JP7531888B2 - Large aperture zoom lens - Google Patents

Description

The present invention relates to an imaging optical system used in imaging devices such as digital cameras and video cameras.

In recent years, imaging devices such as digital cameras and video cameras have become widespread.

Among these, those that have a mirror between the imaging optical system and the image sensor to guide light to the viewfinder optical system are widely known. However, in recent years, imaging devices have been developed that remove the mirror portion and shorten the distance between the imaging optical system and the image sensor.

Among these, imaging devices that use large image sensors but are miniaturized are becoming more common. In order to accommodate the miniaturization of imaging devices, there is a demand for miniaturization of the imaging optical system as well.

In addition, as image sensor pixels become smaller, higher performance is required of the imaging optical system.

In addition, quick focus operation is required to avoid missing photo opportunities.

There is also a demand for bright imaging optics with small F-numbers. Using a bright optics makes it possible to shoot at short shutter speeds even in dark places. It also makes it possible to take advantage of shallow depth of field.

On the other hand, with a large image sensor, when the F-number becomes small, the height of the light rays passing through the imaging optical system becomes large, and the diameter of the focus group becomes large, which increases the weight of the focus group. For this reason, the layout and configuration to reduce the weight of the focus group becomes important.

JP 2016-001349 A JP 2018-197774 A

It is relatively easy to achieve a large aperture ratio with a positive-lead zoom lens while also making the entire system compact. In order to make the focus group small and lightweight and effectively correct various aberrations, it is important to select the focus lens group and appropriately arrange the refractive power of each group.

Patent document 1 discloses a zoom lens with a lightweight focus group.

However, the optical system described above has the problem that the F-number at the telephoto end is about 5.6, which is dark.

Patent document 2 discloses a bright zoom lens with an F-number of about 2.8 at the telephoto end.

However, the optical system described above has a problem in that it has a large number of focus groups and is therefore heavy. If the focus group is heavy, not only does it slow down the speed, but the actuator for operating it also becomes larger, making it unsuitable for making it smaller and lighter.

The present invention is based on a positive-lead type zoom lens and addresses the above-mentioned issues, and aims to provide a small, large-aperture zoom lens that is suitable for use in digital cameras and video cameras, has excellent correction for aberrations, and is capable of rapid focusing.

The large-aperture zoom lens of the present invention comprises, in order from the object side, a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, an aperture stop S, a third lens group L3 having positive refractive power, a fourth lens group L4 having negative refractive power, and a fifth lens group L5 having positive refractive power, wherein the spacing between the lens groups changes during zooming, the fifth lens group L5 is stationary, and focusing is performed by the fourth lens group L4 moving in the optical axis direction, and wherein the following conditional expression is satisfied:
(1) 0.90<f1/fT<2.25
(2) 2.90<|f1/f2|<6.00
(3) 13.0<LTw*FnoT/Ymax<20.0
(8) 1.00<|βT5^2*(1-βT4^2)|<3.70
Where:
fT: focal length of the entire system at infinity at the telephoto end f1: focal length of the first lens unit L1 f2: focal length of the second lens unit L2 LTw: total optical length at the wide-angle end FnoT: F-number at infinity at the telephoto end Ymax: maximum image height
βT4: lateral magnification at infinity at the telephoto end of the fourth lens unit L4
βT5: lateral magnification at infinity at the telephoto end of the fifth lens unit L5

The large aperture zoom lens according to the second aspect of the invention is characterized in that it further satisfies the following conditional expression:
(4) 0.35<|f3/f4|<0.74
Where:
f3: focal length of the third lens group L3 f4: focal length of the fourth lens group L4

The large aperture zoom lens of the third aspect of the invention is characterized in that it further satisfies the following conditional expression:
(5) 0.011<ΔPgF3p_ave
Where:
ΔPgF3p_ave: average value of anomalous dispersion of the positive lenses included in the third lens unit L3, ΔPgF3pi=PgF3pi-0.64833+0.00180×νd3pi
ΔPgF3pi: anomalous dispersion of the i-th positive lens included in the third lens unit L3 PgF3pi: partial dispersion ratio between the g-line and the F-line of the i-th positive lens included in the third lens unit L3 νd3pi: Abbe number of the i-th positive lens included in the third lens unit L3

A large aperture zoom lens according to a fourth aspect of the present invention is characterized in that the following condition is further satisfied:
(6) 0.55<Ymax/BF
Where:
BF: Back focus

A large aperture zoom lens according to a fifth aspect of the present invention is characterized in that the following condition is further satisfied:
(7) 0.45<|f4/fT|<1.10
Where:
f4: focal length of the fourth lens unit L4

The large aperture zoom lens of the sixth aspect of the invention is further characterized in that the fourth lens unit L4 is made up of one negative lens.

A seventh aspect of the present invention is a large-aperture zoom lens characterized by further satisfying the following conditional expression:
(9) 25.8<νd2n−νd2p
Where:
νd2n: average Abbe number of negative lenses included in the second lens unit L2 νd2p: average Abbe number of positive lenses included in the second lens unit L2

In addition, the large-aperture zoom lens of the eighth aspect of the invention is characterized in that the first lens unit L1 further includes one negative lens and one positive lens, and satisfies the following conditional expression:
(10) 1.70<Nd1
(11) 31.0<νd1p−νd1n
Where:
Nd1: average value of refractive index of lenses included in the first lens unit L1 νd1p: average value of Abbe number of positive lenses included in the first lens unit L1 νd1n: Abbe number of negative lenses included in the first lens unit L1

The present invention provides a small, large-aperture zoom lens for digital cameras and camcorders that is well-corrected for aberrations and allows for rapid focus drive.

