JP7094550B2 - Imaging optical system - Google Patents

Description

The present invention relates to an optical system suitable for a photographing lens used in a digital camera, a video camera, or the like, and particularly to a large-diameter imaging optical system having an inner focus.

In recent years, mirrorless cameras such as digital cameras and video cameras have become more and more popular. In many mirrorless cameras, wobbling, which is a reciprocating minute drive of the focus group, is performed during autofocus. In order to perform wobbling with the smallest possible drive system, it is required to reduce the size and weight of the focus group. In addition, since many mirrorless cameras are smaller and lighter than reflex cameras, it is desired to reduce the size of the photographing lens. An example of an imaging optical system of a large-diameter medium-telephoto lens having an angle of view of about 30 ° and an aperture ratio of about 1.2 to 1.8 is described in the patent document.

Japanese Unexamined Patent Publication No. 2012-242690 JP-A-2015-146015 JP-A-2015-141384

A medium-telephoto lens has a longer focal distance than a standard lens, so the total optical length tends to be longer. On the other hand, it has a wider angle of view than a so-called super-telephoto lens and corrects angles of view. Therefore, the telephoto ratio tends to be large. In addition, many users expect that an optical system with an angle of view of about medium telephoto can express using blur, and a large-diameter photographing lens is desired. However, if the aperture is increased, the entrance pupil becomes larger, which makes it difficult to correct spherical aberration and the like. Therefore, it is an issue to reduce the size of the photographing lens while achieving good performance.

Patent Document 1 proposes a large-diameter inner focus type medium telephoto lens having an angle of view of about 30 ° and an FNO of about 1.8. However, since the FNO is about 1.8, the amount of blur is small, and further increasing the aperture is a problem.

Patent Document 2 proposes an inner focus type medium telephoto lens having an angle of view of about 30 ° and a large aperture of about FNO 1.2. While the aperture has been sufficiently increased, the number of lenses constituting the medium telephoto lens is large and the total length of the lens is long, so further miniaturization is an issue.

Patent Document 3 proposes an inner focus type medium telephoto lens having an angle of view of about 30 ° and a large aperture of about FNO 1.2. However, since the focus group is composed of a plurality of lenses, further weight reduction of the focus group is an issue.

The present invention has been made in view of such a situation, and has a so-called medium telephoto angle of view of 20 to 30 °, and a large-diameter inner focus type medium telephoto image with an FNO of about 1.4. It is an object of the present invention to provide an imaging optical system which is suitable for a lens, can reduce the size and weight of the focus group, and at the same time, can reduce the size and weight of the entire optical system, and has good imaging performance.

In order to solve the above problems, the imaging optical system of the present invention has a first lens group G1 having a positive power, an aperture aperture S, and a second lens having a negative power in order from the object side to the image side. It consists of a lens group G2 and a third lens group G3 having a positive power, and the first lens group G1, the aperture aperture S, and the third lens group G3 are fixed to the image plane during focusing. Only the second lens group G2 moves in the optical axis direction, the second lens group G2 is composed of one lens element, and negative power in the first lens group G1 and the third lens group G3 is applied. All the lens elements having the lens element are joined to the lens element having a positive power, and all the lens elements in the first lens group G1 and the third lens group G3 have a positive power and satisfy the following conditional expression. It was characterized by doing.
(1) 0.65 <fG1 / f <1.00
however,
fG1: Focal length of the first lens group G1 f: Focal length of the optical system in the infinity state.

Further, the second invention is an imaging optical system according to the first invention, wherein the third lens group G3 further satisfies the following conditional expression.
(2) 0.60 <fG3 / f <1.00
however,
fG3: The focal length of the third lens group G3.

Further, the third invention is an imaging optical system according to the first or second invention, wherein the lens element of the second lens group G2 satisfies the following conditional expression.
(3) 50.00 <νd_G2
however,
νd_G2: Abbe number with respect to the d line of the lens element of the second lens group G2.

Further, the fourth invention further comprises, in any one of the first to third inventions, two or more lens elements satisfying the following conditional expression in the first lens group G1. Is.
(4) 1.2 <fG1n / fG1 <4.0
however,
fG1n: The focal length of the nth lens element from the object side in the first lens group G1.

Further, in the fifth invention, in any one of the first to fourth inventions, the third lens group G3 is further composed of two lens elements, a front lens element G3a and a rear lens element G3b, and the front lens. It is an imaging optical system characterized in that the element G3a has a joint surface and satisfies the following conditional expression.
(5) 0.40 <G3ar / G3af <0.90
(6) -2.4 <G3acement <-0.9
however,
G3ar: Of the lens elements constituting the third lens group G3, the radius of curvature of the air interface on the image side of the front lens element G3a G3af: Among the lens elements constituting the third lens group G3, the front lens element Radius of curvature of the air interface on the object side of G3a G3acement: Of the lens elements constituting the third lens group G3, the radius of curvature of the first joint surface counted from the image side of the front lens element G3a is the focal length of the entire system. Let it be the inverse value normalized by.

Further, the sixth invention is an imaging optical system according to any one of the first to fifth inventions, further comprising an aspherical surface in the first lens group G1.

Further, in the seventh invention, in any one of the first to sixth inventions, the average value of the anomalous dispersibility of the lens element having a positive power in the first lens group G1 further satisfies the following conditional expression. It is an imaging optical system characterized by.
(7) 0.0100 <ΔPgF_Avg
however,
ΔPgF_Avg: The average value of the anomalous dispersion of the g-line and the F-line of the lens element having a positive power in the first lens group G1 and the g-line of the lens element having a positive power in the first lens group G1. The anomalous dispersibility of the F line is ΔPgF_n = PgF_n-0.6483 + 0.0018 × νd_n
ΔPgF_n: Anomalous dispersibility of g-line and F-line of the lens element having the nth positive power from the object side of the first lens group G1 PgF_n: having the nth positive power from the object side of the first lens group G1. Partial dispersion ratio of g-line and F-line of the lens element νd_n: The number of d-lines of the lens element having the nth positive power from the object side of the first lens group G1.

Further, the eighth invention is characterized in that, in any one of the first to seventh inventions, the third lens group G3 further has a concave surface SG3 on the image side satisfying the following conditional expression. It is an optical system.
(8)-(1 / R_SG3) x ((1 / nd'_SG3)-(1 / nd_SG3)) <-0.0150
however,
R_SG3: Radius of curvature of the surface SG3 nd'_SG3: Refractive index on the image side of the surface SG3 nd_SG3: Refractive index on the object side of the surface SG3.

Further, the ninth invention is an imaging optical system further satisfying the following conditional expression in any one of the first to eighth inventions.
(9) 0.300 <LG2R1 / fG1G2 <0.460
however,
fG1G2: Composite focal length of the first lens group G1 and the second lens group G2 LG2R1: From the image side principal point position of the composite system of the first lens group G1 and the second lens group G2 to the object side surface of the second lens group G2. The distance on the optical axis.

According to the present invention, the lens has a so-called medium telephoto angle of view of 20 to 30 °, and is suitable for a large-diameter inner focus type medium telephoto lens having an FNO of about 1.4, and the focus group is small. At the same time as reducing the weight, the entire optical system can be reduced in size and weight, and an imaging optical system having good imaging performance can be provided.

