Optical system

Abstract

Provided is an optical system comprising a first lens group, a second lens group having a positive refractive power, a third lens group, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power, the optical system being characterized in that when focusing from infinity to extremely close, the refractive power of the fourth lens group is greater than the refractive power of the fifth lens group. The second lens group and the fourth lens group move toward the object side along the optical axis in different trajectories, the second lens group has an aspherical lens (G2asp) having a shape in which the positive refractive power is weakened from the center of the optical axis to the peripheral portion thereof, and the fourth lens group has at least one lens having a positive refractive power and one or more lenses having a negative refractive power.

Description

Technical Field

[0001] The present invention relates to an optical system suitable for use in an imaging device such as a still camera or a video camera, or a projection device, etc. The optical system is appropriately configured to have a large aperture ratio and effectively correct various aberrations while contributing to weight reduction. Background Art

[0002] In recent years, as imaging devices such as digital still cameras and video cameras have become increasingly pixelated, demands have been placed on high optical performance with strong correction of various aberrations from infinity to extreme close-up.

[0003] Furthermore, in recent digital cameras, the focus accuracy of autofocus (hereinafter referred to as AF) has significantly improved, making it possible to accurately focus even in bright optical systems with extremely narrow depth of field. As a result, even at wide open F-numbers, accurate and continuous focus is possible for shooting moving images, significantly expanding the range of image expression. Therefore, there is a desire for an optical system that suppresses field of view fluctuations (hereinafter referred to as focus breathing) during focusing operations, even in bright optical systems.

[0004] On the other hand, in order to achieve high imaging performance from infinity to very close, a method has been proposed in which two lens groups are moved along different trajectories during focus driving.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2022-140076 Patent Document 2: International Publication No. 2021 / 241230

[0006] The optical system described in Patent Document 1 suppresses AF speed variations caused by center-of-gravity shifts and posture differences during focusing by placing the focusing groups in front of and behind the lens group including the aperture stop, with their driving directions facing each other. Furthermore, various aberrations, including distortion, are effectively corrected from infinity to extreme close-up. However, there is a problem: when focusing from infinity to extreme close-up, the lens group with negative refractive power, located on the object side relative to the aperture stop, moves toward the image side, resulting in significant focus breathing.

[0007] The optical system described in Patent Document 2 satisfactorily corrects various aberrations including distortion from infinity to very close, and also appropriately corrects focus breathing. However, there is a problem that the optical system is large and heavy. Summary of the Invention

[0008] The present invention has been completed in view of this situation, and its purpose is to provide an optical system that has a large aperture ratio by appropriately arranging the focusing group and aspherical surfaces, and that achieves miniaturization and weight reduction while well correcting focus breathing and various aberrations including distortion.

[0009] In order to achieve the above-mentioned purpose, the optical system implementing the present invention is characterized in that it is composed of a first lens group G1, a second lens group G2 with positive refractive power, a third lens group G3, a fourth lens group G4 with positive refractive power and a fifth lens group G5 with negative refractive power, which are arranged in sequence from the object side. When focusing from infinity to extreme close, the second lens group G2 and the fourth lens group G4 move toward the object side along different trajectories along the optical axis. The second lens group G2 has an aspheric lens G2asp with a shape that weakens the positive refractive power from the center of the optical axis to the peripheral part, and the fourth lens group G4 has at least one lens with positive refractive power and one or more lenses with negative refractive power.

[0010] Furthermore, the optical system embodying the present invention is characterized in that the fifth lens group G5 satisfies the following conditional expression (1), and the third lens group G3 includes a lens Lp with positive refractive power that satisfies the following conditional expressions (2) and (3) at the same time. (1) 1.10<βG5<1.60 (2) 0.021<Lp_ΔPgF<0.055 (3)1 / (Lp_f×Lp_νd)<0.0020 βG5: Lateral magnification of the fifth lens group G5 when focusing at infinity Lp_ΔPgF: Abnormal partial dispersion ΔPgF of the positive refractive power lens Lp constituting the third lens group G3 Lp_vd: Abbe number vd of the positive refractive power lens Lp constituting the third lens group G3 Lp_f: Focal length of the positive refractive power lens Lp constituting the third lens group G3 when not cemented (mm)

[0011] Furthermore, the optical system embodying the present invention is characterized by satisfying the following conditional expression. (4)1.0<f2 / f4<6.0 (5) (f4 / vd_G4ave) / f<0.050 f: Focal length of the entire optical system when focusing at infinity (mm) f2: Focal length of the second lens group G2 when focusing at infinity (mm) f4: Focal length of the fourth lens group G4 when focusing at infinity (mm) vd_G4ave: average value of the Abbe numbers νd of the positive lenses constituting the fourth lens group G4

[0012] Furthermore, the optical system embodying the present invention is characterized in that the fifth lens group G5 includes an air lens AL satisfying the following conditional expression by two adjacent lenses. (6)-1.00<(R2air+R1air) / (R2air-R1air)<1.00 R1air: The object-side curvature radius of the air lens AL formed by the fifth lens group G5 (mm) R2air: Image-side curvature radius of the air lens AL formed by the fifth lens group G5 (mm)

