JP5475401B2 - Large-aperture telephoto zoom lens with anti-vibration function - Google Patents

Description

The present invention relates to a zoom lens used in a digital still camera or the like, and particularly has a telephoto end angle of view of 13 degrees or less, a zoom ratio of about 3 times, and an open F value in the entire zoom range of about 2.8. The present invention relates to a large-aperture telephoto zoom lens having an anti-vibration function.

Large aperture with anti-vibration function corresponding to a 35 mm image sensor size with a telescopic angle of view of 13 degrees or less, a zoom ratio of about 3 times, and an open F value of about 2.8 over the entire zoom range. Patent Documents 1 and 2 are disclosed as telephoto zoom lenses.

Patented as a large-aperture telephoto zoom lens with a telephoto side angle of view of 13 degrees or less, a zoom ratio of about 3 times, and an open F value of about 2.8 over the entire zoom range, corresponding to the 35 mm image sensor size. Documents 3 and 4 are disclosed.

JP 2003-090958 A

JP 2002-162564 A

Japanese Patent Laid-Open No. 7-140386

JP 2008-216480 A

The optical system disclosed in Patent Document 1 cannot fully correct the under field curvature at an image height of 15 mm or more particularly at the telephoto end. In addition, the amount of peripheral light is not sufficient, and the total length is long. Therefore, improvement of the peripheral light amount and reduction of the total length have been problems.

Although the optical system disclosed in Patent Document 2 is compact in overall length, correction of spherical aberration due to strong power of each group is insufficient, and it can be said that it has high optical performance over the entire zoom range. Absent.

The optical system disclosed in Patent Document 3 has no anti-vibration function, and mounting an anti-vibration function has been a problem.

The optical system disclosed in Patent Document 4 has no anti-vibration function, and mounting an anti-vibration function has been a problem. In addition, there is a problem of improving the focusing speed, which is slow due to the large number of lenses that move during focusing and the heavy weight.

The present invention solves the above-mentioned problems, has a telephoto end angle of view of 13 degrees or less, a zoom ratio of about 3 times, and a compact, open F-number over the entire zoom range of about 2.8 and good optical performance. An object of the present invention is to provide a large-aperture telephoto zoom lens having a proper anti-vibration function.

In order to solve the above-mentioned problem, the first invention according to the present invention has, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a positive refractive power. The fourth lens group G3 includes a third lens group G3 and a fourth lens group G4 having positive refractive power, and performs zooming by moving the second lens group G2 and the third lens group G3 along the optical axis. In the zoom lens, the fourth lens group G4 includes, in order from the object side, a front group G4f having positive refractive power, a middle group G4m having negative refractive power, and a rear group G4r having positive refractive power. The image forming position is displaced by decentering G4m in a direction substantially perpendicular to the optical axis. The front group G4f includes only two lenses having positive refractive power, and the middle group G4m includes lenses having positive refractive power. A cemented lens with a negative refractive power lens and one negative refractive power lens In addition, the rear group G4r provides a large-aperture telephoto zoom lens having an anti-vibration function, including three lenses having positive refractive power and one lens having negative refractive power, and satisfying the following conditions: To do.
(1) 0.80 <βG4mr <1.25
(2) -0.28 <F4m / Ft <-0.18
F4m: focal length of the middle group G4m Ft: focal length of the entire lens system at the telephoto end βG4mr: combined magnification of the middle group G4m and the rear group G4r at all zoom positions

A second invention according to the present invention provides a large-aperture telephoto zoom lens having the image stabilization function according to the first invention, characterized by satisfying the following conditions.
(3) 0.10 <D4f / F4f <0.16
F4f: focal length of the front group G4f D4f: distance along the optical axis between the most object side surface and the most image side surface of the front group G4f

According to a third aspect of the present invention, there is provided a large-aperture telephoto zoom lens having the image stabilization function according to the first aspect of the invention, which satisfies the following conditions.
(4) 1 <(0.8−0.0043 × ν4mn) / (N4mn−1)
N4mn: Refractive index of the negative refractive power lens constituting the cemented lens in the middle group G4m ν4mn: Abbe number of the negative refractive power lens constituting the cemented lens in the middle group G4m

According to a fourth aspect of the present invention, the first lens group G1 includes a fixed G1a lens group that does not move during focusing from the object surface side in order, and moves on the optical axis to perform focusing. The G1a lens group includes one negative refractive power lens and one positive refractive power lens, and the G1b lens group includes only two positive refractive power lenses. A large-aperture telephoto zoom lens having the image stabilization function of the first or second invention is provided.

