JP7706743B2 - Inner focus optical system - Google Patents

Description

This invention relates to an optical system suitable for a photographic lens used in imaging devices such as still cameras and video cameras, and relates to an inner focus optical system that employs an inner focus method suitable for autofocus cameras, has a small rate of change in image height when the focus lens group is subjected to minute vibrations (wobbling) along the optical axis, has a bright F-number of 1.4, and has a focal length of approximately 80 mm in 35 mm format equivalent, or a medium telephoto angle of view.

Shooting lenses with a medium telephoto angle of view have a longer focal length than lenses with a standard angle of view, and therefore tend to have a larger overall optical length. In addition, because the angle of view is wider than that of a super telephoto lens, the telephoto ratio tends to be larger when attempting to correct aberrations related to the angle of view. Furthermore, many users of shooting lenses with a medium telephoto angle of view expect to be able to create photographic expressions using bokeh, and so large aperture shooting lenses are desired. However, increasing the aperture makes the entrance pupil larger, making it difficult to correct spherical aberrations, etc. The challenge is to achieve better performance while still reducing the size.

In addition, mirrorless single-lens cameras, which have become popular in recent years, are often used for video shooting, so the autofocus system often uses an inner focus system in which the focus lens group is made to vibrate slightly (wobble) along the optical axis to constantly determine the focus drive direction. In this case, if the rate of change in image height during wobbling is large, the viewer will notice the change in magnification of the subject on the screen and find it annoying, so a focus system that has a small rate of change in image height in response to focus changes is required.

In response to such demands, Patent Document 1 discloses a large aperture lens that is made up of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power, with an aperture stop disposed between the first lens group G1 and the second lens group G2, and focusing performed by moving the second lens group G2 toward the image plane side. By satisfying certain conditions, the lens has a simple configuration, but is capable of supporting autofocus during video shooting, while reducing the weight of the focus lens, with little aberration fluctuation due to focusing, and is adaptable to brightnesses of approximately an open F-number of 1.4 that employ an inner focus method.

Patent Document 2 also discloses an inner focus optical system with an angle of view of about 40 to 60°, which is made up of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with positive refractive power, and a third lens group G3 with negative refractive power, and when focusing from an object at infinity to an object at close range, the second lens group G2 moves toward the object side, and the first lens group G1 and the third lens group G3 are fixed with respect to the image plane I, the first lens group G1 includes an aperture stop S and is made up of a predetermined lens group, and the third lens group G3 is made up of a predetermined lens group, and by satisfying a predetermined conditional formula, the distance between the inner focus optical system and the image sensor is short, miniaturization is achieved, the F-number is small, the light exit angle can be suppressed, and various aberrations are well corrected from infinity to close range photography.

Patent Document 3 also discloses a lens system that includes a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power, arranged in that order from the object side, and that focuses by moving the second lens group along the optical axis.

Patent Document 4 also discloses that the lens essentially consists of, in order from the object side, a first lens group having positive refractive power, an aperture, and a second lens group having positive refractive power, and that focusing is performed by moving multiple lenses in the second lens group, or the entire second lens group G2, toward the object side.

JP 2013-3324 A JP 2015-75501 A JP 2012-242690 A JP 2015-141384 A

However, in the lens system disclosed in Patent Document 1, the focus lens group and the aperture are adjacent to each other, so when the autofocus focus lens group is subjected to slight vibrations (wobbling) along the optical axis during video shooting, the rate of change in image height is large, and so viewers are aware of the change in magnification of the subject displayed on the screen, which can be annoying.

In addition, in Patent Document 2, the FNO is about 1.8, so the amount of blur is small, and making the aperture even larger is an issue. Furthermore, because the focus lens group is composed of three lenses including a cemented lens, the weight of the focus lens group is not sufficient to make the aperture larger and perform autofocus while generating minute vibrations.

In addition, in Patent Document 3, the FNO is about 1.8, so the amount of blur is small, and further increasing the aperture is an issue.

In addition, in Patent Document 4, the focus lens group is composed of multiple lenses, so the focus lens group is not sufficiently lightweight to perform autofocus while causing minute vibrations (wobbling).