[0013] Furthermore, the optical system embodying the present invention is characterized by satisfying the following conditional expression. (7)0.005<|(G2aspHnr-G2aspHinf) / f2|<0.050 G2aspHinf: Height of the off-axis principal ray when focusing at infinity on the object side of the aspherical lens G2asp (mm) G2aspHnr: Height of the off-axis principal ray at the closest focus on the object side of the aspherical lens G2asp (mm) The off-axis principal ray is the ray f2 passing through the intersection of the aperture stop and the optical axis at the maximum angle of view: The focal length (mm) of the second lens group G2 when focusing at infinity

[0014] Furthermore, the optical system embodying the present invention is characterized in that an aperture stop S is provided in the third lens group G3.

[0015] Furthermore, the optical system embodying the present invention is characterized in that an aspherical lens having positive refractive power is included in the fourth lens group G4.

[0016] Furthermore, the optical system embodying the present invention is characterized in that an aspherical lens having negative refractive power is provided on the most image side of the fifth lens group G5. Effects of the Invention

[0017] According to the present invention, an optical system can be provided that has a large aperture ratio by appropriately arranging the focusing group and the aspherical surface, and that achieves miniaturization and weight reduction while satisfactorily correcting focus breathing and various aberrations including distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a cross-sectional view of the lens at infinity of the optical system of Example 1. Figure 2 This is a diagram showing longitudinal aberrations at infinity for the optical system of Example 1. Figure 3 These are diagrams showing longitudinal aberrations of the optical system of Example 1 at a photographic distance of 395 mm. Figure 4 This is a diagram of lateral aberration at infinity of the optical system of Example 1. Figure 5 This is a diagram showing lateral aberrations of the optical system of Example 1 at a shooting distance of 395 mm. Figure 6 This is a cross-sectional view of the lens at infinity of the optical system of Example 2. Figure 7 This is a diagram of longitudinal aberration at infinity of the optical system of Example 2. Figure 8 This is a diagram showing longitudinal aberrations of the optical system of Example 2 at a shooting distance of 832 mm. Figure 9 This is a diagram of lateral aberration at infinity of the optical system of Example 2. Figure 10 This is a diagram showing lateral aberrations of the optical system of Example 2 at a shooting distance of 832 mm. Figure 11 This is a cross-sectional view of the lens at infinity of the optical system of Example 3. Figure 12 This is a diagram showing longitudinal aberrations at infinity for the optical system of Example 3. Figure 13 This is a diagram showing longitudinal aberrations of the optical system of Example 3 at a shooting distance of 250 mm. Figure 14 This is a diagram of lateral aberration at infinity of the optical system of Example 3. Figure 15 This is a diagram showing lateral aberration of the optical system of Example 3 at a shooting distance of 250 mm. Figure 16 This is a cross-sectional view of the lens at infinity of the optical system of Example 4. Figure 17 This is a diagram showing longitudinal aberrations at infinity for the optical system of Example 4. Figure 18 This is a diagram showing longitudinal aberrations of the optical system of Example 4 at a shooting distance of 394 mm. Figure 19 This is a diagram of lateral aberration at infinity of the optical system of Example 4. Figure 20 This is a diagram showing lateral aberration of the optical system of Example 4 at a shooting distance of 394 mm. Figure 21 This is a cross-sectional view of the lens at infinity of the optical system of Example 5. Figure 22 This is a diagram of longitudinal aberration at infinity of the optical system of Example 5. Figure 23 This is a diagram showing longitudinal aberrations of the optical system of Example 5 at a shooting distance of 250 mm. Figure 24 This is a diagram of lateral aberration at infinity of the optical system of Example 5. Figure 25 This is a diagram of lateral aberration of the optical system of Example 5 at a shooting distance of 250 mm. Figure 26 This is a cross-sectional view of the lens at infinity of the optical system of Example 6. Figure 27 This is a diagram of longitudinal aberration at infinity of the optical system of Example 6. Figure 28 This is a diagram showing longitudinal aberrations of the optical system of Example 6 at a shooting distance of 815 mm. Figure 29 This is a diagram of lateral aberration at infinity of the optical system of Example 6. Figure 30 This is a diagram of lateral aberration of the optical system of Example 6 at a shooting distance of 815 mm. DETAILED DESCRIPTION

[0019] In the optical system of the present invention, the refractive indices of 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. Note that any refractive index not otherwise specified represents the refractive index for the d-line.

[0020] The Abbe number νd, the partial dispersion ratio PgF, and the anomalous partial dispersion ΔPgF are derived from the following formulas. νd=(Nd-1) / (NF-NC) PgF=(Ng-NF) / (NF-NC) ΔPgF=PgF-0.64833+0.00180×νd

[0021] The following embodiments describe an example of the optical system of the present invention, and the present invention is not limited to these embodiments without departing from the spirit and scope of the present invention.

