JP2019144477A - Large-aperture lens - Google Patents

Abstract

To provide a large-aperture lens which is well corrected for chromatic aberration and offers superior optical performance that reduces coloring that appears on edges of blurred images.SOLUTION: A large-aperture lens consists of a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power in order from the object side. The first lens group consists of a 1b lens group G1b comprised of one or more positive lenses and one lens component having negative refractive power, the 1b lens group having positive refractive power as a whole, a 1b lens group G1b comprised of a cemented lens component having negative refractive power, and a 1c lens group G1c having positive refractive power. The second lens group consists of a 2a lens group G2a comprised of one or more positive lenses and a cemented lens component having negative refractive power, an aperture stop S, and a 2b lens group G2b. When shifting focus from infinity to an object at a short distance, the first lens group is stationary with respect to an image plane while the second lens group moves from the image side to the object side along an optical axis. The large-aperture lens satisfies predetermined conditional expressions.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a large-aperture lens that strongly corrects various aberrations such as spherical aberration and axial chromatic aberration among photographic lenses particularly suitable for photographic devices 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 general, as the F value of the optical system is decreased and the brightness is increased, more aberrations occur and the optical performance is degraded. In particular, when an optical system that is brighter in the focal region on the telephoto side than the standard region is obtained, a decrease in optical performance due to axial chromatic aberration becomes significant.

  For correction of axial chromatic aberration, it is common to use a low refractive index, low dispersion optical material having a large positive anomalous dispersion such as fluorite for a lens having a positive refractive power. It is difficult to sufficiently suppress chromatic aberration in a small bright optical system.

  In order to realize a bright optical system with a small F-number, it is necessary to increase the refractive power of each surface and bend the light more strongly to form an image. At that time, positive anomalous dispersion such as fluorite is present. In an optical material having a large low refractive index and low dispersion, it is necessary to further change the curvature to obtain a required refractive power. Then, various aberrations such as spherical aberration, coma aberration, and astigmatism are deteriorated due to the effect of increasing the refractive power of the lens surface, and it is difficult to correct them.

Japanese Patent No. 3254239 JP2016-212346 Patent No. 5395700

  The large-aperture lens described in Patent Document 1 performs floating focusing to suppress performance fluctuations during focusing to a short-distance object having a shortest shooting 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. 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, are strongly corrected to obtain good image quality over the entire screen, and coloration generated at the peripheral portion of the blurred image is reduced. An object of the present invention is to provide a large-aperture optical system that has high optical performance, achieves downsizing of a product without omitting an autofocus mechanism, and has a size suitable for an interchangeable lens.

A first invention for solving the above-described problem 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 includes a first lens group G1a having one or more convex lenses and one concave lens or one cemented concave lens component from the object side and having positive refractive power as a whole, and a cemented lens component having negative refractive power. The second lens group G2 includes a first-b lens group G1b and a first-c lens group G1c having a positive refractive power. The second lens group G2a is composed of a lens group G2a, an aperture stop S, and a second b lens group G2b. The first lens group G1 is fixed with respect to the image plane during focusing from infinity to a close object, and the second lens A large-aperture lens that moves the group G2 along the optical axis from the image plane side to the object side and satisfies the following conditional expression:
(1) -3.8 <ΦG1b / ΦG1 <−0.5
(2) 0.18 <ΦG1 / Φ <0.50
(3) 3.0 <ΦG2 / ΦG1 <7.5
(4) 0.8 <νdL1bp1 × ΔPgFL1bp1
ΦG1: refracting power of the first lens group G1 ΦG1b: refracting power of the first b lens group G1b ΦG2: refracting power of the second lens group G2 Φ: refracting power of the entire system at infinity focusing νdL1bp1: first b lens group G1b Abbe number ΔPgFL1bp1 of the lens having the highest refractive index among the convex lenses constituting the first lens group G1b. Anomalous dispersion of the lens having the highest refractive index among the convex lenses constituting the 1b lens group G1b

The second invention satisfies the following conditional expression, and is a large-aperture lens described in the first invention.
(5) 0.015 <ΔPgFG1Pave
(6) ΔPgFG1Nave <−0.0020
ΔPgFG1Nave: average value of anomalous dispersion of the concave lens of the first lens group G1 ΔPgFG1Pave: average value of the anomalous dispersion of the convex lens of the first lens group G1

A third aspect of the invention is the large-aperture lens according to the first aspect or the second aspect of the invention, wherein the following conditional expression is satisfied.
(7) 0.010 <ΔPgFG2aPave
ΔPgFG2aPave: average value of anomalous dispersion of the convex lens of the 2a lens group G2a

A fourth aspect of the invention is the large-aperture lens according to any one of the first to third aspects, wherein the following conditional expression is satisfied.
(8) 1.85 <NdL2ap1
NdL2ap1: Refractive index of the convex lens located closest to the object side among the lenses constituting the second lens group G2.

A fifth aspect of the invention is a large-aperture lens according to any one of the first to fourth aspects, wherein the following conditional expression is satisfied.
(9) 0.020 <ΔPgFL2ap1
ΔPgFL2ap1: Anomalous dispersion of a convex lens located closest to the object side among the lenses constituting the second lens group G2.

  A sixth invention is the large-aperture lens according to any one of the first to fifth inventions, wherein the second lens group G2 has at least one aspheric lens.

  By satisfying the above-mentioned conditions, the present invention strongly corrects various aberrations, particularly chromatic aberration, and obtains good image quality over the entire screen, and also has high optical performance with reduced coloring that occurs at the periphery of the blurred image. It is possible to reduce the size of the product without omitting the autofocus mechanism and to provide an optical system having a large aperture suitable for an interchangeable lens.

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 999 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 999 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. FIG. 6 is a longitudinal aberration diagram at an imaging distance of 995 mm according to 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 995 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 994 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. 10 is a lateral aberration diagram at an imaging distance of 994 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 997mm 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. It is a lateral aberration figure in photographing distance 997mm concerning 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. FIG. 10 is a longitudinal aberration diagram at an imaging distance of 995 mm according to 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 995 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 1001mm 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. It is a lateral aberration figure in photographing distance 1001mm concerning Example 6 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 7 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 7 of this invention. It is a longitudinal aberration figure in photographing distance 999mm concerning Example 7 of the present invention. It is a lateral aberration diagram at the time of focusing on infinity according to Example 7 of the present invention. It is a lateral aberration figure in photographing distance 999mm concerning Example 7 of the present invention. It is a lens block diagram at the time of infinity focusing which concerns on Example 8 of this invention. It is a longitudinal aberration figure at the time of infinity focusing based on Example 8 of this invention. It is a longitudinal aberration figure in photographing distance 1000mm concerning Example 8 of the present invention. It is a transverse aberration figure at the time of infinity focusing concerning Example 8 of the present invention. FIG. 10 is a lateral aberration diagram at an imaging distance of 1000 mm according to Example 8 of the present invention.