1 is a lens configuration diagram of a large-aperture zoom lens according to a first embodiment of the present invention. FIG. 11 is a lens configuration diagram of a large-aperture zoom lens according to a second embodiment of the present invention. FIG. 11 is a lens configuration diagram of a large-aperture zoom lens according to a third embodiment of the present invention. FIG. 11 is a lens configuration diagram of a large-aperture zoom lens according to a fourth embodiment of the present invention. 4A to 4C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 1 at the wide-angle end in the infinity state. 4 is a longitudinal aberration diagram of the large-aperture zoom lens of Example 1 at a shooting distance of 659 mm at the wide-angle end. 4 is a longitudinal aberration diagram of the large-aperture zoom lens of Example 1 at infinity in the intermediate zoom range. FIG. 4A to 4C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 1 at a shooting distance of 980 mm in the intermediate zoom range. 4 is a longitudinal aberration diagram of the large-aperture zoom lens of Example 1 at the telephoto end in the infinity state. FIG. 4 is a longitudinal aberration diagram of the large-aperture zoom lens of Example 1 at a telephoto end object distance of 1,441 mm. 4A to 4C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 1 at the wide-angle end and at infinity. 4A to 4C are lateral aberration diagrams of the large-aperture zoom lens of Example 1 at a shooting distance of 659 mm at the wide-angle end. 4A to 4C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 1 at infinity in the intermediate zoom range. 4A to 4C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 1 at a shooting distance of 980 mm in the intermediate zoom range. 4A to 4C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 1 at the telephoto end in the infinity state. 4A to 4C are lateral aberration diagrams of the large-aperture zoom lens of Example 1 at a telephoto end object distance of 1,441 mm. 11A and 11B are longitudinal aberration diagrams of the large-aperture zoom lens of Example 2 at the wide-angle end and at infinity. 11A to 11C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 2 at a shooting distance of 672 mm at the wide-angle end. 13A and 13B are longitudinal aberration diagrams of the large-aperture zoom lens of Example 2 at infinity in the intermediate zoom range. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 2 at a shooting distance of 992 mm in the intermediate zoom range. 11A and 11B are longitudinal aberration diagrams of the large-aperture zoom lens of Example 2 at the telephoto end in the infinity state. 11A to 11C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 2 at a telephoto end object distance of 1,439 mm. 11A and 11B are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 2 at the wide-angle end and at infinity. 11A to 11C are lateral aberration diagrams of the large-aperture zoom lens of Example 2 at a shooting distance of 672 mm at the wide-angle end. 11A and 11B are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 2 at infinity in the intermediate zoom range. 13A to 13C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 2 at a shooting distance of 992 mm in the intermediate zoom range. 11A and 11B are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 2 at the telephoto end in the infinity state. 11A to 11C are lateral aberration diagrams of the large-aperture zoom lens of Example 2 at a telephoto end object distance of 1,439 mm. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 3 at the wide-angle end and at infinity. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 3 at a shooting distance of 663 mm at the wide-angle end. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 3 at infinity in the intermediate zoom range. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 3 at a shooting distance of 985 mm in the intermediate zoom range. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 3 at the telephoto end in the infinity state. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 3 at a telephoto end object distance of 1,428 mm. 13A to 13C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 3 at the wide-angle end and at infinity. 13A to 13C are lateral aberration diagrams of the large-aperture zoom lens of Example 3 at a shooting distance of 663 mm at the wide-angle end. 13A to 13C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 3 at infinity in the intermediate zoom range. 13A to 13C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 3 at a shooting distance of 985 mm in the intermediate zoom range. 13A to 13C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 3 at the telephoto end in the infinity state. 13A to 13C are lateral aberration diagrams of the large-aperture zoom lens of Example 3 at a telephoto end object distance of 1,428 mm. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 4 at the wide-angle end and at infinity. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 4 at a shooting distance of 453 mm at the wide-angle end. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 4 at infinity in the intermediate zoom range. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 4 at a shooting distance of 677 mm in the intermediate zoom range. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 4 at the telephoto end in the infinity state. 13A to 13C are longitudinal aberration diagrams of the large-aperture zoom lens of Example 4 at a telephoto end object distance of 1037 mm. 13A to 13C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 4 at the wide-angle end and at infinity. 13A to 13C are lateral aberration diagrams of the large-aperture zoom lens of Example 4 at a shooting distance of 453 mm at the wide-angle end. 13A to 13C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 4 at infinity in the intermediate zoom range. 13A to 13C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 4 at a shooting distance of 677 mm in the intermediate zoom range. 13A to 13C are diagrams illustrating lateral aberration of the large-aperture zoom lens of Example 4 at the telephoto end in the infinity state. 13A to 13C are lateral aberration diagrams of the large-aperture zoom lens of Example 4 at a telephoto end shooting distance of 1037 mm.

The large-aperture zoom lens of the present invention comprises, in order from the object side, a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, an aperture stop S, a third lens group L3 having positive refractive power, a fourth lens group L4 having negative refractive power, and a fifth lens group L5 having positive refractive power, wherein the spacing between the lens groups changes during zooming, the fifth lens group L5 is stationary, and focusing is performed by the fourth lens group L4 moving in the optical axis direction, and wherein the following conditional expression is satisfied:
(1) 0.90<f1/fT<2.25
(2) 2.90<|f1/f2|<6.00
(3) 13.0<LTw*FnoT/Ymax<20.0
Where:
fT: focal length of the entire system at infinity at the telephoto end f1: focal length of the first lens unit L1 f2: focal length of the second lens unit L2 LTw: total optical length at the wide-angle end FnoT: F-number at infinity at the telephoto end Ymax: maximum image height

Condition (1) defines the ratio of the focal length of the first lens unit L1 to the focal length of the entire system at the telephoto end, allowing for both compactness and correction of various aberrations.

When the upper limit of conditional expression (1) is exceeded and the refractive power of the first lens group L1 becomes weak, the light beam convergence effect of the first lens group L1 becomes small, so the height of the light beam incident on the second lens group L2 becomes large, resulting in an increase in the size of the optical system.

When the lower limit of conditional expression (1) is exceeded and the refractive power of the first lens unit L1 becomes strong, it becomes difficult to suppress the astigmatism that occurs in the first lens unit L1.

To further ensure the effects of the present invention, it is preferable to set the upper limit of conditional expression (1) to 2.05 and the lower limit to 1.05.

Conditional expression (2) defines the ratio of the focal lengths of the first lens group L1 and the second lens group L2, thereby achieving both compactness and correction of various aberrations.