[0022] The optical system of the present invention is characterized in that Figure 1 、 Figure 6 、 Figure 11 、 Figure 16 、 Figure 21 and Figure 26As can be seen from the lens structure diagram shown, it is composed of the first lens group G1, the second lens group G2 with positive refractive power, the third lens group G3, the fourth lens group G4 with positive refractive power and the fifth lens group G5 with negative refractive power, which are arranged in sequence from the object side. When focusing from infinity to extreme close, the second lens group G2 and the fourth lens group G4 move toward the object side along different trajectories along the optical axis. The second lens group G2 has an aspheric lens G2asp with a shape that weakens the positive refractive power from the center of the optical axis to the peripheral part. The fourth lens group G4 has at least one lens with positive refractive power and one or more lenses with negative refractive power.

[0023] By moving the two lens groups along different paths as they focus, it is easier to correct various aberrations from infinity to very close, particularly spherical aberration, astigmatism, and coma. Furthermore, in the second lens group G2, which extends toward the object from infinity to very close, by configuring an aspherical lens G2asp with a shape that weakens the positive refractive power from the center of the optical axis to the periphery, it is possible to eliminate the effect of the narrowing of the field of view angle at very close range relative to infinity, thereby suppressing the occurrence of so-called focus breathing. Furthermore, since the same shape has the effect of producing negative distortion, even if the telephoto ratio of the optical system is increased for miniaturization, the occurrence of positive distortion can be suppressed. Furthermore, by configuring at least one lens with positive refractive power and one lens with negative refractive power in the fourth lens group G4, it is possible to suppress chromatic aberration fluctuations associated with focusing, contributing to higher image quality. Moreover, by setting the fifth lens group G5 to negative refractive power, the exit pupil can be brought closer to the image side, thereby suppressing vignetting at the peripheral field angle caused by the diameter limitation of the camera mount, and suppressing the reduction in light intensity that affects image quality.

[0024] Furthermore, the optical system of the present invention is characterized in that the fifth lens group G5 satisfies the following conditional expression (1), and the third lens group G3 includes a lens Lp with positive refractive power that satisfies the following conditional expressions (2) and (3) at the same time. (1) 1.10<βG5<1.60 (2) 0.021<Lp_ΔPgF<0.055 (3)1 / (Lp_f×Lp_νd)<0.0020 βG5: Lateral magnification of the fifth lens group G5 when focusing at infinity Lp_ΔPgF: Abnormal partial dispersion ΔPgF of the positive refractive power lens Lp constituting the third lens group G3 Lp_vd: Abbe number vd of the positive refractive power lens Lp constituting the third lens group G3 Lp_f: Focal length of the positive refractive power lens Lp constituting the third lens group G3 when not cemented (mm)

[0025] Conditional formula (1) specifies the lateral magnification of the 5th lens group G5. Since the 5th lens group G5 has a negative refractive power, it has the effect of magnifying the aberrations generated in the optical system in front of it. In particular, since the axial chromatic aberration is the square of the lateral magnification, the influence cannot be ignored in a lens with a large aperture ratio such as the present invention. On the other hand, if the lateral magnification of the 5th lens group G5 can be increased, it will be beneficial to shorten the total length of the optical system, so it is necessary to make the lateral magnification fall within an appropriate range. If the lateral magnification exceeds the upper limit of conditional formula (1) and becomes larger, the total length of the optical system can be shortened, but it is difficult to fully correct the axial chromatic aberration. If the lateral magnification exceeds the lower limit of conditional formula (1) and becomes smaller, the axial chromatic aberration can be fully corrected, but the optical system becomes larger and is not preferred.

[0026] Regarding the above-mentioned conditional expression (1), in order to further ensure the effect, it is preferable to set the lower limit value to 1.15 and the upper limit value to 1.55. Moreover, setting the lower limit value of the conditional expression (1) to 1.20 and the upper limit value to 1.50 further achieves the effect of the present invention, which is more preferable.

[0027] Conditional equations (2) and (3) define the correlation between the anomalous partial dispersion ΔPgF of the positive refractive power lens Lp used in the third lens group G3, the Abbe number vd, and the focal length f. In a large aperture ratio optical system such as the present invention, it is necessary to strongly correct axial chromatic aberration, which affects the coloring of the entire image. In the optical system of the present invention, since the fifth lens group G5 is a magnifying system, it is important to perform sufficient aberration correction on the front side of the fifth lens group G5. In particular, the third lens group G3 is arranged near the center of the optical system and is located in a position that is advantageous for strongly correcting axial chromatic aberration while minimizing the impact of magnification chromatic aberration. Therefore, it is necessary to appropriately select the lenses used in the third lens group G3. As an effective means of correcting axial chromatic aberration, materials with positive anomalous partial dispersion and very low dispersion are generally selected for positive lenses (for example, HOYA CORPORATION's FCD1). However, due to the low refractive index of these materials, they have an adverse effect on product miniaturization. On the other hand, glass materials such as the positive refractive power lens Lp used in the present invention have a characteristic of having a very high refractive index. Therefore, by using them in a manner that satisfies both conditional expressions (2) and (3), it is possible to achieve both chromatic aberration correction and product miniaturization. In addition, conditional expression (2) defines the range required for the secondary achromatism condition, and conditional expression (3) defines the range required for the primary achromatism condition. If the range is outside the conditional expression, it is difficult to achieve a sufficient achromatic effect.

