Optical system and optical device

Abstract

To provide an optical system that has excellent optical performance while made compact even when lens surfaces are all formed of spherical surfaces, an optical device, and a method of manufacturing optical system.SOLUTION: An optical system OL used for an optical device such as a camera 1 has a first lens group G1 with negative refracting power and a rear group GR with positive refracting power and an aperture diaphragm, in order from an object side. The first lens group G1 and rear group GR are located at a maximum air interval on a side closer to the object than the aperture diaphragm S, and the rear group GR has at least one refractive optical element Lpf and meets predetermined conditions.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, an optical system that realizes a small size and a wide angle of view has been proposed using a so-called Biogon-type lens configuration with a refractive power arrangement of negative-positive-negative (see, for example, Patent Document 1). However, in this type of optical system, as the angle of view increases, the difference in image plane curvature for each wavelength tends to increase, and the optical system described in Patent Document 1 is in need of further improvement in optical performance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The optical system according to the first aspect of the present invention includes, in order from the object side, a first lens group having a negative refractive power, and a rear group having a positive refractive power and an aperture stop comprises , the first lens group and the rear group are separated by a maximum air interval on the object side of the aperture stop, and the rear group has at least one diffractive optical element, The rear group has at least one cemented lens on each of the object side and the image side of the aperture. Each of the cemented lenses has at least one positive lens and a negative lens, and satisfies the conditions of the following formula. 10.0 < fpf / f < 100.0 0.10 < n1 - n2 n3 - n4 < -0.10 However, fpf: the focal length of the diffractive optical surface of the diffractive optical element f: the focal length of the entire optical system n1: The refractive index with respect to the d-line of the medium of the positive lens disposed closest to the object side among the cemented lenses disposed on the object side of the aperture n2: The refractive index with respect to the d-line of the medium of the negative lens disposed closest to the image side among the cemented lenses disposed on the object side of the aperture n3: The refractive index with respect to the d-line of the medium of the positive lens disposed closest to the object side among the cemented lenses disposed on the image side of the aperture n4: The refractive index with respect to the d-line of the medium of the negative lens disposed closest to the image side among the cemented lenses disposed on the image side of the aperture

Brief Description of the Drawings

[0007]

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Mode for Carrying Out the Invention

[0008] Hereinafter, preferred embodiments will be described with reference to the drawings.

[0009] (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 negative refractive power, and a rear group GR having a positive refractive power and an aperture stop S. The first lens group G1 and the rear group GR are separated by the largest air space on the object side of the aperture stop S. Further, the rear group GR has at least one diffractive optical element Lfp. By configuring in this way, while realizing miniaturization of this optical system OL, good optical performance can be obtained.

[0010] Here, the diffractive optical element Lfp includes a diffractive optical surface on which a sawtooth or slit-shaped grating structure is formed concentrically, and has the property of diffracting the light incident on this diffractive optical surface in a direction determined by the grating pitch (the interval between the diffractive grating grooves) and the wavelength of the incident light. Further, the diffractive optical element Lfp (diffractive optical surface) has a negative dispersion value (Abbe number = -3.453), has a large dispersion, and has strong anomalous dispersion (partial dispersion ratio (ng - nF) / (nF - nC) = 0.2956), so it has a strong chromatic aberration correction ability. The Abbe number of optical glass is usually about 30 to 80, but the Abbe number of the diffractive optical element Lfp has a negative value. In other words, the diffractive optical surface of the diffractive optical element Lfp has a dispersion characteristic opposite to that of ordinary glass (refractive optical element), and as the wavelength of light becomes shorter, the refractive power becomes smaller, and the light with a longer wavelength bends more. Therefore, by combining with an ordinary refractive optical element, a large achromatic effect can be obtained. Therefore, by using the diffractive optical element Lfp, it becomes possible to correct chromatic aberration well.

[0011] The diffractive optical element Lfp in this embodiment is a so-called "close-contact multilayer diffractive optical element" in which two diffractive element elements made of different optical materials each having diffractive grating grooves are joined so that the diffractive grating grooves face each other. Therefore, this diffractive optical element can increase the diffraction efficiency in a wide wavelength range including the g-line to the C-line. Therefore, the optical system OL according to this embodiment can be used in a wide wavelength range. Note that the diffraction efficiency indicates the ratio η (= I1 / I0 × 100 [%]) of the intensity I0 of the incident light and the intensity I1 of the first-order diffracted light when using the first-order diffracted light in a transmissive diffractive optical element.

[0012] In addition, the close-contact multilayer diffractive optical element can simplify the manufacturing process compared to a so-called separated multilayer diffractive optical element in which two diffractive element elements having diffractive grating grooves are arranged close to each other so that the diffractive grating grooves face each other. Therefore, it has the advantages of good mass production efficiency and good diffraction efficiency with respect to the incident angle of light rays. Therefore, in the optical system OL according to this embodiment using the close-contact multilayer diffractive optical element, the manufacturing becomes easy and the diffraction efficiency also improves.

[0013] In addition, in devices that only use specific wavelengths, such as surveillance cameras, a configuration in which the diffractive optical element is arranged on the lens surface of the lens component, specifically, a so-called single-layer diffractive optical element in which one diffractive element element is provided on the lens surface and diffractive grating grooves are formed on the air side surface of the diffractive element element may be used.

[0014] Also, it is desirable that the optical system OL according to the first embodiment satisfies the following conditional expression (1-1).

[0015] 10.0 < fpf / f < 100.0 (1-1) However, fpf: Focal length of the diffractive optical surface of the diffractive optical element Lfp f: Focal length of the entire optical system when the optical system OL is focused at infinity

[0016] The conditional expression (1-1) defines the ratio of the focal length of the diffractive optical surface of the diffractive optical element Lfp to the focal length of the entire optical system OL. If it is below the lower limit value of this conditional expression (1-1), the refractive power of the diffractive optical surface of the diffractive optical element Lfp becomes too strong, and the axial chromatic aberration becomes overcorrected, which is not preferable. In order to ensure the effect of the conditional expression (1-1), it is more desirable that the lower limit value of the conditional expression (1-1) be 15.0, 20.0, 21.5, 23.0, and further 24.0. Also, if it exceeds the upper limit value of the conditional expression (1-1), the axial chromatic aberration becomes undercorrected, and the effects such as the improvement of the optical performance by the diffractive optical element Lfp and the miniaturization of the optical system OL cannot be sufficiently obtained, which is not preferable. In order to ensure the effect of the conditional expression (1-1), it is more desirable that the upper limit value of the conditional expression (1-1) be 90.0, 80.0, 70.0, 60.0, 50.0, 45.0, 40.0, 38.5, 37.0, 35.5, and further 34.0.

[0017] Also, in the optical system OL according to the first embodiment, the rear group GR includes, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power. It is desirable that the second lens group G2 and the third lens group G3 be separated by the maximum air space on the image side from the aperture stop S. By configuring in this way, even if all the lens surfaces of the optical system OL are formed as spherical surfaces, miniaturization of this optical system OL can be achieved while obtaining good optical performance. When the air space changes during focusing, the boundary between the second lens group G2 and the third lens group G3 is set to the maximum air space during focusing on a near-distance object.

[0018] Also, in the optical system OL according to the first embodiment, when focusing from infinity to a near-distance object, it is desirable to move the entire optical system OL toward the object side (to adopt a so-called "overall extension" configuration). By configuring in this way, the fluctuation of the image plane during focusing is reduced, and good optical performance can be obtained.

[0019] Also, in the optical system OL according to the first embodiment, the rear group GR includes, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power. Further, it is desirable that the second lens group G2 includes, in order from the object side, a second A lens group G2A having a positive refractive power and an aperture stop S, and a second B lens group G2B having a positive refractive power. In the case of this configuration, focusing from infinity to a near-distance object is not by overall extension, but by moving the second B lens group G2B toward the object side. By configuring in this way, the fluctuation of the image plane during focusing is reduced, and good optical performance can be obtained. Also, by arranging the second B lens group G2B, which is a lens group (or lens component) having a positive refractive power, between the aperture stop S and the third lens group G3 composed of the cemented lenses arranged on the object side and the image side thereof, and moving this second B lens group G2B in the optical axis direction for focusing, the lens group that moves during focusing becomes small, and both miniaturization of the mechanism for focusing and optical performance can be achieved.

[0020] Also, in the optical system OL according to the first embodiment, it is desirable that the diffractive optical element Lpf be disposed on the lens surface or the joint surface of the lens component adjacent to the aperture stop S. By configuring in this way, while suppressing the influence on the off-axis chromatic aberration of magnification, the axial chromatic aberration can be corrected favorably. When the diffractive optical element Lpf is disposed away from the aperture stop S, it becomes difficult to balance the chromatic aberration of magnification and the axial chromatic aberration, which is not preferable. When attempting to correct the chromatic aberration of magnification and the axial chromatic aberration in a state where the diffractive optical element Lpf is disposed away from the aperture stop S, a plurality of diffractive optical elements and aspherical lenses are required. Also, it becomes difficult to adopt an optical system with a negative-positive-negative symmetric refractive power arrangement having a first lens group G1 with a negative refractive power, a second lens group G2 with a positive refractive power, and a third lens group G3 with a negative refractive power as described above. To obtain equivalent performance, it leads to an increase in the size and cost of the optical system OL, which is not preferable.

[0021] Also, it is desirable that the optical system OL according to the first embodiment satisfy the following conditional expression (1-2).

