JP2008112000A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve the miniaturization, etc. of a zoom lens used in an electronic imaging device using a solid-state image sensor such as a CCD. <P>SOLUTION: Starting from the object side, a negative first lens group I consists of a negative first lens 1, a positive or negative second lens 2, and a positive third lens 3, including at least one plastic lens, and a positive second lens group II consists of an aperture stop SD, a positive fourth lens 4, a negative fifth lens 5, and a positive sixth lens 6, including at least one plastic lens. The focal lengths fG1 and fG2 of the first lens group and the second lens group, the distance D2 between the first lens and the second lens, the focal length fw at the edge of a wide angle, and the focal lengths fP1 and fP2 of plastic lenses included in the first and second lens groups, meet the conditional expressions of (1) 0.9≤¾fG1¾/fG2≤1.5, (2) 0.2≤D2/fw≤0.4, and (3) 0.1≤¾1/fP1+1/fP2¾×fw≤1.0. The miniaturization, etc. of a zoom lens is achieved, while securing a zoom ratio of approximately three times. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a zoom lens used in an electronic image pickup apparatus using a solid-state image pickup device such as a CCD. It relates to a zoom lens.

  In recent years, with the widespread use of electronic imaging devices such as digital cameras, the demand for low cost, downsizing, and high performance has been increasing for zoom lenses used in these devices. In particular, the demand for cost reduction is very strong, and it is cheaper than glass lenses (or glass lenses with aspheric surfaces), so plastic lenses (or plastic lenses with aspheric surfaces) are generally used. Has been.

On the other hand, the conventional zoom lens includes a first lens group having negative refractive power and a second lens group having positive refractive power, and the first lens group has negative, negative and positive refractive powers. The second lens group consists of four lenses each having positive, positive, negative, and positive refractive power, and all the lenses are made of glass lenses, ensuring a magnification ratio of about 2 times. Is known (for example, see Patent Document 1).
However, in this zoom lens, the zoom ratio is as small as about 2 times, and since it is composed of seven glass lenses, it is sufficiently reduced in cost and weight to be mounted on a digital camera or the like. It cannot be said that it is done.

In addition, as another zoom lens, a first lens group and a second lens group are provided, and the first lens group includes three lenses each having negative, negative, and positive refractive powers, and the second lens group. However, there are known lenses that are composed of three lenses each having positive, negative, and positive refractive power, include at least four aspheric surfaces, and all lenses can be formed of plastic lenses (for example, Patent Document 2). reference).
However, in this zoom lens, the total lens length with respect to the focal length is long, and it cannot be said that downsizing is sufficiently performed.

JP-A-10-253882 JP 2001-21806

  The present invention has been made in view of the above-mentioned problems of the prior art, and its object is to satisfy low cost, downsizing (shortening the overall lens length), high performance, and the like. On the other hand, an object of the present invention is to provide a zoom lens that can secure a zoom ratio (magnification ratio) of about 3 times and is suitable for a digital camera, a digital video camera, and the like.

The zoom lens of the present invention includes, in order from the object side to the image plane side, a first lens group having negative refractive power, an aperture stop having a predetermined aperture closest to the object side, and has positive refractive power. And the second lens group moves from the wide-angle end to the telephoto end by moving to the object side and moving to the object side, and moving the second lens group monotonously to the object side. The first lens group is a zoom lens that performs image plane variation correction and focus adjustment operation. The first lens group includes a first lens having a negative refractive power and a positive or negative refractive power. A second lens having a positive refractive power, and at least one of the first lens, the second lens, and the third lens is a plastic lens, and the second lens group includes: Fourth lens with positive refractive power, negative refractive power A fifth lens having a positive refractive power, and at least one of the fourth lens, the fifth lens, and the sixth lens is a plastic lens, and the following conditional expressions (1), ( 2), (3),
(1) 0.9 ≦ | fG1 | /fG2≦1.5
(2) 0.2 ≦ D2 / fw ≦ 0.4
(3) 0.1 ≦ | 1 / fP1 + 1 / fP2 | × fw ≦ 1.0
Where fG1: focal length of the first lens group,
fG2: focal length of the second lens group,
D2: an air space on the optical axis of the first lens and the second lens,
fw: focal length at the wide-angle end,
fP1: the focal length of the plastic lens included in the first lens group,
fP2: focal length of the plastic lens included in the second lens group,
It is characterized by satisfying.
According to this configuration, a zoom ratio of about 3 times can be secured while correcting various aberrations satisfactorily by using a negative and positive two-group zoom type and satisfying conditional expressions (1) and (2). In addition, shortening, miniaturization, etc. of the entire lens length can be achieved. In addition, by including at least one plastic lens in each lens group so as to satisfy the conditional expression (3), it is possible to minimize fluctuations in focal length and back focus caused by refractive index changes when temperature changes. A zoom lens with high optical performance can be obtained.
Further, by moving the aperture stop integrally with the second lens group, the optical path difference between the first lens group and the second lens group from the wide-angle end to the telephoto end can be reduced. Can be made thinner.

In the above configuration, the two lens group may employ a configuration including a plastic lens having a positive refractive power and a plastic lens having a negative refractive power.
According to this configuration, it is possible to further minimize the variation of the focal length and the back focus caused by the refractive index change at the time of temperature change, and it is possible to obtain a zoom lens having higher optical performance. Further, by using many plastic lenses, it is possible to achieve significant cost reduction and weight reduction.

