JP2000137164A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact zoom lens having a larger viewing angle at wide-angle end. SOLUTION: This zoom lens includes a 1st lens group G1 having negative refractive power, a 2nd lens group G2 having positive refractive power and a 3rd lens group G3 having positive refractive power in order from the object side. In the case of performing variable power from the wide-angle end to telephoto end, the 1st lens group stands still, the 2nd lens group is moved toward the object and the 3rd lens group is moved, then the 3rd lens group is moved toward the object so as to perform focusing from the long-distance object to the short-distance object. The lens satisfies expressions: 0.15<|(x2/s12w)/(f1/ fw)|<1.0, 0.01<c23w2/(f3*fw)<0.5 and 0.18<s23t2/(f3*ft)<5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a zoom lens, and more particularly, to a compact zoom lens having a wide angle of view and a short overall lens length.

[0002]

2. Description of the Related Art In recent years, as the main body of a portable electronic device such as a portable electronic device or the like has become smaller and lighter, the size of an optical system mounted thereon has been required to be smaller, lower in cost and wider in angle. In such a situation, an optical system having a zoom ratio of about 2 to 3 has been noticed. Further, a wider angle of view at the wide-angle end than before has been required.

In general, most consumer zoom lenses are
A first lens group having a positive refractive power, a second lens group having a negative refractive power for zooming, a third lens group mainly for aberration correction, and a positive lens for image position correction. A so-called four-unit zoom lens, which includes a fourth lens unit having a refractive power of? Such a four-group zoom lens is relatively easy to increase the aperture ratio and increase the magnification. However, since the first lens group has a positive refractive power, it is not suitable for a wide angle of view, and the angle of view at the wide angle end is limited to about 65 °.

On the other hand, as a zoom lens type having a variable magnification ratio of about 2 to 3 and achieving a small size and a wide angle of view, a first lens group having a negative refractive power and a positive lens are generally used. There is known a so-called two-group zoom lens configured with a second lens group. As a three-unit zoom lens, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a zoom ratio of about 2 to 3 times;
A lens comprising a third lens group having a positive refractive power is known.

[0005]

However, the four-unit zoom lens having the above configuration has a large number of component groups, and it is impossible to achieve miniaturization. Also, there is a limit to widening the angle of view. Further, the two-unit zoom lens having the above-described configuration has
Although downsizing and widening the angle of view are advantageous as compared with the four-unit zoom lens having the above-described configuration, the overall length greatly changes because the first lens unit moves during zooming. Also, at the time of zooming and focusing (hereinafter, referred to as focusing), the first lens group, which is relatively large and heavy, is advanced to the object side, so that it becomes mechanically complicated, and the size of the lens barrel increases and the cost increases. There were problems such as conversion. Further, when the first lens group, which is heavier than the other groups, is moved by a motor or the like, a load is applied to the motor, and rapid autofocusing is difficult. Further, when focusing is performed by the first lens group, the front lens diameter becomes large in order to secure the light east at the outermost periphery of the screen during close-up shooting on the wide-angle side, which is not suitable for miniaturization.

Although the conventional three-group zoom lens has a wide angle of view to some extent, it has not been sufficient yet. In addition, since focusing is performed by the first lens group, miniaturization has not been achieved, and the air gap between the respective groups has not been effectively used, so that the lens system has been relatively large. In view of the above problems, an object of the present invention is to provide a compact zoom lens having a larger angle of view at the wide-angle end.

[0007]

According to the present invention, in order to achieve the above object, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power,
A zoom lens including a third lens group having a positive refractive power, wherein the first lens unit is used for zooming from a wide-angle end to a telephoto end.
The lens group is stationary, the second lens group moves in the object direction, the third lens group moves, and the third lens group moves in the object direction to focus from a long-distance object to a short-distance object. Is provided to provide a zoom lens characterized by satisfying the following conditional expressions (1) to (3).

[0008] 0.15 <| (x2 / s12w) / (f1 / fw) | <1.0 (1) 0.01 <c23w 2 / (f3 * fw) <0.5 (2) 0.18 <s23t 2 / (f3 * ft) <5 (3) where fw: focal length of the entire zoom lens at the wide-angle end, ft: focal length of the entire zoom lens at the telephoto end, f1: focal length of the first lens group, f3: focal length of the third lens group, x2 S12w: second moving distance from the image-side principal point of the first lens unit at the wide-angle end to the telephoto end from the wide-angle end to the telephoto end.
S23t: distance from the image-side principal point of the second lens group at the telephoto end to the object-side principal point of the lens group,
C23w: distance between the second lens group and the third lens group at the wide-angle end, at the wide-angle end.