The present invention provides an inner focus optical system that uses the following means to achieve a lightweight focus lens group, a small rate of change in image height when the focus lens group is subjected to slight vibration (wobbling) along the optical axis, a bright F-number of 1.4, and an angle of view of approximately 80 mm in 35 mm equivalent focal length, or medium telephoto.

In order to solve the above problems, the inner focus optical system of the first invention comprises, in order from the object side to the image side, a first lens group G1 consisting of a positive single lens, an aperture stop S, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power, and when focusing from the infinity object side to the close object side, the third lens group G3 moves toward the image side and satisfies the following condition :
(9) 63<VdG1
however,
VdG1: Abbe number of the first lens group G1

The inner focus optical system according to the second aspect of the present invention is characterized in that it satisfies the following conditions:
(1) 0.36<f/f1<1.93
(2) 0.23<f/f2<1.35
(3) -1.91<f/f3<-0.39
(4) 0.24<f/f4<1.65
(5) 0.52<f/f12<2.23
however,
f: focal length of the entire system when focused at infinity f1: focal length of the first lens group G1 f2: focal length of the second lens group G2 f3: focal length of the third lens group G3 f4: focal length of the fourth lens group G4 f12: composite focal length of the first lens group G1 and the second lens group G2

The inner focus optical system according to the third aspect of the present invention is characterized in that it satisfies the following conditions:
(6) 0.22<M4<1.0
however,
M4: Magnification load of the fourth lens group G4 when the object distance is at infinity

The inner focus optical system according to the fourth aspect of the present invention is characterized in that it satisfies the following conditions:
(7) 0.44<|(M4^2×(1-M3^2))|<1.84
however,
M3: Magnification burden of the third lens group G3 when the object distance is at infinity M4: Magnification burden of the fourth lens group G4 when the object distance is at infinity

The fifth aspect of the inner focus optical system is characterized in that the third lens group G3 is made up of a single lens.

The inner focus optical system according to the sixth aspect of the present invention is characterized in that it satisfies the following conditions:
(8) 2.23<D/Y<9.92
however,
D: Length from the aperture to the image plane Y: Maximum image height

The present invention makes it possible to provide an inner focus optical system that employs an inner focus method suitable for autofocus cameras, has a small rate of change in image height when the focus lens group is subjected to slight vibration (wobbling) along the optical axis, has a bright F-number of 1.4, and has a focal length of approximately 80 mm in 35 mm format equivalent, or a medium telephoto angle of view.

FIG. 2 is a lens configuration diagram of the inner focus optical system according to the first embodiment of the present invention at an infinite shooting distance. 5A to 5C are longitudinal aberration diagrams at an infinite shooting distance in Example 1 of the present invention. 5A to 5C are longitudinal aberration diagrams at a magnification of 0.025 in the first embodiment of the present invention. 4A to 4C are diagrams showing lateral aberration at an infinite shooting distance in Example 1 of the present invention. 4A to 4C are lateral aberration diagrams at a shooting magnification of 0.025 times in the first embodiment of the present invention. FIG. 11 is a lens configuration diagram of an inner focus optical system according to a second embodiment of the present invention at an infinite shooting distance. 11A to 11C are longitudinal aberration diagrams at an infinite shooting distance in Example 2 of the present invention. 11A to 11C are longitudinal aberration diagrams at a magnification of 0.025 in Example 2 of the present invention. 7A to 7C are diagrams showing lateral aberration at an infinite shooting distance in Example 2 of the present invention. 7A to 7C are lateral aberration diagrams at a photographing magnification of 0.025 times according to the second embodiment of the present invention. FIG. 11 is a lens configuration diagram of an inner focus optical system according to a third embodiment of the present invention at an infinite shooting distance. 13A to 13C are longitudinal aberration diagrams at an infinite shooting distance in Example 3 of the present invention. 11A to 11C are longitudinal aberration diagrams at a magnification of 0.025 in Example 3 of the present invention. 9A to 9C are diagrams showing lateral aberration at an infinite shooting distance in Example 3 of the present invention. 9A to 9C are lateral aberration diagrams at a photographing magnification of 0.025 times according to the third embodiment of the present invention.

