JP2018005099A - Large-aperture lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily correct various aberrations, particularly chromatic aberration, to obtain good image quality over the entire screen, and to achieve miniaturization of a product without omitting an autofocus mechanism, and the size is suitable for an interchangeable lens. Provides a large aperture lens. SOLUTION: The first lens group G1 having a positive refractive power and the second lens group G2 having a positive refractive power are in order from the object side, and the first lens group G1 has a positive refractive power Lp1. The first lens group G1 is fixed to the image plane when focusing from an infinity object to a short-distance object, and the second lens group has a positive refractive power Lp2 and a negative refractive power lens. The lens group G2 is moved from the image plane side to the object side along the optical axis to obtain a large-diameter lens characterized by satisfying a predetermined condition. [Selection diagram] Fig. 1

Description

  The present invention relates to a large-aperture lens in which various aberrations such as spherical aberration and axial chromatic aberration are particularly corrected among photographic lenses particularly suitable for photographing apparatuses such as digital cameras, silver halide cameras, and video cameras.

  In recent years, with an increase in the number of pixels in a photographing apparatus such as a digital camera, an optical system having high optical performance in which various aberrations are sufficiently corrected is demanded.

  In particular, there is an increasing demand for high-resolution images that can take advantage of blurring before and after the in-focus portion, and in order to obtain such images, high-performance lenses with large aperture lenses with small F-numbers are being developed.

  In addition, an optical system used in a photographing apparatus such as a digital camera is required to have a short overall lens length.

  In general, as the entire optical system is reduced in size, various aberrations, particularly axial chromatic aberration and lateral chromatic aberration, occur more frequently and optical performance tends to deteriorate.

  Chromatic aberration is corrected by using a positive refractive power lens made of low dispersion optical material with anomalous partial dispersion and a negative refractive power lens made of high dispersion optical material. Has been made. In an optical system using a material such as fluorite as an optical material, correction of chromatic aberration can be easily performed when the overall lens length is set relatively long. However, if the total lens length is shortened, a large amount of chromatic aberration occurs, and it is difficult to correct this well.

  This is because the use of the low dispersion and large anomalous partial dispersibility of materials such as fluorite simply reduces the occurrence of chromatic aberration. In order to correct the chromatic aberration of the optical system that has deteriorated as the overall lens length is shortened, for example, in a lens system using a low dispersion glass with a large Abbe number such as fluorite, the curvature is required to obtain a desired refractive power. Need to be larger. For this reason, it is difficult to satisfactorily correct both chromatic aberration and various aberrations such as spherical aberration, coma aberration, and astigmatism generated by increasing the refractive power.

Japanese Patent No. 3254239 JP2015-96915A Japanese Patent No. 5395700

  The large-aperture lens described in Patent Document 1 performs floating focusing to suppress performance fluctuations when focusing to a short-distance object having a shortest imaging magnification of about -1/7. However, since focusing is performed while extending the entire lens system along the optical axis, there is a problem that it is difficult to increase the speed of focusing because the weight driven by autofocus increases.

  The large-aperture lens described in Patent Document 2 has a three-group configuration, and the first group and the third group are fixed, and the inner focus by the two groups is adopted to achieve high speed autofocus. Further, the convenience is enhanced by providing the anti-vibration groups in the three groups. However, there is a problem that correction of chromatic aberration is not sufficient and the F value is as dark as F1.8.

  The large-aperture lens described in Patent Document 3 employs a rear focus method, and performs high-speed autofocus and corrects various aberrations. However, since the axial chromatic aberration is not sufficiently corrected, there is a problem in that when a high-contrast subject is photographed, the peripheral edge of the blur is colored.

  The present invention has been made in view of such a situation, and various aberrations, in particular, chromatic aberration can be corrected satisfactorily to obtain a good image quality over the entire screen, and the autofocus mechanism can be omitted without omitting the product. An object of the present invention is to provide an optical system with a large aperture suitable for an interchangeable lens, which has been reduced in size.

In order to solve the above problems, a large-aperture lens according to the first aspect of the present invention includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group having a positive refractive power. The first lens group G1 includes a lens having a positive refractive power Lp1, a positive refractive power Lp2, and a negative refractive power lens, and is used for focusing from an infinite object to a short-distance object. The first lens group G1 is fixed with respect to the image plane, the second lens group G2 is moved from the image plane side to the object side along the optical axis, and the following conditional expression is satisfied: .
(1) PgFLp1 / νdLp1 <0.0085
(2) 0.0250 <PgFLp2 / νdLp2
(3) 0.010 <(fLp2 / νdLp2) / f1 <0.070
νdLp1: Abbe number of the positive refractive power lens having the largest d-line Abbe number in the first lens group G1 PgFLp1: g-line of the positive refractive power lens having the largest d-line Abbe number in the first lens group G1 And F-line partial dispersion ratio νdLp2: Abbe number of the positive lens having the smallest d-line Abbe number in the first lens group G1 PgFLp2: Positive d-line Abbe number in the first lens group G1 being the smallest Partial dispersion ratio of the g-line to the F-line of the lens with refractive power f1: Focal length fLp2 of the first lens group G1: Focal length of a lens with positive refractive power having the smallest Abbe number of d-line in the first lens group G1

The large-aperture lens according to the second invention of the present invention further includes a lens Lmj (j is an integer of 1 or more) having a negative refractive power that satisfies the following conditional expression in the first invention. G1 has one or more.
(4) ΔPgFLmj <0.0000
(5) 1.40 <νdLp1 / νdLmj <3.20
ΔPgFLmj: Abnormal partial dispersion νdLmj of the g-line and F-line of the lens Lmj with negative refractive power included in the first lens group G1: Abbe number of the lens Lmj with negative refractive power included in the first lens group G1

Further, the large-aperture lens according to the third invention of the present invention is the same as that in the first invention or the second invention, except that all the lenses having a positive refractive power included in the first lens group G1 have the following conditions. It is characterized by satisfying the formula.
(6) 0.00010 <ΔPgFG1av / νdG1av <0.00070
ΔPgFG1av: Average value of anomalous partial dispersion of the g-line and F-line of the positive-power lens included in the first lens group G1 νdG1av: d-line of the positive-power lens included in the first lens group G1 Average value of Abbe number

The large-diameter lens according to the fourth invention of the present invention is the first to third inventions, wherein the second lens group G2 is arranged in order from the object side, the second A lens group G2A, and the aperture stop S. And the second B lens group G2B, the most image side lens of the second A lens group G2A has a concave surface facing the image surface side, and the second B lens group G2B is arranged in order from the object side to the most object side. A refractive surface Sm1 having a concave surface facing the object side and a refractive surface Sm2 having a concave surface facing the object side, and satisfying the following conditional expression.
(7) 0.50 <(1 / RSm2) / (φSm1 + φSm2) <0.90
RSm2: radius of curvature of the refractive surface Sm2 φSm1: refractive power of the refractive surface Sm1 φSm2: refractive power of the refractive surface Sm2

  Further, the large-aperture lens according to the fifth aspect of the present invention is the positive refraction in which the convex surface faces the object side closest to the object side of the first lens group G1 in the first to fourth inventions. It has a power lens.