As described above, the zoom lens of the present invention is a three-unit zoom lens in which the first lens group is fixed during zooming, and the second and third lens groups are zoomed during zooming. A movable zoom tie was adopted. That is, a group having a negative refractive power, which is advantageous for widening the angle, is disposed on the first lens, a second lens group having a positive refractive power, and a third lens group having a focusing function and having a positive refractive power. With this configuration, zooming and adjustment of the image position are performed to achieve a wide angle and a small size.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic structure of a zoom lens according to the present invention is, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a positive refractive power. And a third lens group having the following. During zooming from the wide-angle end to the telephoto end, the first lens group stops, the second lens group moves in the object direction, and the distance between the second lens group and the third lens group changes. In addition, focusing from a long-distance object to a short-distance object is performed by moving the third lens group in the object direction.

In the zoom lens of the present invention, the first lens is
In order to fix the lens group and keep the overall length of the lens system constant, the group having negative refractive power is set as the first lens group, and the second lens group and the third lens group are set as groups having positive refractive power. The distance between the object point and the image point becomes constant while the virtual image by the first lens group having a negative refractive power is zoomed by the second lens group having a positive refractive power and the third lens group having a positive refractive power. The relay method was adopted. In addition, since the above-described configuration provides a so-called retrofocus lens power arrangement, it is easy to increase the back focus, and the optical low-pass filter and infrared cutoff required for an optical system such as an electronic camera. A filter, a cover glass, and the like can be easily arranged between the lens system and an imaging device such as a CCD.

In general, in the focusing method in which the first lens group is moved along the optical axis, the diameter of the front lens tends to be large and heavy in order to secure the luminous flux at the outermost periphery of the screen when shooting at a close range on the wide angle side. Becomes For this reason, in this focusing method, it is difficult to reduce the size. In other words, the first lens group having the largest diameter is preferably fixed during focusing in order to reduce the size of the lens system. In the zoom lens of the present invention, focusing is not performed by the first lens group, but is performed by the third lens group. Therefore, the diameter of the front lens can be reduced as compared with a lens type that performs focusing by the first lens group. The objective lens system can be made smaller.

Further, by performing focusing with the third lens group, it is possible to realize a cylindrical element in the mechanism, and to reduce the cost of the lens barrel and the like. In addition, since the third lens group is relatively lighter than the first lens group, quick focusing can be performed with a small amount of work as compared with a lens that performs focusing using the first lens group. In the present invention, the conditional expression (1) is satisfied in order to achieve a compact lens system.

Conditional expression (1) is a conditional expression relating to the miniaturization of the lens system. This is a conditional expression for appropriately setting the ratio of the distance between the image-side principal point at the wide-angle end and the object-side principal point at the wide-angle end of the second lens unit, and achieving miniaturization. When the lower limit of conditional expression (1) is exceeded, the distance between the image-side principal point at the wide-angle end of the first lens group and the object-side principal point at the wide-angle end of the second lens group is determined from the wide-angle end of the second lens group. The amount of movement due to zooming to the telephoto end is reduced.
Therefore, when a desired zoom ratio is realized, the refractive power is arranged for a high zoom ratio, and the magnification of each lens group is used at a high magnification, which causes an increase in the number of lenses, which is inappropriate.

When the upper limit of conditional expression (1) is exceeded, the amount of movement of the second lens unit due to zooming from the wide-angle end to the telephoto end is shifted from the image-side principal point of the first lens unit at the wide-angle end to the second lens unit. In this case, the first lens group and the second lens group interfere at the telephoto end, which is inappropriate. Also, it is not preferable because a sufficient zoom ratio cannot be secured.

In a wide-angle zoom lens having a negative refractive power preceding the present invention, aberration correction is generally performed as the refractive power of each group is weaker and the imaging magnification of the lens group having a positive refractive power is smaller. Is easy. However, these methods all have a large lens system and cannot achieve a small size.
In the present invention, by setting the focal length of each group to an optimal value, miniaturization, widening of the angle, and good aberration are achieved. The conditional expression (4), which is the condition of the optimum refractive power of the first lens group, is shown below.