[0022] -0.50 < Dpf / TL < 0.50 (1-2) However, Dpf: The distance on the optical axis from the aperture stop S to the diffractive optical surface of the diffractive optical element Lpf (positive when the diffractive optical surface is on the image side of the aperture stop S) TL: The overall optical length of the optical system OL when focused at infinity

[0023] The conditional expression (1-2) defines the ratio of the distance on the optical axis from the aperture stop S to the diffractive optical surface of the diffractive optical element Lpf with respect to the overall optical length of the optical system OL. By configuring it in this way, while suppressing the influence on off-axis magnification chromatic aberration, it is possible to satisfactorily correct the axial chromatic aberration and the difference in field curvature for each wavelength off-axis. In addition, in order to ensure the effect of this conditional expression (1-2), it is more desirable that the upper limit value of the conditional expression (1-2) be 0.40, 0.30, 0.20, and further 0.10. Also, in order to ensure the effect of the conditional expression (1-2), it is more desirable that the lower limit value of the conditional expression (1-2) be -0.40, -0.30, -0.20, -0.10, and further 0.00.

[0024] Moreover, in the optical system OL according to the first embodiment, it is desirable that the rear group GR has at least one cemented lens on each of the object side and the image side of the aperture stop S, and each of the cemented lenses has at least one positive lens and one negative lens. In this optical system OL, the cemented lens disposed on the object side of the aperture stop S has a positive refractive power as a whole. Thereby, not only chromatic aberration but also coma aberration, field curvature, and Petzval sum can be corrected. Also, the cemented lens disposed on the image side of the aperture stop S can correct spherical aberration and chromatic aberration due to the action of the negative refractive power of the cemented surface.

[0025] Moreover, it is desirable that the optical system OL according to the first embodiment satisfies the following conditional expression (1-3).

[0026] 0.10 < n1 - n2 (1-3) However, n1: The refractive index with respect to the d-line of the medium of the positive lens disposed on the most object side of the cemented lens CLF disposed on the most image side among the cemented lenses disposed on the object side of the aperture stop S n2: The refractive index with respect to the d-line of the medium of the negative lens disposed on the most image side of the cemented lens CLF disposed on the most image side among the cemented lenses disposed on the object side of the aperture stop S

[0027] The conditional expression (1-3) defines the difference in refractive indices between the positive lens and the negative lens of the cemented lens CLF, which is the cemented lens arranged closest to the image side among the cemented lenses arranged on the object side of the aperture stop S, that is, on the object side of the aperture stop S and closest to this aperture stop S. By satisfying this conditional expression (1-3), the refractive index of the positive lens becomes larger than that of the negative lens, and it becomes possible to achieve both flatness of the image plane and correction of spherical aberration. If it is below the lower limit value of the conditional expression (1-3), it becomes difficult to correct coma aberration, field curvature, and Petzval sum, which is not preferable. In order to ensure the effect of the conditional expression (1-3), it is more desirable that the lower limit value of the conditional expression (1-3) be 0.13, and further 0.15. Also, in order to make the effect of the conditional expression (1-3) more certain, it is more desirable that the upper limit value of the conditional expression (1-3) be 0.25 (i.e., n1 - n2 < 0.25), and further 0.23.

[0028] Moreover, it is desirable that the optical system OL according to the first embodiment satisfies the following conditional expression (1-4).

[0029] n3 - n4 < -0.10 (1-4) However, n3: The refractive index with respect to the d-line of the medium of the positive lens arranged closest to the object side among the cemented lenses arranged on the image side of the aperture stop S, of the cemented lens CLR arranged closest to the object side n4: The refractive index with respect to the d-line of the medium of the negative lens arranged closest to the image side among the cemented lenses arranged on the image side of the aperture stop S, of the cemented lens CLR arranged closest to the object side

[0030] Conditional expression (1-4) defines the difference in refractive indices between the positive lens and the negative lens of the cemented lens that is arranged closest to the object side among the cemented lenses arranged on the image side of the aperture stop S, that is, the cemented lens CLR that is arranged on the image side of the aperture stop S and closest to this aperture stop S. By satisfying this conditional expression (1-4), the refractive index of the negative lens becomes larger than the refractive index of the positive lens, and various aberrations, particularly spherical aberration and axial chromatic aberration, can be corrected well. If it exceeds the upper limit value of conditional expression (1-4), it becomes difficult to correct spherical aberration and axial chromatic aberration, which is not preferable. In addition, in order to ensure the effect of conditional expression (1-4), it is more desirable that the upper limit value of conditional expression (1-4) be -0.13, and further -0.15. Also, in order to make the effect of conditional expression (1-4) more certain, it is more desirable that the lower limit value of conditional expression (1-4) be -0.55 (that is, -0.55 < n3 - n4), -0.53, and further -0.50.

[0031] Also, in the optical system OL according to the first embodiment, it is desirable that the rear group GR has a cemented lens having at least one positive refractive power on the object side of the aperture stop S and a cemented lens having at least one positive refractive power on the image side of the aperture stop S. When the rear group GR is composed of the second lens group G2 and the third lens group G3, it is desirable that the second lens group G2 has these cemented lenses. Further, when the second lens group G2 is composed of the second A lens group G2A and the second B lens group G2B, it is desirable that the second A lens group G2A has these cemented lenses. In the optical system OL, by arranging the cemented lenses with the aperture stop S in between, it is possible to achieve both the flatness of the image plane and the correction of spherical aberration. Without such a configuration, the curvature radius of the lens surface required for aberration correction becomes too small (the curvature becomes too tight), making manufacturing difficult, which is not preferable. Also, if the curvature is unreasonably loosened, the optical system OL will become larger.

[0032] Also, the optical system OL according to the first embodiment preferably satisfies the following conditional expression (1-5).

[0033] SAG < 0.50 [mm] (1-5) However, SAG: The maximum value of the absolute value of the sag amount within the effective diameter of the surface on which the diffractive optical surface of the diffractive optical element Lpf is formed

[0034] The conditional expression (1-5) defines the maximum value of the absolute value of the sag amount within the effective diameter of the surface on which the diffractive optical surface of the diffractive optical element Lpf is formed. Here, the sag amount refers to the distance along the optical axis from the tangent plane of the apex of each spherical surface to each spherical surface at the height in the direction perpendicular to the optical axis. By satisfying this conditional expression (1-5), the surface on which the diffractive optical surface in the diffractive optical element Lpf is formed can be made to have a loose curvature such that it can be regarded as a plane or a substantially plane, and the manufacturing cost of the diffractive optical element Lpf can be suppressed. In addition, in order to ensure the effect of the conditional expression (1-5), it is more desirable that the upper limit value of the conditional expression (1-5) be 0.45 [mm], 0.40 [mm], 0.35 [mm], and further 0.30 [mm]. In addition, in order to make the effect of the conditional expression (1-5) more certain, it is more desirable that the lower limit value of the conditional expression (1-5) be 0.00 [mm].

[0035] Also, it is desirable that the optical system OL according to the first embodiment be composed only of spherical lenses. By configuring it only with spherical lenses, an increase in manufacturing cost due to using aspherical lenses and a deterioration in the accuracy of the lens surface can be avoided.

[0036] Also, it is desirable that the optical system OL according to the first embodiment satisfy the following conditional expression (1-6).

[0037] 25.0 [°] < ω (1-6) However, ω: The half field angle of the optical system OL

[0038] Conditional expression (1-6) defines the half angle of the optical system OL. If it is below the lower limit value of this conditional expression (1-6), the ratio of the on-axis light to the off-axis light in aberration correction becomes larger. In the symmetric lens configuration as described above, correction of spherical aberration and axial chromatic aberration becomes insufficient, which is not preferable. In order to ensure the effect of the conditional expression (1-6), it is more desirable that the lower limit value of the conditional expression (1-6) be 26.5 [°], 28.0 [°], and further 30.0 [°].

[0039] Also, the optical system OL according to the first embodiment is preferably a single-focus lens. In a zoom lens, the distance between lens groups changes during zooming. Therefore, in the symmetric lens configuration as described above, the symmetry is broken, and there is an excess or deficiency in the chromatic aberration correction ability by the diffractive optical element Lpf, which is not preferable. Also, if the number of lens elements is increased or the movement trajectory of the lens groups during zooming is restricted in an attempt to maintain the optical performance while unreasonably remaining symmetric, the optical system OL becomes larger and the manufacturing cost increases, which is not preferable.

[0040] Also, the optical system OL according to the first embodiment preferably has only one diffractive optical element Lpf. According to the above-described configuration, good optical performance can be obtained with one diffractive optical element Lpf, and the manufacturing cost can be suppressed. Also, if the number of diffractive optical elements increases, diffractive flare increases and the image quality deteriorates, which is not preferable.

[0041] (Second Embodiment) As shown in FIG. 1, the optical system OL according to the second embodiment includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power and having an aperture stop S, and a third lens group G3 having a negative refractive power. The first lens group G1 and the second lens group G2 are separated by the maximum air interval on the object side of the aperture stop S. By configuring in this way, even if all lens surfaces of the optical system OL are formed as spherical surfaces, miniaturization of the optical system OL can be realized while obtaining good optical performance.

[0042] In addition, it is desirable that the optical system OL according to the second embodiment satisfies the following conditional expression (2-1).

[0043] 1.70 < f / BF < 2.85 (2-1) However,[[]] f: The overall focal length of the entire optical system OL when focused at infinity BF: The back focus of the optical system OL when focused at infinity

[0044] The conditional expression (2-1) defines the ratio of the overall focal length of the optical system OL to the back focus. If it is below the lower limit value of this conditional expression (2-1), it becomes difficult to control the Petzval sum and it also becomes difficult to satisfy the incident angle characteristics of the imaging element, which is not preferable. In order to ensure the effect of this conditional expression (2-1), it is more desirable that the lower limit value of the conditional expression (2-1) be 1.73, 1.75, 1.78, and further 1.80. Also, if it exceeds the upper limit value of the conditional expression (2-1), the optical system OL becomes larger, which is not preferable. In order to ensure the effect of the conditional expression (2-1), it is more desirable that the upper limit value of the conditional expression (2-1) be 2.80, 2.75, and further 2.70.

