JP5239083B2 - High magnification zoom lens - Google Patents

Description

  The present invention is a high-magnification zoom lens suitable for a single-lens reflex digital camera. More specifically, the angle of view on the wide-angle side exceeds 75 °, the wide-angle end F-number is about 3 to 4, and the telephoto single F-number is about 6 to 7. The present invention relates to a compact and lightweight high-magnification zoom lens suitable for a single-lens reflex digital camera, which has a zoom ratio of about 15 times and is advantageous for incorporation of an anti-vibration mechanism.

With recent advances in optical design technology and manufacturing technology, zoom lenses have been reduced in size and increased in magnification. For example, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a first lens group having a positive refractive power. And a distance between the first lens group and the second lens group increases during zooming from the wide-angle end state to the telephoto end state, and the second lens group and the third lens group , And the distance between the third lens group and the fourth lens group is changed. The third lens group includes, in order from the object side, a front group having a positive refractive power and a negative refraction. An anti-vibration system comprising: a rear group having power, and performing image plane correction at the time of camera shake by moving only the rear group in a direction substantially orthogonal to the optical axis, and satisfying the following conditional expression: Zoom lens with function.
3.5 <f1 / fw <8.0
However, fw: the focal length of the zoom lens in the wide-angle end state f1: the focal length of the first lens group has been proposed (for example, see Patent Document 1).

JP 2006-106191 A

  Although the zoom lens of Patent Document 1 has an anti-vibration mechanism, the distance from the diaphragm to the anti-vibration correction lens and the anti-vibration correction, although the focal length is 19 to 200 mm and the zoom ratio is small. There is a problem that the distance from the lens to the image plane is small, and it is difficult to incorporate an aperture drive mechanism and a vibration isolation mechanism. In particular, when the focal length is about 18 to 270 mm and the zoom ratio is increased, the distance from the diaphragm to the image stabilization lens and the distance from the image stabilization lens to the image plane are decreased, and the diaphragm drive mechanism and the image stabilization mechanism In addition to the fact that it becomes impossible to incorporate, there arises a problem that the total length of the optical system becomes long and the filter diameter becomes large.

(Object of invention)
The present invention has been made in view of the above-described problems of conventional high-magnification ratio zoom lenses, and increases the distance from the diaphragm to the image stabilization lens and the distance from the image stabilization lens to the image plane. An object of the present invention is to provide a high-magnification ratio zoom lens that facilitates the incorporation of an aperture drive mechanism and an anti-vibration mechanism, and can increase the zoom ratio to a focal length of about 18 to 270 mm.
Another object of the present invention is to provide a high-magnification ratio zoom lens in which the overall length of the optical system is short and the filter diameter is not large.

In the present invention, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens having a positive refractive power The distance between the first lens group and the second lens group is widened by zooming from the wide-angle end to the telephoto end, the distance between the second lens group and the third lens group is narrowed, and the third lens group and the fourth lens group are Move so that the lens group spacing is narrow,
The third lens group, in order from the object side, consists of a front group having a positive refractive power and a rear group having a negative refractive power, and during focusing, the second lens group is moved on the optical axis,
The front group of the third lens group is composed of three or more positive lenses and one or more negative lenses,
The third lens group rear group includes a lens in which a biconcave negative lens and a positive lens are joined in order from the object side,
Performing image plane correction at the time of camera shake by moving only the rear group of the third lens group in the direction orthogonal to the optical axis,
A high zoom ratio zoom lens satisfying the following conditional expression:
−0.18 <f3r / ft <−0.14
However,
f3r: Focal length of the rear group of the third lens group
ft: the focal length of the telephoto end of the entire optical system.

Embodiments of the present invention are as follows.
The rear group of the third lens group includes three or more positive lenses including a positive lens cemented with a negative lens, and one or more negative lenses.
In the high zoom ratio zoom lens, the front group of the third lens group includes at least one positive lens having an Abbe number of 80 or more.
Further, in the high zoom ratio zoom lens, the first lens group includes a cemented lens of a negative lens and a positive lens, and a positive lens, and at least one of both positive lenses has an Abbe number of 80 or more. It is characterized by being.
Further, the first lens group is composed of a cemented lens of a negative lens and a positive lens, and a positive lens, and at least one of the positive lenses has a refractive index of 1.55 or more. .

(Conditional expression of the invention)
If the lower limit of the conditional expression is exceeded, the power of the anti-vibration lens group will be strong, so the shift amount for anti-vibration will be small and the shift lens diameter will be prevented from increasing, but it will be difficult to correct coma at the telephoto end. Become. In addition, the distortion at the wide-angle end greatly fluctuates due to image stabilization. If the upper limit of the conditional expression is exceeded, the shift amount for image stabilization increases, resulting in an increase in the diameter of the shift lens.

The high-magnification ratio zoom lens of the present invention increases the distance from the diaphragm to the image stabilization lens and the distance from the image stabilization lens to the image plane, making it easy to incorporate the aperture drive mechanism and the image stabilization mechanism. The distance can be increased to about 18 to 270 mm and the zoom ratio can be increased.
The contact lens of the present invention also has an effect that the total length of the optical system is short and the filter diameter is not large.

