JPH08254653A - Zoom lens - Google Patents

Abstract

PURPOSE: To obtain a two-group zoom lens which has high power variation about three powers whose diameter is large about F2.0, and which is compact. CONSTITUTION: As to this zoom lens constituted of a first lens group having negative focal distance and a second lens group having positive focal distance in the order from an object side, and changing the focal distance by changing an interval between the first and second groups; the first lens group has the lens constitution of concave, concave, and convex lenses, and the second lens group has the lens constitution of convex, convex, concave, convex lenses, and inside lenses, the power distribution and the shape of the part of the lenses are regulated, so that the zoom lens which has the high power variation about three powers whose diameter is large about F2.0, and which has good optical performance can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens for a video camera, an electronic still camera, a still camera, etc., which has a brightness of about F2.0 on the wide angle side and a zoom ratio of about 3 times. Regarding the lens.

[0002]

2. Description of the Related Art In recent years, video cameras and electronic still cameras are becoming smaller, lighter, and lower in cost. The optical systems used in these devices are also smaller, lighter, and lower in cost. Is becoming stronger.

Conventionally, in the field of still cameras for silver halide photography, a compact and lightweight zoom lens is composed of a first lens group having a negative power and a second lens group having a positive power in order from the object side. A so-called two-group zoom lens is generally used, which performs zooming by changing the distance between both lens groups.

A two-group zoom lens for a video camera and an electronic still camera is disclosed in, for example, Japanese Patent Laid-Open No. 63-265.
The invention of No. 211 is known.

However, in general, this type of two-group zoom lens has a limit of a variable power ratio of about 2 times, and it has not been possible to meet the demand for a high variable power ratio in recent video cameras and electronic still cameras.

To obtain this high zoom ratio, it is conceivable to use a zoom lens having three or more groups, but it is inevitable that the device becomes complicated, and it is sufficient for demands for downsizing, weight reduction, and cost reduction. It is hard to say that it corresponds.

In order to solve this problem, for example, in Japanese Patent Laid-Open No. 242709/1992, a simple structure of a two-group zoom lens enables high zooming of about 3 times and good optical performance. Has realized a compact, lightweight, low-cost zoom lens.

[0008]

However, in this second group zoom lens, the F value is F2.8 on the wide side, and the F side on the wide side of the commercialized zoom lens for a video camera.
The zoom lens is darker than the value of about 1.2 to 2.0.

[0009]

In order to solve the above problems, it is possible to increase the number of lenses or use an aspherical surface, but it is sufficient to meet the demands for downsizing, weight saving, and cost reduction. It is hard to say what to do.

In order to solve the above-mentioned problems, the present invention defines the power of the lens elements which are the constituent elements and the shape factor as the shape so as not to go against size reduction, weight reduction and cost reduction. With a two-group zoom lens, it is possible to achieve an F2.0 equivalent on the wide side.

[0011]

A zoom lens according to the present invention has a first lens group 11 having at least three lenses and having a negative power as a whole, and at least four lenses having a positive power as a whole. The second lens group 12 is arranged in order from the object side, and the focal length is changed by changing the group distance between the first lens group 11 and the second lens group 12.

[0012]

[Equation 5] −1.45 <fa / fb <−1.15 (Equation 5) The condition of the equation 1 is satisfied.

However, the focal length of the first lens group 11 is f
a and the focal length of the second lens group 12 is fb.

In the zoom lens, the first lens group 11 includes, in order from the object side, a negative meniscus lens 1 having a convex surface facing the object side, a negative lens 2 and a positive lens 3, and a second lens group. Reference numeral 12 denotes a positive lens 4, a positive lens 5, a negative lens 6, and a positive lens 7, which are arranged in this order from the object side, which is the first lens group 11 side.

[0015]

[Equation 6] -2.7 <f2 / fW <-1.8 (Equation 6)

[0016]

[Equation 7] 1.0 <f5 / fW <1.7 (Equation 7)

[0017]

[Equation 8] −1.2 <f6 / fW <−0.4 (Equation 8) The conditions of Equations 6, 7, and 8 are satisfied.