  The large-diameter lens according to a sixth aspect of the present invention is characterized in that, in the first to fifth aspects, the second lens group G2 further includes at least one aspheric lens.

  According to the present invention, it is possible to correct various aberrations, particularly chromatic aberration, to obtain a good image quality over the entire screen, and to reduce the size of the product without omitting the autofocus mechanism. Can be provided.

It is a lens block diagram at the time of infinity focusing which concerns on Example 1 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 1 of this invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 849 mm according to Example 1 of the present invention. It is a lateral aberration diagram at the time of focusing on infinity according to Example 1 of the present invention. FIG. 6 is a lateral aberration diagram at an imaging distance of 849 mm according to Example 1 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 2 of this invention. It is a longitudinal aberration diagram at the time of focusing on infinity according to Example 2 of the present invention. It is a longitudinal aberration figure in photographing distance 844mm concerning Example 2 of the present invention. It is a transverse aberration figure at the time of infinity focusing concerning Example 2 of the present invention. FIG. 6 is a lateral aberration diagram at an imaging distance of 844 mm according to Example 2 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 3 of this invention. It is a longitudinal aberration diagram at the time of focusing on infinity according to Example 3 of the present invention. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 845 mm according to Example 3 of the present invention. It is a transverse aberration figure at the time of infinity focusing concerning Example 3 of the present invention. FIG. 6 is a lateral aberration diagram at an imaging distance of 845 mm according to Example 3 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 4 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 4 of this invention. It is a longitudinal aberration figure in photographing distance 848mm concerning Example 4 of the present invention. It is a transverse aberration figure at the time of infinity focusing concerning Example 4 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 848 mm according to Example 4 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 5 of this invention. It is a longitudinal aberration figure at the time of infinity focusing which concerns on Example 5 of this invention. It is a longitudinal aberration figure in photographing distance 841mm concerning Example 5 of the present invention. It is a lateral aberration figure at the time of infinity focusing based on Example 5 of this invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 841 mm according to Example 5 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 6 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 6 of this invention. It is a longitudinal aberration figure in photographing distance 1164mm concerning Example 6 of the present invention. It is a lateral aberration figure at the time of infinity focusing which concerns on Example 6 of this invention. FIG. 10 is a lateral aberration diagram at an imaging distance 1164 mm according to Example 6 of the present invention.

  Examples of large-diameter lenses according to the present invention will be described below.

  In this example, the refractive indexes of the materials for g-line (wavelength 435.8 nm), F-line (486.1 nm), d-line (587.6 nm), and C-line (656.3 nm) are Ng and Nd, respectively. , NF, NC.

Further, the Abbe number νd, the partial dispersion ratio PgF, and the abnormal partial dispersion ΔPgF are derived by the following equations.
νd = (Nd−1) / (NF−NC)
PgF = (Ng-NF) / (NF-NC)
ΔPgF = PgF−0.648833 + 0.00180 × νd

The large-aperture lens according to the present embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, and the first lens group G1 has a positive refractive power. Lp1 having a positive refractive power, Lp2 having a positive refractive power, and a lens having a negative refractive power, and the first lens group G1 is fixed with respect to the image plane during focusing from an object at infinity to a short-distance object The second lens group G2 is moved from the image plane side to the object side along the optical axis, and the following conditional expression is satisfied.
(1) PgFLp1 / νdLp1 <0.0085
(2) 0.0250 <PgFLp2 / νdLp2
(3) 0.010 <(fLp2 / νdLp2) / f1 <0.070
νdLp1: Abbe number of the positive refractive power lens having the largest d-line Abbe number in the first lens group G1 PgFLp1: g-line of the positive refractive power lens having the largest d-line Abbe number in the first lens group G1 And F-line partial dispersion ratio νdLp2: Abbe number of the positive lens having the smallest d-line Abbe number in the first lens group G1 PgFLp2: Positive d-line Abbe number in the first lens group G1 being the smallest Partial dispersion ratio of the g-line to the F-line of the lens with refractive power f1: Focal length fLp2 of the first lens group G1: Focal length of a lens with positive refractive power having the smallest Abbe number of d-line in the first lens group G1

  In the lens configuration of the present embodiment, the first lens group G1 is fixed with respect to the image plane during focusing from an infinitely distant object to a close object, and the lens diameter and weight are smaller than those of the first lens group G1. Since the second lens group G2 is moved from the image plane side to the object side along the optical axis, it is possible to easily increase the focusing speed and simplify the lens barrel mechanism.

  Conditional expressions (1) to (3) indicate the ratio between the Abbe number and the partial dispersion ratio of materials used for the lenses having positive refractive power included in the first lens group G1, and the focal lengths thereof. It prescribes. By satisfying conditional expressions (1) to (3), various aberrations such as spherical aberration can be corrected in a well-balanced manner while favorably correcting chromatic aberration of the entire optical system.

  In the case of a general optical material, the ratio of (partial dispersion ratio) / (Abbe number) is about 0.008 to 0.025, and a material outside this range is a material having a large absolute value of abnormal partial dispersion ΔPgF. be able to.

  A bright lens with a small F value has a shallow depth of field and chromatic aberration is very conspicuous. For this reason, in order to correct chromatic aberration better, it is desirable to use a material having a low dispersion and a small partial dispersion ratio that satisfies the conditional expression (1) as a lens material having a positive refractive power.

  If the upper limit value of conditional expression (1) is exceeded, axial chromatic aberration increases and it is difficult to correct this in the entire system.

  For conditional expression (1), it is preferable to set the upper limit to 0.0080 in order to ensure the above effect. In order to make the effect more reliable, the upper limit is preferably set to 0.0072.

  Here, when trying to correct chromatic aberration only with a lens having a positive refractive power using a low-dispersion material, since these materials have a low refractive index, in order to obtain a desired refractive power, the lens surface Must be increased, resulting in an increase in spherical aberration, curvature of field, and the like.

  In addition, in order to satisfy the achromatic condition, even with a negative refractive power lens used in combination with a positive refractive power lens, the material of the positive refractive power lens shifts to the low dispersion side. It is necessary to shift to the low dispersion side. Low-dispersion materials generally have a low refractive index, so the curvature of the lens surface of a lens with a positive refractive power has to be increased, which causes excessive spherical aberration and images generated by the lens with a positive refractive power. In order to cancel the surface curvature, it is necessary to increase the curvature of the lens having negative refractive power, and as a result, coma aberration and sagittal coma flare increase.

  Therefore, in order to correct various aberrations while correcting chromatic aberration, a lens having a positive refractive power for sharing the refractive power is required. Therefore, it is desirable that the lens having a positive refractive power sharing the refractive power is a material having a high dispersion and a large partial dispersion ratio that satisfies the conditional expression (2).

  In general, an optical material has a refractive index on the short wavelength side higher than a refractive index on the long wavelength side. Further, the shorter the wavelength, the larger the refractive index change with respect to the wavelength change. The change in the refractive index and wavelength curve becomes larger as the Abbe number νd is smaller and the dispersion is large (for example, heavy flint type), or the Abbe number is large and the dispersion is small (for example, fluorophosphate type). The partial dispersion ratio PgF tends to increase.