[0028] If the upper limit of conditional expression (2) is exceeded and the anomalous dispersion of lens Lp increases, the secondary achromatic effect is excessive, which is not preferred. If the lower limit of conditional expression (2) is exceeded and the anomalous dispersion of lens Lp decreases, the secondary achromatic effect is insufficient, making it difficult to perform sufficient chromatic aberration correction. If the upper limit of conditional expression (3) is exceeded and the Abbe number or focal length of lens Lp decreases, the primary achromatic effect cannot be fully performed, making it difficult to perform chromatic aberration correction.

[0029] Regarding the above-mentioned conditional formula (2), in order to further ensure the effect, it is preferable to set the lower limit value to 0.023 and the upper limit value to 0.053. Moreover, by setting the lower limit value of conditional formula (2) to 0.026 and the upper limit value to 0.050, the effect of the present invention can be further achieved, which is more preferable. Similarly, regarding the above-mentioned conditional formula (3), in order to further ensure the effect, it is preferable to set the upper limit value to 0.0017. Moreover, by setting the upper limit value of conditional formula (3) to 0.0013, the effect of the present invention can be further achieved, which is more preferable.

[0030] Furthermore, the optical system of the present invention is characterized by satisfying the following conditional expression. (4)1.0<f2 / f4<6.0 (5) (f4 / vd_G4ave) / f<0.050 f: Focal length of the entire optical system when focusing at infinity (mm) f2: Focal length of the second lens group G2 when focusing at infinity (mm) f4: Focal length of the fourth lens group G4 when focusing at infinity (mm) vd_G4ave: average value of the Abbe numbers νd of the positive lenses constituting the fourth lens group G4

[0031] Conditional equation (4) specifies the focal length ratio of the second lens group G2 and the fourth lens group G4, which serve as the focusing group. The optical system of the present invention employs a floating lens system during focusing, employing a structure that cancels out spherical aberration, field curvature, and coma generated in each focusing group. Furthermore, by keeping the focal length ratio within an appropriate range, the focusing action can be dispersed, thereby suppressing the combined focusing movement of the second lens group G2 and the fourth lens group G4.

[0032] If the upper limit of conditional expression (4) is exceeded and the focal length of the fourth lens group G4 becomes relatively shorter, the amount of focus movement can be suppressed, but the various aberrations cannot be fully offset, making it difficult to fully suppress aberration fluctuations during focusing. On the other hand, if the lower limit of conditional expression (4) is exceeded and the focal length of the fourth lens group G4 becomes relatively longer, the various aberrations can be offset, but the amount of focus movement increases, and the total optical length becomes longer, which is not preferable.

[0033] Regarding the above-mentioned conditional expression (4), in order to further ensure the effect, it is preferable to set the lower limit value to 1.2 and the upper limit value to 5.8. Moreover, by setting the lower limit value of conditional expression (4) to 1.4 and the upper limit value to 5.6, the effect of the present invention can be further achieved, which is more preferable.

[0034] Conditional expression (5) specifies the ratio of the focal length of the fourth lens group G4 as a focusing group to the average value of the Abbe number of the positive lens, and the correlation with the focal length of the entire system. If the focal length of the lens becomes longer or the Abbe number becomes smaller, the amount of chromatic aberration generated increases, so conditional expression (5) specifies the amount of chromatic aberration generated in the fourth lens group G4. Since the fourth lens group G4 is a group with positive refractive power, the Abbe number of the positive lens constituting the group is particularly important. In addition, in order to perform good chromatic aberration correction from infinity to very close, the chromatic aberration generated in the fourth lens group G4 as a focusing group is preferably small. If the upper limit of conditional expression (5) is exceeded and the focal length of the fourth lens group G4 becomes relatively longer or the average value of the Abbe number becomes smaller, it is difficult to fully suppress the chromatic aberration variation during focusing.

[0035] Regarding the above-mentioned conditional expression (5), in order to further ensure the effect, it is preferable to set the upper limit value to 0.045. Moreover, setting the upper limit value of the conditional expression (5) to 0.040 is more preferable because the effect of the present invention can be further achieved.

[0036] Furthermore, in the optical system of the present invention, the fifth lens group G5 is characterized by having an air lens AL satisfying the following conditional expression by two adjacent lenses. (6)-1.00<(R2air+R1air) / (R2air-R1air)<1.00 R1air: The object-side curvature radius of the air lens AL formed by the fifth lens group G5 (mm) R2air: Image-side curvature radius of the air lens AL formed by the fifth lens group G5 (mm)

[0037] Conditional formula (6) specifies the shape of the air lens AL made by the 5th lens group G5, which is called the so-called shape factor. Conditional formula (6) specifies the range within which the air lens AL becomes biconvex. By forming the 5th lens group G5 close to the image plane and in which the diameter of the on-axis beam is easily reduced, it is possible to correct the Petzval sum and the field curvature through the negative refractive effect of both sides. In addition, the curvature radius of R2air is preferably a negative value with the concave surface facing the object side. If the curvature radius of R2air is positive or close to a positive value, the incident angle of the off-axis light to the surface becomes larger, resulting in large coma and astigmatism, making it difficult to achieve high performance. In addition, the curvature radius of R1air is preferably a positive value with the convex surface facing the object side. If the curvature radius of R1air is negative or close to a negative value, it is difficult to fully reduce the light beam closer to the object side than the air lens AL, thereby causing the 4th lens group G4 as the focusing group to become larger, making it impossible to perform high-speed AF action, which is not preferred. Therefore, R1air needs to be a positive value and R2air needs to be a negative value.

