Optical Department

Abstract

To provide an optical system in which a focus group and lens material are appropriately arranged, and which therefore materializes reduction of the weight of the optical system while materializing correction of various aberrations such as chromatic aberration despite a large aperture ratio.SOLUTION: An optical system is provided, which is composed of in order from an object side, a first lens group G1 which has negative refractive power, a second lens group G2 which moves along an optical axis from an image side to the object side during focusing, and a third lens group G3 which has positive refractive power and includes an aperture diaphragm S.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system suitable for a lens used in an imaging device such as a still camera or a video camera, or a projection device. In particular, the present invention relates to an optical system having a large aperture ratio, effectively correcting various aberrations, and appropriately arranged to contribute to weight reduction.

Background Art

[0002] In recent years, with the increase in the number of pixels in digital cameras and the like, high optical performance that strongly corrects various aberrations has been required.

[0003] In addition, for high-speed and accurate focusing and wobbling drive, weight reduction of the lens group that moves during focusing drive is desired.

[0004] Therefore, in a conventional optical system, a configuration has been proposed in which, during focusing drive, the portion from the object side to the aperture stop is fixed, and the focus group is arranged on the image side of the aperture stop to reduce weight.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] The optical system described in Patent Document 1 attempts to suppress various aberrations by appropriately specifying the configuration of the lens group that moves during focusing. However, the correction of the longitudinal chromatic aberration from the C line to the F line is not sufficient from the center to the periphery of the screen. In addition, when adopted in an optical system with a large aperture ratio, there is a problem that the weight of the focus group tends to increase.

[0007] The optical system described in Patent Document 2 achieves a large aperture ratio while keeping the weight of the focusing group low. However, it has drawbacks such as insufficient correction of axial chromatic aberration, lateral chromatic aberration, and sagittal flare, as well as a long overall optical length that tends to make the system bulky. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] This invention has been made in view of the above problems, and aims to provide an optical system that achieves weight reduction while correcting various aberrations such as chromatic aberration, even with a large aperture ratio, by appropriately arranging the focus group and lens material. [Means for solving the problem]

[0009] To solve the aforementioned problems, the optical system according to the present invention is composed of, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 that moves along the optical axis from the image side to the object side when focusing, and a third lens group G3 having positive refractive power and containing an aperture diaphragm S. The third lens group G3 consists, in order from the object side, of a lens group G3A with positive refractive power, an aperture diaphragm S, a lens group G3B with positive refractive power, and a lens group G3C consisting of two negative lenses. Lens group G3C has an aspherical surface such that the negative refractive power increases from the center of the optical axis towards the periphery, and the air gap between the two negative lenses of lens group G3C forms a biconvex air lens K, resulting in an optical system with an F-number less than 2.0 at infinity, satisfying the following conditional equation. It is characterized by the following. (1) - 1.50 <f_G3B / f_G3C<―0.20 (2)0.30<(R_Kr+R_Kf) / (R_Kr-R_Kf) f_G3B: Focal length of lens group G3B when shooting at infinity. f_G3C: Focal length of lens group G3C when shooting at infinity. R_Kf: Radius of curvature of the air lens K. R_Kr: Radius of curvature of the image side of air lens K [Effects of the Invention]

[0010] According to the present invention, by appropriately arranging the focus group and lens material, it is possible to provide an optical system that achieves weight reduction while correcting various aberrations such as chromatic aberration, even with a large aperture ratio. [Brief explanation of the drawing]

[0011] [Figure 1] Lens configuration diagram of the optical system of Example 1 at infinity [Figure 2]Longitudinal aberration diagram of the optical system in Example 1 at infinity [Figure 3] Longitudinal aberration diagram of the optical system in Example 1 at a shooting distance of 226 mm [Figure 4] Lateral aberration diagram of the optical system in Example 1 at infinity [Figure 5] Lateral aberration diagram of the optical system in Example 1 at a shooting distance of 226 mm [Figure 6] Lens configuration diagram of the optical system in Example 2 at infinity [Figure 7] Longitudinal aberration diagram of the optical system in Example 2 at infinity [Figure 8] Longitudinal aberration diagram of the optical system in Example 2 at a shooting distance of 227 mm [Figure 9] Lateral aberration diagram of the optical system in Example 2 at infinity [Figure 10] Lateral aberration diagram of the optical system in Example 2 at a shooting distance of 227 mm [Figure 11] Lens configuration diagram of the optical system in Example 3 at infinity [Figure 12] Longitudinal aberration diagram of the optical system in Example 3 at infinity [Figure 13] Longitudinal aberration diagram of the optical system in Example 3 at a shooting distance of 225 mm [Figure 14] Lateral aberration diagram of the optical system in Example 3 at infinity [Figure 15] Lateral aberration diagram of the optical system in Example 3 at a shooting distance of 225 mm [Figure 16] Lens configuration diagram of the optical system in Example 4 at infinity [Figure 17] Longitudinal aberration diagram of the optical system in Example 4 at infinity [Figure 18] Longitudinal aberration diagram of the optical system in Example 4 at a shooting distance of 245 mm [Figure 19] Lateral aberration diagram of the optical system in Example 4 at infinity [Figure 20] Lateral aberration diagram of the optical system in Example 4 at a shooting distance of 245 mm [Figure 21] Lens configuration diagram of the optical system in Example 5 at infinity [Figure 22] Longitudinal aberration diagram of the optical system in Example 5 at infinity [Figure 23] Longitudinal aberration diagram of the optical system in Example 5 at a shooting distance of 224 mm. [Figure 24] Transverse aberration diagram of the optical system of Example 5 at infinity. [Figure 25] Transverse aberration diagram of the optical system of Example 5 at a shooting distance of 224 mm. [Figure 26] Lens configuration diagram of the optical system of Example 6 at infinity [Figure 27] Longitudinal aberration diagram of the optical system of Example 6 at infinity [Figure 28] Longitudinal aberration diagram of the optical system of Example 6 at a shooting distance of 235 mm [Figure 29] Transverse aberration diagram of the optical system of Example 6 at infinity. [Figure 30] Transverse aberration diagram of the optical system of Example 6 at a shooting distance of 235 mm. [Figure 31] Lens configuration diagram of the optical system of Example 7 at infinity [Figure 32] Longitudinal aberration diagram of the optical system of Example 7 at infinity. [Figure 33] Longitudinal aberration diagram of the optical system of Example 7 at a shooting distance of 219 mm. [Figure 34] Transverse aberration diagram of the optical system of Example 7 at infinity. [Figure 35] Transverse aberration diagram of the optical system of Example 7 at a shooting distance of 219 mm. [Figure 36] Lens configuration diagram of the optical system of Example 8 at infinity [Figure 37] Longitudinal aberration diagram of the optical system of Example 8 at infinity. [Figure 38] Longitudinal aberration diagram of the optical system of Example 8 at a shooting distance of 224 mm. [Figure 39] Transverse aberration diagram of the optical system of Example 8 at infinity. [Figure 40] Transverse aberration diagram of the optical system of Example 8 at a shooting distance of 224 mm. [Modes for carrying out the invention]

[0012] In the optical system of the present invention, the refractive indices of the materials for the g-line (wavelength 435.8 nm), F-line (486.1 nm), d-line (587.6 nm), and C-line (656.3 nm) are denoted as ng, nF, nd, and nC, respectively. Unless otherwise specified, the refractive index for the d-line is indicated.

[0013] Furthermore, the Abbe number νd, partial dispersion ratio PgF, and anomalous partial dispersion ΔPgF are to be derived by the following formulas. νd=(nd-1) / (nF-nC) PgF = (ng - nF) / (nF - nC) ΔPgF=PgF-0.64833+0.00180×νd

[0014] An embodiment relating to the optical system of the present invention will be described in detail below. Note that the following description of the embodiment illustrates an example of the optical system of the present invention, and the present invention is not limited to this embodiment without departing from its spirit.

[0015] As can be seen from the lens configuration diagrams shown in Figures 1, 6, 11, 16, 21, 26, 31, and 36, the optical system of the present invention is characterized by being composed of, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 that moves along the optical axis from the image side to the object side when focusing, and a third lens group G3 having positive refractive power and containing an aperture diaphragm S.

[0016] The optical system of the present invention has a so-called retrofocus type configuration. In such an optical system with a wide angle of view, the difference between the on-axis ray height and the off-axis ray height tends to be large on the object side of the aperture diaphragm, and this is particularly noticeable in lenses positioned on the object side. Therefore, it becomes difficult to simultaneously correct both on-axis and off-axis aberrations on the object side of the aperture diaphragm.

[0017] When correcting off-axis aberrations, particularly field curvature and astigmatism, on the object side rather than at the aperture diaphragm, an effective method is to gently bend the off-axis light beam with the lens on the object side, where the difference between the on-axis and off-axis ray heights is larger. However, this method tends to increase the number of lenses on the object side compared to the aperture diaphragm, leading to an increase in the overall optical length and a larger lens diameter at the object side, resulting in a significant increase in product weight.

[0018] On the other hand, if aberrations occurring on the object side of the aperture diaphragm are to be corrected by a separate lens group rather than by reducing them, the lens configuration on the image side of the aperture diaphragm becomes crucial. In this case, the aberrations that need to be corrected on the image side of the aperture diaphragm become very large. Therefore, it becomes difficult to secure space for focusing while maintaining good optical performance, and in order to focus on the image side of the aperture diaphragm, it is necessary to either increase the size of the optical system to correct the aberrations or prepare a focusing group with multiple elements that sufficiently correct the aberrations, making it difficult to make both the product and the focusing group lightweight.

