Image-forming optical system

Abstract

To provide an image-forming optical system that achieves both of a high image-forming performance and miniaturization / reduced weight while having a large aperture ratio, has a light focus lens group, and suppresses bleeding at the time of focusing.SOLUTION: An image-forming optical system consists of a first lens group, a second lens group, a third lens group with positive refractive power, a fourth lens group with positive refractive power, and a fifth lens group with negative refractive power, in order from the object side to the image side, the first lens group is immobile relative to an image surface at the time of focusing from an object at infinity to a near-distance object, the second lens group travels to an object side along a light axis, the third lens group is immobile relative to an image surface, the fourth lens group travels to an object side along the light axis, the fifth lens group is immobile relative to an image surface, an aperture diaphragm is provided between a lens surface in the furthest image side of the second lens group and a lens surface in the furthest object side of the fourth lens group, and a predetermined conditional expression is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging optical system suitable for a photographic lens used in an imaging device such as a digital camera or video camera. [Background technology]

[0002] In photographic lenses used in imaging devices such as digital cameras, there is a demand for imaging optical systems with a large aperture ratio and a bright F-number, for reasons such as the fact that the amount of blur in front of and behind the focused object distance is increased, thereby widening the range of image expression that makes use of the blur, and the fact that camera shake and subject blur can be more easily suppressed by shortening the exposure time. Conventionally, the following patent documents, for example, are known as imaging optical systems with a large aperture ratio. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7123383 [Patent Document 2] International Publication No. 2022 / 059463 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, photographic lenses used in imaging devices such as digital cameras are being required to have high imaging performance as image sensors become more highly pixelated. Furthermore, as the trend toward mirrorless cameras has led to an increase in compact and lightweight cameras, the imaging optical systems of the photographic lenses combined with these cameras are also being required to be compact and lightweight. Even imaging optical systems with large aperture ratios are being required to achieve both high performance and compactness and light weight.

[0005] In recent years, there has been a demand for faster autofocusing and quieter focus operation, and reducing the weight of the focus lens group is advantageous for achieving this. Furthermore, video shooting using digital cameras has become increasingly common in recent years. Imaging optical systems used in video shooting are required to suppress changes in the angle of view that occur when different in-focus positions are achieved through focusing, a phenomenon known as focus breathing.

[0006] The optical system disclosed in Patent Document 1 achieves high imaging performance with a large aperture ratio, with an F-number of approximately F1.25, and in some embodiments, the amount of focus breathing is small. However, the overall length of the entire optical system is long and the glass material is heavy, making it difficult to achieve a sufficiently small and lightweight design. Another issue is that the number of focus lens elements is large, making it difficult to reduce the weight of the focus lens element. The optical system disclosed in Patent Document 2 achieves high imaging performance with a large aperture ratio, with an F-number of approximately F1.44, and making it difficult to reduce the overall length and glass material weight of the entire optical system. However, the issue is that focus breathing is large during focusing, and the number of focus lens elements is large, making it difficult to reduce the weight of the focus lens element.

[0007] The present invention has been made in consideration of these circumstances, and its object is to provide an imaging optical system that has a large aperture ratio yet combines high imaging performance with compactness and light weight, has a lightweight focus lens group, and suppresses breathing during focusing. [Means for solving the problem]

[0008] In order to achieve the above object, an imaging optical system embodying the present invention comprises, in order from the object side to the image side, a first lens group G1, a second lens group G2, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power; during focusing from an object at infinity to an object at a close distance, the first lens group G1 is stationary with respect to the image plane, the second lens group G2 moves toward the object along the optical axis, the third lens group G3 is stationary with respect to the image plane, the fourth lens group G4 moves toward the object along the optical axis, and the fifth lens group G5 is stationary with respect to the image plane; an aperture stop S is disposed between the lens surface of the second lens group G2 closest to the image and the lens surface of the fourth lens group G4 closest to the object; and the following conditional expression is satisfied: (1) 0.30 <D24 / LT<0.65 however, D24: The distance from the lens surface of the second lens group G2 closest to the image side to the lens surface of the fourth lens group G4 closest to the object side when focusing at infinity LT: Distance from the lens surface closest to the object to the image plane when focused at infinity

[0009] An imaging optical system embodying the present invention comprises, in order from the object side to the image side, a first lens group G1, a second lens group G2, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power, wherein, during focusing from an object at infinity to an object at a close distance, the first lens group G1 is stationary with respect to the image plane, the second lens group G2 moves toward the object along the optical axis, the third lens group G3 is stationary with respect to the image plane, the fourth lens group G4 moves toward the object along the optical axis, and the fifth lens group G5 is stationary with respect to the image plane, an aperture stop S is located between the lens surface of the second lens group G2 closest to the image and the lens surface of the fourth lens group G4 closest to the object, and the fifth lens group G5 includes at least one positive lens, and is characterized by satisfying the following conditional expression: (2) θgFmin5p-0.6483+0.0018×νdmin5p>0.0250 (3) νdmin5p<24.00 however, θgFmin5p: partial dispersion ratio for the g-line and F-line of the positive lens with the smallest Abbe number among at least one positive lens element in the fifth lens group G5 νdmin5p: Abbe number at the d-line of the positive lens having the smallest Abbe number among at least one positive lens element in the fifth lens group G5 [Effects of the Invention]

[0010] According to the imaging optical system embodying the present invention, it is possible to provide an imaging optical system that has a large aperture ratio yet combines high imaging performance with compactness and light weight, has a lightweight focus lens group, and suppresses breathing during focusing. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a lens configuration diagram of an imaging optical system according to a first embodiment of the present invention. [Figure 2] 4A and 4B are longitudinal aberration diagrams of the imaging optical system of Example 1 when focused at infinity. [Figure 3] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 1 at an object distance of 1462 mm. [Figure 4] 4A to 4C are diagrams showing lateral aberrations of the imaging optical system of Example 1 when focused on an object at infinity. [Figure 5] 4A to 4C are diagrams showing lateral aberrations of the imaging optical system of Example 1 at an object distance of 1462 mm. [Figure 6] FIG. 10 is a lens configuration diagram of an imaging optical system according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a longitudinal aberration diagram of the imaging optical system of Example 2 when focused at infinity. [Figure 8] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 2 at an object distance of 1477 mm. [Figure 9] 10A and 10B are diagrams illustrating lateral aberration of the imaging optical system of Example 2 when focused on infinity. [Figure 10] 10A and 10B are diagrams showing lateral aberration of the imaging optical system of Example 2 at an object distance of 1477 mm. [Figure 11] FIG. 10 is a lens configuration diagram of an imaging optical system according to a third embodiment of the present invention. [Figure 12] FIG. 10 is a longitudinal aberration diagram of the imaging optical system of Example 3 when focused at infinity. [Figure 13] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 3 at an object distance of 1260 mm. [Figure 14] 10A and 10B are diagrams illustrating lateral aberration of the imaging optical system of Example 3 when focused at infinity. [Figure 15] 10A and 10B are diagrams showing lateral aberration of the imaging optical system of Example 3 at an object distance of 1260 mm. [Figure 16] FIG. 10 is a lens configuration diagram of an imaging optical system according to a fourth embodiment of the present invention. [Figure 17] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 4 when focused at infinity. [Figure 18] 10A and 10B are longitudinal aberration diagrams of the imaging optical system of Example 4 at an object distance of 1478 mm. [Figure 19] 10A and 10B are diagrams illustrating lateral aberration of the imaging optical system of Example 4 when focused on an object at infinity. [Figure 20] 10A to 10C are diagrams showing lateral aberration of the imaging optical system of Example 4 at an object distance of 1478 mm. [Figure 21] FIG. 10 is a lens configuration diagram of an imaging optical system according to a fifth embodiment of the present invention. [Figure 22] FIG. 10 is a longitudinal aberration diagram of the imaging optical system of Example 5 when focused at infinity. [Figure 23] 10 is a longitudinal aberration diagram of the imaging optical system of Example 5 at a shooting distance of 1098 mm. [Figure 24] 10A and 10B are diagrams illustrating lateral aberration of the imaging optical system of Example 5 when focused at infinity. [Figure 25] 10A to 10C are diagrams showing lateral aberration of the imaging optical system of Example 5 at an object distance of 1098 mm. [Figure 26] FIG. 10 is a lens configuration diagram of an imaging optical system according to a sixth embodiment of the present invention. [Figure 27] FIG. 13 is a longitudinal aberration diagram of the imaging optical system of Example 6 when focused at infinity. [Figure 28] 13A and 13B are longitudinal aberration diagrams of the imaging optical system of Example 6 at an object distance of 1529 mm. [Figure 29] 13A and 13B are diagrams illustrating lateral aberration of the imaging optical system of Example 6 when focused at infinity. [Figure 30] 10A to 10C are diagrams showing lateral aberration of the imaging optical system of Example 6 at an object distance of 1529 mm. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described. When the refractive indices for the g-line (wavelength 435.8 nm), F-line (wavelength 486.1 nm), d-line (wavelength 587.6 nm), and C-line (wavelength 656.3 nm) are ng, nF, nd, and nC, respectively, the Abbe number vd and partial dispersion ratio θgF are expressed by the following equations: vd=(nd-1) / (nF-nC) θgF=(ng-nF) / (nF-nC)

[0013] As can be seen from the lens construction diagrams shown in FIGS. 1, 6, 11, 16, 21, and 26, the imaging optical system of the present invention is composed of, in order from the object side, a first lens group G1, a second lens group G2, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power. During focusing from an object at infinity to an object at a close distance, the first lens group G1 is stationary relative to the image plane, the second lens group G2 moves toward the object along the optical axis, the third lens group G3 is stationary relative to the image plane, the fourth lens group G4 moves toward the object along the optical axis, and the fifth lens group G5 is stationary relative to the image plane. An aperture diaphragm S is located between the lens surface of the second lens group G2 closest to the image and the lens surface of the fourth lens group G4 closest to the object.