However, the focal length at the wide end of the entire system is fW, and the focal lengths of the second, fifth, and sixth lens balls from the object side are f2, f5, and f6.

When the shape factors of the fourth and sixth lens balls from the object side are S4 and S6,

[0020]

[Equation 9] −0.3 <S4 <0.3 (Equation 9)

[0021]

[Equation 10] −1.1 <S6 <−0.3 (Equation 10) The conditions of Equations 9 and 10 are satisfied.

However, the shape factor S is defined by the following equation 11 when the radius of curvature of the lens side on the object side is Ra and the radius of curvature on the image side is Rb.

[0023]

[Equation 11] S = (1 / Ra + 1 / Rb) / (1 / Ra-1 / Rb) (Equation 11) Hereinafter, each condition will be described.

Equation 5 is a condition relating to the ratio of the power of the first lens group 11 and the power of the second lens group 12, and the amount of movement of the first lens group 11 at the time of zooming is reduced to make the entire lens compact. And for filters such as video cameras,
This is a condition for ensuring a sufficient back focus for inserting the face plate. If the lower limit of the expression (1) is exceeded, the power of the first lens group 11 will be weakened, and spherical aberration and distortion can be corrected well, but it becomes difficult to take a long back focus and the first lens at the time of zooming. Group 1
The movement amount of 1 is large, which is not preferable in terms of compactness. On the contrary, if the upper limit of the equation (1) is exceeded, the power of the first lens group 11 becomes strong, which is advantageous in terms of compactness, but it becomes difficult to suppress spherical aberration and distortion.

Expression 6 is a condition regarding the power of the lens 2 having the largest power among the three lenses in the first lens group 11. If the lower limit of the expression (6) is exceeded, the power of the lens (2) becomes small, and it becomes difficult to correct lateral chromatic aberration when the number of lenses is three. There is also a method of increasing the number of lenses to achieve correction of lateral chromatic aberration, but this is not preferable in terms of compactness. On the contrary, if the upper limit of Expression 6 is exceeded, the power of the lens 2 becomes large, and it becomes difficult to suppress various aberrations generated in the lens 2.

Similarly, equations 7 and 8 are conditions relating to the powers of the lenses 5 and 6 having the largest power among the four lenses in the second lens group 12. If the upper limit of the equation 7 and the lower limit of the equation 8 are exceeded, the powers of the lenses 5 and 6 become small, and it becomes difficult to correct the axial chromatic aberration with four lenses. There is also a method of increasing the number of lenses to achieve correction of axial chromatic aberration, but this is not preferable in terms of compactness. On the contrary, when the lower limit of the equation 7 and the upper limit of the equation 4 are exceeded, the powers of the lens 5 and the lens 6 increase,
It becomes difficult to suppress various aberrations generated in the lenses 5 and 6.

The expression (5) is a condition regarding the shape of the lens 4, which is the head lens ball on the object side of the second lens group, which converges and forms an image of the light beam diverged by the first lens group. If the lower limit of expression 9 is exceeded, the radius of curvature of the lens 4 on the object side increases and spherical aberration decreases, but coma aberration is overcorrected and coma aberration during zooming increases, which is undesirable. On the other hand, when the value exceeds the upper limit of Expression 9, the radius of curvature of the lens 4 on the object side becomes small, the spherical aberration is insufficiently corrected, and the aberration variation during zooming becomes large, which is not preferable.

The equation (6) defines the shape of the lens 6, which is the only concave lens in the second lens group that performs the image forming operation. If the lower limit of the expression 10 is exceeded, the spherical aberration is overcorrected, and the spherical aberration and the coma aberration are rapidly deteriorated. On the other hand, if the upper limit of the expression 10 is exceeded, it becomes impossible to correct the spherical aberration generated in the other lens ball (convex lens) of the second lens group 12, and the spherical aberration is insufficiently corrected and the aberration variation at the time of zooming becomes large. It is not preferable.