It is a lens block diagram which concerns on Example 1 of the imaging optical system of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 1. FIG. FIG. 3 is a longitudinal aberration diagram of the imaging optical system of Example 1 at a shooting distance of 500 mm. It is a lateral aberration diagram at the time of infinity focusing of the imaging optical system of Example 1. FIG. FIG. 5 is a lateral aberration diagram of the imaging optical system of Example 1 at a shooting distance of 500 mm. It is a lens block diagram which concerns on Example 2 of the imaging optical system of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 2. FIG. FIG. 3 is a longitudinal aberration diagram of the imaging optical system of Example 2 at a shooting distance of 500 mm. It is a lateral aberration diagram at the time of infinity focusing of the imaging optical system of Example 2. FIG. FIG. 3 is a lateral aberration diagram of the imaging optical system of Example 2 at a shooting distance of 500 mm. It is a lens block diagram which concerns on Example 3 of the imaging optical system of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 3. FIG. FIG. 3 is a longitudinal aberration diagram of the imaging optical system of Example 3 at a shooting distance of 500 mm. It is a lateral aberration diagram at the time of infinity focusing of the imaging optical system of Example 3. FIG. FIG. 3 is a lateral aberration diagram of the imaging optical system of Example 3 at a shooting distance of 500 mm. It is a lens block diagram which concerns on Example 4 of the imaging optical system of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 4. FIG. FIG. 3 is a longitudinal aberration diagram of the imaging optical system of Example 4 at a shooting distance of 500 mm. It is a lateral aberration diagram at the time of infinity focusing of the imaging optical system of Example 4. FIG. FIG. 5 is a lateral aberration diagram of the imaging optical system of Example 4 at a shooting distance of 500 mm. It is a lens block diagram which concerns on Example 5 of the imaging optical system of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 5. FIG. 5 is a longitudinal aberration diagram of the imaging optical system of Example 5 at a shooting distance of 500 mm. It is a lateral aberration diagram at the time of infinity focusing of the imaging optical system of Example 5. FIG. 5 is a lateral aberration diagram of the imaging optical system of Example 5 at a shooting distance of 500 mm. It is a lens block diagram which concerns on Example 6 of the imaging optical system of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 6. 6 is a longitudinal aberration diagram of the imaging optical system of Example 6 at a shooting distance of 500 mm. It is a lateral aberration diagram at the time of infinity focusing of the imaging optical system of Example 6. FIG. 3 is a lateral aberration diagram of the imaging optical system of Example 6 at a shooting distance of 500 mm. It is a lens block diagram which concerns on Example 7 of the imaging optical system of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the imaging optical system of Example 7. FIG. 3 is a longitudinal aberration diagram of the imaging optical system of Example 7 at a shooting distance of 500 mm. It is a lateral aberration diagram at the time of infinity focusing of the imaging optical system of Example 7. FIG. FIG. 5 is a lateral aberration diagram of the imaging optical system of Example 7 at a shooting distance of 500 mm. It is a reference figure of the conditional expression (9).

Hereinafter, embodiments of the present invention will be described. However, the lens element in the present invention is made of a single material and has one interface on the object side and one interface on the image side. Further, the lens element in the present invention has one interface with air on the object side and one on the image side. For example, when a convex lens element and a concave lens element are joined, this joined lens becomes one lens element.

In the imaging optical system of the present invention, the first lens group G1 having a positive power, the aperture aperture S, the second lens group G2 having a negative power, and the second lens group having a positive power are in order from the object side to the image side. It is composed of three lens groups G3, and during focusing, the first lens group G1, the aperture aperture S, and the third lens group G3 are fixed to the image plane, and only the second lens group G2 is optical. Moving in the axial direction, the second lens group G2 is composed of one lens element, and all the lens elements having negative power in the first lens group G1 and the third lens group G3 have positive power. It is bonded to the lens element, and the lens elements in the first lens group G1 and the third lens group G3 are all imaging optical systems having positive power.

The imaging optical system of the present invention is composed of a first lens group G1 having a positive power, a second lens group G2 having a negative power, and a third lens group G3 having a positive power in order from the object side. , A strong telescopic lens configuration is formed between the first lens group G1 and the second lens group G2, and the lengths of the first lens group G1 and the second lens group G2 are shortened to reduce the size of the optical system. At the same time, it is possible to correct the aberration with the third lens group G3.

Since the aperture stop S is between the first lens group G1 and the second lens group G2 which is the focus group, the effective FNO becomes large when focusing at a short distance, and the first lens group G1 and the second lens group G2 are separated. Since it is possible to prevent the light beam at the central angle of view passing through from becoming thick, the first lens group G1 and the second lens group G2 can be miniaturized in the radial direction. Further, since the aperture stop S is not located in the air interval in each group, the separation of the mirror chamber can be prevented and the structure can be simplified. Further, by placing the aperture stop S on the object side of the second lens group G2, the distance between the exit pupil position and the imager becomes larger than when the aperture stop S is placed on the image side of the second lens group G2, and the imager Since the angle of incidence of the light beam on the lens becomes smaller, it is possible to reduce the change in image magnification during wobbling.

At the time of focusing, the axial light flux is converged by the first lens group G1 so that only the second lens group G2, which is miniaturized in the radial direction, moves, so that the movable portion can be reduced in weight. Further, since the second lens group G2 is composed of one lens element, the movable part can be reduced in weight, and the drive system such as a motor required for driving the second lens group G2 can be made compact while supporting wobbling. Can be transformed into.

By joining all the lens elements having negative power in the first lens group G1 and the third lens group G3 to the lens elements having positive power, it is possible to reduce the spacer and the mechanism required for holding the lens. It is advantageous for reducing the size and weight, and it is possible to reduce the manufacturing error of the parts to be stacked.

Since all the lens elements in the first lens group G1 and the third lens group G3 have positive power, the positive power per lens element has a positive power as compared with the case where the lens element has a negative power. Since the power sharing of the lens is reduced, the aberration of the lens element in the group can be shared, and the eccentric sensitivity can be easily reduced.

The conditional equation (1) to be satisfied by the optical system of the present invention defines a preferable range of the ratio of the focal length of the first lens group G1 to the focal length of the optical system.
(1) 0.65 <fG1 / f <1.00
however,
fG1: Focal length of the first lens group G1 f: Focal length of the optical system in the infinity state.

By satisfying the conditional equation (1), the second lens group G2 can be miniaturized in the radial direction, and the spherical aberration generated in the first lens group G1 can be prevented from becoming large, so that the diameter is increased. Can be realized.

When the focal length of the first lens group G1 becomes smaller than the focal length of the optical system beyond the lower limit of the conditional equation (1), the refractive power of the lens elements constituting the first lens group G1 must be increased. This is not desirable because the spherical aberration generated in the first lens group G1 becomes large. Further, if the number of lens elements is increased to alleviate the occurrence of spherical aberration, the axial thickness of the first lens group G1 increases, and the first lens group G1 cannot be miniaturized. When the focal length of the first lens group G1 becomes larger than the focal length of the optical system beyond the upper limit of the conditional expression (1), the second lens group G2 and the third lens group G3 are reduced in the radial direction. Is not desirable because it makes it difficult.

Further, regarding the above-mentioned conditional expression (1), it is preferable to limit the lower limit value to 0.68 because the above-mentioned effect can be more surely obtained. Further, regarding the above-mentioned conditional expression (1), it is preferable to limit the upper limit value to 0.95 because the above-mentioned effect can be more surely obtained.

The conditional equation (2) to be satisfied by the optical system of the present invention defines a preferable range of the ratio of the focal length of the third lens group G3 to the focal length of the optical system.
(2) 0.60 <fG3 / f <1.00
however,
fG3: The focal length of the third lens group G3.

By satisfying the conditional equation (2), it is possible to prevent an increase in distortion, and it is possible to prevent an increase in spherical aberration and curvature of field generated in the third lens group G3, so that the imaging performance is good. Optical system can be realized.

When the focal length of the third lens group G3 exceeds the upper limit of the conditional expression (2) and becomes larger than the focal length of the optical system, the negative distortion generated in the third lens group G3 becomes smaller and the first lens It is not desirable because it becomes difficult to correct the positive distortion generated in the group G1 and the second lens group G2. When the focal length of the third lens group G3 is smaller than the focal length of the optical system beyond the lower limit of the conditional equation (2), it becomes difficult to suppress spherical aberration and curvature of field generated in the third lens group G3. Therefore, it is not desirable.