0.1 <| fw / f1 | <1.3 (4) where fw is the focal length of the entire lens system at the wide-angle end, and f1 is the focal length of the first lens group.

If the upper limit of conditional expression (4) is exceeded, the total length can be reduced, which is advantageous for miniaturization. However, since the refracting power of the first lens unit is increased, negative distortion occurs at the wide-angle end. And aberration correction becomes difficult. In addition, since the load of aberration correction of the first lens group increases due to the increase in refractive power, it is necessary to configure the first lens group with a large number of lenses. Therefore, the lens system becomes large due to the thick lens of the first lens group, the air gap between the first lens group and the second lens group cannot be secured, and not only a desired zoom ratio cannot be obtained, but also miniaturization can be achieved. I can't achieve it.

If the lower limit of conditional expression (4) is exceeded, the refractive power of the first lens unit will be weak and the load of aberration correction will be reduced, but the overall length will be long and miniaturization cannot be achieved. Also,
Since the incident height of the off-axis light beam at the wide-angle end becomes high, the diameter of the first lens group becomes large, and miniaturization cannot be achieved. Further, the effect of the retrofocus styling is weakened, and a sufficient back focus cannot be secured.

Also, the second lens group is given by the following conditional expression (5).
It is desirable to satisfy 0.1 <fw / f2 <0.5 (5) where fw is the focal length of the entire lens system at the wide-angle end, and f2 is the focal length of the second lens group.

Conditional expression (5) relates to the refractive power of the second lens group. If the upper limit of conditional expression (5) is exceeded, the second condition will be satisfied.
The refractive power of the lens group becomes too strong, and it becomes difficult to secure the back focus and the interval between the first lens group and the second lens group, which is not preferable. Further, spherical aberration and astigmatism at the telephoto end are insufficiently corrected, which is not preferable. If the lower limit of conditional expression (5) is exceeded, the refracting power of the second lens unit will be weak and the burden of aberration correction will be reduced, but the amount of movement of the second lens unit due to zooming will increase, and the lens system will be large. Become
Miniaturization is not achieved.

Further, the third lens unit satisfies the following conditional expression (6):
It is desirable to satisfy 0.05 <fW / f3 <0.35 (6) where fw is the focal length of the entire lens system at the wide-angle end, and f3 is the focal length of the third lens group.

Conditional expression (6) is an expression relating to the refractive power of the third lens unit. If the upper limit of conditional expression (6) is exceeded, the third condition will be satisfied.
The refractive power of the lens group becomes too strong, and it becomes difficult to secure the back focus, which is not preferable. Further, spherical aberration and astigmatism at the telephoto end are insufficiently corrected, which is not preferable. Further, when focusing is performed by the third lens group, aberration fluctuation becomes large, which is not preferable. If the lower limit of conditional expression (6) is exceeded, the refractive power of the third lens unit will be weak, and the burden of aberration correction will be reduced.
The amount of movement of the lens group increases, the lens system increases, and miniaturization cannot be achieved. In addition, the third by focusing
The amount of movement of the lens group increases, which is not preferable.

In the zoom lens of the present invention, focusing is performed by moving the third lens group along the optical axis. Focusing can also be performed by each of the first lens unit and the second lens unit. However, during focusing, the front lens diameter is set to secure the light flux at the outermost periphery of the screen during close-up shooting on the wide-angle side. Tends to be large. Therefore, it is not preferable to perform focusing in each of the first lens group and the second lens group.

When focusing is performed by the third lens unit, the above conditional expressions (2) and (3) are satisfied. The conditional expressions (2) and (3) are conditional expressions for appropriately setting the movable range of the third lens unit, which is the focus unit, at the wide-angle end and the telephoto end. If the upper limits of conditional expressions (2) and (3) are exceeded, the refracting power of the third lens unit becomes too strong, and a sufficient back focus cannot be secured, which is not preferable. In addition, aberration fluctuation due to focusing increases, which is not preferable. If the lower limits of the expressions (2) and (3) are exceeded, the refractive power of the third lens unit becomes weak, and the amount of movement of the third lens unit during focusing becomes large. Therefore,
The movable interval for performing focusing cannot be sufficiently secured, and focusing cannot be performed to a desired close distance, which is not appropriate. Further, the back focus becomes too long, and the entire lens system becomes large, which is not preferable.