In the above configuration, when the Abbe number of a lens having positive refractive power in the second lens group is νs and the Abbe number of a lens having negative refractive power is νf, the following conditional expression (4):
(4) | νs−νf | ≧ 10
A configuration that satisfies the above can be adopted.
According to this configuration, by satisfying conditional expression (4), it is possible to satisfactorily correct chromatic aberration that has a large effect on high resolution. In particular, the plastic lens has a lower degree of freedom in selecting the Abbe number than the glass lens. Therefore, by selecting the Abbe number of the plastic lens so as to satisfy the conditional expression (4), chromatic aberration can be corrected well. Can do.

In the above configuration, each of the first lens group and the second lens group may include at least one aspheric surface.
According to this configuration, various aberrations such as spherical aberration, astigmatism, and distortion can be favorably corrected. That is, on the lens near the aperture stop, axial aberration such as spherical aberration is likely to occur, and on the lens located away from the aperture stop, off-axis aberration such as astigmatism and distortion is likely to occur. Accordingly, by providing each of the first lens group and the second lens group with at least one aspheric surface, various aberrations can be corrected well, and a zoom lens with high optical performance can be obtained.

In the above structure, a lens having an aspheric surface may be a plastic lens.
According to this configuration, an aspheric surface can be easily formed, and cost reduction and weight reduction can be achieved.

In the above configuration, the lens having positive or negative refractive power included in the first lens group, and the lens having positive refractive power and the lens having negative refractive power included in the second lens group are each directed toward the peripheral portion. Therefore, it is possible to adopt a configuration having an aspheric surface formed so that the refractive power thereof becomes weaker as the power increases.
According to this configuration, by providing the positive or negative lens of the first lens group and the aspherical surface in which the refractive power of the peripheral portion becomes weak in the positive and negative lenses of the second lens group, spherical aberration and astigmatism Various aberrations such as distortion can be corrected well, and a zoom lens with high optical performance can be obtained. In particular, by providing an aspheric surface to the lens having negative refractive power close to the object side in the first lens group, and to the lens having positive refractive power close to the aperture stop in the second lens group, respectively. Spherical aberration, astigmatism, distortion, etc. can be corrected well, and a thin zoom lens with high optical performance corresponding to a recent high-density image sensor can be obtained.

  According to the zoom lens having the above-described configuration, in the configuration of 6 elements in 6 groups, the power arrangement, the position where the aspherical surface is applied are appropriately set, and the plastic lens is frequently used, so that it is low-cost and small (the total length of the lens Short), high optical performance (high imaging performance), a zoom ratio (magnification ratio) of about 3 times can be secured, and a zoom lens optimal for digital cameras and digital video cameras can be obtained.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
1 and 2 show an embodiment of a zoom lens according to the present invention. FIG. 1 is a lens configuration diagram, and FIG. 2 is a state diagram at the wide-angle end, intermediate position, and telephoto end. is there.

As shown in FIG. 1, this zoom lens includes a first lens group (I) having a negative refractive power in order from the object side to the image plane side, and an aperture stop SD having a predetermined aperture on the most object side. And a second lens group (II) having a positive refractive power. An imaging plane P such as a solid-state imaging device is disposed behind the second lens group (II).
In this zoom lens, as shown by the wide-angle end position, the intermediate position, and the telephoto end position in FIGS. 2A, 2B, and 2C, the first lens group ( I) moves to the image plane side, reverses halfway and moves to the object side, and the second lens group (II) moves monotonously to the object side. The first lens group (I) is adapted to perform image plane variation correction and focus adjustment operations associated with zooming.

  As shown in FIG. 1, the first lens group (I) includes a first lens 1 having negative refractive power and a second lens 2 having relatively weak positive or negative refractive power, which are arranged in order from the object side. The third lens 3 has a positive refractive power. At least one of the first lens 1, the second lens 2, and the third lens 3 is a plastic lens formed of a resin material (plastic).

  As shown in FIG. 1, the second lens group (II) has an aperture stop SD having a predetermined aperture, a fourth lens 4 having a positive refractive power, and a negative refractive power, which are arranged in order from the object side. The fifth lens 5 and the sixth lens 6 having a positive refractive power are formed. At least one of the fourth lens 4, the fifth lens 5, and the sixth lens 6 is a plastic lens formed of a resin material (plastic).

Here, in the configuration in which the first lens 1 to the third lens 3, the aperture stop SD, the fourth lens to the sixth lens, and the image plane P are arranged in order from the object side along the optical axis L, FIG. As shown, each surface is Si (i = 1 to 13), the radius of curvature of each surface Si is Ri (i = 1 to 13), the refractive index for d-line is Ni (i = 1 to 6), and Abbe. The number is represented by ν i (i = 1 to 6), and the distance (thickness, air distance) on each optical axis L from the first lens 1 to the image plane P is represented by Di (i = 1 to 13).
Further, the lens system includes the most object side surface (object side surface of the first lens 1) S1 to the image plane P of the first lens group (I), and the focal points at the wide-angle end, the middle, and the telephoto end of this lens system. The distance is fw, fm, ft, the focal length of the first lens group (I) is fG1, the focal length of the second lens group (II) is fG2, and the distance on the optical axis L between the first lens 1 and the second lens 2 D2, the focal length of the plastic lens included in the first lens group (I) is fP1, the focal length of the plastic lens included in the second lens group (II) is fP2, and the second lens group (II) is positive. The Abbe number of a lens having refractive power is represented by νs, and the Abbe number of a lens having negative refractive power is represented by νf.