The inner focus optical system of this embodiment will be described below. Note that the following description of the embodiment is an example of the optical system of the present invention, and the present invention is not limited to this embodiment within the scope of the gist of the present invention.

As can be seen from the lens configuration diagrams shown in Figures 1, 6, and 11, the inner focus optical system of the present invention consists of, in order from the object side to the image side, a first lens group G1 consisting of a positive single lens, an aperture stop S, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power, and when focusing from the infinity object side to the close object side, the third lens group G3 moves toward the image side.

The reason why the above configuration is necessary is as follows. That is, by making the refractive power of the lens group closer to the object side than the aperture positive, it is possible to reduce the aperture diameter, which tends to become large in large-aperture medium telephoto optical systems.

In addition, by placing the aperture between the first lens group G1 and the second lens group G2 and positioning the aperture as far away from the image plane as possible, the angle of incidence of the off-axis chief ray reaching the image sensor can be reduced, suppressing shading problems and reducing the rate of change in image height when the focus group is subjected to slight vibration (wobbling) during focusing. In addition, by constructing the first lens group G1 from a single lens, the first lens group G1 can be made thinner, and the aperture placed between the first lens group G1 and the second lens group G2 can be positioned closer to the object side.

In addition, by giving positive refractive power to the second lens group G2, which is closer to the image side than the aperture, it is possible to reduce the angle of the off-axis chief ray incident on the subsequent focus lens group relative to the optical axis, which contributes to reducing the rate of change in image height when the focus group is subjected to slight vibrations (wobbling) during focusing.

In addition, by disposing the fourth lens group G4 with positive refractive power, it is not necessary to increase the positive refractive power of the composite system of the first lens group G1 and the second lens group G2, making it possible to suppress the occurrence of spherical aberration and coma aberration.

The third lens group G3 is a focusing group, and while it is desirable for it to be composed of a small number of lenses in order to reduce weight, this can result in insufficient aberration correction, which can lead to aberrations. In particular, the third lens group G3, which has negative refractive power, is positioned at a position where the height of the off-axis chief ray is large, which can lead to positive astigmatism, lateral chromatic aberration, and positive distortion. Therefore, by positioning the fourth lens group G4, which has positive refractive power, at a position where the height of the off-axis chief ray is large, it becomes possible to effectively correct these aberrations.

As a result, it is possible to provide an inner focus optical system that has a small rate of change in image height when the focus lens group is subjected to slight vibrations (wobbling) along the optical axis, a bright F-number of 1.4, and an angle of view of approximately 80 mm in 35 mm equivalent focal length, or about medium telephoto.

Furthermore, it is preferable that the inner focus optical system of this embodiment satisfies the following conditional expression.
(1) 0.36<f/f1<1.93
(2) 0.23<f/f2<1.35
(3) -1.91<f/f3<-0.39
(4) 0.24<f/f4<1.65
(5) 0.52<f/f12<2.23
however,
f: focal length of the entire system when focused at infinity f1: focal length of the first lens group G1 f2: focal length of the second lens group G2 f3: focal length of the third lens group G3 f4: focal length of the fourth lens group G4 f12: composite focal length of the first lens group G1 and the second lens group G2

In conditional formula (1), by appropriately defining the ratio of the focal length of the first lens group G1 to that of the entire system, it is possible to prevent an increase in the aperture diameter, which tends to become large in large-aperture medium telephoto lenses, and to suppress the occurrence of spherical aberration and coma aberration caused by the large aperture.

When the lower limit of conditional expression (1) is exceeded and the positive refractive power of the first lens group G1 becomes small, it becomes difficult to suppress the aperture diameter. In addition, the degree of telephotography of the partial system formed by the first lens group G1 and the second lens group G2 becomes weak, so the reduction in the overall length of the partial system becomes insufficient, making it difficult to reduce the size of the entire system.

On the other hand, if the upper limit of conditional expression (1) is exceeded and the positive refractive power of the first lens group G1 becomes large, it becomes difficult to correct spherical aberration, coma, and astigmatism.

