JP7654253B2 - 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 slight vibration (wobbling) along the optical axis, has a bright F-number of 1.4, and has an angle of view equivalent to 28 to 40 mm in focal length converted to 35 mm.

Traditionally, wide-angle lenses used in photo cameras and still video cameras have been of the retrofocus type. This was to ensure a certain level of back focus for use in single-lens reflex systems that use a mirror-up mechanism.

On the other hand, because mirrorless cameras are often used for video shooting, they often use an inner focus autofocus 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 changes in focus 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 while reducing the weight of the focus lens group to accommodate autofocus during video shooting, while also reducing aberration fluctuations 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 imaging 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 imaging 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.

JP 2013-3324 A JP 2015-75501 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 on the screen, which can be distracting.

In addition, in Patent Document 2, the focus lens group is composed of three lenses including a cemented lens, so the focus lens group is not sufficiently lightweight to perform autofocus while subjecting the lens to minute vibrations.

The present invention provides an inner focus optical system that uses the following means to provide 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 equivalent to 28 to 40 mm in 35 mm equivalent focal length.

In order to solve the above-mentioned problems, the first invention relating to the inner focus optical system of the present invention comprises, in order from the object side to the image side, a first lens group G1 consisting of a negative single lens, an aperture stop S, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power, and is characterized in that when focusing from the infinity object side to the close object side, the third lens group G3 moves toward the object side and the following condition is satisfied :
(2) -0.59≦f2/f1<-0.07
however,
f1: focal length of the first lens group G1
f2: focal length of the second lens group G2

A second aspect of the present invention relating to an inner focus optical system is characterized in that the following conditions are satisfied.
(1) -0.8<f/f1<-0.07
(3) 0.17<f/f3<1.1
(4) -1.5<f/f4<-0.3
where f is the focal length of the entire system when focused at infinity, f1 is the focal length of the first lens group G1, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4.

A third aspect of the present invention relating to an inner focus optical system is characterized in that the following conditions are satisfied.
(5) 1.1<M4<3.6
however,
M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

A fourth aspect of the invention relating to an inner focus optical system is characterized in that the following conditions are satisfied:
(6) 0.6<(M4^2×(1-M3^2))<5.0
however,
M3: Magnification load of the third lens group G3 when focusing on an object at infinity M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

A fifth aspect of the invention relating to an inner focus optical system is characterized in that the following conditions are satisfied:
(7) 60<VdG1
however,
VdG1: Abbe number of the first lens group G1

The sixth aspect of the present invention relating to the inner focus optical system is characterized in that the third lens group G3 having a positive refractive power is composed of a single lens.

A seventh aspect of the invention relating to an inner focus optical system is characterized in that the following conditions are satisfied:
(8) 2.3<D/Y<10.9
however,
D: Length from aperture stop S to 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 an angle of view equivalent to 28 to 40 mm in 35 mm equivalent focal length.

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 Example 1 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 according to a second embodiment 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 magnification of 0.025 in Example 2 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 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 with negative refractive power, an aperture stop S, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power, and when focusing from the infinite object side to the close object side, the third lens group G3 moves toward the object side.

The reason why the above configuration is necessary is as follows. That is, the off-axis chief ray that is incident on the first lens surface at a large angle relative to the optical axis is made gentler by the first lens group G1 with negative refractive power and is emitted to the aperture surface, and is further gentler by the second lens group G2 with positive refractive power. This makes it possible to make the inclination angle of the off-axis chief ray that is incident on the third lens group G3, which is the focus lens group, gentler, which contributes to reducing the rate of change of image height.

In addition, as shading becomes an issue when the angle of incidence on the image sensor becomes large, there is a demand for an optical system that reduces the exit angle of off-axis light beams. As mentioned above, because the angle of the off-axis chief ray incident on the focus lens group with respect to the optical axis is small, it is possible to reduce the angle of incidence of the off-axis chief ray reaching the image sensor without increasing the positive refractive power of the focus lens group. Furthermore, if the refractive power of the focus lens group is small, the lens group becomes lighter, making it easier for the focus lens group to vibrate slightly (wobble).

In addition, by placing a lens group with positive refractive power between the aperture and the focus lens group, the image of the aperture as seen by the focus group is projected far away, making it possible to reduce the rate of change in image height.

In addition, by placing an expansion lens group with negative refractive power on the image side of the focus lens group, the final group, it is possible to reduce the size of the entire system.

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 vibration (wobbling) along the optical axis, and has an angle of view equivalent to 28 to 40 mm in 35 mm equivalent focal length.