The large-diameter lens according to the embodiment of the present invention will be described below. Note that the refractive indices of the materials for g-line (wavelength 435.84 nm), F-line (486.13 nm), d-line (587.56 nm), and C-line (656.27 nm) are Ng, NF, Nd, and NC, respectively. . Then, Abbe number νd, partial dispersion ratio PgF, and abnormal partial dispersion ΔPgF,
νd = (Nd-1) / (NF-NC)
PgF = (Ng-NF) / (NF-NC)
ΔPgF = PgF−0.648833 + 0.00180 × νd
Represent as

The optical system of each 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. The first lens group G1 is 1 from the object side. A first a lens group G1a having a positive refractive power as a whole, and a first b lens group G1b consisting of a cemented lens component having a negative refractive power, which is composed of one or more convex lenses and one concave lens or one cemented concave lens component; The first lens group G1c having a positive refractive power, and the second lens group G2 includes a second a lens group G2a including one or more convex lenses and a cemented concave lens component having a negative refractive power, and an aperture stop. S and the second lens group G2b, and when focusing from infinity to a close object, the first lens group G1 is fixed with respect to the image plane, and the second lens group G2 is imaged along the optical axis. It moves from the surface side to the object side, and satisfies the following conditional expression.
(1) -3.8 <ΦG1b / ΦG1 <−0.5
(2) 0.18 <ΦG1 / Φ <0.50
(3) 3.0 <ΦG2 / ΦG1 <7.5
(4) 0.8 <νdL1bp1 × ΔPgFL1bp1
ΦG1: refracting power of the first lens group G1 ΦG1b: refracting power of the first b lens group G1b ΦG2: refracting power of the second lens group G2 Φ: refracting power of the entire system at infinity focusing νdL1bp1: first b lens group G1b Abbe number ΔPgFL1bp1 of the lens having the highest refractive index among the convex lenses constituting the first lens group G1b. Anomalous dispersion of the lens having the highest refractive index among the convex lenses constituting the 1b lens group G1b

  In the lens configuration, when focusing to a short distance, the first lens group G1 having a relatively large lens diameter and weight is fixed with respect to the image plane, and the second lens group G2 having a relatively small lens diameter and weight is irradiated with light. Since it moves along the axis, it is possible to easily increase the focusing speed and simplify the mechanism.

  In order to correct chromatic aberration in a telephoto lens, it is common to use an optical material such as fluorite with a low refractive index and low dispersion and a large positive anomalous dispersion for the convex lens. In an optical system frequently used for a convex lens, the Petzval sum is deteriorated, the field curvature is increased, and the optical performance is lowered. Therefore, in the present invention, correction of chromatic aberration and Petzval sum is achieved by disposing a subgroup having negative refractive power and disposing an optical material having a low refractive index and low dispersion and a large positive anomalous dispersion on the convex lens in the subgroup. The correction of both. Conditional expression (1) defines the refractive power of the subgroup. By satisfying conditional expression (1), the Petzval sum can be corrected even if a low refractive index and low dispersion optical material is used for the convex lens in the subgroup, and both the correction of chromatic aberration and the correction of Petzval sum are compatible. Contributes to improved performance.

  When the negative refractive power of the 1b lens group G1b increases beyond the lower limit value of the conditional expression (1), it becomes necessary to increase the positive refractive power of the 1c lens group in order to correct it, and spherical aberration occurs. Various aberrations such as astigmatism deteriorate.

  If the negative refractive power of the 1b lens group G1b becomes weaker than the upper limit value of the conditional expression (1), the Petzval sum of the entire system is deteriorated. To correct this, the 1b lens group is configured. It is necessary to select the lower refractive index side for the optical material of the concave lens and the higher refractive index side for the optical material of the convex lens. Especially, the convex lens uses a low refractive index and low dispersion optical material having a large positive anomalous dispersion. Since it becomes impossible, it leads to deterioration of chromatic aberration.

  For conditional expression (1), in order to make the above effect more reliable, by defining the upper limit value to -0.6 and the lower limit value to -3.1, the above-described effect can be more reliably achieved. can do.

  Conditional expression (2) defines the ratio between the refractive power of the entire system at the time of focusing on infinity and the refractive power of the first lens group G1 in order to achieve both miniaturization and high performance. Satisfying conditional expression (2) contributes to both miniaturization and high performance of the optical system.

  If the positive refractive power of the first lens group G1 becomes weaker than the refractive power of the entire system at the time of focusing on infinity exceeding the lower limit value of the conditional expression (2), the total length of the optical system increases, and accordingly the first Since the optical system of the lens group G1 is enlarged, it is difficult to reduce the size and weight.

  When the positive refractive power of the first lens group G1 becomes stronger than the refractive power of the entire system at the time of focusing on infinity exceeding the upper limit value of the conditional expression (2), the F value of the first lens group itself becomes smaller. Therefore, it becomes difficult to correct the aberration of the first lens group. Furthermore, in order to maintain the refractive power of the entire system, the imaging magnification of the second lens group must be increased, and the residual aberration of the first lens group is further increased. This makes it difficult to correct various aberrations such as spherical aberration, astigmatism, and coma aberration in the entire system.

  For conditional expression (2), in order to make the above effect more certain, the above-mentioned effect can be made more reliable by specifying an upper limit value of 0.35 and a lower limit value of 0.20. Can do.

  Conditional expression (3) defines the ratio of the refractive powers of the first lens group G1 and the second lens group G2 in order to achieve both miniaturization and high performance. Satisfying conditional expression (3) contributes to both miniaturization and high performance of the optical system.

  When the lower limit of conditional expression (3) is exceeded and the positive refractive power of the second lens group G2 becomes weak, it becomes difficult to ensure the back focus, and especially when applying this optical system for a single-lens reflex camera, Interference with the return mirror cannot be prevented.

  When the upper limit of conditional expression (3) is exceeded and the positive refractive power of the first lens group G1 becomes weak, the entire length of the optical system increases, and the optical system of the first lens group G1 enlarges accordingly. And weight reduction becomes difficult.

  For conditional expression (3), in order to make the above effect more certain, the above-mentioned effect can be made more reliable by defining the upper limit value at 6.8 and the lower limit value at 3.3. Can do.

  Conditional expression (4) defines the relationship between the Abbe number of the lens having the highest refractive index and the anomalous dispersion among the convex lenses constituting the 1b lens group in order to effectively correct chromatic aberration. A larger value indicates an optical material having a low dispersion and a large positive anomalous dispersion, so that it is effective for correcting chromatic aberration, particularly the secondary spectrum, when used for a convex lens of a cemented lens. Satisfying the conditional expression (4) contributes to high performance of the optical system.

  If the Abbe number of the lens having the highest refractive index out of the convex lenses constituting the 1b lens group exceeds the lower limit of conditional expression (4) and the anomalous dispersion becomes small, the correction effect of chromatic aberration becomes poor. When an optical material having negative anomalous dispersion is used, correction of the secondary spectrum becomes difficult and optical performance is deteriorated.