  The partial dispersion ratio PgF of a general optical material shows an almost uniform change with respect to the change of the Abbe number νd. On the other hand, a material having a large anomalous partial dispersion ΔPgF has a large refractive index change with respect to a wavelength change on the short wavelength side as compared with a general glass material even if the Abbe number is the same.

  The fact that the partial dispersion ratio PgF changes uniformly with respect to the Abbe number νd means that the ratio of the refractive index change of the g-line to F-line with respect to the inclination of the F-line to C-line is constant. Therefore, when the refractive power of the lens is changed to correct the chromatic aberration of the F-line to C-line, the chromatic aberration of the g-line to F-line also changes at a constant rate. For this reason, it is difficult to sufficiently correct chromatic aberration even if only ordinary glass materials are combined.

  On the other hand, when a material having an anomalous partial dispersion is used as a lens, the ratio of the refractive index change of g-line to F-line with respect to the inclination of F-line to C-line is different from that of a normal glass material. The degree of freedom is greatly increased, and chromatic aberration can be corrected well over the entire wavelength range.

  In addition, when trying to correct chromatic aberration and various aberrations satisfactorily using only low dispersion materials such as fluorite and fluorophosphate, it is only necessary to increase the number of lenses of the low dispersion material in order to give the desired refractive power. However, it is necessary to increase the curvature of the lens, and the entire optical system becomes large and heavy. On the other hand, an optical material having a small Abbe number νd and a large dispersion generally has a large refractive index nd. Therefore, the curvature necessary for obtaining a desired refractive power may be small. Therefore, a high effect can be obtained in terms of downsizing the product while performing good aberration correction.

  Therefore, when the lower limit of conditional expression (2) is exceeded and the Abbe number is large and the partial dispersion ratio is small, it is difficult to achieve product miniaturization while performing good aberration correction.

  For conditional expression (2), it is preferable to set the lower limit to 0.0260 in order to ensure the above effect. Moreover, in order to make the effect more reliable, it is better to set the lower limit value to 0.0270.

  Further, it is desirable that the focal length of a lens having a positive refractive power using a material that satisfies the conditional expression (2) satisfies the conditional expression (3).

  In order to perform good chromatic aberration correction in the entire system, it is important to suppress chromatic aberration generated in the first lens group G1 as much as possible. In general, the stronger the refractive power of the lens group, the larger the required chromatic aberration correction amount. However, the chromatic aberration amount generated in a single lens used for chromatic aberration correction increases as the focal length increases and the Abbe number decreases. Conditional expression (3) defines a range necessary for performing good chromatic aberration correction.

  Exceeding the upper limit of conditional expression (3), if the focal length of Lp2 becomes longer or the Abbe number becomes smaller than the focal length of the first lens group G1, the necessary chromatic aberration correction amount is excessively corrected. In particular, the secondary spectrum with the g-line cannot be corrected, and it is difficult to correct this with the entire system.

  On the other hand, if the lower limit of the conditional expression (3) is exceeded and the focal length of Lp2 becomes shorter or the Abbe number becomes larger than the focal length of the first lens group G1, the chromatic aberration correction amount is insufficient, so that sufficient chromatic aberration is achieved. Correction cannot be performed, and it becomes difficult to correct this in the entire system. Further, since the lens thickness increases by increasing the curvature of Lp2, it becomes difficult to reduce the size and weight of the entire system.

  For conditional expression (3), it is preferable to set the lower limit value to 0.013 and the upper limit value to 0.065 in order to make the above effects more reliable.

In addition, the large-aperture lens of the present embodiment has one or more lenses Lmj (j is an integer of 1 or more) having a negative refractive power that satisfies the following conditional expression in the first lens group G1.
(4) ΔPgFLmj <0.0000
(5) 1.40 <νdLp1 / νdLmj <3.20
ΔPgFLmj: Abnormal partial dispersion νdLmj of the g-line and F-line of the lens Lmj with negative refractive power included in the first lens group G1: Abbe number of the lens Lmj with negative refractive power included in the first lens group G1

  Since the Abbe number of the optical material is always positive, it is necessary to combine lenses having positive and negative refractive powers in order to perform achromatization.

  Conditional expressions (4) to (5) define the Abbe number and anomalous partial dispersion of the material used for the negative refractive power lens included in the first lens group G1. By satisfying these conditional expressions, it is possible to correct various aberrations satisfactorily while correcting chromatic aberrations of the entire system.

  In order to satisfy the achromatic condition including correction of the secondary spectrum, it is necessary to increase the difference in the Abbe number between the positive refractive power lens and the negative refractive power lens and to reduce the partial dispersion ratio difference. . At that time, in order to effectively correct chromatic aberration, it is desirable to use a material having a strong anomalous partial dispersibility not only in a lens having a positive refractive power but also in a lens having a negative refractive power.

  In particular, it is preferable to use a material having an abnormal partial dispersion ΔPgF having a negative value. By doing so, it becomes possible to reduce the difference in the partial dispersion ratio. This condition is indicated by conditional expression (4).

  If the upper limit of conditional expression (4) is exceeded and the anomalous partial dispersibility ΔPgF has a positive value, it is difficult to correct the secondary spectrum satisfactorily.

  When the Abbe number of the lens Lmj having a negative refractive power is increased with respect to the Abbe number of the lens Lp1 having a positive refractive power beyond the lower limit value of the conditional expression (5), the curvature of the lens Lmj having a negative refractive power increases. For this reason, spherical aberration, coma aberration, and the like increase, and it is difficult to correct this in the entire system.

  On the other hand, if the ratio of νdLp1 and νdLmj increases beyond the upper limit of conditional expression (5), it is advantageous for correction of axial chromatic aberration. However, if νdLp1 increases as the upper limit is exceeded, the refractive index of the material decreases. For this reason, the curvature of the positive refractive power Lp1 must be increased. As a result, excessive spherical aberration occurs, and it is difficult to correct this in the entire system. Further, if νdLmj becomes smaller as it exceeds the upper limit value, the curvature of the lens Lmj having a negative refractive power becomes smaller, so that astigmatism becomes insufficiently corrected, and it becomes difficult to correct this as a whole system.

  For conditional expression (5), it is preferable to set the lower limit value to 1.50 and the upper limit value to 3.00 in order to make the above effects more reliable.

In addition, the large-aperture lens according to the present embodiment satisfies the following conditional expression for all lenses having a positive refractive power included in the first lens group G1.
(6) 0.00010 <ΔPgFG1av / νdG1av <0.00070
ΔPgFG1av: Average value of anomalous partial dispersion of the g-line and F-line of the positive-power lens included in the first lens group G1 νdG1av: d-line of the positive-power lens included in the first lens group G1 Average value of Abbe number

  When trying to suppress chromatic aberration while satisfactorily correcting various aberrations such as spherical aberration, it is ideal that the material used for the lens having a positive refractive power has a high refractive index and a small dispersion. However, in the case of a general optical material, the refractive index tends to decrease if the Abbe number is increased, and the Abbe number tends to decrease if the refractive index is increased. Therefore, when trying to balance various aberrations such as chromatic aberration and spherical aberration, TAF1 (trade name of HOYA Co., Ltd., d-line refractive index: 1.77250, d-line Abbe is used as a lens having a positive refractive power. There is a tendency to use a lot of materials such as the number 49.62).