The first lens 1 is formed as a glass lens or plastic lens having a negative refractive power, and preferably has a negative refractive power with the convex surface S1 facing the object side and the concave surface S2 facing the image surface side, as shown in FIG. A meniscus-shaped lens having The surfaces S1 and S2 are formed as spherical surfaces or aspheric surfaces, preferably spherical surfaces.
The second lens 2 is formed as a glass lens or a plastic lens, preferably as a plastic lens. As shown in FIG. 1, the second lens 2 is a relatively weak positive or negative with the convex surface S3 facing the object side and the concave surface S4 facing the image surface side. This is a meniscus lens having a refractive power. Further, the surfaces S3 and S4 are formed as spherical surfaces or aspheric surfaces, preferably formed as aspheric surfaces, and more preferably formed as aspheric surfaces whose refractive power becomes weaker toward the peripheral portion.
The third lens 3 is formed as a glass lens or a plastic lens, and as shown in FIG. 1, is a meniscus lens having a positive refractive power with the convex surface S5 facing the object side and the concave surface S6 facing the image surface side. The surfaces S5 and S6 are spherical or aspherical, preferably spherical.
In the first lens 1, the second lens 2, and the third lens 3, at least one is formed as a plastic lens.

The fourth lens 4 is formed as a glass lens or a plastic lens, preferably a plastic lens. As shown in FIG. 1, the fourth lens 4 has both positive refractive powers with the convex surface S8 facing the object side and the convex surface S9 facing the image surface side. It is a convex lens. The fourth lens 4 is preferably formed such that the curvature radius R8 of the convex surface S8 on the object side is smaller than the absolute value | R9 | of the curvature radius of the convex surface S9 on the image side (R8 <| R9 |). . The surfaces S8 and S9 are formed as spherical surfaces or aspheric surfaces, preferably aspheric surfaces.
The fifth lens 5 is formed as a glass lens or a plastic lens, preferably a plastic lens. As shown in FIG. 1, the fifth lens 5 has both negative refractive powers with the concave surface S10 on the object side and the concave surface S11 on the image surface side. It is a concave lens. The fifth lens 5 is preferably formed such that the absolute value | R10 | of the radius of curvature of the concave surface S10 on the object side is larger than the radius of curvature R11 of the concave surface S11 on the image side (| R10 |> R11). . The surfaces S10 and S11 are formed as spherical surfaces or aspherical surfaces, preferably aspherical surfaces, and more preferably aspherical surfaces whose refractive power becomes weaker toward the periphery.
The sixth lens 6 is formed as a glass lens or a plastic lens, and as shown in FIG. 1, is a biconvex lens having a positive refractive power with the convex surface S12 facing the object side and the convex surface S13 facing the image surface side. . The surfaces S12 and S13 are formed as spherical surfaces or aspherical surfaces.
At least one of the fourth lens 4, the fifth lens 5, and the sixth lens 6 is formed as a plastic lens.

In addition to the above configuration, the focal length fG1 of the first lens group (I), the focal length fG2 of the second lens group (II), and the air distance D2 on the optical axis L of the first lens 1 and the second lens 2 The focal length fw at the wide-angle end of the lens system, the focal length fP1 of the plastic lens included in the first lens group (I), and the focal length fP2 of the plastic lens included in the second lens group (II) are as follows: (1), (2), (3),
(1) 0.9 ≦ | fG1 | /fG2≦1.5
(2) 0.2 ≦ D2 / fw ≦ 0.4
(3) 0.1 ≦ | 1 / fP1 + 1 / fP2 | × fw ≦ 1.0
It is formed to satisfy.

Conditional expression (1) defines the power arrangement of the lens groups (I) and (II). That is, if the value of | fG1 | / fG2 exceeds the upper limit value, it is necessary to increase the power of each surface of the lens, the burden of aberration correction on each surface increases, and the eccentric error sensitivity of each lens increases. Also, it becomes difficult to ensure a sufficient zoom ratio. On the other hand, if the value of | fG1 | / fG2 exceeds the lower limit, the angle of view becomes narrow with the same number of lenses, and a sufficient zoom ratio can be secured. It becomes difficult.
Therefore, by forming so that the value of | fG1 | / fG2 satisfies the conditional expression (1), the maximum length of the lens system can be reduced to about 36 mm or less, and a reduction in size can be achieved. 2ω) is about 60 °, and a zoom ratio (magnification ratio) of about 3 times can be secured.

Conditional expression (2) defines the relationship between the lens interval and the focal length at the wide-angle end in the first lens group (I). If the value of D2 / fw exceeds the upper limit value, the power of the first lens group (I) becomes too small, making it difficult to correct curvature of field, and the exit angle becomes large so that the image side telecentricity is reduced. On the other hand, if the value of D2 / fw exceeds the lower limit, the power of the first lens group (I) becomes too large, and it becomes difficult to correct field curvature.
Therefore, by forming so that the value of D2 / fw satisfies the conditional expression (2), it is possible to satisfactorily correct the field curvature while ensuring the image side telecentricity.

  Conditional expression (3) defines the focal length of the plastic lens included in each lens group. In general, a plastic lens has a larger change in refractive index when a temperature changes than a glass lens, and a change in focal length and back focus caused by the change also increases. Therefore, by including at least one plastic lens in each of the lens groups (I) and (II) so as to satisfy the conditional expression (3), the focal length and the back focus caused by the refractive index change at the time of temperature change are reduced. Variations can be minimized and a zoom lens with high optical performance can be obtained.