[0019] Therefore, by arranging the lenses in the following order from the object side: the first lens group G1, the second lens group G2 which moves during focusing, and the third lens group G3 which contains the aperture diaphragm S, it becomes possible to optimize the configuration on the image side from the aperture diaphragm, which is important for correcting aberrations as mentioned above. This makes it possible to correct off-axis aberrations to the maximum extent while preventing the overall size of the lens from increasing.

[0020] Furthermore, in the optical system of the present invention, the second lens group G2 that moves during focusing has a negative refractive power and moves along the optical axis from the image side to the object side. Because the group with negative refractive power on the object side of the aperture diaphragm S moves from the image side to the object side, a large negative distortion occurs from infinity to close range, and the incident angle on the object side is largest at close range.

[0021] Furthermore, even if the second lens group G2 is moved along the optical axis from the object side to the image side with positive refractive power, significant negative distortion occurs from infinity to near focus, and the incident angle on the object side is largest at near focus. However, if the goal is to secure as much peripheral light as possible at the more important infinity focus, the second lens group G2, which is the focusing group, is closer to the object at infinity focus, so its diameter tends to increase, which is undesirable in order to secure sufficient light. Therefore, it is desirable for the second lens group G2 to move along the optical axis from the image side to the object side from infinity to near focus.

[0022] Furthermore, the optical system of the present invention is characterized in that the third lens group G3 is composed of, in order from the object side, a lens group G3A having positive refractive power, an aperture diaphragm S, a lens group G3B having positive refractive power, and a lens group G3C having an aspherical surface composed of two negative lenses such that the negative refractive power increases from the center of the optical axis to the periphery, and the air gap between the two negative lenses of lens group G3C forms a biconvex air lens K, and the optical system has an F number less than 2.0 when shooting at infinity, and satisfies the following conditional equation. (1) - 1.50 <f_G3B / f_G3C<―0.20 (2)0.30<(R_Kr+R_Kf) / (R_Kr-R_Kf) f_G3B: Focal length of lens group G3B when shooting at infinity. f_G3C: Focal length of lens group G3C when shooting at infinity. R_Kf: Radius of curvature of the air lens K. R_Kr: Radius of curvature of the image side of air lens K

[0023] Generally, in wide-angle lenses, while axial aberration can be corrected relatively easily when brightness is increased, off-axis aberration cannot be fully corrected, making it difficult to achieve high performance. As mentioned above, the optical system of the present invention has a configuration that allows for strong correction of off-axis aberration, making it possible to maintain high imaging performance even with wide-angle lenses with a large aperture ratio, especially optical systems with an F-number smaller than 2.0.

[0024] The G3C lens group is positioned where the difference between the on-axis and off-axis ray heights is large. In a lens group with this type of ray path, it is possible to strongly correct off-axis aberrations. Therefore, by arranging an aspherical lens in the G3C lens group such that the negative refractive power increases from the optical axis center toward the periphery, it is possible to effectively correct field curvature and distortion without increasing the number of lenses, thereby achieving both miniaturization and high imaging performance simultaneously.

[0025] Furthermore, compared to conventional retrofocus type configurations, the G3C lens group, which has negative refractive power, is positioned on the image side of the optical system. This makes the entire optical system closer to a symmetrical system, allowing for a greater correction of off-axis aberrations, including distortion.

[0026] Condition (1) is a condition for appropriately setting the focal lengths of lens groups G3B and G3C. By satisfying condition (1), it becomes possible to bring the exit pupil position of the optical system closer to the image side, thereby shortening the overall length of the optical system.

[0027] If the refractive power of lens group G3C becomes relatively stronger than that of lens group G3B, exceeding the lower limit of condition (1), it becomes possible to bring the exit pupil position of the optical system closer to the image side. However, this is undesirable because the outermost angle rays passing through lens group G3C diverge strongly, making it difficult to ensure sufficient back focus and telecentricity.

[0028] Furthermore, if the refractive power of lens group G3C becomes relatively weaker than that of lens group G3B, exceeding the upper limit of condition (1), it becomes difficult to bring the exit pupil position of the optical system close enough to the image plane, resulting in an undesirable increase in the overall optical length.

[0029] Furthermore, setting the lower limit of conditional equation (1) to -1.30 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (1) to -1.00 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0030] Furthermore, setting the upper limit of conditional equation (1) to -0.30 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the upper limit of conditional equation (1) to -0.50 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0031] Conditional equation (2) is a conditional equation for appropriately setting the shape factor of the biconvex air lens K formed between the two negative lenses of lens group G3C. As mentioned above, lens group G3C, in which the air lens K is formed, has a large difference between the on-axis and off-axis ray heights, and is positioned to strongly refract upper rays in particular. In addition, the difference in on-axis ray heights between the object side and the image side of the air lens K also changes significantly, so it is necessary to appropriately control the aberrations that occur on each surface.

[0032] The object-side surface of air lens K is an aplanatic surface, which means it contributes little to spherical aberration and sagittal flare. However, it strongly deflects upward rays from off-axis light beams, resulting in higher-order coma and astigmatism. Furthermore, the image-side surface of air lens K strongly refracts on-axis light beams, which is particularly advantageous for correcting spherical aberration and sagittal flare.

[0033] Furthermore, it is even better to apply the aspherical element placed in lens group G3C to the image-side surface of air lens K. In addition to correcting the aforementioned field curvature and distortion, this also makes it possible to effectively correct sagittal flare.

[0034] If the shape factor of the air lens K becomes smaller than the lower limit of condition (2), then if the absolute value of the radius of curvature R_Kf of the air lens K becomes too large, there will be insufficient correction of higher-order coma aberration and astigmatism. If the absolute value of the radius of curvature R_Kr of the air lens K becomes too small, there will be excessive correction of sagittal flare. Both of these are undesirable.

[0035] Furthermore, setting the lower limit of conditional equation (2) to 0.40 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (2) to 0.50 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0036] Furthermore, the optical system of the present invention is characterized in that the image-side lens of the lens group G3B is a positive lens and satisfies the following condition. (3) 1.75 <nd_G3B_r (4) 0.000 < ΔPgF_G3B_r nd_G3B_r: Refractive index nd of the positive lens located closest to the image in lens group G3B ΔPgF_G3B_r: Anomalous partial dispersion of the positive lens located closest to the image in lens group G3B.

[0037] In wide-angle to standard-angle optical systems, a known method for simultaneously correcting axial and lateral chromatic aberration involves applying a glass material with low wavelength dispersion and high anomalous dispersion to a lens with positive refractive power, positioned on the image side of the aperture. However, such glass materials often have low refractive indices, which negatively impacts the control of field curvature. Furthermore, even if axial and lateral chromatic aberrations can be corrected, suppressing color flare at the edges of the image remains difficult.

[0038] Therefore, by replacing a portion of the lens with positive refractive power on the image side from the aperture diaphragm S with a material having high refractive index and high anomalous partial dispersion that simultaneously satisfies conditions (3) and (4), it becomes possible to correct chromatic aberration while also addressing field curvature and chromatic flare.

[0039] Furthermore, to correct chromatic aberration, using a material with high anomalous partial dispersion at a position where off-axis light rays pass through the outer edge of the lens can enhance the effect. Therefore, by placing a positive lens that simultaneously satisfies conditions (3) and (4) at the image end of lens group G3B, it is possible to maximize the ability to correct the aforementioned chromatic aberration.

[0040] If the refractive index of the positive lens located closest to the image in lens group G3B becomes lower than the lower limit of condition (3), it becomes necessary to increase the curvature to ensure sufficient refractive power, which makes it difficult to simultaneously address field curvature and chromatic flare, and is therefore undesirable.

[0041] Furthermore, setting the lower limit of conditional equation (3) to 1.80 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (3) to 1.85 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0042] Furthermore, if the anomalous partial dispersion of the positive lens located closest to the image sensor in lens group G3B becomes smaller than the lower limit of condition (4), the correction of chromatic aberration becomes insufficient, which is undesirable.

[0043] Furthermore, setting the lower limit of conditional equation (4) to 0.005 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (4) to 0.010 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0044] Furthermore, the optical system of the present invention is characterized by satisfying the following conditional equation. (5)-2.00 <f1_2 / f3<―0.30 (6) 0.000 <ave_ΔPgF_G3B_P (7) 40.0 <ave_νd_G3B_P (8) ave_ΔPgF_G3B_N<0.020 (9)ave_νd_G3B_N<35.0 f1_2: Combined focal length of the first lens group G1 and the second lens group G2 when shooting at infinity. f3: Focal length of the third lens group G3 when shooting at infinity. ave_ΔPgF_G3B_P: The average value of the anomalous partial dispersion ΔPgF of the positive refractive power lenses constituting the lens group G3B. ave_νd_G3B_P: The average value of the Abbe number νd of the positive refractive power lenses that make up the G3B lens group. ave_ΔPgF_G3B_N: Average value of the anomalous partial dispersion ΔPgF of the negative refractive power lenses constituting lens group G3B. ave_νd_G3B_N: The average value of the Abbe number νd of the negative refractive power lenses that make up the G3B lens group.

[0045] The optical system of the present invention has a so-called retrofocus type configuration. Therefore, the lens configuration has a strong negative refractive power on the object side and a strong positive refractive power on the image side.

[0046] Conditional equation (5) is a conditional equation for appropriately setting the ratio of the combined focal length of the first lens group G1 and the second lens group G2 to the focal length of the third lens group G3. In comparison to the retrofocus type described above, the combined system of the first lens group G1 and the second lens group G2 corresponds to a group with a strong negative refractive power, and the third lens group G3 corresponds to a group with a strong positive refractive power. By satisfying conditional equation (5), it becomes possible to secure back focus while keeping the overall optical length down.