When the upper limit of conditional expression (2) is exceeded and the refractive power of the first lens group L1 becomes weak, the height of the light beam incident on the second lens group L2 increases as described above, leading to an increase in the size of the optical system. Alternatively, when the refractive power of the second lens group L2 becomes strong, it becomes difficult to suppress the coma aberration at the telephoto end and the astigmatism at the wide-angle end that occur in the second lens group L2.

When the lower limit of conditional expression (2) is exceeded and the refractive power of the first lens unit L1 becomes too strong, it becomes difficult to suppress the astigmatism that occurs in the first lens unit L1 as described above. Alternatively, when the refractive power of the second lens unit L2 becomes too weak, the amount of movement of the second lens unit L2 during zooming becomes large, leading to an increase in the overall length.

To further ensure the effects of the present invention, it is preferable to set the upper limit of conditional expression (2) to 5.40 and the lower limit to 3.40.

Conditional formula (3) defines the ratio of the total optical length at the wide-angle end to the F-number at the telephoto end and the maximum image height, thereby achieving both compactness and correction of various aberrations. Here, the total optical length is the distance on the optical axis from the surface closest to the object to the image plane.

In general, the smaller the F-number of an optical system, the higher the axial rays passing through it. Also, the higher the maximum image height, the higher the off-axial rays passing through the group closest to the object side or closest to the image plane side. This corresponds to the FnoT/Ymax component in conditional formula (3) becoming smaller. In order to correct the various aberrations in such a situation, it is effective to increase the overall length of the optical system and make the incident rays on each surface within the optical system gentler, but to achieve this while also making the optical system more compact, it is necessary to set the overall length appropriately according to the F-number at the telephoto end and the maximum image height.

If the upper limit of conditional expression (3) is exceeded and the total optical length at the wide-angle end becomes large relative to the ratio of the F-number at the telephoto end to the maximum image height, it becomes easier to suppress the various aberrations that occur throughout the entire system, but the total length of the optical system becomes large. Alternatively, the F-number at the telephoto end becomes large, making it difficult to achieve a bright optical system.

When the lower limit of conditional expression (3) is exceeded and the total optical length at the wide-angle end becomes small relative to the ratio of the F-number at the telephoto end to the maximum image height, the total length is kept small, but the bending of light rays within the optical system becomes greater, increasing the aberrations that occur in each group, making it difficult to satisfactorily correct fluctuations such as astigmatism during zooming and spherical aberration and coma at the telephoto end.

To further ensure the effects of the present invention, it is preferable to set the upper limit of conditional expression (3) to 19.0 and the lower limit to 14.0.

By placing the aperture stop S between the second lens group L2 and the third lens group L3, the light ray height can be reduced, which is advantageous for radial miniaturization. In addition, the aperture stop S is preferably placed on the leading surface of the third lens group L3 and moves together with it, which simplifies the mechanism and makes it easier to miniaturize.

By keeping the fifth lens group L5 fixed during zooming, it is possible to provide a dustproof mechanism and a drip-proof mechanism without complicating the mechanism.

The large aperture zoom lens of the present invention is further characterized by satisfying the following conditional expression:
(4) 0.35<|f3/f4|<0.74
Where:
f3: focal length of the third lens group L3 f4: focal length of the fourth lens group L4

Conditional expression (4) stipulates the ratio of the focal lengths of the third lens group L3 and the fourth lens group L4, thereby achieving correction of various aberrations.

If the upper limit of conditional expression (4) is exceeded and the refractive power of the third lens group L3 becomes weak, the convergence of the light rays emerging from the third lens group L3 becomes weak, and the diameter of the fourth lens group L4 becomes large, making it difficult to make the focus group small and lightweight. Or, if the refractive power of the fourth lens group L4 becomes strong, it becomes difficult to correct astigmatism. In addition, the sensitivity of the fourth lens group to decentering increases, which is undesirable.

When the lower limit of conditional expression (4) is exceeded and the refractive power of the third lens group L3 becomes strong, it becomes difficult to effectively correct spherical aberration and coma aberration at the telephoto end. Alternatively, when the refractive power of the fourth lens group L4 becomes weak, the moving distance of the fourth lens group L4 during focusing becomes large, making it difficult to reduce the overall length of the optical system or increasing the minimum shooting distance.

To further ensure the effects of the present invention, it is preferable to set the upper limit of conditional expression (4) to 0.68 and the lower limit to 0.39.

The large aperture zoom lens of the present invention is further characterized by satisfying the following conditional expression:
(5) 0.011<ΔPgF3p_ave
Where:
ΔPgF3p_ave: average value of anomalous dispersion of the positive lenses included in the third lens unit L3, ΔPgF3pi=PgF3pi-0.64833+0.00180×νd3pi
ΔPgF3pi: anomalous dispersion of the i-th positive lens included in the third lens unit L3 PgF3pi: partial dispersion ratio between the g-line and the F-line of the i-th positive lens included in the third lens unit L3 νd3pi: Abbe number of the i-th positive lens included in the third lens unit L3

Conditional expression (5) specifies the anomalous dispersion of the positive lens included in the third lens group L3, thereby appropriately correcting axial chromatic aberration and lateral chromatic aberration.

When the lower limit of conditional expression (5) is exceeded and the anomalous dispersion of the positive lens in the third lens unit L3 becomes small, the correction of the secondary spectrum becomes insufficient, making it difficult to suppress fluctuations in axial chromatic aberration and lateral chromatic aberration during zooming.

To further ensure the effects of the present invention, it is preferable to set the lower limit of conditional expression (5) to 0.015.

The large aperture zoom lens of the present invention is further characterized by satisfying the following conditional expression:
(6) 0.55<Ymax/BF
Where:
BF: Back focus

Conditional formula (6) specifies the ratio of maximum image height to back focus. Here, back focus is the air-equivalent length on the optical axis from the fifth lens group closest to the image plane to the image plane. By setting the back focus appropriately, it is possible to make the entire system compact.

If the lower limit of conditional expression (6) is exceeded and the back focus becomes large, the overall length becomes large, which is undesirable.

To further ensure the effects of the present invention, it is preferable to set the lower limit of conditional expression (6) to 0.60.

The large aperture zoom lens of the present invention is further characterized by satisfying the following conditional expression:
(7) 0.45<|f4/fT|<1.10
Where:
f4: focal length of the fourth lens unit L4

Conditional formula (7) defines the ratio of the focal length of the fourth lens unit L4 to the focal length of the entire system at the telephoto end, allowing for both compactness and correction of various aberrations.