Further, regarding the above-mentioned conditional expression (2), it is preferable to limit the lower limit value to 0.65 because the above-mentioned effect can be more surely obtained. Further, regarding the above-mentioned conditional expression (2), it is preferable to limit the upper limit value to 0.95 because the above-mentioned effect can be more surely obtained.

When the second lens group G2, which is the focus group, is composed of one lens element in order to reduce the weight, the chromatic aberration generated in the second lens group G2 is reduced in order to obtain good imaging performance over the entire focusing range. The challenge is to do.

The conditional expression (3) defines an appropriate range of Abbe numbers of the lens elements of the second lens group G2.
(3) 50.00 <νd_G2
however,
νd_G2: Abbe number with respect to the d line of the lens element of the second lens group G2.

The imaging optical system in the present invention is good in the entire focusing range because the chromatic aberration of magnification generated in the second lens group G2 can be reduced by satisfying the conditional equation (3) in the lens element constituting the second lens group G2. Imaging performance can be obtained.

When the Abbe number of the lens element of the second lens group G2 becomes smaller than the lower limit of the conditional expression (3), the fluctuation of the chromatic aberration of magnification during focusing becomes large, and good imaging performance is obtained over the entire focusing range. It is not desirable because it makes things difficult.

Further, regarding the above-mentioned conditional expression (3), it is preferable to limit the lower limit value to 55.00 because the above-mentioned effect can be more surely obtained.

Since the entrance pupil diameter of a large-diameter medium-telephoto lens is large, the light beam incident on the first lens group G1 is large, and spherical aberration and coma are more likely to occur in the first lens group G1 than in a small-diameter photographing lens. .. In a lens element in which spherical aberration or coma aberration is largely generated, the eccentric coma aberration generated by the eccentricity between the lens elements tends to be large. Therefore, it is an issue to suppress the occurrence of spherical aberration and coma aberration in the lens element of the first lens group G1. Generally, the larger the angle of incidence of light rays on the interface, the greater the monochromatic aberration. Therefore, it is desirable to gently bend the axial marginal rays in order to suppress the occurrence of spherical aberration and coma. In order to gently bend the light beam in each group of photographing lenses, the number of lens elements is increased, and the light beam can be gently bent by dispersing the refractive power required in each group.

In the conditional equation (4), among the lens elements constituting the first lens group G1, the focal length of the lens element mainly responsible for the refractive power of the first lens group G1 is compared with the focal length of the first lens group G1. It defines a preferable range. The medium telephoto lens for photography of the present invention has two or more lens elements satisfying the following conditional equations as lens elements constituting the first lens group G1, so that the refractive force as the lens element is the refractive force of the first lens group G1. Since it can be made smaller than that of the lens element, spherical aberration and coma generated in the lens element can be reduced, and eccentricity error sensitivity can be reduced.
(4) 1.2 <fG1n / fG1 <4.0
however,
fG1n: The focal length of the nth lens element from the object side in the first lens group G1.

When there is one lens element constituting the first lens group G1, it is not desirable because it is difficult to suppress spherical aberration, coma aberration, and axial chromatic aberration generated in the first lens group G1 and good imaging performance cannot be obtained. .. When the number of lens elements having a focal distance satisfying the internal conditional expression (4) of the lens elements constituting the first lens group G1 is one or less, the lens element of the first lens group G1 not satisfying the conditional expression (4). When at least one of the lenses has a focal distance lower than the lower limit of the conditional expression (4), the refractive force of the lens element is close to the refractive force of the first lens group G1 and the refractive force of the lens element is the first lens group G1. Since it becomes large with respect to the refractive force, it is difficult to suppress spherical aberration and coma aberration generated in the lens element, and it is difficult to reduce the eccentric sensitivity, which is not desirable. When there is one or less lens elements having a focal length that satisfies the internal conditional expression of the lens elements constituting the first lens group G1, all the lens elements of the first lens group G1 that do not satisfy the conditional expression (4) When the focal length exceeds the conditional equation, it is necessary to increase the number of lens elements constituting the first lens group G1 in order to maintain the refractive force of the first lens group G1, and it becomes difficult to shorten the total lens length. Not desirable.

Further, regarding the above-mentioned conditional expression (4), it is preferable to limit the lower limit value to 1.3 because the above-mentioned effect can be more surely obtained. Further, regarding the above-mentioned conditional expression (4), it is preferable to limit the upper limit value to 3.8 because the above-mentioned effect can be more surely obtained.

The third lens group G3 of the present invention is composed of a front lens element G3a and a rear lens element G3b, and their focal lengths are both positive, but their respective aberration sharing is different, and the front lens element G3a is under and rear. The lens element G3b of the above causes an excessive astigmatism, whereby the astigmatism of the third lens group G3 as a whole is suppressed to a small value. In addition, by generating astigmatism with different signs, the front lens element G3a or the rear lens element G3b in the third lens group G3 can be used to light the performance deterioration phenomenon such as one-sided blur that occurs in the entire system during manufacturing. By shifting and centering in the direction orthogonal to the axis during manufacturing, it is possible to improve the performance quality rate by correcting one-sided blur.

Conditional expression (5) defines a preferable range for the ratio of the radius of curvature of the air interface on the object side and the radius of curvature of the air interface on the image side of the front lens element G3a among the lens elements constituting the third lens group G3. Is. As a result, the front lens element G3a has an aplanatic shape, and it is possible to achieve a large aperture, which is one of the objects of the present invention. With this aplanatic shape, it is possible to achieve a large diameter without aggravating the spherical aberration of the entire system, but astigmatism remains excessive as a side effect. This remaining astigmatism is offset by the rear lens element G3b among the lens elements constituting the third lens group G3, but the conditional expression (5) is required to limit the residual amount. ..
(5) 0.40 <G3ar / G3af <0.90
however,
G3ar: Of the lens elements constituting the third lens group G3, the radius of curvature of the air interface on the image side of the front lens element G3a G3af: Among the lens elements constituting the third lens group G3, the front lens element Let it be the radius of curvature of the air interface on the object side of G3a.

When the lower limit of the conditional expression (5) is exceeded and G3ar becomes relatively small or G3af becomes relatively large, the focal length of the front lens element G3a becomes large and over-astigmatism occurs. Further, in order to maintain the focal length of the entire system, the focal length of the rear lens element G3b must be shortened, and astigmatism becomes further over. In particular, since the meridional image plane swings excessively toward the peripheral image height, the contrast of the peripheral image height is lowered and the resolution is lowered, which is not preferable. When the upper limit of the conditional expression (5) is exceeded and G3ar becomes relatively large or G3af becomes relatively small, the focal length of the front lens element G3a becomes small and under-point astigmatism occurs. Further, in order to maintain the focal length of the entire system, the focal length of the rear lens element G3b must be lengthened, which is not preferable because astigmatism becomes further under. In particular, the outermost image plane of the meridional has a remarkable under-image plane shift.

Conditional expression (6) defines a preferable range for the reciprocal of the value obtained by normalizing the radius of curvature of the first joint surface counted from the image side of the front lens element G3a with the focal length of the entire system. This makes it possible to correct the excessive spherical aberration remaining in the combined system of the first lens group G1 and the second lens group G2. In the optical system of the present invention, the second lens group G2 is used as a single lens element in order to reduce the weight of the second lens group G2 which is the AF drive group. Further, in order to shorten the total length of the optical system of the entire system, the refractive power of the second lens group G2 is strengthened, and the composite system of the first lens group G1 and the second lens group G2 is a strong telescopic type, so that the first lens group Excessive spherical aberration remains in the combined system of G1 and the second lens group G2. In order to correct this excessive spherical aberration, the spherical aberration was corrected as a whole system by providing a joint surface in the front lens element G3a in the third lens group G3 so that the spherical aberration becomes under.
(6) -2.4 <G3acement <-0.9
however,
G3acement: The radius of curvature of the first joint surface counted from the image side of the front lens element G3a is an inverse value normalized by the focal length of the entire system.