According to a fifth aspect of the present invention, there is provided a large-aperture telephoto zoom lens having the image stabilization function according to the first to third aspects, wherein the following conditions are satisfied.
(5) 0.80 <L23w / Fw <0.93
L23w: Distance from the front surface of the second lens group G2 to the final surface of the third lens group G3 at the wide angle end Fw: Focal length of the entire lens system at the wide angle end

The present invention relates to a zoom lens used in a digital still camera or the like. In particular, the angle of view at the telephoto end is 13 degrees or less, the zoom ratio is about 3 times, and the open F-number over the entire zoom range is 2. A large-aperture telephoto zoom lens having an anti-vibration function of about .8 can be provided.

Sectional view of the zoom lens of Example 1 at infinity at the wide-angle end Longitudinal aberration diagram of the zoom lens of Example 1 at infinity at the wide-angle end Longitudinal aberration diagram of the zoom lens of Example 1 at infinity at the telephoto end Lateral aberration diagram in the standard state at infinity at the wide-angle end of the zoom lens of Example 1 Transverse aberration diagram in the standard state at infinity at the telephoto end of the zoom lens of Example 1 Transverse aberration diagram during vibration isolation at infinity at the wide-angle end of the zoom lens of Example 1 Transverse aberration diagram during vibration isolation at infinity at the telephoto end of the zoom lens of Example 1 Sectional view of the zoom lens of Embodiment 2 at infinity at the wide-angle end Longitudinal aberration diagram at infinity at the wide-angle end of the zoom lens in Example 2 Longitudinal aberration diagram of the zoom lens of Example 2 at infinity at the telephoto end Transverse aberration diagram in the standard state at infinity at the wide-angle end of the zoom lens of Example 2 Transverse aberration diagram in the standard state at infinity at the telephoto end of the zoom lens of Example 2 Lateral aberration diagram during image stabilization at infinity at the wide-angle end of the zoom lens of Example 2 Lateral aberration diagram during vibration isolation at infinity at the telephoto end of the zoom lens of Example 2 Sectional view of the zoom lens of Embodiment 3 at infinity at the wide-angle end Longitudinal aberration diagram of the zoom lens of Example 3 at infinity at the wide-angle end Longitudinal aberration diagram at infinity of the telephoto end of the zoom lens of Example 3 Transverse aberration diagram in the standard state at infinity at the wide-angle end of the zoom lens of Example 3 Transverse aberration diagram in the standard state at infinity at the telephoto end of the zoom lens of Example 3 Lateral aberration diagram during vibration isolation at infinity at the wide-angle end of the zoom lens of Example 3 Lateral aberration diagram during vibration isolation at infinity at the telephoto end of the zoom lens of Example 3 Sectional view of the zoom lens of Embodiment 4 at infinity at the wide-angle end Longitudinal aberration diagram at infinity at the wide-angle end of the zoom lens in Example 4 Longitudinal aberration diagram at infinity at the telephoto end of the zoom lens of Example 4 Transverse aberration diagram in the standard state at infinity at the wide-angle end of the zoom lens in Example 4 Transverse aberration diagram in the standard state at infinity at the telephoto end of the zoom lens of Example 4 Lateral aberration diagram during vibration isolation at infinity at the wide-angle end of the zoom lens in Example 4 Lateral aberration diagram during vibration isolation at infinity at the telephoto end of the zoom lens of Example 4 Sectional view of the zoom lens of Embodiment 5 at infinity at the wide-angle end Longitudinal aberration diagram at infinity at the wide-angle end of the zoom lens in Example 5 Longitudinal aberration diagram at infinity of the telephoto end of the zoom lens of Example 5 Transverse aberration diagram in the standard state at infinity at the wide-angle end of the zoom lens in Example 5 Transverse aberration diagram in the standard state at infinity at the telephoto end of the zoom lens of Example 5 Lateral aberration diagram during vibration isolation at infinity at the wide-angle end of the zoom lens in Example 5 Lateral aberration diagram during vibration isolation at infinity at the telephoto end of the zoom lens of Example 5

In order from the object side, the first lens group G1 having positive refractive power, the second lens group G2 having negative refractive power, the third lens group G3 having positive refractive power, and the fourth lens group G4 having positive refractive power. The second lens group G2 and the third lens group G3 are moved along the optical axis to perform zooming. The fourth lens group G4 includes, in order from the object side, a front group G4f having positive refractive power, a middle group G4m having negative refractive power, and a rear group G4r having positive refractive power. The imaging position is moved by decentering in a direction substantially perpendicular to the axis.