Regarding conditional expression (1), it is preferable to limit the lower limit to 0.48 and the upper limit to 1.45 to ensure the above-mentioned effect.

Condition (2) appropriately defines the ratio of the focal length of the second lens group G2 to that of the entire system, thereby suppressing increases in the overall optical length and the rate of change of image height, and suppressing the occurrence of spherical aberration and coma aberration due to a larger aperture.

When the lower limit of conditional expression (2) is exceeded and the positive refractive power of the second lens group G2 becomes small, the angle of the off-axis chief ray incident on the third lens group G3, which is the focus lens group, with respect to the optical axis cannot be reduced, so the rate of change in image height when the focus group is subjected to slight vibration (wobbling) during focusing becomes large, which is undesirable. In addition, in order to maintain the focal length of the entire system, it is necessary to reduce the negative refractive power of the third lens group G3 as well, and the amount of movement of the third lens group G3 during focusing increases, which undesirably increases the overall length of the optical system.

On the other hand, if the upper limit of conditional expression (2) is exceeded and the positive refractive power of the second lens group G2 becomes large, it becomes difficult to correct spherical aberration and coma aberration when the aperture is increased.

Regarding conditional expression (2), it is preferable to limit the lower limit to 0.30 and the upper limit to 1.01 to ensure the above-mentioned effect.

In conditional expression (3), by appropriately defining the ratio of the focal length of the third lens group G3, which is the focus lens group, to the focal length of the entire system when focused at infinity, it is possible to suppress aberration fluctuations during focusing.

When the lower limit of conditional expression (3) is exceeded and the negative refractive power of the third lens group G3 becomes large, the amount of movement of the third lens group G3 during focusing becomes small, which is advantageous in terms of space, but it becomes difficult to simultaneously correct the fluctuations in spherical aberration and astigmatism during focusing.

On the other hand, if the upper limit of conditional expression (3) is exceeded and the negative refractive power of the third lens group G3 becomes small, the amount of movement of the third lens group G3 during focusing becomes large, and the overall length of the optical system becomes large. In addition, the amount of amplitude during wobbling must be increased, which is undesirable since it places a load on the actuator.

Regarding conditional expression (3), it is preferable to limit the lower limit to -1.43 and the upper limit to -0.52 in order to ensure the above-mentioned effect.

Conditional expression (4) appropriately defines the ratio of the focal length of the fourth lens group G4 to the focal length of the entire system, making it possible to correct residual aberration up to the focus lens group and improve the performance of the entire system.

When the lower limit of conditional expression (4) is exceeded and the positive refractive power of the fourth lens group G4 becomes small, the imaging magnification of the fourth lens group G4 becomes large and the effect of reducing the residual image aberration up to the focus lens group becomes small, making it difficult to achieve high performance.

On the other hand, if the upper limit of conditional expression (4) is exceeded and the positive refractive power of the fourth lens group G4 becomes large, the imaging magnification of the fourth lens group G4 will decrease, making it easier to correct aberrations, but this is not desirable as it will increase the size of the entire system.

Regarding conditional expression (4), it is preferable to limit the lower limit to 0.31 and the upper limit to 1.23 to ensure the above-mentioned effect.

Conditional formula (5) appropriately defines the ratio between the composite focal length of the first lens group G1 and the second lens group G2 and the focal length of the entire system, making it possible to suppress spherical aberration and coma aberration while suppressing increases in the amount of movement required for focusing and the overall optical length in a large aperture ratio lens.

When the lower limit of conditional expression (5) is exceeded and the composite refractive power of the first lens group G1 and the second lens group G2 becomes small, the magnification of the composite system of the third lens group G3 and the fourth lens group G4 becomes small. In other words, the magnification M3 of the third lens group G3 becomes small, or the magnification M4 of the fourth lens group G4 becomes small. Considering that the magnification M3 of the third lens group G3 is greater than 1.0 in the present invention, the focus sensitivity becomes small, so the amount of movement of the third lens group G3 required for focusing becomes large. Therefore, the air gap required for focusing is insufficient. In addition, when the positive refractive power of the composite system of the first lens group G1 and the second lens group G2 becomes relatively small and the magnification of the composite system of the third lens group G3 and the fourth lens group G4 becomes small, the telephoto ratio becomes large, and the optical total length of the large aperture ratio lens increases.