When the upper limit of conditional expression (7) is exceeded and the refractive power of the fourth lens group L4 becomes weak, the movement distance of the fourth lens group L4 during focusing becomes large, making it difficult to reduce the overall length of the optical system.

When the lower limit of conditional expression (7) is exceeded and the refractive power of the fourth lens unit L4 becomes strong, it becomes difficult to suppress the astigmatism generated in the fourth lens unit L4, and the aberration fluctuation during focusing becomes large. In addition, the amount of aberration fluctuation when the fourth lens unit L4 is decentered also becomes large, which is undesirable.

To further ensure the effects of the present invention, it is preferable to set the upper limit of conditional expression (7) to 0.95 and the lower limit to 0.57.

The large aperture zoom lens of the present invention is further characterized by satisfying the following conditional expression:
(8) 1.00<|βT5^2*(1-βT4^2)|<3.70
Where:
βT4: lateral magnification at infinity at the telephoto end of the fourth lens unit L4 βT5: lateral magnification at infinity at the telephoto end of the fifth lens unit L5

Condition (8) defines the image surface sensitivity of the fourth lens unit L4.

When the upper limit of conditional expression (8) is exceeded and the absolute value of the image plane sensitivity becomes large, the amount of image plane fluctuation relative to the amount of movement of the fourth lens group L4 becomes large, making focus control difficult. Also, it becomes difficult to suppress the decentering sensitivity of the fourth lens group L4.

When the lower limit of conditional expression (8) is exceeded and the absolute value of the image plane sensitivity becomes small, the amount of image plane fluctuation relative to the amount of movement of the fourth lens group L4 becomes small, so the amount of movement of the fourth lens group L4 during focusing increases, making it difficult to reduce the size. Or, it becomes difficult to reduce the minimum shooting distance.

To further ensure the effects of the present invention, it is preferable to set the upper limit of conditional expression (8) to 3.40 and the lower limit to 1.40.

The large aperture zoom lens of the present invention is further characterized in that the fourth lens group L4 is composed of one negative lens.

By constructing the fourth lens group L4 from a single lens, it is possible to reduce weight and enable quick operation during focusing.

The large aperture zoom lens of the present invention is further characterized by satisfying the following conditional expression:
(9) 25.8<νd2n−νd2p
Where:
νd2n: average Abbe number of negative lenses included in the second lens unit L2 νd2p: average Abbe number of positive lenses included in the second lens unit L2

Conditional formula (9) specifies the difference between the average Abbe number of the negative lenses included in the second lens group L2 and the average Abbe number of the positive lenses, thereby appropriately correcting axial chromatic aberration and lateral chromatic aberration. Since the second lens group L2 is responsible for a large magnification change in the optical system, suppressing the chromatic aberration generated in the second lens group L2 makes it possible to effectively suppress the fluctuation of chromatic aberration during zooming.

In order to achieve achromatism in the second lens group L2, it is effective to increase the difference in Abbe number between the positive lens and the negative lens used in the second lens group L2. Alternatively, achromatism can be achieved by increasing the refractive power of the positive or negative lens used in the second lens group L2, but this is not preferable because it increases astigmatism at the wide-angle end and coma at the telephoto end.

If the lower limit of conditional expression (9) is exceeded and the difference in the average Abbe number between the negative lens and the positive lens in the second lens unit L2 becomes small, the correction of axial chromatic aberration and lateral chromatic aberration in the second lens unit L2 becomes insufficient, and the fluctuation of chromatic aberration due to zooming becomes large, which is undesirable.

To further ensure the effects of the present invention, it is preferable to set the lower limit of conditional expression (9) to 27.0.

In addition, the large aperture zoom lens of the present invention is characterized in that the first lens unit L1 includes one negative lens and one positive lens, and satisfies the following conditional expression:
(10) 1.70<Nd1
(11) 31.0<νd1p−νd1n
Where:
Nd1: average value of refractive index of lenses included in the first lens unit L1 νd1p: average value of Abbe number of positive lenses included in the first lens unit L1 νd1n: Abbe number of negative lenses included in the first lens unit L1

In the first lens group L1, there is a large fluctuation in spherical aberration, coma, and distortion during zooming. In order to keep these aberrations small throughout the entire zoom range, it is effective to use a lens with a high refractive index and a gentle curvature. In addition, by making the difference in Abbe numbers between the negative and positive lenses large and performing achromatism in the first lens group L1, it is possible to keep axial chromatic aberration and lateral chromatic aberration small throughout the entire zoom range.

When the lower limit of conditional expression (10) is exceeded and the average refractive index of the lenses used in the first lens group L1 becomes small, the curvature of each surface becomes large, making it difficult to correct astigmatism and distortion.

To further ensure the effects of the present invention, it is preferable to set the lower limit of conditional expression (10) to 1.741.73.

If the lower limit of conditional expression (11) is exceeded and the difference between the average Abbe number of the positive lenses in the first lens group L1 and the Abbe number of the negative lenses becomes small, the achromatism in the first lens group L1 becomes insufficient, making it difficult to correct lateral chromatic aberration in particular.

To further ensure the effects of the present invention, it is preferable to set the lower limit of conditional expression (11) to 33.0.

Next, we will explain the lens configuration of an embodiment of the large aperture zoom lens of the present invention. In the following explanation, the lens configuration will be described in order from the object side to the image side.

Figure 1 is a lens configuration diagram of a large aperture zoom lens according to the first embodiment of the present invention.

Example 1 is composed of, in order from the object side, a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, an aperture stop S, a third lens group L3 having positive refractive power, a fourth lens group L4 having negative refractive power, and a fifth lens group L5 having positive refractive power. When changing magnification from the wide-angle end to the telephoto end, the distance between the first lens group L1 and the second lens group L2 becomes larger, the distance between the second lens group L2 and the third lens group L3 becomes smaller, the distance between the third lens group L3 and the fourth lens group L4 becomes larger, the distance between the fourth lens group L4 and the fifth lens group L5 becomes larger, and the fifth lens group L5 is stationary. When focusing, the fourth lens group L4 moves in the optical axis direction.