Furthermore, it is preferable that the inner focus optical system of this embodiment satisfies the following conditional expression.
(1) -0.8<f/f1<-0.07
(2) -1.2<f2/f1<-0.07
(3) 0.17<f/f3<1.1
(4) -1.5<f/f4<-0.3
where f is the focal length of the entire system when focused at infinity, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4.

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 reduce the angle of incidence of light rays at the peripheral angle of view and transfer the light rays to the subsequent optical system.

When the lower limit of conditional expression (1) is exceeded and the negative refractive power of the first lens group G1 becomes large, the curvature of the concave surface in the first lens group becomes even larger, which causes positive spherical aberration. In addition, the angle of incidence and height of the axial ray on the second lens group G2 become large, which causes high-order aberrations and makes aberration correction difficult. In addition, the back focus becomes long, which increases the overall length of the optical system.

On the other hand, when the upper limit of conditional expression (1) is exceeded and the negative refractive power of the first lens group G1 becomes small, the inclination angle of the lower ray passing through the aperture stop S is not alleviated, so the angle of incidence of the lower ray entering the subsequent lens group becomes large, making it difficult to correct the coma flare of the lower ray.

Regarding conditional expression (1), it is preferable to limit the lower limit to -0.6 and the upper limit to -0.1 to ensure the aforementioned effect.

In conditional expression (2), by appropriately defining the ratio of the focal lengths of the second lens group G2 and the first lens group G1, it is possible to maintain the maximum peripheral angle of view and achieve a large aperture ratio .

When the lower limit of conditional expression (2) is exceeded and the positive refractive power of the second lens group G2 becomes relatively small, or the negative refractive power of the first lens group G1 becomes large, the overall refractive power cannot be secured unless the positive refractive power of the third lens group G3, which is the focus lens group, is strengthened. This makes it difficult to simultaneously correct the fluctuations in spherical aberration and astigmatism during focusing.

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 relatively large or the negative refractive power of the first lens group G1 becomes small, it becomes difficult to correct spherical aberration and coma aberration when the aperture ratio is large.

Regarding conditional expression (2), it is preferable to limit the lower limit to -0.9 and the upper limit to -0.1 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 positive refractive power of the third lens group G3 becomes relatively 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.

On the other hand, if the upper limit of conditional expression (3) is exceeded and the positive refractive power of the third lens group G3 becomes relatively 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.

Regarding conditional expression (3), it is preferable to limit the lower limit to 0.2 and the upper limit to 0.8 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 negative refractive power of the fourth lens group G4 becomes large, the imaging magnification of the fourth lens group G4 shifts in the enlarging direction. To return the power of the entire system, the conjugate distance between the third lens group G3 and the fourth lens group G4 must be increased, and the axial marginal ray height in the fourth lens group G4 becomes low, causing the spherical aberration to become under. To correct this under spherical aberration, the remaining under spherical aberration in the second lens group G2 and the third lens group G3 must be corrected more, which is undesirable since it involves an increase in the number of lenses.

On the other hand, if the upper limit of conditional expression (4) is exceeded and the negative refractive power of the fourth lens group G4 becomes small, the negative component of the Petzval sum becomes insufficient, making it difficult to correct the curvature of field. This is also undesirable in terms of making the entire system compact.

Regarding conditional expression (4), it is preferable to limit the lower limit to -1.1 and the upper limit to -0.4 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:
(5) 1.1<M4<3.6
however,
M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

Conditional formula (5) defines the imaging magnification of the fourth lens group G4. As mentioned above, the inner focus optical system of the present invention has a retrofocus type refractive power arrangement, which is disadvantageous in terms of reducing the overall length. Therefore, by making the imaging magnification of the fourth lens group G4, which is the final group, a magnifying system, the increase in size due to the retrofocus type refractive power arrangement is suppressed.

When the lower limit of conditional expression (5) is exceeded and the imaging magnification of the fourth lens group G4 becomes small, it becomes difficult to make the entire system compact.

On the other hand, if the upper limit of conditional expression (5) is exceeded and the imaging magnification of the fourth lens group G4 becomes large, this is advantageous for making the entire system smaller, but the residual aberration up to the focus lens group doubles, making it difficult to correct that aberration.

Regarding conditional expression (5), it is preferable to limit the lower limit to 1.2 or even 1.3, and the upper limit to 3.0 or even 2.5, in order 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:
(6) 0.6<(M4^2×(1-M3^2))<5.0
however,
M3: Magnification load of the third lens group G3 when focusing on an object at infinity M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

Conditional expression (6) 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 (6) 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 (6) 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 large movements of the imaging surface, making it difficult to drive and control the third lens group G3, which is the focus lens group, within the focusing range during autofocus.

