The purpose is to provide a large-aperture-ratio internal focusing telephoto lens applicable to a wider photographing area by equipping a vibration reduction function capable to satisfactorily correct a camera shake and the like with securing superb optical performance. The large-aperture-ratio internal focusing telephoto lens includes, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, and a third lens group G 3 having positive refractive power. The second lens group G 2 is moved along an optical axis upon changing focus from infinity to a close-range object. The first lens group G 1 has at least two cemented lenses and satisfies a given conditional expression. Either one of the cemented lens satisfies a given conditional expression.

Description

12 parts

›The disclosure of the following priority application is…

The disclosure of the following priority application is herein incorporated by reference:

Japanese Patent Application No. 2004-139123 filed on May 7, 2004.

›BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging objective lens suitable for a single-lens-reflex camera and an electric still camera and in particular to a large-aperture-ratio internal focusing telephoto lens.

2. Related Background Art

In a telephoto lens, optical performance tends to deteriorate so far with increasing longitudinal and lateral chromatic aberrations in accordance with extending the focal length or miniaturizing the optical system by shortening the total lens length. In Japanese Patent Application Laid-Open No. 6-201988, for example, it has been known that a focusing mechanism of a large-aperture-ratio internal focusing telephoto lens is small with securing optical performance by suppressing chromatic aberration such that a low dispersion positive lens having anomalous dispersion such as fluorite and a high dispersion negative lens are used in a front lens group where a paraxial ray height and an off-axial principal ray height passing thereof tend to become relatively high.

However, in a conventional large-aperture-ratio internal focusing telephoto lens, since the dimension of a focusing mechanism has to be still large, reduction of burden to a motor has not been sufficient. When a telephoto lens of this kind is made to be a vibration reduction lens, it causes problems that the diameters of a focusing lens group as well as a vibration reduction lens group become large and burden to the actuator becomes large.

›SUMMARY OF THE INVENTION

The present invention is made in view of the aforementioned problems and has an object to provide a large-aperture-ratio internal focusing telephoto lens applicable to a wider photographing area by equipping a vibration reduction function capable to satisfactorily correct a camera shake and the like with securing superb optical performance.

According to a first aspect of the present invention, a large-aperture-ratio internal focusing telephoto lens includes, in order from an object, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power. The second lens group is moved along an optical axis upon changing focus from infinity to a close-range object. The first lens group includes at least two cemented lenses.

In the first aspect of the present invention, it is preferable that either one of the cemented lens satisfies the following conditional expression (1):

20 <νp−νn (1)

where νp denotes Abbe number of the positive lens element in the cemented lens, and νn denotes Abbe number of the negative lens element in the cemented lens.

In the first aspect of the present invention, the first lens group preferably satisfies the following conditional expression (2):

0.4 <f 1 /f< 0.8 (2)

where f denotes the focal length of the large-aperture-ratio internal focusing telephoto lens, and f 1 denotes the focal length of the first lens group.

In the first aspect of the present invention, it is preferable that the first lens group includes at least four positive lens elements and at least two negative lens elements and the following conditional expression (3) is preferably satisfied:

2.7 <f 1 /(− f 2 )<5 (3)

where f 2 denotes the focal length of the second lens group G 2 .

In the first aspect of the present invention, it is preferable that the second lens group includes at least two negative lens elements and at least two positive lens elements and the following conditional expression (4) is preferably satisfied:

0.1<(− f 2 )/ f <0.3 (4).

Other features and advantages according to the present invention will be readily under stood from the detailed description of the preferred embodiments in conjunction with the accompanying drawings.

›BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 1 of the present invention.

FIG. 2A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 1 focusing at infinity and FIG. 2B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 1 focusing at infinity upon vibration reduction.

FIG. 3A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 1 focusing at a closest shooting distance and FIG. 3B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 1 focusing at a closest shooting distance upon vibration reduction.

FIG. 4 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 2 of the present invention.

FIG. 5A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 2 focusing at infinity and FIG. 5B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 2 focusing at infinity upon vibration reduction.

FIG. 6A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 2 focusing at a closest shooting distance and FIG. 6B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 2 focusing at a closest shooting distance upon vibration reduction.

FIG. 7 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 3 of the present invention.