[0014] In a lens configuration in which the fourth lens group G4 with positive refractive power, located closer to the image plane than the aperture stop S, is moved along the optical axis toward the object when focusing from an object at infinity to a close distance, positioning the fourth lens group G4 away from the aperture stop S makes it easier to suppress focus breathing, but on the other hand, if the height of the peripheral chief ray increases, fluctuations in aberrations during focusing, particularly fluctuations in astigmatism and coma, become greater. Increasing the number of lenses to suppress aberration fluctuations leads to an increase in the size of the entire optical system.

[0015] Therefore, when focusing from an object at infinity to an object at a close distance, in addition to the fourth lens group G4, the second lens group G2, which is positioned closer to the object than the aperture stop S, is extended along the optical axis toward the object to cancel out the aberration fluctuation that occurs during focusing. This makes it easy to achieve both suppression of aberration fluctuation and focus breathing that occur during focusing while reducing the size of the entire optical system.

[0016] In addition, the first lens group G1, which is located closest to the object in the optical system, and the fifth lens group G5, which is located closest to the image, are fixed relative to the image plane during focusing, and the lens elements that move during focusing are not exposed to the outside, which makes it easy to improve dust-proof and drip-proof performance. Because the fifth lens group G5 has negative refractive power, the exit pupil position can be moved closer to the image plane, making it easy to suppress the amount of vignetting of peripheral light rays due to restrictions on the camera mount diameter.

[0017] Furthermore, the imaging optical system of the present invention is characterized in that it satisfies the following conditional expression: (1) 0.30 <D24 / LT<0.65 however, D24: The distance from the lens surface of the second lens group G2 closest to the image side to the lens surface of the fourth lens group G4 closest to the object side when focusing at infinity LT: Distance from the lens surface closest to the object to the image plane when focused at infinity

[0018] Conditional formula (1) defines a preferable range for the appropriate placement of the second lens group G2 and the fourth lens group G4. As mentioned above, in order to suppress focus breathing, it is desirable to place the fourth lens group G4 at a position appropriately distant from the aperture stop S toward the image side, and it is also desirable to place the second lens group G2 at a position appropriately distant from the aperture stop S toward the object side, where the height of the peripheral chief ray is somewhat high, in order to offset the astigmatism and coma aberrations that occur when the fourth lens group G4 moves during focusing. In order to properly space both the second lens group G2 and the fourth lens group G4 from the aperture stop S, the distance between the second lens group G2 and the fourth lens group G4 must be set appropriately.

[0019] If the distance between the second lens group G2 and the fourth lens group G4 becomes small by exceeding the lower limit of conditional expression (1), it becomes difficult to suppress both focus breathing and aberration fluctuations during focusing.On the other hand, if the distance between the second lens group G2 and the fourth lens group G4 becomes large by exceeding the upper limit of conditional expression (1), it becomes difficult to position the first lens group G1 and the fifth lens group G5, which are fixed during focusing, or the fourth lens group G4 must be positioned near the mount in a position where radial restrictions are severe, making it difficult to position a focus actuator.

[0020] It is to be noted that, with regard to conditional expression (1), it is desirable to set the lower limit to 0.35 and the upper limit to 0.60, thereby making it possible to ensure the above-mentioned effect.

[0021] Furthermore, in the imaging optical system of the present invention, the fifth lens group G5 has at least one positive lens, which makes it easier to suppress chromatic aberrations that occur in the fifth lens group G5, which has negative refractive power.

[0022] It is also desirable to satisfy the following conditional expression: (2) θgFmin5p-0.6483+0.0018×νdmin5p>0.0250 (3) νdmin5p<24.00 however, θgFmin5p: partial dispersion ratio for the g-line and F-line of the positive lens with the smallest Abbe number among the positive lenses in the fifth lens group G5 νdmin5p: Abbe number for the d-line of the positive lens having the smallest Abbe number among the positive lenses in the fifth lens group G5

[0023] Conditions (2) and (3) define desirable characteristics for the material of at least one positive lens element in the fifth lens group G5 in order to effectively correct chromatic aberration, including secondary spectrum. Because the fifth lens group G5 is located close to the image plane, the height of the peripheral chief ray is high, and in an imaging optical system with a large aperture ratio, the axial ray diameter is also large, so the lenses in the fifth lens group G5 contribute to the correction of both lateral chromatic aberration and axial chromatic aberration.

[0024] To effectively correct chromatic aberration, including secondary spectra, it is desirable to use a material with high anomalous dispersion (a larger partial dispersion ratio than ordinary materials) for the positive lens element. Optical glasses with particularly high anomalous dispersion can be broadly divided into low-refractive-index, low-dispersion glasses and high-refractive-index, high-dispersion glasses. The fifth lens group G5 has negative refractive power, and if a low-refractive-index, low-dispersion material were used for the positive lens element, the first-order achromatization within the fifth lens group G5 would be insufficient. Therefore, it is preferable to select a material with a high refractive index and high dispersion. Furthermore, using a high-refractive-index material for the positive lens element also makes it easier to suppress the Petzval sum of the entire lens system and effectively correct astigmatism.

[0025] If the anomalous dispersion of at least one positive lens in the fifth lens group G5 decreases beyond the lower limit of conditional expression (2), it becomes difficult to effectively correct axial chromatic aberration including secondary spectrum and chromatic aberration of magnification.

[0026] It is to be noted that, preferably, the lower limit of conditional expression (2) should be set to 0.0300, thereby making it possible to ensure the above-mentioned effect.

[0027] If the Abbe number of at least one positive lens element in the fifth lens element becomes large enough to exceed the upper limit of conditional expression (3), then the optical glasses that satisfy conditional expression (2) are currently limited to those in the low refractive index, low dispersion region, which results in insufficient first-order achromatism within the fifth lens group G5 and makes it difficult to suppress the Petzval sum of the entire lens system and to effectively correct astigmatism.

[0028] It is to be noted that, preferably, the upper limit of conditional expression (3) should be set to 20.50, thereby making it possible to ensure the above-mentioned effect.

[0029] Furthermore, in the imaging optical system of the present invention, the fifth lens group G5 is characterized by having at least two positive lenses. If the fifth lens group G5 had only one positive lens that satisfied conditional expressions (2) and (3), the Abbe number would be small and a slight change in the power of the positive lens would significantly change the balance of chromatic aberration, reducing the degree of freedom in correcting various aberrations other than chromatic aberration, such as spherical aberration. Therefore, by arranging a positive lens in the fifth lens group G5 in addition to the positive lens that satisfies conditional expressions (2) and (3), it becomes easier to simultaneously correct chromatic aberration and various other aberrations.

[0030] The present invention is also characterized in that the following conditional expressions are satisfied. (4) νdmax5p-νdmin5p>15.00 however, νdmax5p: Abbe number at the d-line of the positive lens having the largest Abbe number among the at least two positive lenses in the fifth lens group G5 νdmin5p: Abbe number at the d-line of the positive lens having the smallest Abbe number among the at least two positive lenses in the fifth lens group G5

[0031] Conditional expression (4) defines a preferable range for the difference in Abbe number between the positive lens with the largest Abbe number and the positive lens with the smallest Abbe number, among the at least two positive lenses in the fifth lens group G5.

[0032] If the difference in Abbe number between the positive lens with the largest Abbe number and the positive lens with the smallest Abbe number becomes small beyond the lower limit of conditional expression (4), then the Abbe numbers of all of the positive lenses in fifth lens group G5 will become small in combination with conditional expression (3), reducing the degree of freedom for correcting chromatic aberration and other aberrations and making it difficult to achieve good aberration correction.

[0033] It is to be noted that, preferably, the lower limit of conditional expression (4) should be set to 20.00, thereby making it possible to ensure the above-mentioned effect.

[0034] Furthermore, in the imaging optical system of the present invention, the fourth lens group G4 is characterized by comprising one or two positive lens elements and one negative lens element. Although the fourth lens group G4 has positive refractive power, the placement of a negative lens element to suppress chromatic aberration within the fourth lens group G4 makes it easy to suppress fluctuations in chromatic aberration during focusing. If the number of lenses in the focus lens group increases and the weight increases, this will be disadvantageous in terms of speeding up autofocus and quietness during focus drive, and will also require a large actuator, making it difficult to make the photographic lens small and lightweight. Therefore, it is desirable to have a configuration of one or two positive lenses and one negative lens.