Hereinafter, embodiments of the high zoom ratio zoom lens according to the present invention will be described.
Focal length f = 18.40 ~ 71.10 ~ 264.21mm
f = 18.40-71.10-264.21
Fno = 3.50-5.24-6.32
2ω = 76.5〜23.1〜6.3 °

Changes due to zooming of the intervals D5, D14, D27 and the back focus BF are as follows.
Focal length f 18.400 71.099 264.210
D5 2.058 39.047 68.462
D14 30.539 11.868 1.055
D27 7.717 3.529 2.329
Back focus BF 38.685 75.562 97.163

The underlined surface numbers 6, 24, and 28 are aspheric surfaces. The aspheric surface is expressed by the following equation (1), where the optical axis is x, the height perpendicular to the optical axis is H, the radius of curvature is r, the cone count is A, and the n-th aspherical surface count is An. It is represented by

Each astigmatism coefficient of each surface is as follows.
R6
A = 1.0
A4 = 7.56725E-06
A6 = -7.65747E-09
A8 = -2.26456E-11
A10 = 1.23747E-13
R24
A = 1.0
A4 = 7.89296E-06
A6 = 9.60742E-09
A8 = 3.69345E-11
A10 = -7.34306E-13
R28
A = 1.0
A4 = -3.19107E-05
A6 = -5.55382E-09
A8 = -3.27936E-11
A10 = 3.69412E-13

The focal length of each lens group is shown.
First lens group LG1 focal length f1 = 108.563
Second lens group LG2 Focal length f2 = −13.813
Third lens group LG3 focal length f3 = 45.230
4th lens group LG4 focal length f4 = 48.815
Front group focal length f3a of the third lens group LG3 = 26.822
Rear lens focal length f3b = −40.500 of the third lens group LG3

The value of the conditional expression of the invention of the embodiment is shown below.
f3r / ft = −0.153

  The aberration of the high magnification ratio zoom lens according to the embodiment of the present invention is shown in the accompanying drawings. In the diagrams of the on-axis spherical aberration and coma aberration, d indicates the d-line (587.56 nm), and g indicates the g-line (435.83 nm). In the diagram of astigmatism, Y = 14.5 indicates the image height, the solid line indicates the spherical aberration, and the dotted line indicates the meridional aberration. In the distortion diagram, Y = 14.5 represents the image height.

1 is an optical cross-sectional view at a telephoto end of a high magnification ratio zoom lens according to an embodiment of the present invention. It is an aberration diagram showing on-axis spherical aberration, astigmatism, and distortion at the wide angle end. It is an aberration diagram showing coma aberration at the wide angle end. FIG. 6 is an aberration diagram showing on-axis spherical aberration, astigmatism, and distortion in the intermediate range. It is an aberration diagram which shows the coma aberration in an intermediate area. FIG. 5 is an aberration diagram showing on-axis spherical aberration, astigmatism, and distortion at the telephoto end. It is an aberration diagram showing the coma aberration at the telephoto end. FIG. 10 is a coma aberration diagram for each angle of view when the third lens unit is shifted +0.07 mm in the vertical direction with respect to the optical axis at the wide angle end. It is a coma aberration diagram of each angle of view when the third lens group is shifted +0.47 mm in the vertical direction with respect to the optical axis at the telephoto end. It is a coma aberration diagram of each angle of view when the third lens group is shifted by −0.47 mm in the vertical direction with respect to the optical axis at the telephoto end.

Explanation of reference numerals 1, 2, 3,... Surface number LG1, LG2, LG3,.

Claims (5)

In order from the object side, it consists of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with positive refractive power However, due to zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group increases, the distance between the second lens group and the third lens group decreases, and the distance between the third lens group and the fourth lens group increases. Move so that
The third lens group, in order from the object side, consists of a front group having a positive refractive power and a rear group having a negative refractive power, and during focusing, the second lens group is moved on the optical axis ,
The front group of the third lens group is composed of three or more positive lenses and one or more negative lenses,
The third lens group rear group includes a lens in which a biconcave negative lens and a positive lens are joined in order from the object side,
Performing image plane correction at the time of camera shake by moving only the rear group of the third lens group in the direction orthogonal to the optical axis,
A high zoom ratio zoom lens satisfying the following conditional expression:
-0.18 <f3r / ft <-0.14
However,
f3r: Focal length of the rear group of the third lens group
ft: Focal length at the telephoto end of the entire optical system 2. The high magnification ratio according to claim 1, wherein the rear group of the third lens group includes three or more positive lenses including a positive lens cemented with a negative lens, and one or more negative lenses. Zoom lens.   2. The high zoom ratio zoom lens according to claim 1, wherein the front group of the third lens group includes at least one positive lens having an Abbe number of 80 or more.   2. The first lens group according to claim 1, wherein the first lens group includes a cemented lens of a negative lens and a positive lens, and a positive lens, and at least one of the positive lenses has an Abbe number of 80 or more. High magnification ratio zoom lens.   The first lens group includes a cemented lens of a negative lens and a positive lens, and a positive lens, and at least one of the positive lenses has a refractive index of 1.55 or more. 1 high magnification ratio zoom lens.

Images