According to the zoom lens satisfying the above-described configuration, the negative and positive two-group zoom type is satisfied, and the conditional expressions (1) and (2) are satisfied. The angle of view (2ω) is about 60 °, a zoom ratio of about 3 times can be secured, the overall length of the lens can be shortened, the size of the lens can be reduced, etc., and each conditional expression (3) can be satisfied. By including at least one plastic lens in the lens groups (I) and (II), the focal length and back focus fluctuation caused by the refractive index change at the time of temperature change are minimized while achieving low cost and light weight. A zoom lens with high optical performance can be obtained.
Further, by moving the aperture stop SD integrally with the second lens group (II), the optical path difference in the first lens group (I) and the second lens group (II) from the wide-angle end to the telephoto end is reduced. Therefore, it is possible to achieve downsizing and thinning when retracted.

In the above configuration, the second lens group (II) preferably includes a plastic lens having a positive refractive power and a plastic lens having a negative refractive power, that is, at least one of the fourth lens 6 and the sixth lens 6. One is formed as a plastic lens, and the fifth lens 5 is formed as a plastic lens.
According to this, the focal length and the back focus fluctuation caused by the refractive index change at the time of temperature change can be further minimized, and a zoom lens having higher optical performance can be obtained. Further, by using many plastic lenses, it is possible to achieve significant cost reduction and weight reduction.

In the above configuration, in the second lens group (II), an Abbe number νs of a lens having a positive refractive power (that is, the fourth lens 4 or the sixth lens 6) and a lens having a negative refractive power (that is, a fifth lens). The Abbe number νf of the lens 5) is preferably the following conditional expression (4):
(4) | νs−νf | ≧ 10
It is formed so as to satisfy.
By satisfying conditional expression (4), it is possible to satisfactorily correct chromatic aberration that has a large effect on high resolution. In particular, the plastic lens has a lower degree of freedom in selecting the Abbe number than the glass lens. Therefore, by selecting the Abbe number of the plastic lens so as to satisfy the conditional expression (4), chromatic aberration can be corrected well. Can do.

In the above configuration, the first lens group (I) and the second lens group (II) preferably each include at least one aspheric surface, that is, the first lens 1, the second lens 2, and the third lens 3. Among the six surfaces on the object side and the image plane side, at least one surface is formed as an aspherical surface, and the fourth lens 4, the fifth lens 5, and the sixth lens 6 have six surfaces on the object side and the image plane side. Of these, at least one surface is formed as an aspherical surface.
According to this, various aberrations such as spherical aberration, astigmatism and distortion can be favorably corrected. That is, on the lens near the aperture stop SD, axial aberration such as spherical aberration is likely to occur, and on the lens located away from the aperture stop SD, off-axis aberration such as astigmatism and distortion occurs. easy. Therefore, by providing each of the first lens group (I) and the second lens group (II) with at least one aspheric surface, various aberrations can be corrected well, and a zoom lens with high optical performance can be obtained.
Here, the lens having an aspheric surface is preferably formed as a plastic lens. According to this, compared with the case of a glass lens, an aspherical surface can be formed easily, and cost reduction and weight reduction can be achieved.

In the above configuration, preferably, the positive refractive power of the lens having the positive refractive power (second lens 2 or third lens 3) and the second lens group (II) included in the first lens group (I) is set. The aspherical surface formed such that the lens (the fourth lens 4 or the sixth lens 6) and the lens having the negative refractive power (the fifth lens 5) have a refractive power that decreases toward the periphery. Is formed.
According to this, in the positive or negative lens of the first lens group (I) and the positive and negative lenses of the second lens group (II), by providing an aspheric surface where the refractive power of the peripheral portion becomes weak, Various aberrations such as spherical aberration, astigmatism and distortion can be corrected well, and a zoom lens with high optical performance can be obtained.
In particular, the first lens group (I) has a negative refractive power close to the object side (the first lens 1 or the second lens 2), and the second lens group (II) has a position near the aperture stop SD. By providing each lens (fourth lens 4) having a positive refractive power with an aspheric surface, spherical aberration, astigmatism, distortion, etc. can be corrected satisfactorily, and this is compatible with recent high-density imaging devices. A thin zoom lens with high optical performance can be obtained.

Here, the expression representing the aspheric surface is defined by the following expression.
Z = Cy ² / [1+ (1-εC ² y ² ) ^1/2 ] + Dy ⁴ + Ey ⁶ + Fy ⁸ + Gy ¹⁰
Where Z: distance from the tangent plane of the aspherical vertex of the point on the aspherical surface whose height from the optical axis L is y, y: height from the optical axis, C: curvature at the vertex of the aspherical surface (= 1) / R), ε: cone coefficient, D, E, F, G: aspheric coefficient.

  An example with specific numerical values of the zoom lens having the above configuration is shown as Example 1 below.

The lens configuration in Example 1 is as shown in FIGS. 1 and 2, and numerical data of conditional expressions (1) to (4), main specifications of the first lens 6 to the sixth lens 6, and various numerical data. (Setting value) is as follows.
In Example 1, the second lens 2, the fourth lens 4, and the fifth lens 5 are formed as plastic lenses, and both surfaces S3 and S4 of the second lens 2, both surfaces S8 and S9 of the fourth lens 4, Both surfaces S10 and S11 of the fifth lens 5 are aspherical.