  If the value of conditional expression (4) is 1.2 or more, the effect is more certain.

Further, the large-diameter lens of the present invention satisfies the following conditional expression.
(5) 0.015 <ΔPgFG1Pave
(6) ΔPgFG1Nave <−0.0020
ΔPgFG1Pave: average value of anomalous dispersion of the convex lens of the first lens group G1 ΔPgFG1Nave: average value of the anomalous dispersion of the concave lens of the first lens group G1

  In a bright optical system having a small F-number from the standard range to the telephoto side, a decrease in optical performance due to axial chromatic aberration is particularly problematic. Further, correction of primary chromatic aberration alone is not sufficient, and correction of the secondary spectrum is not sufficient. This may cause the edges of a blurred image to be colored, or purple fringes to be generated at the edges of a high-luminance object. In correcting the secondary spectrum, it is important to sufficiently correct the primary chromatic aberration and appropriately select and arrange an optical material in consideration of each anomalous dispersion.

  Conditional expression (5) defines the average value of the anomalous dispersion of the convex lenses constituting the first lens group G1. The convex lens can effectively correct the secondary spectrum by using an optical material having a large positive anomalous dispersion. Satisfying conditional expression (5) contributes to the enhancement of optical performance.

  If the average value of the anomalous dispersion of the convex lens of the first lens group G1 becomes smaller than the lower limit value of the conditional expression (5), the correction of the secondary spectrum becomes difficult and the optical performance deteriorates.

  In addition, if the value of conditional expression (5) is 0.02 or more, the effect becomes more certain.

  As shown in the conditional expression (5), when an optical material having a large positive anomalous dispersion is used for the convex lens, the correction of the secondary spectrum is possible. In the optical system alone, correction of the secondary spectrum is insufficient. If correction of the secondary spectrum that relies on a convex lens using a positive anomalous dispersion optical material, the number of convex lenses must be increased, the optical system becomes larger, and the Petzval sum of the entire system is increased. As a result, it becomes difficult to correct curvature of field and optical performance deteriorates.

  Therefore, effective correction of the secondary spectrum while minimizing the deterioration of the Petzval sum of the entire system by using an optical material having a large negative anomalous dispersion for the concave lens constituting the first lens group G1. Is possible.

  Conditional expression (6) defines the average value of the anomalous dispersion of the concave lens of the first lens group G1. The concave lens can effectively correct the secondary spectrum by using an optical material having a large negative anomalous dispersion. Satisfying conditional expression (6) contributes to the enhancement of optical performance.

  If the average value of the anomalous dispersion of the concave lens of the first lens group G1 exceeds the upper limit value of the conditional expression (6), the correction of the secondary spectrum becomes difficult and the optical performance deteriorates.

  If the value of conditional expression (6) is −0.0030 or less, the effect is more certain.

Further, the large-diameter lens of the present invention satisfies the following conditional expression.
(7) 0.010 <ΔPgFG2aPave
ΔPgFG2aPave: average value of anomalous dispersion of the convex lens of the 2a lens group G2a

  As described above, the axial chromatic aberration, particularly the secondary spectrum can be corrected by selecting an optical material in consideration of anomalous dispersion for each lens of the first lens group G1. However, correction of the secondary spectrum is not sufficient in a telephoto optical system having a particularly small F value and bright as shown in the present invention. It is necessary to select an optical material in consideration of anomalous dispersion for each lens of the second a lens group G2a that is movable when focusing from infinity to a short distance. This is defined by conditional expression (7).

  Conditional expression (7) defines the average value of the anomalous dispersion of the convex lenses of the 2a lens group G2a. By using an optical material having a large positive anomalous dispersion for the convex lens of the second-a lens group G2a, the secondary spectrum can be effectively corrected. Satisfying conditional expression (7) contributes to correction of longitudinal chromatic aberration.

  If the lower limit of conditional expression (7) is exceeded and the anomalous dispersion of the convex lens of the second-a lens group G2a becomes small, it is difficult to sufficiently correct the secondary spectrum.

  In addition, if the value of conditional expression (7) is 0.014 or more, the effect becomes more certain.

Further, the large-diameter lens of the present invention satisfies the following conditional expression.
(8) 1.85 <NdL2ap1
NdL2ap1: Refractive index of the convex lens located closest to the object side among the lenses constituting the second lens group G2.

  Conditional expression (8) defines the refractive index of the convex lens located closest to the object side among the lenses constituting the second lens group G2. The second lens group G2 is a focus group that moves from an infinite distance to an object at a short distance, and it is essential to reduce the size of the focus group in order to realize autofocus and automatic iris with a practical lens barrel size. is there. In particular, since the diameter of the lens on the image side of the stop is limited by the camera mount, further miniaturization is required. By using a high refractive index material for the convex lens located closest to the object among the lenses constituting the second lens group G2, it is possible to achieve both correction of astigmatism and field curvature and downsizing of the focus group. Satisfying conditional expression (8) contributes to miniaturization of the product while favorably correcting aberrations.

  If the lower limit of conditional expression (8) is exceeded and the refractive index of the convex lens located closest to the object side among the lenses constituting the second lens group G2 becomes low, the Petzval sum deteriorates, and astigmatism, field curvature Correction becomes difficult.

  If the value of conditional expression (8) is 1.90 or more, the effect is more certain.

Further, the large-diameter lens of the present invention satisfies the following conditional expression.
(9) 0.020 <ΔPgFL2ap1
ΔPgFL2ap1: Anomalous dispersion of a convex lens located closest to the object side among the lenses constituting the second lens group G2.

  Conditional expression (9) defines the anomalous dispersion of the convex lens located closest to the object among the lenses constituting the second lens group G2. For the convex lens located closest to the object side among the lenses constituting the second lens group G2 in the conditional expression (8), an optical material having a high refractive index is effective for facilitating correction of astigmatism and field curvature. On the other hand, among the lenses constituting the second lens group G2, the convex lens located closest to the object side has a relatively small positive anomalous dispersion even with an optical material having a refractive index of about 1.90 or more. When such an optical material is used, correction of the secondary spectrum is insufficient. An optical material having a large positive anomalous dispersion is suitable for sufficiently correcting the secondary spectrum. Conditional expression (9) defines this. Satisfying conditional expression (9) contributes to correction of longitudinal chromatic aberration.

  If the lower limit of conditional expression (9) is exceeded and the anomalous dispersion of the convex lens located closest to the object among the lenses constituting the second lens group G2 becomes small, sufficient correction of the secondary spectrum becomes difficult.

  If the value of conditional expression (9) is 0.025 or more, the effect is more certain.

  In order to improve the optical performance of the large-diameter lens of the present invention, it is desirable to employ at least one aspheric lens in the second lens group G2.

  This aspheric lens is preferably arranged for the purpose of correcting spherical aberration. By employing an aspheric lens, it is possible to reduce the burden of aberration correction when correcting spherical aberration generated with positive refractive power with negative refractive power.