[0045] In addition, it is desirable that the optical system OL according to the second embodiment satisfies the following conditional expression (2-2).

[0046] 0.50 < f2 / f < 2.00 (2-2) However,[[]] f2: The focal length of the second lens group G2 when focused at infinity f: The overall focal length of the entire optical system OL when focused at infinity

[0047] The conditional expression (2-2) defines the ratio of the focal length of the second lens group G2 to the focal length of the entire optical system OL. If it is below the lower limit value of this conditional expression (2-2), it becomes difficult to control the Petzval sum, and it also becomes difficult to satisfy the incident angle characteristics of the imaging device, which is not preferable. In order to ensure the effect of the conditional expression (2-2), it is more desirable that the lower limit value of the conditional expression (2-2) be 0.60, 0.70, and further 0.75. Also, if it exceeds the upper limit value of the conditional expression (2-2), the optical system OL becomes large-sized, which is not preferable. In order to ensure the effect of the conditional expression (2-2), it is more desirable that the upper limit value of the conditional expression (2-2) be 1.80, 1.50, 1.30, 1.20, and further 1.10.

[0048] Also, in the optical system OL according to the second embodiment, it is desirable that the second lens group G2 and the third lens group G3 be separated by the maximum air space on the image side from the aperture stop S. By configuring in this way, even if all the lens surfaces of the optical system OL are formed as spherical surfaces, it is possible to realize miniaturization of this optical system OL while obtaining good optical performance. When the air space changes during focusing, the boundary between the second lens group G2 and the third lens group G3 is set to the maximum air space during focusing on a near-distance object.

[0049] Also, it is desirable that the optical system OL according to the second embodiment satisfy the following conditional expression (2-3).

[0050] 1.40 < Y / BF < 2.50 (2-3) However, Y: The maximum image height of the optical system OL BF: The back focus of the optical system OL at infinity focus

[0051] The conditional expression (2-3) defines the ratio of the maximum image height to the back focus of the optical system OL. If it is below the lower limit value of this conditional expression (2-3), it becomes difficult to control the Petzval sum and it also becomes difficult to satisfy the incident angle characteristics of the imaging device, which is not preferable. In order to ensure the effect of the conditional expression (2-3), it is more desirable to set the lower limit value of the conditional expression (2-3) to 1.45, 1.50, 1.53, 1.55, and further 1.58. Also, if it exceeds the upper limit value of the conditional expression (2-3), the optical system OL becomes larger, which is not preferable. In order to ensure the effect of the conditional expression (2-3), it is more desirable to set the upper limit value of the conditional expression (2-3) to 2.45, 2.40, 2.20, and further 2.00.

[0052] Also, the optical system OL according to the second embodiment preferably satisfies the following conditional expression (2-4).

[0053] 6.00 < TL / BF < 7.00 (2-4) However, TL: The overall optical length of the optical system OL at infinity focus BF: The back focus of the optical system OL at infinity focus

[0054] The conditional expression (2-4) defines the ratio of the overall optical length to the back focus of the optical system OL. If it is below the lower limit value of this conditional expression (2-4), it becomes difficult to control the Petzval sum and it also becomes difficult to satisfy the incident angle characteristics of the imaging device, which is not preferable. In order to ensure the effect of the conditional expression (2-4), it is more desirable to set the lower limit value of the conditional expression (2-4) to 6.20, 6.35, and further 6.50. Also, if it exceeds the upper limit value of the conditional expression (2-4), the optical system OL becomes larger, which is not preferable. In order to ensure the effect of the conditional expression (2-4), it is more desirable to set the upper limit value of the conditional expression (2-4) to 6.85, 6.80, 6.75, and further 6.70.

[0055] Also, in the optical system OL according to the second embodiment, it is desirable that the lens L1 closest to the object side is a negative meniscus lens. By configuring in this way, it is possible to satisfactorily correct field curvature and distortion aberration. When the lens L1 closest to the object side is not a negative meniscus lens, it is not preferable because the optical system OL becomes large-sized.

[0056] Also, in the optical system OL according to the second embodiment, it is desirable that the second lens L2 from the object side is a negative meniscus lens. By configuring in this way, it is possible to satisfactorily correct field curvature and distortion aberration. When the second lens L2 from the object side is not a negative meniscus lens, it is not preferable because the optical system OL becomes large-sized.

[0057] Also, in the optical system OL according to the second embodiment, it is desirable that the third lens group G3 has at least one negative meniscus lens Ln with a convex surface facing the image side. By configuring in this way, it is possible to satisfactorily correct field curvature and distortion aberration. When the third lens group G3 does not include a negative meniscus lens Ln with a convex surface facing the image side, it is not preferable because the optical system OL becomes large-sized.

[0058] Also, in the optical system OL according to the second embodiment, it is desirable that the second lens group G2 has at least one cemented lens on each of the object side and the image side of the aperture stop S. By adopting a configuration in which at least one cemented lens is arranged on each of the object side and the image side with the aperture stop S interposed therebetween, it is possible to achieve both the flatness of the image plane and the correction of spherical aberration. If not configured in this way, the radius of curvature of the lens surface required for aberration correction becomes too small (too steep), making manufacturing difficult, which is not preferable. Also, if the curvature is unreasonably relaxed, the optical system OL becomes large-sized, which is not preferable.

[0059] Also, the optical system OL according to the second embodiment preferably satisfies the following conditional expression (2-5).

[0060] 40.0[mm] < TL < 80.0[mm] (2-5) However, TL: The overall optical length when the optical system OL is focused at infinity

[0061] Conditional expression (2-5) defines the overall optical length of the optical system OL. If it is below the lower limit value of this conditional expression (2-5), it becomes difficult to control the Petzval sum and it also becomes difficult to satisfy the incident angle characteristics of the imaging element, so this is not preferable. In order to ensure the effect of this conditional expression (2-5), it is more desirable that the lower limit value of the conditional expression (2-5) be 45.0 [mm], 50.0 [mm], and further 58.0 [mm]. Also, if it exceeds the upper limit value of the conditional expression (2-5), the optical system OL becomes larger, so this is not preferable. In order to ensure the effect of this conditional expression (2-5), it is more desirable that the upper limit value of the conditional expression (2-5) be 75.0 [mm], 70.0 [mm], and further 67.0 [mm].

[0062] Also, in the optical system OL according to the second embodiment, when focusing from infinity to a near-distance object, it is desirable to move the entire optical system OL toward the object side (overall extension). By configuring it in this way, the fluctuation of the image plane at the time of focusing is reduced, and good optical performance can be obtained.

[0063] Also, in the optical system OL according to the second embodiment, it is desirable that the second lens group G2 has, in order from the object side, a second A lens group G2A having a positive refractive power and having an aperture stop S, and a second B lens group G2B having a positive refractive power. In the case of this configuration, focusing from infinity to a near-distance object is achieved by moving the second B lens group G2B toward the object side instead of overall extension. By configuring it in this way, the fluctuation of the image plane at the time of focusing is reduced, and good optical performance can be obtained. Also, a second B lens group G2B, which is a lens group (or lens component) having a positive refractive power, is disposed between the aperture stop S and the second A lens group G2A and the third lens group G3 composed of cemented lenses disposed on the object side and the image side thereof, and by moving this second B lens group G2B in the optical axis direction for focusing, the lens group that moves at the time of focusing becomes smaller, and it is possible to achieve both miniaturization of the mechanism for focusing and optical performance.

[0064] Moreover, it is desirable that the optical system OL according to the second embodiment satisfies the following conditional expression (2-6).

[0065] 0.70 < f2A / f < 1.20 (2-6) However,[[]] f2A: Focal length of the second A lens group G2A f: Focal length of the entire optical system OL when focused at infinity

[0066] The conditional expression (2-6) defines the ratio of the focal length of the second A lens group G2A to the focal length of the entire optical system OL. If it is below the lower limit value of this conditional expression (2-6), it becomes difficult to control the Petzval sum and it also becomes difficult to satisfy the incident angle characteristics of the imaging element, which is not preferable. In order to ensure the effect of the conditional expression (2-6), it is more desirable that the lower limit value of the conditional expression (2-6) be 0.75, and further 0.80. Also, if it exceeds the upper limit value of the conditional expression (2-6), the optical system OL becomes larger, which is not preferable. In order to ensure the effect of the conditional expression (2-6), it is more desirable that the upper limit value of the conditional expression (2-6) be 1.15, 1.10, 1.05, and further 1.02.

[0067] Note that the conditions and configurations described above each exhibit the effects described above, and are not limited to those that satisfy all the conditions and configurations. Even those that satisfy any one condition or configuration, or any combination of conditions or configurations, can obtain the above-described effects.

[0068] 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 interchangeable-lens camera equipped with 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: optical low pass filter) (not shown). Then, the subject image is photoelectrically converted by a photoelectric conversion element (imaging element) provided in the imaging unit 3 to generate an image of the subject. This image is displayed on an EVF (Electronic View Finder: electronic view finder) 4 provided in the camera 1. Thereby, the photographer can observe the subject through the EVF 4.

[0069] Also, when a release button (not shown) is pressed by the photographer, the image photoelectrically converted by the imaging unit 3 is stored in a memory (not shown). In this way, the photographer can photograph the subject with this camera 1. In this embodiment, an example of a mirrorless camera has been described. However, even when the optical system OL according to this embodiment is mounted on a single-lens reflex type camera that has a quick return mirror in the camera body and observes the subject through a finder optical system, the same effects as those of the above camera 1 can be achieved.