On the other hand, if the upper limit of conditional expression (5) is exceeded and the composite refractive power of the first lens group G1 and the second lens group G2 becomes large, it becomes difficult to correct the spherical aberration and coma aberration of the composite system of the first lens group G1 and the second lens group G2, and the magnification of the composite system of the third lens group G3 and the fourth lens group G4 becomes large. The spherical aberration and coma aberration of the composite system, which are aggravated by the increase in the refractive power of the composite system of the first lens group G1 and the second lens group G2, are multiplied, making it more difficult to correct aberrations.

Regarding conditional expression (5), it is preferable to limit the lower limit to 0.70 and the upper limit to 1.68 to ensure the above-mentioned effect.

Furthermore, it is desirable for the inner focus optical system of the present invention to satisfy the following conditional expression:
(6) 0.22<M4<1.0
however,
M4: Magnification load of the fourth lens group G4 when the object distance is at infinity

Conditional formula (6) defines the imaging magnification of the fourth lens group G4. By making the imaging magnification of the fourth lens group G4, which is the final lens group, of the inner focus optical system of the present invention a reduction system, it is possible to improve the performance of the entire system without amplifying the residual aberration up to the focus lens group.

When the lower limit of conditional expression (6) is exceeded and the imaging magnification of the fourth lens group G4 becomes small, the residual aberration up to the focus group is reduced, but the overall system becomes large, which is undesirable.

On the other hand, if the upper limit of conditional expression (6) is exceeded and the imaging magnification of the fourth lens group G4 exceeds 1, the residual aberration up to the focus lens group increases, making it difficult to correct that aberration.

Regarding conditional expression (6), it is preferable to limit the lower limit to 0.29 and the upper limit to 0.86 in order to ensure the above-mentioned effect.

Furthermore, it is desirable for the inner focus optical system of the present invention to satisfy the following conditional expression:
(7) 0.44<|(M4^2×(1-M3^2))|<1.84
however,
M3: Magnification burden of the third lens group G3 when the object distance is at infinity M4: Magnification burden of the fourth lens group G4 when the object distance is at infinity

Conditional expression (7) defines the sensitivity of the imaging surface when the third lens group G3 moves during focusing. By appropriately defining this value, it becomes possible to precisely control the drive of the focus lens group within the focusing range during autofocus.

When the lower limit of conditional expression (7) is exceeded and the sensitivity of the imaging surface when moving during focusing decreases, the amount of movement of the focus lens group increases, causing greater fluctuations in the chief ray height of the focus lens group due to wobbling, weakening the effect of suppressing image height fluctuations, and making it difficult to suppress image height fluctuations due to wobbling.

On the other hand, if the upper limit of conditional expression (7) is exceeded and the sensitivity of the imaging surface when moving during focusing increases, the amount of movement of the focus lens group decreases, so that even small movements of the focus lens group cause the imaging surface to move significantly, making it difficult to drive and control the third lens group G3, which is the focus lens group, within the focusing range during autofocus. Also, if the sensitivity of the imaging surface increases, that is, the power of the third lens group G3 becomes stronger, it becomes difficult to correct aberrations unless the number of components of the third lens group G3 is increased. Increasing the number of components leads to an increase in weight, making it difficult to cause micro-vibrations (wobbling) during focusing.

Regarding conditional expression (7), it is preferable to limit the lower limit to 0.59 and the upper limit to 1.38 to ensure the above-mentioned effect.

Furthermore, in the inner focus optical system of the present invention, it is desirable that the third lens group G3 with positive refractive power is made up of a single lens. This allows the focus group to be made lighter, and the actuator for driving the focus can be made smaller, thereby enabling a reduction in product size.

Furthermore, in the inner focus optical system of the present invention, it is desirable to satisfy the following conditional expression:
(8) 2.23<D/Y<9.92
however,
D: Length from aperture stop S to image plane Y: Maximum image height

Conditional formula (8) makes it possible to suppress image height fluctuations that occur during wobbling by appropriately defining the ratio of the length from the aperture stop S to the image plane to the maximum image height.