[0047] If the positive refractive power of the third lens group G3 becomes stronger, or the negative refractive power of the combined system of the first lens group G1 and the second lens group G2 becomes weaker, the overall optical length will be shortened, but it will become difficult to secure the back focus, which is undesirable.

[0048] If the positive refractive power of the third lens group G3 weakens, or if the negative refractive power of the combined system of the first lens group G1 and the second lens group G2 strengthens, it becomes easier to secure the back focus, but this is undesirable because the overall optical length increases.

[0049] Furthermore, setting the lower limit of conditional equation (5) to -1.50 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (5) to -1.00 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0050] Furthermore, setting the upper limit of conditional equation (5) to -0.40 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the upper limit of conditional equation (5) to -0.50 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0051] Conditional equations (6) and (7) are conditions for appropriately setting the average value of the anomalous partial dispersion ΔPgF and the average value of the Abbe number νd for the positive refractive power lenses that constitute the lens group G3B.

[0052] As mentioned above, in order to simultaneously correct axial chromatic aberration and lateral chromatic aberration, it is effective to use a glass material with low wavelength dispersion and high anomalous partial dispersion on the image side of the aperture, in a lens with positive refractive power. By using a glass material that satisfies both conditions (6) and (7) simultaneously in lens group G3B, it becomes possible to effectively correct chromatic aberration.

[0053] If the average value of the anomalous partial dispersion of the positive refractive power lenses constituting lens group G3B decreases beyond the lower limit of condition equation (6), it becomes undesirable because axial chromatic aberration cannot be adequately corrected within lens group G3B.

[0054] Furthermore, if the average Abbe number of the positive refractive power lenses constituting lens group G3B decreases beyond the lower limit of condition equation (7), it becomes difficult to correct chromatic aberration and color flare at image heights beyond the middle of the screen, which is undesirable.

[0055] Furthermore, setting the lower limit of conditional equation (6) to 0.005 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (6) to 0.010 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0056] Furthermore, setting the lower limit of conditional equation (7) to 42.0 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (7) to 45.0 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0057] Conditional equations (8) and (9) are conditions for appropriately setting the average value of the anomalous partial dispersion ΔPgF and the average value of the Abbe number νd for the negative refractive power lenses that constitute the lens group G3B.

[0058] For negative refractive power lenses used on the image side of the aperture, it is effective to use glass materials with high wavelength dispersion and low anomalous partial dispersion, the opposite of the positive refractive power lenses mentioned above. Therefore, by using glass materials that simultaneously satisfy conditions (8) and (9) in lens group G3B, it becomes possible to effectively correct chromatic aberration.

[0059] If the average value of the anomalous partial dispersion of the negative refractive power lenses constituting lens group G3B exceeds the upper limit of condition (8), it becomes undesirable because axial chromatic aberration cannot be adequately corrected within lens group G3B.

[0060] Furthermore, if the average Abbe number of the negative refractive power lenses constituting lens group G3B exceeds the upper limit of condition (9), the first-order achromatic effect will not be fully exhibited, which is undesirable.

[0061] Furthermore, setting the upper limit of conditional equation (8) to 0.017 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (8) to 0.013 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0062] Furthermore, setting the upper limit of conditional expression (9) to 34.0 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the upper limit of conditional expression (9) to 32.0 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0063] Furthermore, the optical system of the present invention is characterized in that the first lens group G1 is composed of, in order from the object side, a front group G1A consisting only of negative meniscus lenses with their convex surfaces facing the object side, and a rear group G1B having positive refractive power and having a positive lens positioned closest to the object, and satisfies the following conditional equation. (10)-10.00 <f1 / f<―0.50 (11) 1.55 <ave_nd_G1A_N f: Focal length of the entire lens system when shooting at infinity. f1: Focal length of the first lens group G1 when shooting at infinity. ave_nd_G1A_N: The average value of the refractive index nd of the negative refractive power lenses that make up lens group G1A.

[0064] The first lens group G1 functions as a so-called wide converter and consists of a negative front group G1A and a positive rear group G1B. Of these, the negative front group G1A is composed solely of negative meniscus lenses with their convex surfaces facing the object, and is effective in suppressing off-axis aberrations, particularly distortion and astigmatism. Furthermore, using an aspherical element within the front group G1A makes it possible to further enhance the correction effect of distortion and astigmatism, which is more desirable.

[0065] Furthermore, the positive rear group G1B has the positive lens positioned closest to the object. This allows for a reduction in the diameter of the subsequent lenses, resulting in a reduction in the overall weight of the lens and the ability to secure space for the focus unit without increasing the lens diameter.

[0066] Conditional equation (10) is a conditional equation for appropriately setting the focal length of the first lens group G1.

[0067] By satisfying condition (10), it becomes possible to widen the field of view of the optical system while preventing the radial enlargement of the first lens group G1.

[0068] If the refractive power of the first lens group G1 weakens beyond the lower limit of condition (10), it will no longer be able to adequately function as a wide converter, which is undesirable as it will prevent widening the field of view.

[0069] Furthermore, if the refractive power of the first lens group G1 increases beyond the upper limit of condition (10), the retrofocus type becomes stronger, which is undesirable because it leads to an increase in the overall optical length and radial enlargement.

[0070] Furthermore, setting the lower limit of conditional equation (10) to -8.00 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (10) to -5.00 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0071] Furthermore, setting the upper limit of conditional expression (10) to -1.00 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the upper limit of conditional expression (10) to -2.00 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0072] Conditional equation (11) is a conditional equation for appropriately setting the average value of the refractive index nd of the negative refractive power lenses that constitute the lens group G1A.

[0073] By satisfying condition (11), it becomes possible to keep the number of lenses constituting the lens group G1A to two or fewer while effectively correcting astigmatism. Furthermore, since the number of lenses constituting the group located closest to the object can be reduced, it becomes possible to simultaneously achieve a reduction in product weight and miniaturization.

[0074] If the average value of the refractive index nd of the negative refractive power lenses constituting lens group G1A decreases beyond the lower limit of condition equation (11), astigmatism will bulge once in the middle of the image, making it difficult to maintain a good image across the entire image. Alternatively, in order to maintain a good state of astigmatism, it may become necessary to increase the number of lenses constituting lens group G1A to three or more, which leads to an undesirable increase in the size and weight of the optical system.

[0075] Furthermore, setting the lower limit of conditional equation (11) to 1.60 is preferable because it allows for a better achievement of the effects of the present invention. Moreover, setting the lower limit of conditional equation (11) to 1.63 is even more preferable because it allows for a further achievement of the effects of the present invention.

[0076] Furthermore, the optical system of the present invention is characterized in that the second lens group G2 is composed of two or fewer lenses.

[0077] This configuration makes it possible to reduce the weight of the lens group that moves during focusing.

[0078] Furthermore, it is preferable to use only one lens element in the second lens group G2, as this allows for further weight reduction of the lens group that moves during focusing.

[0079] Next, the lens configuration of an embodiment of the 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 plane side. Also, the notation Ln in the embodiment refers to the nth lens from the object side. [Examples]

[0080] Figure 1 is a lens configuration diagram of the optical system of Embodiment 1 of the present invention. It consists of a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power. Focusing from infinity to close is achieved by the movement of the second lens group G2 from the image side to the object side.

[0081] The first lens group G1 consists of a subgroup G1A with negative refractive power and a subgroup G1B with positive refractive power. Subgroup G1A consists of a negative meniscus lens L1 with aspherical surfaces on both sides and a convex surface facing the object, and a negative meniscus lens L2 with a convex surface facing the object. Subgroup G1B consists of a positive meniscus lens L3 with a convex surface facing the image, a biconcave negative lens L4, and a biconvex positive lens L5.

[0082] The second lens group G2 consists of a negative meniscus lens L6 with its convex surface facing the image side.

[0083] The third lens group G3 consists of a subgroup G3A with positive refractive power, an aperture diaphragm S, a subgroup G3B with positive refractive power, and a subgroup G3C with negative refractive power. Subgroup G3A consists of a positive meniscus lens L7 with a convex surface facing the object, a positive lens L8 with aspherical surfaces on both sides and a biconvex shape, a negative meniscus lens L9 with a convex surface facing the object, and a positive meniscus lens L10 with a convex surface facing the image. Subgroup G3B consists of a cemented lens made of a positive meniscus lens L11 with a concave surface facing the object and a negative meniscus lens L12 with a concave surface facing the object, a cemented lens made of a negative meniscus lens L13 with a convex surface facing the object and a biconvex positive lens L14, and a biconvex positive lens L15. The subgroup G3C consists of a negative meniscus lens L16 with its convex surface facing the object, and a negative lens L17 with aspherical surfaces on both sides and a biconcave shape. The biconvex air lens K is formed between L16 and L17. [Examples]

[0084] Figure 6 is a lens configuration diagram of the optical system of Embodiment 2 of the present invention. It consists of a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power. Focusing from infinity to close is achieved by the movement of the second lens group G2 from the image side to the object side.

[0085] The first lens group G1 consists of a subgroup G1A with negative refractive power and a subgroup G1B with positive refractive power. Subgroup G1A consists of a negative meniscus lens L1 with an aspherical surface facing the object and a convex surface facing the object, and a negative meniscus lens L2 with a convex surface facing the object. Subgroup G1B consists of a positive meniscus lens L3 with a convex surface facing the image, a biconcave negative lens L4, and a biconvex positive lens L5.