  Conditional expression (6) defines the optimum condition of the material used for the positive refractive power lens included in the first lens group G1. By satisfying this condition, it is possible to satisfactorily correct various aberrations such as spherical aberration while satisfactorily correcting chromatic aberration.

  If the average value of the anomalous partial dispersion of the g-line and the F-line is large or the average value of the Abbe number of the d-line is small beyond the upper limit of the conditional expression (6), the correction of the secondary spectrum is advantageous. However, since the Abbe number becomes small, it becomes difficult to correct the primary spectrum, and the chromatic aberration cannot be sufficiently corrected by the first lens group G1. Further, even if chromatic aberration is suppressed by other lens groups, the balance of various aberrations such as spherical aberration and astigmatism is lost, making it difficult to obtain good image quality over the entire screen.

  Exceeding the lower limit of conditional expression (6), if the average value of the anomalous partial dispersion of g-line and F-line is small or the average value of Abbe number of d-line is large, it is advantageous for correcting the primary spectrum. However, it becomes difficult to sufficiently correct the secondary spectrum with the g-line due to the decrease in the abnormal partial dispersion, and the chromatic aberration cannot be sufficiently corrected by the first lens group G1. In general, a material having a large Abbe number used for positive refractive power has a low refractive index, and therefore, in order to obtain a desired refractive power on each lens surface, the curvature must be increased. The surface curvature increases, and it becomes difficult to correct this in the entire system.

  Regarding conditional expression (6), it is preferable to set the lower limit value to 0.00020 and the upper limit value to 0.00060 in order to make the above effects more reliable.

In the large-aperture lens of this example, the second lens group G2 is composed of a second A lens group G2A, an aperture stop S, and a second B lens group G2B in this order from the object side, and is the most image of the second A lens group G2A. The lens on the surface side has a concave surface facing the image surface side, and the second B lens group G2B has, in order from the object side, a refractive surface Sm1 with the concave surface facing the object side closest to the object side, and a concave surface facing the object side. Further, it has a refractive surface Sm2 and satisfies the following conditional expression.
(7) 0.50 <(1 / RSm2) / (φSm1 + φSm2) <0.90
RSm2: radius of curvature of the refractive surface Sm2 φSm1: refractive power of the refractive surface Sm1 φSm2: refractive power of the refractive surface Sm2

The refractive power φ is expressed by using the refractive index ndobj of the d-line of the medium on the object side, the refractive index ndimg of the d-line on the image plane side, and the radius of curvature R of the refractive surface on a certain refractive surface. And is defined by the following equation.
φ = (ndimg−ndobj) / R

  In general, in a so-called double Gauss type configuration in which lenses are arranged symmetrically with respect to an aperture, spherical aberration and astigmatism can be corrected satisfactorily, but coma due to focusing is difficult to correct. There is. This is because when the focus lens group is moved from infinity to a short distance, the incident ray height of the off-axis marginal ray on the surface facing the strong concave surface on the object side rises, and the incident angle of the ray becomes tight. This is to generate a large amount of coma flare.

  In order to reduce coma, the curvature of the surface with a strong concave surface facing the object side may be reduced. In order to reduce the curvature, it is necessary to increase the refractive index of the material and share the refractive power. However, the method using the higher refractive index is insufficient to correct the astigmatism corrected on this surface. It is not preferable.

  Therefore, in the present invention, two lenses having a concave surface facing the object side are arranged on the image plane side from the stop, and the lens on the image plane side has a negative refractive power, thereby serving as a field flattener. ing. By doing so, it is possible to satisfactorily correct spherical aberration and astigmatism, which are likely to be a problem with a large aperture lens, while correcting coma. Conditional expression (7) defines the desirable range.

  If the radius of curvature of the refracting surface Sm2 becomes smaller than the upper limit of conditional expression (7), it will be advantageous in correcting astigmatism, but the angle of incidence of off-axis marginal rays will become tight, so under coma flare will be reduced. It becomes impossible to suppress.

  On the other hand, if the radius of curvature of the refracting surface Sm2 exceeds the lower limit of the conditional expression (7), the amount of astigmatism correction that this surface should carry becomes insufficient, and it cannot function as a field flattener. .

  Regarding conditional expression (7), it is preferable to set the lower limit value to 0.55 and the upper limit value to 0.85 in order to make the above effects more reliable.

  The large-aperture lens of the present embodiment has a lens having a positive refractive power with a convex surface facing the object side on the most object side of the first lens group G1.

  In general, since the effective diameter of the lens on the object side is large in the large-aperture lens, the ratio of the weight occupied by the lens group closest to the object side in the entire weight increases. Therefore, to reduce the weight of the entire system, it is effective to reduce the lens diameter of the lens unit closest to the object side.

  In addition, in order to perform focusing at high speed, it is necessary to reduce the weight of the second lens group G2, which is a focus lens group, and for this purpose, it is necessary to reduce the on-axis marginal ray height in the second lens group G2.

  When the lens closest to the object side in the first lens group G1 is a lens having a negative refractive power, since the axial marginal ray jumps up, the lens diameter of the entire system is enlarged, and the weight of the entire system is suppressed. It becomes difficult to make an optical system capable of high-speed focusing.

  On the other hand, when the lens on the most object side in the first lens group G1 is a positive refractive power lens having a convex surface facing the object side, the curvature of the negative refractive power lens included in the first lens group G1 is increased. However, since the size of the lens diameter can be suppressed, astigmatism and distortion can be suppressed within the lens group without increasing the weight of the entire system.

  Further, in the large-diameter lens of the present embodiment, the second lens group G2 has at least one aspheric lens.

  For the purpose of correcting spherical aberration, it is desirable to provide an aspheric lens in the second lens group G2. By adopting an aspheric lens, it is possible to reduce the burden of correcting the aberration of a lens having a negative refractive power when correcting a spherical aberration generated by a lens having a positive refractive power with a lens having a negative refractive power. .

  As a result, the refractive power of the lens with negative refractive power can be weakened, and the curvature of the surface with the concave surface facing the object side can be reduced, so the occurrence of coma and sagittal coma flare can be suppressed. It becomes.

  This aspherical lens can effectively obtain the above effect if it is arranged on the object side of the stop. However, since the axial ray height is high on the object side of the stop, a large-aperture aspherical lens is required in this case. Therefore, the processing cost is increased, which is not preferable. On the other hand, disposing an aspheric lens closer to the image plane than the stop can reduce the lens diameter, which is advantageous in terms of processability of the aspheric lens.

  The aspherical shape of this aspherical lens is an aspherical surface that weakens the positive refractive power as it moves away from the optical axis in order to correct spherical aberration that occurs with positive refractive power, or is away from the optical axis. Therefore, it is preferable to use an aspheric surface that enhances the negative refractive power.

