. It is also preferable because degradation of imaging performance is minimal even when the image plane is misaligned. If the lens surface is aspherical, the aspherical surface may be any of the following aspherical surfaces: a ground aspherical surface, a glass-molded aspherical surface in which glass is molded into an aspherical shape, or a hybrid aspherical surface in which a resin is molded into an aspherical shape on the surface of glass. The lens surface may also be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

[0090] The aperture stop S is preferably disposed on the object side or image plane side of the second lens group G2, but it is also possible to use the lens frame to fulfill that role instead of providing a member as an aperture stop.

[0091] Furthermore, each lens surface may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high contrast and high optical performance.

[0092] An outline of a manufacturing method for the optical system OL according to this embodiment will be described below with reference to FIG. 18. First, a first lens group G1 having a diffractive optical element, a second lens group G2 that moves during focusing, and a rear group GR having at least one lens group are prepared (Step S100). Next, a positive lens is arranged closest to the object in the first lens group G1 (Step S200). Then, the positive lens is arranged so as to satisfy the condition defined by the above-mentioned predetermined conditional expression (for example, conditional expression (1)) (Step S300).

[0093] With the above-described configuration, it is possible to provide an optical system and an optical device with good imaging performance. [Example]

[0094] Each embodiment of the present invention will be described below with reference to the drawings, in which Figures 1, 3, 5, 7, 9, 11, 13, and 15 are cross-sectional views showing the configurations and refractive power distributions of optical systems (OL1 to OL8) according to first to eighth embodiments.

[0095] In each embodiment, the phase shape ψ of the diffractive optical surface of the diffractive optical element Lpf is expressed by the following equation (b).

[0096] ψ(h,n) =(2π / (n×λ0))×(C2h 2 +C4h 4 ) (b) however, h: Height perpendicular to the optical axis n: order of diffracted light λ0: Design wavelength Ci: Phase coefficient (i=2,4)

[0097] Furthermore, the refractive power φD of the diffractive optical surface expressed by equation (b) for an arbitrary wavelength λ and an arbitrary diffraction order n is expressed as the following equation (c) using the lowest-order phase coefficient C2.

[0098] φD(λ,n) = -2×C2×n×λ / λ0 (c)

[0099] In the tables of each example, diffractive optical surfaces are marked with a # symbol to the right of the surface number.

[0100] In the eighth embodiment, the aspherical surface is expressed by the following equation (d), where y is the height in the direction perpendicular to the optical axis, S(y) is the distance along the optical axis from the tangent plane of the vertex of each aspherical surface at height y to each aspherical surface (amount of sag), r is the radius of curvature of the reference spherical surface (paraxial radius of curvature), K is the conic constant, and An is the n-th order aspherical coefficient.

[0101] S(y)=(y 2 / r) / {1+(1-K×y 2 / r 2 ) 1 / 2} +A4×y 4 +A6×y 6 +A8×y 8 +A10×y 10 (d)

[0102] Here, in each example, the second-order aspherical coefficient A2 is 0. In the table for the eighth example, aspherical surfaces are marked with an * to the right of the surface number.

[0103] In each example, "En" is "×10 -n " indicates.

[0104] Furthermore, the following examples show specific examples of the present invention, and the present invention is not limited to these examples.

[0105] [First Example] 1 shows the configuration of an optical system OL1 according to Example 1. This optical system OL1 is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear lens group GL having negative refractive power. The rear lens group GL is also composed of a third lens group G3.

[0106] The first lens group G1 is composed of, in order from the object side, a positive meniscus lens L11 with a convex surface facing the object side, a positive meniscus lens L12 with a convex surface facing the object side, a diffractive optical element Lpf with a PF element Epf provided on the image-plane side lens surface of the positive meniscus lens L13 with a convex surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L14 and a biconcave negative lens L15, a positive meniscus lens L16 with a convex surface facing the object side, and a cemented lens formed by cementing a biconcave negative lens L17 and a biconvex positive lens L18. The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of, from the object side, a cemented lens formed by cementing a biconvex positive lens L31 and a negative meniscus lens L32 having a concave surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L33 and a biconcave negative lens L34, a biconcave negative lens L35, a cemented lens formed by cementing a biconvex positive lens L36 and a biconcave negative lens L37, a cemented lens formed by cementing a negative meniscus lens L38 having a convex surface facing the object side and a positive meniscus lens L39 having a convex surface facing the object side, and a cemented lens formed by cementing a biconvex positive lens L310 and a negative meniscus lens L311 having a concave surface facing the object side. The aperture stop S is disposed on the object side of the second lens group G2 (between the first lens group G1 and the second lens group G2). Of the positive lenses included in the first lens group G1, the positive lens having the smallest Abbe number for the d-line of the medium is the biconvex positive lens L18.

[0107] The PF element Epf of the diffractive optical element Lpf has two diffractive element elements made of different optical materials, and these two diffractive element elements are bonded to each other, with a diffractive optical surface being formed on the bonded surface of the diffractive element elements (the same applies to the following examples).

[0108] In this optical system OL1, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the image plane.

[0109] Table 1 below lists the specifications of optical system OL1. In Table 1, f denotes the focal length of the entire optical system OL1, FNO denotes the F-number, ω denotes the half angle of view [°], Y denotes the maximum image height, TL denotes the overall length, and BF denotes the back focus. Here, the overall length TL denotes the optical axial distance (actual distance) from the lens surface closest to the object (surface No. 1) to the image plane I when focused at infinity. The back focus BF denotes the optical axial distance (air-equivalent length) from the lens surface closest to the image plane (surface No. 36) to the image plane I when focused at infinity. In the lens data, column m denotes the order of the lens surfaces from the object side along the direction of light ray travel (surface number), column r denotes the radius of curvature of each lens surface, column d denotes the optical axial distance (surface spacing) from each optical surface to the next optical surface, and columns nd and vd denote the refractive index and Abbe number for the d-line (λ=587.6 nm). A radius of curvature of 0.0000 indicates a flat surface, and the refractive index of air, 1.000000, is omitted. The lens group focal length indicates the surface number and focal length of the first surface of each lens group.

[0110] Here, the focal length f, radius of curvature r, surface spacing d, and other length units listed in the following specifications are generally in millimeters, but this is not a limitation because the optical system can achieve the same optical performance even when proportionally enlarged or reduced. The explanations of these symbols and specifications tables also apply to the following examples.