The first lens group L1 consists of, from the object side, a cemented lens made of a biconcave lens and a biconvex lens, and a positive meniscus lens with its convex surface facing the object side.

The second lens group L2 consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a biconcave lens, a biconvex lens, and a negative meniscus lens with a convex surface facing the image surface side.

The third lens group L3 consists of, in order from the object side, a biconvex lens, a cemented lens consisting of a biconcave lens and a biconvex lens, a negative meniscus lens with its convex surface facing the image side, a positive meniscus lens with its convex surface facing the object side, and a biconvex lens.

The fourth lens group L4 consists of a negative meniscus lens with its convex surface facing the object side.

The fifth lens group L5 consists of a positive meniscus lens with its convex surface facing the image surface.

Figure 2 is a lens configuration diagram of a large aperture zoom lens according to the second embodiment of the present invention.

Example 2 is composed of, in order from the object side, a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, an aperture stop S, a third lens group L3 having positive refractive power, a fourth lens group L4 having negative refractive power, and a fifth lens group L5 having positive refractive power. When changing magnification from the wide-angle end to the telephoto end, the distance between the first lens group L1 and the second lens group L2 becomes larger, the distance between the second lens group L2 and the third lens group L3 becomes smaller, the distance between the third lens group L3 and the fourth lens group L4 becomes larger, the distance between the fourth lens group L4 and the fifth lens group L5 becomes larger, and the fifth lens group L5 is stationary. When focusing, the fourth lens group L4 moves in the optical axis direction.

The first lens group L1 consists of, in order from the object side, a cemented lens of a negative meniscus lens with a convex surface facing the object side and a biconvex lens, and a positive meniscus lens with a convex surface facing the object side.

The second lens group L2 consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a cemented lens consisting of a biconcave lens and a biconvex lens, and a negative meniscus lens with a convex surface facing the image surface side.

The third lens group L3 consists of, in order from the object side, a biconvex lens, a cemented lens of a negative meniscus lens with its convex surface facing the object side and a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, and a biconvex lens.

The fourth lens group L4 consists of a negative meniscus lens with its convex surface facing the object side.

The fifth lens group L5 consists of a positive meniscus lens with its convex surface facing the image surface.

Figure 3 is a diagram showing the lens configuration of a large aperture zoom lens according to a third embodiment of the present invention.

Example 3 is composed of, in order from the object side, a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, an aperture stop S, a third lens group L3 having positive refractive power, a fourth lens group L4 having negative refractive power, and a fifth lens group L5 having positive refractive power. When changing magnification from the wide-angle end to the telephoto end, the distance between the first lens group L1 and the second lens group L2 becomes larger, the distance between the second lens group L2 and the third lens group L3 becomes smaller, the distance between the third lens group L3 and the fourth lens group L4 becomes larger, the distance between the fourth lens group L4 and the fifth lens group L5 becomes larger, and the fifth lens group L5 is stationary. When focusing, the fourth lens group L4 moves in the optical axis direction.

The first lens group L1 consists of, in order from the object side, a cemented lens of a negative meniscus lens with a convex surface facing the object side and a biconvex lens, and a positive meniscus lens with a convex surface facing the object side.

The second lens group L2 consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a cemented lens of a biconcave lens and a positive meniscus lens with a convex surface facing the object side, a negative meniscus lens with a convex surface facing the image side, and a positive meniscus lens with a convex surface facing the image side.

The third lens group L3 consists of, in order from the object side, a biconvex lens, a negative meniscus lens with its convex surface facing the object side, a biconvex lens, a cemented lens consisting of a negative meniscus lens with its convex surface facing the object side and a biconvex lens, and a biconvex lens.

The fourth lens group L4 consists of a negative meniscus lens with its convex surface facing the object side.

The fifth lens group L5 consists of a biconvex lens and a biconcave lens.

Figure 4 is a lens configuration diagram of a large aperture zoom lens according to the fourth embodiment of the present invention.

Example 4 is composed of, in order from the object side, a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, an aperture stop S, a third lens group L3 having positive refractive power, a fourth lens group L4 having negative refractive power, and a fifth lens group L5 having positive refractive power. When changing magnification from the wide-angle end to the telephoto end, the distance between the first lens group L1 and the second lens group L2 becomes larger, the distance between the second lens group L2 and the third lens group L3 becomes smaller, the distance between the third lens group L3 and the fourth lens group L4 becomes larger, the distance between the fourth lens group L4 and the fifth lens group L5 becomes larger, and the fifth lens group L5 is stationary. When focusing, the fourth lens group L4 moves in the optical axis direction.

The first lens group L1 consists of, in order from the object side, a cemented lens of a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens with a convex surface facing the object side, and a positive meniscus lens with a convex surface facing the object side.

The second lens group L2 consists of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a cemented lens consisting of a biconcave lens and a biconvex lens, and a negative meniscus lens with a convex surface facing the image surface side.

The third lens group L3 consists of, in order from the object side, a biconvex lens, a cemented lens of a negative meniscus lens with its convex surface facing the object side and a positive meniscus lens with its convex surface facing the object side, a cemented lens of a biconcave lens and a biconvex lens, and a biconvex lens.

The fourth lens group L4 consists of a negative meniscus lens with its convex surface facing the object side.

The fifth lens group L5 consists of a biconvex lens.

Next, we will explain numerical examples of each embodiment of the large aperture zoom lens according to the present invention.

In [Surface Data], the surface number is the lens surface or aperture stop number counted from the object side, r is the radius of curvature of each surface, d is the spacing between each surface, nd is the refractive index for the d line (wavelength 587.56 nm), vd is the Abbe number for the d line, and ΔPgF is anomalous dispersion.

An asterisk (*) next to a surface number indicates that the lens surface is aspheric. Also, BF stands for back focus.

The (Aperture) next to a surface number indicates that an aperture stop is located at that position. The radius of curvature for the plane or aperture stop is marked ∞ (infinity).