It is preferable that the zoom lens system satisfies the following conditional expression (7). -0.4 <1 / β2t <0 (7) where β2t is the imaging magnification of the second lens unit at the telephoto end.

This conditional expression (7) is a lateral magnification which the second lens group carries at the telephoto end, and is an expression for defining the size of the screen to be used by a feasible lens configuration.
When the ratio exceeds the upper limit of conditional expression (7), when the zoom ratio is constant,
Although it is easy to secure the back focus, the magnification taken by the zoom unit becomes a high magnification state. Therefore, it is difficult and unsuitable to correct various aberrations. If the lower limit of conditional expression (7) is exceeded,
It is easy to simply widen the angle, but it is inappropriate because the second lens group and the third lens group interfere with each other and it is difficult to secure the back focus at the wide angle end.

In the zoom lens according to the present invention, the first lens unit is sequentially arranged from the object side in the order of a first negative meniscus lens component,
In the case where the lens is composed of the second negative lens component and the third positive lens component,
By introducing at least one aspheric surface into at least one of the first negative meniscus lens component and the second negative lens component, it becomes possible to favorably correct distortion and spherical aberration on the telephoto side. In particular, in a zoom type in which negative refractive power precedes as in the present invention, it is extremely difficult to correct distortion on the wide-angle side, which has been an obstacle to miniaturization. In order to satisfactorily correct the distortion, which is an obstacle, the correction can be made by weakening the refractive power of the first lens unit or by disposing a lens having a positive refractive power on the object side of the first lens unit. However, downsizing has not been achieved because the first lens group is large.

In the present invention, by introducing an aspherical surface into the first lens group, it becomes possible to satisfactorily correct the distortion, and furthermore, the refractive power of the first lens group is increased by the aspherical correcting action. As a result, the lens system can be reduced in size. In the embodiment of the present invention, an example in which an aspherical surface is introduced into the image-side surface of the first negative meniscus lens component is shown as the most effective example. Here, it is more effective to make the introduced aspherical surface such that the positive refractive power increases as the distance from the optical axis increases.

[0030]

Embodiments of the present invention will be described below. In each embodiment, the aspherical shape X (y) is represented by the following equation. X (y) = y ² / [r * [1+ (1-k * y ² * r ² ) ^1/2 ]] + C4 * y ⁴ + C6 * y ⁶ + C8 * y ⁸ +
In C10 * y ¹⁰ where, y is the distance from the optical axis, k is the conical coefficient, r is the vertex radius of curvature, C4, C6, C8 and C
Reference numeral 10 denotes fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients.

Focusing from a long-distance object to a short-distance object is performed by moving the third lens group to the object side. In Tables 1 to 4 shown below, f is the focal length, F.NO is the F-number, 2ω is the angle of view, Bf is the back focus, and D0 is the distance from the object to the first surface during close-up shooting. Represents a distance, and β represents a photographing magnification. Furthermore,
The surface number indicates the order of the lens from the object side along the traveling direction of the light beam, and the refractive index and Abbe's number are d-line (λ = 5
87.6 nm). The movement amount of the lens group due to focusing is the movement amount of each position from infinity. A positive value indicates the image plane direction, and a negative value indicates the object direction.

In each aberration diagram of each embodiment, FNO
Is the F number, A is the half angle of view, d is the d line (λ = 587.6n
m) shows the g-line (λ = 435.8 nm). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. [First Embodiment] FIG. 1 is a diagram showing a lens configuration of a first embodiment of the present invention. The first lens group G1 includes a biconvex lens L1 and a negative meniscus lens L having a convex surface facing the object side.
2 and a negative meniscus lens L3 having a convex surface facing the object side having an aspheric surface on the second surface. Second lens group G2
Is composed of a single biconvex lens L4 having an aspheric surface on the first surface, and the third lens group G3 is composed of a biconvex lens L5, a negative meniscus lens L6 having a concave surface facing the object side, and a cemented lens. You. During zooming from the wide-angle end to the telephoto end, the first lens group G1 is stationary, and both the second lens group G2 and the third lens group G3 move in the object direction.
The air gap between the lens group G1 and the second lens group G2 decreases, and the air gap between the second lens group G2 and the third lens group G3 decreases near the wide-angle end and increases near the telephoto end.