When the lower limit of the conditional expression (6) is exceeded and the G3 element becomes smaller, the under spherical aberration becomes larger, and the excessive spherical aberration generated in the combined system of the first lens group G1 and the second lens group G2 is overcorrected, which is preferable. do not have. When the upper limit of the conditional expression (6) is exceeded and the G3 element becomes large, it is not possible to generate an under spherical aberration that cancels the excessive spherical aberration generated in the combined system of the first lens group G1 and the second lens group G2. It becomes difficult to increase the diameter.

Further, regarding the above-mentioned conditional expression (5), it is preferable to limit the lower limit value to 0.45 because the above-mentioned effect can be more surely obtained. Further, regarding the above-mentioned conditional expression (5), it is preferable to limit the lower limit value to 0.50 because the above-mentioned effect can be more surely obtained. Further, regarding the above-mentioned conditional expression (5), it is preferable to limit the upper limit value to 0.80 because the above-mentioned effect can be more surely obtained. Further, regarding the above-mentioned conditional expression (6), it is preferable to limit the lower limit value to −2.0 because the above-mentioned effect can be more surely obtained. Further, regarding the above-mentioned conditional expression (6), it is preferable to limit the upper limit value to −1.2 because the above-mentioned effect can be more surely obtained.

Since the imaging optical system in the present invention has an aspherical surface in the first lens group G1, spherical aberration generated in the first lens group G1 can be corrected, and an optical system with good imaging performance can be realized. ..

Since the large-diameter photographing lens has a shallow depth of focus, the image spread on the imager surface is larger than that of the small-diameter photographing lens even if it has the same amount of axial chromatic aberration and the remaining secondary spectrum. Therefore, in order to obtain good imaging performance in a large-diameter photographing lens, it is an issue to sufficiently reduce the axial chromatic aberration and the remaining secondary spectrum.

The conditional expression (7) defines a preferable range of the average value of the anomalous dispersibility of the lens element having a positive power in the first lens group G1. In the imaging optical system of the present invention, the secondary spectrum of axial chromatic aberration can be reduced by satisfying the conditional expression by the lens element having a positive power in the first lens group G1, and good imaging performance is obtained. be able to.
(7) 0.0100 <ΔPgF_Avg
however,
ΔPgF_Avg: The average value of the anomalous dispersibility of the lens element having a positive power in the first lens group G1, and the anomalous dispersibility of the g-line and the F-line of the lens element having a positive power in the first lens group G1. Is ΔPgF_n = PgF_n-0.6483 + 0.0018 × νd_n
ΔPgF_n: Anomalous dispersibility of g-line and F-line of the lens element having the nth positive power from the object side of the first lens group G1 PgF_n: having the nth positive power from the object side of the first lens group G1. Partial dispersion ratio of g-line and F-line of the lens element νd_n: The number of d-lines of the lens element having the nth positive power from the object side of the first lens group G1.

If the average value of the anomalous dispersibility of the lens element having a positive power in the first lens group G1 becomes smaller than the lower limit of the conditional expression (7), the second-order spectrum of the axial chromatic aberration may be sufficiently corrected. This is not desirable because good imaging performance cannot be obtained.

Further, regarding the above-mentioned conditional expression (7), it is preferable to limit the lower limit value to 0.0130 because the above-mentioned effect can be more surely obtained.

Since the depth of focus of a large-diameter photographic lens is shallow, the spread of the image on the imager surface is larger than that of a small-diameter photographic lens even if the same amount of curvature of field occurs. Therefore, in order to obtain good imaging performance in a large-diameter photographing lens, it is a problem to sufficiently correct the curvature of field.

The medium telephoto lens for photography of the present invention satisfies the conditional expression (8) in the third lens group G3 and has a concave surface SG3 on the image side, so that the Petzval sum can be reduced and the curvature of field is corrected. It is possible to obtain good imaging performance.
(8)-(1 / R_SG3) x ((1 / nd'_SG3)-(1 / nd_SG3)) <-0.0150
however,
R_SG3: Radius of curvature of the surface SG3 nd'_SG3: Refractive index on the image side of the surface SG3 nd_SG3: Refractive index on the object side of the surface SG3.

When the third lens group G3 satisfies the conditional expression (8) and does not have the concave surface SG3 on the image side, it is difficult to reduce the Petzval sum, and the curvature of field cannot be sufficiently corrected, so that good imaging performance is obtained. Not desirable because it cannot be obtained. Alternatively, if an attempt is made to reduce the Petzval sum in order to correct curvature of field, the radius of curvature of the convergent surface will be lowered as a whole, and it is necessary to increase the number of lens elements in order to secure the refractive power of the third lens group G3. Therefore, it is difficult and undesired to miniaturize the third lens group G3.

Further, regarding the above-mentioned conditional expression (8), it is preferable to limit the upper limit value to −0.0170 because the above-mentioned effect can be more surely obtained.

FIG. 36 is a reference diagram of the conditional expression (9). Since the large-diameter medium-telephoto lens has a large entrance pupil diameter, the second lens group G2, which is a focus group for which weight reduction is desired, also tends to increase in the radial direction. Therefore, in a large-diameter medium-telephoto lens of about F1.4, it is an issue to reduce the weight of the second lens group G2, which is the focus group. The incident height of the axial marginal ray on the second lens group G2 with respect to the entrance pupil diameter in the infinity state is the first lens group G1 with respect to the focal length of the combined system of the first lens group G1 and the second lens group G2. The larger the distance between the image side principal point of the composite system of the second lens group G2 and the side surface of the object of the second lens group G2, the smaller the distance.

The conditional equation (9) to be satisfied by the optical system of the present invention is the distance on the optical axis between the image side principal point of the composite system of the first lens group G1 and the second lens group G2 and the object side surface of the second lens group G2. It defines a preferable range of the ratio of the focal lengths of the synthetic system of the first lens group G1 and the second lens group G2. By satisfying the conditional equation (9), the incident height of the axial marginal light beam incident on the second lens group G2 can be made appropriate, the second lens group G2 can be miniaturized in the radial direction, and the third lens group can be miniaturized. G3 also tends to be miniaturized in the radial direction. By arranging a focusing mechanism or the like on the outside of the second lens group G2 and the third lens group G3, which are miniaturized in the radial direction, the outer peripheral portion of the product can be made thinner, and a compact and lightweight photographing lens can be realized. ..
(9) 0.300 <LG2R1 / fG1G2 <0.460
however,
fG1G2: Composite focal length of the first lens group G1 and the second lens group G2 LG2R1: From the image side principal point position of the composite system of the first lens group G1 and the second lens group G2 to the object side surface of the second lens group G2. The distance on the optical axis.

The distance on the optical axis between the image side main point of the composite system of the first lens group G1 and the second lens group G2 and the object side surface of the second lens group G2 and the first lens group beyond the lower limit of the conditional equation (9). When the ratio of the focal length of the composite system of G1 and the second lens group G2 becomes smaller, the height of the axial marginal ray incident on the second lens group G2 becomes higher, so that the second lens group G2 becomes smaller in the radial direction. Not desirable because it cannot be done. Exceeding the upper limit of the conditional expression (9), the distance on the optical axis between the image side main point of the composite system of the first lens group G1 and the second lens group G2 and the object side surface of the second lens group G2 and the first lens group When the ratio of the focal distance of the composite system of G1 and the second lens group G2 becomes large, the incident height of the axial marginal light beam incident on the second lens group G2 becomes low, so that the outermost object side surface of the first lens group G1 It is necessary to lower the axial marginal ray between the lens and the side of the object of the second lens group G2, but if the axial marginal ray is to be gently bent in order to prevent the occurrence of spherical aberration and coma, the first lens group It is necessary to increase the distance on the optical axis between the outermost side surface of the G1 and the side surface of the object of the second lens group G2, which is not desirable because it is disadvantageous in reducing the total optical length.