[Aspheric Data] shows the coefficient values that give the aspheric shape of the lens surfaces marked with an * in [Surface Data]. The shape of the aspheric surface is expressed by the following formula, where y is the displacement from the optical axis in a direction perpendicular to the optical axis, z is the displacement (sag) from the intersection of the aspheric surface and the optical axis in the direction of the optical axis, r is the radius of curvature of the reference sphere, K is the Conic coefficient, and A4, A6, ..., A16 are the aspheric coefficients of degrees 4 to 16, respectively.

[Various data] shows values such as zoom ratio and focal length for each focal length state.

[Variable Distance Data] shows the variable distance and BF values for each focal length state.

[Lens group data] shows the surface number of each lens group closest to the object and the composite focal length of the entire group.

In addition, for all the values of the following specifications, the focal length f, radius of curvature r, lens surface spacing d, and other length units are given in millimeters (mm) unless otherwise specified, but this is not limited to this because the optical system provides equivalent optical performance with proportional magnification and proportional reduction.

A list of the corresponding values of the conditional expressions in each of these examples is also provided.

In addition, in the aberration diagrams 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 surface and meridional image surface, respectively.

Numerical Example 1
Unit: mm
[Surface data]
Surface number rd nd vd ΔPgF
Object surface ∞ (d0)
1 -321.1993 0.9000 1.92286 20.88
2 347.9829 3.6927 1.72916 54.67
3 -201.0484 0.1500
4 46.3874 5.8985 1.72916 54.67
5 213.5397 (d5)
6* 83.1978 0.9000 1.80610 40.73
7* 17.8323 7.8084
8 -28.2682 0.9000 1.59282 68.62
9 61.9525 0.1500
10 41.7123 3.5899 1.80518 25.46
11 -57.0261 2.9569
12 -20.8578 0.9000 1.65844 50.85
13 -36.5708 (d13)
14(Aperture) ∞ 1.5000
15* 20.9852 7.0309 1.80610 40.73 -0.0056
16* -114.8239 2.7952
17 -144.3245 0.9000 1.77047 29.74
18 12.9617 6.0527 1.43700 95.10 0.0564
19 -60.2886 1.5316
20 -25.8972 0.9000 1.64769 33.84
21 366.4017 0.1500
22 43.8429 2.0333 1.49700 81.61 0.0374
23 267.5177 0.1500
24* 80.1385 3.4405 1.85135 40.10 -0.0067
25* -29.6845 (d25)
26 291.8256 0.9000 1.59410 60.47
27 32.2449 (d27)
28 -206.6340 2.4694 1.70300 52.38
29 -65.4703 (BF)

[Aspheric data]
6th 7th 15th
K 0.0000 -1.0000 0.0000
A4 1.1372E-05 2.6070E-05 -4.7029E-06
A6 -1.5411E-07 -4.1729E-08 -3.2220E-09
A8 2.3962E-09 -6.0508E-10 -6.7350E-11
A10 -2.0024E-11 4.1837E-11 2.6266E-13
A12 9.8220E-14 -5.3924E-13 0.0000E+00
A14 -2.5676E-16 3.0936E-15 0.0000E+00
A16 2.7933E-19 -6.5591E-18 0.0000E+00

16th 24th 25th
K 0.0000 0.0000 0.0000
A4 8.0211E-06 -1.3933E-05 3.4806E-06
A6 -1.5467E-08 5.7132E-08 1.7678E-08
A8 1.3127E-11 -7.1209E-10 -2.1644E-10
A10 1.8586E-13 2.3139E-12 -1.7559E-12
A12 0.0000E+00 3.2282E-15 1.3389E-14
A14 0.0000E+00 0.0000E+00 0.0000E+00
A16 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
Zoom ratio 2.39
Wide Angle Mid Telephoto Focal Length 28.45 44.92 67.89
F-number 2.99 3.01 3.05
Full angle of view 2ω 77.14 49.39 33.45
Image height Y 21.63 21.63 21.63
Lens length 116.93 122.20 135.55

[Variable interval data]
Wide Angle Mid-Telephoto
d0∞∞∞∞
d5 1.5000 10.9388 18.8948
d13 17.2869 6.9159 1.5000
d25 4.1441 7.6297 6.2301
d27 6.0810 8.7975 21.0021
BF 30.2211 30.2211 30.2211

[Lens group data]
Group Initial surface Focal length
L1 1 77.97
L2 6 -20.55
L3 15 27.23
L4 26 -61.10
L5 28 135.35

Numerical Example 2
Unit: mm
[Surface data]
Surface number rd nd vd ΔPgF
Object surface ∞ (d0)
1 301.5427 1.7000 1.92286 20.88
2 109.0112 5.3827 1.59282 68.62
3 -420.2221 0.1500
4 48.2783 6.3926 1.72916 54.67
5 169.5303 (d5)
6* 157.1243 1.5600 1.76802 49.24
7* 15.9737 6.4275
8 -25.1624 0.9000 1.59282 68.62
9 72.0745 6.9624 1.80518 25.46
10 -36.0493 2.4882
11 -17.6913 0.9000 1.69350 53.20
12* -32.1181 (d12)
13(Aperture) ∞ 1.5000
14* 26.3392 5.9439 1.80610 40.73 -0.0056
15* -138.6003 0.1500
16 36.2478 4.4438 1.91082 35.25
17 15.3777 6.2193 1.43700 95.10 0.0564
18 -82.2980 0.7620
19 -120.2303 0.9000 1.80610 33.27
20 17.7724 4.5333 1.49700 81.61 0.0374
21 -700.8686 3.3242
22* 41.8217 4.6031 1.69350 53.20 -0.0059
23* -34.4672 (d23)
24 263.0985 0.8000 1.69680 55.46
25 30.0171 (d25)
26 -154.5230 5.9552 1.88100 40.14
27 -63.7772 (BF)

[Aspheric data]
6th 7th 12th
K 0.0000 -1.0000 0.0000
A4 1.8454E-05 4.1084E-05 -8.7428E-06
A6 -1.2565E-07 1.4276E-07 -1.0607E-08
A8 1.6797E-09 -6.0771E-09 -1.1083E-10
A10 -1.2503E-11 1.8470E-10 0.0000E+00
A12 5.4553E-14 -2.3326E-12 0.0000E+00
A14 -1.2377E-16 1.4499E-14 0.0000E+00
A16 1.1356E-19 -3.3103E-17 0.0000E+00