When the lower limit of conditional expression (8) is exceeded and the ratio of the length from the aperture stop S to the image plane to the maximum image height becomes small, the angle of incidence to the off-axis image plane becomes large, causing large fluctuations in the focus lens group chief ray height during wobbling, making it difficult to suppress image height fluctuations during wobbling.

On the other hand, if the upper limit of conditional expression (8) is exceeded and the ratio of the length from the aperture stop S to the image plane to the maximum image height becomes large, the overall optical system becomes large, which is undesirable.

Regarding conditional expression (8), it is preferable to limit the lower limit to 2.97 and the upper limit to 7.44 to ensure the above-mentioned effect.

Furthermore, in the inner focus optical system of the present invention, it is desirable to satisfy the following conditional expression:
(9) 63<VdG1
however,
VdG1: Abbe number of the first lens group G1

Conditional expression (9) makes it possible to suppress chromatic aberration occurring in the first lens group G1 by appropriately defining the Abbe number of the first lens group G1, which is a single lens.

If the lower limit of conditional expression (9) is exceeded and the Abbe number of the first lens group G1 becomes small, chromatic aberration will worsen, making it difficult to correct this throughout the entire lens system.

It is preferable to set the lower limit of conditional expression (9) to 67 to ensure the above-mentioned effect.

The inner focus optical system of the present invention is more effective when it has the following configuration:

In the inner focus optical system of the present invention, the first lens group G1 and the third lens group G3 are composed of single lenses, but by making the first lens group G1 and the third lens group G3 achromatic or giving them an aspheric effect using cemented lenses, diffractive optical surfaces, or metalens structure surfaces, it is possible to reduce chromatic aberration in the entire system and suppress fluctuations in chromatic aberration, spherical aberration, coma aberration, and astigmatism due to focus movement.

Next, we will explain the lens configuration of an embodiment of the inner focus optical system of the present invention. In the following explanation, the lens configuration will be described in order from the object side to the image side.

Furthermore, specific numerical data for each example is provided.

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), and vd is the Abbe number for the d line.

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, A8, A10, and A12 are the aspheric coefficients of 4th, 6th, 8th, 10th, and 12th orders, respectively.

[Various data] shows values such as focal length when the shooting distance is INF.

[Variable Distance Data] shows the variable surface distance and BF values when the shooting distance is INF and the shooting magnification is specified.

[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 △S and △M represent the sagittal image surface and meridional image surface, respectively.

Figure 1 is a lens configuration diagram of an inner focus optical system according to a first embodiment of the present invention.

The lens configuration of the inner focus optical system in FIG. 1 is composed of, from the object side to the image side, a first lens group G1 with positive refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power.

The first lens group G1 is composed of a biconvex lens.

The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

The second lens group G2 is composed of a cemented lens consisting of a biconcave lens and a positive meniscus lens whose image-side surface is aspheric and whose convex surface faces the object side, and a biconvex lens.

The third lens group G3 is composed of a negative meniscus lens with its convex surface facing the object side, and focusing from an object at infinity to a close object is performed by moving the third lens group G3 toward the image side along the optical axis.

The fourth lens group G4 is composed of a biconvex lens, a negative meniscus lens with a convex surface facing the object side, a positive meniscus lens with a convex surface facing the object side, and a biconcave lens.

The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Next, the specifications of the inner focus optical system of Example 1 are shown below.