<Value of conditional expression>
(1) | fG1 | / fG2 = | −11.91 | /10.29=1.16→0.9≦1.16≦1.5
(2) D2 / fw = 2.00 / 6.37 = 0.31 → 0.2 ≦ 0.31 ≦ 0.4
(3) | 1 / fP1 + 1 / fP2 | × fw = | 1 / 999.77 + 1 / 33.98 | × 6.37 = 0.19 → 0.1 ≦ 0.19 ≦ 1.0
(4) | νs−νf | = | 56.3-30.3 | = 26.0 → 26.0 ≧ 10

<Specification specifications>
Object distance = ∞ (wide angle end) to ∞ (middle) to ∞ (telephoto end), focal length of lens system (fw, fm, ft) = 6.37 mm (wide angle end) to 12.53 mm (middle) to 18. 47 mm (telephoto end), zoom ratio (magnification ratio) = 2.90, F number (FNo.) = 3.30 (wide angle end) to 4.40 (middle) to 5.53 (telephoto end), angle of view (Ω) = 30.65 ° (wide angle end) to 16.71 ° (middle) to 11.55 ° (telephoto end), exit pupil position = −15.87 mm (wide angle end) to −21.30 mm (middle) -26.39 mm (telephoto end), total lens length (distance from the front surface S1 of the first lens 1 to the rear surface S13 of the sixth lens 6) = 23.76 mm (wide angle end)-14.31 mm (intermediate)-11. 17 mm (telephoto end), full length of lens system (distance from front surface S1 to image plane P of first lens 1) = 36.0 mm (wide-angle end) to 31.98 mm (intermediate) to 33.93 mm (telephoto end), back focus (air conversion distance from the rear surface S13 to the image plane P of the sixth lens 6) = 12.24 mm (wide-angle end) to 17.67 mm (middle) to 22.76 mm (telephoto end), focal length of the first lens group (I) =-11.91 mm, focal length of the second lens group (II) = 10.29 mm

<Curvature radius>
R1 = 22.350 mm, R2 = 4.639 mm, R3 = 36.114 mm (aspheric surface), R4 = 38.412 mm (aspheric surface), R5 = 12.689 mm, R6 = 26.179 mm, R7 = ∞ (aperture stop) ), R8 = 4.096 mm (aspherical surface), R9 = −27.137 mm (aspherical surface), R10 = −87.958 mm (aspherical surface), R11 = 3.909 mm (aspherical surface), R12 = 9.300 mm, R13 = -15.717mm

<Spacing on the optical axis>
D1 = 1.00 mm, D2 = 2.00 mm, D3 = 1.00 mm, D4 = 0.15 mm, D5 = 1.50 mm, D6 = variable, D7 = 0.00 mm, D8 = 2.42 mm, D9 = 0. 10 mm, D10 = 0.60 mm, D11 = 0.48 mm, D12 = 1.30 mm, D13 = variable

<Refractive index (Nd)>
N1 = 1.772500, N2 = 1.525120, N3 = 1.846660, N4 = 1.525120, N5 = 1.583810, N6 = 1.571350
<Abbe number (νd)>
ν1 = 49.6, ν2 = 56.3, ν3 = 23.8, ν4 = 56.3, ν5 = 30.3, ν6 = 53.0

<Zoom interval (D6, D13)>
D6 = 13.23 mm (wide angle end) to 3.76 mm (middle) to 0.61 mm (telephoto end),
D13 = 12.24 mm (wide-angle end) to 17.67 mm (intermediate) to 22.76 mm (telephoto end)

<Numerical data of aspheric coefficient>
<S3>
ε = 0.000000, D = −5.186680 × 10 ⁻⁴ , E = 1.462302 × 10 ⁻⁴ , F = −7.336640 × 10 ⁻⁶ , G = 1.223165 × 10 ⁻⁷
<S4>
ε = 0.0000, D = −1.174260 × 10 ⁻³ , E = 1.077326 × 10 ⁻⁴ , F = −6.3372640 × 10 ⁻⁶ , G = 2.641300 × 10 ⁻⁸
<S8>
ε = −3.0004447, D = 4.585869 × 10 ⁻³ , E = −2.044620 × 10 ⁻⁴ , F = 1.7634949 × 10 ⁻⁵ , G = −1.031310 × 10 ⁻⁶
<S9>
ε = −0.956484, D = 2.512762 × 10 ⁻⁴ , E = −1.537330 × 10 ⁻⁵ , F = −3.813590 × 10 ⁻⁶ , G = −9.793460 × 10 ⁻⁷
<S10>
ε = 0.000000, D = −2.862330 × 10 ⁻⁴ , E = 2.680847 × 10 ⁻⁶ , F = −5.1747390 × 10 ⁻⁷ , G = −1.009770 × 10 ⁻⁶
<S11>
ε = 0.005639, D = −1.418780 × 10 ⁻⁴ , E = −4.538710 × 10 ⁻⁷ , F = 4.045888 × 10 ⁻⁷ , G = −1.5747780 × 10 ⁻⁷

In the first embodiment, various aberrations (spherical aberration, astigmatism, distortion, lateral chromatic aberration) at the wide-angle end, the intermediate position, and the telephoto end are the results shown in FIGS. 3, 4, and 5, respectively. In the astigmatism in FIGS. 3 to 5, S represents an aberration on the sagittal plane, and M represents an aberration on the meridional plane.
According to the first embodiment, the zoom ratio is 2.90, the total length of the lens system is 36.00 mm at the maximum, the F-number at the wide-angle end is 3.30, and various aberrations are well corrected, and the optical performance is high. A small zoom lens can be obtained.

The lens configuration in Example 2 is as shown in FIG. 6 and FIG. 7. Numerical data of conditional expressions (1) to (4), main specifications of the first lens 6 to the sixth lens 6, various numerical data (Setting value) is as follows.
In Example 2, the second lens 2, the fourth lens 4, the fifth lens 5, and the sixth lens 6 are formed as plastic lenses, and both the surfaces S 3 and S 4 of the second lens 2 and the fourth lens 4 are formed. Both surfaces S8 and S9, both surfaces S10 and S11 of the fifth lens 5, and both surfaces S12 and S13 of the sixth lens 6 are formed as aspherical surfaces.