  Next, the lens configuration and numerical examples of the examples according to the large-aperture lens of the present invention will be described. In the following description, lens configurations are described in order from the object side to the image plane side.

  In [Surface data], the surface number is the number of the lens surface or aperture stop counted from the object side, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, and nd is for the d-line (wavelength 587.56 nm). The refractive index, vd is the Abbe number with respect to the d line, and PgF is the partial dispersion ratio.

  The * (asterisk) attached to the surface number indicates that the lens surface shape is an aspherical surface. BF represents back focus.

  The (diaphragm) attached to the surface number indicates that the aperture stop is located at that position. ∞ (infinity) is entered in the radius of curvature for a plane or aperture stop.

  [Aspherical data] indicates the values of the coefficients that give the aspherical shape of the lens surface marked with * in [Surface data]. The shape of the aspherical surface is expressed by the following formula. In the following equation, y is the displacement from the optical axis in the direction perpendicular to the optical axis, z is the displacement (sag amount) in the optical axis direction from the intersection of the aspherical surface and the optical axis, and r is the radius of curvature of the reference spherical surface. The conic coefficient is represented by K. The fourth, sixth, eighth, tenth, and twelfth order aspherical coefficients are represented by A4, A6, A8, A10, and A12, respectively.

  [Various data] shows values such as the focal length when focusing on infinity.

  [Variable interval data] indicates the variable interval and the value of BF in each shooting distance state.

  [Lens Group Data] indicates the lens surface number closest to the object side constituting each lens group and the combined focal length of the entire lens group.

  In all the values of the following specifications, the focal length f, the radius of curvature r, the lens surface interval d, and other length units described are in millimeters (mm) unless otherwise specified. In the system, the same optical performance can be obtained even in proportional expansion and proportional reduction, and the present invention is not limited to this.

  FIG. 1 is a lens configuration diagram of the large-diameter lens according to Example 1 when focused on infinity.

  The large-diameter lens in FIG. 1 includes a first lens group G1 having a positive refractive power that is fixed with respect to the image plane during focusing from an object at infinity to an object at close distance, and an object side from the image plane side during focusing. The second lens group G2 having a positive refractive power that moves to the right.

  The first lens group G1 includes a cemented lens including a positive meniscus lens having a convex surface facing the object side, a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens Lm1 having a convex surface facing the object side. The lens includes a negative lens having a shape, a negative lens Lm2 having a biconcave shape, a positive lens Lp2 having a biconvex shape, and a positive lens Lp1 having a biconvex shape.

  The second lens group G2 includes a second A lens group G2A having a positive refractive power, an aperture stop S, and a second B lens group G2B having a positive refractive power. When focusing from an object at infinity to a near object, The second A lens group G2A and the second B lens group G2B move together from the image plane side to the object side.

  The second A lens group G2A is composed of a cemented lens composed of a positive meniscus lens having a convex surface facing the object side, a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side. .

  The second lens group G2B includes a cemented lens composed of a negative lens having a biconcave shape and an object side lens surface being a refractive surface Sm1, and a biconvex positive lens, and a biconcave lens surface having an object side having a refractive surface Sm2. A certain negative lens is composed of a biconvex positive lens having both aspheric surfaces.

Numerical example 1
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 108.0180 5.2096 1.83481 42.72 0.5646
2 228.9981 0.1500
3 70.5874 9.5508 1.59282 68.62 0.5440
4 427.8716 1.9877 1.61340 44.27 0.5633
5 53.9116 10.8732
6 -397.6081 1.7031 1.54814 45.82 0.5699
7 287.8138 5.3074
8 -144.4601 1.6985 1.73800 32.26 0.5898
9 144.4601 5.3228
10 334.4430 3.8524 1.92286 20.88 0.6388
11 -529.3902 1.0000
12 76.6709 10.1634 1.49700 81.61 0.5387
13 -205.2843 (d13)
14 62.9651 4.5258 1.88300 40.80 0.5654
15 120.1023 0.1500
16 31.7566 9.0246 1.80420 46.50 0.5571
17 76.5961 1.2643 1.73800 32.26 0.5898
18 23.2599 10.9387
(Aperture) ∞ 4.7987
20 -56.0955 0.9536 1.73800 32.26 0.5898
21 31.3349 7.4056 1.88300 40.80 0.5654
22 -170.7874 2.9841
23 -54.9942 2.3550 1.64769 33.84 0.5923
24 217.6652 0.1500
25 * 85.2890 8.0000 1.85135 40.10 0.5694
26 * -54.0642 (d26)
27 ∞ 1.4500 1.52301 58.59 0.5449
28 ∞ BF
Image plane ∞

[Aspherical data]
25 faces 26 faces
K 0.000000 0.000000
A4 -1.473089E-06 2.140059E-06
A6 1.381523E-10 -1.260138E-09
A8 2.077557E-11 2.708648E-11
A10 -7.423427E-14 -9.869988E-14
A12 1.589502E-16 1.951291E-16

[Various data]
INF
Focal length 83.50
F number 1.46
Full angle of view 2ω 28.92
Statue height Y 21.63
Total lens length 165.50

[Variable interval data]
INF shooting distance 849mm
d0 ∞ 683.3000
d13 16.5967 6.2796
d26 37.0800 47.3970
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length G1 1 320.03
G2 14 89.83
G2A 14 174.70
G2B 19 104.99

  FIG. 6 is a lens configuration diagram of the large aperture lens according to Example 2 when focusing on infinity.

  The large-diameter lens in FIG. 6 includes a first lens group G1 having a positive refractive power fixed with respect to the image plane during focusing from an object at infinity to an object at close distance, and an object side from the image plane side during focusing. The second lens group G2 having a positive refractive power that moves to the right.

  The first lens group G1 includes a positive meniscus lens having a convex surface facing the object side, a positive meniscus lens Lp1 having a convex surface facing the object side, a negative meniscus lens Lm1 having a convex surface facing the object side, a biconcave negative lens, It is composed of a plano-convex lens Lp2 having a convex surface on the side and a biconvex positive lens Lp1.

  The second lens group G2 includes a second A lens group G2A having a positive refractive power, an aperture stop S, and a second B lens group G2B having a positive refractive power. When focusing from an object at infinity to a near object, The second A lens group G2A and the second B lens group G2B move together from the image plane side to the object side.

  The second A lens group G2A includes a positive meniscus lens having a convex surface facing the object side, a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side.

  The second lens group G2B includes a cemented lens composed of a negative lens having a biconcave shape and an object side lens surface being a refractive surface Sm1, and a biconvex positive lens, and a biconcave lens surface having an object side having a refractive surface Sm2. A certain negative lens is composed of a biconvex positive lens having both aspheric surfaces.