[0029]

EXAMPLES Numerical examples of the present invention whose lens sectional views are shown in FIGS. 1, 4 and 7 will be shown below. In the numerical example, r (i) is the i-th lens surface s (i) in order from the object side.
Is the radius of curvature of d (i) from the lens surface s (i) to s (i +
1) is the distance on the optical axis, N (j) and ν (j) are the refractive index and Abbe number of the j-th lens in order from the object side, f is the focal length, and 2ω is the angle of view.

In the numerical data of the embodiment, the plane-parallel plate arranged closest to the image plane is a filter, face plate, etc. used in a video camera or the like.

[Numerical Example 1] FNO = 1: 2.16 to 4.73 f = 5.40 to 14.90 2ω = 58.13 to 22.77 (corresponding to 1/3 inch sensor) s rd N ν 1 8.164 0.600 1.8340 37.3 2 4.358 1.960 3 -33.018 0.600 1.8340 37.3 4 13.302 0.100 5 7.789 1.890 1 8467 23.9 6 32.409 Variable 7 (Aperture) Variable 8 16.766 1.780 1.7725 49.6 9 -19.213 0.100 10 4.838 2.655 1.7725 49.611 37.837 0.135 12-118.490 0.600 1.8467 23.9 13 3.396 0.790 14 19.422 1.270 1.8340 37.3 15-7 .651 variable 16 ∞ 4.400 1.5168 64.2 17 ∞ In order to express the relationship between the movement amounts of the first lens group 11 and the second lens group 12, the focal length f and the lens surface distance are variable d. The values of (6), d (7) and d (15) are shown below.

F 5.40 10.12 14.90 d (6) 6.197 1.429 1.950 d (7) 8.372 4.856 1.300 d (15) 3.000 6.516 10 .072 The conditional expressions shown above have the following values.

Fa / fb = -1.34 f2 / fW = -2.09 f5 / fW = 1.29 f6 / fW = -0.72 S4 = 0.07 S6 = -0.94 Further, as shown in FIG. FIG. 3 shows aberration diagrams at the wide end and the tele end.

[Numerical Example 2] FNO = 1: 2.14 to 3.44 f = 3.65 to 9.95 2ω = 63.24 to 25.49 (corresponding to 1/4 inch sensor) s rd N ν 1 12.373 1.000 1.8052 25.5 2 4.525 2.150 3 -13.000 0.500 1.8340 37.3 4 13.000 0.100 5 9.489 2.400 1 8467 23.9 6 -21.611 Variable 7 (Aperture) Variable 8 24.116 1.525 1.8340 37.3 9 -26.596 0.100 10 5.133 3.000 1.7725 49.6 11 -14.592 0.070 12 -11.693 0.500 1.8467 23.9 13 3.829 0.500 14 29.506 2.650 1.8340 37.3 15- 4.094 Variable 16 ∞ 4.400 1.5168 64.2 17 ∞ In order to represent the relationship of the movement amount of the first lens group 11 and the second lens group 12, the focal length f and the lens surface distance are variable. The values of d (6), d (7) and d (15) are shown below.

F 3.65 7.16 9.95 d (6) 12.490 2.745 1.300 d (7) 6.294 3.510 1.300 d (15) 1.000 3.784 5 .994 Further, the conditional expressions shown above have the following values.

Fa / fb = -1.26 f2 / fW = -2.11 f5 / fW = 1.44 f6 / fW = -0.92 S4 = 0.05 S6 = -0.51 Further, as shown in FIG. FIG. 6 shows aberration diagrams at the wide end and the tele end.