<Value of conditional expression>
(1) | fG1 | / fG2 = | −11.73 | /10.23=1.15→0.9≦1.15≦1.5
(2) D2 / fw = 2.00 / 6.39 = 0.31 → 0.2 ≦ 0.31 ≦ 0.4
(3) | 1 / fP1 + 1 / fP2 | × fw = | 1 / 999.68 + 1 / 32.03 | × 6.39 = 0.21 → 0.1 ≦ 0.21 ≦ 1.0
(4) | νs−νf | = 56.3-30.3 = 26.0 → 26.0 ≧ 10

<Specification specifications>
Object distance = ∞ (wide angle end) to ∞ (middle) to ∞ (telephoto end), focal length of lens system (fw, fm, ft) = 6.39 mm (wide angle end) to 12.72 mm (middle) to 18. 49 mm (telephoto end), zoom ratio (magnification ratio) = 2.90, F number (FNo.) = 3.31 (wide angle end) to 4.51 (middle) to 5.60 (telephoto end), angle of view (Ω) = 30.58 ° (wide angle end) to 16.47 ° (middle) to 11.54 ° (telephoto end), exit pupil position = −26.10 mm (wide angle end) to −21.43 mm (middle) -26.04 mm (telephoto end), total lens length (distance from the front surface S1 of the first lens 1 to the rear surface S13 of the sixth lens 6) = 23.44 mm (wide angle end)-14.09 mm (intermediate)-11. 13 mm (telephoto end), full length of lens system (distance from front surface S1 to image surface P of first lens 1) = 35.6 mm (wide-angle end) to 31.95 mm (intermediate) to 33.97 mm (telephoto end), back focus (air conversion distance from the rear surface S13 to the image plane P of the sixth lens 6) = 12.23 mm (wide-angle end) to 17.86 mm (middle) to 22.84 mm (telephoto end), focal length of the first lens group (I) =-11.73 mm, focal length of the second lens group (II) = 10.23 mm

<Curvature radius>
R1 = 22.713mm, R2 = 4.583mm, R3 = 37.069mm (aspherical), R4 = 39.515mm (aspherical), R5 = 12.881mm, R6 = 27.704mm, R7 = ∞ (aperture stop) ), R8 = 4.101 mm (aspheric surface), R9 = −27.357 mm (aspheric surface), R10 = −99.973 mm (aspheric surface), R11 = 3.962 mm (aspheric surface), R12 = 8.268 mm ( Aspherical), R13 = −16.265 mm (aspherical)

<Spacing on the optical axis>
D1 = 1.00 mm, D2 = 2.00 mm, D3 = 1.00 mm, D4 = 0.15 mm, D5 = 1.50 mm, D6 = variable, D7 = 0.00 mm, D8 = 2.42 mm, D9 = 0. 10 mm, D10 = 0.60 mm, D11 = 0.44 mm, D12 = 1.30 mm, D13 = variable

<Refractive index (Nd)>
N1 = 1.772500, N2 = 1.525120, N3 = 1.846660, N4 = 1.525120, N5 = 1.58816, N6 = 1.525120
<Abbe number (νd)>
ν1 = 49.6, ν2 = 56.3, ν3 = 23.8, ν4 = 56.3, ν5 = 30.3, ν6 = 56.3

<Zoom interval (D6, D13)>
D6 = 12.93 mm (wide angle end) to 3.57 mm (middle) to 0.63 mm (telephoto end),
D13 = 12.23 mm (wide-angle end) to 17.86 mm (intermediate) to 22.84 mm (telephoto end)

<Numerical data of aspheric coefficient>
<S3>
ε = 0.000000, D = -4.707120 × 10 ⁻⁴ , E = 1.458679 × 10 ⁻⁴ , F = −7.564290 × 10 ⁻⁶ , G = 1.526972 × 10 ⁻⁷
<S4>
ε = 0.000000, D = −1.159790 × 10 ⁻³ , E = 1.055462 × 10 ⁻⁴ , F = −6.405860 × 10 ⁻⁶ , G = 3.9900760 × 10 ⁻⁸
<S8>
ε = −3.022216, D = 4.599386 × 10 ⁻³ , E = −2.050030 × 10 ⁻⁴ , F = 1.686159 × 10 ⁻⁵ , G = −1.097940 × 10 ⁻⁶
<S9>
ε = 5.889468, D = 1.771182 × 10 ⁻⁴ , E = −2.3346760 × 10 ⁻⁵ , F = −4.669980 × 10 ⁻⁶ , G = −1.113540 × 10 ⁻⁶
<S10>
ε = 0.000000, D = −2.359100 × 10 ⁻⁴ , E = 5.156900 × 10 ⁻⁶ , F = −3.787820 × 10 ⁻⁷ , G = −1.027030 × 10 ⁻⁶
<S11>
ε = 0.014505, D = −1.120530 × 10 ⁻⁴ , E = −8.484840 × 10 ⁻⁶ , F = 3.933409 × 10 ⁻⁶ , G = 8.583800 × 10 ⁻⁷
<S12>
ε = −0.100953, D = −2.198110 × 10 ⁻⁵ , E = −5.539850 × 10 ⁻⁶ , F = 1.324705 × 10 ⁻⁶ , G = −1.452810 × 10 ⁻⁷
<S13>
ε = −3.7747379, D = 1.137374 × 10 ⁻⁴ , E = 4.145669 × 10 ⁻⁵ , F = 4.214437 × 10 ⁻⁷ , G = −5.053530 × 10 ⁻⁷

In Example 2 above, various aberrations (spherical aberration, astigmatism, distortion, lateral chromatic aberration) at the wide-angle end, intermediate position, and telephoto end are the results shown in FIGS. 8, 9, and 10, respectively. In the astigmatism in FIGS. 8 to 10, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane.
According to the second embodiment, the zoom ratio is 2.90, the total length of the lens system is 35.67 mm at the maximum, the F-number at the wide angle end is 3.31, and various aberrations are well corrected, and the optical performance is high. A small zoom lens can be obtained.

