JP7706746B2 - 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 tendency to have a large optical length because their focal length is longer than that of standard angle of view lenses. In addition, because their angle of view is wider than that of super telephoto lenses, 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 shooting lenses with a large aperture ratio are desired. However, when the aperture ratio is increased, the entrance pupil becomes larger, making it difficult to correct spherical aberrations, etc. The challenge is to achieve better performance while 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 negative 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 infinity object side to the close object side, the third lens group G3 moves toward the object 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) 0.39<f/f1<2.29
(2) -2.71<f/f2<-0.30
(3) 0.62<f/f3<3.33
(4) -1.57<f/f4<-0.29
(5) 0.18<f/f12<0.76
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) 1.0<M4<2.74
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) 0.64<(M4^2×(1-M3^2))<3.51
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) 1.95<D/Y<8.71
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 negative 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 infinity 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: By making the refractive power of the lens group on the object side of the aperture positive, it is possible to suppress the diameter of the aperture, which tends to become large in a large aperture ratio medium telephoto optical system.

Also, by making the second lens group G2, which is closer to the image side than the aperture, negative refractive power, the partial system consisting of the first lens group G1 and the second lens group G2 can be made a telephoto type, making it possible to shorten the overall length of the partial system. Furthermore, by making the third lens group G3, which is a focus lens group, positive refractive power and placing the fourth lens group G4, which is a magnification system and has negative refractive power, behind it, the partial system consisting of the third lens group G3 and the fourth lens group G4 can also be made a telephoto type, and shortening the overall lengths of these two partial systems makes it possible to shorten the overall length of the entire system.

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, making it possible to suppress shading problems. It is also possible to reduce the rate of change in image height when the focus lens group is subjected to slight vibration (wobbling) in the direction along the optical axis. Furthermore, by constructing the first lens group G1 from a single lens, it is possible to make the first lens group G1 thinner, and the position of the aperture placed between the first lens group G1 and the second lens group G2 can be positioned closer to the object side.

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) 0.39<f/f1<2.29
(2) -2.71<f/f2<-0.30
(3) 0.62<f/f3<3.33
(4) -1.57<f/f4<-0.29
(5) 0.18<f/f12<0.76
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 expression (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 a large aperture ratio medium telephoto lens, and to suppress the occurrence of spherical aberration and coma aberration due to the large aperture ratio.

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 0.52 and the upper limit to 1.72 in order 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 the occurrence of spherical aberration and coma due to a large aperture ratio.

When the lower limit of the conditional expression (2) is exceeded and the negative refractive power of the second lens group G2 becomes large, the positive refractive power of the third lens group G3, which is the focus lens group, must be increased in order to ensure the overall refractive power. This makes it difficult to simultaneously correct the fluctuations in spherical aberration and astigmatism during focusing. It also makes it difficult to correct spherical aberration and coma when the aperture ratio is large.

On the other hand, if the upper limit of conditional expression (2) is exceeded and the negative refractive power of the second lens group G2 becomes small, the negative component of the Petzval sum becomes insufficient, making it difficult to correct the curvature of field. This increases the overall length of the partial system formed by the first lens group G1 and the second lens group G2, which undesirably increases the overall length of the entire system.

Regarding conditional expression (2), it is preferable to limit the lower limit to -2.03 and the upper limit to -0.40 to ensure the aforementioned 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 0.83 and the upper limit to 2.50 in order to ensure the above-mentioned effect.

Conditional formula (4) appropriately defines the ratio of the focal length of the fourth lens group G4 to the entire system. By appropriately defining the ratio of the focal length of the fourth lens group G4 to the entire system, it becomes possible to appropriately correct residual aberration up to the focus lens group in the fourth lens group G4, thereby improving the performance of the entire system.

In the present invention, the spherical aberration of the composite system composed of the focus lens group is over-corrected, and the spherical aberration of the fourth lens group G4 is under-corrected, thereby balancing the spherical aberration of the entire system. This is for the following reasons. The fourth lens group G4 has negative refractive power, but if the fourth lens group G4 is composed of only negative lenses, the positive distortion aberration increases, and the angle of incidence of light rays toward the peripheral image height on the imager increases, which is undesirable because the image height change rate increases when the focus lens group is subjected to micro-vibration (wobbling). Therefore, the above problem is suppressed by adding a positive lens as a component of the fourth lens group G4. However, as a side effect, the spherical aberration of the fourth lens group G4 tends to be under-corrected, so the spherical aberration of the composite system composed of the focus lens group is over-corrected to balance the spherical aberration of the entire system.