[0070] Note that the content described below can be appropriately adopted as long as the optical performance is not impaired.

[0071] In this embodiment, an optical system OL having a two-group or three-group configuration has been shown. However, the above configuration conditions and the like are also applicable to other group configurations such as four groups and five groups. Also, a configuration in which a lens or a lens group is added closest to the object side or a configuration in which a lens or a lens group is added closest to the image plane side may be used. Specifically, a configuration in which a lens group whose position with respect to the image plane is fixed at the time of focusing is added closest to the image plane side can be considered. Also, a lens group refers to a portion having at least one lens separated by an air interval that changes at the time of focusing, unless otherwise specified. Also, a lens component refers to a single lens or a cemented lens in which a plurality of lenses are cemented together.

[0072] Also, it may be used as a focusing group that moves a single or a plurality of lens groups or partial lens groups in the optical axis direction to perform focusing from an infinite object to a close object. In this case, the focusing group can also be applied to autofocus and is also suitable for motor driving (such as an ultrasonic motor) for autofocus. In particular, it is preferable that the entire optical system OL or at least a part of the second lens group G2 is used as the focusing group, and the positions of the other lenses with respect to the image plane are fixed during focusing. Considering the load on the motor, the focusing group is preferably composed of a single lens or one lens component.

[0073] Also, it may be used as an anti-shake group that moves a lens group or partial lens group so as to have a displacement component in a direction orthogonal to the optical axis, or rotates (swings) in a plane direction including the optical axis to correct image blur caused by camera shake.

[0074] Also, the lens surface may be formed as a spherical surface or a flat surface, or may be formed as an aspherical surface. When the lens surface is a spherical surface or a flat surface, it is preferable because lens processing and assembly adjustment become easy, and deterioration of optical performance due to errors in processing and assembly adjustment can be prevented. Also, it is preferable because deterioration of the rendering performance is small even when the image plane is displaced. When the lens surface is an aspherical surface, the aspherical surface may be any of an aspherical surface by grinding, a glass mold aspherical surface formed by molding glass into an aspherical shape, and a composite aspherical surface formed by forming resin on the surface of glass into an aspherical shape. Also, the lens surface may be a diffractive surface, and the lens may be a gradient-index lens (GRIN lens) or a plastic lens.

[0075] The aperture stop S is preferably disposed within the second lens group G2, but the role may be substituted by the frame of the lens without providing a member as the aperture stop.

[0076] Furthermore, an antireflection film having a high transmittance in a wide wavelength range may be applied to each lens surface in order to reduce flare and ghost and achieve high-contrast optical performance.

[0077] The outline of the manufacturing method of the optical system OL according to the present embodiment will be described with reference to FIG. 18. First, a first lens group G1 having a negative refractive power and a rear group GR having a positive refractive power and an aperture stop S are prepared (step S100). Next, at least one diffractive optical element Lpf is disposed in the rear group GR (step S200), and the first lens group G1 and the rear group GR are disposed so as to be separated by the maximum air space on the object side from the aperture stop S (step S300). Then, these lens groups are disposed so as to satisfy predetermined conditions (for example, the above-described conditional expressions (1-1) and (2-1)) (step S400).

[0078] As described above, conventionally, a so-called Biogon-type optical system using a refractive power arrangement of negative-positive-negative symmetry has been known. When using this optical system, good imaging performance can be obtained over a wide angle of view with a small number of lenses. However, when miniaturized, it is difficult to secure a back focus with respect to the focal length. Therefore, it has not been actively adopted in single-lens reflex cameras having a mirror box, and it has been common to use a retrofocus-type optical system. However, in recent lenses for mirrorless cameras, since the back focus can be shortened, a symmetric lens configuration is attracting attention again.

[0079] In a so-called Biogon-type optical system, by utilizing its symmetry, it is common to correct the axial aberration mainly with a lens group having a positive refractive power in the center including the aperture stop, and correct the off-axis aberration with the lens groups having negative refractive powers before and after it. At this time, when correcting the axial chromatic aberration by using a joint surface with a small radius of curvature and a strong refractive power in the lens group having a positive refractive power in the center, the light ray incident angle on the joint surface is significantly different from that of the axial light beam for a light beam with a large angle of view. Therefore, especially as going to the periphery of the pupil, the chromatic aberration correction becomes insufficient, and a phenomenon occurs in which the inclination of the image plane is different for each wavelength.

[0080] On the other hand, a diffractive lens (diffractive optical element Lpf) having a diffractive optical surface can be formed on a lens surface with an arbitrary curvature, and while having a positive refractive power, it has a strong negative lens chromatic aberration correction effect with an Abbe number equivalent value of -3.453. Therefore, the optical system OL according to the present embodiment arranges a diffractive optical surface formed substantially on a plane in a lens group having a positive refractive power near the aperture stop S, and by combining the properties of the above-described diffractive lens and a symmetric optical arrangement, it is a small and wide-angle lens mainly for a mirrorless camera, and realizes extremely excellent image plane flatness and chromatic aberration correction while having a small and simple lens configuration.

[0081] From the above, even if all the lens surfaces are formed as spherical surfaces, it is possible to provide an optical system, an optical device, and a method for manufacturing an optical system that achieve miniaturization while having good optical performance.

Example

[0082] Hereinafter, each example will be described with reference to the drawings. Note that FIGS. 1, 3, 5, 7, 9, 11, 13, and 15 are cross-sectional views showing the configuration and refractive index distribution of the optical system OL (OL1 to OL8) according to each example.

[0083] In each example, the phase shape ψ of the diffractive optical surface of the diffractive optical element Lpf is represented by the following equation (a).

[0084] ψ(h,n) = (2π / (n×λ0))×(C2h 2 +C4h 4 +C6h 6 ) (a) However, h: Height in the direction perpendicular to the optical axis n: Order of diffracted light λ0: Design wavelength Ci: Phase coefficient (i = 2, 4, 6)

[0085] Also, the refractive power φD of the diffractive optical surface represented by equation (a) for an arbitrary wavelength λ and an arbitrary diffraction order n is represented as follows by equation (b) using the lowest-order phase coefficient C2.

[0086] φD(λ,n) = -2×C2×n×λ / λ0 (b)

[0087] In the tables of the respective embodiments, a diffraction optical surface is marked with an asterisk (*) on the right side of the surface number.

[0088] Also, in each embodiment, "E-n" means "×10 -n ".

[0089] [First Embodiment] FIG. 1 is a diagram showing the configuration of an optical system OL1 according to the first embodiment. This optical system OL1 is configured to include, in order from the object side, a first lens group G1 having a negative refractive power, and a rear group GR having a positive refractive power and an aperture stop S. The rear group GR is configured to include, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power.

[0090] The first lens group G1 is composed of a negative meniscus lens L11 (L1) with a convex surface facing the object side. The second lens group G2 includes, in order from the object side, a negative meniscus lens L21 (L2) with a convex surface facing the object side, a cemented positive lens CLF formed by cementing a biconvex positive lens L22 and a biconcave negative lens L23, an aperture stop S, and a diffraction optical element Lpf, a positive meniscus lens L24 with a concave surface facing the object side, and a cemented positive lens CLR formed by cementing a negative meniscus lens L25 with a concave surface facing the object side. The third lens group G3 is composed of a negative meniscus lens L31 (Ln) with a convex surface facing the image side. In this way, in this first embodiment, the diffraction optical element Lpf is a cemented lens included in the second lens group G2 that constitutes the rear group GR, and is disposed on the lens surface on the object side of the positive meniscus lens L24 that constitutes the cemented positive lens CLR adjacent to the image side of the aperture stop S.

[0091] This optical system OL1 is configured to move the entire optical system OL1 toward the object side when focusing from infinity to a near-distance object.

[0092] Table 1 below lists the specifications of the optical system OL1. In this Table 1, f shown in the overall specifications represents the focal length of the entire system, FNO represents the F-number, ω represents the half field angle [°], Y represents the maximum image height, TL represents the overall optical length, and BF represents the back focus, which represent the values at infinity focus. Here, the overall optical length TL indicates the distance on the optical axis from the lens surface on the object side (the first surface) to the image plane I. Also, the back focus BF indicates the distance on the optical axis from the lens surface on the image side (the 13th surface) to the image plane I. Note that the values of the overall optical length TL and the back focus BF are in terms of air-equivalent length. In addition, in the lens data, m in the first column represents the order (surface number) of the lens surfaces from the object side along the direction of light propagation, r in the second column represents the radius of curvature of each lens surface, d in the third column represents the distance on the optical axis (spacing between surfaces) from each optical surface to the next optical surface, nd and νd in the fourth and fifth columns represent the refractive index and Abbe number for the d-line (λ = 587.6 nm), and Er in the sixth column (shows only the values of diffractive optical surfaces) represents the effective diameter. Also, a radius of curvature of ∞ indicates a plane, and the refractive index of air 1.00000 is omitted. In addition, the diffractive optical element Lpf shows only the information of the diffractive optical surface. Note that the lens group focal lengths indicate the surface number and the focal length of the start surfaces of each of the first to third lens groups G1 to G3.

[0093] Here, although the unit of the focal length f, radius of curvature r, surface interval d, and other lengths listed in all the following specification values is generally "mm", the optical system can obtain equivalent optical performance even with proportional magnification or reduction, so it is not limited to this. Also, the explanations of these symbols and the explanations of the specification table are the same in the following examples.