  As a result, the negative refractive power for correcting the spherical aberration generated by the positive refractive power can be weakened, and the curvature of the concave surface closest to the object side of the second b lens group G2b can be relaxed. The occurrence of sagittal coma flare can be suppressed.

  This aspherical lens is preferably arranged on the image side from the stop. Since the axial ray height is higher on the object side than the stop, a large-aperture aspheric lens is necessary, which increases processing costs and is not preferable. If this aspherical lens is arranged on the image side from the stop, the diameter of the lens can be reduced, which is advantageous in terms of workability.

  In addition, this aspherical surface corrects spherical aberration that occurs with positive refractive power, so that the aspherical surface weakens the positive refractive power as it moves away from the optical axis, or increases the negative refractive power as it moves away from the optical axis. A spherical surface is preferable.

Next, a lens configuration of an example according to the imaging optical system of the present invention is described.
In the following description, the lens configuration is described in order from the object side to the image 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, and eighth-order aspheric coefficients are represented by A4, A6, and A8, 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 stated focal length f, radius of curvature r, lens surface interval d, and other length units are in millimeters (mm) unless otherwise specified. In the system, the same optical performance can be obtained 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-aperture lens in FIG. 1 has a first lens group G1 having a positive refractive power fixed to the image plane during focusing from an object at infinity to a short-distance object. The second lens group G2 having a positive refractive power that moves toward the center.

  The first lens group G1 includes a first-a lens group G1a having a positive refractive power from the object side, a first-b lens group G1b having a negative refractive power, and a first-c lens group G1c having a positive refractive power.

  The first-a lens group G1a includes three positive meniscus lenses having a convex surface facing the object side and a concave lens having a convex surface facing the object side.

  The first lens group G1b is composed of a cemented lens having a concave surface facing the object side and having a negative refractive power.

  The first c lens group G1c is composed of a cemented lens having a convex surface facing the object side and having a positive refractive power.

  The second lens group G2 includes a second a lens group G2a having a positive refractive power from the object side, an aperture stop S, and a second b lens group G2b having a positive refractive power.

  The second-a lens group G2a includes two positive meniscus lenses having a convex surface facing the object surface and a cemented lens having negative refractive power having the convex surface facing the object side.

  The second lens group G2b is composed of two cemented lenses having negative refractive power with a concave surface facing the object side from the object side, and a biconvex lens in which both lens surfaces are aspherical.

Subsequently, specification values of the large-aperture lens according to Example 1 are shown below.
Numerical example 1
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 115.7436 5.4407 1.65844 50.85 0.5575
2 180.1804 0.3000
3 74.5000 6.0183 1.43700 95.10 0.5334
4 100.3863 0.3000
5 63.4310 12.3856 1.43700 95.10 0.5334
6 249.4535 2.9002
7 216.1665 2.2000 1.61310 44.36 0.5604
8 49.5173 15.8891
9 -248.4001 4.6130 1.43700 95.10 0.5334
10 -95.8446 1.8000 1.61340 44.27 0.5633
11 -500.0000 1.0000
12 67.9843 10.4346 1.83481 42.72 0.5648
13 -211.9683 1.8000 1.61340 44.27 0.5633
14 67.2983 (d14)
15 53.7906 4.5962 1.92286 20.88 0.6388
16 94.6373 0.3000
17 46.5373 4.1734 1.61997 63.88 0.5425
18 66.7867 0.3000
19 40.7185 6.9541 1.59282 68.63 0.5441
20 275.0000 1.3000 1.85478 24.80 0.6122
21 28.4253 7.5444
(Aperture) ∞ 5.4041
23 -50.8188 0.9000 1.65412 39.68 0.5737
24 29.5160 7.5115 1.87071 40.73 0.5682
25 -196.5287 2.2670
26 -76.2095 3.5767 1.91082 35.25 0.5821
27 -35.1809 0.9000 1.64769 33.84 0.5923
28 124.7179 0.3000
29 * 68.8532 4.9326 1.84915 40.00 0.5694
30 * -92.2688 (d30)
31 ∞ 1.4500 1.52301 58.59 0.5449
32 ∞ BF


[Aspherical data]
29 faces 30 faces
K 0 0
A4 -1.27386E-06 1.98113E-06
A6 -1.15209E-10 1.20129E-10
A8 0 1.65076E-12

[Various data]
INF
Focal length 101.85
F number 1.46
Full angle of view 2ω 23.85
Statue height Y 21.63
Total lens length 171.92

[Variable interval data]
Shooting distance INF 999
d0 ∞ 826.8724
d14 15.8705 3.0000
d30 37.5626 50.4932
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length
G1 1 334.47
G2 15 90.25
G1a 1 1015.80
G1b 9 -421.69
G1c 12 203.76
G2a 15 355.09
G2b 23 83.54

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

  6 has 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 from the image plane side to the object side during focusing. The second lens group G2 having a positive refractive power that moves toward the center.

  The first lens group G1 includes a first-a lens group G1a having a positive refractive power from the object side, a first-b lens group G1b having a negative refractive power, and a first-c lens group G1c having a positive refractive power.

  The first-a lens group G1a is composed of two positive meniscus lenses having a convex surface facing the object side from the object side and a cemented lens having negative refractive power having the convex surface facing the object side.

  The first lens group G1b is composed of a cemented lens having a concave surface facing the object side and having a negative refractive power.

  The first c lens group G1c is composed of a cemented lens having a convex surface facing the object side and having a positive refractive power.

  The second lens group G2 includes a second a lens group G2a having a positive refractive power from the object side, an aperture stop S, and a second b lens group G2b having a positive refractive power.

  The second-a lens group G2a includes two positive meniscus lenses having a convex surface facing the object surface and a cemented lens having negative refractive power having the convex surface facing the object side.

  The second lens group G2b is composed of two cemented lenses having negative refractive power with a concave surface facing the object side from the object side, and a biconvex lens in which both lens surfaces are aspherical.

Subsequently, various values of the large diameter lens according to Example 2 are shown below.
Numerical example 2
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 148.8937 6.3628 1.65844 50.85 0.5575
2 400.8029 0.3000
3 88.8052 7.7121 1.43700 95.10 0.5334
4 186.3141 0.3000
5 63.4922 10.2180 1.43700 95.10 0.5334
6 179.5482 3.1552 1.61340 44.27 0.5633
7 53.6846 13.1608
8 -2496.1579 4.3228 1.43700 95.10 0.5334
9 -155.5309 1.8000 1.61340 44.27 0.5633
10 96.9720 1.0000
11 67.3521 9.7521 1.83481 42.72 0.5648
12 -262.9426 1.8000 1.61340 44.27 0.5633
13 87.8711 (d13)
14 55.9775 4.3603 1.92286 20.88 0.6388
15 94.4046 0.3000
16 51.4948 4.2937 1.55032 75.50 0.5400
17 81.4925 0.3000
18 40.6596 7.9142 1.59282 68.63 0.5441
19 -3711.1109 1.3000 1.74077 27.76 0.6076
20 27.5023 7.7790
(Aperture) ∞ 4.3136
22 -57.0428 0.9000 1.65412 39.68 0.5737
23 27.2148 7.7486 1.87071 40.73 0.5682
24 -358.4172 2.5557
25 -76.1439 2.9982 1.91082 35.25 0.5821
26 -41.1144 0.9000 1.64769 33.84 0.5923
27 114.8214 0.3000
28 * 64.8502 5.9302 1.84915 40.00 0.5694
29 * -84.3052 (d29)
30 ∞ 1.4500 1.52301 58.59 0.5449
31 ∞ BF