Numerical Example 1
Unit: mm
[Face data]
Surface number rd nd vd
Object surface ∞ (d0)
1 34.1270 5.1016 1.55032 75.50
2 -898.3192 11.3889
3 (Aperture) ∞ 3.0957
4 -30.0949 1.0000 1.77047 29.74
5 17.8867 4.1428 1.90043 37.37
6* 45.9266 1.0000
7 38.0979 5.8176 1.90043 37.37
8 -35.5538 (d8)
9 74.7250 0.8000 1.55032 75.50
10 18.5696 (d10)
11 23.7587 4.9203 1.55032 75.50
12 -57.2260 0.1500
13 44.2765 3.4436 1.85883 30.00
14 17.5452 2.0806
15 18.5164 4.4612 1.95375 32.32
16 134.4886 0.9391
17 -122.1286 0.8000 1.85883 30.00
18 24.1072 5.0000
19 ∞ 4.1400 1.51633 64.14
20∞(BF)
Image plane ∞

[Aspheric data]
6 sides
K 0.00000
A4 1.78255E-05
A6 6.75482E-09
A8 -3.27662E-11
A10 8.01385E-14

[Various data]
INF
Focal length 43.13
F-number 1.48
Full angle of view 2ω 29.27
Image height Y 11.15
Lens length 71.82

[Variable interval data]
INF Magnification 0.025
d0∞1726.6835
d8 1.5321 2.7505
d10 9.6679 8.4495
BF 2.3351 2.3352

[Lens group data]
Group starting plane focal length
G1 1 59.86
G2 4 63.97
G3 9 -45.13
G4 11 52.42

Figure 6 is a lens configuration diagram of an inner focus optical system according to a second embodiment of the present invention.

The lens configuration of the inner focus optical system in FIG. 6 is composed of, from the object side to the image side, a first lens group G1 with positive refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power.

The first lens group G1 is composed of a biconvex lens.

The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

The second lens group G2 is composed of a biconcave lens whose image-side surface is aspheric, and a biconvex lens.

The third lens group G3 is composed of a negative meniscus lens with its convex surface facing the object side, and focusing from an object at infinity to a close object is performed by moving the third lens group G3 toward the image side along the optical axis.

The fourth lens group G4 is composed of a biconvex lens, a biconcave lens, a positive meniscus lens with a convex surface facing the object side, and a negative meniscus lens with a convex surface facing the object side.

The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Next, the specifications of the inner focus optical system of Example 2 are shown below.

Numerical Example 2
Unit: mm
[Face data]
Surface number rd nd vd
Object surface ∞ (d0)
1 25.5266 6.4611 1.55032 75.50
2 -241.8706 2.8318
3(Aperture) ∞ 4.1686
4 -23.2921 0.8000 1.92119 23.96
5* 328.1107 1.1979
6 144.3305 6.1277 1.95375 32.32
7 -24.1816 (d7)
8 50.0554 0.8000 1.43700 95.10
9 15.7499 (d9)
10 17.8356 4.5875 1.90043 37.37
11 -57.5770 0.8110
12 -53.6074 0.8000 2.00069 25.46
13 16.1658 5.1678
14 20.7510 3.4930 1.90043 37.37
15 54.2461 0.1500
16 28.0661 0.8000 1.43700 95.10
17 16.8952 4.0000
18 ∞ 4.1400 1.51633 64.14
19∞(BF)
Image plane ∞

[Aspheric data]
5 sides
K 0.00000
A4 1.91625E-05
A6 -1.99519E-09
A8 -4.78759E-11
A10 -3.10704E-14

[Various data]
INF
Focal length 40.94
F-number 1.48
Full angle of view 2ω 30.83
Image height Y 11.15
Lens total length 60.00

[Variable interval data]
INF Magnification 0.025
d0∞1644.3993
d7 1.5321 2.6645
d9 8.2722 7.1398
BF 3.8595 3.8595

[Lens group data]
Group starting plane focal length
G1 1 42.32
G2 4 89.96
G3 8 -52.96
G4 10 69.09

Figure 11 is a lens configuration diagram of an inner focus optical system according to a third embodiment of the present invention.

The lens configuration of the inner focus optical system in FIG. 11 is composed of, from the object side to the image side, a first lens group G1 with positive refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power.

The first lens group G1 is composed of a biconvex lens.

The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

The second lens group G2 is composed of a negative meniscus lens with aspheric surfaces on both sides and a concave surface facing the object side, and a biconvex lens.

The third lens group G3 is composed of a negative meniscus lens with its convex surface facing the object side, and focusing from an object at infinity to a close object is performed by moving the third lens group G3 toward the image side along the optical axis.