The sixth surface from the object of the first lens group G1 and the second surface from the object of the second lens group G2 are aspherical. Table 1 below lists values of specifications of the first embodiment of the present invention.

[0034]

[Table 1] f = 2.9 to 4.0 to 5.8 F.NO = 2.22 to 2.54 to 2.72 2ω = 80.35 to 61.94 to 43.75 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 49.871 1.700 1.846660 23.82 L1 G1 2 -141.331 0.084 3 8.856 0.420 1.772500 49.68 L2 4 2.921 2.000 5 20.420 2.500 1.491080 57.57 L3 6 9.063 (d6 = variable) 7 0.000 0.562 S 8 11.114 4.719 1.491080 57.57 L4 G2 9-6.311 (d9 = variable) 10 22.852 2.250 1.603110 60.64 L 0.700 1.846660 23.82 L6 12 -8.799 (d12 = variable) 13 0.000 3.000 1.516800 64.10 L7 14 0.000 2.217 (Aspheric coefficient) 6th surface 8th surface k = 1.0000 k = 1.0000 C4 = -2.21770E-03 C4 = -1.35540E -03 C6 = -2.82010E-04 C6 = -1.26280E-05 C8 = -1.48230E-06 C8 = -3.40250E-06 (Variable interval for zooming) f 2.90 4.00 5.80 d = 6 7.143 4.297 1.172 d = 9 2.109 4.266 4.784 d = 12 2.597 3.286 5.893 (Moving distance at close focus) f 2.90 4.00 5.80 β -0.0274 -0.0379 -0.0555 D0 100.000 100.000 100.000 Third Lens group movement amount -0.109 -0.194 -0.351 (Conditional value) f1 = -5.2 f2 = 9.0 f3 = 15.0 fw = 2.90 ft = 5.80 x2 = 5.971 s12w = 12.196 s23t = 7.492 c23w = 2.109 β2t = -3.7111 Figure 2, 3 and 4 are graphs showing various aberrations of the first example with respect to the d-line (λ = 587.6 nm) and the g-line (λ = 435.8 nm).
FIG. 2 shows various aberration diagrams at the wide-angle end, FIG. 3 shows various aberration diagrams at the intermediate angle of view, and FIG. 4 shows various aberration diagrams at the telephoto end.

As is clear from the aberration diagrams, in this embodiment, various aberrations are favorably corrected in each focal length state. [Second Embodiment] FIG. 5 is a diagram showing a lens configuration of a second embodiment of the present invention. The first lens group G1 has a negative meniscus lens L1 having an aspherical surface on the first surface and having a convex surface facing the object side, a negative meniscus lens L2 having a convex surface facing the object side, and a convex surface facing the object side. And a positive meniscus lens L3. The second lens group G2 is composed of a single biconvex lens L4 having an aspheric surface on the first surface.
Reference numeral 3 denotes a cemented lens of a biconvex lens L5 and a negative meniscus lens L6 having a concave surface facing the object side. During zooming from the wide-angle end to the telephoto end, the first lens group G1 is stationary, the second lens group G2 and the third lens group G3 both move in the object direction, and the first lens group G1 and the second lens group G3 move in the object direction.
The air gap with the lens group G2 decreases, and the second lens group G2
The air gap between the zoom lens and the third lens group G3 decreases near the wide-angle end and increases near the telephoto end. The first surface of the first lens group G1 from the object and the first surface of the second lens group G2 from the object are aspherical.

Table 2 below summarizes data values of the second embodiment of the present invention.

[0037]