[0111] (Table 1) First Example [Overall specifications] f = 585.0002 FNO = 5.7100 ω[°]= 2.10557 Y = 21.6 TL = 309.4549 BF = 95.6894 [Lens data] mrd nd νd object surface ∞ 1 198.3492 8.5332 1.487490 70.32 2 1056.3396 0.2000 3 97.9481 13.9490 1.487490 70.32 4 411.8100 37.8970 5 116.0369 7.0000 1.516800 64.13 6 131.4346 0.2000 1.529500 36.27 7# 131.4346 0.3000 1.549800 50.91 8 131.4346 5.0000 9 65.7068 9.3004 1.487490 70.32 10 -2050.4055 2.3000 1.903660 31.27 11 61.4265 2.0000 12 85.9524 5.7962 1.497820 82.57 13 486.7361 20.4814 14 -118.7660 2.0000 1.950000 29.37 15 70.1339 7.4700 1.755750 24.71 16 -82.2312 4.0746 17 0.0000 d1 Aperture Stop S 18 150.0827 1.2000 1.487490 70.32 19 55.8583 d2 20 530.3423 2.8063 1.575010 41.51 21 -89.2692 1.2000 2.001000 29.12 22 -204.0519 3.0000 23 103.1226 5.4513 1.672700 32.18 24 -48.5264 1.2000 1.497820 82.57 25 56.1112 4.6753 26 -74.6931 1.2000 1.696800 55.52 27 53.4710 3.0000 28 38.0170 10.0000 1.603420 38.03 29 -30.9083 1.2000 1.497820 82.57 30 68.5697 2.4552 31 1018.2057 1.2000 1.772500 49.62 32 31.3787 5.0191 1.603420 38.03 33 1387.8678 0.2000 34 54.4867 8.3630 1.603420 38.03 35 -26.8376 1.2000 1.922860 20.88 36 -169.6934 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 205.9 Second lens group G2 18 -183.3 Third lens group G3 20 -147.5

[0112] In this optical system OL1, the seventh surface is a diffractive optical surface. Table 2 below shows the diffractive optical surface data, that is, the design wavelength λ0, the order n, and the values of each of the phase coefficients C2 and C4.

[0113] (Table 2) [Diffractive optical surface data] m λ0 n C2 C4 7 587.6 1.0 -4.96241E-05 1.65424E-09

[0114] In this optical system OL1, the axial air distance d0 between the object and the first lens group G1, the axial air distance d1 between the first lens group G1 and the aperture stop S, and the axial air distance d2 between the second lens group G2 and the third lens group G3 change during focusing. Table 3 below shows the variable distances during focusing at infinity and during close distance focusing. Note that d0 indicates the distance from the surface (first surface) of the optical system OL1 closest to the object to the object, f indicates the focal length, β indicates the magnification, and BF indicates the back focus. These explanations also apply to the following examples.

[0115] (Table 3) [Variable Interval Data] Focused state Infinity Close distance f 585.00017 - β - -0.18866 d0 ∞ 3090.5451 d1 4.00000 29.28428 d2 44.58471 4.60934 BF 95.68940 95.6894

[0116] FIG. 2 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this optical system OL1 when focused at infinity and at close distances. In each diagram, FNO represents the F-number, NA represents the numerical aperture, and Y represents the image height. Note that in the spherical aberration diagram, the F-number or numerical aperture value corresponding to the maximum aperture is shown, while in the astigmatism and distortion diagrams, the maximum image height is shown, and in the coma diagram, the value of each image height is shown. d represents the d-line (λ=587.6 nm), and g represents the g-line (λ=435.8 nm). In the astigmatism diagram, the solid line represents the sagittal image plane, and the dashed line represents the meridional image plane. The same symbols as in this embodiment are used in the aberration diagrams for each embodiment shown below. These aberration diagrams demonstrate that this optical system OL1 effectively corrects various aberrations.

[0117] [Second Example] 3 shows the configuration of an optical system OL2 according to Example 2. This optical system OL2 is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear lens group GL having negative refractive power. The rear lens group GL is also composed of a third lens group G3.

[0118] The first lens group G1 is composed of, in order from the object side, a biconvex positive lens L11, a positive meniscus lens L12 with a convex surface facing the object side, a diffractive optical element Lpf with a PF element Epf provided on the image-plane side lens surface of the positive meniscus lens L13 with a convex surface facing the object side, a cemented lens formed by cementing a positive meniscus lens L14 with a convex surface facing the object side and a negative meniscus lens L15 with a convex surface facing the object side, a positive meniscus lens L16 with a convex surface facing the object side, and a cemented lens formed by cementing a negative meniscus lens L17 with a convex surface facing the object side and a positive meniscus lens L18 with a convex surface facing the object side. The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of, in order from the object side, a cemented lens formed by cementing a positive meniscus lens L31 having a concave surface facing the object side to a negative meniscus lens L32 having a concave surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L33 to a biconcave negative lens L34, a biconcave negative lens L35, a cemented lens formed by cementing a biconvex positive lens L36 to a biconcave negative lens L37, a cemented lens formed by cementing a biconcave negative lens L38 to a biconvex positive lens L39, and a cemented lens formed by cementing a biconvex positive lens L310 to a negative meniscus lens L311 having a concave surface facing the object side. The aperture stop S is disposed on the object side of the second lens group G2 (between the first lens group G1 and the second lens group G2). Of the positive lenses included in the first lens group G1, the positive lens having the smallest Abbe number for the d-line of the medium is the positive meniscus lens L18.

[0119] In this optical system OL2, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the image plane.

[0120] Table 4 below lists the specifications of the optical system OL2.

[0121] (Table 4) Second Example [Overall specifications] f = 585.00008 FNO = 5.7100 ω[°]= 2.08967 Y = 21.6 TL = 311.4549 BF = 74.44520 [Lens data] mrd nd νd object surface ∞ 1 256.7991 8.0000 1.487490 70.32 2 -10718.8210 0.2000 3 126.8427 9.0000 1.487490 70.32 4 304.0593 46.3492 5 104.9091 7.0000 1.516800 64.13 6 165.7799 0.2000 1.529500 36.27 7# 165.7799 0.3000 1.549800 50.91 8 165.7799 5.0000 9 77.8329 7.7320 1.487490 70.32 10 186.6794 2.3000 1.903660 31.27 11 60.4528 2.0000 12 55.5648 8.9778 1.518600 69.89 13 180.2474 36.1145 14 503.2004 2.0000 1.902650 35.77 15 34.5282 5.8266 1.663820 27.35 16 14816.1980 4.0000 17 0.0000 d1 Aperture Stop S 18 200.8922 1.2000 1.497820 82.57 19 50.2042 d2 20 -236.9030 3.1882 1.575010 41.51 21 -41.3579 1.2000 2.001000 29.12 22 -71.0261 3.0000 23 94.0731 4.5855 1.717360 29.57 24 -59.5874 1.2000 1.593190 67.90 25 55.9640 4.0002 26 -102.2571 1.2000 1.772500 49.62 27 69.6362 4.8061 28 33.5531 9.8502 1.595510 39.21 29 -29.3690 1.2000 1.497820 82.57 30 56.6631 3.3836 31 -251.0099 1.2000 1.883000 40.69 32 29.4179 5.6817 1.620040 36.40 33 -962.9336 0.2000 34 67.6496 10.2804 1.737999 32.33 35 -21.7365 1.2000 1.922860 20.88 36 -108.3418 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 217.2 Second lens group G2 18 -134.8 Third lens group G3 20 -233.5

[0122] In this optical system OL2, the seventh surface is a diffractive optical surface. Table 5 below shows the diffractive optical surface data, that is, the design wavelength λ0, the order n, and the values of each phase coefficient C2 and C4.