FIG. 8A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 3 focusing at infinity and FIG. 8B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 3 focusing at infinity upon vibration reduction.

FIG. 9A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 3 focusing at a closest shooting distance and FIG. 9B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 3 focusing at a closest shooting distance upon vibration reduction.

FIG. 10 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 4 of the present invention.

FIG. 11A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 4 focusing at infinity and FIG. 11B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 4 focusing at infinity upon vibration reduction.

FIG. 12A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 4 focusing at a closest shooting distance and FIG. 12B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 4 focusing at a closest shooting distance upon vibration reduction.

FIG. 13 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 5 of the present invention.

FIG. 14A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 5 focusing at infinity and FIG. 14B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 5 focusing at infinity upon vibration reduction.

FIG. 15A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 5 focusing at a closest shooting distance and FIG. 15B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 5 focusing at a closest shooting distance upon vibration reduction.

FIG. 16 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 6 of the present invention.

FIG. 17A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 6 focusing at infinity and FIG. 17B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 6 focusing at infinity upon vibration reduction.

FIG. 18A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 6 focusing at a closest shooting distance and FIG. 18B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 6 focusing at a closest shooting distance upon vibration reduction.

›DESCRIPTION OF THE PREFERRED EMBODIMENTS · 1 of 2

A large-aperture-ratio internal focusing telephoto lens according to the present invention is explained below with reference to accompanying drawings.

The large-aperture-ratio internal focusing telephoto lens according to the present invention has a longer total lens length in comparison with an ordinary lens. Since the center of gravity of the lens comes considerably away from a camera, probability of causing camera shake, in particular, with hand-held shooting becomes high. In order to solve the problem, it is necessary to introduce a vibration reduction function that is carried out by moving a portion of the lens system perpendicularly to the optical axis.

In order to construct a vibration reduction mechanism with a simple construction, it is preferable that a first lens group G 1 having positive refractive power and a second lens group G 2 having negative refractive power, which carries out focusing, roughly form an afocal optical system and a third lens group G 3 , which is a master lens group, is used as a vibration reduction lens group.

In order to reduce burden to the motor for focusing and to the actuator for vibration reduction, it is necessary that the diameters of the second lens group and the third lens group are small.

In the large-aperture-ratio internal focusing telephoto lens according to the present invention, the f-number (FNO) of the whole optical system is substantially equal to that of the third lens group G 3 . Accordingly, spherical aberration has to be corrected at a height that is a ray height of a regular f-number in addition to a moving amount of the third lens group G 3 perpendicular to the optical axis.

In order to construct the third lens group G 3 with fewer lens elements such as a positive, a negative, and a positive lens elements, it is preferable that each lens element has high refractive index. Accordingly, g-line component of longitudinal chromatic aberration tends to be under-correction.

The first lens group G 1 is considerably high speed having an f-number (FNO) of about 1.1 and spherical aberration becomes largely under-correction, so that it is preferable that production of high order spherical aberration is suppressed and spherical aberration of each line is made to be equal. Moreover, it is preferable that g-line component of longitudinal chromatic aberration is under-correction.

The second lens group G 2 corrects spherical aberration and astigmatism produced by the first lens group G 1 and chromatic aberration produced by the whole optical system.

The large-aperture-ratio internal focusing telephoto lens according to the present invention includes, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, and a third lens group G 3 having positive refractive power. When the lens changes focus from infinity to a close-range object, the second lens group G 2 is moved along the optical axis. The first lens group G 1 includes at least two cemented lenses and either one of the cemented lens preferably satisfies the following conditional expression (1):

20 <νp−νn (1)

where νp denotes Abbe number of a positive lens element in the cemented lens in the first lens group G 1 , and νn denotes Abbe number of a negative lens element in the cemented lens in the first lens group G 1 .

The first lens group preferably satisfies the following conditional expression (2):

0.4 <f 1 /f <0.8 (2)

where f denotes the focal length of the large-aperture-ratio internal focusing telephoto lens, and f 1 denotes the focal length of the first lens group G 1 .