[0086] The second lens group G2 consists of a negative meniscus lens L6 with its convex surface facing the image side.

[0087] The third lens group G3 consists of a subgroup G3A with positive refractive power, an aperture diaphragm S, a subgroup G3B with positive refractive power, and a subgroup G3C with negative refractive power. Subgroup G3A consists of a positive meniscus lens L7 with a convex surface facing the object, a positive lens L8 with aspherical surfaces on both sides and a biconvex shape, a negative meniscus lens L9 with a convex surface facing the object, and a positive meniscus lens L10 with a convex surface facing the image. Subgroup G3B consists of a cemented lens made of a positive meniscus lens L11 with a concave surface facing the object and a negative meniscus lens L12 with a concave surface facing the object, a cemented lens made of a negative meniscus lens L13 with a convex surface facing the object and a biconvex positive lens L14, and a biconvex positive lens L15. The subgroup G3C consists of a negative meniscus lens L16 with its convex surface facing the object, and a negative lens L17 with aspherical surfaces on both sides and a biconcave shape. The biconvex air lens K is formed between L16 and L17. [Examples]

[0088] Figure 11 is a lens configuration diagram of the optical system of Embodiment 3 of the present invention. It consists of a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power. Focusing from infinity to close is achieved by the movement of the second lens group G2 from the image side to the object side.

[0089] The first lens group G1 consists of a subgroup G1A with negative refractive power and a subgroup G1B with positive refractive power. Subgroup G1A consists of a negative meniscus lens L1 with both sides aspherical and convex towards the object, and a negative meniscus lens L2 with a convex surface facing the object. Subgroup G1B consists of a positive meniscus lens L3 with a convex surface facing the object, a biconcave negative lens L4, and a biconvex positive lens L5.

[0090] The second lens group G2 consists of a biconcave negative lens L6.

[0091] The third lens group G3 consists of a subgroup G3A with positive refractive power, an aperture diaphragm S, a subgroup G3B with positive refractive power, and a subgroup G3C with negative refractive power. Subgroup G3A consists of a biconvex positive lens L7, a biconvex positive lens L8 with aspherical surfaces on both sides, a biconcave negative lens L9, and a positive meniscus lens L10 with its convex surface facing the object. Subgroup G3B consists of a cemented lens made of a positive meniscus lens L11 with its concave surface facing the object and a negative meniscus lens L12 with its concave surface facing the object, a cemented lens made of a negative meniscus lens L13 with its convex surface facing the object and a biconvex positive lens L14, and a biconvex positive lens L15. The subgroup G3C consists of a negative meniscus lens L16 with its convex surface facing the object, and a negative lens L17 with aspherical surfaces on both sides and a biconcave shape. The biconvex air lens K is formed between L16 and L17. [Examples]

[0092] Figure 16 is a lens configuration diagram of the optical system of Embodiment 4 of the present invention. It consists of a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power. Focusing from infinity to close is achieved by the movement of the second lens group G2 from the image side to the object side.

[0093] The first lens group G1 consists of a subgroup G1A with negative refractive power and a subgroup G1B with positive refractive power. Subgroup G1A consists of a negative meniscus lens L1 with both sides aspherical and convex towards the object. Subgroup G1B consists of a positive meniscus lens L2 with a convex towards the object, a biconcave negative lens L3, and a biconvex positive lens L4.

[0094] The second lens group G2 consists of a biconcave negative lens L5.

[0095] The third lens group G3 consists of a subgroup G3A with positive refractive power, an aperture diaphragm S, a subgroup G3B with positive refractive power, and a subgroup G3C with negative refractive power. Subgroup G3A consists of a positive lens L6 with both sides aspherical and biconvex, a negative lens L7 with a biconcave shape, and a positive meniscus lens L8 with its convex surface facing the object. Subgroup G3B consists of a cemented lens made of a positive meniscus lens L9 with its concave surface facing the object and a negative meniscus lens L10 with its concave surface facing the object, a cemented lens made of a negative meniscus lens L11 with its convex surface facing the object and a biconvex positive lens L12, and a biconvex positive lens L13. Subgroup G3C consists of a negative meniscus lens L14 with its convex surface facing the object and a negative lens L15 with both sides aspherical and biconcave, and a biconvex air lens K is formed between L14 and L15. [Examples]

[0096] Figure 21 is a lens configuration diagram of the optical system of Embodiment 5 of the present invention. It consists of a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power. Focusing from infinity to close is achieved by the movement of the second lens group G2 from the image side to the object side.

[0097] The first lens group G1 consists of a subgroup G1A with negative refractive power and a subgroup G1B with positive refractive power. Subgroup G1A consists of a negative meniscus lens L1 with an aspherical surface facing the object and a convex surface facing the object, and a negative meniscus lens L2 with aspherical surfaces on both sides and a convex surface facing the object. Subgroup G1B consists of a positive meniscus lens L3 with a convex surface facing the object, a biconcave negative lens L4, and a biconvex positive lens L5.

[0098] The second lens group G2 consists of a negative meniscus lens L6 with its convex surface facing the image side.

[0099] The third lens group G3 consists of a positive refractive power subgroup G3A, an aperture diaphragm S, a positive refractive power subgroup G3B, and a negative refractive power subgroup G3C. Subgroup G3A consists of a cemented lens comprising a positive lens L7 with both sides aspherical and biconvex, a positive lens L8 with a biconvex shape, and a negative meniscus lens L9 with its convex surface facing the image side. Subgroup G3B consists of a cemented lens comprising a positive lens L10 with a biconvex shape and a negative lens L11 with a biconcave shape, a cemented lens comprising a negative meniscus lens L12 with its convex surface facing the object side and a positive lens L13 with a biconvex shape, and a positive lens L14 with a biconvex shape. Subgroup G3C consists of a negative meniscus lens L15 with its convex surface facing the object side, a negative lens L16 with both sides aspherical and biconcave, and a biconvex air lens K is formed between L15 and L16. [Examples]

[0100] Figure 26 is a lens configuration diagram of the optical system of Embodiment 6 of the present invention. It consists of a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power. Focusing from infinity to close is achieved by the movement of the second lens group G2 from the image side to the object side.

[0101] The first lens group G1 consists of a subgroup G1A with negative refractive power and a subgroup G1B with positive refractive power. Subgroup G1A consists of a negative meniscus lens L1 with aspherical surfaces on both sides and a convex surface facing the object, and a negative meniscus lens L2 with aspherical surfaces on both sides and a convex surface facing the object. Subgroup G1B consists of a positive lens L3 with a biconvex shape, a cemented lens consisting of a negative lens L4 with a biconcave shape and a positive meniscus lens L5 with a convex surface facing the object, and a positive lens L6 with a biconvex shape.

[0102] The second lens group G2 consists of a negative meniscus lens L7 with its convex surface facing the image side.

[0103] The third lens group G3 consists of a positive refractive power subgroup G3A, an aperture diaphragm S, a positive refractive power subgroup G3B, and a negative refractive power subgroup G3C. Subgroup G3A consists of a cemented lens comprising a positive lens L8 with both surfaces aspherical and biconvex, a negative meniscus lens L9 with its convex surface facing the object, and a biconvex positive lens L10. Subgroup G3B consists of a cemented lens comprising a positive meniscus lens L11 with its concave surface facing the object and a negative meniscus lens L12 with its concave surface facing the object, a cemented lens comprising a negative meniscus lens L13 with its convex surface facing the object and a biconvex positive lens L14, and a biconvex positive lens L15. Subgroup G3C consists of a negative meniscus lens L16 with its convex surface facing the object, a negative lens L17 with both surfaces aspherical and biconcave, and a biconvex air lens K is formed between L16 and L17. [Examples]

[0104] Figure 31 is a lens configuration diagram of the optical system of Embodiment 7 of the present invention. It consists of a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power. Focusing from infinity to close is achieved by the movement of the second lens group G2 from the image side to the object side.

[0105] The first lens group G1 consists of a subgroup G1A with negative refractive power and a subgroup G1B with positive refractive power. Subgroup G1A consists of a negative meniscus lens L1 with both sides aspherical and convex towards the object. Subgroup G1B consists of a positive meniscus lens L2 with a convex side facing the image, a cemented lens consisting of a biconcave negative lens L3 and a positive meniscus lens L4 with a convex side facing the object, and a positive meniscus lens L5 with a convex side facing the object.

[0106] The second lens group G2 consists of a negative meniscus lens L6 with its convex surface facing the image side.

[0107] The third lens group G3 consists of a subgroup G3A with positive refractive power, an aperture diaphragm S, a subgroup G3B with positive refractive power, and a subgroup G3C with negative refractive power. Subgroup G3A consists of a cemented lens consisting of a positive lens L7 with both sides aspherical and biconvex, a positive lens L8 with biconvex shape, and a negative lens L9 with biconcave shape. Subgroup G3B consists of a cemented lens consisting of a positive meniscus lens L10 with the concave side facing the object and a negative meniscus lens L11 with the concave side facing the object, a cemented lens consisting of a negative meniscus lens L12 with the convex side facing the object and a positive lens L13 with biconvex shape, and a positive lens L14 with biconvex shape. Subgroup G3C consists of a negative meniscus lens L15 with the convex side facing the object and a negative lens L16 with both sides aspherical and biconcave, and a biconvex air lens K is formed between L15 and L16. [Examples]

[0108] Figure 36 is a lens configuration diagram of the optical system of Embodiment 8 of the present invention. It consists of a first lens group G1 with negative refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power. Focusing from infinity to close is achieved by the movement of the second lens group G2 from the image side to the object side.