[0123] (Table 5) [Diffractive optical surface data] m λ0 n C2 C4 7 587.6 1.0 -4.55065E-05 6.56102E-11

[0124] In this optical system OL2, the axial air distance d0 between the object and the first lens group G1, the axial air distance d1 between the first lens group G1 and the aperture stop S, and the axial air distance d2 between the second lens group G2 and the third lens group G3 change during focusing. Table 6 below shows the variable distances when focusing at infinity and when focusing at close range.

[0125] (Table 6) [Variable Interval Data] Focused state Infinity Close distance f 585.00008 - β - -0.18912 d0 ∞ 3088.5451 d1 4.00000 29.76301 d2 30.63380 4.87079 BF 74.44520 74.44520

[0126] Fig. 4 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this optical system OL2 when focused at infinity and when focused at close distances. These diagrams show that various aberrations are well corrected for in this optical system OL2.

[0127] [Third Example] 5 shows the configuration of an optical system OL3 according to Example 3. This optical system OL3 is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear lens group GL having negative refractive power. The rear lens group GL is also composed of a third lens group G3.

[0128] The first lens group G1 is composed of, in order from the object side, a biconvex positive lens L11, a positive meniscus lens L12 with a convex surface facing the object side, a diffractive optical element Lpf with a PF element Epf provided on the image-plane side lens surface of the positive meniscus lens L13 with a convex surface facing the object side, a cemented lens formed by cementing a negative meniscus lens L14 with a convex surface facing the object side and a biconvex positive lens L15, a cemented lens formed by cementing a biconvex positive lens L16 and a biconcave negative lens L17, and a cemented lens formed by cementing a biconcave negative lens L18 and a biconvex positive lens L19. The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of, in order from the object side, a cemented lens formed by cementing a negative meniscus lens L31 having a convex surface facing the object side and a biconvex positive lens L32, a biconcave negative lens L33, a cemented lens formed by cementing a biconcave negative lens L34 and a biconvex positive lens L35, a cemented lens formed by cementing a biconvex positive lens L36 and a biconcave negative lens L37, a cemented lens formed by cementing a biconvex positive lens L38, a biconcave negative lens L39 and a positive meniscus lens L310 having a convex surface facing the object side, and a cemented lens formed by cementing a biconvex positive lens L311 and a negative meniscus lens L312 having a concave surface facing the object side. An aperture stop S is disposed on the image side of the second lens group G2 (between the second lens group G2 and the third lens group G3). Of the positive lenses included in the first lens group G1, the positive lens having the smallest Abbe number for the d-line of the medium is the biconvex positive lens L19.

[0129] In this optical system OL3, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the image plane.

[0130] Table 7 below lists the specifications of the optical system OL3.

[0131] (Table 7) Third Example [Overall specifications] f = 999.99972 FNO = 8.1600 ω[°]= 1.22886 Y = 21.6 TL = 419.0888 BF = 84.30629 [Lens data] mrd nd νd object surface ∞ 1 268.7128 10.8775 1.487490 70.32 2 -2672.1391 0.2000 3 116.5428 14.0606 1.487490 70.32 4 322.3537 58.1581 5 130.0360 7.0000 1.516800 64.13 6 142.9490 0.2000 1.529500 36.27 7# 142.9490 0.3000 1.549800 50.91 8 142.9490 13.9998 9 221.0597 2.8967 1.850260 32.35 10 66.9470 10.0000 1.487490 70.32 11 -10794.8470 2.5000 12 73.9911 10.6970 1.487490 70.32 13 -286.5976 1.6241 1.834000 37.18 14 97.1167 26.7475 15 -20459.2230 2.5058 1.902650 35.77 16 63.1106 5.5966 1.808090 22.74 17 -966.5886 d1 18 446.8149 1.2000 1.487490 70.32 19 94.2997 d2 20 0.0000 30.0896 Aperture Stop S 21 1180.5271 1.2000 1.883000 40.69 22 39.2566 3.1265 1.720467 34.71 23 -163.6972 3.4467 24 -219.7919 1.2000 1.593190 67.90 25 38.7994 4.2256 26 -97.9560 1.2000 1.593190 67.90 27 33.0021 4.4839 1.717360 29.57 28 -1429.3587 3.2000 29 31.1058 7.4309 1.567320 42.58 30 -89.4330 1.5069 1.883000 40.69 31 817.9183 10.2551 32 81.6733 5.6315 1.737999 32.33 33 -34.7206 2.0000 1.883000 40.69 34 23.5273 3.6692 1.654115 39.68 35 45.4280 5.0000 36 48.4921 9.6222 1.737999 32.33 37 -25.9571 2.0000 1.945944 17.98 38 -135.4658 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 320.7 Second lens group G2 18 -245.5 Third lens group G3 20 -160.6

[0132] In this optical system OL3, the seventh surface is a diffractive optical surface. Table 8 below shows the diffractive optical surface data, that is, the design wavelength λ0, the order n, and the values of each of the phase coefficients C2 and C4.

[0133] (Table 8) [Diffractive optical surface data] m λ0 n C2 C4 7 587.6 1.0 -4.38195E-05 -5.85224E-10

[0134] In this optical system OL3, the axial air distance d0 between the object and the first lens group G1, the axial air distance d1 between the first lens group G1 and the second lens group G2, and the axial air distance d2 between the second lens group G2 and the aperture stop S change during focusing. Table 9 below shows the variable distances when focusing at infinity and when focusing at close range.

[0135] (Table 9) [Variable Interval Data] Focused state Infinity Close distance f 999.99972 - β - -0.1330 d0 ∞ 7580.9112 d1 8.57559 32.49421 d2 58.35509 34.43646 BF 84.30629 84.30629

[0136] Fig. 6 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this optical system OL3 when focused at infinity and when focused at close distances. These diagrams show that various aberrations are well corrected for in this optical system OL3.

[0137] [Fourth Example] 7 shows the configuration of an optical system OL4 according to Example 4. This optical system OL4 is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear lens group GL having negative refractive power. The rear lens group GL is also composed of a third lens group G3.