[0094] (Table 1) First Embodiment [Overall Specifications] f = 23.981 FNO = 2.871 ω[°] = 30.987 Y = 14.4 TL (air-equivalent length) = 59.023 BF (air-equivalent length) = 8.978 [Lens Data] m r d nd νd Er Object surface ∞ D0 1 16.03861 1.200 1.67790 50.67 2 10.94624 8.099 3 12.21850 1.200 1.67000 57.35 4 9.90966 6.512 5 25.31860 4.928 1.78590 44.17 6 -11.52570 1.200 1.60342 38.03 7 124.95862 1.124 8 ∞ 3.651 Aperture stop S 9* -57.25408 6.452 1.69680 55.52 5.230 10 -8.03258 1.200 1.85026 32.35 11 -15.36411 13.279 12 -12.08909 1.200 1.48749 70.32 13 -25.71286 BF Image surface ∞ [Focal length of lens group] Focal length of the starting surface of the lens group The first lens group G1 1 -56.208 The rear group GR 3 21.740 The second lens group G2 3 20.486 The third lens group G3 12 -48.195

[0095] In this optical system OL1, the 9th surface is a diffractive optical surface. Table 2 below shows the diffractive optical surface data, namely the design wavelength λ0, the order n, and the values of each phase coefficient C2, C4, and C6.

[0096] (Table 2) [Diffractive optical surface data] m λ0 n C2 C4 C6 9 546.1 1 -6.89587E-04 1.78844E-05 -1.78350E-07

[0097] Also, in this optical system OL1, the back focus BF changes during focusing. Table 3 below shows the variable intervals when focusing on an object at infinity, an object at an intermediate distance, and an object at a short distance. Here, D0 represents the distance from the most object-side surface (the first surface) of the optical system OL1 to the object, f represents the focal length, and β represents the magnification. This explanation is the same for the following embodiments.

[0098] (Table 3) [Variable Interval Data] Focus State Infinity Intermediate Distance Short Distance f 23.981 - - β - -0.033 -0.100 D0 ∞ 731.885 245.138 BF 8.978 9.769 11.373

[0099] The spherical aberration diagram, astigmatism diagram, distortion aberration diagram, longitudinal chromatic aberration diagram, and coma aberration diagram of this optical system OL1 in the infinity focus state are shown in FIG. 2. In each aberration diagram, FNO represents the F-number, NA represents the numerical aperture, and Y represents the image height. In the spherical aberration diagram, the value of the F-number or numerical aperture corresponding to the maximum aperture is shown. In the astigmatism diagram and distortion aberration diagram, the maximum value of the image height is shown. In the coma aberration diagram, the value of each image height is shown. d represents the d-line (λ = 587.6 nm), g represents the g-line (λ = 435.8 nm), F represents the F-line (λ = 486.1 nm), and C represents the C-line (λ = 656.3 nm). In the astigmatism diagram, the solid line represents the sagittal image plane, and the dashed line represents the meridional image plane. Also, in the aberration diagrams of each of the following embodiments, the same reference numerals as in this embodiment are used. From these aberration diagrams, it can be seen that this optical system OL1 has good correction of various aberrations and excellent imaging performance.

[0100] [Second Embodiment] FIG. 3 is a diagram showing the configuration of the optical system OL2 according to the second embodiment. This optical system OL2 includes, in order from the object side, a first lens group G1 having a negative refractive power, and a rear group GR having a positive refractive power and an aperture stop S. The rear group GR includes, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power.

[0101] The first lens group G1 includes, in order from the object side, a negative meniscus lens L11 (L1) with a convex surface facing the object side, and a negative meniscus lens L12 (L2) with a convex surface facing the object side. The second lens group G2 includes, in order from the object side, a cemented positive lens CLF formed by cementing a biconvex positive lens L21 and a biconcave negative lens L22, an aperture stop S, a plano-concave negative lens L23 with a concave surface facing the object side, a diffractive optical element Lpf, a plano-convex positive lens L24 with a convex surface facing the image side, and a cemented positive lens CLR formed by cementing a negative meniscus lens L25 with a concave surface facing the object side. The third lens group G3 includes, in order from the object side, a negative meniscus lens L31 (Ln) with a convex surface facing the image side, and a biconvex positive lens L32. Thus, in this second embodiment, the diffractive optical element Lpf is a cemented lens included in the second lens group G2 that constitutes the rear group GR, and is disposed on the cemented surface between the plano-concave negative lens L23 and the plano-convex positive lens L24 that constitute the cemented positive lens CLR adjacent to the image side of the aperture stop S.

[0102] This optical system OL2 is configured to move the entire optical system OL2 toward the object side when focusing from infinity to a near-distance object.

[0103] The following Table 4 lists the values of the specifications of the optical system OL2.

[0104] (Table 4) Second Embodiment [Overall Specifications] f = 23.984 FNO = 2.874 ω[°] = 31.481 Y = 14.4 TL (air equivalent length) = 59.030 BF (Air equivalent length) = 8.980 [Lens data] m r d nd νd Er Object plane ∞ D0 1 19.88343 1.500 1.48749 70.32 2 10.40841 4.831 3 12.07334 1.500 1.48749 70.32 4 9.37509 7.742 5 24.38560 4.999 1.79952 42.09 6 -11.51863 1.500 1.59270 35.27 7 237.61201 1.065 8 ∞ 1.327 Aperture stop S 9 -41.05505 1.500 1.65844 50.83 10* ∞ 5.324 1.65844 50.83 5.124 11 -8.42080 1.200 2.00100 29.12 12 -13.84080 13.962 13 -11.33895 1.500 1.62588 35.72 14 -24.64630 0.100 15 269.00940 2.000 2.00100 29.12 16 -101.84874 BF Image plane ∞ [Focal length of lens groups] Lens group Starting surface Focal length First lens group G1 1 -30.759 Rear group GR 4 18.782 Second lens group G2 4 18.278 Third lens group G3 13 -71.479

[0105] In this optical system OL2, the tenth surface is a diffractive optical surface. Table 5 below shows the diffractive optical surface data, namely the values of the design wavelength λ0, the order n, and the phase coefficients C2, C4, and C6 for each position.

[0106] (Table 5) [Diffractive optical surface data] m λ0 n C2 C4 C6 10 587.6 1 -8.51119E-04 1.13845E-05 -1.14338E-07

[0107] Also, in this optical system OL2, the back focus BF changes during focusing. Table 6 below shows the variable intervals when focusing on an object at infinity, an intermediate distance, and a short distance.

[0108] (Table 6) [Variable interval data] Focus state Infinity Intermediate distance Short distance f 23.984 - - β - -0.033 -0.100 D0 ∞ 731.393 244.584 BF 8.980 9.771 11.376

[0109] The spherical aberration diagram, astigmatism diagram, distortion diagram, longitudinal chromatic aberration diagram, and coma aberration diagram of this optical system OL2 in the infinity focus state are shown in FIG. 4. From these aberration diagrams, it can be seen that this optical system OL2 has good correction of various aberrations and excellent imaging performance.

[0110] [Third Embodiment] FIG. 5 is a diagram showing the configuration of the optical system OL3 according to the third embodiment. This optical system OL3 is configured to include, in order from the object side, a first lens group G1 having a negative refractive power, and a rear group GR having a positive refractive power and an aperture stop S. Further, the rear group GR is configured to include, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power. Furthermore, the second lens group G2 is configured to include, in order from the object side, a second A lens group G2A having a positive refractive power and an aperture stop S, and a second B lens group G2B having a positive refractive power.

[0111] The first lens group G1 is configured to include, in order from the object side, a negative meniscus lens L11 (L1) with a convex surface facing the object side, and a negative meniscus lens L12 (L2) with a convex surface facing the object side. The second A lens group G2A is configured to include, in order from the object side, a cemented positive lens CLF formed by cementing a biconvex positive lens L21 and a biconcave negative lens L22, an aperture stop S, and a cemented positive lens CLR formed by cementing a diffractive optical element Lpf, a biconvex positive lens L23, and a negative meniscus lens L24 with a concave surface facing the object side. The second B lens group G2B is configured to include a positive meniscus lens L25 with a concave surface facing the object side. The third lens group G3 is configured to include a negative meniscus lens L31 (Ln) with a convex surface facing the image side. Thus, in this third embodiment, the diffractive optical element Lpf is a cemented lens included in the second A lens group G2A that constitutes the rear group GR, and is disposed on the lens surface on the object side of the biconvex positive lens L23 that constitutes the cemented positive lens CLR adjacent to the image side of the aperture stop S.

[0112] This optical system OL3 is configured to move the second B lens group G2B toward the object side when focusing from infinity to a close object.

[0113] The following Table 7 lists the values of the specifications of the optical system OL3.

[0114] (Table 7) Third Embodiment [Overall Specifications] f = 23.988 FNO = 4.050 ω[°] = 31.380 Y = 14.4 TL (equivalent air length) = 58.983 BF (equivalent air length) = 8.983 [Lens Data] m r d nd νd Er Object plane ∞ D0 1 21.36199 1.500 1.48749 70.32 2 10.05274 1.469 3 11.41554 1.500 1.48749 70.32 4 9.64234 9.540 5 26.02343 5.040 1.80440 39.61 6 -11.02102 1.500 1.63980 34.55 7 59.58547 1.146 8 ∞ 4.122 Aperture stop S 9* 295.87946 5.821 1.51823 58.82 4.821 10 -8.00000 1.200 2.00100 29.12 11 -11.87330 D11 12 -110.05544 1.973 2.00100 29.12 13 -47.98308 D13 14 -15.48090 1.500 1.51742 52.20 15 -176.87577 BF Image plane ∞ [Focal Length of Lens Group] Lens Group Starting Surface Focal Length First lens group G1 1 -31.687 Rear group GR 5 18.228 Second lens group G2 5 19.888 Second A lens group G2A 5 19.868 Second B lens group G2B 12 83.660 Third lens group G3 14 -32.894

[0115] In this optical system OL3, the ninth surface is a diffractive optical surface. Table 8 below shows the diffractive optical surface data, namely the design wavelength λ0, the order n, and the values of the respective phase coefficients C2, C4, and C6.