Regarding conditional expression (6), it is preferable to limit the lower limit to 0.75, or even 0.9, and the upper limit to 4.0, or even 3.3, in order 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:
(7) 60<VdG1
however,
VdG1: Abbe number of the first lens group G1

Condition (7) specifies the Abbe number of the first lens group G1 in order to achieve high performance.

If the lower limit of conditional expression (7) is exceeded and the Abbe number of the first lens group G1 becomes small, lateral chromatic aberration will worsen and it will be difficult to correct this throughout the entire lens system.

In addition, by setting the lower limit of the above-mentioned conditional formula (7) to 65.0, the above-mentioned effect can be more reliably achieved.

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) 2.3<D/Y<10.9
however,
D: Length from aperture stop S to image plane Y: Maximum image height

Conditional expression (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, and the fluctuation in the height of the chief ray of the focus lens group during wobbling becomes large, making it difficult to suppress the fluctuation in image height 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 3.1 and the upper limit to 8.2 in order 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 third lens group G3 is composed of a single lens, but by achromatizing the focus lens group with a cemented lens or a diffractive optical surface, it is also possible to suppress fluctuations in chromatic aberration caused by the movement of the focus lens group during focusing.

Next, we will explain various numerical examples related to the inner focus optical system of 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 distance between each surface, nd is the refractive index for the d line (wavelength λ=587.56 nm), and νd is the Abbe number for the d line. Also, BF represents the back focus.

For surfaces with numbers (apertures), the radius of curvature for the plane or aperture diaphragm is entered as ∞ (infinity). Also, the refractive index of air, n = 1.0000, is omitted.

[Aspheric Data] shows the coefficient values that give the aspheric shape of the lens surface marked with an * in [Surface Data]. The shape of the aspheric surface is expressed by the following formula, where y is the displacement in the direction perpendicular to the optical axis, z is the displacement (sag amount) from the intersection of the aspheric surface and the optical axis in the direction of the optical axis, K is the Conic coefficient, and A4, A6, A8, A10, and A12 are the aspheric coefficients of the 4th, 6th, 8th, 10th, and 12th orders, respectively.

[Various data] shows values such as focal length.

[Variable Distance Data] shows the variable distance and BF (back focus) values for each shooting distance state or shooting magnification 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. Note that for all of 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.

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 plane and meridional image plane, respectively. Furthermore, in the lens configuration diagrams shown in Figures 1, 6, and 11, S represents the aperture stop, FL represents the optical filter, I represents the image plane, and the dashed line passing through the center represents the optical axis.

In the following explanation, the lens configuration will be described from the object side to the image side.

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 consisting of a negative single lens, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power.

The first lens group G1 is composed of a negative meniscus lens with an aspheric image-side surface and a convex surface facing the object side.

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 with an aspheric surface on the object side and a biconvex lens with an aspheric surface on the image side, a positive meniscus lens with an aspheric surface on the image side and a concave surface facing the object side, and a biconvex lens.

The third lens group G3 is composed of a positive meniscus lens whose object-side surface is aspheric and whose convex surface faces the object side, and focusing from an object at infinity to a close-up object is performed by moving the third lens group G3 toward the object side along the optical axis.

The fourth lens group G4 is composed of a negative meniscus lens whose object-side surface is aspheric and whose convex surface faces 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 1 are shown below.

Numerical Example 1
Unit: mm
[Surface data]
Surface number rd nd vd
Object surface ∞ (d0)
1 16.5324 0.8000 1.43700 95.10
2* 13.0321 8.4338
3(Aperture) ∞ 11.2836
4* -9.3039 1.0000 1.59270 35.45
5 118.9830 7.8841 1.77250 49.62
6* -13.9342 1.0000
7 -60.8112 4.2208 1.49700 81.61
8* -47.8484 0.1500
9 30.0170 7.5282 1.49700 81.61
10 -47.0744 (d10)
11* 22.9318 3.7241 1.55032 75.50
12 106.9436 (d12)
13* 84.7571 0.8000 1.92119 23.96
14 22.2836 10.0000
15 ∞ 4.1400 1.51633 64.14
16∞(BF)
Image plane ∞