[0138] The first lens group G1 is composed of, in order from the object side, a biconvex positive lens L11, a positive meniscus lens L12 with a convex surface facing the object side, a diffractive optical element Lpf with a PF element Epf provided on the image-plane side lens surface of the positive meniscus lens L13 with a convex surface facing the object side, a cemented lens formed by cementing a positive meniscus lens L14 with a convex surface facing the object side and a negative meniscus lens L15 with a convex surface facing the object side, a positive meniscus lens L16 with a convex surface facing the object side, and a cemented lens formed by cementing a biconcave negative lens L17 and a biconvex positive lens L18. The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of, in order from the object side, a cemented lens formed by cementing a biconcave negative lens L31 and a biconvex positive lens L32, a biconcave negative lens L33, a cemented lens formed by cementing a biconcave negative lens L34 and a biconvex positive lens L35, a cemented lens formed by cementing a biconvex positive lens L36 and a biconcave negative lens L37, a cemented lens formed by cementing a biconcave negative lens L38 and a biconvex positive lens L39, a cemented lens formed by cementing a biconvex positive lens L310 and a biconcave negative lens L311, and a cemented lens formed by cementing a biconvex positive lens L312 and a biconcave negative lens L313. An aperture stop S is disposed on the image side of the second lens group G2 (between the second lens group G2 and the third lens group G3). Of the positive lenses included in the first lens group G1, the positive lens with the smallest Abbe number for the d-line of the medium is the biconvex positive lens L18.

[0139] In this optical system OL4, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the image plane.

[0140] Table 10 below lists the specifications of the optical system OL4.

[0141] (Table 10) Fourth Example [Overall specifications] f = 999.96318 FNO = 8.1600 ω[°]= 1.22353 Y = 21.6 TL = 419.4549 BF = 94.37907 [Lens data] mrd nd νd object surface ∞ 1 519.3503 8.3069 1.487490 70.32 2 -1148.6620 0.2000 3 127.9584 13.3914 1.487490 70.32 4 344.4064 79.0796 5 114.2251 7.0000 1.516800 64.13 6 154.1141 0.1000 1.529500 36.27 7# 154.1141 0.2500 1.549800 50.91 8 154.1141 10.6237 9 91.6865 10.0000 1.487490 70.32 10 2798.7715 2.3000 1.903660 31.27 11 65.1594 2.0000 12 67.6949 9.0709 1.487490 70.32 13 780.3038 23.6453 14 -196.7990 1.2000 1.732110 46.18 15 109.6535 5.7885 1.663820 27.35 16 -175.2636 d1 17 504.3668 1.2000 1.487490 70.32 18 92.7728 d2 19 0.0000 13.8858 Aperture Stop S 20 -130.6366 1.2000 2.001000 29.12 21 47.2332 3.1612 1.730371 32.23 22 -71.5789 3.4144 23 -236.3231 1.2000 1.772500 49.62 24 49.6984 2.9728 25 -115.6087 1.2000 1.593190 67.90 26 41.3816 3.4871 1.795040 28.69 27 -612.0200 3.2000 28 30.5076 6.1577 1.612660 44.46 29 -37.3580 1.2000 1.593190 67.90 30 218.9654 3.0689 31 -326.2570 1.8000 1.953750 32.33 32 24.8675 5.2938 1.612930 36.94 33 -90.5368 14.8971 34 85.0536 5.7888 1.730371 32.23 35 -32.6053 1.8000 1.772500 49.62 36 34.9782 1.0342 37 36.9993 7.5539 1.850000 27.03 38 -35.3416 1.8000 1.945944 17.98 39 154.0811 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 256.6 Second lens group G2 17 -233.4 Third lens group G3 19 -91.6

[0142] In this optical system OL4, the seventh surface is a diffractive optical surface. Table 11 below shows the diffractive optical surface data, that is, the design wavelength λ0, the order n, and the values of each phase coefficient C2 and C4.

[0143] (Table 11) [Diffractive optical surface data] m λ0 n C2 C4 7 587.6 1.0 -4.47066E-05 -2.42983E-10

[0144] In this optical system OL4, the axial air distance d0 between the object and the first lens group G1, the axial air distance d1 between the first lens group G1 and the second lens group G2, and the axial air distance d2 between the second lens group G2 and the aperture stop S change during focusing. Table 12 below shows the variable distances when focusing at infinity and when focusing at close range.

[0145] (Table 12) [Variable Interval Data] Focused state Infinity Close distance f 999.99979 - β - -0.13123 d0 ∞ 7580.5451 d1 8.69620 24.48434 d2 58.10735 42.31921 BF 94.37907 94.37907

[0146] Fig. 8 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this optical system OL4 when focused at infinity and when focused at close distances. These diagrams show that various aberrations are well corrected for in this optical system OL4.

[0147] [Fifth Example] 9 shows the configuration of an optical system OL5 according to Example 5. This optical system OL5 is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear lens group GL having negative refractive power. The rear lens group GL is also composed of a third lens group G3.

[0148] The first lens group G1 is composed of, in order from the object side, a positive meniscus lens L11 with a convex surface facing the object side, a positive meniscus lens L12 with a convex surface facing the object side, a diffractive optical element Lpf with a PF element Epf provided on the image-plane side lens surface of the positive meniscus lens L13 with a convex surface facing the object side, a cemented lens formed by cementing a negative meniscus lens L14 with a convex surface facing the object side and a biconvex positive lens L15, a cemented lens formed by cementing a biconvex positive lens L16 and a biconcave negative lens L17, and a cemented lens formed by cementing a biconcave negative lens L18 and a biconvex positive lens L19. The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of, from the object side, a cemented lens formed by cementing a biconcave negative lens L31 and a biconvex positive lens L32, a biconcave negative lens L33, a cemented lens formed by cementing a biconcave negative lens L34 and a biconvex positive lens L35, a cemented lens formed by cementing a biconvex positive lens L36 and a negative meniscus lens L37 having a concave surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L38 and a biconcave negative lens L39, a biconvex positive lens L310, and a cemented lens formed by cementing a positive meniscus lens L311 having a concave surface facing the object side and a negative meniscus lens L312 having a concave surface facing the object side. An aperture stop S is disposed on the image side of the second lens group G2 (between the second lens group G2 and the third lens group G3). Of the positive lenses included in the first lens group G1, the positive lens having the smallest Abbe number for the d-line of the medium is the biconvex positive lens L19.

[0149] In this optical system OL5, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the image plane.

[0150] Table 13 below lists the specifications of the optical system OL5.