Numerical example 2
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 80.3912 5.1058 1.80420 46.50 0.5571
2 127.1974 0.1500
3 72.4577 7.4631 1.45860 90.19 0.5350
4 165.7074 1.2201
5 145.3036 2.4264 1.61340 44.27 0.5633
6 52.2429 12.9634
7 -142.5551 1.7248 1.69895 30.05 0.6028
8 128.3074 6.4074
9 287.4070 3.3270 1.98612 16.48 0.6657
10 ∞ 1.0000
11 69.7914 10.5993 1.45860 90.19 0.5350
12 -269.5342 (d12)
13 76.9868 4.7535 1.88300 40.80 0.5654
14 191.6702 0.1500
15 32.9949 9.4626 1.80420 46.50 0.5571
16 88.6586 1.5933
17 103.5600 1.7183 1.73800 32.26 0.5898
18 23.4452 10.4386
(Aperture) ∞ 4.6804
20 -57.1023 0.9377 1.73800 32.26 0.5898
21 30.0748 7.7903 1.83481 42.72 0.5646
22 -115.7764 2.3218
23 -49.9739 2.2192 1.62004 36.30 0.5872
24 250.6316 0.1505
25 * 87.0385 8.0000 1.85135 40.10 0.5694
26 * -53.1080 (d26)
27 ∞ 1.4500 1.52301 58.59 0.5449
28 ∞ BF
Image plane ∞

[Aspherical data]
25 faces 26 faces
K 0.000000 0.000000
A4 -1.679331E-06 1.665451E-06
A6 -2.122071E-10 -1.388479E-09
A8 3.463682E-12 5.936169E-12
A10 -1.957210E-15 -5.010397E-15
A12 0.000000E + 00 0.000000E + 00

[Various data]
INF
Focal length 83.54
F number 1.47
Full angle of view 2ω 28.88
Statue height Y 21.63
Total lens length 160.52

[Variable interval data]
INF shooting distance 844mm
d0 ∞ 683.3000
d12 14.3836 4.0620
d26 37.0800 47.4015
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length G1 1 363.10
G2 13 89.87
G2A 13 185.54
G2B 19 95.73

  FIG. 11 is a lens configuration diagram of the large-diameter lens according to Example 3 when focusing on infinity.

  The large-diameter lens in FIG. 11 includes a first lens group G1 having a positive refractive power that is fixed with respect to the image plane during focusing from an object at infinity to an object at short distance, and an object side from the image plane side during focusing. The second lens group G2 having a positive refractive power that moves to the right.

  The first lens group G1 includes a positive meniscus lens Lp1 having a convex surface facing the object side, a positive meniscus lens Lp1 having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a biconcave negative lens Lm1. It is composed of a cemented lens composed of a positive meniscus lens having a convex surface facing the object side, and a biconvex positive lens Lp2.

  The second lens group G2 includes a second A lens group G2A having a positive refractive power, an aperture stop S, and a second B lens group G2B having a positive refractive power. When focusing from an object at infinity to a near object, The second A lens group G2A and the second B lens group G2B move together from the image plane side to the object side.

  The second A lens group G2A includes a cemented lens including a positive meniscus lens having a convex surface facing the object side, a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side.

  The second lens group G2B includes a cemented lens composed of a negative lens having a biconcave shape and an object side lens surface being a refractive surface Sm1, and a biconvex positive lens, and a biconcave lens surface having an object side having a refractive surface Sm2. It is composed of a cemented lens composed of a certain negative lens and a biconvex positive lens, and a positive meniscus lens having a convex surface facing the image surface side where both lens surfaces are aspherical.

Numerical Example 3
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 129.6234 5.1244 1.59282 68.62 0.5440
2 388.6185 0.1500
3 66.4812 7.0326 1.59282 68.62 0.5440
4 135.7949 2.6387
5 179.5819 1.8932 1.54072 47.20 0.5677
6 49.5879 13.2668
7 -125.9734 1.7307 1.73800 32.26 0.5898
8 44.2182 11.2944 1.72916 54.67 0.5452
9 367.6648 1.0005
10 85.9993 7.6949 1.80809 22.76 0.6285
11 -674.5276 (d11)
12 77.7400 4.4633 1.83481 42.72 0.5646
13 205.5764 0.1500
14 32.7511 8.2255 1.80420 46.50 0.5571
15 91.3457 1.2693 1.73800 32.26 0.5898
16 24.5320 10.6078
(Aperture) ∞ 4.8474
18 -56.8372 0.9699 1.73800 32.26 0.5898
19 48.8821 6.2233 1.88300 40.80 0.5654
20 -121.8546 2.1914
21 -56.0967 1.0008 1.64769 33.84 0.5923
22 37.7052 5.9241 1.88300 40.80 0.5654
23 -148.3544 1.5104
24 * -192.6161 5.0000 1.85135 40.10 0.5694
25 * -60.1694 (d25)
26 ∞ 1.4500 1.52301 58.59 0.5449
27 ∞ BF
Image plane ∞

[Aspherical data]
24 faces 25 faces
K 0.000000 0.000000
A4 -6.691731E-07 2.375045E-06
A6 1.231483E-09 1.142373E-10
A8 2.335687E-11 2.569350E-11
A10 -8.515821E-15 -8.657905E-15
A12 0.000000E + 00 0.000000E + 00

[Various data]
INF
Focal length 83.50
F number 1.47
Full angle of view 2ω 28.72
Statue height Y 21.63
Total lens length 161.52

[Variable interval data]
INF shooting distance 845mm
d0 ∞ 683.3000
d11 17.7842 7.2898
d25 37.0800 47.5744
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length G1 1 298.32
G2 12 89.41
G2A 12 176.39
G2B 17 108.22

  FIG. 16 is a lens configuration diagram of the large-diameter lens according to Example 4 when focusing on infinity.

  The large-diameter lens of FIG. 16 includes a first lens group G1 having a positive refractive power fixed with respect to the image plane during focusing from an object at infinity to a short-distance object, and an object side from the image plane side during focusing. The second lens group G2 having a positive refractive power that moves to the right.

  The first lens group G1 includes a positive meniscus lens having a convex surface facing the object side, a positive meniscus lens Lp1 having a convex surface facing the object side, a negative meniscus lens Lm1 having a convex surface facing the object side, a biconcave negative lens Lm2, The lens includes a biconcave negative lens Lm3, a biconvex positive lens Lp2, and a biconvex positive lens Lp1.

  The second lens group G2 includes a second A lens group G2A having a positive refractive power, an aperture stop S, and a second B lens group G2B having a positive refractive power. When focusing from an object at infinity to a near object, The second A lens group G2A and the second B lens group G2B move from the image plane side to the object side at different moving speeds.

  The second A lens group G2A includes a cemented lens including a positive meniscus lens having a convex surface facing the object side, a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side.

  The second lens group G2B includes a cemented lens composed of a negative lens having a biconcave shape and an object side lens surface being a refractive surface Sm1, and a biconvex positive lens, and a biconcave lens surface having an object side having a refractive surface Sm2. A certain negative lens is composed of a biconvex positive lens having both aspheric surfaces.