[0116] (Table 8) [Diffractive optical surface data] m λ0 n C2 C4 C6 9 546.1 1 -7.42734E-04 1.37826E-05 -2.86196E-07

[0117] Also, in this optical system OL3, the axial air interval D11 between the second A lens group G2A and the second B lens group G2B, the axial air interval D13 between the second B lens group G2B and the third lens group G3B, and the back focus BF change during focusing. Table 9 below shows the variable intervals at infinity focus, intermediate distance object focus, and close distance object focus.

[0118] (Table 9) [Variable interval data] Focus state Infinity Intermediate distance Close distance f 23.988 - - β - -0.033 -0.100 D0 ∞ 709.099 223.276 D11 8.955 7.287 4.391 D13 4.736 6.404 9.299 BF 8.983 8.991 9.006

[0119] The spherical aberration diagram, astigmatism diagram, distortion aberration diagram, chromatic aberration of magnification diagram, and coma aberration diagram of this optical system OL3 in the infinity focus state are shown in FIG. 6. From these respective aberration diagrams, it can be seen that this optical system OL3 has good correction of various aberrations and excellent imaging performance.

[0120] [Fourth Embodiment] FIG. 7 is a diagram showing the configuration of the optical system OL4 according to the fourth embodiment. This optical system OL4 is configured to include, in order from the object side, a first lens group G1 having a negative refractive power, and a rear group GR having a positive refractive power and an aperture stop S. Further, the rear group GR is configured to include, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power. Furthermore, the second lens group G2 is configured to include, in order from the object side, a second A lens group G2A having a positive refractive power and an aperture stop S, and a second B lens group G2B having a positive refractive power.

[0121] The first lens group G1 is configured to include, in order from the object side, a negative meniscus lens L11 (L1) with a convex surface facing the object side, and a negative meniscus lens L12 (L2) with a convex surface facing the object side. The second A lens group G2A is configured to include, in order from the object side, a cemented positive lens CLF formed by cementing a biconvex positive lens L21 and a biconcave negative lens L22, an aperture stop S, a diffractive optical element Lpf, a positive meniscus lens L23 with a concave surface facing the object side, and a cemented positive lens CLR formed by cementing a negative meniscus lens L24 with a concave surface facing the object side. The second B lens group G2B is configured to include, in order from the object side, a cemented positive lens formed by cementing a positive meniscus lens L25 with a concave surface facing the object side and a positive meniscus lens L26 with a concave surface facing the object side. The third lens group G3 is configured to include, in order from the object side, a negative meniscus lens L31 (Ln) with a convex surface facing the image side, and a positive meniscus lens L32 with a convex surface facing the object side. Thus, in this fourth embodiment, the diffractive optical element Lpf is a cemented lens included in the second A lens group G2A that constitutes the rear group GR, and is disposed on the lens surface on the object side of the positive meniscus lens L23 that constitutes the cemented positive lens CLR adjacent to the image side of the aperture stop S.

[0122] This optical system OL4 is configured to move the second B lens group G2B toward the object side when focusing from infinity to a near-distance object.

[0123] Table 10 below lists the values of the specifications of the optical system OL4.

[0124] (Table 10) Example 4 [Overall specifications] f = 23.988 FNO = 4.215 ω[°] = 31.442 Y = 14.4 TL (air equivalent length) = 58.983 BF (air equivalent length) = 8.983 [Lens data] m r d nd νd Er Object surface ∞ D0 1 21.24797 1.500 1.55041 63.30 2 9.12680 2.063 3 12.74601 1.500 1.48749 70.32 4 11.16905 7.354 5 26.10580 4.158 1.79791 34.93 6 -10.44097 1.500 1.64417 30.27 7 85.60711 1.107 8 ∞ 4.052 Aperture stop S 9* -308.44886 5.668 1.59902 59.56 4.812 10 -8.00000 1.200 2.00100 29.12 11 -12.45555 D11 12 -124.00125 1.518 1.48749 70.32 13 -124.02496 1.899 1.95743 31.05 14 -52.55027 D14 15 -15.04770 1.500 1.75500 52.34 16 -40.53560 0.100 17 791.75533 1.501 1.75500 52.34 18 928.14834 BF Image surface ∞ [Focal length of lens group] Focal length of the starting surface of the lens group First lens group G1 1 -26.168 Rear group GR 5 16.935 Second lens group G2 5 18.894 Second A lens group G2A 5 18.625 Second B lens group G2B 12 93.515 Third lens group G3 15 -32.655

[0125] In this optical system OL4, the ninth surface is a diffractive optical surface. Table 11 below shows the diffractive optical surface data, namely the design wavelength λ0, the order n, and the values of the phase coefficients C2, C4, and C6 for each position.

[0126] (Table 11) [Diffractive optical surface data] m λ0 n C2 C4 C6 9 546.1 1 -6.26395E-04 1.24962E-05 -2.29715E-07

[0127] Also, in this optical system OL4, the axial air gap D11 between the second A lens group G2A and the second B lens group G2B, the axial air gap D14 between the second B lens group G2B and the third lens group G3B, and the back focus BF change during focusing. Table 12 below shows the variable intervals when focusing on an object at infinity, an object at an intermediate distance, and an object at a close distance.

[0128] (Table 12) [Variable interval data] Focus state Infinity Intermediate distance Close distance f 23.988 - - β - -0.033 -0.100 D0 ∞ 712.061 226.190 D11 8.692 7.098 4.363 D14 4.688 6.321 9.147 BF 8.983 8.989 9.003

[0129] The spherical aberration diagram, astigmatism diagram, distortion aberration diagram, chromatic aberration of magnification diagram, and coma aberration diagram of this optical system OL4 in the infinity focusing state are shown in FIG. 8. From these respective aberration diagrams, it can be seen that this optical system OL4 has good correction of various aberrations and has excellent imaging performance.

[0130] [Fifth Embodiment] FIG. 9 is a diagram showing the configuration of an optical system OL5 according to the fifth embodiment. This optical system OL5 is configured to include, in order from the object side, a first lens group G1 having a negative refractive power, and a rear group GR having a positive refractive power and an aperture stop S. The rear group GR is configured to include, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power. Further, the second lens group G2 is configured to include, in order from the object side, a second A lens group G2A having a positive refractive power and an aperture stop S, and a second B lens group G2B having a positive refractive power.

[0131] The first lens group G1 is configured to include, in order from the object side, a negative meniscus lens L11 (L1) with a convex surface facing the object side, and a negative meniscus lens L12 (L2) with a convex surface facing the object side. The second A lens group G2A is configured to include, in order from the object side, a cemented positive lens CLF formed by cementing a biconvex positive lens L21 and a biconcave negative lens L22, an aperture stop S, and a cemented positive lens CLR formed by cementing a diffractive optical element Lpf, a biconvex positive lens L23, and a negative meniscus lens L24 with a concave surface facing the object side. The second B lens group G2B is configured to include, in order from the object side, a cemented positive lens formed by cementing a positive meniscus lens L25 with a concave surface facing the object side and a positive meniscus lens L26 with a concave surface facing the object side. The third lens group G3 is configured to include, in order from the object side, a negative meniscus lens L31 with a convex surface facing the object side, and a negative meniscus lens L32 (Ln) with a convex surface facing the image side. In this way, in this fifth embodiment, the diffractive optical element Lpf is a cemented lens included in the second A lens group G2A that constitutes the rear group GR, and is disposed on the lens surface on the object side of the biconvex positive lens L23 that constitutes the cemented positive lens CLR adjacent to the image side of the aperture stop S.

[0132] This optical system OL5 is configured to move the second lens group G2B toward the object side when focusing from infinity to a close-distance object.

[0133] The following Table 13 lists the specifications of the optical system OL5.

[0134] (Table 13) Fifth Embodiment [Overall Specifications] f = 18.293 FNO = 4.002 ω[°] = 39.062 Y = 14.4 TL (Air-equivalent length) = 58.989 BF (Air-equivalent length) = 8.989 [Lens Data] m r d nd νd Er Object plane ∞ D0 1 17.96245 1.125 1.81437 42.33 2 10.16460 3.568 3 24.56861 1.125 1.48749 70.32 4 13.76218 7.884 5 28.10367 6.309 2.00100 29.12 6 -12.39694 1.125 1.80089 22.94 7 209.32730 3.028 8 ∞ 4.094 Aperture stop S 9* 233.13868 6.087 1.48749 70.32 4.881 10 -8.00000 0.900 1.88875 25.36 11 -15.07175 D11 12 -356.60228 2.631 2.00100 29.12 13 -25.92059 2.087 1.48749 70.32 14 -18.92698 D14 15 87.06521 1.125 1.48749 70.32 16 23.51537 5.579 17 -10.56837 1.500 1.95757 27.65 18 -15.79295 BF Image plane ∞ [Focal length of lens group] Focal length of the starting surface of the lens group First lens group G1 1 -20.092 Rear group GR 5 16.448 Second lens group G2 5 17.531 Second lens group G2A 5 19.748 Second lens group G2B 12 23.634 Third lens group G3 15 -23.718

[0135] In this optical system OL5, the ninth surface is a diffractive optical surface. Table 14 below shows the diffractive optical surface data, that is, the values of the design wavelength λ0, the order n, and the phase coefficients C2, C4, and C6 for each position.

[0136] (Table 14) [Diffractive optical surface data] m λ0 n C2 C4 C6 9 546.1 1 -8.15028E-04 1.49786E-05 -4.57919E-07

[0137] Also, in this optical system OL5, the axial air gap D11 between the second lens group G2A and the second lens group G2B, the axial air gap D14 between the second lens group G2B and the third lens group G3B, and the back focus BF change during focusing. Table 15 below shows the variable intervals at infinity focus, intermediate distance object focus, and close distance object focus.