14th 15th 22nd 23rd
K 0.0000 0.0000 0.0000 0.0000
A4 -5.9824E-06 7.1138E-06 -9.5463E-06 -1.2657E-06
A6 7.3757E-09 5.0485E-09 1.7207E-08 -1.7659E-08
A8 -7.0805E-11 -6.4302E-11 -1.5316E-10 7.0788E-11
A10 1.9028E-13 1.9461E-13 -1.8714E-13 -1.6128E-12
A12 0.0000E+00 0.0000E+00 2.5627E-15 5.0914E-15
A14 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
A16 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
Zoom ratio 2.39
Wide Angle Mid Telephoto Focal Length 28.50 45.00 68.01
F-number 2.94 2.90 2.91
Full angle of view 2ω 76.72 49.23 33.11
Image height Y 21.63 21.63 21.63
Lens length 129.98 138.50 152.69

[Variable interval data]
Wide Angle Mid-Telephoto
d0∞∞∞∞
d5 1.5000 11.9579 22.6782
d12 13.5203 5.2929 1.5000
d23 2.6176 7.6368 8.1882
d25 8.0865 9.3604 16.0650
BF 32.2575 32.2576 32.2575

[Lens group data]
Group Initial surface Focal length
L1 1 80.13
L2 6 -16.14
L3 14 26.34
L4 24 -48.69
L5 26 119.59

Numerical Example 3
Unit: mm
[Surface data]
Surface number rd nd vd ΔPgF
Object surface ∞ (d0)
1 397.4862 1.6000 1.92119 23.96
2 114.8642 5.4145 1.59282 68.62
3 -347.2293 0.1500
4 46.7141 5.8516 1.72916 54.67
5 128.9627 (d5)
6* 98.9336 1.6000 1.80610 40.73
7 18.0351 5.7008
8 -81.2030 1.1500 1.43700 95.10
9 24.2629 2.6106 1.73037 32.23
10 73.5856 4.9932
11 -18.6479 1.1500 1.87070 40.73
12 -42.0439 0.1500
13 -168.8506 1.8886 1.92286 20.88
14 -43.9831 (d14)
15(Aperture) ∞ 1.5000
16* 37.9187 3.1576 1.80610 40.73 -0.0056
17* -86.3546 0.5174
18 421.5607 1.1000 1.60342 38.01
19 38.5501 6.0129
20 42.9473 6.2765 1.43700 95.10 0.0564
21 -24.0059 0.1500
22 75.4194 1.1000 1.85451 25.15
23 23.2057 3.8404 1.43700 95.10 0.0564
24 -185.5709 0.1500
25* 185.1682 1.6604 1.85135 40.10 -0.0067
26* -124.0532 (d26)
27 723.2923 1.1000 1.72916 54.67
28 29.4276 (d28)
29* 52.2417 7.0338 1.80610 40.73
30* -39.7651 0.1500
31 -70.7356 0.9000 1.83481 42.72
32 45.7963 (BF)

[Aspheric data]
6th 16th 17th
K 0.0000 0.0000 0.0000
A4 5.2200E-06 -5.1541E-06 1.5777E-05
A6 -6.5230E-09 4.3631E-08 5.2266E-08
A8 5.0765E-11 -1.6168E-10 -1.0009E-10
A10 -1.5247E-13 0.0000E+00 0.0000E+00
A12 3.0388E-16 0.0000E+00 0.0000E+00
A14 0.0000E+00 0.0000E+00 0.0000E+00
A16 0.0000E+00 0.0000E+00 0.0000E+00

25th page 26th page 29th page 30th page
K 0.0000 0.0000 0.0000 0.0000
A4 -1.1919E-05 -6.4057E-06 5.5848E-06 1.2820E-05
A6 -2.6652E-08 -2.6850E-08 1.3239E-09 -9.3151E-09
A8 3.5710E-10 4.0043E-10 -6.7867E-12 1.0107E-12
A10 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
A12 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
A14 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
A16 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
Zoom ratio 2.39
Wide Angle Mid Telephoto Focal Length 28.50 45.01 68.01
F-number 2.89 2.91 2.90
Full angle of view 2ω 77.24 49.62 33.70
Image height Y 21.63 21.63 21.63
Lens length 123.00 129.09 145.12

[Variable interval data]
Wide Angle Mid-Telephoto
d0∞∞∞∞
d5 1.5000 11.8223 25.7756
d14 15.0288 4.9604 1.5000
d26 2.1000 5.2475 4.3207
d28 9.4741 12.1654 18.6266
BF 27.9888 27.9889 27.9888

[Lens group data]
Group Initial surface Focal length
L1 1 87.38
L2 6 -19.42
L3 16 23.79
L4 27 -42.10
L5 29 151.00

Numerical Example 4
Unit: mm
[Surface data]
Surface number rd nd vd ΔPgF
Object surface ∞ (d0)
1 76.0119 1.7000 1.92286 20.88
2 51.0306 5.1333 1.59282 68.62
3 111.0725 0.1500
4 51.7946 6.5046 1.72916 54.67
5 351.5780 (d5)
6* 178.4607 1.5600 1.80610 40.73
7* 17.6583 6.3109
8 -47.9410 0.9000 1.59282 68.62
9 27.8356 3.1502 1.92286 20.88
10 -452.6276 3.2178
11 -18.4217 0.9000 1.69350 53.20
12* -37.3181 (d12)
13(Aperture) ∞ 4.0546
14* 21.0823 7.3443 1.80610 40.73 -0.0056
15* -51.4955 1.5451
16 224.9973 1.6573 1.85451 25.15
17 17.4829 3.7018 1.43700 95.10 0.0564
18 41.0239 3.0121
19 -97.0491 0.9000 1.80610 40.73
20 22.0309 7.0633 1.49700 81.61 0.0374
21 -28.7329 0.1500
22* 27.3505 5.2925 1.69350 53.20 -0.0059
23* -62.7702 (d23)
24 195.4117 0.8000 1.69350 53.34
25 23.4489 (d25)
26 88.4411 3.9406 1.69680 55.46
27 -73.1412 (BF)