[Aspherical data]
28 faces 29 faces
K 0 0
A4 -1.83614E-0 1.84629E-06
A6 -1.50424E-1 4.19931E-11
A8 0 1.92462E-12

[Various data]
INF
Focal length 102.38
F number 1.46
Full angle of view 2ω 23.63
Statue height Y 21.63
Total lens length 167.66

[Variable interval data]
Shooting distance INF 995
d0 ∞ 826.8724
d13 15.8705 3.0000
d29 37.5626 50.5468
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length
G1 1 402.35
G2 14 86.34
G1a 1 307.15
G1b 8 -130.75
G1c 11 147.86
G2a 14 271.98
G2b 22 84.30

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

  11 has a first lens group G1 having a positive refracting power that is fixed with respect to the image plane during focusing from an object at infinity to a short-distance object, and from the image plane side to the object side during focusing. The second lens group G2 having a positive refractive power that moves toward the center.

  The first lens group G1 includes a first-a lens group G1a having a positive refractive power from the object side, a first-b lens group G1b having a negative refractive power, and a first-c lens group G1c having a positive refractive power.

  The first-a lens group G1a includes three positive meniscus lenses having a convex surface facing the object side from the object side and a negative meniscus lens having a convex surface facing the object side.

  The first lens group G1b is composed of a cemented lens having a convex surface facing the object side and having a negative refractive power.

  The first c lens group G1c is composed of a cemented lens having a convex surface facing the object side and having a positive refractive power.

  The second lens group G2 includes a second a lens group G2a having a positive refractive power from the object side, an aperture stop S, and a second b lens group G2b having a positive refractive power.

  The second-a lens group G2a includes two positive meniscus lenses having a convex surface facing the object surface and a cemented lens having negative refractive power having the convex surface facing the object side.

The second lens group G2b is composed of two cemented lenses having negative refractive power with a concave surface facing the object side from the object side, and a biconvex lens in which both lens surfaces are aspherical.

Subsequently, specification values of the large-aperture lens according to Example 3 are shown below.
Numerical example 3
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 140.0817 6.2300 1.65844 50.85 0.5574
2 323.3865 0.3000
3 96.3564 7.1418 1.43700 95.10 0.5335
4 195.4487 0.3000
5 70.7786 9.1061 1.43700 95.10 0.5335
6 177.0092 4.7886
7 292.1758 2.2000 1.61340 44.27 0.5633
8 59.1273 9.0589
9 162.9902 5.9737 1.43700 95.10 0.5335
10 -301.6999 1.8000 1.72047 34.71 0.5834
11 98.6498 1.0000
12 65.5095 9.9061 1.91082 35.25 0.5821
13 -308.8045 1.8000 1.65412 39.68 0.5737
14 73.0064 (d14)
15 54.7872 4.3652 1.92286 20.88 0.6388
16 90.6572 0.3000
17 51.3497 4.2449 1.55032 75.50 0.5400
18 80.0374 0.3000
19 42.4911 8.0775 1.59282 68.63 0.5441
20 -424.2628 1.3000 1.72825 28.32 0.6058
21 27.7117 7.7161
(Aperture) ∞ 4.7515
23 -54.7992 0.9000 1.65412 39.68 0.5736
24 27.4844 7.9729 1.87071 40.73 0.5681
25 -237.1687 2.2922
26 -80.2746 3.1419 1.91082 35.25 0.5821
27 -40.3204 0.9000 1.64769 33.84 0.5923
28 136.8587 0.3000
29 * 71.5761 4.9376 1.84915 40.00 0.5695
30 * -93.0490 (d30)
31 ∞ 1.4500 1.52301 58.59 0.5449
32 ∞ BF

[Aspherical data]
29 faces 30 faces
K 0 0
A4 -1.49036E-06 1.82324E-06
A6 4.11465E-10 8.11154E-10
A8 0 2.20680E-12

[Various data]
INF
Focal length 103.31
F number 1.46
Full angle of view 2ω 23.43
Statue height Y 21.63
Total lens length 167.37

[Variable interval data]
Shooting distance INF 994
d0 ∞ 826.8724
d14 16.2501 3.0000
d30 37.5630 50.8731
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length
G1 1 379.36
G2 15 87.79
G1a 1 511.83
G1b 9 -183.27
G1c 12 153.75
G2a 15 308.63
G2b 23 83.62

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

  16 has 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 from the image plane side to the object side during focusing. The second lens group G2 having a positive refractive power that moves toward the center.

  The first lens group G1 includes a first-a lens group G1a having a positive refractive power from the object side, a first-b lens group G1b having a negative refractive power, and a first-c lens group G1c having a positive refractive power.

  The first-a lens group G1a includes two positive meniscus lenses having a convex surface facing the object side from the object side and a negative meniscus lens having a convex surface facing the object side.

  The first lens group G1b is composed of a cemented lens having a concave surface facing the object side and having a negative refractive power.

  The first c lens group G1c is composed of a cemented lens having a convex surface facing the object side and having a positive refractive power.

  The second lens group G2 includes a second a lens group G2a having a positive refractive power from the object side, an aperture stop S, and a second b lens group G2b having a positive refractive power.

  The second-a lens group G2a includes two positive meniscus lenses having a convex surface facing the object surface and a cemented lens having negative refractive power having the convex surface facing the object side.

  The second lens group G2b is composed of two cemented lenses having negative refractive power with a concave surface facing the object side from the object side, and a biconvex lens in which both lens surfaces are aspherical.