If the lower limit of conditional expression (4) is exceeded and the negative refractive power of the fourth lens group G4 becomes large, the spherical aberration of the fourth lens group G4 becomes even more under, which is undesirable. In addition, the imaging magnification of the fourth lens group G4 shifts in the enlargement direction, so in order to restore the power of the entire system, it is necessary to widen the conjugate distance between the third lens group G3 and the fourth lens group G4. If this distance is widened, over-spherical aberration occurs, making it easier to offset the spherical aberration that has increased in the under direction, but widening the distance is undesirable because it increases the size of the entire system. In addition, in order to independently correct the spherical aberration that has increased in the under direction, it is necessary to correct a lot of the under-spherical aberration remaining in the first lens group G1 and the third lens group G3, which is undesirable because 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. In addition, the imaging magnification of the fourth lens group G4 becomes reduced, making it easier to correct aberrations, but this is not desirable as it increases the size of the entire system.

Regarding conditional expression (4), it is preferable to limit the lower limit to -1.17 and the upper limit to -0.39 to ensure the above-mentioned effect.

In order to reduce the residual aberration of the fourth lens group G4 itself, the lenses that make up the fourth lens group G4 must be one positive lens and two negative lenses.

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 combined refractive power of the first and second lens groups G1 and G2 becomes small, the refractive power of the third lens group G3 must be increased or the magnification of the fourth lens group G4 must be decreased in order to maintain the refractive power of the entire system. In the present invention, the magnification of the fourth lens group G4 is set as a magnification, so the refractive power of the third lens group G3 must be increased. This reduces the amount of movement of the third lens group G3 required for focusing, but it becomes difficult to suppress aberration fluctuations during focusing while leaving the third lens group G3 composed of a single lens.

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, the refractive power of the third lens group G3 must be reduced or the magnification of the fourth lens group G4 must be increased to maintain the refractive power of the entire system. If the refractive power of the third lens group G3 is reduced, the amount of movement of the third lens group G3 required for focusing increases, so if a focus space is secured, the total optical length increases, hindering miniaturization. Furthermore, if the magnification of the fourth lens group G4 increases, the spherical aberration and coma aberration of the composite system, which worsen as the refractive power of the composite system of the first lens group G1 and the second lens group G2 increases, are multiplied, making it more difficult to correct aberrations.

Regarding conditional expression (5), it is preferable to limit the lower limit to 0.24 and the upper limit to 0.57 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:
(6) 1.0<M4<2.74
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. The inner focus optical system of the present invention achieves a compact overall system by making the imaging magnification of the fourth lens group G4, which is the final lens group, a magnified system.

When the lower limit of conditional expression (6) is exceeded and the imaging magnification of the fourth lens group G4 becomes small, the telephoto effect of the entire system is reduced, making it difficult to make the entire system compact.

On the other hand, if the upper limit of conditional expression (6) is exceeded and the imaging magnification of the fourth lens group G4 becomes large, the telephoto effect becomes stronger, which is advantageous for making the entire system smaller, but the residual aberration up to the focus lens group is multiplied, making it difficult to correct that aberration.

Regarding conditional expression (6), it is preferable to limit the lower limit to 1.1 and the upper limit to 2.06 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) 0.64<(M4^2×(1-M3^2))<3.51
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 0.86 and the upper limit to 2.63 in order 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) 1.95<D/Y<8.71
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 2.60 and the upper limit to 6.53 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:
(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 negative 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 positive meniscus lens with its 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 whose image-side surface is aspheric and whose concave surface faces the object side, a biconvex lens, and a negative meniscus lens whose object-side surface is aspheric and whose convex surface faces the object side.

The third lens group G3 is composed of a positive 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 object side along the optical axis.

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

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 24.8849 6.3708 1.49700 81.61
2 264.6310 5.0814
3 (Aperture) ∞ 3.3946
4 -33.3802 0.8000 2.00100 29.13
5* -131.5077 0.1500
6 60.0057 5.3630 1.90043 37.37
7 -34.9359 0.1500
8* 86.0823 0.8000 1.65412 39.62
9 16.1247 (d9)
10 16.2795 4.4166 1.55032 75.50
11 102.2351 (d11)
12 36.4441 2.9588 1.80610 33.27
13 13.3521 3.4796
14 26.5370 4.3206 1.90043 37.37
15 -33.7164 2.8610
16* -24.9791 0.8000 1.72342 37.99
17 41.9832 3.0000
18 ∞ 4.1400 1.51633 64.14
19∞(BF)
Image plane ∞

[Aspheric data]
5 sides 8 sides 16 sides
K 0.00000 0.00000 0.00000
A4 3.30176E-05 2.77895E-05 1.78694E-05
A6 -7.41734E-08 -1.36539E-07 2.94679E-07
A8 1.68699E-10 4.12143E-10 -2.50626E-09
A10 -1.90760E-13 -7.75838E-13 1.62075E-11

[Various data]
INF
Focal length 43.13
F-number 1.47
Full angle of view 2ω 28.71
Image height Y 11.15
Lens total length 60.00

[Variable interval data]
INF Magnification 0.025
d0∞1734.1134
d9 4.9943 4.1651
d11 1.0000 1.8292
BF 5.9192 5.9191

[Lens group data]
Group starting plane focal length
G1 1 54.78
G2 3 -72.15
G3 10 34.55
G4 12 -61.24

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 negative 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 biconvex lens whose image-side surface is aspheric.