Further, regarding the above-mentioned conditional expression (9), it is preferable to limit the lower limit value to 0.350 because the above-mentioned effect can be more surely obtained. Further, regarding the above-mentioned conditional expression (9), it is preferable to limit the upper limit value to 0.450 because the above-mentioned effect can be more surely obtained.

In the imaging optical system of the present invention, it is more effective to include the following configurations. It is desirable to have an aspherical surface in the third lens group G3 in order to surely correct the astigmatism generated in the third lens group G3.

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

In [plane data], the surface number is the number of the lens surface or aperture aperture counted from the object side, r is the refractive index of each surface, d is the distance between the surfaces, and nd is the d line (wavelength λ = 587.56 nm). The refractive index, νd is the Abbe number with respect to the d line, and PgF is the partial dispersion ratio of the g line (wavelength λ = 435.84 nm) and the F line (wavelength λ = 486.13 nm). Further, BF represents back focus, and the description of the refractive index n = 1.0000 of air is omitted.

The radius of curvature ∞ (infinity) with respect to a flat surface or an aperture stop is entered in the area numbered (aperture).

In [Aspherical surface data], each coefficient value that gives the aspherical surface shape of the lens surface marked with * in [Surface data] is shown. The shape of the aspherical surface is y for the displacement in the direction orthogonal to the optical axis, z for the displacement (sag amount) in the optical axis direction from the intersection of the aspherical surface and the optical axis, and K, 4, 6, 8 for the conic coefficient. When the 10th and 12th order aspherical elements are set as A4, A6, A8, A10, and A12, respectively, the coordinates of the aspherical surface shall be expressed by the following equation.

[Various data] shows values such as the focal length at each shooting distance.

[Variable interval data] shows the variable interval and the BF (back focus) value at each shooting distance.

[Lens group data] shows the surface number on the most object side constituting each lens group and the combined focal length of the entire group.

In all the following specification values, the focal length f, the radius of curvature r, the lens surface spacing d, and other length units are described in millimeters (mm) unless otherwise specified, but optics. The system is not limited to this because the same optical performance can be obtained in both proportional expansion and proportional reduction.

Further, in the aberration diagram corresponding to each embodiment, d, g, and C represent the d-line, g-line, and C-line, respectively, and ΔS and ΔM represent the sagittal image plane and the meridional image plane, respectively. Further, in the lens configuration diagram shown in FIGS. 1, 6, 11, 16, 21, 26, 31, S is the aperture diaphragm, I is the image plane, F is the filter in the camera, and the alternate long and short dash line passing through the center is the optical axis.

FIG. 1 is a lens configuration diagram of an imaging optical system according to a first embodiment of the present invention. The first lens group G1 is composed of a convex meniscus lens L11 having a convex surface facing the object side, a biconvex positive lens L12, a concave meniscus lens L13 having a convex surface facing the object side, and a biconvex positive lens L14. It is composed of a bonded lens element and has a positive refractive power as a whole. Further, both the side surface of the object and the side surface of the image of the biconvex positive lens L12 have a predetermined aspherical shape.

The second lens group G2 is composed of a concave meniscus lens L21 having a convex surface facing the object side, and has a negative refractive power as a whole. The second lens group G2 moves toward the image side along the optical axis when focusing from infinity to close range.

The third lens group G3 includes a front lens element G3a, which is a junction lens element composed of a concave meniscus lens L31 having a convex surface facing the object side, a biconvex positive lens L32, and a biconcave negative lens L33, and a biconcave shape. It is composed of a rear lens element G3b which is a junction lens element composed of a negative lens L34 and a biconvex positive lens L35, and has a positive refractive force as a whole. Further, the surface of the biconvex positive lens L35 on the image side has a predetermined aspherical shape.

Subsequently, the specification values of the imaging optical system according to the first embodiment are shown below.

Numerical Example 1
Unit: mm
[Surface data]
Face number rd nd vd PgF
Physical surface ∞ (d0)
1 33.9542 3.3759 1.94595 17.98 0.6544
2 44.5748 4.1307
3 * 38.9630 5.4692 1.55332 71.68 0.5402
4 * -967.9319 0.3493
5 121.8447 0.8000 1.85478 24.80
6 20.1256 10.3690 1.72916 54.67 0.5452
7 -482.9027 1.7197
8 (aperture) ∞ (d8)
9 836.6145 0.8000 1.56384 60.67
10 20.5218 (d10)
11 31.5674 0.8000 1.64769 33.84
12 23.7758 4.7179 1.90043 37.37
13 -39.7321 0.8000 1.59270 35.44
14 18.7021 4.0685
15 -182.9100 0.8000 1.51742 52.15
16 20.4182 5.0178 1.77250 49.50
17 * -110.5563 14.5792
18 ∞ 2.0000 1.51680 64.20
19 ∞ (BF)
Image plane ∞

[Aspherical data]
3 sides 4 sides 17 sides
K 0.00000E + 00 0.00000E + 00 0.00000E + 00
A4 -2.34453E-06 3.09778E-06 7.09747E-06
A6 -5.31720E-09 -7.37705E-09 -1.64875E-08
A8 1.20622E-11 2.61383E-11 3.00160E-10
A10 -2.01173E-14 -5.23565E-14 -2.16479E-12
A12 1.16443E-17 4.15742E-17 6.45973E-15

[Various data]
INF Shooting distance 500mm
Focal length 53.95 52.16
F number 1.46 1.62
Full angle of view 2ω 28.62 25.05
Image height Y 14.20 14.20
Lens total length 74.93 74.93

[Variable interval data]
INF Shooting distance 500mm
d0 ∞ 425.0723
d8 2.7902 8.3091
d10 11.3404 5.8216
BF 1.0000 1.0000

[Lens group data]
Focal length of group origin
G1 1 43.50
G2 9 -37.32
G3 11 42.42
G3a 11 102.19
G3b 15 60.65

FIG. 6 is a lens configuration diagram of the imaging optical system according to the second embodiment of the present invention. The first lens group G1 includes a convex meniscus lens L11 having a convex surface facing the object side, a convex meniscus lens L12 having a convex surface facing the object side, and a concave meniscus lens L13 having a convex surface facing the object side. It is composed of a bonded lens element composed of a lens L14 and has a positive refractive force as a whole. Further, both the side surface of the object and the side surface of the image of the convex meniscus lens L12 having the convex surface facing the object side have a predetermined aspherical shape.

The second lens group G2 is composed of a concave meniscus lens L21 having a convex surface facing the object side, and has a negative refractive power as a whole. The second lens group G2 moves toward the image side along the optical axis when focusing from infinity to close range.

The third lens group G3 includes a front lens element G3a which is a junction lens element composed of a biconvex positive lens L31 and a biconcave negative lens L32, a concave meniscus lens L33 having a convex surface facing the object side, and a biconvex shape. It is composed of the rear lens element G3b, which is a junction lens element composed of the positive lens L34, and has a positive refractive force as a whole. Further, the surface of the biconvex positive lens L34 on the image side has a predetermined aspherical shape.

Subsequently, the specification values of the imaging optical system according to the second embodiment are shown below.