The lens configuration in Example 3 is as shown in FIGS. 11 and 12, and numerical data of conditional expressions (1) to (4), main specifications of the first lens 6 to the sixth lens 6, and various numerical data. (Setting value) is as follows.
In Example 3, the second lens 2, the fourth lens 4, and the fifth lens 5 are formed as plastic lenses, and both surfaces S3, S4 of the second lens 2, both surfaces S8, S9 of the fourth lens 4, Both surfaces S10 and S11 of the fifth lens 5 are aspherical.

<Value of conditional expression>
(1) | fG1 | / fG2 = | −10.78 | /9.78=1.10→0.9≦1.10≦1.5
(2) D2 / fw = 2.35 / 6.44 = 0.36 → 0.2 ≦ 0.36 ≦ 0.4
(3) | 1 / fP1 + 1 / fP2 | × fw = | 1 / 43.11 + 1 / 9.78 | × 6.44 = 0.81 → 0.1 ≦ 0.81 ≦ 1.0
(4) | νs−νf | = 56.3-30.3 = 26.0 → 26.0 ≧ 10

<Specification specifications>
Object distance = ∞ (wide angle end) to ∞ (middle) to ∞ (telephoto end), focal length of lens system (fw, fm, ft) = 6.44 mm (wide angle end) to 13.23 mm (middle) to 18. 48 mm (telephoto end), zoom ratio (magnification ratio) = 2.87, F number (FNo.) = 3.28 (wide angle end) to 4.63 (middle) to 5.75 (telephoto end), angle of view (Ω) = 31.43 ° (wide angle end) to 16.49 ° (middle) to 12.02 ° (telephoto end), exit pupil position = −15.44 mm (wide angle end) to −21.68 mm (middle) -26.36 mm (telephoto end), total lens length (distance from the front surface S1 of the first lens 1 to the rear surface S13 of the sixth lens 6) = 21.69 mm (wide angle end)-13.38 mm (intermediate)-11. 02 mm (telephoto end), full length of lens system (distance from front surface S1 to image plane P of first lens 1) = 33.5 mm (wide-angle end) to 31.42 mm (intermediate) to 33.84 mm (telephoto end), back focus (air conversion distance from the rear surface S13 to the image plane P of the sixth lens 6) = 11.90 mm (wide-angle end) to 18.04 mm (intermediate) to 22.82 mm (telephoto end), focal length of the first lens group (I) =-10.78 mm, focal length of the second lens group (II) = 9.78 mm

<Curvature radius>
R1 = 12.542 mm, R2 = 4.205 mm, R3 = 64.158 mm (aspherical), R4 = 16.644 mm (aspherical), R5 = 14.590 mm, R6 = 62.777 mm, R7 = ∞ (aperture stop) ), R8 = 3.712 mm (aspherical surface), R9 = −16.585 mm (aspherical surface), R10 = −107.030 mm (aspherical surface), R11 = 3.897 mm (aspherical surface), R12 = 13.923 mm, R13 = -13.137mm

<Spacing on the optical axis>
D1 = 1.00 mm, D2 = 2.35 mm, D3 = 1.00 mm, D4 = 0.20 mm, D5 = 1.20 mm, D6 = variable, D7 = 0.00 mm, D8 = 2.00 mm, D9 = 0. 20 mm, D10 = 0.61 mm, D11 = 0.70 mm, D12 = 1.10 mm, D13 = variable

<Refractive index (Nd)>
N1 = 1.788000, N2 = 1.525120, N3 = 1.880890, N4 = 1.525120, N5 = 1.58816, N6 = 1.487490
<Abbe number (νd)>
ν1 = 47.4, ν2 = 56.3, ν3 = 22.8, ν4 = 56.3, ν5 = 30.3, ν6 = 70.2

<Zoom interval (D6, D13)>
D6 = 11.33 mm (wide angle end) to 2.92 mm (middle) to 0.66 mm (telephoto end),
D13 = 11.90 mm (wide angle end) to 18.04 mm (middle) to 22.82 mm (telephoto end)

<Numerical data of aspheric coefficient>
<S3>
ε = 0.000000, D = −1.523580 × 10 ⁻⁴ , E = −8.2277850 × 10 ⁻⁵ , F = 1.382730 × 10 ⁻⁵ , G = −4.886780 × 10 ⁻⁷
<S4>
ε = 8.042613, D = −1.274670 × 10 ⁻³ , E = −9.258680 × 10 ⁻⁵ , F = 1.203515 × 10 ⁻⁵ , G = −5.592820 × 10 ⁻⁷
<S8>
ε = −2.4266653, D = 5.301889 × 10 ⁻³ , E = −7.3329900 × 10 ⁻⁵ , F = 1.785280 × 10 ⁻⁵ , G = 2.347466 × 10 ⁻⁷
<S9>
ε = 0.000000, D = 7.109590 × 10 ⁻⁴ , E = −2.8875390 × 10 ⁻⁵ , F = 4.430397 × 10 ⁻⁵ , G = −6.191380 × 10 ⁻⁶
<S10>
ε = 0.000000, D = −3.086610 × 10 ⁻³ , E = 2.980100 × 10 ⁻⁴ , F = −8.270250 × 10 ⁻⁶ , G = −4.6609120 × 10 ⁻⁶
<S11>
ε = −0.262314, D = −1.381880 × 10 ⁻³ , E = 6.9923957 × 10 ⁻⁴ , F = −8.316870 × 10 ⁻⁵ , G = 1.096331 × 10 ⁻⁵