[0038] Furthermore, if the upper limit of conditional expression (6) is exceeded and the radius of curvature of R1air becomes smaller, the negative refractive power on the object side of the air lens AL becomes too strong, thereby causing large positive distortion aberration, which is not preferable. If the lower limit of conditional expression (6) is exceeded and the radius of curvature of R2air becomes larger, the angle of incidence of off-axis light on this surface becomes too small, resulting in an inability to fully correct coma aberration, which is not preferable.

[0039] Regarding the above-mentioned conditional expression (6), in order to further ensure the effect, it is preferable to set the lower limit to -0.50 and the upper limit to 0.95. Moreover, by setting the lower limit of the conditional expression (6) to 0.00 and the upper limit to 0.90, the effect of the present invention can be further achieved, which is more preferable.

[0040] Furthermore, the optical system of the present invention is characterized by satisfying the following conditional expression. (7)0.005<|(G2aspHnr-G2aspHinf) / f2|<0.050 G2aspHinf: Height of the off-axis principal ray when focusing at infinity on the object side of the aspherical lens G2asp (mm) G2aspHnr: Height of the off-axis principal ray at the closest focus on the object side of the aspherical lens G2asp (mm) The off-axis principal ray is the ray f2 passing through the intersection of the aperture stop and the optical axis at the maximum angle of view: The focal length (mm) of the second lens group G2 when focusing at infinity

[0041] Conditional equation (7) specifies the ratio of the focus variation of the height of the off-axis principal ray on the object side through the aspheric lens G2asp of the second lens group G2 to the focal length of the second lens group G2. Using the aspheric lens G2asp in the second lens group G2 is an effective method for suppressing focus breathing, but in order to fully exert its effect, it is important to significantly change the height of the off-axis principal ray passing through the aspheric lens G2asp during focusing. In order to significantly shift the light passage position, it is sufficient to lengthen the focal length of the second lens group G2 and ensure the focus shift amount. However, at the same time, the focusing effect is reduced, resulting in an increase in the thrust direction, so it needs to fall within an appropriate range.

[0042] If the upper limit of conditional expression (7) is exceeded and the absolute value of the focal length of the second lens group G2 becomes shorter, the aberration fluctuation during focusing becomes larger, making it difficult to suppress focus breathing while properly correcting various aberrations. If the lower limit of conditional expression (7) is exceeded and the absolute value of the focal length of the second lens group G2 becomes longer, the aberration fluctuation during focusing or focus breathing can be suppressed, but the optical system will become larger in the thrust direction, which is not preferred.

[0043] Regarding the above-mentioned conditional expression (7), in order to further ensure the effect, it is preferable to set the lower limit value to 0.007 and the upper limit value to 0.045. Moreover, by setting the lower limit value of conditional expression (7) to 0.009 and the upper limit value to 0.040, the effect of the present invention can be further achieved, which is more preferable.

[0044] Furthermore, the optical system of the present invention is characterized in that an aperture stop S is provided in the third lens group G3.

[0045] The third lens group G3 is positioned near the center of the optical system of the present invention. Therefore, by placing an aperture stop S at this location, the center of the optical system can be brought closer to the center of the pupil. This facilitates symmetric optical power configuration of the optical system, facilitating correction of various aberrations, including distortion, and improving optical performance. Furthermore, since the focusing group can be separated front and back via the aperture stop S, the actuator driving the focus and the units for the aperture stop S can be independently positioned, minimizing the increase in the image perpendicular to the optical axis. Furthermore, since the upper and lower marginal rays are easily positioned at symmetrical distances relative to the principal ray, the amount of peripheral light can be easily restored when the aperture is stopped down, minimizing unnatural images even when electronic correction is performed.

[0046] Furthermore, the optical system of the present invention is characterized in that an aspherical lens having positive refractive power is arranged in the fourth lens group G4.

[0047] The fourth lens group G4 is the image-side focusing group. It not only focuses but also eliminates aberrations generated by the second lens group G2, which serves as the object-side focusing group. In particular, strong correction is required for spherical aberration and coma generated by the second lens group G2. However, using multiple lenses to correct these aberrations would make the fourth lens group G4 larger and heavier, which would not only increase the size of the actuator but also prevent high-speed AF operation, making this undesirable. However, since spherical aberration and coma are monochromatic aberrations, they can be corrected by configuring aspherical lenses within the fourth lens group G4. Furthermore, the fourth lens group G4 has positive refractive power, so the aspherical lenses used for correction are preferably positive. This allows for excellent correction of various aberrations while reducing the number of lenses, thereby reducing the weight of the focusing movable unit and achieving both high-speed AF and high performance.