In the fourth lens group G4 of the large-aperture telephoto zoom lens having the image stabilization function of the present invention, the front group G4f having positive refracting power is composed of only two lenses having positive refracting power, and generates spherical aberration and coma aberration. It is configured to suppress as much as possible. Further, by reducing the composite magnification of the middle group G4m and the rear group G4r, the incidence angle of the F-number light beam on the middle group G4m is reduced, and the occurrence of various aberrations, particularly higher-order spherical aberration, can be suppressed. .

However, in the fourth lens group G4, if the combined magnification of the middle group G4m and the rear group G4r is too small, the diameter of the middle group G4m becomes large, and it is difficult to arrange the vibration-proof mechanism. Therefore, it is desirable to satisfy the following conditional expressions (1) and (2).
(1) 0.80 <βG4mr <1.25
(2) -0.28 <F4m / Ft <-0.18
F4m: focal length of the middle group G4m Ft: focal length of the entire lens system at the telephoto end βG4mr: combined magnification of the middle group G4m and the rear group G4r at all zoom positions

Conditional expression (1) determines the composite magnification of the middle group G4m and the rear group G4r in the fourth lens group G4. If the upper limit of conditional expression (1) is exceeded, the angle of incidence of the F-number light beam on the middle group G4m will become tight, and it will be difficult to satisfactorily correct spherical aberration that suddenly becomes under the vicinity of the marginal end of the telephoto end. If the lower limit of conditional expression (1) is exceeded, it is impossible to achieve both the entire length of the fourth lens group G4 and the reduction in the diameter of the middle group G4m.

Conditional expression (2) defines the ratio of the focal length of the middle group G4m in the fourth lens group G4 to the focal length of the entire system at the telephoto end. Exceeding the upper limit of conditional expression (2) makes it difficult to correct astigmatism, particularly at the telephoto end. When the lower limit of conditional expression (2) is exceeded, it is difficult to secure a sufficient camera shake correction angle at the telephoto end.

In the fourth lens group G4 of the large-aperture telephoto zoom lens having the image stabilization function of the present invention, the axial thickness of G4f composed of only two lenses having positive refractive power is increased, so that the light enters the middle group G4m. It is possible to correct an under curvature of field particularly at the telephoto end while reducing the ray height. Therefore, it is desirable to satisfy the following conditional expression (3).
(3) 0.10 <D4f / F4f <0.16
F4f: focal length of fourth lens group front group G4f D4f: distance along the optical axis between the most object side surface and the most image side surface of fourth lens group front group G4f

Conditional expression (3) defines the ratio of the focal length of the fourth lens unit front group G4f and the distance along the optical axis between the most object-side surface and the most image-side surface of G4f. Exceeding the upper limit of conditional expression (3) causes an increase in material cost and a decrease in workability. Exceeding the lower limit of conditional expression (3) makes it difficult to correct under field curvature, especially at the telephoto end, and to efficiently reduce the height of light incident on the fourth lens group. I can't.

In the fourth lens group G4 of the large-aperture telephoto zoom lens having the image stabilization function of the present invention, the front group G4f having a positive refractive power is composed of only two positive refractive power lenses, and chromatic aberration correction is performed in the fourth lens group. It will be done for the entire G4. At this time, since the burden on the chromatic aberration correction of the middle group G4m alone is reduced and the degree of freedom in selecting the material is increased, the following conditional expression (4) is particularly satisfied in the large-aperture telephoto zoom lens having the image stabilization function of the present invention. I decided to.
(4) 1 <(0.8−0.0043 × ν4mn) / (N4mn−1)
N4mn: the refractive index of the negative refractive power lens constituting the middle group G4m and the cemented lens ν4mn: the Abbe number of the negative refractive power lens constituting the middle group G4m and the cemented lens

Conditional expression (4) defines the range of the refractive index and the Abbe number of the negative refractive power lens constituting the cemented lens among the middle group G4m in the fourth lens group G4. Since the material within the range defined by the conditional expression (4) has a low specific gravity, it is possible to reduce the weight of the middle group G4m, which is a movable part.