[0109] The first lens group G1 consists of a subgroup G1A with negative refractive power and a subgroup G1B with positive refractive power. Subgroup G1A consists of a negative meniscus lens L1 with both sides aspherical and the convex side facing the object. Subgroup G1B consists of a positive meniscus lens L2 with the convex side facing the image, a biconcave negative lens L3, and a biconvex positive lens L4.

[0110] The second lens group G2 consists of a negative meniscus lens L5 with its convex surface facing the image side.

[0111] The third lens group G3 consists of a subgroup G3A with positive refractive power, an aperture diaphragm S, a subgroup G3B with positive refractive power, and a subgroup G3C with negative refractive power. Subgroup G3A consists of a positive meniscus lens L6 with its convex surface facing the object, a positive lens L7 with both sides aspherical and biconvex, a negative lens L8 with a biconcave shape, and a positive meniscus lens L9 with its convex surface facing the image. Subgroup G3B consists of a cemented lens made of a positive meniscus lens L10 with its concave surface facing the object and a negative meniscus lens L11 with its concave surface facing the object, a cemented lens made of a negative meniscus lens L12 with its convex surface facing the object and a positive meniscus lens L13 with its convex surface facing the object, and a positive lens L14 with a biconvex shape. The subgroup G3C consists of a negative meniscus lens L15 with its convex surface facing the object, and a negative lens L16 with aspherical surfaces on both sides and a biconcave shape. The biconvex air lens K is formed between L15 and L16.

[0112] The following shows specific numerical data for each embodiment of the imaging optical system of the present invention described above.

[0113] In the [surface data], the surface number is the number of the lens surface or aperture diaphragm counted from the object side, r is the radius of curvature of each surface, d is the spacing between each surface, nd is the refractive index for the d line (wavelength 587.56 nm), vd is the Abbe number for the d line, and PgF indicates the partial dispersion ratio for the g line (wavelength 435.8 nm) and the F line (wavelength 486.1 nm).

[0114] The asterisk (*) next to the lens surface number indicates that the lens surface is aspherical. BF represents the back focus.

[0115] The (diaphragm) appended to the surface number indicates that an aperture diaphragm is located at that position. The radius of curvature relative to the plane or aperture diaphragm is indicated with ∞ (infinity). Furthermore, the refractive index of air, n=1.0000, is omitted from the description.

[0116] The [Aspherical Data] section shows the coefficient values ​​that give the aspherical shape of the lens surface marked with an asterisk (*) in the [Surface Data] section. The shape of the aspherical surface is defined as follows, where y is the displacement from the optical axis in the direction perpendicular to the optical axis, z is the displacement (sag) in the direction of the optical axis from the intersection of the aspherical surface and the optical axis, r is the radius of curvature of the reference sphere, K is the conic coefficient, and A4, A6, A8, A10, A12, A14, and A16 are the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order aspherical coefficients, respectively, and the coordinates of the aspherical surface are expressed by the following formula.

[0117] TIFF0007878689000001.tif17166

[0118] The [Various Data] section shows values ​​such as the zoom ratio and focal length at each focal length state.

[0119] The [Variable Interval Data] section shows the variable interval and BF values ​​for each shooting distance and each shooting magnification state.

[0120] The [Lens Group Data] shows the number of the object-side surface in each lens group and the combined focal length of the entire group.

[0121] In addition, for all the specifications listed below, the units of focal length f, radius of curvature r, lens plane spacing d, and other lengths are millimeters (mm) unless otherwise specified. However, since equivalent optical performance can be obtained in both proportional magnification and proportional reduction in the optical system, this is not the only unit of measurement.

[0122] Furthermore, in the aberration diagrams corresponding to each embodiment, d, g, and C represent the d line, g line, and C line, respectively, and △S and △M represent the sagittal image plane and meridional image plane, respectively.

[0123] Numerical Example 1 Unit: mm [Surface data] Face number rd nd vd PgF Object surface ∞ (d0) 1* 161.7900 2.8000 1.69350 53.18 0.5482 2* 32.1600 5.3700 3 55.0200 1.1000 1.77250 49.62 0.5503 4 27.5400 14.0300 5 -64.1800 3.3100 2.00100 29.13 0.5994 6 -42.3300 1.7200 7 -39.6800 1.0000 1.71700 47.98 0.5556 8 154.7400 0.1500 9 65.0800 6.2100 2.00100 29.13 0.5994 10 -146.5000 (d10) 11 -42.4900 1.0000 1.51680 64.20 0.5342 12 -244.6900 (d12) 13 38.7200 4.8000 1.95375 32.32 0.5900 14 500.2700 0.1200 15* 56.1000 4.0000 1.69350 53.20 0.5465 16* -200.0000 0.9600 17 753.2600 1.0000 1.86966 20.02 0.6433 18 44.1300 4.5500 19 -133.1200 2.8300 1.55032 75.50 0.5399 20 -52.8000 2.3100 21 (aperture) ∞ 3.5600 22 -228.8400 8.3500 1.59282 68.62 0.5440 23 -18.3400 1.0000 1.85451 25.15 0.6102 24 -322.3600 0.1500 25 61.6500 1.0000 1.85451 25.15 0.6102 26 20.6300 8.1400 1.75500 52.32 0.5472 27 -144.0200 1.4800 28 44.4500 6.2600 1.92286 20.88 0.6388 29 -62.0800 0.6000 30 69.2200 1.0000 1.54814 45.82 0.5699 31 28.7400 4.8500 32* -143.1800 1.6200 1.80610 40.73 0.5693 33* 207.3800 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 15, Page 16, Page 32, Page 33 K 0.0000E+00 -1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A4 3.4261E-06 3.5765E-06 -6.4052E-06 1.9734E-06 -1.8625E-05 5.5601E-06 A6 -1.8342E-09 2.2043E-09 6.1089E-09 1.1349E-08 -2.8534E-09 2.2982E-08 A8 1.6244E-12 -2.6363E-12 -2.7557E-11 -5.3746E-11 -7.2938E-11 -2.9978E-11 A10 -1.1413E-15 1.1577E-14 2.2574E-13 2.2412E-13 1.6668E-13 -1.4588E-14 A12 2.6109E-19 -1.4151E-17 -6.8516E-16 -4.6122E-16 0.0000E+00 0.0000E+00 A14 0.0000E+00 0.0000E+00 6.5730E-19 2.1969E-19 0.0000E+00 0.0000E+00 A16 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 [Various Data] INF Focal length 20.33 F-number 1.46 Full angle of view 2ω 96.47 Image height Y 21.63 Lens length: 129.04 [Variable interval data] INF 226mm d0 ∞ 97.4379 d10 11.3900 3.7932 d12 2.0000 9.5968 BF 20.3784 20.3784 [Lens group data] Group starting plane focal length G1 1 -57.92 G2 11 -99.66 G3 13 31.86 G1A 1 -30.91 G1B 5 120.72 G3A 13 37.61 G3B 22 27.26 G3C 30 -47.41

[0124] Numerical Example 2 Unit: mm [Surface data] Face number rd nd vd PgF Object surface ∞ (d0) 1* 200.0000 2.8000 1.51633 64.06 0.5333 2 32.5800 5.3200 3 55.3700 1.0000 1.83481 42.72 0.5646 4 24.6000 14.1700 5 -59.5900 3.2200 1.92286 20.88 0.6388 6 -39.5600 1.4500 7 -36.5700 1.0000 1.72342 37.99 0.5819 8 134.5600 0.1500 9 63.6800 6.5900 2.00100 29.13 0.5994 10 -105.2700 (d10) 11 -42.1700 1.0000 1.56883 56.04 0.5484 12 -245.8300 (d12) 13 36.2300 5.4100 1.90043 37.37 0.5765 14 1000.0000 0.7000 15* 97.0800 4.0000 1.77250 49.46 0.5539 16* -200.0000 0.6600 17 295.9200 1.0000 1.86966 20.02 0.6433 18 51.2600 4.1400 19 -182.8700 2.8400 1.59282 68.62 0.5440 20 -60.0400 2.4700 21 (aperture) ∞ 3.6800 22 -176.3800 9.0700 1.61997 63.88 0.5424 23 -17.5800 1.0000 1.85451 25.15 0.6102 24 -275.0200 0.1500 25 59.2900 1.0000 1.85451 25.15 0.6102 26 20.3900 8.2900 1.75500 52.32 0.5472 27 -143.1000 1.3300 28 43.2300 6.4800 1.86966 20.02 0.6433 29 -58.6500 0.6000 30 91.1500 1.0000 1.60342 38.01 0.5827 31 31.8400 4.5400 32* -144.9600 1.6200 1.80610 40.73 0.5693 33* 205.6000 (BF) Image plane ∞ [Aspherical data] Page 1, Page 15, Page 16, Page 32, Page 33 K 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A4 5.0861E-06 -9.1048E-06 -1.1208E-06 -1.9122E-05 5.0940E-06 A6 -3.3479E-09 1.1587E-08 1.7688E-08 -5.6453E-09 2.0717E-08 A8 3.4015E-12 -5.4047E-11 -8.8004E-11 -6.1843E-11 -3.6881E-11 A10 -2.0680E-15 6.0849E-13 7.4216E-13 1.5778E-13 0.0000E+00 A12 6.3781E-19 -1.9480E-15 -2.3344E-15 0.0000E+00 0.0000E+00 A14 0.0000E+00 1.8791E-18 2.2267E-18 0.0000E+00 0.0000E+00 A16 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 [Various Data] INF Focal length 20.36 F-number 1.46 Full angle of view 2ω 96.42 Image height Y 21.63 Lens length: 129.06 [Variable interval data] INF 227mm d0 ∞ 97.7171 d10 10.0200 3.3892 d12 2.0000 8.6308 BF 20.3590 20.3590 [Lens group data] Group starting plane focal length G1 1 -58.98 G2 11 -89.64 G3 13 31.36 G1A 1 -30.09 G1B 5 114.32 G3A 13 36.15 G3B 22 27.09 G3C 30 -44.87