[0035] Furthermore, in the imaging optical system of the present invention, when focusing from an object at infinity to an object at a close distance, the second lens group G2 and the fourth lens group G4 move toward the object along the optical axis along different trajectories. Increasing the degree of freedom in the amount of movement of the second lens group G2 and the fourth lens group G4 makes it easier to suppress fluctuations in various aberrations during focusing.

[0036] Furthermore, the imaging optical system of the present invention is characterized in that it satisfies the following conditional expression: (5) 0.50<(1-β4^2)×β4R^2<2.50 (6) |((1-β2^2)×β2R^2) / ((1-β4^2)×β4R^2)|<0.50 however, β4: Lateral magnification of the fourth lens group G4 when focusing at infinity β4R: Lateral magnification of the lens system located closer to the image than the fourth lens group G4 when focusing at infinity β2: Lateral magnification of the second lens group G2 when focusing at infinity β2R: Lateral magnification of the lens system located closer to the image than the second lens group G2 when focusing at infinity

[0037] The fourth lens group G4, which has positive refractive power and is located closer to the image than the aperture stop S, is responsible for most of the focusing action, making it easier to suppress breathing during focusing. Therefore, it is preferable to set the focus sensitivity of the fourth lens group G4 to an appropriate value, and then set the focus sensitivity of the second lens group G2 to a value smaller than that of the fourth lens group G4. Conditional expression (5) defines a preferable range for the focus sensitivity of the fourth lens group G4.

[0038] If the lower limit of conditional expression (5) is exceeded and the focus sensitivity of the fourth lens group G4 decreases, the amount of movement required to achieve the desired minimum focusing distance increases, and the overall lens length and the actuator must be increased to ensure movement space, making it difficult to reduce the size and weight of the photographic lens. On the other hand, if the upper limit of conditional expression (5) is exceeded and the focus sensitivity of the fourth lens group G4 increases, the positive refractive power of the fourth lens group G4 increases and the sensitivity of the fourth lens group G4 to decentration increases, i.e., the amount of performance degradation when decentration occurs increases. The fourth lens group G4 is prone to decentration because it moves during focusing, and if the sensitivity of the fourth lens group G4 to decentration exceeds the upper limit, it becomes difficult to suppress individual variations in the imaging performance of the photographic lens.

[0039] It should be noted that, with regard to conditional expression (5), it is desirable to set the lower limit to 0.65 and the upper limit to 2.00, thereby making it possible to ensure the above-mentioned effect.

[0040] Conditional expression (6) defines a preferable range for the ratio between the focus sensitivity of the second lens group G2 and the focus sensitivity of the fourth lens group G4.

[0041] If the upper limit of conditional expression (6) is exceeded and the ratio of the focus sensitivity of the second lens group G2 becomes large, it becomes difficult to sufficiently suppress breathing during focusing.

[0042] It is to be noted that, preferably, the upper limit of conditional expression (6) should be set to 0.40, thereby making it possible to ensure the above-mentioned effect.

[0043] Furthermore, in the imaging optical system of the present invention, the third lens group G3 has at least two positive lenses and at least two negative lenses. By increasing the number of positive and negative lenses in the third lens group G3, where the axial light beam diameter is large near the aperture stop S, it becomes easier to effectively correct various aberrations, particularly axial chromatic aberration, spherical aberration, and coma, even in an imaging optical system with a large aperture ratio.

[0044] The present invention is also characterized in that the following conditional expressions are satisfied. (7) νdmax3p-νdmin3p>30.00 (8) θgFmax3p-0.6483+0.0018×νdmax3p>0.0120 (9) θgFmin3p-0.6483+0.0018×νdmin3p>0.0200 however, νdmax3p: Abbe number at the d-line of the positive lens having the largest Abbe number among the at least two positive lenses in the third lens group G3 νdmin3p: Abbe number at the d-line of the positive lens having the smallest Abbe number among the at least two positive lenses included in the third lens group G3 θgFmax3p: partial dispersion ratio for the g-line and F-line of the positive lens with the largest Abbe number among the at least two positive lenses in the third lens group G3 θgFmin3p: partial dispersion ratio for the g-line and F-line of the positive lens with the smallest Abbe number among the at least two positive lenses in the third lens group G3

[0045] In order to effectively correct chromatic aberration, including secondary spectrum, it is desirable to use a material with high anomalous dispersion (a larger partial dispersion ratio than normal materials) for the positive lens element. In particular, using a material with high anomalous dispersion for the positive lens element near the aperture makes it easier to effectively correct on-axis chromatic aberration. Optical glasses that exist as materials with particularly high anomalous dispersion can be broadly divided into low refractive index, low dispersion glasses and high refractive index, high dispersion glasses.

[0046] If low-refractive-index, low-dispersion materials were used for all positive lenses in the third lens group G3, the curvature of the positive lenses would need to be increased to obtain the necessary positive refractive power, which would increase the overall length and weight of the lens system, making it difficult to make the photographic lens smaller and lighter. Furthermore, the Petzval sum would increase, making it difficult to suppress astigmatism. On the other hand, if high-refractive-index, high-dispersion materials were used for all positive lenses in the third lens group G3, the chromatic aberration generated within the third lens group G3 would increase, making it difficult to effectively correct chromatic aberration throughout the entire lens system.

[0047] Therefore, it is desirable to have both a positive lens made of a material with a low refractive index, low dispersion, and high anomalous dispersion, and a positive lens made of a material with a high refractive index, high dispersion, and high anomalous dispersion. Conditional formula (7) defines a preferable range for the difference in Abbe number between the positive lens with the largest Abbe number and the positive lens with the smallest Abbe number in the third lens group G3.

[0048] If the lower limit of conditional expression (7) is exceeded, and the difference in Abbe number between the positive lens element with the largest Abbe number and the positive lens element with the smallest Abbe number in the third lens group G3 becomes small, it becomes difficult to provide, with currently available optical glass, both a positive lens element made of a material with a low refractive index, low dispersion, and high anomalous dispersion, and a positive lens element made of a material with a high refractive index, high dispersion, and high anomalous dispersion, making it difficult to simultaneously achieve good correction of chromatic aberrations, including secondary spectrum, good correction of aberrations other than chromatic aberration, and a compact, lightweight photographic lens.

[0049] It is to be noted that, preferably, the lower limit of conditional expression (7) should be set to 35.00, thereby making it possible to ensure the above-mentioned effect.

[0050] Conditional expression (8) defines a preferable range for the anomalous dispersion of the positive lens having the largest Abbe number in the third lens group G3.

[0051] If the lower limit of conditional expression (8) is exceeded and the anomalous dispersion of the positive lens having the largest Abbe number in the third lens group G3 becomes small, it becomes difficult to effectively correct chromatic aberrations including secondary spectrum, particularly axial chromatic aberration.

[0052] It is to be noted that, preferably, the lower limit of conditional expression (8) should be set to 0.0150, thereby making it possible to ensure the above-mentioned effect.

[0053] Condition (9) defines a preferable range for the anomalous dispersion of the positive lens having the smallest Abbe number in the third lens group G3.

[0054] If the lower limit of conditional expression (9) is exceeded and the anomalous dispersion of the positive lens having the largest Abbe number in the third lens group G3 becomes small, it becomes difficult to effectively correct chromatic aberrations including secondary spectrum, particularly axial chromatic aberration.

[0055] It is to be noted that, preferably, the lower limit of conditional expression (9) should be set to 0.0250, thereby making it possible to ensure the above-mentioned effect.

[0056] Furthermore, the imaging optical system of the present invention is characterized in that it satisfies the following conditional expression: (10) D2S / LT>0.06 (11) D4S / LT>0.15 however, D2S: The distance from the lens surface closest to the image in the second lens group G2 to the aperture stop S when focusing at infinity D4S: Distance from the lens surface closest to the object in the fourth lens group G4 to the aperture stop S when focusing at infinity LT: Distance from the lens surface closest to the object to the image plane when focused at infinity

[0057] Conditional expression (10) defines a preferable range for the appropriate placement of the second lens group G2 and the aperture stop S. It is desirable that the second lens group G2 be placed at a position that is an appropriate distance from the aperture stop S toward the object side, where the height of the peripheral chief ray is somewhat high, in order to offset the astigmatism and coma that occur when the fourth lens group G4 moves during focusing.

[0058] If the distance between the second lens group G2 and the aperture stop S becomes small beyond the lower limit of condition (10), it becomes difficult to suppress fluctuations in various aberrations, particularly fluctuations in astigmatism and coma, during focusing.

[0059] It is to be noted that, preferably, the lower limit of conditional expression (10) should be set to 0.10, thereby making it possible to ensure the above-mentioned effect.