[Table 2] f = 2.83 to 4.0 to 5.8 F.NO = 2.39 to 2.73 to 3.01 2ω = 80.27 to 60.94 to 43.58 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 8.737 0.700 1.805182 25.35 L1 G1 2 3.282 2.000 3 52.356 0.621 1.744429 49.52 L2 4 4.210 0.600 5 5.222 1.321 1.805182 25.35 L3 6 18.605 (d6 = variable) 7 0.000 0.562 S 8 9.519 4.719 1.612720 58.54 L4 G2 9 -10.638 (d9 = variable) 10 10.584 3.000 1.603110 60.64 116.060-00 1.846660 23.82 L6 12 -11.938 (d12 = variable) 13 0.000 4.000 1.516800 64.10 L7 14 0.000 1.465 (Aspherical surface coefficient) 1st surface 8th surface k = 1.0000 k = 1.0000 C4 = 6.45990E-04 C4 = -2.36130E-04 C6 = 2.96210E-05 C6 = -2.42980E-05 C8 = 1.68000E-07 C8 = -3.40250E-06 C10 = -1.86000E-09 (variable interval in zooming) f 2.83 4.00 5.80 d = 6 7.296 4.220 1.053 d = 9 2.366 4.760 5.287 d = 12 1.381 2.063 4.702 (moving distance at close focus) f 2.83 4.00 5.80 β -0.0271 -0.0384 -0.0562 D0 100.000 100.000 10 0.000 Third lens group movement amount -0.106 -0.198 -0.357 (Conditional value) f1 = -5.20 f2 = 9.00 f3 = 15.00 fw = 2.83 ft = 5.80 x2 = 6.243 s12w = 12.505 s23t = 7.738 c23w = 2.366 β2t = -3.6557 FIGS. 6, 7 and 8 are graphs showing various aberrations of the second embodiment with respect to the d-line (λ = 587.6 nm) and the g-line (λ = 435.8 nm).
6 shows various aberration diagrams at the wide angle end, FIG. 7 shows various aberration diagrams at the intermediate angle of view, and FIG. 8 shows various aberration diagrams at the telephoto end.

As is clear from the aberration diagrams, in this embodiment, various aberrations are favorably corrected in each focal length state. [Third Embodiment] FIG. 9 is a diagram showing a lens configuration of a third embodiment of the present invention. The first lens group G1 includes a positive meniscus lens L1 having a convex surface facing the object side, a negative meniscus lens L2 having a convex surface facing the object side, and a negative meniscus lens L2 having a convex surface facing the object side having an aspheric surface on the second surface. Meniscus lens L
3 The second lens group G2 is composed of a single biconvex lens L4 having an aspheric surface on the first surface, and the third lens group G3
Is composed of a cemented lens composed of a biconvex lens L5 and a negative meniscus lens L6 having a concave surface facing the object side.
Upon zooming from the wide-angle end to the telephoto end, the first lens group G1
Is stationary, both the second lens group G2 and the third lens group G3 move in the object direction, the air gap between the first lens group G1 and the second lens group G2 decreases, and the second lens group G2 The air gap with the third lens group G3 decreases near the wide-angle end,
It expands near the telephoto end. The sixth surface from the object of the first lens group G1 and the second surface from the object of the second lens group G2 are aspherical.

Table 3 below summarizes the data values of the third embodiment of the present invention.

[0040]

[Table 3] f = 2.5 to 4.0 to 5.6 F.NO = 2.16 to 2.50 to 2.66 2ω = 89.19 to 62.29 to 45.56 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 26.624 1.471 1.846660 23.82 L1 G1 2 170.636 0.072 3 7.818 0.350 1.772500 49.68 L2 4 2.617 2.000 5 -84.991 2.000 1.491080 57.57 L3 6 12.531 (d6 = variable) 7 0.000 0.562 S 8 11.622 4.457 1.491080 57.57 L4 G2 9 -5.690 (d9 = variable) 10 17.475 2.250 1.603110 60.64 L5. 0.700 1.846660 23.82 L6 12 -9.842 (d12 = variable) 13 0.000 3.000 1.516800 64.10 L7 14 0.000 2.079 (Aspherical surface coefficient) 6th surface 8th surface k = 1.0000 k = 1.0000 C4 = -2.13650E-03 C4 = -1.29390E -03 C6 = -3.83210E-04 C6 = -7.60230E-05 C8 = -1.48230E-06 C8 = -3.40250E-06 (Variable interval in zooming) f 2.5 4.0 5.6 d = 6 7.177 3.300 0.837 d = 9 1.792 4.354 4.058 d = 12 2.363 3.678 6.436 (Moving distance at close focus) f 2.50 4.00 5.60 β -0.0238 -0.0382 -0.0540 D0 100.000 100.000 100.000 Third Movement of lens group -0.0823 -0.1886 -0.3221 (Conditional value) f1 = -4.50 f2 = 8.50 f3 = 15.00 fw = 2.50 ft = 5.60 x2 = 6.340 s12w = 12.102 s23t = 6.358 c23w = 1.792 β2t = -4.8240 Figure 10, 11 and 12 are graphs showing various aberrations of the third embodiment with respect to the d-line (λ = 587.6 nm) and the g-line (λ = 435.8 nm). FIG. 10 is a diagram showing various aberrations at the wide-angle end, and FIG.
1 shows various aberration diagrams at the intermediate angle of view, and FIG. 12 shows various aberration diagrams at the telephoto end.