[0125] Numerical Example 3 Unit: mm [Surface data] Face number rd nd vd PgF Object surface ∞ (d0) 1* 89.3100 2.8000 1.77250 49.50 0.5518 2* 25.5200 5.0000 3 45.8200 1.0000 1.91082 35.25 0.5821 4 26.1800 8.8900 5 84.3500 3.5300 1.90366 31.31 0.5947 6 265.7400 6.7600 7 -50.1600 1.0000 1.55032 75.50 0.5399 8 115.0800 0.1500 9 62.6300 6.5700 2.00100 29.13 0.5994 10 -134.5400 (d10) 11 -41.6600 1.0000 1.48749 70.44 0.5305 12 1116.3700 (d12) 13 50.2600 5.0500 1.87071 40.73 0.5681 14 -114.6900 0.1200 15* 145.0900 4.0000 1.85135 40.10 0.5694 16* -200.0000 1.7200 17 -172.8600 1.0000 1.86966 20.02 0.6433 18 82.6400 1.4400 19 77.9100 2.7600 1.55032 75.50 0.5399 20 833.4400 4.3100 21 (aperture) ∞ 3.7400 22 -145.7400 8.1300 1.49700 81.61 0.5387 23 -17.7700 1.0000 1.85451 25.15 0.6102 24 -48.1300 0.1500 25 588.0900 1.0000 1.85451 25.15 0.6102 26 20.8800 8.7100 1.80420 46.50 0.5571 27 -85.0100 1.6600 28 47.2200 6.6500 1.92286 20.88 0.6388 29 -59.2100 0.6000 30 65.8300 1.0000 1.78472 25.72 0.6157 31 32.7300 4.9900 32* -156.4300 1.6200 1.85135 40.10 0.5694 33* 203.5200 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 15, Page 16, Page 32, Page 33 K 0.0000E+00 -1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A4 1.0953E-06 1.9692E-06 -5.8903E-07 3.7871E-06 -2.3474E-05 -3.9442E-06 A6 -1.3149E-09 -1.4252E-09 -1.8469E-09 -5.6753E-09 -5.4781E-08 -2.7081E-08 A8 7.2362E-13 -2.7897E-12 6.6558E-11 9.4737E-11 3.6094E-10 3.1984E-10 A10 -2.1431E-16 -2.6636E-15 -3.4185E-13 -5.1629E-13 -9.9561E-13 -8.5448E-13 A12 2.5379E-20 3.6899E-18 6.9529E-16 1.0979E-15 1.0477E-15 7.3504E-16 A14 0.0000E+00 0.0000E+00 -5.0592E-19 -8.3086E-19 0.0000E+00 0.0000E+00 A16 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 [Various Data] INF Focal length 20.29 F-number 1.46 Full angle of view 2ω 94.46 Image height Y 21.63 Lens length: 129.05 [Variable interval data] INF 225mm d0 ∞ 96.2400 d10 10.6800 3.5577 d12 2.0000 9.1223 BF 20.0244 20.0244 [Lens group data] Group starting plane focal length G1 1 -75.93 G2 11 -82.36 G3 13 31.77 G1A 1 -26.68 G1B 5 69.50 G3A 13 38.11 G3B 22 25.35 G3C 30 -45.27

[0126] Numerical Example 4 Unit: mm [Surface data] Face number rd nd vd PgF Object surface ∞ (d0) 1* 62.6600 2.5000 1.69350 53.20 0.5465 2* 19.0800 13.1400 3 72.3800 3.5800 1.98613 16.48 0.6654 4 218.6700 6.0200 5 -32.1500 2.2800 1.76182 26.61 0.6122 6 93.9300 0.1500 7 55.1800 5.7800 2.00100 29.13 0.5994 8 -70.0300 (d8) 9 -29.6100 1.0000 1.59410 60.47 0.5550 10 428.5400 (d10) 11* 57.4400 7.7100 1.85135 40.10 0.5694 12* -37.6000 0.1500 13 -67.0400 1.0000 1.80809 22.76 0.6285 14 142.8400 0.1500 15 56.4000 3.4300 1.91082 35.25 0.5821 16 462.4500 3.2600 17 (aperture) ∞ 3.5500 18 -212.1100 8.2000 1.59282 68.62 0.5440 19 -21.0100 1.0000 1.85451 25.15 0.6102 20 -1000.0000 0.1500 21 38.9700 1.0000 1.73037 32.23 0.5898 22 24.7100 9.2900 1.59282 68.62 0.5440 23 -68.1000 0.1500 24 44.1300 5.1600 1.86966 20.02 0.6433 25 -190.1100 0.1500 26 70.9800 1.0000 1.74077 27.76 0.6076 27 35.3500 7.9200 28* -154.2500 1.4000 1.80610 40.73 0.5693 29* 200.6700 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 11, Page 12, Page 28, Page 29 K 0.0000E+00 -1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A4 -2.0709E-06 5.1042E-06 -1.9004E-06 5.1631E-06 -2.7858E-05 -5.1073E-07 A6 1.1079E-08 1.3709E-08 7.7478E-10 6.6432E-11 -4.7622E-08 -2.3273E-08 A8 -2.8760E-11 -2.1587E-11 6.0556E-12 4.2336E-12 1.5314E-10 2.0673E-10 A10 5.7455E-14 7.9435E-14 0.0000E+00 0.0000E+00 -7.6497E-14 -3.1510E-13 A12 -6.2835E-17 -5.2293E-17 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A14 3.0069E-20 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A16 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 [Various Data] INF Focal length 23.67 F-number 1.46 Full angle of view 2ω 84.80 Image height Y 21.63 Lens length: 118.50 [Variable interval data] INF 245mm d0 ∞ 126.1227 d8 7.2400 3.7235 d10 2.0000 5.5165 BF 20.1427 20.1427 [Lens group data] Group starting plane focal length G1 1 -112.02 G2 9 -46.58 G3 11 24.85 G1A 1 -40.51 G1B 3 95.91 G3A 11 30.55 G3B 18 30.77 G3C 26 -49.04

[0127] Numerical Example 5 Unit: mm [Surface data] Face number rd nd vd PgF Object surface ∞ (d0) 1* 81.9000 2.6000 1.69350 53.20 0.5465 2 18.1200 9.9600 3* 43.2500 1.6700 1.59271 66.97 0.5366 4* 23.4500 5.5100 5 61.2700 3.2300 1.86966 20.02 0.6433 6 1000.0000 3.7400 7 -34.6400 1.8600 1.80420 46.50 0.5571 8 48.4400 0.7700 9 37.9400 6.3600 1.95375 32.32 0.5900 10 -73.7200 (d10) 11 -35.7600 1.0000 1.80420 46.50 0.5571 12 -338.1600 (d12) 13* 152.4500 3.9900 1.59271 66.97 0.5366 14* -53.0900 0.1500 15 40.5600 6.4500 1.59282 68.62 0.5440 16 -25.4600 1.0000 1.75500 52.32 0.5472 17 -42.0300 2.6900 18 (aperture) ∞ 3.3400 19 254.0600 5.9100 1.55032 75.50 0.5399 20 -17.5800 1.0000 1.90110 27.06 0.6070 21 149.7800 0.3000 22 53.2000 1.0000 1.85451 25.15 0.6102 23 19.8500 8.9200 1.72916 54.67 0.5452 24 -47.9700 0.3800 25 38.2900 5.5900 2.00272 19.32 0.6450 26 -62.4600 0.1500 27 136.1800 1.0000 1.80518 25.46 0.6156 28 26.9100 3.6900 29* -127.7500 1.4000 1.80610 40.73 0.5693 30* 166.2100 (BF) Image plane ∞ [Aspherical data] Page 1, Page 3, Page 4, Page 13, Page 14, Page 29 K 0.0000E+00 0.0000E+00 -1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A4 1.0609E-05 -3.9031E-06 1.0072E-05 -1.6268E-06 5.8582E-06 -1.1375E-05 A6 -2.9060E-09 -4.0125E-09 2.7807E-08 4.9547E-09 6.2491E-09 -4.3711E-09 A8 -2.3052E-11 4.8755E-11 -2.2587E-10 9.8938E-12 1.2508E-11 -4.5367E-10 A10 9.5651E-14 3.1606E-13 1.5838E-12 0.0000E+00 0.0000E+00 8.8058E-13 A12 -1.6089E-16 -7.6771E-16 -6.5494E-16 0.0000E+00 0.0000E+00 0.0000E+00 A14 1.3220E-19 4.9426E-19 -3.8277E-18 0.0000E+00 0.0000E+00 0.0000E+00 A16 -4.1834E-23 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 30 surfaces K 0.0000E+00 A4 2.6291E-05 A6 8.0176E-08 A8 -3.4130E-10 A10 3.8806E-13 A12 0.0000E+00 A14 0.0000E+00 A16 0.0000E+00 [Various data] INF Focal length 16.37 F-number 1.84 Full frame angle 2ω 105.57 Image height Y 21.63 Overall lens length 111.17 [Variable interval data] INF 224mm d0 ∞ 113.0752 d10 4.8700 2.6861 d12 2.000^0 4.1839 BF 20.6389 20.6389 [Lens group data] Group Starting surface Focal length G1 1 -47.89 It should be noted that in the translation of "d12 2.000^0 4.1839", it is not clear what the "2.000^0" means in the original text. I translated it as "2.000^0" as it is, but it might need further clarification in the context of the original patent content.G2 11 -49.80 G3 13 22.75 G1A 1 -22.51 G1B 5 79.40 G3A 13 25.50 G3B 19 21.29 G3C 27 -27.67