In the large-aperture-ratio internal focusing telephoto lens securing optical performance with keeping the total lens length short, it is preferable that refractive power of each lens element in the first lens group G 1 having positive refractive power is strong. However, when each power is made to be strong, it becomes difficult to make spherical aberration to be small. In order to correct spherical aberration and chromatic aberration, it is necessary to include an lens element having negative refractive power. However, when the first lens group G 1 has only one cemented lens, the radius of curvature of the cemented surface becomes small and high order spherical aberration is produced, so that it is preferable that the first lens group G 1 has at least two cemented lenses. Although it is effective for correcting spherical aberration to separate the cemented surface locating along the optical axis away from the aperture stop, curvatures of the sagittal image plane and the meridional image plane become conspicuous on the periphery of the image, so that it is undesirable.

Conditional expression (1) defines an appropriate range of Abbe numbers of the cemented lens elements in the first lens group G 1 .

When the value νp−νn is equal to or falls below the lower limit of conditional expression (1), refractive power of the cemented surface as a divergent surface becomes strong and high order spherical aberration is produced, so that it is undesirable. In order to secure the effect of the present invention, it is preferable to set the lower limit of conditional expression (1) to 30.

Conditional expression (2) defines an appropriate range of the focal length of the first lens group G 1 .

When the ratio f 1 /f is equal to or falls below the lower limit of conditional expression (2), the focal length f 1 of the first lens group G 1 becomes short and high order spherical aberration is produced, so that it becomes difficult to suppress variation in spherical aberration upon changing focus from infinity to a close-range object.

On the other hand, when the ratio f 1 /f is equal to or exceeds the upper limit of conditional expression (2), the focal length f 1 of the first lens group G 1 becomes long and a moving amount of the second lens group G 2 which is the focusing lens group becomes large, so that it becomes difficult to secure peripheral quantity of light.

In order to secure the effect of the present invention, it is preferable to set the upper limit of conditional expression (2) to 0.7 and the lower limit of conditional expression (2) to 0.5.

›DESCRIPTION OF THE PREFERRED EMBODIMENTS · 2 of 2

In the large-aperture-ratio internal focusing telephoto lens according to the present invention having the construction described above, the first lens group G 1 includes at least four positive lens elements and at least two negative lens elements and the following conditional expression (3) is preferably satisfied:

2.7 <f 1 /(− f 2 )<5 (3)

where f 2 denotes the focal length of the second lens group G 2 .

Conditional expression (3) defines an appropriate range of the ratio of the focal length of the first lens group G 1 to that of the second lens group G 2 .

When the ratio f 1 /(−f 2 ) is equal to or falls below the lower limit of conditional expression (3), a distance between the first lens group G 1 and the second lens group G 2 becomes small and the diameters of the second lens group G 2 and the third lens group G 3 become large, so that it is undesirable to construct an autofocus or a vibration reduction mechanism.

On the other hand, when the ratio f 1 /(−f 2 ) is equal to or exceeds the upper limit of conditional expression (3), the focal length of the second lens group G 2 becomes short and the height of the on-axis bundle of ray passing through the second lens group G 2 becomes low, so that spherical aberration produced in the first lens group G 1 becomes difficult to be corrected by the second lens group G 2 . Moreover, a principal ray of the oblique incident rays also passes through the second lens group G 2 at a low height, so that astigmatism made to be under-correction in the first lens group G 1 becomes difficult to be corrected by the second lens group G 2 .

In order to secure the effect of the present invention, it is preferable to set the upper limit of conditional expression (3) to 3.5 and the lower limit of conditional expression (3) to 2.75.

In the large-aperture-ratio internal focusing telephoto lens according to the present invention, it is preferable that the second lens group G 2 includes at least two negative lens elements and at least two positive lens elements and the following conditional expression (4) is preferably satisfied:

0.1<(− f 2 )/ f <0.3 (4).

Conditional expression (4) defines an appropriate range of the focal length of the second lens group G 2 .

When the ratio (−f 2 )/f is equal to or falls below the lower limit of conditional expression (4), the focal length f 2 of the second lens group G 2 becomes short and the height of the principal ray of oblique incident rays passing through the most object side surface of the first lens group G 1 becomes high, so that the diameter of the first lens group G 1 becomes large. When a cemented surface is arranged in the second lens group G 2 as shown in an example explained later, the radius of curvature of the cemented surface becomes small, so that spherical aberration becomes over-correction.