[Aspheric data]
2nd 4th 6th 8th
K 0.00000 0.00000 0.00000 0.00000
A4 -1.40793E-05 -8.88714E-05 1.82252E-05 -4.24503E-05
A6 -2.89659E-07 1.09131E-06 3.28042E-07 -7.69984E-08
A8 2.08183E-09 -2.16044E-08 -6.43814E-10 4.34939E-10
A10 -2.06973E-11 5.16629E-10 1.19666E-11 -1.36630E-12
A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00
11th page 13th page
K 0.00000 0.00000
A4 -2.49208E-05 -2.02672E-05
A6 -1.59829E-09 -7.31503E-08
A8 3.63229E-11 1.09107E-10
A10 -3.70201E-14 -5.44753E-13
A12 0.00000E+00 0.00000E+00

[Various data]
INF
Focal length 20.59
F-number 1.45
Full angle 2ω 57.90
Image height Y 11.15
Lens total length 70.00

[Variable interval data]
INF Magnification 0.025
d0∞802.9404
d10 3.4674 3.0390
d12 1.9000 2.3284
BF 3.6679 3.6729

[Lens group data]
Group Initial surface Focal length
G1 1 -151.38
G2 4 21.19
G3 11 52.22
G4 13 -33.02

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, in order from the object side to the image side, a first lens group G1 with negative refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power.

The first lens group G1 is composed of a negative meniscus lens with an aspheric surface on the object side and a convex surface facing the object side.

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, a positive meniscus lens with an aspheric surface on the image side and a concave surface facing the object side, and a positive meniscus lens with an aspheric surface on the image side and a concave surface facing the object side.

The third lens group G3 is composed of a positive meniscus lens whose object-side surface is aspheric and whose convex surface faces the object side, and focusing from an object at infinity to a close-up object is performed by moving the third lens group G3 toward the object side along the optical axis.

The fourth lens group G4 is composed of a negative meniscus lens with aspheric surfaces on both sides and 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
[Surface data]
Surface number rd nd vd
Object surface ∞ (d0)
1* 21.6358 1.0000 1.43700 95.10
2 11.8032 12.0243
3(Aperture) ∞ 6.0000
4* -17.6757 0.8000 2.00100 29.13
5* -23.3398 0.2000
6 -33.3919 9.6580 1.55032 75.50
7* -13.9686 0.1500
8 -302.7976 7.3989 1.55032 75.50
9* -19.0939 (d9)
10* 16.4632 3.9436 1.55032 75.50
11 30.0419 (d11)
12* 17.6203 0.8822 2.00069 25.46
13* 10.5251 10.0000
14 ∞ 4.1400 1.51633 64.14
15∞(BF)
Image plane ∞

[Aspheric data]
1st page 4th page 5th page 7th page
K 0.00000 0.00000 0.00000 0.00000
A4 1.68673E-05 -1.91370E-04 -8.26959E-05 -2.30008E-05
A6 -9.42904E-09 -3.54452E-07 2.20792E-07 1.01783E-07
A8 1.85045E-09 -2.00137E-08 -1.14459E-08 2.54191E-10
A10 -1.31681E-11 1.50464E-10 1.68067E-10 -2.59168E-12
A12 5.14341E-14 -8.09649E-13 -5.48010E-13 9.40185E-15
9th page 10th page 12th page 13th page
K 0.00000 0.00000 0.00000 0.00000
A4 5.49428E-05 1.07735E-05 2.10924E-05 -1.39508E-05
A6 -3.84536E-07 6.16213E-08 -6.37444E-07 -2.74455E-07
A8 1.87536E-09 -3.09031E-09 5.68264E-09 -7.13238E-09
A10 -4.62376E-12 3.27738E-11 -4.94840E-11 5.31543E-11
A12 5.42171E-15 -1.26989E-13 2.89265E-13 -3.42216E-13

[Various data]
INF
Focal length 21.20
F-number 1.49
Full angle 2ω 55.03
Image height Y 11.15
Lens total length 69.00

[Variable interval data]
INF Magnification 0.025
d0∞832.6781
d9 2.1204 1.8138
d11 1.9000 2.2065
BF 8.7826 8.7876

[Lens group data]
Group Initial surface Focal length
G1 1 -61.33
G2 4 20.65
G3 10 60.00
G4 12 -27.85

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 negative refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power.

The first lens group G1 is composed of a negative meniscus lens whose object-side surface is aspheric and whose convex surface faces the object side.

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, a positive meniscus lens with an aspheric surface on the image side and a concave surface facing the object side, and a positive meniscus lens with an aspheric surface on the image side and a concave surface facing the object side.

The third lens group G3 is composed of a positive meniscus lens whose object-side surface is aspheric and whose convex surface faces the object side, and focusing from an object at infinity to a close-up object is performed by moving the third lens group G3 toward the object side along the optical axis.

The fourth lens group G4 is composed of a negative meniscus lens with aspheric surfaces on both sides and 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 3 are shown below.