The fourth lens group G4 is composed of a biconvex lens, a negative meniscus lens with a convex surface facing the object side, a positive meniscus lens with a convex surface facing the object side, and a biconcave lens.

The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

Next, the specifications of the inner focus optical system of Example 3 are shown below.

Numerical Example 3
Unit: mm
[Face data]
Surface number rd nd vd
Object surface ∞ (d0)
1 27.1866 5.5665 1.49700 81.61
2 -302.5054 4.8027
3 (Aperture) ∞ 4.2303
4* -23.7007 0.8000 2.00100 29.13
5* -197.6945 0.6455
6 87.9892 7.6418 1.78590 43.93
7 -21.4660 (d7)
8 54.4190 0.8000 1.48749 70.44
9 17.1158 (d9)
10 20.4687 4.8138 1.55032 75.50
11 -47.6140 0.1500
12 50.0356 1.8746 1.72342 37.99
13 15.6628 2.3301
14 17.7761 3.0620 1.87071 40.73
15 42.3950 2.3206
16 -31.2943 0.8000 1.53172 48.84
17 25.4846 3.0000
18 ∞ 4.1400 1.51633 64.14
19∞(BF)
Image plane ∞

[Aspheric data]
4th 5th
K 0.00000 0.00000
A4 -5.74762E-07 2.52381E-05
A6 -8.76044E-08 -7.86326E-08
A8 4.25894E-11 3.21558E-10
A10 4.68070E-13 -3.90983E-13

[Various data]
INF
Focal length 40.10
F-number 1.48
Full angle of view 2ω 30.81
Image height Y 11.15
Lens total length 60.00

[Variable interval data]
INF Magnification 0.025
d0∞1608.7297
d7 1.5321 2.6891
d9 6.8539 5.6969
BF 4.6362 4.6362

[Lens group data]
Group starting plane focal length
G1 1 50.47
G2 4 68.17
G3 8 -51.58
G4 10 85.19

Conditional Expression Corresponding Value Example 1 Example 2 Example 3
(1) 0.72 0.97 0.79
(2) 0.67 0.46 0.59
(3) -0.96 -0.77 -0.78
(4) 0.82 0.59 0.47
(5) 1.04 1.12 1.07
(6) 0.44 0.57 0.53
(7) 0.90 0.92 0.88
(8) 4.96 4.55 4.45
(9) 75.50 75.50 81.61

G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group S Aperture stop FL Optical filter I Image surface

Claims (6)

An inner focus optical system comprising, in order from the object side to the image side, a first lens group G1 consisting of a positive single lens, an aperture stop S, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power, wherein when focusing from the infinity object side to the close object side, the third lens group G3 moves toward the image side and the following condition is satisfied :
(9) 63<VdG1
however,
VdG1: Abbe number of the first lens group G1 2. The inner focus optical system according to claim 1, wherein the following condition is satisfied:
(1) 0.36<f/f1<1.93
(2) 0.23<f/f2<1.35
(3) -1.91<f/f3<-0.39
(4) 0.24<f/f4<1.65
(5) 0.52<f/f12<2.23
however,
f: focal length of the entire system when focused at infinity f1: focal length of the first lens group G1 f2: focal length of the second lens group G2 f3: focal length of the third lens group G3 f4: focal length of the fourth lens group G4 f12: composite focal length of the first lens group G1 and the second lens group G2 3. The inner focus optical system according to claim 1, wherein the following condition is satisfied:
(6) 0.22<M4<1.0
however,
M4: Magnification load of the fourth lens group G4 when the object distance is at infinity 4. The inner focus optical system according to claim 1, wherein the following condition is satisfied:
(7) 0.44<|(M4^2×(1-M3^2))|<1.84
however,
M3: Magnification burden of the third lens group G3 when the object distance is at infinity M4: Magnification burden of the fourth lens group G4 when the object distance is at infinity The inner focus optical system according to any one of claims 1 to 4, characterized in that the third lens group G3 consists of a single lens. 6. The inner focus optical system according to claim 1, wherein the following condition is satisfied:
(8) 2.23<D/Y<9.92
however,
D: Length from the aperture to the image plane Y: Maximum image height

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