In the large-aperture telephoto zoom lens having the image stabilization function of the present invention, the first lens group G1 is moved in focus from the object side to the fixed G1a lens group that does not move during focusing. The G1b lens group includes one negative refractive power lens and one positive refractive power lens, and the G1b lens group includes only two positive refractive power lenses. It is characterized by that. By constituting the G1b lens group only with positive refracting power lenses, the curvature of each surface can be relaxed, and the occurrence of higher-order spherical aberration and coma can be suppressed. Further, since the G1b lens group can be reduced in weight, the focusing speed can be improved. Preferably, the entire first lens group G1 is composed of one negative refracting power lens and three positive refracting power lenses, so that the overall length of the first lens group G1 can be shortened, and the amount of peripheral light is secured. The total weight can be reduced.

In addition, in the large-aperture telephoto zoom lens having an image stabilization function according to the present invention, the overall length of the zooming unit composed of the second lens group G2 and the third lens group G3 is designed to be short, so that the zoom lens has a compact overall length. Can be realized.

However, if the overall length of the zooming portion is made too short, the powers of the second lens group G2 and the third lens group G3 become strong, making it difficult to correct various aberrations. Therefore, it is desirable to satisfy the following conditions.
(5) 0.80 <L23w / Fw <0.93
L23w: Distance from the front surface of the second lens group G2 to the final surface of the third lens group G3 at the wide angle end Fw: Focal length of the entire lens system at the wide angle end

Conditional expression (4) defines the ratio of the distance from the leading surface of the second lens group G2 at the wide-angle end to the final surface of the third lens group G3 and the focal length of the entire lens system at the wide-angle end. If the upper limit of conditional expression (4) is exceeded, the powers of the second lens group G2 and the third lens group G3 become loose, which is advantageous for correcting various aberrations that occur during zooming, but the total lens length becomes long. If the lower limit of conditional expression (4) is exceeded, the power of the second lens group G2 and the third lens group G3 will become strong, and it will be difficult to correct spherical aberration that occurs particularly during zooming. In addition, it is difficult to control product variations with respect to manufacturing tolerances, and sufficient optical performance cannot be achieved over the entire zoom range.

Numerical examples 1 to 5 according to the variable magnification imaging optical system of the present invention are shown below.

In each numerical example, f in the overall specifications is a focal length. Fno indicates the F number, and 2ω indicates the diagonal field angle. The numbers in the lens specifications are the surface number of the lens from the object side, R is the radius of curvature of the lens surface, D is the distance between the lens surfaces, nd is the refractive index of the d-line (wavelength 587.56 nm), and νd is the d-line reference. Indicates the Abbe number. Bf represents back focus. In the figure, d-line, g-line, and C-line are aberrations at respective wavelengths. ΔS represents a sagittal image plane of d line, and ΔM represents a meridional image plane of d line.

In Example 1, the fourth lens group includes, in order from the object side, a front group G4f having positive refractive power, a middle group G4m having negative refractive power, and a rear group G4r having positive refractive power. The image forming position is displaced by decentering in a direction substantially perpendicular to the axis. The front group G4f includes two lenses having positive refractive power, and the middle group G4m includes a lens having positive refractive power and a negative refractive power. The rear lens group G4r is composed of three lenses having a positive refractive power and one lens having a negative refractive power.

In Example 2, the fourth lens group includes, in order from the object side, a front group G4f having a positive refractive power, a middle group G4m having a negative refractive power, and a rear group G4r having a positive refractive power. The image forming position is displaced by decentering in a direction substantially perpendicular to the axis. The front group G4f includes two lenses having positive refractive power, and the middle group G4m includes a lens having positive refractive power and a negative refractive power. The rear lens group G4r is composed of three lenses having a positive refractive power and one lens having a negative refractive power.