Numerical Example 2
Unit: mm
[Surface data]
Face number rd nd vd PgF
Physical surface ∞ (d0)
1 31.7461 3.0409 1.94595 17.98 0.6544
2 36.4041 9.2788
3 * 29.8814 5.7403 1.55332 71.68 0.5402
4 * 296.9065 0.1500
5 99.7368 0.8000 1.85478 24.80
6 21.7335 8.1252 1.72916 54.67 0.5452
7 -176.0596 1.6175
8 (aperture) ∞ (d8)
9 292.3920 0.8000 1.56384 60.67
10 18.4511 (d10)
11 35.6035 4.5089 1.90043 37.37
12 -30.0393 0.8000 1.59270 35.44
13 20.1730 2.3248
14 489.6780 1.7414 1.58144 40.89
15 25.0294 3.8095 1.88202 37.22
16 * -1141.3008 15.0066
17 ∞ 2.0000 1.51680 64.20
18 ∞ (BF)
Image plane ∞

[Aspherical data]
3 sides 4 sides 16 sides
K 0.00000E + 00 0.00000E + 00 0.00000E + 00
A4 -2.62337E-06 5.78550E-06 2.64412E-06
A6 -2.39470E-09 -2.40920E-09 0.00000E + 00
A8 -1.71717E-12 4.00301E-12 0.00000E + 00
A10 0.00000E + 00 0.00000E + 00 0.00000E + 00
A12 0.00000E + 00 0.00000E + 00 0.00000E + 00

[Various data]
INF Shooting distance 500mm
Focal length 55.60 52.50
F number 1.46 1.59
Full angle of view 2ω 27.60 24.67
Image height Y 14.20 14.20
Lens total length 77.22 77.22

[Variable interval data]
INF Shooting distance 500mm
d0 ∞ 422.7752
d8 2.8323 7.3082
d10 13.6485 9.1726
BF 1.0000 1.0000

[Lens group data]
Focal length of group origin
G1 1 39.12
G2 9 -34.97
G3 11 49.28
G3a 11 127.92
G3b 14 71.78

FIG. 11 is a lens configuration diagram of the imaging optical system according to the third embodiment of the present invention. The first lens group G1 is a junction composed of a convex meniscus lens L11 convex toward the object side, a biconvex positive lens L12, a concave meniscus lens L13 having a convex surface facing the object side, and a biconvex positive lens L14. It is composed of lens elements and has a positive refractive power as a whole. Further, both the side surface of the object and the side surface of the image of the biconvex positive lens L12 have a predetermined aspherical shape.

The second lens group G2 is composed of a concave meniscus lens L21 having a convex surface facing the object side, and has a negative refractive power as a whole. The second lens group G2 moves toward the image side along the optical axis when focusing from infinity to close range.

The third lens group G3 includes a front lens element G3a which is a junction lens element composed of a biconvex positive lens L31 and a biconcave negative lens L32, a biconcave negative lens L33, and a biconvex positive lens L34. It is composed of a rear lens element G3b, which is a bonded lens element, and has a positive refractive power as a whole. Further, the surface of the biconvex positive lens L34 on the image side has a predetermined aspherical shape.

Subsequently, the specification values of the imaging optical system according to the third embodiment are shown below.

Numerical Example 3
Unit: mm
[Surface data]
Face number rd nd vd PgF
Physical surface ∞ (d0)
1 30.5001 3.4252 1.94595 17.98 0.6544
2 39.3278 4.3498
3 * 47.3199 4.6621 1.55332 71.68 0.5402
4 * -438.6045 0.1866
5 128.0112 0.8000 1.85478 24.80
6 19.2529 8.4833 1.72916 54.67 0.5452
7 -1028.0399 2.2577
8 (aperture) ∞ (d8)
9 543.3057 0.8000 1.49700 81.61
10 23.1240 (d10)
11 23.9620 4.6985 1.88300 40.80
12 -41.1807 1.4407 1.59270 35.44
13 17.4302 3.2892
14 -50.6597 0.8000 1.56732 42.84
15 27.8744 6.3475 1.85135 40.10
16 * -79.6899 14.5768
17 ∞ 2.0000 1.51680 64.20
18 ∞ (BF)
Image plane ∞

[Aspherical data]
3 sides 4 sides 16 sides
K 0.00000E + 00 0.00000E + 00 0.00000E + 00
A4 -5.10823E-06 7.46453E-09 1.65086E-05
A6 -2.58579E-09 -1.72093E-09 -1.17051E-08
A8 -6.32835E-12 -1.24073E-12 6.54809E-10
A10 6.08874E-15 -9.07755E-16 -4.09925E-12
A12 7.00989E-18 9.47739E-18 1.62642E-14

[Various data]
INF Shooting distance 500mm
Focal length 53.66 51.93
F number 1.45 1.61
Full angle of view 2ω 28.13 24.65
Image height Y 14.20 14.20
Lens total length 75.43 75.43

[Variable interval data]
INF Shooting distance 500mm
d0 ∞ 424.5741
d8 2.6167 9.8699
d10 13.6918 6.4386
BF 1.0000 1.0000

[Lens group data]
Focal length of group origin
G1 1 48.29
G2 9 -48.62
G3 11 47.27
G3a 11 72.97
G3b 14 101.75

FIG. 16 is a lens configuration diagram of the imaging optical system according to the fourth embodiment of the present invention. The first lens group G1 includes a convex meniscus lens L11 having a convex surface facing the object side, a convex meniscus lens L12 having a convex surface facing the object side, a concave meniscus lens L13 having a convex surface facing the object side, and a convex surface toward the object side. It is composed of a bonded lens element composed of a directed convex meniscus lens L14, and has a positive refractive force as a whole. Further, both the side surface of the object and the side surface of the image of the convex meniscus lens L12 having the convex surface facing the object side have a predetermined aspherical shape.

The second lens group G2 is composed of a concave meniscus lens L21 having a convex surface facing the object side, and has a negative refractive power as a whole. The second lens group G2 moves toward the image side along the optical axis when focusing from infinity to close range.

The third lens group G3 includes a biconvex positive lens L31, a front lens element G3a which is a junction lens element composed of a biconcave negative lens L32, a biconcave negative lens L33, and a biconvex positive lens. It is composed of a rear lens element G3b, which is a junction lens element made of L34, and has a positive refractive power as a whole. Further, the surface of the biconvex positive lens L34 on the image side has a predetermined aspherical shape.

Subsequently, the specification values of the imaging optical system according to the fourth embodiment are shown below.

Numerical Example 4
Unit: mm
[Surface data]
Face number rd nd vd PgF
Physical surface ∞ (d0)
1 39.1045 4.1510 1.94595 17.98 0.6544
2 52.8935 7.9728
3 * 37.1352 5.9807 1.55332 71.68 0.5402
4 * 455.9748 0.3997
5 100.9342 0.8000 1.85478 24.80
6 19.1534 8.6384 1.72916 54.67 0.5452
7 508.7468 6.1662
8 (aperture) ∞ (d8)
9 392.6307 0.8000 1.58313 59.38
10 22.8677 (d10)
11 25.5022 4.9008 1.87070 40.73
12 -32.5774 0.8000 1.62004 36.30
13 19.3851 3.1330
14 -58.5786 0.8000 1.54814 45.82
15 24.1531 4.2049 1.88202 37.22
16 * -95.4165 14.6354
17 ∞ 2.0000 1.51680 64.20
18 ∞ (BF)
Image plane ∞

[Aspherical data]
3 sides 4 sides 16 sides
K 0.00000E + 00 0.00000E + 00 0.00000E + 00
A4 -1.76683E-06 1.56895E-06 1.40862E-05
A6 4.27821E-10 1.08233E-09 3.90724E-09
A8 -9.50302E-12 -1.53454E-11 2.05205E-10
A10 2.18147E-14 5.14904E-14 -2.96973E-13
A12 -1.27338E-17 -5.28304E-17 1.97130E-15

[Various data]
INF Shooting distance 500mm
Focal length 57.61 55.94
F number 1.44 1.66
Full angle of view 2ω 26.61 22.36
Image height Y 14.20 14.20
Lens total length 81.17 81.17

[Variable interval data]
INF Shooting distance 500mm
d0 ∞ 418.8291
d8 0.3013 7.8795
d10 14.4868 6.9086
BF 1.0000 1.0000

[Lens group data]
Focal length of group origin
G1 1 49.65
G2 9 -41.67
G3 11 41.77
G3a 11 78.90
G3b 14 72.84

FIG. 21 is a lens configuration diagram of the imaging optical system according to the fifth embodiment of the present invention. The first lens group G1 includes a convex meniscus lens L11 having a convex surface facing the object side, a convex meniscus lens L12 having a convex surface facing the object side, and a concave meniscus lens L13 having a convex surface facing the object side. It is composed of a bonded lens element composed of a lens L14 and has a positive refractive force as a whole. Further, both the side surface of the object and the side surface of the image of the convex meniscus lens L12 having the convex surface facing the object side have a predetermined aspherical shape.