Subsequently, specification values of the large-aperture lens according to Example 4 are shown below.
Numerical example 4
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 85.6120 12.3160 1.59282 68.63 0.5441
2 458.7719 0.3000
3 64.4906 7.5979 1.43700 95.10 0.5335
4 102.3846 6.2369
5 167.7157 2.2000 1.61340 44.27 0.5633
6 53.1815 15.5839
7 -182.2473 4.5069 1.43700 95.10 0.5335
8 -85.4275 1.8000 1.61340 44.27 0.5633
9 -9376.1589 1.0000
10 73.7526 10.2373 1.81600 46.62 0.5567
11 -154.9000 1.8000 1.61340 44.27 0.5633
12 76.2067 (d12)
13 75.5345 3.7216 1.92286 20.88 0.6388
14 130.7918 0.3000
15 49.6854 4.5433 1.72916 54.67 0.5452
16 80.6570 0.3000
17 37.9275 8.1019 1.59282 68.63 0.5441
18 579.3915 1.3000 1.69895 30.05 0.6028
19 27.4914 7.8083
20 ∞ 6.0049
21 -41.7222 3.2790 1.59282 68.63 0.5441
22 -30.2996 0.9000 1.65412 39.68 0.5736
(Aperture) -161.8290 1.4463
24 -134.8107 4.7768 1.95375 32.32 0.5900
25 -31.5815 0.9000 1.68893 31.16 0.5989
26 92.3257 0.3000
27 * 58.7797 7.0365 1.84915 40.00 0.5695
28 * -76.4136 (d28)
29 ∞ 1.4500 1.52301 58.59 0.5449
30 ∞ BF

[Aspherical data]
27 faces 28 faces
K 0 0
A4 -1.34538E-06 7.95788E-07
A6 7.16339E-10 6.26328E-10
A8 0 -1.26638E-13

[Various data]
INF
Focal length 101.85
F number 1.45
Full angle of view 2ω 23.87
Statue height Y 21.63
Total lens length 170.09

[Variable interval data]
Shooting distance INF 997
d0 ∞ 826.8724
d12 15.7659 3.0000
d28 37.5800 50.2088
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length
G1 1 435.00
G2 16 84.82
G1a 1 501.13
G1b 9 -226.65
G1c 13 206.03
G2a 16 160.12
G2b 24 99.95

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

  21 has 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 from the image plane side to the object side during focusing. The second lens group G2 having a positive refractive power that moves toward the center.

  The first lens group G1 includes a first-a lens group G1a having a positive refractive power from the object side, a first-b lens group G1b having a negative refractive power, and a first-c lens group G1c having a positive refractive power.

  The first-a lens group G1a includes three positive meniscus lenses having a convex surface facing the object side from the object side and a negative meniscus lens having a convex surface facing the object side.

  The first lens group G1b is composed of a cemented lens having a convex surface facing the object side and having a negative refractive power.

  The first c lens group G1c is composed of a cemented lens having a convex surface facing the object side and having a positive refractive power.

  The second lens group G2 includes a second a lens group G2a having a positive refractive power from the object side, an aperture stop S, and a second b lens group G2b having a positive refractive power.

  The second-a lens group G2a includes two positive meniscus lenses having a convex surface facing the object surface and a cemented lens having negative refractive power having the convex surface facing the object side.

  The second lens group G2b is composed of two cemented lenses having negative refractive power with a concave surface facing the object side from the object side, and a biconvex lens in which both lens surfaces are aspherical.

Subsequently, specification values of the large aperture lens according to Example 5 are shown below.
Numerical example 5
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 128.0780 7.5613 1.65844 50.85 0.5574
2 403.3458 0.3000
3 88.1573 5.9855 1.43700 95.10 0.5335
4 134.9147 0.3000
5 67.9896 7.6133 1.43700 95.10 0.5335
6 119.9000 5.8068
7 209.5511 2.2000 1.61340 44.27 0.5633
8 58.6284 10.9201
9 415.7584 5.2502 1.59282 68.63 0.5441
10 -183.1569 1.8000 1.61340 44.27 0.5633
11 92.9849 1.0000
12 60.5606 9.1444 1.83481 42.72 0.5648
13 4282.4046 1.8000 1.63775 42.41 0.5605
14 73.3355 (d14)
15 68.7996 3.8932 1.92286 20.88 0.6388
16 118.4362 0.3000
17 51.0869 4.6608 1.55032 75.50 0.5400
18 89.6048 0.3000
19 45.0701 8.0241 1.59282 68.63 0.5441
20 739.4855 3.9890 1.85478 24.80 0.6122
21 31.9388 6.7882
(Aperture) ∞ 4.1526
23 -61.9917 0.9000 1.60342 38.01 0.5827
24 30.9854 6.5784 1.95375 32.32 0.5900
25 1717.1833 2.8655
26 -82.2138 3.3632 1.91082 35.25 0.5821
27 -38.8028 0.9000 1.68893 31.16 0.5989
28 138.4029 0.3000
29 * 70.0089 5.6683 1.84915 40.00 0.5695
30 * -91.0116 (d30)
31 ∞ 1.4500 1.52301 58.59 0.5449
32 ∞ BF

[Aspherical data]
29 faces 30 faces
K 0 0
A4 -2.55803E-06 1.23327E-06
A6 2.30151E-10 9.20080E-10
A8 0 4.57577E-13

[Various data]
INF
Focal length 103.75
F number 1.46
Full angle of view 2ω 23.33
Statue height Y 21.63
Total lens length 168.75

[Variable interval data]
Shooting distance INF 995
d0 ∞ 826.8724
d14 16.3846 3.0000
d30 37.5495 50.9341
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length
G1 1 423.53
G2 15 87.44
G1a 1 486.54
G1b 9 -190.77
G1c 12 173.18
G2a 15 357.58
G2b 23 79.61

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

  26 has a first lens group G1 having a positive refractive power fixed to the image plane during focusing from an object at infinity to a short distance object, and from the image plane side to the object side during focusing. The second lens group G2 having a positive refractive power that moves toward the center.

  The first lens group G1 includes a first-a lens group G1a having a positive refractive power from the object side, a first-b lens group G1b having a negative refractive power, and a first-c lens group G1c having a positive refractive power.

  The first-a lens group G1a includes three positive meniscus lenses having a convex surface facing the object side from the object side and a negative meniscus lens having a convex surface facing the object side.

  The 1b lens group G1b is composed of a cemented lens having a negative refractive power as a whole, with a concave surface facing the object side, and three lenses of a convex lens, a concave lens, and a convex lens cemented from the object side.

  The first c lens group G1c is composed of a cemented lens having a convex surface facing the object side and having a positive refractive power.

  The second lens group G2 includes a second a lens group G2a having a positive refractive power from the object side, an aperture stop S, and a second b lens group G2b having a positive refractive power.

  The second-a lens group G2a includes two positive meniscus lenses having a convex surface facing the object surface and a cemented lens having negative refractive power having the convex surface facing the object side.

  The second lens group G2b is composed of two cemented lenses having negative refractive power with a concave surface facing the object side from the object side, and a biconvex lens in which both lens surfaces are aspherical.