In Example 3, the fourth lens group includes, in order from the object side, a front group G4f having positive refractive power, a middle group G4m having negative refractive power, and a rear group G4r having positive refractive power. The image forming position is displaced by decentering in a direction substantially perpendicular to the axis. The front group G4f includes two lenses having positive refractive power, and the middle group G4m includes a lens having positive refractive power and a negative refractive power. The rear lens group G4r is composed of three lenses having a positive refractive power and one lens having a negative refractive power.

In Example 4, the fourth lens group includes, in order from the object side, a front group G4f having positive refractive power, a middle group G4m having negative refractive power, and a rear group G4r having positive refractive power. The image forming position is displaced by decentering in a direction substantially perpendicular to the axis. The front group G4f includes two lenses having positive refractive power, and the middle group G4m includes a lens having positive refractive power and a negative refractive power. The rear lens group G4r is composed of three lenses having a positive refractive power and one lens having a negative refractive power.

In Example 5, the fourth lens unit includes, in order from the object side, a front group G4f having positive refractive power, a middle group G4m having negative refractive power, and a rear group G4r having positive refractive power. The image forming position is displaced by decentering in a direction substantially perpendicular to the axis. The front group G4f includes two lenses having positive refractive power, and the middle group G4m includes a lens having positive refractive power and a negative refractive power. The rear lens group G4r is composed of three lenses having a positive refractive power and one lens having a negative refractive power.

The variable magnification optical system of each numerical example satisfies all the above conditions.

G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group G1a Front group G1b of the first lens group Rear group G4f of the first lens group G4m of the front group G4m of the fourth lens group Middle group G4r Rear group S of the fourth lens group I Diaphragm I Image surface d d line g g line C C line ΔS Sagittal image surface ΔM Meridional image surface

Claims (5)

In order from the object side, the first lens group G1 having positive refractive power, the second lens group G2 having negative refractive power, the third lens group G3 having positive refractive power, and the fourth lens group G4 having positive refractive power. In the four-group zoom lens that is configured to perform zooming by moving the second lens group G2 and the third lens group G3 along the optical axis, the fourth lens group G4 is arranged in order from the object side. It comprises a front group G4f having a refractive power, a middle group G4m having a negative refractive power, and a rear group G4r having a positive refractive power. The middle group G4m is decentered in a direction substantially perpendicular to the optical axis to displace the imaging position. The front group G4f includes only two lenses having a positive refractive power, and the middle group G4m includes a cemented lens of a lens having a positive refractive power and a lens having a negative refractive power and one lens having a negative refractive power. In addition, the rear group G4r includes three lenses having positive refractive power and negative bending It contains one power of the lens, large aperture telephoto zoom lens with a vibration reduction function that satisfies the following conditions.
(1) 0.80 <βG4mr <1.25
(2) -0.28 <F4m / Ft <-0.18
F4m: focal length of the middle group G4m Ft: focal length of the entire lens system at the telephoto end βG4mr: combined magnification of the middle group G4m and the rear group G4r at all zoom positions The large-aperture telephoto zoom lens having an image stabilization function according to claim 1, wherein the following conditions are satisfied.
(3) 0.10 <D4f / F4f <0.16
F4f: focal length of the front group G4f D4f: distance along the optical axis between the most object side surface and the most image side surface of the front group G4f The large-aperture telephoto zoom lens having an anti-vibration function according to claim 1 or 2, wherein the following conditions are satisfied.
(4) 1 <(0.8−0.0043 × ν4mn) / (N4mn−1)
N4mn: Refractive index of the negative refractive power lens constituting the cemented lens in the middle group G4m ν4mn: Abbe number of the negative refractive power lens constituting the cemented lens in the middle group G4m The first lens group G1 is composed of a fixed G1a lens group that does not move in focus from the object plane side in order, and a G1b lens group that moves on the optical axis and performs focusing, and the G1a lens group is 4. The apparatus according to claim 1, further comprising: one negative refractive power lens and one positive refractive power lens, wherein the G1b lens group includes only two positive refractive power lenses. A large-aperture telephoto zoom lens having an anti-vibration function as described in 1. The large-aperture telephoto zoom lens having a vibration-proof function according to any one of claims 1 to 4, wherein the following conditions are satisfied. .
(5) 0.80 <L23w / Fw <0.93
L23w: Distance from the front surface of the second lens group G2 to the final surface of the third lens group G3 at the wide angle end Fw: Focal length of the entire lens system at the wide angle end

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