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 positive meniscus lens with a convex surface facing the object side, and a negative meniscus lens with an aspheric surface facing the object side and a convex surface facing the object side.

The third lens group G3 is composed of a biconvex lens, and focusing from an object at infinity to an object at a close distance is performed by moving the third lens group G3 toward the object along the optical axis.

The fourth lens group G4 is composed of a negative meniscus lens with a convex surface facing the object side, a biconvex lens, and a negative meniscus lens with an aspheric surface facing the object side and a concave 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 23.3632 7.9992 1.55032 75.50
2* -160.1903 3.4400
3 (Aperture) ∞ 0.5000
4 18.0334 2.8668 1.90043 37.37
5 18.5055 2.0444
6* 59.4395 0.8000 1.95150 29.83
7 16.9284 (d7)
8 15.9988 4.5987 1.55032 75.50
9 -130.3185 (d9)
10 86.4453 0.8000 1.72342 37.99
11 13.4679 4.2369
12 42.4635 8.9820 1.90043 37.37
13 -24.4658 3.9285
14* -12.8288 0.8000 1.61310 44.36
15 -47.4260 3.0000
17 ∞ 4.1400 1.51633 64.14
18∞(BF)
Image plane ∞

[Aspheric data]
2 sides 6 sides 14 sides
K 0.00000 0.00000 0.00000
A4 8.66321E-06 -1.27276E-05 1.06941E-04
A6 -1.48730E-08 -7.74944E-08 4.83146E-07
A8 2.44521E-11 3.38220E-10 -3.49591E-09
A10 -1.90874E-14 -9.19347E-13 2.77248E-11

[Various data]
INF
Focal length 43.13
F-number 1.47
Full angle of view 2ω 28.72
Image height Y 11.15
Lens total length 55.00

[Variable interval data]
INF Magnification 0.025
d0∞1737.9805
d7 4.4939 3.7850
d9 1.0000 1.7089
BF 1.3696 1.3697

[Lens group data]
Group starting plane focal length
G1 1 37.63
G2 4 -31.87
G3 8 26.18
G4 10 -73.75

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 negative 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 positive meniscus lens whose image-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 positive meniscus lens with a convex surface facing the object side, and a negative meniscus lens with an aspheric surface on the image side and a convex surface facing the object side.

The third lens group G3 is composed of a biconvex lens, and focusing from an object at infinity to an object at a close distance is performed by moving the third lens group G3 toward the object along the optical axis.

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

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 20.4221 6.7866 1.55032 75.50
2* 61.5604 2.7570
3 (Aperture) ∞ 0.5000
4 28.3132 4.0590 1.90043 37.37
5 86.9006 1.6479
6 113.2986 0.8000 1.95150 29.83
7* 17.5484 (d7)
8 14.4817 5.1258 1.55032 75.50
9 -732.1173 (d9)
10 47.8498 0.8000 1.72342 37.99
11 12.0509 4.1929
12 44.2549 9.0427 1.90043 37.37
13 -24.2491 2.8409
14* -17.8322 0.8000 1.61310 44.36
15 194.7325 3.0000
16 ∞ 4.1400 1.51633 64.14
17∞(BF)
Image plane ∞

[Aspheric data]
2nd floor 7th floor 14th floor
K 0.00000 0.00000 0.00000
A4 -2.68715E-07 3.02055E-05 3.73810E-05
A6 9.61148E-09 1.49020E-07 6.21285E-07
A8 -2.42155E-11 -8.88368E-11 -5.62426E-09
A10 5.77072E-14 1.02418E-11 3.10005E-11

[Various data]
INF
Focal length 43.13
F-number 1.47
Full angle of view 2ω 28.69
Image height Y 11.15
Lens total length 55.00

[Variable interval data]
INF Magnification 0.025
d0∞1738.7004
d7 4.1572 3.5471
d9 1.0000 1.6100
BF 3.3501 3.3501

[Lens group data]
Group starting plane focal length
G1 1 52.46
G2 4 -54.84
G3 8 25.87
G4 10 -55.10

Example corresponding values Example 1 Example 2 Example 3
(1) 0.79 1.15 0.82
(2) -0.60 -1.35 -0.79
(3) 1.25 1.65 1.67
(4) -0.70 -0.58 -0.78
(5) 0.36 0.38 0.36
(6) 1.19 1.29 1.37
(7) 1.29 1.51 1.76
(8) 4.35 3.91 4.08
(9) 81.61 75.50 75.50

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 negative 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 :
(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) 0.39<f/f1<2.29
(2) -2.71<f/f2<-0.30
(3) 0.62<f/f3<3.33
(4) -1.57<f/f4<-0.29
(5) 0.18<f/f12<0.76
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) 1.0<M4<2.74
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) 0.64<(M4^2×(1-M3^2))<3.51
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) 1.95<D/Y<8.71
however,
D: Length from the aperture to the image plane Y: Maximum image height

Images