[0151] (Table 13) Fifth Example [Overall specifications] f = 779.93334 FNO = 6.4201 ω[°]= 1.56305 Y = 21.6 TL = 393.4548 BF = 63.44872 [Lens data] mrd nd νd object surface ∞ 1 228.0072 10.6000 1.487490 70.32 2 3048.3506 0.2000 3 118.0101 15.0000 1.437001 95.10 4 443.8711 66.0687 5 130.0360 7.0000 1.516800 64.13 6 142.9490 0.2000 1.529500 36.27 7# 142.9490 0.3000 1.549800 50.91 8 142.9490 9.1685 9 306.0027 2.2000 1.834000 37.18 10 63.6978 11.7000 1.518600 69.89 11 -951.1005 3.0000 12 95.7831 9.4000 1.518600 69.89 13 -169.4233 2.2000 1.834000 37.18 14 157.8539 28.9675 15 -307.2847 2.1000 1.804000 46.60 16 104.5358 4.5000 1.805180 25.45 17 -292.1429 d1 18 2622.8877 1.2000 1.497820 82.57 19 78.5937 d2 20 0.0000 6.1329 Aperture Stop S 21 -3223.9611 3.0000 1.883000 40.69 22 38.4921 4.1000 1.720467 34.71 23 -105.4185 3.4242 24 -258.2146 1.2000 1.593190 67.90 25 42.3067 4.2000 26 -81.0825 1.2000 1.593190 67.90 27 38.5510 4.4000 1.717360 29.57 28 -735.4086 3.2000 29 39.2389 7.9000 1.552981 55.07 30 -57.5685 3.0000 1.805180 25.45 31 -272.9721 19.7309 32 63.7192 8.0000 1.737999 32.33 33 -36.6300 2.5000 1.883000 40.69 34 34.0088 2.0000 35 37.8029 7.3000 1.654115 39.68 36 -183.6449 10.0000 37 -114.0641 6.1000 1.737999 32.33 38 -30.0300 2.6000 1.922860 20.88 39 -148.7894 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 265.9 Second lens group G2 18 -162.8 Third lens group G3 20 -195.1

[0152] In this optical system OL5, the seventh surface is a diffractive optical surface. Table 14 below shows the diffractive optical surface data, that is, the design wavelength λ0, the order n, and the values of each of the phase coefficients C2 and C4.

[0153] (Table 14) [Diffractive optical surface data] m λ0 n C2 C4 7 587.6 1.0 -3.93586E-05 -5.57153E-10

[0154] In this optical system OL5, the axial air distance d0 between the object and the first lens group G1, the axial air distance d1 between the first lens group G1 and the second lens group G2, and the axial air distance d2 between the second lens group G2 and the aperture stop S change during focusing. Table 15 below shows the variable distances when focusing at infinity and when focusing at close range.

[0155] (Table 15) [Variable Interval Data] Focused state Infinity Close distance f 779.93334 - β - -0.16874 d0 ∞ 4606.5452 d1 6.00000 29.93769 d2 50.19530 26.25760 BF 63.44872 63.44872

[0156] Fig. 10 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this optical system OL5 when focused at infinity and when focused at close distances. These diagrams show that various aberrations are well corrected for in this optical system OL5.

[0157] [Sixth Example] 11 shows the configuration of an optical system OL6 according to Example 6. This optical system OL6 is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear lens group GL having negative refractive power. The rear lens group GL is also composed of a third lens group G3.

[0158] The first lens group G1 is composed of, in order from the object side, a biconvex positive lens L11, a positive meniscus lens L12 with a convex surface facing the object side, a diffractive optical element Lpf with a PF element Epf provided on the image-plane side lens surface of the positive meniscus lens L13 with a convex surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L14 and a biconcave negative lens L15, a positive meniscus lens L16 with a convex surface facing the object side, and a cemented lens formed by cementing a biconcave negative lens L17 and a biconvex positive lens L18. The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of, from the object side, a cemented lens formed by cementing a biconcave negative lens L31 and a biconvex positive lens L32, a biconcave negative lens L33, a cemented lens formed by cementing a biconcave negative lens L34 and a positive meniscus lens L35 with its convex surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L36 and a biconcave negative lens L37, a cemented lens formed by cementing a biconcave negative lens L38 and a biconvex positive lens L39, a cemented lens formed by cementing a biconvex positive lens L310 and a biconcave negative lens L311, and a cemented lens formed by cementing a biconvex positive lens L312 and a biconcave negative lens L313. An aperture stop S is disposed on the image side of the second lens group G2 (between the second lens group G2 and the third lens group G3). Of the positive lenses included in the first lens group G1, the positive lens with the smallest Abbe number for the d-line of the medium is the biconvex positive lens L18.

[0159] In this optical system OL6, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the image plane.

[0160] The specifications of the optical system OL6 are listed below in Table 16. In the lens data shown in Table 16, the 14th surface is a virtual surface and is not shown in FIG.

[0161] (Table 16) Sixth Example [Overall specifications] f = 779.99933 FNO = 6.41999 ω[°]= 1.56363 Y = 21.6 TL = 393.4547 BF = 74.56937 [Lens data] mrd nd νd object surface ∞ 1 488.6452 7.9000 1.487490 70.32 2 -1584.8559 0.2000 3 136.4730 13.4000 1.487490 70.32 4 465.0973 89.1101 5 114.2433 7.0000 1.516800 64.13 6 154.1141 0.1000 1.529500 36.27 7# 154.1141 0.2500 1.549800 50.91 8 154.1141 5.0000 9 94.8010 8.9096 1.487490 70.32 10 -2064.0654 2.3000 1.903660 31.27 11 65.7160 2.5000 12 66.1740 9.5854 1.497820 82.57 13 2165.2785 0.0000 14 0.0000 17.5002 15 -277.4112 2.0000 1.667550 41.87 16 70.4454 7.5446 1.663820 27.35 17 -263.5468 d1 18 523.4497 1.2000 1.487490 70.32 19 94.5055 d2 20 0.0000 6.7123 Aperture S 21 -393.7363 1.2000 2.001000 29.12 22 43.8736 2.9870 1.730371 32.23 23 -94.2293 3.3713 24 -288.4503 1.2000 1.772500 49.62 25 45.6878 3.0157 26 -164.6808 1.2000 1.627496 59.24 27 35.6904 3.4759 1.795040 28.69 28 248.6215 3.4478 29 33.0750 7.7564 1.612660 44.46 30 -36.1356 1.8000 1.593190 67.90 31 720.1003 3.0000 32 -89.4524 1.8000 1.953750 32.33 33 33.3333 6.2498 1.612930 36.94 34 -55.1763 4.5000 35 59.9212 6.8358 1.730371 32.23 36 -36.3245 1.8000 1.772500 49.62 37 33.3333 3.0000 38 39.9579 10.7333 1.850000 27.03 39 -35.6438 1.8000 1.945944 17.98 40 166.9500 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 237.1 Second lens group G2 18 -236.8 Third lens group G3 20 -105.9

[0162] In this optical system OL6, the seventh surface is a diffractive optical surface. Table 17 below shows the diffractive optical surface data, that is, the design wavelength λ0, the order n, and the values of each of the phase coefficients C2 and C4.

[0163] (Table 17) [Diffractive optical surface data] m λ0 n C2 C4 7 587.6 1.0 -4.02091E-05 -2.29061E-10

[0164] In this optical system OL6, the axial air distance d0 between the object and the first lens group G1, the axial air distance d1 between the first lens group G1 and the second lens group G2, and the axial air distance d2 between the second lens group G2 and the aperture stop S change during focusing. Table 18 below shows the variable distances when focusing at infinity and when focusing at close range.