As is clear from the aberration diagrams, in this embodiment, various aberrations are favorably corrected in each focal length state. [Fourth Embodiment] FIG. 13 is a view showing the lens arrangement of a fourth embodiment of the present invention. The first lens group G1 includes a biconvex lens L1, a negative meniscus lens L2 having a convex surface on the object side, and a positive meniscus lens L3 having an aspheric surface on the second surface and having a concave surface on the object side. Second lens group G
Reference numeral 2 denotes a single biconvex lens L4 having an aspheric surface on the first surface, and the third lens group G3 includes a cemented lens of a negative meniscus lens L5 having a convex surface facing the object side and a biconvex lens L6. You. During zooming from the wide-angle end to the telephoto end, the first lens group G1 is stationary, the second lens group G2 moves in the object direction, and the first lens group G1 and the second lens group G
2, the air gap between the second lens group G2 and the third lens group G3 changes. The sixth surface from the object of the first lens group G1 and the second surface from the object of the second lens group G2 are aspherical.

Table 4 below summarizes the data values of the fourth embodiment of the present invention.

[0043]

[Table 4] f = 2.9 to 4.0 to 5.8 F.NO = 2.22 to 2.54 to 2.72 2ω = 80.35 to 61.94 to 43.75 Surface number Curvature radius Surface spacing Refractive index Abbe number 1 56.198 1.700 1.860741 23.01 L1 G1 2 -54.099 0.084 3 18.293 0.420 1.748099 52.30 L2 4 2.603 2.000 5 -17.188 1.370 1.603110 60.64 L3 6 -15.397 (d6 = variable) 7 0.000 0.562 S 8 21.092 4.607 1.612720 58.54 L4 G2 9 -5.573 (d9 = variable) 10 11.037 1.120 11 4.047 4.000 1.603110 60.64 L6 12 -22.541 (d12 = variable) 13 0.000 4.000 1.516800 64.10 L7 14 0.000 0.883 (Aspheric coefficient) 6th surface 8th surface k = 1.0000 k = 1.0000 C4 = -2.40920E-03 C4 = -1.94050 E-03 C6 = -1.03570E-04 C6 = -2.20670E-05 C8 = -1.48230E-06 C8 = -3.40250E-06 (variable interval in variable magnification) f 2.90 4.00 5.80 d = 6 5.895 3.387 0.625 d = 9 1.232 3.977 4.659 d = 12 1.836 1.599 3.679 (Moving distance in close focus) f 2.90 4.00 5.80 β -0.0274 -0.0379 -0.0555 D0 100.000 100.000 100.000 3 lens group movement amount -0.1510 -0.2929 -0.5067 (Conditional value) f1 = -5.2 f2 = 7.7 f3 = 24.0 fw = 2.90 ft = 5.80 x2 = 5.270 s12w = 11.981 s23t = 6.429 c23w = 1.232 β2t = -1.8289 Figure 14 15 and 16 are graphs showing various aberrations of the fourth embodiment with respect to d-line (λ = 587.6 nm) and g-line (λ = 435.8 nm). FIG. 14 is a diagram showing various aberrations at the wide-angle end, and FIG.
5 shows various aberration diagrams at the intermediate angle of view, and FIG. 16 shows various aberration diagrams at the telephoto end.

As is clear from the aberration diagrams, in this embodiment, various aberrations are favorably corrected in each focal length state. Table 5 below shows the values of the conditional expressions in each example.