On the other hand, when the ratio (−f 2 )/f is equal to or exceeds the upper limit of conditional expression (4), the focal length f 2 of the second lens group G 2 becomes long, so that the diameter of the second lens group G 2 becomes large and the diameter of the third lens group G 3 also becomes large.

In order to secure the effect of the present invention, it is preferable to set the upper limit of conditional expression (4) to 0.25 and the lower limit of conditional expression (4) to 0.15.

Then, each example of the present invention is explained with reference to accompanying drawings.

›Examples6

›EXAMPLE 1

FIG. 1 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 1 of the present invention.

In FIG. 1 , the large-aperture-ratio internal focusing telephoto lens is composed of, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, an aperture stop S, and a third lens group G 3 having positive refractive power. The first lens group G 1 is composed of, in order from the object, a positive meniscus lens L 11 having a convex surface facing to the object, a cemented lens constructed by a double convex positive lens L 12 cemented with a double concave negative lens L 13 , a positive meniscus lens L 14 having a convex surface facing to the object, and a cemented lens constructed by a negative meniscus lens L 15 having a convex surface facing to the object cemented with a positive meniscus lens L 16 having a convex surface facing to the object. The second lens group G 2 is composed of, in order from the object, a cemented lens constructed by a positive meniscus lens L 21 having a concave surface facing to the object cemented with a double concave negative lens L 22 , and a cemented lens constructed by a positive meniscus lens L 23 having a concave surface facing to the object cemented with a double concave negative lens L 24 . The third lens group G 3 is composed of, a double convex positive lens L 31 , a negative meniscus lens L 32 having a concave surface facing to the object, and a positive meniscus lens L 33 having a concave surface facing to the object.

Upon changing focus from infinity to a close-range object, the second lens group G 2 is moved along the optical axis. Upon carrying out vibration reduction, the third lens group G 3 is moved perpendicularly to the optical axis as a whole so as to correct image blur on the image plane I.

Various values associated with Example 1 are listed in Table 1. In [Specifications], f denotes the focal length, FNO denotes the f-number, and 2ω denotes an angle of view (°). In [Lens Data], the first column shows the lens surface number counted in order from the object side, the second column “r” shows a radius of curvature of the lens surface, the third column “d” shows a distance between adjacent lens surfaces, the fourth column “νd” shows Abbe number of the medium at d-line (λ=587.6 nm), the fifth column “nd” shows refractive index of the medium at d-line, and the sixth column “ng” shows refractive index of the medium at g-line (λ=435.8 nm). In the second column “r”, “∞” denotes a plane surface. In the fifth column “nd” and the sixth column “ng”, refractive index of the air 1.000000 is omitted. In [Variable Distances], the focal length f or the shooting magnification β, and the variable distances are shown. B.f. denotes the back focal length.

In [Values for Conditional Expressions], values for respective conditional expressions are shown.

In the tables for various values, “mm” is generally used for the unit of length such as the focal length, the radius of curvature, and the distance between optical surfaces. However, since an optical system proportionally enlarged or reduced its dimension can be obtained similar optical performance, the unit is not necessary to be limited to “mm” and any other suitable unit can be used.

The explanation of reference symbols is the same in the other examples, so that duplicated explanations are omitted.

FIG. 2A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 1 focusing at infinity. FIG. 2B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 1 focusing at infinity upon vibration reduction. FIG. 3A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 1 focusing at a closest shooting distance. FIG. 3B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 1 focusing at a closest shooting distance upon vibration reduction.

In respective graphs, FNO denotes the f-number, NA denotes the numerical aperture, Y denotes an image height, d denotes d-line (λ=587.6 nm), and g denotes g-line (λ=435.8 nm). In graphs showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. In the following Examples, the same reference symbols as Example 1 are used, so that duplicated explanations are omitted.

As is apparent from respective graphs, the large-aperture-ratio internal focusing telephoto lens according to Example 1 shows superb optical performance correcting various aberrations.

›EXAMPLE 2

FIG. 4 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 2 of the present invention.