[0165] (Table 18) [Variable Interval Data] Focused state Infinity Close distance f 779.99933 - β - -0.16674 d0 ∞ 4606.5453 d1 6.00000 29.75122 d2 62.50000 38.74878 BF 74.56937 74.56937

[0166] Fig. 12 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this optical system OL6 when focused at infinity and when focused at close distances. These diagrams show that various aberrations are well corrected for in this optical system OL6.

[0167] [Seventh Example] 13 is a diagram showing the configuration of an optical system OL7 according to Example 7. This optical system OL7 is composed of, from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear lens group GL having negative refractive power. The rear lens group GL is composed of, from the object side, a third lens group G3 having negative refractive power, a fourth lens group G4 having positive refractive power, and a fifth lens group G5 having negative refractive power.

[0168] The first lens group G1 is composed of, from the object side, a biconvex positive lens L11, a positive meniscus lens L12 with a convex surface facing the object side, a diffractive optical element Lpf with a PF element Epf provided on the image-plane-side lens surface of the positive meniscus lens L13 with a convex surface facing the object side, a cemented lens formed by cementing a negative meniscus lens L14 with a convex surface facing the object side and a positive meniscus lens L15 with a convex surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L16 and a biconcave negative lens L17, and a cemented lens formed by cementing a biconcave negative lens L18 and a biconvex positive lens L19. The second lens group G2 is composed of a negative meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of, from the object side, a cemented lens formed by cementing a biconcave negative lens L31 and a biconvex positive lens L32. The fourth lens group G4 is composed of a biconvex positive lens L41. The fifth lens group G5 is composed of a biconcave negative lens L51, a cemented lens formed by cementing a biconcave negative lens L52 and a positive meniscus lens L53 having a convex surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L54 and a negative meniscus lens L55 having a concave surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L56 and a biconcave negative lens L57, a biconvex positive lens L58, and a cemented lens formed by cementing a positive meniscus lens L59 having a concave surface facing the object side and a negative meniscus lens L510 having a concave surface facing the object side. An aperture stop S is disposed on the image side of the second lens group G2 (between the second lens group G2 and the third lens group G3). Of the positive lenses included in the first lens group G1, the positive lens having the smallest Abbe number for the d-line of the medium is the biconvex positive lens L19.

[0169] In this optical system OL7, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the image plane and moving the fourth lens group G4 toward the object.

[0170] The specifications of the optical system OL7 are listed below in Table 19. Note that the rear group GR in the lens group focal length is the value when focused at infinity.

[0171] (Table 19) Seventh Example [Overall specifications] f = 779.91908 FNO = 6.4199 ω[°]= 1.58017 Y = 21.6 TL = 393.3977 BF = 51.39765 [Lens data] mrd nd νd object surface ∞ 1 424.3476 8.3660 1.487490 70.32 2 -1652.1838 0.2000 3 105.5654 15.9140 1.437001 95.10 4 319.2044 75.8188 5 114.0000 7.0000 1.516800 64.13 6 154.0000 0.2000 1.529500 36.27 7# 154.0000 0.3000 1.549800 50.91 8 154.0000 11.0246 9 261.9525 2.2658 1.903660 31.27 10 122.0744 6.0040 1.518600 69.89 11 1366.9052 3.0060 12 76.1365 10.1384 1.518600 69.89 13 -158.3236 2.5000 1.902650 35.77 14 87.1741 32.6651 15 -122.0270 2.0000 1.816000 46.59 16 361.4186 3.4772 1.808090 22.74 17 -127.0101 d1 18 215.9032 1.2000 1.497820 82.57 19 79.3475 d2 20 0.0000 5.6136 Aperture Stop S 21 -112.9018 1.2000 1.883000 40.69 22 63.7923 3.0550 1.603420 38.03 23 -69.3917 d3 24 79.5932 2.3590 1.552981 55.07 25 -450.0840 d4 26 -1062.0041 1.2000 1.772500 49.62 27 38.6281 4.3403 28 -94.0940 1.2000 1.627496 59.24 29 37.5442 4.1672 1.808090 22.74 30 473.5817 3.3752 31 40.0000 6.1265 1.552981 55.07 32 -68.3848 1.5000 1.808090 22.74 33 -1055.9517 11.9061 34 67.5522 7.2276 1.737999 32.33 35 -44.5483 2.0000 1.883000 40.69 36 40.0000 2.1173 37 45.3449 7.0622 1.737999 32.33 38 -89.9302 15.0000 39 -54.7362 5.0820 1.788800 28.43 40 -26.7010 2.0000 1.945944 17.98 41 -103.9165 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 330.6 Second lens group G2 18 -252.7 Rear group GR 20 -190.4 Third lens group G3 20 -304.5 4th lens group G4 24 122.5 Fifth lens group G5 26 -94.6

[0172] In this optical system OL7, the seventh surface is a diffractive optical surface. Table 20 below shows the diffractive optical surface data, that is, the design wavelength λ0, the order n, and the values of each of the phase coefficients C2 and C4.

[0173] (Table 20) [Diffractive optical surface data] m λ0 n C2 C4 7 587.6 1.0 -3.90875E-05 -6.61767E-10

[0174] In this optical system OL7, the axial air distance d0 between the object and the first lens group G1, the axial air distance d1 between the first lens group G1 and the second lens group G2, the axial air distance d2 between the second lens group G2 and the aperture stop S, the axial air distance d3 between the third lens group G3 and the fourth lens group G4, and the axial air distance d4 between the fourth lens group G4 and the fifth lens group G5 change during focusing. Table 21 below shows the variable distances when focusing at infinity and when focusing at close range.

[0175] (Table 21) [Variable Interval Data] Focused state Infinity Close distance f 585.00017 - β - -0.16536 d0 ∞ 4606.6023 d1 7.44308 50.07294 d2 50.75570 8.12583 d3 8.45431 2.99768 d4 6.73510 12.19172 BF 51.39765 51.39765

[0176] Fig. 14 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this optical system OL7 when focused at infinity and when focused at close distances. These diagrams show that various aberrations are well corrected for in this optical system OL7.

[0177] [Eighth Example] 15 is a diagram showing the configuration of an optical system OL8 according to Example 8. This optical system OL8 is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a rear lens group GL having negative refractive power. The rear lens group GL is also composed of a third lens group G3.