Numerical Example 3
Unit: mm
[Surface data]
Surface number rd nd vd
Object surface ∞ (d0)
1* 27.1914 1.0000 1.43700 95.10
2 10.0936 12.7736
3(Aperture) ∞ 6.0000
4* -30.0120 0.8508 2.00100 29.13
5* -53.3912 1.7718
6 -41.4334 8.6118 1.55032 75.50
7* -12.2177 0.1500
8 -56.6140 5.3874 1.55032 75.50
9* -20.3936 (d9)
10* 14.0151 5.0507 1.55032 75.50
11 147.4922 (d11)
12* 46.2372 0.8000 2.00069 25.46
13* 14.3389 10.0000
14 ∞ 4.1400 1.51633 64.14
15∞(BF)
Image plane ∞

[Aspheric data]
1st page 4th page 5th page 7th page
K 0.00000 0.00000 0.00000 0.00000
A4 4.48878E-05 -2.11513E-04 -5.34965E-05 -5.45601E-05
A6 -2.36839E-07 -4.75439E-07 5.85872E-07 6.06646E-07
A8 4.69680E-09 -3.32328E-08 -1.39203E-08 -4.04763E-09
A10 -2.95829E-11 2.87499E-10 1.27005E-10 1.46435E-11
A12 8.85833E-14 -4.97839E-12 -2.24767E-13 -1.63059E-14
9th page 10th page 12th page 13th page
K 0.00000 0.00000 0.00000 0.00000
A4 1.39162E-05 -4.24251E-05 6.94070E-06 2.53039E-05
A6 -4.03449E-07 3.12725E-08 -1.32935E-08 2.19366E-07
A8 1.96105E-09 -4.70035E-10 1.33767E-08 1.58321E-08
A10 -4.70167E-12 -2.03415E-11 -1.70921E-10 -7.18284E-11
A12 3.65647E-15 1.37417E-13 3.72324E-13 -1.16628E-12

[Various data]
INF
Focal Length 14.65
F-number 1.47
Full angle 2ω 74.12
Image height Y 11.15
Lens total length 65.00

[Variable interval data]
INF Magnification 0.025
d0∞571.5706
d9 2.6271 2.4853
d11 1.9000 2.0419
BF 3.9367 3.9417

[Lens group data]
Group Initial surface Focal length
G1 1 -37.40
G2 4 22.23
G3 10 27.77
G4 12 -21.03

Also shown is a list of values corresponding to the conditional expressions in each of these embodiments.
[Conditional expression corresponding value]
Conditional Expression Example 1 Example 2 Example 3
(1) f/f1 -0.14 -0.35 -0.39
(2) f2/f1 -0.14 -0.34 -0.59
(3) f/f3 0.39 0.35 0.53
(4) f/f4 -0.62 -0.76 -0.70
(5) M4 1.49 1.75 1.78
(6) (M4^2×(1-M3^2)) 1.18 1.70 2.54
(7) VdG1 95.10 95.10 95.10
(8) D/Y 5.45 5.02 4.59

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 (7)

An inner focus optical system comprising, in order from the object side to the image side, a first lens group G1 consisting of a negative single lens, an aperture stop S, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power, wherein when focusing from the infinity object side to the close object side, the third lens group G3 moves toward the object side, and the following condition is satisfied :
(2) -0.59≦f2/f1<-0.07
however,
f1: focal length of the first lens group G1
f2: focal length of the second lens group G2 2. The inner focus optical system according to claim 1, wherein the following condition is satisfied:
(1) -0.8<f/f1<-0.07
(3) 0.17<f/f3<1.1
(4) -1.5<f/f4<-0.3
where f is the focal length of the entire system when focused at infinity, f1 is the focal length of the first lens group G1, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4. 3. The inner focus optical system according to claim 1, wherein the following condition is satisfied:
(5) 1.1<M4<3.6
however,
M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity 4. The inner focus optical system according to claim 1, wherein the following condition is satisfied:
(6) 0.6<(M4^2×(1-M3^2))<5.0
however,
M3: Magnification load of the third lens group G3 when focusing on an object at infinity M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity 5. The inner focus optical system according to claim 1, wherein the following condition is satisfied:
(7) 60<VdG1
however,
VdG1: Abbe number of the first lens group G1 The inner focus optical system according to any one of claims 1 to 5, characterized in that the third lens group G3 having a positive refractive power is composed of a single lens. 7. The inner focus optical system according to claim 1, wherein the following condition is satisfied:
(8) 2.3<D/Y<10.9
however,
D: Length from aperture stop S to image plane Y: Maximum image height

Images