In Example 3, various aberrations (spherical aberration, astigmatism, distortion, and lateral chromatic aberration) at the wide-angle end, the intermediate position, and the telephoto end are the results shown in FIGS. 13, 14, and 15, respectively. In the astigmatism in FIGS. 13 to 15, S represents an aberration on the sagittal plane, and M represents an aberration on the meridional plane.
According to the third embodiment, the zoom ratio is 2.87, the total length of the lens system is 35.59 mm at the maximum, the F-number at the wide-angle end is 3.28, and various aberrations are well corrected, and the optical performance is high. A small zoom lens can be obtained.

  As described above, the zoom lens according to the present invention has a configuration of 6 elements in 6 groups, appropriately sets the power arrangement and the position where the aspheric surface is applied, and uses a lot of plastic lenses, thereby reducing the cost and size ( (Short lens length), high optical performance (high imaging performance), and a zoom ratio (magnification ratio) of about 3 times can be secured, so it can be applied as a zoom lens for digital cameras and digital video cameras In addition, it is also useful in other lens optical systems that require a reduction in size.

It is a lens block diagram which shows one Embodiment of the zoom lens which concerns on this invention. FIG. 2 illustrates operations of the zoom lens illustrated in FIG. 1, and (a), (b), and (c) are state diagrams at the wide-angle end, the middle, and the telephoto end. FIG. 4 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide angle end in the zoom lens according to the first exemplary embodiment. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at an intermediate position in the zoom lens of Example 1; FIG. 4 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end in the zoom lens according to the first exemplary embodiment. It is a lens block diagram which shows other embodiment of the zoom lens which concerns on this invention. FIG. 7 shows operations of the zoom lens shown in FIG. 6, and (a), (b), and (c) are state diagrams at the wide-angle end, the middle, and the telephoto end. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide angle end in the zoom lens according to Example 2; FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at an intermediate position in the zoom lens according to Example 2; FIG. 7 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end in the zoom lens according to the second exemplary embodiment. It is a lens block diagram which shows other embodiment of the zoom lens which concerns on this invention. FIG. 12 shows operations of the zoom lens shown in FIG. 11, and (a), (b), and (c) are state diagrams at the wide-angle end, the middle, and the telephoto end. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide angle end in the zoom lens according to Example 3; FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at an intermediate position in the zoom lens according to Example 3; FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end in the zoom lens according to Example 3;

Explanation of symbols

I 1st lens group II 2nd lens group 1 1st lens 2 2nd lens 3 3rd lens SD Aperture stop 4 4th lens 5 5th lens 6 6th lens L Optical axis P Image plane fw Focal length at wide angle end fG1 Focal length fG2 of the first lens group Focal length fP1 of the second lens group Focal length fP2 of the plastic lens included in the first lens group Focal length D2 of the plastic lens included in the second lens group First and second lenses The air interval νs on the optical axis of the lens Abbe number of the lens having positive refractive power included in the second lens group νf The Abbe number of the lens having negative refractive power included in the second lens group

Claims (6)

In order from the object side to the image plane side, a first lens group having a negative refractive power and a second lens group including an aperture stop having a predetermined aperture on the most object side and having a positive refractive power are provided. The first lens group moves to the image plane side, reverses from the middle and moves to the object side, and the second lens group monotonously moves to the object side to perform zooming from the wide angle end to the telephoto end, The first lens group is a zoom lens that performs image surface variation correction and focus adjustment operation,
The first lens group includes a first lens having negative refractive power, a second lens having positive or negative refractive power, and a third lens having positive refractive power, and the first lens, second lens At least one of the lens and the third lens is a plastic lens,
The second lens group includes a fourth lens having a positive refractive power, a fifth lens having a negative refractive power, a sixth lens having a positive refractive power, and the fourth lens, the fifth lens, And at least one of the sixth lenses is a plastic lens,
The following conditional expressions (1), (2), (3),
(1) 0.9 ≦ | fG1 | /fG2≦1.5
(2) 0.2 ≦ D2 / fw ≦ 0.4
(3) 0.1 ≦ | 1 / fP1 + 1 / fP2 | × fw ≦ 1.0
Where fG1: focal length of the first lens group,
fG2: focal length of the second lens group,
D2: an air space on the optical axis of the first lens and the second lens,
fw: focal length at the wide-angle end,
fP1: the focal length of the plastic lens included in the first lens group,
fP2: focal length of the plastic lens included in the second lens group,
A zoom lens characterized by satisfying The two lens groups include a plastic lens having a positive refractive power and a plastic lens having a negative refractive power.
The zoom lens according to claim 1. In the second lens group, when the Abbe number of a lens having a positive refractive power is νs and the Abbe number of a lens having a negative refractive power is νf,
Conditional expression (4) below,
(4) | νs−νf | ≧ 10
The zoom lens according to claim 2, wherein: Each of the first lens group and the second lens group includes at least one aspheric surface,
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The lens having the aspheric surface is a plastic lens.
The zoom lens according to claim 4. The lens having positive or negative refractive power included in the first lens group, and the lens having positive refractive power and the lens having negative refractive power included in the second lens group respectively move toward the periphery. And has an aspheric surface formed so that its refractive power becomes weak,
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens.

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