[0178] The first lens group G1 is composed of, in order from the object side, a biconvex aspherical positive lens L11 whose object-side lens surface and image-side lens surface are aspherical, a diffractive optical element Lpf having a PF element Epf provided on the image-side lens surface of a positive meniscus lens L12 whose convex surface faces the object side, a cemented lens formed by cementing a biconvex positive lens L13 and a biconcave negative lens L14, and a cemented lens formed by cementing a negative meniscus lens L15 whose convex surface faces the object side and a biconvex positive lens L16. The second lens group G2 is composed of a negative meniscus lens L21 whose convex surface faces the object side. The third lens group G3 is composed of, in order from the object side, a cemented lens formed by cementing a biconvex positive lens L31 and a biconcave negative lens L32, a biconcave negative lens L33, a cemented lens formed by cementing a biconvex positive lens L34 and a biconcave negative lens L35, a cemented lens formed by cementing a negative meniscus lens L36 having a convex surface facing the object side and a biconvex positive lens L37, a cemented lens formed by cementing a biconcave negative lens L38 and a positive meniscus lens L39 having a convex surface facing the object side, and a positive meniscus lens L310 having a convex surface facing the object side. The aperture stop S is disposed on the object side of the second lens group G2 (between the first lens group G1 and the second lens group G2). Of the positive lenses included in the first lens group G1, the positive lens having the smallest Abbe number for the d-line of the medium is the biconvex positive lens L16.

[0179] In this optical system OL8, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the image plane.

[0180] The specifications of the optical system OL8 are listed in Table 22. In the lens data shown in Table 22, the 16th surface is a virtual surface and is not shown in FIG.

[0181] (Table 22) Example 8 [Overall specifications] f = 390.019 FNO = 4.600 ω [°] = 3.14 Y = 21.6 TL = 247.546 BF = 45.26893 [Lens data] mrd nd νd object surface ∞ 1* 112.6999 11.4142 1.487490 70.32 2* -804.3009 76.3821 3 68.8075 4.7100 1.516800 64.13 4 158.5341 0.1000 1.528300 36.18 5# 158.5341 0.2500 1.548900 51.30 6 158.5341 15.1436 7 66.3631 4.6902 1.487490 70.32 8 -320.7208 1.2000 1.846660 23.80 9 58.0531 18.7361 10 85.2798 1.1000 1.900430 37.37 11 40.5271 4.0337 1.663820 27.35 12 -284.0294 3.0000 13 0.0000 d1 Aperture Stop S 14 121.7747 1.0000 1.581440 40.98 15 30.8413 d2 16 0.0000 0.4000 17 56.7050 4.0000 1.603420 38.03 18 -34.3098 1.0000 1.593490 67.00 19 41.4738 1.8000 20 -31189.2380 1.0000 1.900430 37.37 21 56.5306 1.5000 22 27.8447 6.8000 1.581440 40.98 23 -22.6989 1.0000 1.593190 67.90 24 33.3615 2.9413 25 50.2032 1.0000 1.945944 17.98 26 20.4619 7.4000 1.770470 29.74 27 -41.9379 1.5000 28 -41.1217 1.0000 1.900430 37.37 29 24.9456 4.2000 1.770470 29.74 30 106.7270 0.2000 31 42.9809 3.4000 1.770470 29.74 32 355.9859 BF Image plane ∞ [Lens group focal length] Lens group First surface Focal length First lens group G1 1 147.0 Second lens group G2 14 -71.3 Third lens group G3 17 -224.8

[0182] In this optical system OL8, the fifth surface is a diffractive optical surface. Table 23 below shows the diffractive optical surface data, that is, the design wavelength λ0, the order n, and the values of each phase coefficient C2 and C4.

[0183] (Table 23) [Diffractive optical surface data] m λ0 n C2 C4 5 587.6 1.0 -1.14484E-04 3.49966E-09

[0184] In this optical system OL8, the first and second lens surfaces are each formed aspherically. Table 24 below shows the surface number m and aspherical surface data, that is, the conic constant K and the values of each aspherical surface coefficient A4 to A10.

[0185] (Table 24) [Aspherical data] m K A4 A6 A8 A10 1 1.000 -2.56030E-08 -7.13730E-13 0.00000E+00 0.00000E+00 2 1.000 3.78499E-08 -7.98960E-14 0.00000E+00 0.00000E+00

[0186] In this optical system OL8, the axial air distance d0 between the object and the first lens group G1, the axial air distance d1 between the first lens group G1 and the second lens group G2, and the axial air distance d2 between the second lens group G2 and the aperture stop S change during focusing. Table 25 below shows the variable distances when focusing at infinity and when focusing at close range.

[0187] (Table 25) [Variable Interval Data] Focused state Infinity Close distance f 390.01858 - β - -0.16368 d0 ∞ 2250.1757 d1 3.00000 16.36518 d2 18.37538 5.00920 BF 45.26893 45.26893

[0188] Fig. 16 shows diagrams of spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma for this optical system OL8 when focused at infinity and when focused at close distances. These diagrams show that various aberrations are well corrected for in this optical system OL8.

[0189] [Conditional expression corresponding value] The values corresponding to the conditional expressions (1) to (15) in the first to eighth examples are shown in Table 26 below.

[0190] (Table 26) (1)TL / f (2)θgFp1 (3)TLpf / TL (4) d1 / dG1 (5)TLs / TL (6)-fr / f (7)νdp1 (8)d1 / TL (9) f1 / f (10)-f2 / f (11)dpf / TL (12)fpf / f (13)dL1L2 / TL (14)θgfp1+0.00316×νdp1 (15)ndp1 First Example Second Example Third Example Fourth Example fpf 10075.749 10987.441 11410.445 11184.031 θgFp1 0.6291 0.6319 0.6288 0.6319 TLpf 67.779 70.749 90.496 108.078 TLs 126.502 145.000 235.494 240.968 d1 37.897 46.349 58.158 79.080 dG1 122.427 141.000 167.364 172.956 dpf 37.897 46.349 58.158 79.080 dL1L2 22.682 17.200 25.138 21.898 (1) 0.529 0.532 0.419 0.419 (2) 0.6291 0.6319 0.6288 0.6319 (3) 0.219 0.227 0.216 0.258 (4) 0.310 0.329 0.347 0.457 (5) 0.409 0.466 0.562 0.574 (6) 0.252 0.399 0.161 0.092 (7) 24.71 27.35 22.74 27.35 (8) 0.122 0.149 0.139 0.189 (9) 0.352 0.371 0.321 0.257 (10) 0.313 0.230 0.245 0.233 (11) 0.122 0.149 0.139 0.189 (12) 17.223 18.782 11.410 11.184 (13) 0.073 0.055 0.060 0.052 (14) 0.707 0.718 0.701 0.718 (15) 1.756 1.664 1.808 1.664 5th Example 6th Example 7th Example 8th Example fpf 12703.704 12434.996 12791.813 4367.423 θgFp1 0.6157 0.6319 0.6288 0.6319 TLpf 99.069 117.710 107.499 92.606 TLs 230.000 243.000 240.279 140.760 d1 66.069 89.110 75.819 76.382 dG1 172.605 173.300 180.880 137.760 dpf 66.069 89.110 75.819 76.382 dL1L2 25.800 21.500 24.480 11.412 (1) 0.504 0.504 0.504 0.635 (2) 0.6157 0.6319 0.6288 0.6319 (3) 0.252 0.299 0.273 0.374 (4) 0.383 0.514 0.419 0.554 (5) 0.585 0.618 0.611 0.569 (6) 0.250 0.136 0.244 0.576 (7) 25.45 27.35 22.74 27.35 (8) 0.168 0.226 0.193 0.309 (9) 0.341 0.304 0.424 0.377 (10) 0.209 0.304 0.324 0.183 (11) 0.168 0.226 0.193 0.309 (12) 16.288 15.942 16.401 11.198 (13) 0.066 0.055 0.062 0.046 (14) 0.696 0.718 0.701 0.718 (15) 1.805 1.664 1.808 1.664 [Explanation of symbols]