[0060] Conditional expression (11) defines a preferable range for the appropriate placement of the fourth lens group G4 and aperture stop S. As mentioned above, in order to suppress focus breathing, it is desirable to place the fourth lens group G4 at a position that is an appropriate distance away from the aperture stop S toward the image side.

[0061] If the distance between the fourth lens group G4 and the aperture stop S becomes small beyond the lower limit of conditional expression (11), it becomes difficult to suppress focus breathing.

[0062] It is to be noted that, preferably, the lower limit of conditional expression (11) should be set to 0.20, thereby making it possible to ensure the above-mentioned effect.

[0063] Furthermore, in the imaging optical system of the present invention, the third lens group G3 is characterized by being composed of, from the object side, a 3a lens group G3a having a negative refractive power, an aperture stop S, and a 3b lens group G3b having a positive refractive power. In an imaging optical system with a large aperture ratio, it is preferable to initially widen the F-number light beam diameter and then converge it toward the image plane in order to effectively correct spherical aberration and coma. On the other hand, to reduce the weight of the second lens group G2 and the fourth lens group G4, which move during focusing, it is preferable to reduce the F-number light beam diameter in the second lens group G2 and the fourth lens group G4. To achieve both of these, it is desirable to have a configuration in which the object side of the third lens group G3 has a negative refractive power and the image side has a positive refractive power, so that the F-number light beam diameter within the third lens group G3 diverges and then converges toward the fourth lens group G4.

[0064] In addition, the negative refractive power of the 3a-th lens group G3a moves the entrance pupil position toward the object side, lowering the ray heights of peripheral rays in the first lens group G1 and the second lens group G2 and making it easier to reduce the lens diameter and make the photographic lens smaller and lighter. In addition, the positive refractive power of the 3b-th lens group G3b moves the exit pupil position toward the object side, reducing the ray incidence angle of peripheral chief rays incident on the image plane and making it easier to maintain the allowable range of ray incidence angles for the image sensor. In addition, the positive refractive power of the 3b-th lens group G3b reduces the angle between the optical axis and peripheral chief rays incident on the fourth lens group G4, making it easier to suppress focus breathing during focusing.

[0065] The present invention is also characterized in that the following conditional expressions are satisfied. (12) -3.00 <f3a / f<-0.50 (13) 0.50 <f3b / f<3.00 however, f: focal length of the entire lens system when focused at infinity f3a: focal length of the 3ath lens group G3a f3b: focal length of the third lens group G3b

[0066] Conditional expression (12) defines a preferable range for the ratio of the focal length of the 3a-th lens group G3a to the focal length of the entire lens system.

[0067] If the negative refractive power of the 3a lens group G3a becomes weaker than the lower limit of conditional expression (12), the F-number light beam cannot be sufficiently widened within the 3a lens group G3, making it difficult to effectively correct various aberrations, particularly spherical aberration and coma. Also, if the negative refractive power of the 3a lens group G3a becomes weaker, the entrance pupil position of the entire lens system moves toward the image side, and if an attempt is made to maintain peripheral illumination, the lens diameters of the first lens group G1 and the second lens group G2 become larger, making it difficult to make the photographic lens compact and lightweight.

[0068] On the other hand, if the negative refractive power of the 3a lens group G3a becomes strong beyond the upper limit of conditional expression (12), the positive refractive power of the 3b lens group G3b becomes strong in order to maintain the refractive power of the 3rd lens group G3 as a whole, the 3a lens group G3a and the 3b lens group G3b become more sensitive to decentration, and it becomes difficult to suppress individual variations in the imaging performance of the photographic lens. Also, if the negative refractive power of the 3a lens group G3a becomes strong, the entrance pupil position of the entire lens system moves toward the object side, the height of the peripheral chief ray in the second lens group G2 becomes lower, and it becomes difficult to cancel out and suppress fluctuations in various aberrations generated in the fourth lens group G4 during focusing.

[0069] It should be noted that, with regard to conditional expression (12), it is desirable to set the lower limit to -2.00 and the upper limit to -0.70, thereby making it possible to ensure the above-mentioned effect.

[0070] Conditional expression (13) defines a preferable range for the ratio of the focal length of the 3bth lens group G3b to the focal length of the entire lens system.

[0071] If the positive refractive power of the 3b lens group G3b becomes too strong beyond the lower limit of conditional expression (13), the negative refractive power of the 3a lens group G3a becomes too strong in order to maintain the refractive power of the 3rd lens group G3 as a whole, the 3a lens group G3a and the 3b lens group G3b become more sensitive to decentration, and it becomes difficult to suppress individual variations in the imaging performance of the photographic lens. Also, if the positive refractive power of the 3b lens group G3b becomes too strong, the exit pupil position of the entire lens system moves toward the object, and if an attempt is made to maintain peripheral illumination, the lens diameters of the 4th lens group G4 and the 5th lens group G5 become larger, making it difficult to make the photographic lens small and lightweight.

[0072] On the other hand, if the upper limit of conditional expression (13) is exceeded and the positive refractive power of the 3b lens group G3b becomes weak, the F-number light beam cannot be sufficiently converged toward the fourth lens group G4, the lens diameter of the fourth lens group G4 increases, and it becomes difficult to make the photographic lens compact and lightweight. Also, if the positive refractive power of the 3b lens group G3b becomes weak, the exit pupil position of the entire lens system moves toward the image side, increasing the angle of incidence of light rays on the image plane, making it difficult to maintain the allowable range of incident light angles of the image sensor. Also, the angle between the peripheral chief ray incident on the fourth lens group G4 and the optical axis becomes large, making it difficult to suppress focus breathing during focusing.

[0073] It is to be noted that, with regard to conditional expression (13), it is desirable to set the lower limit to 0.70 and the upper limit to 2.00, thereby making it possible to ensure the above-mentioned effect.

[0074] It is more preferable that the imaging optical system of the present invention further has the following configuration.

[0075] By introducing aspherical surfaces into the second lens group G2 and the fourth lens group G4, it becomes easier to suppress fluctuations in spherical aberration, coma, and field curvature during focusing.

[0076] By introducing an aspherical surface into the third lens group G3, it becomes easier to suppress various aberrations, particularly spherical aberration and coma.

[0077] By introducing into the fifth lens group G5 an aspherical surface shaped to increase the negative refractive power from the optical axis center to the periphery, it becomes easier to suppress various aberrations, particularly astigmatism.

[0078] By arranging two or more pairs of cemented lenses in the third lens group G3, it becomes easier to suppress various aberrations, particularly axial chromatic aberration, while suppressing sensitivity to decentration.

[0079] Next, the lens configuration of an embodiment of the imaging optical system of the present invention will be described. In the following description, the lens configuration will be described in order from the object side to the image side. [Example]

[0080] FIG. 1 is a lens configuration diagram of an imaging optical system according to a first embodiment of the present invention.

[0081] From the object side, the lens is composed of a first lens group G1 with negative refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power, and when focusing from an object at infinity to a close object, the second lens group G2 moves toward the object along the optical axis, and the fourth lens group G4 moves toward the object along the optical axis.

[0082] The first lens group G1 is composed of a negative meniscus lens with a convex surface facing the object side.

[0083] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the object side, and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0084] The third lens group G3 is composed of a 3a lens group G3a with negative refractive power, an aperture stop S, and a 3b lens group G3b with positive refractive power. The 3a lens group G3a is composed of a cemented lens consisting of a positive meniscus lens with its convex surface facing the image side and a biconcave lens, and a cemented lens consisting of a biconcave lens and a positive meniscus lens with its convex surface facing the object side. The 3b lens group G3b is composed of a biconvex lens, a biconvex lens, and a cemented lens consisting of a biconcave lens and a biconvex lens. The object-side surface and image-side surface of the biconvex lens arranged on the object side have a predetermined aspherical shape.

[0085] The fourth lens group G4 is composed of a negative meniscus lens with its convex surface facing the object side, and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0086] The fifth lens group G5 consists of a positive meniscus lens with its convex surface facing the image side, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconcave lens. The object-side and image-side surfaces of the biconcave lens located on the image side have predetermined aspherical shapes. [Example]

[0087] FIG. 6 is a lens configuration diagram of an imaging optical system according to a second embodiment of the present invention.

[0088] From the object side, the lens is composed of a first lens group G1 with positive refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power, and when focusing from an object at infinity to a close object, the second lens group G2 moves toward the object along the optical axis, and the fourth lens group G4 moves toward the object along the optical axis.

[0089] The first lens group G1 is composed of a positive meniscus lens with its convex surface facing the object side.

[0090] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the object side, and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0091] The third lens group G3 is composed of a 3a lens group G3a with negative refractive power, an aperture stop S, and a 3b lens group G3b with positive refractive power. The 3a lens group G3a is composed of a biconcave lens and a cemented lens consisting of a biconcave lens and a biconvex lens. The 3b lens group G3b is composed of a biconvex lens, a cemented lens consisting of a biconcave lens and a positive meniscus lens with its convex surface facing the object side, and a cemented lens consisting of a negative meniscus lens with its convex surface facing the object side and a biconvex lens. The object-side surface and image-side surface of the biconvex lens arranged on the object side have predetermined aspherical shapes.