Subsequently, specification values of the large-aperture lens according to Example 6 are shown below.
Numerical example 6
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 118.9921 9.1465 1.65844 50.85 0.5574
2 656.7877 0.3000
3 83.3810 5.3723 1.43700 95.10 0.5335
4 115.1062 0.3000
5 78.9460 5.8885 1.43700 95.10 0.5335
6 121.6933 5.5440
7 197.8334 2.2000 1.61310 44.36 0.5604
8 58.7612 12.5360
9 -792.9935 3.7355 1.43700 95.10 0.5335
10 -168.2895 1.0000 1.61310 44.36 0.5604
11 76.1452 5.1013 1.59282 68.63 0.5441
12 200.5086 1.0000
13 65.1634 9.4130 1.80420 46.50 0.5571
14 -455.9270 1.8000 1.63775 42.41 0.5605
15 81.5353 (d15)
16 57.9913 3.8042 1.94595 17.98 0.6544
17 85.7121 0.3000
18 51.9245 4.4942 1.59282 68.63 0.5441
19 88.4075 0.3000
20 41.6033 8.5657 1.59282 68.63 0.5441
21 5998.9072 1.3000 1.74077 27.76 0.6076
22 27.3712 7.7711
(Aperture) ∞ 4.2715
24 -59.8055 0.9000 1.56732 42.84 0.5742
25 28.9313 7.0145 1.87071 40.73 0.5681
26 10064.4349 2.8390
27 -81.6714 2.6665 1.91082 35.25 0.5821
28 -44.4966 0.9000 1.69895 30.05 0.6028
29 161.7882 0.3000
30 * 75.8764 9.2642 1.88202 37.22 0.5768
31 * -8.55E + 01 (d31)
32 ∞ 1.4500 1.52301 58.59 0.5449
33 ∞ BF

[Aspherical data]
30 faces 31 faces
K 0 0
A4 -2.53189E-06 9.94955E-07
A6 0 2.18739E-10
A8 0 1.07296E-12

[Various data]
INF
Focal length 102.18
F number 1.46
Full angle of view 2ω 23.71
Statue height Y 21.63
Total lens length 173.83

[Variable interval data]
Shooting distance INF 1001
d0 ∞ 826.8724
d15 15.7872 3.0000
d31 37.5630 50.4102
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length
G1 1 399.50
G2 16 87.42
G1a 1 484.04
G1b 9 -206.30
G1c 13 182.69
G2a 16 373.38
G2b 24 79.93

  FIG. 31 is a lens configuration diagram of the large-diameter lens according to Example 7 when focusing on infinity.

  31 has 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 from the image plane side to the object side during focusing. The second lens group G2 having a positive refractive power that moves toward the center.

  The first lens group G1 includes a first-a lens group G1a having a positive refractive power from the object side, a first-b lens group G1b having a negative refractive power, and a first-c lens group G1c having a positive refractive power.

  The first-a lens group G1a includes three positive meniscus lenses having a convex surface facing the object side from the object side and a negative meniscus lens having a convex surface facing the object side.

  The first lens group G1b is composed of a cemented lens having a concave surface facing the object side and having a negative refractive power.

  The first c lens group G1c is composed of a cemented lens having a convex surface facing the object side and having a positive refractive power.

  The second lens group G2 includes a second a lens group G2a having a positive refractive power from the object side, an aperture stop S, and a second b lens group G2b having a positive refractive power.

  The second-a lens group G2a includes two positive meniscus lenses having a convex surface facing the object surface and a cemented lens having negative refractive power having the convex surface facing the object side.

  The second lens group G2b is composed of two cemented lenses having negative refractive power with a concave surface facing the object side from the object side, and a biconvex lens in which both lens surfaces are aspherical.

Subsequently, specification values of the large-aperture lens according to Example 7 are shown below.
Numerical example 7
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 102.4036 5.5582 1.65844 50.85 0.5574
2 149.2820 0.3000
3 74.5000 9.4445 1.43700 95.10 0.5335
4 158.9528 0.3000
5 79.5482 9.0637 1.43700 95.10 0.5335
6 241.3612 4.3160
7 387.4299 2.2000 1.61340 44.27 0.5633
8 53.8748 14.6956
9 -265.8666 4.3917 1.43700 95.10 0.5335
10 -103.1399 1.8000 1.61340 44.27 0.5633
11 -500.0000 1.0000
12 73.5443 10.6775 1.83481 42.72 0.5648
13 -149.8448 1.8000 1.61340 44.27 0.5633
14 73.8135 (d14)
15 69.4099 3.7022 1.92286 20.88 0.6388
16 114.7865 0.3000
17 47.6366 4.6001 1.55032 75.50 0.5400
18 79.7832 0.3000
19 43.6382 7.2273 1.59282 68.63 0.5441
20 3165.0277 1.5512 1.71736 29.50 0.6034
21 29.3287 7.3681
(Aperture) ∞ 4.6152
23 -50.6131 0.9000 1.65412 39.68 0.5737
24 28.8753 7.8896 1.87071 40.73 0.5681
25 -471.6988 2.4139
26 -88.4472 3.8604 1.91082 35.25 0.5821
27 -34.6117 0.9000 1.67270 32.17 0.5962
28 121.0744 0.3000
29 * 68.0671 5.0259 1.84915 40.00 0.5695
30 * -88.4873 (d30)
31 ∞ 1.4500 1.52301 58.59 0.5449
32 ∞ BF

[Aspherical data]
29 faces 30 faces
K 0 0
A4 -1.16039E-06 2.13317E-06
A6 7.86933E-11 4.73264E-10
A8 0 1.59334E-12

[Various data]
INF
Focal length 101.85
F number 1.46
Full angle of view 2ω 23.85
Statue height Y 21.63
Total lens length 172.51

[Variable interval data]
Shooting distance INF 999
d0 ∞ 826.8724
d15 15.9931 3.0000
d30 37.5630 50.6161
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length
G1 1 305.79
G2 15 91.08
G1a 1 1067.88
G1b 9 -470.59
G1c 12 196.54
G2a 15 294.36
G2b 23 91.54

  FIG. 36 is a lens configuration diagram of the large-diameter lens according to Example 8 when focusing on infinity.

  36 has 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 from the image plane side to the object side during focusing. The second lens group G2 having a positive refractive power that moves toward the center.

  The first lens group G1 includes a first-a lens group G1a having a positive refractive power from the object side, a first-b lens group G1b having a negative refractive power, and a first-c lens group G1c having a positive refractive power.

  The first-a lens group G1a includes three positive meniscus lenses having a convex surface facing the object side from the object side and a negative meniscus lens having a convex surface facing the object side.

  The first lens group G1b is composed of a cemented lens having a concave surface facing the object side and having a negative refractive power.

  The first c lens group G1c is composed of a cemented lens having a convex surface facing the object side and having a positive refractive power.

  The second lens group G2 includes a second a lens group G2a having a positive refractive power from the object side, an aperture stop S, and a second b lens group G2b having a positive refractive power.

  The second-a lens group G2a includes two positive meniscus lenses having a convex surface facing the object surface and a cemented lens having negative refractive power having the convex surface facing the object side.

  The second lens group G2b is composed of two cemented lenses having negative refractive power with a concave surface facing the object side from the object side, and a biconvex lens in which both lens surfaces are aspherical.