[0191] 1 Camera (optical equipment) OS (OS1~OS8) optical system G1 First lens group G2 Second lens group GR Rear lens group G3 3rd lens group G4 4th lens group G5 5th lens group Lpf Diffractive Optical Element S Aperture Stop

Claims

1. A diffractive optical element is included. From the object side, a first lens group; and a second lens group that moves during focusing; a rear group having at least one lens group; the first lens group has a positive lens, An optical system that satisfies the following condition: 0.60 < θgFp1 < 1.00 0.10 < TLpf / TL < 0.40 however, θgFp1: partial dispersion ratio of the medium of the positive lens in the first lens group that has the smallest Abbe number for the d-line of the medium TLpf: the distance on the optical axis from the lens surface closest to the object side of the optical system to the diffractive optical surface of the diffractive optical element when focused at infinity TL: total length of the optical system when focused at infinity

2. an aperture stop; From the object side, a first lens group having a diffractive optical element; a second lens group that moves during focusing; a rear group having at least one lens group; the diffractive optical element is disposed closer to an image plane than the largest air gap in the first lens group, An optical system that satisfies the following condition: 0.30 < d1 / dG1 < 0.60 0.30 < TLs / TL < 0.70 however, d1: the maximum value of the air gap on the optical axis within the first lens group dG1: the distance on the optical axis from the lens surface of the first lens group closest to the object to the lens surface of the first lens group closest to the image plane TLs: the distance on the optical axis from the lens surface closest to the object side of the optical system to the aperture stop when focused at infinity TL: total length of the optical system when focused at infinity

3. the first lens group has the diffractive optical element The optical system of claim 1 .

4. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.40 < TL / f < 0.65 however, TL: total length of the optical system when focused at infinity f: focal length of the entire optical system when focused at infinity

5. The diffractive optical element is disposed closer to the object side than the negative lens component closest to the object side. The optical system according to any one of claims 1 to 4.

6. The first lens group has two positive lenses arranged on the object side of the diffractive optical element. The optical system according to any one of claims 1 to 5.

7. 7. The optical system according to claim 1, wherein the following condition is satisfied: 0.05 < -fr / f < 2.50 however, fr: focal length of the rear group when focused at infinity f: focal length of the entire optical system when focused at infinity

8. The first lens group has a positive refractive power. The optical system according to any one of claims 1 to 7.

9. The diffractive optical element is two diffractive element elements made of different optical materials, the two diffractive element elements being cemented together; A diffractive optical surface is formed on the cemented surface of the diffractive element element. The optical system according to any one of claims 1 to 8.

10. The diffractive optical element is It has a lens component, One of the two diffractive element elements is cemented to the object side lens surface or the image plane side lens surface of the lens component. The optical system of claim 9.

11. The diffractive optical element has one of the two diffractive element elements in contact with air. The optical system of claim 9.

12. 12. The optical system according to claim 1, wherein the following condition is satisfied: 12.0 < νdp1 < 32.0 however, νdp1: the Abbe number of the positive lens in the first lens group that has the smallest Abbe number for the d-line of the medium

13. 13. The optical system according to claim 1, which satisfies the following condition: 0.10 < d1 / TL < 0.31 however, d1: the maximum value of the air gap on the optical axis within the first lens group TL: total length of the optical system when focused at infinity

14. 14. The optical system according to claim 1, wherein the following condition is satisfied: 0.20 < f1 / f < 0.50 however, f1: focal length of the first lens group f: focal length of the entire optical system when focused at infinity

15. 15. The optical system according to claim 1, which satisfies the following condition: 0.15 < -f2 / f < 0.40 however, f2: focal length of the second lens group f: focal length of the entire optical system when focused at infinity

16. 16. The optical system according to claim 1, which satisfies the following condition: 0.10 < dpf / TL < 0.31 however, dpf: air distance on the optical axis between the diffractive optical element and a lens arranged adjacent to the diffractive optical element on the object side TL: total length of the optical system when focused at infinity

17. 17. The optical system according to claim 1, which satisfies the following condition: 8.0 < fpf / f < 22.0 however, fpf: focal length of the diffractive optical surface of the diffractive optical element f: focal length of the entire optical system when focused at infinity

18. The first lens group has two positive lenses on the object side of the largest air gap among the air gaps on the optical axis within the first lens group. The optical system according to any one of claims 1 to 17.

19. 18. The optical system according to claim 1, which satisfies the following condition: dL1L2 / TL < 0.080 however, dL1L2: the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image plane of the lens group that is located closer to the object than the largest air gap in the first lens group TL: total length of the optical system when focused at infinity

20. An aperture stop is provided on the object side of the second lens group. The optical system according to any one of claims 1 to 19.

21. An aperture stop is provided on the image plane side of the second lens group. The optical system according to any one of claims 1 to 19.

22. 22. The optical system according to claim 1, wherein the following condition is satisfied: θgFp1 + 0.00316×νdp1 > 0.706 however, θgFp1: partial dispersion ratio of the medium of the positive lens in the first lens group that has the smallest Abbe number for the d-line of the medium νdp1: the Abbe number of the positive lens in the first lens group that has the smallest Abbe number for the d-line of the medium

23. The lens arranged on the object side of the largest air gap among the air gaps on the optical axis in the first lens group is composed of one positive lens. The optical system according to any one of claims 1 to 22.

24. The second lens group has a negative refractive power. The optical system according to any one of claims 1 to 23.

25. The rear group has a lens group that moves during focusing. The optical system according to any one of claims 1 to 24.

26. The rear group comprises, in order from the object side, a third lens group; and a fourth lens group that moves during focusing; a fifth lens group; The optical system according to any one of claims 1 to 25.

27. 27. The optical system according to claim 1, which satisfies the following condition: ndp1 < 1.810 however, ndp1: the refractive index of the positive lens in the first lens group with the smallest Abbe number for the d-line of the medium

28. An optical instrument comprising the optical system according to any one of claims 1 to 27.

Images