[0092] The fourth lens group G4 is composed of a biconcave lens and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0093] The fifth lens group G5 is composed of a biconvex lens, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconcave lens. The object-side and image-side surfaces of the biconcave lens located on the image side have predetermined aspherical shapes. [Example]

[0094] FIG. 11 is a diagram showing the lens arrangement of an imaging optical system according to a third embodiment of the present invention.

[0095] From the object side, the lens is composed of a first lens group G1 with negative refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power, and when focusing from an object at infinity to a close object, the second lens group G2 moves toward the object along the optical axis, and the fourth lens group G4 moves toward the object along the optical axis.

[0096] The first lens group G1 is composed of a negative meniscus lens with a convex surface facing the object side, and another negative meniscus lens with a convex surface facing the object side. The object-side surface and image-side surface of the negative meniscus lens arranged on the object side have a predetermined aspherical shape.

[0097] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the object side, and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0098] The third lens group G3 is composed of a 3a lens group G3a with negative refractive power, an aperture stop S, and a 3b lens group G3b with positive refractive power. The 3a lens group G3a is composed of a biconcave lens and a cemented lens consisting of a biconcave lens and a biconvex lens. The 3b lens group G3b is composed of a biconvex lens, a cemented lens consisting of a biconcave lens and a positive meniscus lens with its convex surface facing the object side, and a cemented lens consisting of a negative meniscus lens with its convex surface facing the object side and a biconvex lens. The object-side surface and image-side surface of the biconvex lens arranged on the object side have predetermined aspherical shapes.

[0099] The fourth lens group G4 is composed of a biconcave lens and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0100] The fifth lens group G5 is composed of a biconvex lens, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconcave lens. The object-side and image-side surfaces of the biconcave lens located on the image side have predetermined aspherical shapes. [Example]

[0101] FIG. 16 is a lens configuration diagram of an imaging optical system according to a fourth embodiment of the present invention.

[0102] From the object side, the lens is composed of a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power, and when focusing from an object at infinity to a close object, the second lens group G2 moves toward the object along the optical axis, and the fourth lens group G4 moves toward the object along the optical axis.

[0103] The first lens group G1 is composed of a positive meniscus lens with its convex surface facing the object side.

[0104] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the object side, and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0105] The third lens group G3 is composed of a 3a lens group G3a with negative refractive power, an aperture stop S, and a 3b lens group G3b with positive refractive power. The 3a lens group G3a is composed of a biconcave lens and a cemented lens consisting of a biconcave lens and a biconvex lens. The 3b lens group G3b is composed of a biconvex lens, a cemented lens consisting of a biconcave lens and a positive meniscus lens with its convex surface facing the object side, and a cemented lens consisting of a negative meniscus lens with its convex surface facing the object side and a biconvex lens. The object-side surface and image-side surface of the biconvex lens arranged on the object side have predetermined aspherical shapes.

[0106] The fourth lens group G4 is composed of a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconvex lens. The object-side and image-side surfaces of the biconvex lens placed on the image side have a predetermined aspherical shape.

[0107] The fifth lens group G5 is composed of a biconvex lens, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconcave lens. The object-side and image-side surfaces of the biconcave lens located on the image side have predetermined aspherical shapes. [Example]

[0108] FIG. 21 is a lens configuration diagram of an imaging optical system according to a fifth embodiment of the present invention.

[0109] From the object side, the lens is composed of a first lens group G1 with negative refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power, and when focusing from an object at infinity to a close object, the second lens group G2 moves toward the object along the optical axis, and the fourth lens group G4 moves toward the object along the optical axis.

[0110] The first lens group G1 consists of a negative meniscus lens with a convex surface facing the object side, and a cemented lens consisting of a biconcave lens and a positive meniscus lens with a convex surface facing the object side. The object-side and image-side surfaces of the negative meniscus lens have predetermined aspherical shapes.

[0111] The second lens group G2 is composed of a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0112] The third lens group G3 is composed of a 3a lens group G3a with negative refractive power, an aperture stop S, and a 3b lens group G3b with positive refractive power. The 3a lens group G3a is composed of a biconcave lens and a cemented lens consisting of a biconcave lens and a biconvex lens. The 3b lens group G3b is composed of a biconvex lens, a cemented lens consisting of a biconcave lens and a positive meniscus lens with its convex surface facing the object side, and a cemented lens consisting of a negative meniscus lens with its convex surface facing the object side and a biconvex lens. The object-side surface and image-side surface of the biconvex lens arranged on the object side have predetermined aspherical shapes.

[0113] The fourth lens group G4 is composed of a biconcave lens and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0114] The fifth lens group G5 is composed of a biconvex lens, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconcave lens. The object-side and image-side surfaces of the biconcave lens located on the image side have predetermined aspherical shapes. [Example]

[0115] FIG. 26 is a lens configuration diagram of an imaging optical system according to a sixth embodiment of the present invention.

[0116] From the object side, the lens is composed of a first lens group G1 with positive refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power, and when focusing from an object at infinity to a close object, the second lens group G2 moves toward the object along the optical axis, and the fourth lens group G4 moves toward the object along the optical axis.

[0117] The first lens group G1 is composed of a positive meniscus lens with its convex surface facing the object side.

[0118] The second lens group G2 is composed of a negative meniscus lens with a convex surface facing the object side, and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0119] The third lens group G3 is composed of a 3a lens group G3a with negative refractive power, an aperture stop S, and a 3b lens group G3b with positive refractive power. The 3a lens group G3a is composed of a biconcave lens and a cemented lens consisting of a biconcave lens and a biconvex lens. The 3b lens group G3b is composed of a biconvex lens and a cemented triplet lens consisting of a biconvex lens, a biconcave lens, and a biconvex lens. The object-side surface and image-side surface of the biconvex lens arranged on the object side have a predetermined aspherical shape.

[0120] The fourth lens group G4 is composed of a biconcave lens and a biconvex lens, the object-side surface and the image-side surface of which have a predetermined aspherical shape.

[0121] The fifth lens group G5 is composed of a biconvex lens, a cemented lens consisting of a biconvex lens and a biconcave lens, and a biconcave lens. The object-side and image-side surfaces of the biconcave lens located on the image side have predetermined aspherical shapes.

[0122] Specific numerical data for each of the embodiments of the imaging optical system of the present invention described above will be shown below.

[0123] In the [Surface Data], the surface number is the lens surface or aperture stop number counted from the object side, r is the radius of curvature of each surface, d is the spacing between surfaces, nd is the refractive index for the d-line (587.6 nm), vd is the Abbe number for the d-line, and θgF is the partial dispersion ratio.

[0124] An asterisk (*) next to a surface number indicates that the lens surface is aspherical, and BF represents the back focal length.

[0125] The (diaphragm) next to the surface number indicates that an aperture diaphragm is located at that position. The radius of curvature for the plane or aperture diaphragm is marked as ∞ (infinity).

[0126] [Aspherical Data] shows the coefficient values ​​that give the aspherical shape of lens surfaces marked with an * in [Surface Data]. The aspherical shape is defined as follows: y is the displacement from the optical axis in a direction perpendicular to the optical axis, z is the displacement (sag) from the intersection of the aspherical surface and the optical axis in the direction of the optical axis, r is the radius of curvature of the reference sphere, K is the Conic coefficient, and A4, A6, A8, ... are the aspherical coefficients of each order, respectively. The coordinates of the aspherical shape are expressed by the following equation:

[0127] TIFF2025167449000002.tif19147

[0128] [Various Data] shows values ​​such as focal length at each shooting distance and in focus state.

[0129] [Variable Distance Data] shows the variable distance and BF values ​​for each shooting distance and focus state.

[0130] [Lens Group Data] shows the surface number of each lens group closest to the object and the composite focal length of the entire group.

[0131] In addition, for all of the values ​​of the following specifications, the focal length f, radius of curvature r, lens surface spacing d, and other length units are given in millimeters (mm) unless otherwise specified; however, this is not a limitation, as optical systems can achieve equivalent optical performance with proportional magnification and proportional reduction.

[0132] Also shown is a list of values ​​corresponding to the conditional expressions in each of these embodiments.

[0133] In the aberration diagrams corresponding to the respective examples, d, g, and C represent the d-line, g-line, and C-line, respectively, and ΔS and ΔM represent the sagittal image surface and meridional image surface, respectively.