The second lens group G2 is composed of a concave meniscus lens L21 having a convex surface facing the object side, and has a negative refractive power as a whole. The second lens group G2 moves toward the image side along the optical axis when focusing from infinity to close range.

The third lens group G3 includes a front lens element G3a which is a junction lens element composed of a biconvex positive lens L31 and a biconcave negative lens L32, a biconcave negative lens L33, and a biconvex positive lens L34. It is composed of a rear lens element G3b, which is a bonded lens element, and has a positive refractive power as a whole. Further, the surface of the biconvex positive lens L34 on the image side has a predetermined aspherical shape.

Subsequently, the specification values of the imaging optical system according to the fifth embodiment are shown below.

Numerical Example 5
Unit: mm
[Surface data]
Face number rd nd vd PgF
Physical surface
1 31.4768 3.0034 1.98612 16.48 0.6656
2 36.3209 6.2352
3 * 35.6121 5.1927 1.49710 81.56 0.5383
4 * 258.0773 0.1501
5 77.8695 0.8000 1.85478 24.80
6 20.5208 9.2848 1.72916 54.67 0.5452
7 -252.5848 1.7715
8 (aperture) ∞ (d8)
9 616.0076 0.8000 1.51823 58.96
10 20.9158 (d10)
11 27.0072 4.8499 1.90043 37.37
12 -41.0464 0.8000 1.59270 35.44
13 17.9406 3.3199
14 -49.8639 0.8000 1.51742 52.15
15 25.6210 8.2703 1.77250 49.50
16 * -66.6951 15.1506
17 ∞ 2.0000 1.51680 64.20
18 ∞ (BF)
Image plane ∞

[Aspherical data]
3 sides 4 sides 16 sides
K 0.00000E + 00 0.00000E + 00 0.00000E + 00
A4 -2.89101E-06 3.11510E-06 1.07309E-05
A6 -6.48243E-09 -7.79983E-09 -2.16783E-08
A8 1.20264E-11 3.27149E-11 5.64320E-10
A10 -1.68759E-14 -7.56883E-14 -4.27409E-12
A12 -2.28961E-17 4.42086E-17 1.38220E-14

[Various data]
INF Shooting distance 500mm
Focal length 56.76 54.28
F number 1.46 1.61
Full angle of view 2ω 26.90 23.87
Image height Y 14.20 14.20
Lens total length 79.61 79.61

[Variable interval data]
INF Shooting distance 500mm
d0 ∞ 420.3948
d8 2.6512 8.3761
d10 13.5257 7.8008
BF 1.0000 1.0000

[Lens group data]
Focal length of group origin
G1 1 43.57
G2 9 -41.80
G3 11 50.87
G3a 11 93.98
G3b 14 88.50

FIG. 26 is a lens configuration diagram of the imaging optical system according to the sixth embodiment of the present invention. The first lens group G1 includes a convex meniscus lens L11 having a convex surface facing the object side, a convex meniscus lens L12 having a convex surface facing the object side, and a concave meniscus lens L13 having a convex surface facing the object side. It is composed of a bonded lens element composed of a lens L14 and has a positive refractive force as a whole. Further, both the side surface of the object and the side surface of the image of the convex meniscus lens L12 having the convex surface facing the object side have a predetermined aspherical shape.

The second lens group G2 is composed of a concave meniscus lens L21 having a convex surface facing the object side, and has a negative refractive power as a whole. The second lens group G2 moves toward the image side along the optical axis when focusing from infinity to close range.

The third lens group G3 includes a front lens element G3a, which is a junction lens element composed of a concave meniscus lens L31 having a convex surface facing the object side, a biconvex positive lens L32, and a biconcave negative lens L33, and a biconcave shape. It is composed of a rear lens element G3b which is a junction lens element composed of a negative lens L34 and a biconvex positive lens L35, and has a positive refractive force as a whole. Further, the surface of the biconvex positive lens L35 on the image side has a predetermined aspherical shape.

Subsequently, the specification values of the imaging optical system according to the sixth embodiment are shown below.

Numerical Example 6
Unit: mm
[Surface data]
Face number rd nd vd PgF
Physical surface ∞ (d0)
1 32.0168 2.8947 1.98612 16.48 0.6656
2 36.0145 7.1106
3 * 34.6460 5.4124 1.49710 81.56 0.5383
4 * 202.1427 0.1533
5 74.0623 0.8037 1.85478 24.80
6 21.4917 9.6636 1.72916 54.67 0.5452
7 -208.0971 1.6215
8 (aperture) ∞ (d8)
9 752.3346 0.8000 1.51680 64.20
10 20.5005 (d10)
11 32.8089 0.8000 1.64769 33.84
12 26.8042 5.1066 1.90043 37.37
13 -36.0319 0.8000 1.59270 35.44
14 20.4813 2.5761
15 -124.2339 7.1161 1.51742 52.15
16 28.6442 3.9021 1.77250 49.50
17 * -169.7310 14.7676
18 ∞ 2.0000 1.51680 64.20
19 ∞ (BF)
Image plane ∞

[Aspherical data]
3 sides 4 sides 17 sides
K 0.00000E + 00 0.00000E + 00 0.00000E + 00
A4 -2.59735E-06 3.43490E-06 7.64254E-06
A6 -6.18156E-09 -6.92521E-09 -1.90602E-08
A8 1.32611E-11 3.22294E-11 3.74129E-10
A10 -1.89574E-14 -7.56086E-14 -2.58522E-12
A12 -2.69040E-17 3.89828E-17 7.28668E-15

[Various data]
INF Shooting distance 500mm
Focal length 58.91 55.74
F number 1.46 1.61
Full angle of view 2ω 26.15 23.24
Image height Y 14.20 14.20
Lens total length 82.61 82.61

[Variable interval data]
INF Shooting distance 500mm
d0 ∞ 417.3943
d8 2.7389 8.3003
d10 13.3384 7.7771
BF 1.0000 1.0000

[Lens group data]
Focal length of group origin
G1 1 43.00
G2 9 -40.79
G3 11 54.25
G3a 11 90.85
G3b 15 105.21

FIG. 31 is a lens configuration diagram of the imaging optical system according to the seventh embodiment of the present invention. The first lens group G1 is composed of a convex meniscus lens L11 having a convex surface facing the object side, a biconvex positive lens L12, a concave meniscus lens L13 having a convex surface facing the object side, and a biconvex positive lens L14. It is composed of a bonded lens element and has a positive refractive power as a whole. Further, both the side surface of the object and the side surface of the image of the biconvex positive lens L12 have a predetermined aspherical shape.

The second lens group G2 is composed of a concave meniscus lens L21 having a convex surface facing the object side, and has a negative refractive power as a whole. The second lens group G2 moves toward the image side along the optical axis when focusing from infinity to close range.

The third lens group G3 includes a front lens element G3a, which is a junction lens element composed of a concave meniscus lens L31 having a convex surface facing the object side, a biconvex positive lens L32, and a biconcave negative lens L33, and a biconcave shape. It is composed of a rear lens element G3b which is a junction lens element composed of a negative lens L34 and a biconvex positive lens L35, and has a positive refractive force as a whole. Further, the surface of the biconvex positive lens L35 on the image side has a predetermined aspherical shape.

Subsequently, the specification values of the imaging optical system according to the seventh embodiment are shown below.