Numerical Example 4
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 104.0442 4.4464 1.72916 54.67 0.5452
2 167.8974 0.1500
3 61.9455 9.6589 1.55032 75.50 0.5399
4 154.9253 0.4340
5 122.6403 2.8438 1.61340 44.27 0.5633
6 54.8348 12.7043
7 -143.9032 1.7088 1.73800 32.26 0.5898
8 223.6970 4.9280
9 -208.5938 1.7316 1.73800 32.26 0.5898
10 208.5938 4.3329
11 304.2910 4.7667 1.92286 20.88 0.6388
12 -304.2910 1.0000
13 109.7199 9.4961 1.55032 75.50 0.5399
14 -142.6359 (d14)
15 55.3534 4.4778 1.88300 40.80 0.5654
16 91.4164 0.1508
17 32.7021 8.4339 1.80420 46.50 0.5571
18 56.2353 1.6471 1.69895 30.05 0.6028
19 23.7920 (d19)
(Aperture) ∞ 4.7467
21 -57.4621 1.3979 1.73800 32.26 0.5898
22 30.4304 7.8411 1.88300 40.80 0.5654
23 -286.5983 2.1988
24 -73.5440 1.4194 1.67270 32.17 0.5962
25 116.0752 0.5209
26 * 74.3249 8.0000 1.85135 40.10 0.5694
27 * -55.4665 (d27)
28 ∞ 1.4500 1.52301 58.59 0.5449
29 ∞ BF
Image plane ∞

[Aspherical data]
26 faces 27 faces
K 0.000000 0.000000
A4 -2.314554E-06 1.341936E-06
A6 -6.999263E-10 -1.267249E-09
A8 0.000000E + 00 0.000000E + 00
A10 0.000000E + 00 0.000000E + 00
A12 0.000000E + 00 0.000000E + 00

[Various data]
INF
Focal length 83.44
F number 1.46
Full angle of view 2ω 29.13
Statue height Y 21.63
Total lens length 166.36

[Variable interval data]
INF shooting distance 848mm
d0 ∞ 681.5000
d14 16.6759 6.0661
d19 11.1146 11.3807
d27 37.0799 47.4637
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length G1 1 277.79
G2 15 94.56
G2A 15 181.64
G2B 20 113.78

  FIG. 21 is a lens configuration diagram of the large aperture lens according to Example 5 when focusing on infinity.

  The large-diameter lens shown in FIG. 21 includes a first lens group G1 having a positive refractive power fixed with respect to the image plane during focusing from an object at infinity to an object at short distance, and an object side from the image plane side during focusing. The second lens group G2 having a positive refractive power that moves to the right.

  The first lens group G1 includes a positive meniscus lens Lp2 having a convex surface directed toward the object side, a positive meniscus lens Lp1 having a convex surface directed toward the object side, a negative meniscus lens Lm1 having a convex surface directed toward the object side, and a biconcave negative lens Lm2. And a cemented lens composed of a biconvex positive lens, and a positive meniscus lens having a convex surface facing the object side.

  The second lens group G2 includes a second A lens group G2A having a positive refractive power, an aperture stop S, and a second B lens group G2B having a positive refractive power. When focusing from an object at infinity to a near object, The second A lens group G2A and the second B lens group G2B move together from the image plane side to the object side.

  The second A lens group G2A includes a cemented lens including a positive meniscus lens having a convex surface facing the object side, a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side.

  The second lens group G2B includes a cemented lens composed of a negative lens having a biconcave shape and an object side lens surface being a refractive surface Sm1, and a biconvex positive lens, and a biconcave lens surface having an object side having a refractive surface Sm2. It is composed of a cemented lens composed of a certain negative lens and a biconvex positive lens, and a positive meniscus lens having a convex surface facing the image surface side where both lens surfaces are aspherical.

Numerical Example 5
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 146.0289 4.1719 1.92286 20.88 0.6388
2 328.8858 0.1500
3 64.9702 9.2754 1.43700 95.10 0.5335
4 290.4683 1.5359
5 278.6202 1.8739 1.73800 32.26 0.5898
6 57.9301 11.9467
7 -123.0990 1.7416 1.65412 39.62 0.5736
8 52.3054 12.2854 1.72916 54.67 0.5452
9 -242.0377 1.0000
10 62.0533 4.0444 1.80809 22.76 0.6285
11 87.8751 (d11)
12 75.4541 4.4315 1.91082 35.25 0.5821
13 188.4556 0.1500
14 33.0216 9.2295 1.72916 54.67 0.5452
15 177.6957 1.2630 1.73800 32.26 0.5898
16 25.1881 10.0882
(Aperture) ∞ 4.9328
18 -53.8221 0.9618 1.74077 27.76 0.6076
19 41.7012 6.6796 1.88300 40.80 0.5654
20 -122.3119 2.1708
21 -56.6353 1.0000 1.51680 64.20 0.5342
22 36.3843 5.4685 1.80420 46.50 0.5571
23 -486.9016 0.9651
24 * -388.8661 5.0000 1.85135 40.10 0.5694
25 * -62.2981 (d25)
26 ∞ 1.4500 1.52301 58.59 0.5449
27 ∞ BF
Image plane ∞

[Aspherical data]
24 faces 25 faces
K 0.000000 0.000000
A4 -1.010028E-06 2.580705E-06
A6 3.774320E-09 2.874951E-09
A8 2.325378E-11 2.349002E-11
A10 7.082329E-15 1.486692E-14
A12 0.000000E + 00 0.000000E + 00

[Various data]
INF
Focal length 83.51
F number 1.46
Full angle of view 2ω 28.75
Statue height Y 21.63
Total lens length 157.23

[Variable interval data]
INF shooting distance 841mm
d0 ∞ 683.3000
d11 17.3378 6.9248
d25 37.0800 47.4930
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length G1 1 343.06
G2 12 85.50
G2A 12 180.96
G2B 17 97.68

  FIG. 26 is a lens configuration diagram of the large-diameter lens according to Example 6 when focusing on infinity.

  The large-diameter lens in FIG. 26 includes a first lens group G1 having a positive refractive power that is fixed with respect to the image plane during focusing from an object at infinity to an object at close distance, and an object side from the image plane side during focusing. The second lens group G2 having a positive refractive power that moves to the right.

  The first lens group G1 includes a positive meniscus lens Lp2 having a convex surface facing the object side, a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a plano-concave lens having a concave surface facing the object side Lm1, and a positive meniscus lens Lp1 having a convex surface facing the object side.

  The second lens group G2 includes a second A lens group G2A having a positive refractive power, an aperture stop S, and a second B lens group G2B having a positive refractive power. When focusing from an object at infinity to a near object, The second A lens group G2A and the second B lens group G2B move from the image plane side to the object side at different moving speeds.

  The second A lens group G2A includes a cemented lens including a positive meniscus lens having a convex surface facing the object side, a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side.

  The second lens group G2B includes a cemented lens composed of a negative lens having a biconcave shape and a refractive surface Sm1 on the object side and a positive meniscus lens having a convex surface facing the object, and a biconcave lens surface on the object side. The lens includes a negative lens having a refractive surface Sm2, and a biconvex positive lens having both aspheric surfaces.