[0134] Numerical Example 1 Unit: mm [Face Data] Surface number rd nd vd θgF Object surface ∞ (d0) 1 167.6789 1.5000 1.48749 70.44 0.5306 2 82.1737 (d2) 3 74.6020 1.0000 1.51680 64.20 0.5343 4 27.5648 5.2807 5* 60.0819 5.5743 1.77377 47.17 0.5557 6* -175.7567 (d6) 7 -253.3953 4.2381 2.00100 29.13 0.5995 8 -53.8752 1.0000 1.48749 70.44 0.5306 9 29.6674 7.1121 10 -40.8245 0.9000 1.73037 32.23 0.5899 11 52.5872 4.4152 1.86966 20.02 0.6435 12 400.9216 1.4150 13 (Aperture) ∞ 1.6234 14* 80.2928 7.7904 1.77377 47.17 0.5557 15* -104.3501 0.1500 16 68.2204 8.5345 1.72916 54.67 0.5453 17 -137.1949 0.1500 18 -1015.0352 1.0000 1.85478 24.80 0.6122 19 28.3858 13.4407 1.59282 68.62 0.5440 20 -113.2611 (d20) 21 96.0501 0.9000 1.78880 28.43 0.6009 22 51.6996 0.1500 23* 32.2560 10.0050 1.76450 49.09 0.5528 24* -72.8148 (d24) 25 -184.7089 3.5090 1.59282 68.62 0.5440 26 -65.5065 0.1500 27 542.8836 4.2916 1.98612 16.48 0.6656 28 -62.8269 1.0000 1.73037 32.23 0.5899 29 30.7717 4.4908 30* -200.0000 1.4934 1.85135 40.10 0.5695 31* 300.0000 (BF) Image plane ∞ [Aspherical data] 5th floor 6th floor 14th floor 15th floor 23rd floor K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 -2.03707E-06 9.15268E-07 -3.80694E-06 -4.53933E-06 -5.05513E-06 A6 -2.14268E-09 -3.73451E-10 -4.82319E-09 -2.18530E-09 -2.41545E-10 A8 -7.96874E-12 -1.37775E-11 6.78481E-12 0.00000E+00 -1.50502E-11 A10 -1.89790E-14 0.00000E+00 -2.44617E-15 0.00000E+00 8.76725E-15 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 24 pages 30 pages 31 pages K 0.00000 0.00000 0.00000 A4 4.97489E-06 4.89669E-05 6.27914E-05 A6 -9.98378E-09 -3.89051E-07 -3.66759E-07 A8 4.11965E-12 9.02051E-10 8.36129E-10 A10 0.00000E+00 -5.64056E-13 1.25753E-13 A12 0.00000E+00 0.00000E+00 -1.80050E-15 [Various data] INF 1462mm Focal length 33.98 33.62 F-number 1.24 1.25 Full angle of view 2ω 65.29 65.28 Image height Y 21.63 21.63 Lens length 129.30 129.30 [Variable Interval Data] INF 1462mm d0 ∞ 1333.0502 d2 7.9666 7.4157 d6 3.0000 3.5509 d20 6.6195 6.1542 d24 2.5000 2.9652 BF 18.0998 18.0998 [Lens group data] Group Starting plane Focal length G1 1 -332.47 G2 3 153.57 G3 7 142.83 G4 21 38.28 G5 25 -52.80 G3a 7 -33.54 G3b 14 37.87

[0135] Numerical Example 2 Unit: mm [Face Data] Surface number rd nd vd θgF Object surface ∞ (d0) 1 82.3764 3.9192 1.80809 22.76 0.6287 2 130.8893 (d2) 3 114.6913 0.9000 1.54072 47.20 0.5678 4 25.5542 6.8043 5* 56.8249 5.0982 1.80610 40.73 0.5694 6* -211.8812 (d6) 7 -148.2676 1.1795 1.48749 70.44 0.5306 8 30.6500 7.5007 9 -36.5540 1.7147 1.69895 30.05 0.6028 10 90.4412 4.6177 1.94594 17.98 0.6546 11 -125.9694 0.8682 12 (Aperture) ∞ 2.1148 13* 90.0023 9.1378 1.77377 47.17 0.5557 14* -48.2139 0.2057 15 -138.5636 1.0225 1.78880 28.43 0.6009 16 38.9207 6.5952 1.75500 52.32 0.5473 17 240.3404 0.6848 18 52.3045 1.0136 1.85451 25.15 0.6103 19 27.2000 12.8779 1.59282 68.62 0.5440 20 -90.7789 (d20) 21 -848.1912 0.9000 1.69895 30.05 0.6028 22 138.1440 0.1500 23* 46.2651 7.6904 1.76450 49.09 0.5528 24* -76.0969 (d24) 25 296.4918 3.4967 1.75500 52.32 0.5473 26 -104.4793 0.1532 27 820.4806 4.6992 1.98612 16.48 0.6656 28 -45.0663 1.0168 1.78880 28.43 0.6009 29 31.6000 5.3461 30* -169.2643 1.2141 1.85135 40.10 0.5695 31* 1000.0000 (BF) Image plane ∞ [Aspherical data] 5th floor 6th floor 13th floor 14th floor 23rd floor K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 -1.99816E-06 -4.72277E-07 -1.03559E-06 7.71680E-07 -1.71933E-06 A6 -1.32897E-09 -3.38850E-10 -1.87709E-09 -1.40925E-09 7.19596E-10 A8 -2.08157E-11 -2.11984E-11 -7.13483E-12 -8.22545E-12 -1.65373E-11 A10 3.95950E-15 2.31760E-14 1.19593E-14 9.14549E-15 1.66871E-14 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 24 pages 30 pages 31 pages K 0.00000 0.00000 0.00000 A4 3.82753E-06 2.91423E-05 4.31949E-05 A6 -5.16977E-09 -2.82416E-07 -2.72422E-07 A8 -8.71093E-12 6.89447E-10 7.46965E-10 A10 1.35974E-14 -5.19770E-13 -4.31810E-13 A12 0.00000E+00 0.00000E+00 -6.05302E-16 [Various data] INF 1477mm Focal length 34.60 34.14 F-number 1.24 1.24 Full angle of view 2ω 63.74 63.79 Image height Y 21.63 21.63 Lens length 128.74 128.74 [Variable Interval Data] INF 1477mm d0 ∞ 1348.7267 d2 7.5696 7.0438 d6 3.5035 4.0289 d20 6.9518 6.3311 d24 2.2921 2.9132 BF 17.4972 17.4972 [Lens group data] Group Starting plane Focal length G1 1 265.45 G2 3 280.37 G3 7 84.37 G4 21 49.37 G5 25 -68.06 G3a 7 -35.31 G3b 13 39.46

[0136] Numerical Example 3 Unit: mm [Face Data] Surface number rd nd vd θgF Object surface ∞ (d0) 1* 94.7921 1.5000 1.59201 67.02 0.5358 2* 48.6723 3.0156 3 55.2220 1.5000 1.69680 55.46 0.5426 4 39.2576 (d4) 5 39.7403 0.9000 1.51823 58.96 0.5442 6 30.3135 7.4857 7* 54.3443 5.0541 1.85135 40.10 0.5695 8* -171.9304 (d8) 9 -305.7766 1.1491 1.48749 70.44 0.5306 10 25.6370 9.1574 11 -35.9149 1.7577 1.69895 30.05 0.6028 12 97.0893 4.2569 1.98612 16.48 0.6656 13 -132.2556 0.9733 14 (Aperture) ∞ 2.0076 15* 102.0923 9.1365 1.76802 49.24 0.5516 16* -46.2530 0.8805 17 -158.2138 1.0207 1.78880 28.43 0.6009 18 37.0523 6.3876 1.75500 52.32 0.5473 19 162.0452 0.7727 20 49.4853 1.0025 1.85451 25.15 0.6103 21 27.4275 12.7850 1.57144 71.61 0.5419 22 -86.9564 (d22) 23 -204.2242 0.9000 1.72825 28.32 0.6075 24 306.2991 0.1500 25* 45.7000 7.4944 1.76802 49.24 0.5516 26* -86.2845 (d26) 27 135.7686 3.6953 1.80420 46.50 0.5573 28 -124.2184 0.1509 29 281.5753 4.7389 1.98612 16.48 0.6656 30 -50.0937 1.1733 1.85451 25.15 0.6103 31 33.1672 5.3679 32* -161.0607 1.1378 1.88202 37.22 0.5770 33* 600.5507 (BF) Image plane ∞ [Aspherical data] 1st floor 2nd floor 7th floor 8th floor 15th floor K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 2.19188E-06 1.42073E-06 -3.59436E-06 -1.68468E-07 8.01180E-07 A6 -1.07210E-09 7.47233E-11 -6.23641E-09 -4.99666E-09 -2.64253E-09 A8 -1.02593E-12 -3.03689E-12 -6.34003E-12 -6.69818E-12 -9.63329E-12 A10 2.69264E-16 0.00000E+00 -3.42557E-14 -1.40147E-14 1.32493E-14 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 16th page 25th page 26th page 32nd page 33rd page K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 1.90304E-06 -4.45820E-07 4.15630E-06 1.74585E-05 3.35467E-05 A6 -2.24204E-09 -1.62173E-09 -6.71816E-09 -2.55742E-07 -2.46584E-07 A8 -9.14348E-12 -1.12051E-11 -3.43582E-12 7.74246E-10 8.76116E-10 A10 7.88368E-15 6.43830E-15 4.07609E-15 -6.91919E-13 -9.31271E-13 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 -2.16641E-16 [Various data] INF 1260mm Focal length 28.80 28.66 F-number 1.24 1.25 Full angle of view 2ω 75.31 75.02 Image height Y 21.63 21.63 Lens length 132.26 132.26 [Variable Interval Data] INF 1260mm d0 ∞ 1128.1378 d4 7.1420 6.7193 d8 3.0228 3.4450 d22 6.6117 6.0117 d26 2.3802 2.9808 BF 17.5511 17.5511 [Lens group data] Group Starting plane Focal length G1 1 -91.50 G2 5 58.90 G3 9 98.20 G4 23 51.50 G5 27 -79.32 G3a 9 -33.02 G3b 15 40.91