[0138] (Table 15) [Variable interval data] Focus state Infinity Intermediate distance Close distance f 18.293 - - β - -0.033 -0.100 D0 ∞ 542.354 171.140 D11 0.874 0.612 0.100 D14 0.959 1.261 1.863 BF 8.989 8.993 9.002

[0139] The spherical aberration diagram, astigmatism diagram, distortion aberration diagram, longitudinal chromatic aberration diagram, and coma aberration diagram of this optical system OL5 in the infinity focus state are shown in Fig. 10. From these aberration diagrams, it can be seen that this optical system OL5 has good correction of various aberrations and excellent imaging performance.

[0140] [Sixth Embodiment] Fig. 11 is a diagram showing the configuration of an optical system OL6 according to the sixth embodiment. This optical system OL6 is configured to include, in order from the object side, a first lens group G1 having a negative refractive power, and a rear group GR having a positive refractive power and an aperture stop S. The rear group GR is configured to include, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power. Further, the second lens group G2 is configured to include, in order from the object side, a second A lens group G2A having a positive refractive power and an aperture stop S, and a second B lens group G2B having a positive refractive power.

[0141] The first lens group G1 is composed of, in order from the object side, a negative meniscus lens L11 (L1) with a convex surface facing the object side and a negative meniscus lens L12 (L2) with a convex surface facing the object side. Further, the second A lens group G2A is composed of, in order from the object side, a cemented positive lens CLF formed by cementing a biconvex positive lens L21 and a negative meniscus lens L22 with a concave surface facing the object side, an aperture stop S, a diffractive optical element Lpf, and a cemented positive lens CLR formed by cementing a plano-convex positive lens L23 with a convex surface facing the image side and a negative meniscus lens L24 with a concave surface facing the object side. Further, the second B lens group G2B is composed of, in order from the object side, a cemented positive lens formed by cementing a positive meniscus lens L25 with a concave surface facing the object side and a positive meniscus lens L26 with a concave surface facing the object side. Further, the third lens group G3 is composed of, in order from the object side, a negative meniscus lens L31 with a convex surface facing the object side and a negative meniscus lens L32 (Ln) with a convex surface facing the image side. Thus, in this sixth embodiment, the diffractive optical element Lpf is a cemented lens included in the second A lens group G2A that constitutes the rear group GR, and is disposed on the object-side lens surface of the plano-convex positive lens L23 that constitutes the cemented positive lens CLR adjacent to the image side of the aperture stop S.

[0142] This optical system OL6 is configured to move the second B lens group G2B toward the object side when focusing from infinity to a close-distance object.

[0143] The following Table 16 lists the values of the specifications of the optical system OL6.

[0144] (Table 16) Sixth Embodiment [Overall Specifications] f = 16.496 FNO = 3.982 ω[°] = 41.989 Y = 14.4 TL (air equivalent length) = 58.991 BF (air equivalent length) = 8.991 [Lens Data] m r d nd νd Er Object plane ∞ D0 1 17.95551 1.500 1.90366 31.27 2 9.45663 3.974 3 30.53518 1.500 1.75500 52.33 4 14.24498 4.706 5 24.53863 9.521 2.00100 29.12 6 -10.81292 1.500 1.80809 22.74 7 -80.96594 3.487 8 ∞ 3.240 Aperture Stop S 9* ∞ 5.332 1.51680 64.13 4.000 10 -8.00000 1.200 1.90200 25.26 11 -16.62411 D11 12 -217.69362 2.216 2.00100 29.12 13 -30.90633 2.178 1.75500 52.33 14 -19.04082 D14 15 41.88173 1.500 1.60311 60.69 16 22.19367 5.631 17 -9.53474 1.500 1.80809 22.74 18 -13.81902 BF Image plane ∞ [Focal length of lens group] Focal length of the starting surface of the lens group First lens group G1 1 -13.537 Rear group GR 5 14.761 Second lens group G2 5 17.613 Second A lens group G2A 5 16.089 Second B lens group G2B 12 23.208 Third lens group G3 15 -28.393

[0145] In this optical system OL6, the ninth surface is a diffractive optical surface. Table 17 below shows the diffractive optical surface data, namely the values of the design wavelength λ0, the order n, and the phase coefficients C2, C4, and C6 for each position.

[0146] (Table 17) [Diffractive optical surface data] m λ0 n C2 C4 C6 9 546.1 1 -9.28322E-04 2.02885E-05 -7.96094E-07

[0147] Also, in this optical system OL6, the axial air gap D11 between the second A lens group G2A and the second B lens group G2B, the axial air gap D14 between the second B lens group G2B and the third lens group G3B, and the back focus BF change during focusing. Table 18 below shows the variable intervals at infinity focus, intermediate distance object focus, and close distance object focus.

[0148] (Table 18) [Variable interval data] Focus state Infinity Intermediate distance Close distance f 16.496 - - β - -0.032 -0.100 D0 ∞ 500.000 154.218 D11 0.915 0.645 0.100 D14 0.100 0.404 1.028 BF 8.991 8.994 9.002

[0149] The spherical aberration diagram, astigmatism diagram, distortion aberration diagram, longitudinal chromatic aberration diagram, and coma aberration diagram of this optical system OL6 in the infinity focus state are shown in FIG. 12. From these aberration diagrams, it can be seen that this optical system OL6 has good correction of various aberrations and excellent imaging performance.

[0150] [Example 7] FIG. 13 is a diagram showing the configuration of the optical system OL7 according to the seventh embodiment. This optical system OL7 is configured to include, in order from the object side, a first lens group G1 having a negative refractive power, and a rear group GR having a positive refractive power and an aperture stop S. The rear group GR is configured to include, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power.

[0151] The first lens group G1 is configured to include, in order from the object side, a negative meniscus lens L11 (L1) with a convex surface facing the object side, a negative meniscus lens L12 (L2) with a convex surface facing the object side, and a positive meniscus lens L13 with a convex surface facing the object side. The second lens group G2 is configured to include, in order from the object side, a cemented positive lens CLF formed by cementing a biconvex positive lens L21 and a biconcave negative lens L22, an aperture stop S, a diffractive optical element Lpf, a positive meniscus lens L23 with a concave surface facing the object side, and a cemented positive lens CLR formed by cementing a negative meniscus lens L24 with a concave surface facing the object side. The third lens group G3 is configured to include a negative meniscus lens L31 (Ln) with a convex surface facing the image side. Thus, in this seventh embodiment, the diffractive optical element Lpf is a cemented lens included in the second lens group G2 that constitutes the rear group GR, and is disposed on the lens surface on the object side of the positive meniscus lens L23 that constitutes the cemented positive lens CLR adjacent to the image side of the aperture stop S.

[0152] This optical system OL7 is configured to move the entire optical system OL7 toward the object side when focusing from infinity to a close-distance object.

[0153] The following Table 19 lists the values of the specifications of the optical system OL7.

[0154] (Table 19) Seventh embodiment [Overall specifications] f = 23.976 FNO = 4.006 ω[°] = 42.857 Y = 21.6 TL (air equivalent length) = 59.034 BF (Air Equivalent Length) = 8.974 [Lens Data] m r d nd νd Er Object Plane ∞ D0 1 40.87493 1.200 1.68893 31.07 2 12.55162 3.939 3 16.61277 1.200 1.75500 52.33 4 11.88168 2.197 5 18.93858 2.521 2.00100 29.12 6 31.94129 5.922 7 27.45496 4.189 1.74100 52.76 8 -13.20340 1.200 1.53996 59.52 9 469.28604 1.025 10 ∞ 2.876 Aperture Stop S 11* -71.41699 5.782 1.56384 60.71 5.091 12 -8.00000 1.200 2.00100 29.12 13 -12.44706 15.610 14 -12.73486 1.200 1.83400 37.18 15 -21.65004 BF Image Plane ∞ [Focal Length of Lens Group] Lens Group Starting Surface Focal Length First Lens Group G1 1 -33.304 Rear Group GR 7 18.813 Second Lens Group G2 7 19.495 Third Lens Group G3 14 -39.499

[0155] In this optical system OL7, the 11th surface is a diffractive optical surface. Table 20 below shows the diffractive optical surface data, namely the values of the design wavelength λ0, the order n, and the phase coefficients C2, C4, and C6 for each position.

[0156] (Table 20) [Diffractive optical surface data] m λ0 n C2 C4 C6 11 546.1 1 -7.75911E-04 1.42453E-05 -2.83676E-07

[0157] In addition, the back focus BF in this optical system OL7 changes during focusing. The following Table 21 shows the variable intervals when focusing on an object at infinity, at an intermediate distance, and at a short distance.

[0158] (Table 21) [Variable interval data] Focus state Infinity Intermediate distance Short distance f 23.976 - - β - -0.033 -0.100 D0 ∞ 730.000 250.000 BF 8.974 9.772 11.367

[0159] The spherical aberration diagram, astigmatism diagram, distortion diagram, chromatic aberration of magnification diagram, and coma diagram of this optical system OL7 in the infinity focus state are shown in Fig. 14. From these aberration diagrams, it can be seen that this optical system OL7 has good correction of various aberrations and excellent imaging performance.

[0160] [Eighth embodiment] Fig. 15 is a diagram showing the configuration of an optical system OL8 according to the eighth embodiment. This optical system OL8 is composed of, in order from the object side, a first lens group G1 having a negative refractive power, and a rear group GR having a positive refractive power and an aperture stop S. The rear group GR is composed of, in order from the object side, a second lens group G2 having a positive refractive power and an aperture stop S, and a third lens group G3 having a negative refractive power.