Numerical Example 6
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 203.6799 4.7092 1.98612 16.48 0.6657
2 677.9113 0.1500
3 66.0690 10.3433 1.59282 68.62 0.5440
4 163.8560 2.2446
5 207.2689 2.5306 1.84666 23.78 0.6191
6 60.6115 14.6761
7 -204.4567 2.0323 1.61310 44.36 0.5604
8 ∞ 0.1500
9 61.3154 10.4558 1.49700 81.61 0.5387
10 285.4995 (d10)
11 58.4521 4.8136 1.83481 42.72 0.5646
12 98.3694 0.1500
13 34.5553 9.0892 1.83481 42.72 0.5646
14 66.3268 1.3878 1.74077 27.76 0.6076
15 24.7956 (d15)
(Aperture) ∞ 4.4148
17 -76.2930 1.2974 1.61310 44.36 0.5604
18 33.7597 8.2786 1.88300 40.80 0.5654
19 275.9716 3.3189
20 -67.6392 1.7530 1.67270 32.17 0.5962
21 183.8387 0.1503
22 * 77.1835 7.4669 1.85135 40.10 0.5694
23 * -70.8782 (d23)
24 ∞ 1.4500 1.52301 58.59 0.5449
25 ∞ BF
Image plane ∞

[Aspherical data]
22 faces 23 faces
K 0.000000 0.000000
A4 -2.287818E-06 1.245935E-06
A6 6.603720E-10 -1.080248E-11
A8 0.000000E + 00 0.000000E + 00
A10 0.000000E + 00 0.000000E + 00
A12 0.000000E + 00 0.000000E + 00

[Various data]
INF
Focal length 104.76
F number 1.46
Full angle of view 2ω 22.99
Statue height Y 21.63
Total lens length 164.26

[Variable interval data]
INF shooting distance 1164mm
d0 ∞ 1000.0000
d10 24.3767 10.0722
d15 11.5242 15.5868
d23 36.5000 46.7419
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length G1 1 291.25
G2 11 112.70
G2A 11 223.55
G2B 18 142.98

The conditional expression corresponding values corresponding to each of the above embodiments are shown below.
[Conditional expression values]
Conditional expression / Example 1 2 3
(1) PgFLp1 / νdLp1 0.0066 0.0059 0.0079
(2) PgFLp2 / νdLp2 0.0306 0.0404 0.0276
(3) (fLp2 / νdLp2) / f 0.033 0.049 0.014
(4) ΔPgFLm1 -0.0053 -0.0053 -0.0005
ΔPgFLm2 -0.0005--
ΔPgFLm3---
(5) νdLp1 / νdLm1 1.84 2.04 2.13
νdLp1 / νdLm2 2.53--
νdLp1 / νdLm3---
(6) ΔPgFG1av / νdG 0.00036 0.00057 0.00026
(7) (1 / RSm2) / (φSm1 + φSm2) 0.73 0.79 0.73

Conditional expression / Example 4 5 6
(1) PgFLp1 / νdLp1 0.0072 0.0056 0.0066
(2) PgFLp2 / νdLp2 0.0306 0.0306 0.0404
(3) (fLp2 / νdLp2) / f 0.029 0.039 0.061
(4) ΔPgFLm1 -0.0053 -0.0005 -0.0081
ΔPgFLm2 -0.0005 -0.0034-
ΔPgFLm3 -0.0005--
(5) νdLp1 / νdLm1 1.71 2.95 1.84
νdLp1 / νdLm2 2.34 2.40-
νdLp1 / νdLm3 2.34--
(6) ΔPgFG1av / νdG 0.00035 0.00052 0.00062
(7) (1 / RSm2) / (φSm1 + φSm2) 0.62 0.77 0.82

G1 first lens group G2 second lens group G2A second A lens group G2B second B lens group Lp1 lens Lp2 having the largest Abbe number of d line in the first lens group G1, dp line in the first lens group G1 Lens Lmj having the smallest Abbe number and negative refractive power satisfying conditional expressions (4) to (5) in the first lens group G1 (j is an integer of 1 or more)
Sm1 Refractive surface with the concave surface facing the object side closest to the object side in the second B lens group G2B Sm2 Refractive surface with the concave surface facing the object side with the second B lens group G2B S Aperture stop LPF Low pass filter I Image surface

Claims (6)

In order from the object side, the first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power,
The first lens group G1 has a positive refractive power Lp1, a positive refractive power Lp2, and a negative refractive power lens.
When focusing from an object at infinity to a near object, the first lens group G1 is fixed with respect to the image plane, and the second lens group G2 is moved from the image plane side to the object side along the optical axis.
A large-aperture lens that satisfies the following conditional expression:
(1) PgFLp1 / νdLp1 <0.0085
(2) 0.0250 <PgFLp2 / νdLp2
(3) 0.010 <(fLp2 / νdLp2) / f1 <0.070
νdLp1: Abbe number of the positive refractive power lens having the largest d-line Abbe number in the first lens group G1 PgFLp1: g-line of the positive refractive power lens having the largest d-line Abbe number in the first lens group G1 And F-line partial dispersion ratio νdLp2: Abbe number of the positive lens having the smallest d-line Abbe number in the first lens group G1 PgFLp2: Positive d-line Abbe number in the first lens group G1 being the smallest Partial dispersion ratio of the g-line to the F-line of the lens with refractive power f1: Focal length fLp2 of the first lens group G1: Focal length of a lens with positive refractive power having the smallest Abbe number of d-line in the first lens group G1 2. The large-aperture lens according to claim 1, wherein the first lens group G1 has at least one lens Lmj (j is an integer of 1 or more) having negative refractive power that satisfies the following conditional expression.
(4) ΔPgFLmj <0.0000
(5) 1.40 <νdLp1 / νdLmj <3.20
ΔPgFLmj: Abnormal partial dispersion νdLmj of the g-line and F-line of the lens Lmj with negative refractive power included in the first lens group G1: Abbe number of the lens Lmj with negative refractive power included in the first lens group G1 3. The large-aperture lens according to claim 1, wherein the following conditional expression is satisfied with respect to all lenses having a positive refractive power included in the first lens group G <b> 1.
(6) 0.00010 <ΔPgFG1av / νdG1av <0.00070
ΔPgFG1av: Average value of anomalous partial dispersion of the g-line and F-line of the positive-power lens included in the first lens group G1 νdG1av: d-line of the positive-power lens included in the first lens group G1 Average value of Abbe number The second lens group G2 includes, in order from the object side, a second A lens group G2A, an aperture stop S, and a second B lens group G2B.
The most image side lens of the second A lens group G2A has a concave surface facing the image side,
The second B lens group G2B has, in order from the object side, a refracting surface Sm1 with a concave surface facing the object side closest to the object side, and a refracting surface Sm2 with a concave surface facing the object side.
The large-aperture lens according to claim 1, wherein the following conditional expression is satisfied.
(7) 0.50 <(1 / RSm2) / (φSm1 + φSm2) <0.90
RSm2: radius of curvature of the refractive surface Sm2 φSm1: refractive power of the refractive surface Sm1 φSm2: refractive power of the refractive surface Sm2   5. The large-aperture lens according to claim 1, further comprising a lens having a positive refractive power with a convex surface facing the object side closest to the object side of the first lens group G <b> 1.   The large aperture lens according to any one of claims 1 to 5, wherein the second lens group G2 includes at least one aspheric lens.

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