[0137] Numerical Example 4 Unit: mm [Face Data] Surface number rd nd vd θgF Object surface ∞ (d0) 1 79.9095 4.5124 1.80518 25.46 0.6157 2 180.3451 (d2) 3 200.3905 0.9000 1.51742 52.15 0.5590 4 25.8198 7.1040 5* 94.0454 4.3904 1.80610 40.73 0.5694 6* -135.3500 (d6) 7 -375.6892 1.1915 1.48749 70.44 0.5306 8 33.4117 7.4422 9 -38.2018 1.9348 1.69895 30.05 0.6028 10 94.4096 4.7329 1.94594 17.98 0.6546 11 -126.8471 0.8748 12 (Aperture) ∞ 2.1774 13* 98.9799 8.9333 1.76802 49.24 0.5516 14* -45.9955 0.1500 15 -182.9166 1.0009 1.78880 28.43 0.6009 16 36.6502 5.6564 1.75500 52.32 0.5473 17 118.9691 0.6689 18 53.9604 0.9957 1.85478 24.80 0.6122 19 27.2000 11.9882 1.59282 68.62 0.5440 20 -107.0696 (d20) 21 119.6636 3.1490 1.85033 42.70 0.5646 22 -610.7073 0.9000 1.71736 29.50 0.6040 23 131.9346 0.1500 24* 62.1377 6.1694 1.76450 49.09 0.5528 25* -96.7368 (d25) 26 265.3800 3.6356 1.72916 54.67 0.5453 27 -108.7245 0.1762 28 999.9854 4.8652 2.10420 17.02 0.6631 29 -46.7803 0.9987 1.78880 28.43 0.6009 30 31.6000 5.1917 31* -497.5253 1.1360 1.85135 40.10 0.5695 32* 191.3150 (BF) Image plane ∞ [Aspherical data] 5th floor 6th floor 13th floor 14th floor 24th floor K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 -5.50843E-06 -2.35431E-06 -3.83949E-07 1.62332E-06 1.26983E-06 A6 -2.58748E-09 -2.10400E-09 -2.38464E-09 -2.97927E-09 -6.40624E-10 A8 -4.62993E-11 -2.43714E-11 -1.23969E-12 -1.88147E-12 -8.19666E-12 A10 1.38891E-13 1.11334E-13 1.27103E-15 -2.37828E-16 -5.69434E-15 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 25th page 31st page 32nd page K 0.00000 0.00000 0.00000 A4 4.61982E-06 2.58439E-05 4.10690E-05 A6 -6.48191E-09 -2.95776E-07 -2.91383E-07 A8 -3.17177E-12 6.50046E-10 7.44110E-10 A10 -4.98458E-15 -3.57841E-13 -2.14493E-13 A12 0.00000E+00 0.00000E+00 -8.29753E-16 [Various data] INF 1478mm Focal length 34.67 34.16 F-number 1.24 1.24 Full angle of view 2ω 63.40 63.57 Image height Y 21.63 21.63 Lens length 128.59 128.59 [Variable Interval Data] INF 1478mm d0 ∞ 1349.2275 d2 7.4542 6.9325 d6 2.8661 3.3878 d20 6.9115 6.2697 d25 2.5080 3.1499 BF 17.8293 17.8293 [Lens group data] Group Starting plane Focal length G1 1 174.70 G2 3 -989.52 G3 7 105.82 G4 21 46.60 G5 26 -76.67 G3a 7 -41.52 G3b 13 43.94

[0138] Numerical Example 5 Unit: mm [Face Data] Surface number rd nd vd θgF Object surface ∞ (d0) 1* 115.0394 1.5000 1.59201 67.02 0.5358 2* 39.6227 14.6720 3 -123.9483 1.5000 1.72916 54.67 0.5453 4 47.0768 5.2801 1.68893 31.16 0.5990 5 230.8656 (d5) 6* 109.1490 3.0852 1.85135 40.10 0.5695 7* -98.0735 (d7) 8 -95.4932 0.9923 1.48749 70.44 0.5306 9 48.4515 6.5745 10 -29.3130 0.8000 1.68430 26.81 0.6232 11 147.5931 3.7554 2.10420 17.02 0.6631 12 -101.0873 0.8775 13 (Aperture) ∞ 2.0696 14* 148.4027 8.6325 1.88202 37.22 0.5770 15* -41.1751 1.0272 16 -83.3833 0.9970 1.78880 28.43 0.6009 17 43.0208 5.9288 1.72916 54.67 0.5453 18 473.3018 0.6807 19 49.0439 0.9930 1.85451 25.15 0.6103 20 27.2000 13.0076 1.55032 75.50 0.5401 21 -74.5715 (d21) 22 -223.7021 0.9000 1.85451 25.15 0.6103 23 253.1168 0.5623 24* 48.4689 6.7909 1.76802 49.24 0.5516 25* -122.0664 (d25) 26 77.8376 4.8196 1.72916 54.67 0.5453 27 -97.0943 0.1500 28 241.5131 4.5434 1.98612 16.48 0.6656 29 -53.1134 0.9926 1.85451 25.15 0.6103 30 33.8507 5.2634 31* -500.0000 1.0997 1.85135 40.10 0.5695 32* 251.7105 (BF) Image plane ∞ [Aspherical data] 1st floor 2nd floor 6th floor 7th floor 14th floor K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 7.83206E-06 3.68758E-06 -7.90695E-06 3.15033E-06 4.88161E-06 A6 -5.95444E-09 -1.97667E-09 2.61153E-09 4.10816E-09 -6.46948E-09 A8 3.35408E-12 -7.86501E-12 -6.65409E-11 -5.24594E-11 -9.46448E-12 A10 -4.44137E-16 0.00000E+00 -1.24027E-14 0.00000E+00 1.46878E-14 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 15th page 24th page 25th page 31st page 32nd page K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 5.04605E-06 -1.31408E-07 2.67238E-06 8.39995E-06 2.77784E-05 A6 -7.82063E-10 -8.28939E-09 -1.11613E-08 -2.54153E-07 -2.57106E-07 A8 -1.37881E-11 -5.68225E-12 1.37079E-13 7.81620E-10 1.00732E-09 A10 1.44160E-14 -1.38089E-14 -1.27364E-14 -5.32859E-13 -1.37859E-12 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 5.23411E-16 [Various data] INF 1098mm Focal length 24.70 24.61 F-number 1.24 1.25 Full angle of view 2ω 84.14 84.05 Image height Y 21.63 21.63 Lens length 133.63 133.63 [Variable Interval Data] INF 1098mm d0 ∞ 964.6255 d5 5.1005 4.7962 d7 2.7839 3.0878 d21 7.4484 6.5846 d25 2.3231 3.1872 BF 18.4823 18.4823 [Lens group data] Group Starting plane Focal length G1 1 -47.62 G2 6 61.10 G3 8 76.13 G4 22 67.32 G5 26 -211.72 G3a 8 -40.38 G3b 14 38.78