[0128] Numerical Example 6 Unit: mm [Surface data] Face number rd nd vd PgF Object surface ∞ (d0) 1* 62.1400 2.7000 1.69350 53.20 0.5465 2* 14.3400 12.5600 3* 70.0600 1.3400 1.85135 40.10 0.5694 4* 37.9900 3.9900 5 616.5100 4.3600 1.86966 20.02 0.6433 6 -49.3700 1.9600 7 -36.8000 1.0000 1.75500 52.32 0.5472 8 25.5500 2.5100 1.69895 30.05 0.6028 9 36.9800 1.0000 10 31.9300 5.3600 1.85451 25.15 0.6102 11 -171.7000 (d11) 12 -37.3600 1.0000 1.87071 40.73 0.5681 13 -338.6400 (d13) 14* 41.5000 4.2100 1.80610 40.73 0.5693 15* -57.2600 0.1500 16 47.6600 1.0000 1.86966 20.02 0.6433 17 21.4900 5.7700 1.55032 75.50 0.5399 18 -56.0200 2.4700 19 (Aperture) ∞ 4.1700 20 -39.2900 4.3700 1.49700 81.61 0.5387 21 -14.8800 1.0000 1.85451 25.15 0.6102 22 -87.8200 0.1500 23 51.5300 1.0000 1.84666 23.78 0.6191 24 24.5000 8.2100 1.59282 68.62 0.5440 25 -33.2100 0.4300 26 38.3900 6.2100 1.94595 17.98 0.6544 27 -64.4800 0.1500 28 87.4800 1.0000 1.84666 23.78 0.6191 29 31.2500 3.7600 30* -300.0000 1.4000 1.85135 40.10 0.5694 31* 107.0700 (BF) Image plane ∞ [Aspherical data] Surface 1 Surface 2 Surface 3 Surface 4 Surface 14 Surface 15 K 0.0000E+00 -1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A4 2.9462E-06 2.0531E-05 -8.7632E-06 -1.5685E-06 -1.6209E-06 4.5156E-06 A6 -8.4010E-09 2.3222E-08 -1.1146E-08 -1.0099E-09 -6.4113E-11 2.4720E-09 A8 2.1510E-11 -1.3181E-10 -5.0559E-10 -6.4909E-10 1.7417E-11 1.3644E-11 A10 -2.4710E-14 8.1842E-13 3.0554E-12 4.8294E-12 0.0000E+00 0.0000E+00 A12 1.6072E-17 -2.0343E-15 -5.9173E-15 -1.1744E-14 0.0000E+00 0.0000E+00 A14 -2.4688E-21 1.5234E-18 3.8456E-18 1.3375E-17 0.0000E+00 0.0000E+00 A16 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 Pages 30 and 31 K 0.0000E+00 0.0000E+00 A4 -1.7599E-05 2.0743E-05 A6 -2.9468E-08 1.8362E-08 A8 -5.4063E-10 -3.0150E-10 A10 1.8727E-12 8.2096E-13 A12 -1.5205E-15 -7.4403E-16 H14 0.0000E+00 0.0000E+00 A16 0.0000E+00 0.0000E+00 [Various Data] INF Focal length 14.42 F-number 1.85 Full angle of view 2ω 114.55 Image height Y 21.63 Lens length: 110.82 [Variable interval data] INF 235mm d0 ∞ 123.9383 d11 4.7200 3.3494 d13 2.0000 3.3706 BF 20.8662 20.8662 [Lens group data] Group starting plane focal length G1 1 -32.66 G2 12 -48.30 G3 14 22.70 G1A 1 -19.45 G1B 5 98.58 G3A 14 22.62 G3B 20 22.28 G3C 28 -34.69

[0129] Numerical Example 7 Unit: mm [Surface data] Face number rd nd vd PgF Object surface ∞ (d0) 1* 91.5100 2.9000 1.69350 53.18 0.5482 2* 18.2700 17.2800 3 -89.1600 3.6400 1.80420 46.50 0.5571 4 -48.3400 1.2600 5 -43.1900 1.0000 1.49700 81.61 0.5387 6 29.4300 5.5000 1.77047 29.74 0.5950 7 75.9500 1.1800 8 81.3200 3.2200 1.92119 23.96 0.6201 9 970.4900 (d9) 10 -32.5700 1.0000 1.80420 46.50 0.5571 11 -107.6600 (d11) 12* 53.5300 5.8300 1.85135 40.10 0.5694 13* -55.2600 1.1600 14 47.5600 6.6100 1.55032 75.50 0.5399 15 -39.4700 1.0000 1.92286 20.88 0.6388 16 1065.4900 3.2800 17 (aperture) ∞ 5.3100 18 -35.5600 4.9700 1.43700 95.10 0.5335 19 -17.7100 1.0000 1.76634 35.83 0.5791 20 -56.1200 0.1500 21 47.5800 1.0000 1.85451 25.15 0.6102 22 25.4500 8.6600 1.55032 75.50 0.5399 23 -40.4800 2.2100 24 34.7900 6.6200 2.00069 25.46 0.6135 25 -107.5600 0.1500 26 113.1600 1.0000 1.72825 28.32 0.6058 27 32.4100 4.0400 28* -197.2100 1.4000 1.80610 40.73 0.5693 29* 148.4100 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 12, Page 13, Page 28, Page 29 K 0.0000E+00 -1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A4 -2.9001E-07 8.5896E-06 -1.9413E-08 2.4163E-06 -6.9173E-06 2.3975E-05 A6 -7.5028E-10 4.4022E-09 6.1738E-09 1.9076E-09 1.9338E-08 4.7563E-08 A8 2.4033E-12 -1.4100E-11 -8.1435E-12 3.3885E-12 -3.4862E-10 -2.5536E-10 A10 -2.4611E-15 8.0185E-14 2.4959E-14 4.8761E-15 8.2124E-13 3.0460E-13 A12 8.6550E-19 -9.4242E-17 0.0000E+00 0.0000E+00 -5.8487E-16 -8.8055E-17 A14 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A16 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 [Various Data] INF Focal length 18.21 F-number 1.45 Full angle of view 2ω 100.96 Image height Y 21.63 Lens length: 123.54 [Variable interval data] INF 219mm d0 ∞ 95.2003 d9 9.0500 5.5381 d11 2.0000 5.5119 BF 21.1183 21.1183 [Lens group data] Group starting plane focal length G1 1 -51.29 G2 10 -58.41 G3 12 28.34 G1A 1 -33.46 G1B 3 166.49 G3A 12 29.83 G3B 18 21.89 G3C 26 -38.27

[0130] Numerical Example 8 Unit: mm [Surface data] Face number rd nd vd PgF Object surface ∞ (d0) 1* 64.1300 2.5000 1.76450 49.10 0.5528 2* 17.7200 15.5700 3 -81.9200 3.7300 2.00100 29.13 0.5994 4 -46.8100 1.7800 5 -39.6600 1.0000 1.72342 37.99 0.5819 6 67.1700 0.5400 7 48.6100 5.7300 1.85451 25.15 0.6102 8 -133.0500 (d8) 9 -38.2400 1.1700 1.54072 47.20 0.5677 10 -289.6600 (d10) 11 46.0700 4.1700 1.91082 35.25 0.5821 12 1000.0000 0.1200 13* 68.0800 4.4500 1.69350 53.20 0.5465 14* -131.9500 1.8400 15 -128.6500 1.0000 1.86966 20.02 0.6433 16 371.0700 2.1600 17 -320.4700 2.9300 1.55032 75.50 0.5399 18 -62.8000 2.2000 19 (aperture) ∞ 4.8700 20 -98.0500 8.8000 1.59282 68.62 0.5440 21 -17.3500 1.0000 1.85451 25.15 0.6102 22 -88.5700 0.1500 23 59.2600 1.0000 1.85451 25.15 0.6102 24 19.1600 8.5600 1.75500 52.32 0.5472 25 1000.0000 0.1500 26 41.1900 7.6500 1.92286 20.88 0.6388 27 -56.5000 0.6000 28 130.6300 1.0000 1.71736 29.50 0.6039 29 38.5700 3.9500 30* -149.3700 1.5500 1.80610 40.73 0.5693 31* 194.2800 (BF) Image plane ∞ [Aspherical data] Page 1, Page 2, Page 13, Page 14, Page 30, Page 31 K 0.0000E+00 -1.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 A4 4.2385E-07 1.2850E-05 -9.0708E-07 4.6523E-06 -6.6083E-06 2.1603E-05 A6 2.4168E-09 1.5250E-08 5.4395E-09 3.0914E-09 9.4332E-09 4.2226E-08 A8 -8.0350E-12 -1.7593E-12 -4.0135E-11 -5.0437E-11 -8.0443E-10 -8.1611E-10 A10 1.3221E-14 1.1440E-13 6.3282E-13 8.2729E-13 3.7352E-12 3.8864E-12 A12 -1.1091E-17 -2.1078E-16 -2.5488E-15 -3.7404E-15 -6.3954E-15 -8.3224E-15 A14 3.9716E-21 -2.5898E-20 3.8572E-18 6.4195E-18 3.7937E-18 6.6948E-18 A16 0.0000E+00 9.0151E-22 -1.9261E-21 -3.7704E-21 0.0000E+00 0.0000E+00 [Various Data] INF Focal length 20.16 F-number 1.46 Full angle of view 2ω 95.16 Image height Y 21.63 Lens length: 123.54 [Variable interval data] INF 224mm d0 ∞ 100.6721 d8 9.4500 4.1894 d10 2.5000 7.7606 BF 21.4237 21.4237 [Lens group data] Group starting plane focal length G1 1 -46.90 G2 9 -81.61 G3 11 29.13 G1A 1 -32.79 G1B 3 201.30 G3A 11 32.58 G3B 20 27.17 G3C 28 -43.25

[0131] Furthermore, a list of corresponding values ​​for the conditional expressions in each of these examples is shown.