Subsequently, specification values of the large-aperture lens according to Example 8 are shown below.
Numerical example 8
Unit: mm
[Surface data]
Surface number rd nd vd PgF
Object ∞ (d0)
1 90.2454 7.8712 1.65844 50.85 0.5574
2 167.6210 0.3000
3 76.2920 5.6698 1.43700 95.10 0.5335
4 100.7741 0.3000
5 72.9762 10.0895 1.43700 95.10 0.5335
6 231.4844 2.0000
7 157.4610 2.2000 1.63775 42.41 0.5605
8 46.8356 17.1883
9 -182.8104 3.7870 1.43700 95.10 0.5335
10 -98.0729 1.8000 1.63775 42.41 0.5605
11 -500.0000 1.0000
12 59.9826 10.5828 1.80420 46.50 0.5571
13 -343.9519 1.8000 1.63775 42.41 0.5605
14 66.2039 (d14)
15 62.9670 4.3362 1.92286 20.88 0.6388
16 118.1340 0.3000
17 54.1666 3.9883 1.59282 68.63 0.5441
18 81.0490 0.3000
19 43.7504 8.4873 1.59282 68.63 0.5441
20 -207.2733 1.3000 1.69895 30.05 0.6028
21 28.3650 7.5794
(Aperture) ∞ 4.9939
23 -49.6245 0.9000 1.65412 39.68 0.5737
24 30.7397 8.5593 1.87071 40.73 0.5681
25 -229.5974 2.1096
26 -90.0548 3.7067 1.91082 35.25 0.5821
27 -36.1967 0.9000 1.67270 32.17 0.5962
28 127.5561 0.3000
29 * 70.3380 4.9106 1.84915 40.00 0.5695
30 * -91.4394 (d30)
31 ∞ 1.4500 1.52301 58.59 0.5449
32 ∞ BF

[Aspherical data]
29 faces 30 faces
K 0 0
A4 -1.05290E-06 1.94516E-06
A6 2.36212E-10 6.27849E-10
A8 0 7.62259E-13

[Various data]
INF
Focal length 101.85
F number 1.46
Full angle of view 2ω 23.76
Statue height Y 21.63
Total lens length 173.00

[Variable interval data]
Shooting distance INF 1000
d0 ∞ 826.8724
d15 15.7304 3.0000
d30 37.5626 50.3245
BF 1.0000 1.0000

[Lens group data]
Group Start surface Focal length
G1 1 371.80
G2 15 87.20
G1a 1 849.37
G1b 9 -316.40
G1c 12 195.15
G2a 15 259.88
G2b 23 86.77

The conditional expression corresponding values corresponding to each of the above embodiments are shown below.
ex1 ex2 ex3 ex4
(1) -3.8 <ΦG1b / ΦG1 <-0.5 -0.793 -3.077 -2.070 -1.919
(2) 0.18 <ΦG1 / Φ <0.50 0.305 0.254 0.272 0.234
(3) 3.0 <ΦG2 / ΦG1 <7.5 3.706 4.660 4.321 5.129
(4) 0.8 <νdL1bp1 * ΔPgFL1bp 5.35 5.35 5.35 5.35
(5) 0.015 <ΔPgFG1Pave 0.0326 0.0326 0.0333 0.0310
(6) ΔPgFG1Nave <-0.0020 -0.0063 -0.0053 -0.0037 -0.0053
(7) 0.010 <ΔPgFG2aPave 0.0188 0.0250 0.0250 0.0142
(8) 1.85 <NdL2ap1 1.92286 1.92286 1.92286 1.92286
(9) 0.02 <ΔPgFL2ap1 0.0281 0.0281 0.0281 0.0281

ex5 ex6 ex7 ex8
(1) -3.8 <ΦG1b / ΦG1 <-0.5 -2.220 -1.937 -0.650 -1.175
(2) 0.18 <ΦG1 / Φ <0.50 0.245 0.256 0.333 0.274
(3) 3.0 <ΦG2 / ΦG1 <7.5 4.844 4.570 3.358 4.263
(4) 0.8 <νdL1bp1 * ΔPgFL1bp 1.32 1.32 5.35 5.35
(5) 0.015 <ΔPgFG1Pave 0.0252 0.0302 0.0326 0.0324
(6) ΔPgFG1Nave <-0.0020 -0.0074 -0.0092 -0.0053 -0.0115
(7) 0.010 <ΔPgFG2aPave 0.0250 0.0257 0.0250 0.0222
(8) 1.85 <NdL2ap1 1.92286 1.94595 1.92286 1.92286
(9) 0.02 <ΔPgFL2ap1 0.0281 0.0384 0.0281 0.0281

G1 1st lens group G2 2nd lens group G1a 1a lens group G1b 1b lens group G1c 1c lens group G2a 2a lens group G2b 2b lens group LPF Low pass filter I Image surface S Aperture stop

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 is composed of one or more convex lenses and one concave lens or one cemented concave lens component from the object side. The first lens group G1 has a positive refractive power as a whole, and has a negative refractive power. A first-b lens group G1b made of a cemented lens component, and a first-c lens group G1c having a positive refractive power;
The second lens group G2 includes a second a lens group G2a composed of one or more convex lenses and a cemented concave lens component having negative refractive power, an aperture stop S, and a second b lens group G2b.
When focusing from infinity to a short distance 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. Large-aperture lens characterized by satisfying
(1) -3.8 <ΦG1b / ΦG1 <−0.5
(2) 0.18 <ΦG1 / Φ <0.50
(3) 3.0 <ΦG2 / ΦG1 <7.5
(4) 0.8 <νdL1bp1 × ΔPgFL1bp1
ΦG1: refracting power of the first lens group G1 ΦG1b: refracting power of the first b lens group G1b ΦG2: refracting power of the second lens group G2 Φ: refracting power of the entire system at infinity focusing νdL1bp1: first b lens group G1b Abbe number ΔPgFL1bp1 of the lens having the highest refractive index among the convex lenses constituting the first lens group G1b. Anomalous dispersion of the lens having the highest refractive index among the convex lenses constituting the 1b lens group G1b
The large-aperture lens according to claim 1, wherein the following conditional expression is satisfied.
(5) 0.015 <ΔPgFG1Pave
(6) ΔPgFG1Nave <−0.0020
ΔPgFG1Nave: average value of anomalous dispersion of the concave lens of the first lens group G1 ΔPgFG1Pave: average value of the anomalous dispersion of the convex lens of the first lens group G1
The large-aperture lens according to claim 1 or 2, wherein the following conditional expression is satisfied.
(7) 0.010 <ΔPgFG2aPave
ΔPgFG2aPave: average value of anomalous dispersion of the convex lens of the 2a lens group G2a
The large-aperture lens according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
(8) 1.85 <NdL2ap1
NdL2ap1: Refractive index of the convex lens located closest to the object side among the lenses constituting the second lens group G2.
The large-aperture lens according to claim 1, wherein the following conditional expression is satisfied.
(9) 0.020 <ΔPgFL2ap1
ΔPgFL2ap1: Anomalous dispersion of a convex lens located closest to the object side among the lenses constituting the second lens group G2.
  The large-diameter lens according to any one of claims 1 to 6, wherein the second lens group G2 includes at least one aspherical lens.

Images