[0048] Furthermore, the optical system of the present invention is characterized in that an aspherical lens having negative refractive power is arranged on the most image side of the fifth lens group G5.

[0049] The fifth lens group G5 is positioned at a location where the off-axis ray height is higher than the on-axis ray height. Among lens groups employing this light transmission method, off-axis aberrations are particularly effectively corrected. Therefore, by configuring aspherical lenses with increasingly negative refractive power from the center of the optical axis toward the periphery in the fifth lens group G5, it is possible to effectively correct field curvature and distortion without increasing the number of lens elements, while achieving both miniaturization and high performance. Furthermore, aspherical lenses function more effectively when positioned at a location where the difference between the on-axis and off-axis ray heights is large, and therefore are preferably positioned closest to the image side.

[0050] 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 side. [Example 1]

[0051] Figure 1 This is a lens configuration diagram of an optical system according to Example 1 of the present invention. The optical system comprises 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. Focusing from infinity to extreme close range is achieved by moving the second lens group G2 and the fourth lens group G4 toward the object along different trajectories.

[0052] The first lens group G1 is composed of a biconcave negative lens and a biconvex positive lens.

[0053] The second lens group G2 is composed of a cemented lens composed of a biconvex positive lens G2asp having an aspherical object-side surface and a biconcave negative lens.

[0054] The third lens group G3 consists of a positive meniscus lens with its concave surface facing the object side, a biconcave negative lens, an aperture stop S, a cemented lens consisting of a biconcave negative lens and a biconvex positive lens, a biconvex positive lens with double aspheric surfaces, and a cemented lens consisting of a positive meniscus lens Lp with its concave surface facing the object side and a biconcave negative lens.

[0055] The fourth lens group G4 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconvex positive lens with an aspherical object-side surface.

[0056] The fifth lens group G5 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconcave negative lens with double aspheric surfaces. An air lens AL is formed between the cemented lens and the negative lens. [Example 2]

[0057] Figure 6 This is a lens configuration diagram of an optical system according to Example 2 of the present invention. This optical system comprises 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. Focusing from infinity to extreme close-up is achieved by moving the second lens group G2 and the fourth lens group G4 toward the object along different trajectories.

[0058] The first lens group G1 is composed of a positive meniscus lens with a convex surface facing the object side, a positive meniscus lens with a convex surface facing the object side, and a negative meniscus lens with a convex surface facing the object side.

[0059] The second lens group G2 is composed of a positive meniscus lens G2asp having a convex surface facing the object side and an aspherical object-side surface.

[0060] The third lens group G3 is composed of a cemented lens consisting of a biconvex positive lens Lp and a biconcave negative lens, an aperture stop S, a cemented lens consisting of a biconcave negative lens and a positive meniscus lens with the convex side facing the object side, a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a cemented lens consisting of a biconvex positive lens and a negative meniscus lens with the concave side facing the object side.

[0061] The fourth lens group G4 is composed of a negative meniscus lens with a convex surface facing the object side, and a biconvex positive lens with an aspherical object-side surface.

[0062] The fifth lens group G5 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconcave negative lens with double aspheric surfaces. An air lens AL is formed between the cemented lens and the negative lens. [Example 3]

[0063] Figure 11 This is a lens configuration diagram of an optical system according to Example 3 of the present invention. This optical system comprises 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. Focusing from infinity to extreme close-up is achieved by moving the second lens group G2 and the fourth lens group G4 toward the object along different trajectories.

[0064] The first lens group G1 is composed of a positive meniscus lens with a convex surface facing the object side.

[0065] The second lens group G2 is composed of a biconcave negative lens and a biconvex positive lens G2asp having aspherical surfaces on both sides.

[0066] The third lens group G3 consists of a biconcave negative lens, a cemented lens consisting of a positive meniscus lens Lp with its concave surface facing the object side and a negative meniscus lens with its concave surface facing the object side, an aperture stop S, a biconvex positive lens with double aspheric surfaces, and a cemented lens consisting of a negative meniscus lens with its convex surface facing the object side and a biconvex positive lens.

[0067] The fourth lens group G4 is composed of a biconcave negative lens and a biconvex positive lens with aspherical surfaces on both sides.

[0068] The fifth lens group G5 consists of a biconvex positive lens, a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconcave negative lens with double aspheric surfaces. An air lens AL is formed between the cemented lens and the negative lens. [Example 4]

[0069] Figure 16 This is a lens configuration diagram of an optical system according to Example 4 of the present invention. This optical system comprises 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. Focusing from infinity to extreme close-up is achieved by moving the second lens group G2 and the fourth lens group G4 toward the object along different trajectories.

[0070] The first lens group G1 is composed of a biconcave negative lens and a biconvex positive lens.

[0071] The second lens group G2 is composed of a cemented lens composed of a biconvex positive lens G2asp having an aspherical object-side surface and a biconcave negative lens.

[0072] The third lens group G3 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, an aperture stop S, a cemented lens consisting of a biconcave negative lens and a biconvex positive lens, and a positive meniscus lens Lp with its concave surface facing the object side.