[0132] [Conditional expression corresponding value] Conditional Expression Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 (1) -0.58 -0.60 -0.56 -0.63 -0.77 -0.64 -0.57 -0.63 (2) 0.67 0.64 0.65 0.63 0.65 0.81 0.72 0.59 (3) 1.92 1.87 1.92 1.87 2.00 1.95 2.00 1.92 (4) 0.028 0.031 0.028 0.031 0.031 0.038 0.011 0.028 (5) -0.84 -0.82 -0.86 -0.92 -0.71 -0.57 -0.67 -0.76 (6) 0.013 0.011 0.019 0.023 0.018 0.032 0.032 0.013 (7) 47.3 45.4 49.7 52.4 49.8 56.1 65.4 47.3 (8) 0.007 0.007 0.007 0.003 0.007 0.010 0.001 0.007 (9) 25.2 25.2 25.2 28.7 26.1 24.5 30.5 25.2 (10) -2.85 -2.90 -3.74 -4.73 -2.93 -2.26 -2.82 -2.33 (11) 1.73 1.68 1.84 1.69 1.64 1.77 1.69 1.76

[0133] The technology disclosed in this embodiment is not limited to the above-described embodiments and examples, and various modifications are possible. The shapes and numerical values ​​of each part shown in each of the above numerical examples are all examples for implementing this technology, and the technical scope of this technology should not be interpreted as being limited by them.

[0134] Furthermore, this technology can take the following configuration. [1] The lens system consists of, in order from the object side, a first lens group G1 with negative refractive power, a second lens group G2 that moves along the optical axis from the image side to the object side when focusing, and a third lens group G3 that has positive refractive power and contains an aperture diaphragm S. 、 The third lens group G3 is composed of, in order from the object side, a lens group G3A having positive refractive power, the aperture diaphragm S, a lens group G3B having positive refractive power, and a lens group G3C consisting of two negative lenses. The lens group G3C has an aspherical surface such that the negative refractive power increases from the optical axis center toward the periphery, and the air gap between the two negative lenses of the lens group G3C forms a biconvex air lens K, resulting in an optical system with an F-number less than 2.0 at infinity, satisfying the following conditional equation. An optical system characterized by [this]. (1) - 1.50 <f_G3B / f_G3C<―0.20 (2)0.30<(R_Kr+R_Kf) / (R_Kr-R_Kf) f_G3B: Focal length of the aforementioned lens group G3B when shooting at infinity. f_G3C: Focal length of the aforementioned lens group G3C when shooting at infinity. R_Kf: Radius of curvature of the air lens K on the object side. R_Kr: Radius of curvature of the image side of the air lens K. [2] The optical system according to [1], characterized in that the image-side lens of the lens group G3B is a positive lens and satisfies the following condition. (3) 1.75 <nd_G3B_r (4) 0.000 < ΔPgF_G3B_r nd_G3B_r: Refractive index nd of the positive lens located closest to the image in the lens group G3B. ΔPgF_G3B_r: Anomalous partial dispersion ΔPgF of the positive lens positioned closest to the image in the lens group G3B. [3] An optical system according to any one of [1] to [2], characterized in that it satisfies the following conditional equation. (5)-2.00 <f1_2 / f3<―0.30 (6) 0.000 <ave_ΔPgF_G3B_P (7) 40.0 <ave_νd_G3B_P (8) ave_ΔPgF_G3B_N<0.020 (9)ave_νd_G3B_N<35.0 f1_2: Combined focal length of the first lens group G1 and the second lens group G2 when shooting at infinity. f3: Focal length of the third lens group G3 when shooting at infinity. ave_ΔPgF_G3B_P: The average value of the anomalous partial dispersion ΔPgF of the positive refractive power lenses constituting the lens group G3B. ave_νd_G3B_P: The average value of the Abbe number νd of the positive refractive power lenses constituting the lens group G3B. ave_ΔPgF_G3B_N: The average value of the anomalous partial dispersion ΔPgF of the negative refractive power lenses constituting the lens group G3B. ave_νd_G3B_N: The average value of the Abbe number νd of the negative refractive power lenses constituting the lens group G3B. [4] The optical system according to any one of [1] to [3], wherein the first lens group G1 is composed of a front group G1A consisting only of negative meniscus lenses with their convex surfaces facing the object, and a rear group G1B having positive refractive power and having a positive lens positioned closest to the object, and satisfies the following conditional equation. (10)-10.00 <f1 / f<―0.50 (11) 1.55 <ave_nd_G1A_N f: Focal length of the entire lens system when shooting at infinity. f1: Focal length of the first lens group G1 when shooting at infinity. ave_nd_G1A_N: The average value of the refractive index nd of the negative refractive power lenses constituting the front group G1A. [5] The optical system according to any one of [1] to [4], characterized in that the second lens group G2 consists of two or fewer lenses. [Explanation of Symbols]

[0135] G1 First Lens Group G2 Second Lens Group G3 3rd lens group G1A, the front group of the first lens group G1A G1B: Rear group G1B of the first lens group G1. G3A Third lens group G3A subgroup G3B: Part of the third lens group G3B G3C Third lens group G3 subgroup G3C A biconvex air lens formed within subgroup G3C of lens group G3 of lens group K. S Aperture diaphragm I image plane CC line (wavelength λ=656.3nm) dd line (wavelength λ=587.6nm) gg line (wavelength λ=435.8nm)

Claims

1. Starting from the object side, the system consists of a first lens group G1 with negative refractive power, a second lens group G2 that moves along the optical axis from the image side to the object side when focusing, and a third lens group G3 that has positive refractive power and contains an aperture diaphragm S. The third lens group G3 is composed of, in order from the object side, a lens group G3A having positive refractive power, the aperture diaphragm S, a lens group G3B having positive refractive power, and a lens group G3C consisting of two negative lenses, wherein the lens group G3C has an aspherical surface such that the negative refractive power increases from the optical axis center toward the periphery, and the air gap between the two negative lenses of the lens group G3C forms a biconvex air lens K, and the optical system is characterized by having an F number less than 2.0 when shooting at infinity and satisfying the following conditional equation. (1) -1.50<f_G3B / f_G3C<-0.20 (2) 0.30<(R_Kr+R_Kf) / (R_Kr−R_Kf) f_G3B: Focal length of lens group G3B when shooting at infinity. f_G3C: Focal length of lens group G3C when shooting at infinity. R_Kf: Radius of curvature of the air lens K on the object side. R_Kr: Radius of curvature on the image side of the air lens K.

2. The optical system according to Claim 1, characterized in that the image-side lens of the lens group G3B is a positive lens and satisfies the following condition. (3) 1.75<nd_G3B_r (4) 0.000<ΔPgF_G3B_r nd_G3B_r: The refractive index nd of the positive lens located closest to the image in the lens group G3B. ΔPgF_G3B_r: Anomalous partial dispersion ΔPgF of the positive lens positioned closest to the image in the lens group G3B.

3. The optical system according to any one of claims 1 to 2, characterized in that it satisfies the following conditional expression. (5) -2.00<f1_2 / f3<-0.30 (6) 0.000<ave_ΔPgF_G3B_P (7) 40.0<ave_νd_G3B_P (8) ave_ΔPgF_G3B_N<0.020 (9) ave_νd_G3B_N<35.0 f1_2: Combined focal length of the first lens group G1 and the second lens group G2 when shooting at infinity. f3: Focal length of the third lens group G3 when shooting at infinity. ave_ΔPgF_G3B_P: The average value of the anomalous partial dispersion ΔPgF of the positive refractive power lenses constituting the lens group G3B. ave_νd_G3B_P: The average value of the Abbe number νd of the positive refractive power lenses constituting the lens group G3B. ave_ΔPgF_G3B_N: The average value of the anomalous partial dispersion ΔPgF of the negative refractive power lenses constituting the lens group G3B. ave_νd_G3B_N: The average value of the Abbe number νd of the negative refractive power lenses constituting the lens group G3B.

4. The optical system according to any one of claims 1 to 2, characterized in that the first lens group G1 is composed of a front group G1A consisting only of negative meniscus lenses with their convex surfaces facing the object, and a rear group G1B having positive refractive power and having a positive lens positioned closest to the object, and satisfying the following conditional equation. (10) -10.00<f1 / f<-0.50 (11) 1.55<ave_nd_G1A_N f: Focal length of the entire lens system when shooting at infinity f1: Focal length of the first lens group G1 when shooting at infinity. ave_nd_G1A_N: The average value of the refractive index nd of the negative refractive power lenses constituting the front group G1A.

5. The optical system according to any one of claims 1 to 2, characterized in that the second lens group G2 is composed of two or fewer lenses.

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