[0161] The first lens group G1 is composed of a negative meniscus lens L11 (L1) with a convex surface facing the object side. The second lens group G2, in order from the object side, includes a negative meniscus lens L21 (L2) with a convex surface facing the object side, a negative meniscus lens L22 with a convex surface facing the object side, a cemented positive lens CLF formed by cementing a biconvex positive lens L23 and a biconcave negative lens L24, an aperture stop S, a plano-concave negative lens L25 with a concave surface facing the object side, a diffractive optical element Lpf, a plano-convex positive lens L26 with a convex surface facing the object side, and a cemented positive lens CLR formed by cementing a negative meniscus lens L27 with a concave surface facing the object side. The third lens group G3, in order from the object side, is composed of a negative meniscus lens L31 (Ln) with a convex surface facing the image side and a positive meniscus lens L32 with a concave surface facing the object side. Thus, in this eighth embodiment, the diffractive optical element Lpf is a cemented lens included in the second lens group G2 that constitutes the rear group GR, and is disposed on the cemented surface of the plano-concave negative lens L25 and the plano-convex positive lens L26 that constitute the cemented positive lens CLR adjacent to the image side of the aperture stop S.

[0162] This optical system OL8 is configured to move the entire optical system OL8 toward the object side when focusing from infinity to a close-distance object.

[0163] The following Table 22 lists the values of the specifications of the optical system OL8.

[0164] (Table 22) Eighth Embodiment [Overall Specifications] f = 23.994 FNO = 2.104 ω[°] = 31.750 Y = 14.4 TL (Air-equivalent length) = 65.988 BF (Air-equivalent length) = 9.987 [Lens Data] m r d nd νd Er Object Plane ∞ D0 1 19.57950 1.500 1.64687 54.08 2 12.11150 9.004 3 13.60580 1.500 1.80809 22.74 4 10.67270 1.643 5 15.41970 1.547 2.00100 29.12 6 14.62640 4.307 7 27.42500 6.145 1.96647 30.61 8 -12.20390 1.500 1.69840 26.86 9 108.97430 1.246 10 ∞ 1.469 Aperture stop S 11 -51.78240 1.500 1.65844 50.83 12* ∞ 7.334 1.65844 50.83 6.860 13 -9.06798 1.200 1.88192 25.13 14 -16.39399 12.506 15 -12.27896 1.500 1.59406 35.11 16 -21.46146 0.100 17 -616.69357 2.000 2.00100 29.12 18 -70.29584 BF Image plane ∞ [Focal length of lens group] Focal length of the starting surface of the lens group First lens group G1 1 -53.293 Rear group GR 3 23.920 Second lens group G2 3 21.907 Third lens group G3 15 -168.822

[0165] In this optical system OL8, the 12th surface is a diffractive optical surface. Table 23 below shows the diffractive optical surface data, namely the values of the design wavelength λ0, the order n, and the phase coefficients C2, C4, and C6 for each position.

[0166] (Table 23) [Diffractive optical surface data] m λ0 n C2 C4 C6 12 587.6 1 -7.68732E-04 8.84819E-06 -1.01108E-07

[0167] Also, in this optical system OL8, the back focus BF changes during focusing. The following Table 24 shows the variable intervals at infinity focus, intermediate distance object focus, and close distance object focus.

[0168] (Table 24) [Variable interval data] Focus state Infinity Intermediate distance Close distance f 23.994 - - β - -0.033 -0.100 D0 ∞ 727.075 239.044 BF 9.987 10.777 12.384

[0169] The spherical aberration diagram, astigmatism diagram, distortion aberration diagram, magnification chromatic aberration diagram, and coma aberration diagram of this optical system OL8 in the infinity focus state are shown in FIG. 16. From these respective aberration diagrams, it can be seen that this optical system OL8 has good correction of various aberrations and excellent imaging performance.

[0170] [Condition formula corresponding values] The corresponding values of the condition formulas (1-1) to (1-6), (2-1) to (2-6) in the first to eighth embodiments are shown in the following Table 25.

[0171] (Table 25) (1-1) fpf / f (1-2) Dpf / TL (1-3) n1-n2 (1-4) n3-n4 (1-5) SAG (1-6) ω (2-1) f / BF (2-2) f2 / f (2-3) Y / BF (2-4) TL / BF (2-5) TL (2-6) f2A / f First Embodiment, Second Embodiment, Third Embodiment, Fourth Embodiment fpf 673.862 587.462 625.644 741.844 Dpf 3.651 2.827 4.122 4.052 (1-1) 28.100 24.494 26.082 30.925 (1-2) 0.062 0.048 0.070 0.069 (1-3) 0.182 0.207 0.165 0.154 (1-4) -0.153 -0.343 -0.483 -0.402 (1-5) 0.239 0.000 0.039 0.037 (1-6) 30.987 31.481 31.380 31.442 (2-1) 2.671 2.671 2.670 2.670 (2-2) 0.854 0.762 0.829 0.788 (2-3) 1.604 1.604 1.603 1.603 (2-4) 6.572 6.570 6.568 6.568 (2-5) 59.023 59.030 58.983 58.983 (2-6) - - 0.828 0.776 Fifth Embodiment, Sixth Embodiment, Seventh Embodiment, Eighth Embodiment fpf 570.149 500.567 598.892 650.422 Dpf 4.094 3.240 2.876 2.969 (1-1) 31.168 30.345 24.979 27.101 (1-2) 0.069 0.055 0.049 0.045 (1-3) 0.200 0.192 0.201 0.268 (1-4) -0.401 -0.383 -0.437 -0.223 (1-5) 0.051 0.000 0.174 0.000 (1-6) 39.062 41.989 42.857 31.750 (2-1) 2.035 1.835 2.672 2.400 (2-2) 0.958 1.068 0.813 0.913 (2-3) 1.602 1.602 2.407 1.440 (2-4) 6.564 6.562 6.575 6.600 (2-5) 58.989 58.991 59.034 65.988 (2-6) 1.080 0.975 - -

Explanation of Symbols

[0172] 1 Camera (Optical Device) OL (OL1~OL8) Optical System G1 First Lens Group GR Rear Group G2 Second Lens Group G2A Second A Lens Group G2B Second B Lens Group G3 Third Lens Group S Aperture Stop Lpf Diffractive Optical Element

Claims

1. Comprising, in order from the object side, a first lens group having a negative refractive power, and a rear group having a positive refractive power and an aperture stop, wherein the first lens group and the rear group are separated by the maximum air space on the object side of the aperture stop, the rear group has at least one diffractive optical element, the rear group has at least one cemented lens on each of the object side and the image side of the aperture stop, each of the cemented lenses has at least one positive lens and one negative lens, an optical system satisfying the conditions of the following formula. 10.0 < fpf / f < 100.0 0.10 < n1 - n2 n3 - n4 < -0.10 However, fpf: the focal length of the diffractive optical surface of the diffractive optical element f: the overall focal length of the optical system n1: the refractive index with respect to the d-line of the medium of the positive lens disposed most on the object side of the cemented lens disposed most on the image side among the cemented lenses disposed on the object side of the aperture stop n2: the refractive index with respect to the d-line of the medium of the negative lens disposed most on the image side of the cemented lens disposed most on the image side among the cemented lenses disposed on the object side of the aperture stop n3: the refractive index with respect to the d-line of the medium of the positive lens disposed most on the object side of the cemented lens disposed most on the object side among the cemented lenses disposed on the image side of the aperture stop n4: the refractive index with respect to the d-line of the medium of the negative lens disposed most on the image side of the cemented lens disposed most on the object side among the cemented lenses disposed on the image side of the aperture stop

2. The rear group comprises, in order from the object side, a second lens group having a positive refractive power and having the aperture stop, and a third lens group having a negative refractive power, wherein the second lens group and the third lens group are separated by the maximum air space on the image side of the aperture stop. The optical system according to claim 1.

3. The rear group comprises, in order from the object side, a second lens group having a positive refractive power and having the aperture stop, and a third lens group having a negative refractive power, wherein the second lens group comprises, in order from the object side, a second A lens group having a positive refractive power and having the aperture stop, and a second B lens group having a positive refractive power and moving toward the object side when focusing from infinity to a near-distance object. The optical system according to claim 1.

4. The diffractive optical element is disposed on the lens surface or the cemented surface of the lens component adjacent to the aperture stop. The optical system according to any one of claims 1 to 3.

5. The optical system according to any one of claims 1 to 4, satisfying the conditions of the following formula. -0.50 < Dpf / TL < 0.50 However, Dpf: The distance on the optical axis from the aperture to the diffractive optical surface of the diffractive optical element TL: The overall optical length of the optical system **Claim 6** The rear group has a cemented lens having at least one positive refractive power on the object side of the aperture, The optical system according to any one of claims 1 to 5, having a cemented lens having at least one positive refractive power on the image side of the aperture. **Claim 7** The optical system according to any one of claims 1 to 6, satisfying the condition of the following formula. SAG < 0.50 [mm] However, SAG: The maximum value of the absolute value of the sag amount within the effective diameter of the surface on which the diffractive optical surface of the diffractive optical element is formed **Claim 8** The optical system according to any one of claims 1 to 7, consisting only of spherical lenses. **Claim 9** The optical system according to any one of claims 1 to 8, satisfying the condition of the following formula. 25.0 [°] < ω However, ω: The semi-field angle of the optical system **Claim 10** The optical system according to any one of claims 1 to 9, which is a single-focus lens. **Claim 11** The optical system according to any one of claims 1 to 10, having only one diffractive optical element. **Claim 12** An optical device having the optical system according to any one of claims 1 to 11.

Images