[0073] The fourth lens group G4 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconvex positive lens with an aspherical object-side surface.

[0074] The fifth lens group G5 is composed of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a biconcave negative lens with double aspheric surfaces. An air lens AL is formed between the cemented lens and the negative lens. [Example 5]

[0075] Figure 21 This is a lens configuration diagram of an optical system according to Example 5 of the present invention. This optical system comprises 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. Focusing from infinity to extreme close-up is achieved by moving the second lens group G2 and the fourth lens group G4 toward the object along different trajectories.

[0076] The first lens group G1 is composed of a biconcave negative lens, a negative meniscus lens with its convex surface facing the object side, and a biconvex positive lens.

[0077] The second lens group G2 is composed of a biconvex positive lens G2asp having aspherical surfaces on both sides.

[0078] The third lens group G3 is composed of a cemented lens consisting of a positive meniscus lens Lp with its concave surface facing the object side and a biconcave negative lens, an aperture stop S, a cemented lens consisting of a biconcave negative lens and a positive meniscus lens with its convex surface facing the object side, and a biconvex positive lens.

[0079] The fourth lens group G4 is composed of a cemented lens composed of a biconcave negative lens and a biconvex positive lens, and a biconvex positive lens with aspherical surfaces on both sides.

[0080] The 5th lens group G5 is composed of a positive meniscus lens with its concave surface facing the object side, a cemented lens consisting of a negative meniscus lens with its convex surface facing the object side and a positive meniscus lens with its convex surface facing the object side, and a negative lens that is biconcave and aspherical on both sides, and an air lens AL is formed between the cemented lens and the negative lens. [Example 6]

[0081] Figure 26 This is a lens configuration diagram of an optical system according to Example 6 of the present invention. This optical system comprises a first lens group G1 of positive refractive power, a second lens group G2 of positive refractive power, a third lens group G3 of negative refractive power, a fourth lens group G4 of positive refractive power, and a fifth lens group G5 of negative refractive power. Focusing from infinity to extreme close range is achieved by moving the second lens group G2 and the fourth lens group G4 along different trajectories from the image side toward the object side.

[0082] The first lens group G1 is composed of a positive meniscus lens with its convex surface facing the object side, a positive meniscus lens with its convex surface facing the object side, and a cemented lens consisting of a positive meniscus lens with its convex surface facing the object side and a negative meniscus lens with its convex surface facing the object side.

[0083] The second lens group G2 is composed of a positive meniscus lens G2asp having a convex surface facing the object side and an aspherical object-side surface.

[0084] The third lens group G3 is composed of a negative meniscus lens with its convex surface facing the object side, an aperture stop S, a cemented lens composed of a biconcave negative lens and a biconvex positive lens, and a biconvex positive lens Lp.

[0085] The fourth lens group G4 is composed of a negative meniscus lens with a convex surface facing the object side, and a biconvex positive lens with aspherical surfaces on both sides.

[0086] The fifth lens group G5 consists of a cemented lens consisting of a biconvex positive lens and a biconcave negative lens, and a negative meniscus lens with a concave surface facing the object side and an aspherical object-side surface. An air lens AL is formed between the cemented lens and the negative meniscus lens.

[0087] Specific numerical data of each embodiment of the imaging optical system of the present invention are shown below.

[0088] In [Surface Data], the surface number indicates the number of the lens surface or aperture stop counted from the object side, r indicates the radius of curvature of each surface, d indicates the interval between the surfaces, nd indicates the refractive index with respect to the d-line (587.6 nm), vd indicates the Abbe number with respect to the d-line, and PgF indicates the partial dispersion ratio for the g-line (wavelength 435.8 nm) and the F-line (486.1 nm).

[0089] The * (asterisk) attached to the surface number indicates that the lens surface shape is aspherical. Also, BF represents the back focus.

[0090] The "(Stop)" next to the surface number indicates the location of the aperture stop. ∞ (infinity) is written for the radius of curvature relative to the plane or aperture stop.

[0091] The coefficient values for the aspheric shape of the lens surface marked with an * in the [Surface Data] section are shown in [Aspheric Surface Data]. Regarding the aspheric shape, the coordinates of the aspheric surface are expressed as follows: y represents the displacement from the axial direction perpendicular to the optical axis, z represents the displacement (perpendicularity) from the intersection of the aspheric surface and the optical axis toward the optical axis, r represents the radius of curvature of the reference sphere, K represents the conic coefficient, and A4, A6, A8, and so on, are used for the aspheric coefficients of each order.

[0092]

[0093] [Various Data] shows values such as focal length in the focused state at each shooting distance.

[0094] The variable interval data shows the variable interval and BF value in the focused state at each shooting distance.

[0095] The "Lens Group Data" shows the number of the surface closest to the object side constituting each lens group and the composite focal length of the entire group.

[0096] In addition, in all the following specifications, unless otherwise specified, the focal length f, curvature radius r, lens surface spacing d, and other length units are described in millimeters (mm). However, in optical systems, equivalent optical performance can be achieved even when the scale is enlarged or reduced, so this is not a limitation.