In FIG. 4 , the large-aperture-ratio internal focusing telephoto lens is composed of, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, an aperture stop S, and a third lens group G 3 having positive refractive power. The first lens group G 1 is composed of, in order from the object, a double convex positive lens L 11 , a cemented lens constructed by a double convex positive lens L 12 cemented with a double concave negative lens L 13 , and a cemented lens constructed by a positive meniscus lens L 14 having a convex surface facing to the object, a negative meniscus lens L 15 having a convex surface facing to the object, and a positive meniscus lens L 16 having a convex surface facing to the object. The second lens group G 2 is composed of, in order from the object, a double concave negative lens L 21 , and a cemented lens constructed by a positive meniscus lens L 22 having a concave surface facing to the object cemented with a double concave negative lens L 23 . The third lens group G 3 is composed of, in order from the object, a double convex positive lens L 31 , a negative meniscus lens L 32 having a concave surface facing to the object, and a positive meniscus lens L 33 having a concave surface facing to the object.

Various values associated with Example 2 are listed in Table 2.

FIG. 5A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 2 focusing at infinity. FIG. 5B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 2 focusing at infinity upon vibration reduction. FIG. 6A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 2 focusing at a closest shooting distance. FIG. 6B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 2 focusing at a closest shooting distance upon vibration reduction.

As is apparent from respective graphs, the large-aperture-ratio internal focusing telephoto lens according to Example 2 shows superb optical performance correcting various aberrations.

›EXAMPLE 3

FIG. 7 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 3 of the present invention.

In FIG. 7 , the large-aperture-ratio internal focusing telephoto lens is composed of, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, an aperture stop S, and a third lens group G 3 having positive refractive power. The first lens group G 1 is composed of, in order from the object, a double convex positive lens L 11 , a cemented lens constructed by a double convex positive lens L 12 cemented by a double concave negative lens L 13 , a positive meniscus lens L 14 having a convex surface facing to the object, and a cemented lens constructed by a negative meniscus lens L 15 having a convex surface facing to the object cemented with a positive meniscus lens L 16 having a convex surface facing to the object. The second lens group G 2 is composed of, in order from the object, a cemented lens constructed by a positive meniscus lens L 21 having a concave surface facing to the object cemented with a double concave negative lens L 22 , and a cemented lens constructed by a positive meniscus lens L 23 having a concave surface facing to the object cemented with a double concave negative lens L 24 . The third lens group G 3 is composed of, in order from the object, a double convex positive lens L 31 , a negative meniscus lens L 32 having a concave surface facing to the object, and a double convex positive lens L 33 .

Various values associated with Example 3 are listed in Table 3.

FIG. 8A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 3 focusing at infinity. FIG. 8B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 3 focusing at infinity upon vibration reduction. FIG. 9A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 3 focusing at a closest shooting distance. FIG. 9B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 3 focusing at a closest shooting distance upon vibration reduction.

As is apparent from respective graphs, the large-aperture-ratio internal focusing telephoto lens according to Example 3 shows superb optical performance correcting various aberrations.

›EXAMPLE 4

FIG. 10 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 4 of the present invention.

In FIG. 10 , the large-aperture-ratio internal focusing telephoto lens is composed of, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, an aperture stop S, and a third lens group G 3 having positive refractive power. The first lens group G 1 is composed of, in order from the object, a positive meniscus lens L 11 having a convex surface facing to the object, a positive meniscus lens L 12 having a convex surface facing to the object, a cemented lens constructed by a double convex positive lens L 13 cemented with a double concave negative lens L 14 , and a cemented lens constructed by a negative meniscus lens L 15 having a convex surface facing to the object cemented with a positive meniscus lens L 16 having a convex surface facing to the object. The second lens group G 2 is composed of, in order from the object, a negative meniscus lens L 21 having a convex surface facing to the object, and a cemented lens constructed by a positive meniscus lens L 22 having a concave surface facing to the object cemented with a double concave negative lens L 23 . The third lens group G 3 is composed of, in order from the object, a double convex positive lens L 31 , a negative meniscus lens L 32 having a concave surface facing to the object, and a double convex positive lens L 33 .

Various values associated with Example 4 are listed in Table 4.

FIG. 11A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 4 focusing at infinity. FIG. 11B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 4 focusing at infinity upon vibration reduction. FIG. 12A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 4 focusing at a closest shooting distance. FIG. 12B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 4 focusing at a closest shooting distance upon vibration reduction.