[0045]

[Table 5] (List of conditional expression values) First embodiment Second embodiment Third embodiment Fourth embodiment | (x2 / s12w) / (f1 / fw) | 0.2730 0.2718 0.2911 0.2453 c23w ² / (f3 * fw ) 0.1023 0.0449 0.0856 0.0218 s23t ² / (f3 * ft) 0.6448 0.6886 0.4815 0.2970 │fw / f1 │ 0.5577 0.5444 0.5556 0.5577 fw / f2 0.3222 0.3145 0.2941 0.3766 fw / f3 0.1933 0.1887 0.1667 0.1208 1 / β2t -0.2694 -0.2735 -0.2073- 0.5467 Thus, according to each embodiment, the first lens having negative refractive power
By arranging lens groups and making the entire system into three groups,
Wide angle of view and miniaturization were achieved. In addition, by using an aspherical lens, distortion and various aberrations can be satisfactorily corrected. Further, by focusing by the third lens group, the diameter of the first lens can be further reduced, and a high-performance zoom lens having a small overall lens system can be provided.

[0046]

As described above, according to the present invention, it is possible to provide a small zoom lens having a larger angle of view at the wide-angle end.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a zoom lens according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating various aberrations at the wide-angle end of the zoom lens according to Example 1;

FIG. 3 is a diagram illustrating various aberrations of the zoom lens according to the first example at an intermediate angle of view.

FIG. 4 is a diagram illustrating various types of aberration at the telephoto end of the zoom lens according to the first example.

FIG. 5 is a diagram showing a configuration of a zoom lens according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating various aberrations at the wide-angle end of the zoom lens according to Example 2;

FIG. 7 is a diagram illustrating various aberrations of the zoom lens according to Example 2 at an intermediate angle of view.

FIG. 8 is a diagram illustrating various types of aberration at the telephoto end of the zoom lens according to Example 2;

FIG. 9 is a diagram showing a configuration of a zoom lens according to a third embodiment of the present invention.

FIG. 10 is a diagram illustrating various aberrations at the wide-angle end of the zoom lens according to Example 3;

FIG. 11 is a diagram of various types of aberration at an intermediate angle of view of the zoom lens according to Example 3;

FIG. 12 is a diagram illustrating various types of aberration at the telephoto end of the zoom lens according to Example 3;

FIG. 13 is a diagram showing a configuration of a zoom lens according to a fourth embodiment of the present invention.

FIG. 14 is a diagram illustrating various aberrations at the wide-angle end of the zoom lens according to Example 4;

FIG. 15 is a diagram illustrating various aberrations of the zoom lens according to Example 4 at an intermediate angle of view.

FIG. 16 is a diagram of various types of aberration at the telephoto end of the zoom lens according to Example 4;

[Explanation of symbols]

 G1 First lens group G2 Second lens group G3 Third lens group S Aperture L1 to L6 Each lens

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA03 LA01 MA08 MA14 PA05 PA18 PB06 QA02 QA07 QA12 QA14 QA17 QA22 QA25 QA26 QA34 QA37 QA41 QA42 QA45 RA05 RA12 RA13 SA14 SA16 SA19 SA63 SA64 SA72 SB04 SB12 SB23

Claims (3)

[Claims] 1. A first lens having a negative refractive power in order from the object side.
A zoom lens including a lens group, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, wherein the first lens group is used for zooming from a wide-angle end to a telephoto end. Is stationary, the second lens group moves toward the object,
The third lens group is moved, the third lens group is moved in the object direction to focus from a long-distance object to a short-distance object, and fw is the focal length at the wide-angle end of the entire zoom lens, ft Is the focal length of the entire zoom lens at the telephoto end, f1 is the focal length of the first lens group, f3 is the focal length of the third lens group, and x2 is the wide-angle end to the telephoto end of the second lens group. S12w is the distance from the image-side principal point of the first lens group at the wide-angle end to the object-side principal point of the second lens group, and s23t is the second distance at the telephoto end. When the distance from the image-side principal point of the lens group to the object-side principal point of the third lens group, and c23w is the vertex distance between the second lens group and the third lens group at the wide-angle end, A zoom lens that satisfies the conditions. 0.15 <| (x2 / s12w) / (f1 / fw) | <1.0 0.01 <c23w 2 / (f3 * fw) <0.5 0.18 <s23t 2 / (f3 * ft) <5 2. The zoom lens according to claim 1, wherein said first lens group has an aspherical surface. 3. The zoom lens according to claim 1, wherein at the time of zooming from the wide-angle end to the telephoto end, the air gap between the first lens unit and the second lens unit is reduced.
The zoom lens according to claim 1, wherein an air gap between the second lens group and the third lens group is increased.