[Aspheric data]
6th 7th 12th
K 0.0000 -1.0000 0.0000
A4 3.8156E-05 5.5157E-05 -5.5841E-06
A6 -3.3476E-07 1.2470E-07 -9.3132E-09
A8 2.6548E-09 -1.0790E-08 -7.6429E-11
A10 -1.3464E-11 2.4819E-10 0.0000E+00
A12 4.3517E-14 -2.6977E-12 0.0000E+00
A14 -7.9816E-17 1.5038E-14 0.0000E+00
A16 6.2068E-20 -3.3103E-17 0.0000E+00

14th 15th 22nd 23rd
K 0.0000 0.0000 0.0000 0.000
A4 -1.2608E-05 2.2303E-05 -3.0570E-06 -1.6127E-08
A6 -2.3878E-09 -4.6114E-08 3.3256E-09 1.9900E-08
A8 -5.3956E-11 5.6120E-11 -3.4129E-11 -4.5031E-11
A10 0.0000E+00 0.0000E+00 7.0541E-15 3.2661E-14
A12 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
A14 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
A16 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

[Various data]
Zoom ratio 2.62
Wide Angle Mid Telephoto Focal Length 18.50 30.00 48.50
F-number 1.94 2.02 2.10
Full angle of view 2ω 77.86 50.43 31.58
Image height Y 14.20 14.20 14.20
Lens length 115.36 121.66 137.89

[Variable interval data]
Wide Angle Mid-Telephoto
d0∞∞∞∞
d5 1.5000 8.6506 19.2242
d12 16.5034 6.3407 1.5000
d23 2.1000 5.8596 6.7878
d25 4.4739 10.0253 19.6030
BF 21.7908 21.7907 21.7908

[Lens group data]
Group Initial surface Focal length
L1 1 81.14
L2 6 -15.22
L3 14 24.73
L4 24 -38.50
L5 26 58.03

[Conditional expression corresponding value]
Ex1 Ex2 Ex3 Ex4
Conditional expression 1 f1/fT 1.15 1.18 1.28 1.67
Conditional expression 2 |f1/f2| 3.79 4.96 4.50 5.33
Conditional expression 3 LTw*FnoT/Ymax 16.18 17.49 16.49 17.06
Conditional expression 4 |f3/f4| 0.45 0.54 0.57 0.64
Conditional expression 5 ΔPgF3p_ave 0.020 0.021 0.025 0.021
Conditional expression 6 Ymax/BF 0.72 0.67 0.77 0.65
Conditional expression 7 |f4/fT| 0.90 0.72 0.62 0.79
Condition 8 |βT5^2*(1-βT4^2)| 1.82 2.31 2.95 1.97
Conditional expression 9 νd2n-νd2p 27.95 31.57 32.30 33.30
Conditional expression 10 Nd1 1.79 1.75 1.75 1.75
Conditional expression 11 νd1p-νd1n 33.79 40.77 37.69 40.77

L1 First lens unit L2 Second lens unit L3 Third lens unit L4 Fourth lens unit L5 Fifth lens unit S Aperture stop I Image surface

Claims (8)

The optical system includes, in order from the object side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, an aperture stop S, a third lens unit L3 having a positive refractive power, a fourth lens unit L4 having a negative refractive power, and a fifth lens unit L5 having a positive refractive power.
The distance between the lens groups changes during zooming, and the fifth lens group L5 does not move.
The fourth lens group L4 moves in the optical axis direction to perform focusing.
A large aperture zoom lens characterized by satisfying the following conditional expressions:
(1) 0.90<f1/fT<2.25
(2) 2.90<|f1/f2|<6.00
(3) 13.0<LTw*FnoT/Ymax<20.0
(8) 1.00<|βT5^2*(1-βT4^2)|<3.70
Where:
fT: focal length of the entire system at infinity at the telephoto end f1: focal length of the first lens unit L1 f2: focal length of the second lens unit L2 LTw: total optical length at the wide-angle end FnoT: F-number at infinity at the telephoto end Ymax: maximum image height
βT4: lateral magnification at infinity at the telephoto end of the fourth lens unit L4
βT5: lateral magnification at infinity at the telephoto end of the fifth lens unit L5 2. The large aperture zoom lens according to claim 1, wherein the following condition is satisfied:
(4) 0.35<|f3/f4|<0.74
Where:
f3: focal length of the third lens group L3 f4: focal length of the fourth lens group L4 3. The large-aperture zoom lens according to claim 1, wherein the following condition is satisfied:
(5) 0.011<ΔPgF3p_ave
Where:
ΔPgF3p_ave: average value of anomalous dispersion of the positive lenses included in the third lens unit L3, ΔPgF3pi=PgF3pi-0.64833+0.00180×νd3pi
ΔPgF3pi: anomalous dispersion of the i-th positive lens included in the third lens unit L3 PgF3pi: partial dispersion ratio between the g-line and the F-line of the i-th positive lens included in the third lens unit L3 νd3pi: Abbe number of the i-th positive lens included in the third lens unit L3 4. A large-aperture zoom lens according to claim 1, wherein the following condition is satisfied:
(6) 0.55<Ymax/BF
Where:
BF: Back focus 5. A large-aperture zoom lens according to claim 1, wherein the following condition is satisfied:
(7) 0.45<|f4/fT|<1.10
Where:
f4: focal length of the fourth lens unit L4 6. The large-aperture zoom lens according to claim 1 , wherein the fourth lens unit L4 is made up of one negative lens. 7. A large-aperture zoom lens according to claim 1, wherein the following condition is satisfied:
(9) 25.8<νd2n−νd2p
Where:
νd2n: average Abbe number of negative lenses included in the second lens unit L2 νd2p: average Abbe number of positive lenses included in the second lens unit L2 8. The large-aperture zoom lens according to claim 1, wherein the first lens unit L1 includes one negative lens and one positive lens, and the following condition is satisfied: 1<n<1 >= 1/2<n <1 .
(10) 1.70<Nd1
(11) 31.0<νd1p−νd1n
Where:
Nd1: average value of refractive index of lenses included in the first lens unit L1 νd1p: average value of Abbe number of positive lenses included in the first lens unit L1 νd1n: Abbe number of negative lenses included in the first lens unit L1

Images