[0139] Numerical Example 6 Unit: mm [Face Data] Surface number rd nd vd θgF Object surface ∞ (d0) 1 120.8926 3.3509 1.84666 23.78 0.6192 2 306.8164 (d2) 3 126.3024 0.9000 1.51742 52.15 0.5590 4 27.5246 6.2274 5* 45.0000 4.6421 1.80610 40.73 0.5694 6* -285.7738 (d6) 7 -2066.8136 1.0078 1.48749 70.44 0.5306 8 21.3943 8.3667 9 -33.6067 2.0692 1.69895 30.05 0.6028 10 117.9840 4.1137 1.92286 20.88 0.6390 11 -78.6745 0.8163 12 (Aperture) ∞ 2.3138 13* 110.5707 6.3329 1.76802 49.24 0.5516 14* -60.0330 0.1500 15 110.9117 4.1224 1.75500 52.32 0.5473 16 -120.1517 1.0158 1.85478 24.80 0.6122 17 27.2000 9.8200 1.59410 60.47 0.5552 18 -61.9670 (d18) 19 -200.7333 0.9000 1.67270 32.17 0.5963 20 182.4502 1.8118 21* 45.8337 6.3895 1.76802 49.24 0.5516 22* -73.7807 (d22) 23 197.7845 2.8057 1.78590 43.94 0.5612 24 -144.4221 0.1500 25 200.0000 4.2390 1.94594 17.98 0.6546 26 -50.9976 1.1293 1.77047 29.74 0.5951 27 31.6284 4.4915 28* -500.0000 1.1255 1.80610 40.73 0.5694 29* 114.4699 (BF) Image plane ∞ [Aspherical data] 5th floor 6th floor 13th floor 14th floor 21st floor K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 -6.25289E-06 -1.93144E-06 8.43891E-07 -1.26374E-06 -1.77131E-06 A6 -1.62472E-08 -1.31903E-08 -3.32828E-10 -1.31661E-09 -1.47259E-09 A8 -1.21580E-11 1.58345E-12 -2.73552E-11 -2.87924E-11 -2.02120E-11 A10 -8.90998E-14 -6.47222E-14 5.21322E-14 4.30521E-14 4.36026E-14 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 22nd page 28th page 29th page K 0.00000 0.00000 0.00000 A4 3.27386E-06 1.43374E-05 2.77700E-05 A6 -7.04768E-09 -2.46816E-07 -2.46462E-07 A8 -5.31985E-12 1.03650E-09 1.16696E-09 A10 3.28319E-14 -1.39238E-12 -1.98700E-12 A12 0.00000E+00 0.00000E+00 7.65809E-16 [Various data] INF 1529mm Focal length 36.05 35.58 F-number 1.45 1.46 Full angle of view 2ω 62.10 62.04 Image height Y 21.63 21.63 Lens total length 115.00 115.00 [Variable Interval Data] INF 1529mm d0 ∞ 1413.6465 d2 5.9558 5.5964 d6 2.4890 2.8475 d18 7.1836 6.5259 d22 2.3268 2.9853 BF 18.7543 18.7543 [Lens group data] Group Starting plane Focal length G1 1 233.70 G2 3 126.83 G3 7 110.09 G4 19 49.65 G5 23 -70.14 G3a 7 -33.73 G3b 13 41.15

[0140] [Conditional expression corresponding value] EX1 EX2 EX3 EX4 EX5 EX6 (1) 0.47 0.47 0.46 0.45 0.42 0.43 (2) 0.0470 0.0470 0.0470 0.0454 0.0470 0.0387 (3) 16.48 16.48 16.48 17.02 16.48 17.98 (4) 52.14 35.84 30.02 37.65 38.19 25.96 (5) 1.82 1.36 1.22 1.36 0.81 1.29 (6) 0.004 0.027 0.022 0.014 0.333 0.110 (7) 48.60 50.64 55.13 50.64 58.48 39.59 (8) 0.0192 0.0192 0.0225 0.0192 0.0277 0.0157 (9) 0.0312 0.0387 0.0470 0.0387 0.0454 0.0283 (10) 0.17 0.15 0.15 0.15 0.12 0.16 (11) 0.30 0.32 0.31 0.30 0.31 0.27 (12) -0.99 -1.02 -1.15 -1.20 -1.63 -0.94 (13) 1.11 1.14 1.42 1.27 1.57 1.14 [Explanation of symbols]

[0141] G1 First lens group G2 Second lens group G3 3rd lens group G3a 3a lens group G3b 3bth lens group G4 4th lens group G5 5th lens group S aperture stop I image plane

Claims

1. The lens comprises, in order from the object side to the image side, a first lens group G1, a second lens group G2, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power, During focusing from an object at infinity to an object at a close distance, the first lens group G1 does not move with respect to the image plane, the second lens group G2 moves toward the object along the optical axis, the third lens group G3 does not move with respect to the image plane, the fourth lens group G4 moves toward the object along the optical axis, and the fifth lens group G5 does not move with respect to the image plane, an aperture stop S is provided between the lens surface of the second lens group G2 closest to the image side and the lens surface of the fourth lens group G4 closest to the object side; An imaging optical system characterized by satisfying the following conditional expressions: (1) 0.30<D24 / LT<0.65 however, D24: the distance from the lens surface of the second lens group G2 closest to the image side to the lens surface of the fourth lens group G4 closest to the object side when focusing at infinity LT: Distance from the lens surface closest to the object to the image plane when focusing at infinity

2. the fifth lens group G5 has at least one positive lens, 2. The imaging optical system according to claim 1, wherein the following condition is satisfied: (2) θgFmin5p-0.6483+0.0018×νdmin5p>0.0250 (3) νdmin5p<24.00 however, θgFmin5p: partial dispersion ratio for the g-line and the F-line of the positive lens having the smallest Abbe number among the at least one positive lens included in the fifth lens group G5 νdmin5p: Abbe number for the d-line of the positive lens having the smallest Abbe number among the at least one positive lens included in the fifth lens group G5

3. The lens comprises, in order from the object side to the image side, a first lens group G1, a second lens group G2, a third lens group G3 with positive refractive power, a fourth lens group G4 with positive refractive power, and a fifth lens group G5 with negative refractive power, During focusing from an object at infinity to an object at a close distance, the first lens group G1 does not move with respect to the image plane, the second lens group G2 moves toward the object along the optical axis, the third lens group G3 does not move with respect to the image plane, the fourth lens group G4 moves toward the object along the optical axis, and the fifth lens group G5 does not move with respect to the image plane, an aperture stop S is provided between the lens surface of the second lens group G2 closest to the image side and the lens surface of the fourth lens group G4 closest to the object side; the fifth lens group G5 has at least one positive lens, An imaging optical system characterized by satisfying the following conditional expressions: (2) θgFmin5p-0.6483+0.0018×νdmin5p>0.0250 (3) νdmin5p<24.00 however, θgFmin5p: partial dispersion ratio for the g-line and the F-line of the positive lens having the smallest Abbe number among the at least one positive lens included in the fifth lens group G5 νdmin5p: Abbe number for the d-line of the positive lens having the smallest Abbe number among the at least one positive lens included in the fifth lens group G5

4. the fifth lens group G5 has at least two positive lenses, 4. The imaging optical system according to claim 2, wherein the following condition is satisfied: (4) νdmax5p−νdmin5p>15.00 however, νdmax5p: Abbe number for the d-line of the positive lens having the largest Abbe number among the at least two positive lenses included in the fifth lens group G5 νdmin5p: Abbe number for the d-line of the positive lens having the smallest Abbe number among the at least two positive lenses included in the fifth lens group G5

5. 4. The imaging optical system according to claim 1, wherein the fourth lens group G4 is made up of one or two positive lenses and one negative lens.

6. 4. The imaging optical system according to claim 1, wherein, when focusing from an object at infinity to an object at a close distance, the second lens group G2 and the fourth lens group G4 move toward the object along different trajectories along the optical axis.

7. 4. The imaging optical system according to claim 1, wherein the following condition is satisfied: (5) 0.50<(1-β4^2)×β4R^2<2.50 (6) |((1-β2^2)×β2R^2) / ((1-β4^2)×β4R^2)|<0.50 however, β4: lateral magnification of the fourth lens group G4 when focused at infinity β4R: lateral magnification of the lens system located on the image side of the fourth lens group G4 when focusing at infinity β2: lateral magnification of the second lens group G2 when focused at infinity β2R: lateral magnification of the lens system located on the image side of the second lens group G2 when focusing at infinity

8. the third lens group G3 has at least two positive lenses and at least two negative lenses, 4. The imaging optical system according to claim 1, wherein the following condition is satisfied: (7) νdmax3p−νdmin3p>30.00 (8) θgFmax3p-0.6483+0.0018×νdmax3p>0.0120 (9) θgFmin3p-0.6483+0.0018×νdmin3p>0.0200 however, νdmax3p: Abbe number for the d-line of the positive lens having the largest Abbe number among the at least two positive lenses included in the third lens group G3 νdmin3p: Abbe number for the d-line of the positive lens having the smallest Abbe number among the at least two positive lenses included in the third lens group G3 θgFmax3p: partial dispersion ratio for the g-line and the F-line of the positive lens having the largest Abbe number among the at least two positive lenses included in the third lens group G3 θgFmin3p: partial dispersion ratio for the g-line and the F-line of the positive lens having the smallest Abbe number among the at least two positive lenses included in the third lens group G3

9. 4. The imaging optical system according to claim 1, wherein the following condition is satisfied: (10) D2S / LT>0.06 (11) D4S / LT>0.15 however, D2S: the distance from the lens surface of the second lens group G2 closest to the image side to the aperture stop S when focusing at infinity D4S: Distance from the lens surface of the fourth lens group G4 closest to the object to the aperture stop S when focusing at infinity LT: Distance from the lens surface closest to the object to the image plane when focusing at infinity

10. The third lens group G3 is composed of, in order from the object side, a third-a lens group G3a having a negative refractive power, the aperture stop S, and a third-b lens group G3b having a positive refractive power, 4. The imaging optical system according to claim 1, wherein the following condition is satisfied: (12) -3.00<f3a / f<-0.50 (13) 0.50<f3b / f<3.00 however, f: focal length of the entire lens system when focused at infinity f3a: focal length of the 3a-th lens group G3a f3b: focal length of the third lens group G3b

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