[Numerical Example 3] FNO = 1: 2.27 to 3.45 f = 3.70 to 10.54 2ω = 62.61 to 24.10 (corresponding to 1/4 inch sensor) s rd N ν 1 10.465 0.800 1.8340 37.3 2 5.015 2.610 3 -19.229 0.500 1.8340 37.3 4 12.524 0.100 5 9.538 2.480 1 8467 23.9 6 -57.822 Variable 7 (Aperture) Variable 8 26.456 1.450 1.8340 37.3 9-23.878 0.200 10 5.457 2.600 1.7859 43.9 11 -11.408 0.030 12 -10.480 1.600 1.8467 23.9 13 3.758 0.470 14 50.708 1.270 1.7859 43.9 15 14.689 Variable 16 ∞ 4.400 1.5168 64.2 17 ∞ In order to represent the relationship between the movement amounts of the first lens group 11 and the second lens group 12, the focal length f and the lens surface distance are variable. The values of d (6), d (7) and d (15) are shown below.

F 3.70 7.27 10.54 d (6) 15.820 4.429 2.300 d (7) 6.765 4.176 1.800 d (15) 1.030 3.618 5 .994 Further, the conditional expressions shown above have the following values.

Fa / fb = -1.38 f2 / fW = -2.44 f5 / fW = 1.36 f6 / fW = -0.84 S4 = -0.05 S6 = -0.47 Further, FIG. And FIG. 9 shows aberration diagrams at the wide end and the tele end.

[0040]

According to the present invention, a high zoom ratio of about 3 times and F
A compact zoom lens having a large aperture of about 2.0 and good optical performance can be obtained with a simple two-group zoom lens.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of a first embodiment of the present invention.

FIG. 2 is an aberration diagram at the wide end according to the first embodiment of the present invention.

FIG. 3 is an aberration diagram at a telephoto end according to the first embodiment of the present invention.

FIG. 4 is a lens cross-sectional view of a second embodiment of the present invention.

FIG. 5 is an aberration diagram at the wide end according to the second example of the present invention.

FIG. 6 is an aberration diagram at a telephoto end according to a second embodiment of the present invention.

FIG. 7 is a lens cross-sectional view of a third embodiment of the present invention.

FIG. 8 is an aberration diagram at a wide end according to Example 3 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end according to the third embodiment of the present invention.

[Explanation of symbols]

 1 ... Lens, 2 ... Lens, 3 ... Lens, 4 ... Lens, 5 ... Lens, 6 ... Lens, 7 ... Lens, 8 ... Aperture, 11 ... First lens group, 12 ... Second lens group.

Claims (3)

[Claims] 1. An object comprising a first lens group having at least three lenses and having a negative power as a whole, and a second lens group having at least four lenses and having a positive power as a whole. A zoom lens which is arranged in order from the side and which changes the focal length by changing the group distance between the first lens group and the second lens group and satisfies the following conditions. ## EQU1 ## −1.45 <fa / fb <−1.15 (Expression 1) However, the focal length of the first lens group is fa and the focal length of the second lens group is fb. 2. The first lens group according to claim 1, wherein a negative meniscus lens having a convex surface facing the object side, a negative lens, and a positive lens are arranged in order from the object side, and the second lens group is A positive lens, a positive lens, a negative lens, and a positive lens are arranged in order from the object side, which is one lens group side,
A zoom lens that meets the following conditions. ## EQU00002 ## -2.7 <f2 / fW <-1.8 1.0 <f5 / fW <1.7-1.2 <f6 / fW <-0.4 (Equation 2) However, all The focal length at the wide end of the system is fW, and the focal lengths of the second, fifth, and sixth lens balls from the object side are f
2, f5 and f6. 3. The shape factors of the fourth and sixth lens balls from the object side are S4 and S6.
When, and a zoom lens that meets the following conditions. [Formula 3] −0.3 <S4 <0.3 −1.1 <S6 <−0.3 (Formula 3) However, the shape factor S is the radius of curvature of the object side of the lens ball is Ra, and the image is When the radius of curvature on the surface side is Rb, it is defined by the following formula. ## EQU00004 ## S = (1 / Ra + 1 / Rb) / (1 / Ra-1 / Rb) ... (Equation 4)