Numerical Example 7
Unit: mm
[Surface data]
Face number rd nd vd PgF
Physical surface ∞ (d0)
1 35.2328 3.9226 1.92286 20.88 0.6388
2 48.1184 4.1002
3 * 41.2817 5.5059 1.55332 71.68 0.5402
4 * -619.9853 0.5405
5 144.0641 0.8000 1.85478 24.80
6 22.1541 10.0348 1.72916 54.67 0.5452
7 -298.7277 1.9192
8 (aperture) ∞ (d8)
9 745.2086 0.8000 1.56384 60.67
10 20.4697 (d10)
11 34.2102 0.8000 1.64769 33.84
12 21.8906 4.8419 1.90043 37.37
13 -39.1927 0.8000 1.59270 35.44
14 19.2520 3.5315
15 -209.7439 0.9869 1.51742 52.15
16 22.3314 4.6070 1.77250 49.50
17 * -104.1056 14.5573
18 ∞ 2.0000 1.51680 64.20
19 ∞ (BF)
Image plane ∞
[Aspherical data]
3 sides 4 sides 17 sides
K 0.00000E + 00 0.00000E + 00 0.00000E + 00
A4 -2.48765E-06 3.12633E-06 7.21813E-06
A6 -5.54294E-09 -7.71263E-09 -2.72744E-08
A8 1.15354E-11 2.50878E-11 4.10054E-10
A10 -2.24793E-14 -5.05037E-14 -2.49707E-12
A12 1.84505E-17 4.29791E-17 6.34453E-15

[Various data]
INF Shooting distance 500mm
Focal length 53.70 51.79
F number 1.46 1.62
Full angle of view 2ω 28.54 24.99
Image height Y 14.20 14.20
Lens total length 74.78 74.78

[Variable interval data]
INF Shooting distance 500mm
d0 ∞ 425.2180
d8 2.7965 8.3276
d10 11.2376 5.7064
BF 1.0000 1.0000

[Lens group data]
Focal length of group origin
G1 1 43.45
G2 9 -37.34
G3 11 42.31
G3a 11 99.96
G3b 15 61.60

The following [Conditional Expression Corresponding Value] shows a list of corresponding values of each example corresponding to each conditional expression.

[Conditional expression correspondence value]
Conditional expression 1 Conditional expression 2 Conditional expression 3 Conditional expression 4 (1) Conditional expression 4 (2) Conditional expression 5
Examples fG1 / f fG3 / f νd_G2 fG1n / fG1 fG1n / fG1 G3ar / G3af
1 0.81 0.79 60.67 1.6 3.0 0.59
2 0.70 0.89 60.67 1.5 3.7 0.57
3 0.90 0.88 81.61 1.6 2.5 0.73
4 0.86 0.73 59.38 1.5 2.8 0.76
5 0.77 0.90 58.96 1.9 3.0 0.66
6 0.73 0.92 64.20 1.9 2.6 0.62
7 0.81 0.79 60.67 1.6 2.9 0.56

Conditional expression 6 Conditional expression 7 Conditional expression 8 Conditional expression 9
Example G3acement ΔPgF_Avg-(1 / R_SG3) * ((1 / nd'_SG3)-(1 / nd_SG3) LG2R1 / fG1G2
1 -1.4 0.0182 -0.0199 0.413
2 -1.9 0.0182 -0.0184 0.415
3 -1.3 0.0182 -0.0214 0.367
4 -1.8 0.0182 -0.0197 0.448
5 -1.4 0.0264 -0.0207 0.378
6 -1.6 0.0264 -0.0182 0.379
7 -1.4 0.0148 -0.0193 0.419

As is clear from the various aberration diagrams of each embodiment, according to the present invention, the angle of view is 20 to 30 °, which is a so-called medium telephoto angle of view, and the FNO is about 1.4 in a large-diameter inner focus type. It is suitable for a telephoto lens, and at the same time, the focus group can be made smaller and lighter, and at the same time, the entire optical system can be made smaller and lighter, and it is possible to provide an imaging optical system having good imaging performance.

G1 1st lens group G2 2nd lens group G3 3rd lens group G3a Front lens element of 3rd lens group G3b Rear lens element of 3rd lens group S Aperture aperture F In-camera filter I Image plane

Claims (9)

From the object side to the image side, it is composed of a first lens group G1 having a positive power, an aperture stop S, a second lens group G2 having a negative power, and a third lens group G3 having a positive power.
At the time of focusing, the first lens group G1, the aperture stop S, and the third lens group G3 are fixed to the image plane, and only the second lens group G2 moves in the optical axis direction.
The second lens group G2 is composed of one lens element.
All the lens elements having a negative power in the first lens group G1 and the third lens group G3 are joined to the lens elements having a positive power.
An imaging optical system characterized in that all the lens elements in the first lens group G1 and the third lens group G3 have positive power and satisfy the following conditional expression.
(1) 0.65 <fG1 / f <1.00
however,
fG1: Focal length of the first lens group G1 f: Focal length of the optical system in the infinity state. The imaging optical system according to claim 1, wherein the third lens group G3 satisfies the following conditional expression.
(2) 0.60 <fG3 / f <1.00
however,
fG3: The focal length of the third lens group G3. The imaging optical system according to claim 1 or 2, wherein the lens element of the second lens group G2 satisfies the following conditional expression.
(3) 50.00 <νd_G2
however,
νd_G2: Abbe number with respect to the d line of the lens element of the second lens group G2. The imaging optical system according to any one of claims 1 to 3, wherein the first lens group G1 has two or more lens elements satisfying the following conditional expression.
(4) 1.2 <fG1n / fG1 <4.0
however,
fG1n: The focal length of the nth lens element from the object side in the first lens group G1. The third lens group G3 is composed of two lens elements, a front lens element G3a and a rear lens element G3b, and the front lens element G3a has a bonding surface and satisfies the following conditional expression. The imaging optical system according to any one of 1 to 4.
(5) 0.40 <G3ar / G3af <0.90
(6) -2.4 <G3acement <-0.9
however,
G3ar: Of the lens elements constituting the third lens group G3, the radius of curvature of the air interface on the image side of the front lens element G3a G3af: Among the lens elements constituting the third lens group G3, the front lens element Radius of curvature of the air interface on the object side of G3a G3acement: Of the lens elements constituting the third lens group G3, the radius of curvature of the first joint surface counted from the image side of the front lens element G3a is the focal length of the entire system. Let it be the inverse value normalized by. The imaging optical system according to any one of claims 1 to 5, wherein the first lens group G1 has an aspherical surface. The imaging optical system according to any one of claims 1 to 6, wherein the average value of the anomalous dispersibility of the lens element having a positive power in the first lens group G1 satisfies the following conditional expression. ..
(7) 0.0100 <ΔPgF_Avg
however,
ΔPgF_Avg: The average value of the anomalous dispersion of the g-line and the F-line of the lens element having a positive power in the first lens group G1 and the g-line of the lens element having a positive power in the first lens group G1. The anomalous dispersibility of the F line is ΔPgF_n = PgF_n-0.6483 + 0.0018 × νd_n
ΔPgF_n: Anomalous dispersibility of g-line and F-line of the lens element having the nth positive power from the object side of the first lens group G1 PgF_n: having the nth positive power from the object side of the first lens group G1. Partial dispersion ratio of g-line and F-line of the lens element νd_n: The number of d-lines of the lens element having the nth positive power from the object side of the first lens group G1. The imaging optical system according to any one of claims 1 to 7, wherein the third lens group G3 has a concave surface SG3 on the image side satisfying the following conditional expression.
(8)-(1 / R_SG3) x ((1 / nd'_SG3)-(1 / nd_SG3)) <-0.0150
however,
R_SG3: Radius of curvature of the surface SG3 nd'_SG3: Refractive index on the image side of the surface SG3 nd_SG3: Refractive index on the object side of the surface SG3. The imaging optical system according to any one of claims 1 to 8, wherein the imaging optical system satisfies the following conditional expression.
(9) 0.300 <LG2R1 / fG1G2 <0.460
however,
fG1G2: Composite focal length of the first lens group G1 and the second lens group G2 LG2R1: From the image side principal point position of the composite system of the first lens group G1 and the second lens group G2 to the object side surface of the second lens group G2. The distance on the optical axis.

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