[0097] Furthermore, a list of corresponding values of the conditional expressions in these respective embodiments is shown.

[0098] Furthermore, 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 plane and the meridional image plane, respectively.

[0099] Numerical Example 1 Unit: mm [Surface data] [Aspherical surface data] [Various data] [Variable interval data] [Lens group data]

[0100] Numerical Example 2 Unit: mm [surface data] [Aspherical surface data] [Various data] [Variable interval data] [Lens group data]

[0101] Numerical Example 3 Unit: mm [surface data] [Aspherical surface data] [Various data] [Variable interval data] [Lens group data]

[0102] Numerical Example 4 Unit: mm [surface data] [Aspherical surface data] [Various data] [Variable interval data] [Lens group data]

[0103] Numerical Example 5 Unit: mm [surface data] [Aspherical surface data] [Various data] [Variable interval data] [Lens group data]

[0104] Numerical Example 6 Unit: mm [surface data] [Aspherical surface data] [Various data] [Variable interval data] [Lens group data]

[0105] [Conditional value] Explanation of symbols

[0106] G1-first lens group, G2-second lens group, G3-third lens group, G4-fourth lens group, G5-fifth lens group, G2asp-an aspherical lens with a shape that weakens the positive refractive power from the center of the optical axis to the peripheral portion, arranged in the second lens group G2, Lp-a lens with positive refractive power that satisfies conditional expressions (2) and (3) and is arranged in the third lens group G3, AL-an air lens that satisfies conditional expression (6) formed in the fifth lens group G5, S-aperture stop, I-image plane.

Claims

1. An optical system, characterized in that: The lens is composed of the first lens group (G1), the second lens group (G2) with positive refractive power, the third lens group (G3), the fourth lens group (G4) with positive refractive power, and the fifth lens group (G5) with negative refractive power, arranged in this order from the object side. When focusing from infinity to extreme close, the second lens group (G2) and the fourth lens group (G4) move toward the object side along different trajectories along the optical axis. The second lens group (G2) includes an aspherical lens (G2asp) having a shape in which the positive refractive power is weakened from the center of the optical axis to the periphery. The fourth lens group (G4) includes at least one lens having positive refractive power and at least one lens having negative refractive power.

2. The optical system according to claim 1, wherein The fifth lens group (G5) satisfies the following conditional expression (1), and the third lens group (G3) includes a lens (Lp) having positive refractive power that satisfies the following conditional expressions (2) and (3) at the same time. (1)1.10＜βG5＜1.60 (2) 0.021<Lp_ΔPgF<0.055 (3)1 / (Lp_f×Lp_νd)<0.0020 βG5 is the lateral magnification of the fifth lens group (G5) when focusing at infinity, Lp_ΔPgF is the anomalous partial dispersion ΔPgF of the positive refractive power lens (Lp) constituting the third lens group (G3), Lp_vd is the Abbe number vd of the positive refractive power lens (Lp) constituting the third lens group (G3), Lp_f is the focal length of the positive refractive power lens (Lp) constituting the third lens group (G3) in a non-cemented state, expressed in mm.

3. The optical system according to claim 1, wherein: The following conditions are met: (4)1.0<f2 / f4<6.0 (5) (f4 / vd_G4ave) / f<0.050 f is the focal length of the entire optical system in mm when focused at infinity, f2 is the focal length of the second lens group (G2) when focusing at infinity in mm, f4 is the focal length of the fourth lens group (G4) when focusing at infinity in mm. vd_G4ave is the average value of the Abbe numbers νd of the positive lenses constituting the fourth lens group (G4).

4. The optical system according to any one of claims 1 to 3, characterized in that The fifth lens group (G5) comprises an air lens (AL) satisfying the following conditional expression by two adjacent lenses: (6)-1.00<(R2air+R1air) / (R2air-R1air)<1.00 R1air is the object-side curvature radius of the air lens (AL) formed by the fifth lens group (G5) in mm. R2air is the image-side curvature radius of the air lens (AL) formed by the fifth lens group (G5) in mm.

5. The optical system according to any one of claims 1 to 3, characterized in that The following conditions are met: (7)0.005<|(G2aspHnr-G2aspHinf) / f2|<0.050 G2aspHinf is the height of the off-axis principal ray when focusing at infinity on the object side of the aspheric lens (G2asp) in mm, G2aspHnr is the height of the off-axis principal ray at the closest focus on the object side of the aspheric lens (G2asp) in mm, In addition, the off-axis principal ray is set as the ray passing through the intersection of the aperture stop and the optical axis at the maximum field angle. f2 is the focal length of the second lens group (G2) when focusing at infinity in mm.

6. The optical system according to any one of claims 1 to 3, characterized in that The third lens group (G3) includes an aperture stop (S).

7. The optical system according to any one of claims 1 to 3, characterized in that The fourth lens group (G4) includes an aspherical lens having positive refractive power.

8. The optical system according to any one of claims 1 to 3, characterized in that An aspherical lens having negative refractive power is provided at the position closest to the image side of the fifth lens group (G5).

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