As is apparent from respective graphs, the large-aperture-ratio internal focusing telephoto lens according to Example 4 shows superb optical performance correcting various aberrations.

›EXAMPLE 5

FIG. 13 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 5 of the present invention.

In FIG. 13 , the large-aperture-ratio internal focusing telephoto lens is composed of, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, an aperture stop S, and a third lens group G 3 having positive refractive power. The first lens group G 1 is composed of, in order from the object, a double convex positive lens L 11 , a cemented lens constructed by a double convex positive lens L 12 cemented with a double concave negative lens L 13 , a positive meniscus lens L 14 having a convex surface facing to the object, and a cemented lens constructed by a negative meniscus lens L 15 having a convex surface facing to the object cemented with a positive meniscus lens L 16 having a convex surface facing to the object. The second lens group G 2 is composed of, in order from the object, a cemented lens constructed by a double convex positive lens L 21 cemented with a double concave negative lens L 22 , and a cemented lens constructed by a positive meniscus lens L 23 having a concave surface facing to the object cemented with a double concave negative lens L 24 . The third lens group G 3 is composed of, in order from the object, a double convex positive lens L 31 , a negative meniscus lens L 32 having a concave surface facing to the object, and a double convex positive lens L 33 .

Various values associated with Example 5 are listed in Table 5.

FIG. 14A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 5 focusing at infinity. FIG. 14B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 5 focusing at infinity upon vibration reduction. FIG. 15A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 5 focusing at a closest shooting distance. FIG. 15B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 5 focusing at a closest shooting distance upon vibration reduction.

As is apparent from respective graphs, the large-aperture-ratio internal focusing telephoto lens according to Example 5 shows superb optical performance correcting various aberrations.

›EXAMPLE 6

FIG. 16 is a diagram showing a sectional view of a large-aperture-ratio internal focusing telephoto lens according to Example 6 of the present invention.

In FIG. 16 , the large-aperture-ratio internal focusing telephoto lens is composed of, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, an aperture stop S, and a third lens group G 3 having positive refractive power. The first lens group G 1 is composed of, in order from the object, a double convex positive lens L 11 , a cemented lens constructed by a double convex positive lens L 12 cemented with a double concave negative lens L 13 , a cemented lens constructed by a double convex positive lens L 14 cemented with a double concave negative lens L 15 , and a cemented lens constructed by a negative meniscus lens L 16 having a convex surface facing to the object cemented with a positive meniscus lens L 17 having a convex surface facing to the object. The second lens group G 2 is composed of, in order from the object, a negative meniscus lens L 21 having a convex surface facing to the object, and a cemented lens constructed by a positive meniscus lens L 22 having a concave surface facing to the object cemented with a double concave negative lens L 23 . The third lens group G 3 is composed of, in order from the object, a double convex positive lens L 31 , a negative meniscus lens L 32 having a concave surface facing to the object, and a positive meniscus lens L 33 having a concave surface facing to the object.

Various values associated with Example 6 are listed in Table 6.

FIG. 17A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 6 focusing at infinity. FIG. 17B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 6 focusing at infinity upon vibration reduction. FIG. 18A shows various aberrations of the large-aperture-ratio internal focusing telephoto lens according to Example 6 focusing at a closest shooting distance. FIG. 18B shows coma of the large-aperture-ratio internal focusing telephoto lens according to Example 6 focusing at a closest shooting distance upon vibration reduction.

As is apparent from respective graphs, the large-aperture-ratio internal focusing telephoto lens according to Example 6 shows superb optical performance correcting various aberrations.

As described above, the present invention provides a large-aperture-ratio internal focusing telephoto lens applicable to a wider photographing area by equipping a vibration reduction function capable to satisfactorily correct a camera shake and the like with securing superb optical performance.

Additional advantages and modification will readily occur to those skilled in the art. Therefore, the invention in its broader aspect is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

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8 codes

IPC · International Patent Classification

Section G — Physics

G02B13/02
G02B27/64
G02B15/14
G02B9/14

USPC · US Patent Classification

359/745359/785359/787359/786

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2 RCE

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Ricky L Mack

art unit 2873 · TC 2800

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Citations: 13 back · 6 forward

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