JP2007033476A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which is thinned and made small in size. <P>SOLUTION: The zoom lens is equipped with: a first lens group I; a second lens group II having positive refractive power; and a third lens group III having positive refractive power in order from an object side. The second lens group and the third lens group are moved to perform variable power from a wide angle end to a telephoto end and also correct the fluctuation of an image surface caused with the variable power. The first lens group I comprises a negative lens 1 and a prism 2 reflecting an optical path; the second lens group II comprises an aperture diaphragm SD, a positive lens 3 and a negative lens 4; and the third lens group III comprises a positive lens 5. Relation between a distance TL on an optical axis in a lens system from the surface S1 nearest to the object side of the first lens group I to an image surface P and a focal distance fw at the wide angle end of the lens system satisfies 4<TL/fw<10. Thus, the wide-angle zoom lens which is bright, small in size, thin in thickness and light in weight is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a zoom lens applied to an electronic imaging device using a solid-state imaging device such as a CCD, and more particularly to a small zoom lens suitable for a digital still camera, a mobile camera, and the like.

2. Description of the Related Art In recent years, due to remarkable technological progress of solid-state imaging devices used for digital still cameras, video cameras, and the like, CCDs and the like have been rapidly reduced in size and performance. For this reason, zoom lenses mounted on electronic imaging devices are also required to be smaller, lighter, and thinner.
In reducing the thickness of a zoom lens, the thickness of the lens system from the most object-side surface to the image plane, that is, the depth thickness becomes a problem.

In order to cope with this problem, an optical system has been proposed in which a reflecting surface such as a prism is provided in the lens system and the optical path is bent (see, for example, Patent Document 1 and Patent Document 2).
However, these zoom lenses still have a large number of lenses, which is insufficient in terms of size reduction, weight reduction, cost reduction, and the like. In particular, cellular phones, personal digital assistants (PDAs), and the like are strongly required to be further reduced in size and thickness. Therefore, zoom lenses to be mounted on them need to be smaller and thinner. is there.

JP 2000-131610 A Japanese Patent Laid-Open No. 10-20191

  The present invention has been made in view of the above-mentioned problems of the prior art, and its object is to adopt a very simple configuration of four lenses and one prism. Appropriately set the lens shape, aspherical position, etc., which can be compatible with recent high-density solid-state image sensors, wide angle of view, brighter, cheaper, digital still cameras, mobile cameras, etc. It is to provide a small zoom lens applicable to the above.

The zoom lens of the present invention includes a first lens group, a second lens group having a positive refractive power as a whole, and a third lens group having a positive refractive power as a whole, in order from the object side toward the image plane. A zoom lens that corrects image plane variation accompanying zooming and zooming from the wide-angle end to the telephoto end by moving the second lens group and the third lens group, and the first lens group has negative refraction. The second lens group includes an aperture stop having a predetermined aperture, a positive lens having a positive refractive power, and a negative lens having a negative refractive power. The third lens group is composed of a positive lens having a positive refractive power, and the distance on the optical axis in the lens system from the most object side surface to the image plane of the first lens group is TL, and the wide-angle end of the lens system When the focal length at is fw, Condition (1),
(1) 4 <TL / fw <10
It is characterized by satisfying.
According to this configuration, the light beam incident on the first lens group is bent at a substantially right angle by the prism, and the second lens group and the third lens group are moved to ensure a zoom ratio of about 3 times. The image is changed on the image plane of the solid-state imaging device by correcting the telephoto zoom and the image plane variation accompanying the zoom. Here, by adopting a lens configuration consisting of four lenses and one prism as a whole and satisfying the conditional expression (1), a wide-angle, bright, small, thin and light zoom lens can be obtained.

In the above configuration, the prism of the first lens group may employ a configuration in which at least one of the object side and the image plane side is formed to be convexly curved so as to have a positive refractive power. it can.
According to this configuration, by forming a convexly curved surface on the prism to have positive refractive power, the number of lenses can be reduced, and the weight and cost can be reduced.

The said structure WHEREIN: The structure currently formed with the resin material can be employ | adopted for the prism of a 1st lens group.
According to this configuration, the prism is formed of a resin material, thereby reducing the weight, the cost, and the optical path length.

In the above configuration, when the Abbe numbers of the positive lens and the negative lens in the second lens group are νs and νf, respectively, the following conditional expression (2),
(2) | νf−νs |> 40
Can be adopted.
According to this configuration, by setting the positive lens and the negative lens forming the second lens group so as to satisfy the conditional expression (2), it is possible to satisfactorily correct chromatic aberration that greatly affects performance enhancement. .

In the above configuration, the first lens group, the second lens group, and the third lens group may each include a lens having at least one aspheric surface.
According to this configuration, it is possible to satisfactorily correct off-axis aberrations such as on-axis aberrations such as spherical aberration, astigmatism and distortion while reducing the number of lenses, and in recent high-density solid-state image sensors. A suitable high-performance zoom lens can be obtained.

In the above configuration, the first lens group, the second lens group, and the third lens group include at least two resin lenses that are formed of a resin material and have different positive and negative refractive powers, and the focal length fp of the resin lens. When the value obtained by adding the reciprocal of Σ is Σ (1 / fp), the following conditional expression (3):
(3) | Σ (1 / fp) | <0.03
Can be adopted.
According to this configuration, the influence on the back focus due to the temperature change can be reduced, and the power of the lens can be set to be appropriately large.

In the above configuration, when the focal length of the second lens group is f2 and the focal length at the wide-angle end of the lens system is fw, the following conditional expression (4):
(4) 1.5 <| f2 / fw | <3.5
Can be adopted.
According to this configuration, a zoom ratio of about 3 times can be secured, and high optical performance can be obtained.

  According to the zoom lens having the above-described configuration, the lens shape, the position where the aspherical surface is applied, the glass material, and the like are appropriately set even though a very simple lens configuration including four lenses and one prism is employed. As a result, it is possible to obtain a small zoom lens that has optical performance compatible with recent high-density image sensors, has a wide angle of view, is bright, is cheaper, and is suitable for digital still cameras, mobile cameras, and the like. .

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
FIG. 1 is a configuration diagram showing an embodiment of a zoom lens according to the present invention, and FIGS. 2A, 2B, and 2C are optical path diagrams at a wide-angle end, an intermediate position, and a telephoto end.
As shown in FIG. 1, the zoom lens includes a first lens group (I), a second lens group (II) having a positive refractive power as a whole, and a positive overall. A third lens group (III) having refractive power is provided. The glass filters 6 and 7 are disposed behind the third lens group (III), and the image plane P of the solid-state imaging device is disposed behind the glass filters 6 and 7.
In this configuration, as shown in FIG. 2, the second lens group (II) and the third lens group (III) move in the direction of the optical axis L to change the magnification from the wide-angle end to the telephoto end. The accompanying image plane variation is corrected.

The first lens group (I) is formed by a negative lens 1 having negative refractive power and a prism 2 that bends the optical path.
The second lens group (II) is formed by an aperture stop SD having a predetermined aperture, a positive lens 3 having a positive refractive power, and a negative lens 4 having a negative refractive power. The aperture stop SD is disposed at a position retracted in the optical axis L direction from the object-side surface of the positive lens 3.
The third lens group (III) is formed by a positive lens 5 having a positive refractive power.

  Here, the negative lens 1, the prism 2, the positive lens 3, the negative lens 4, the positive lens 5, the glass filters 6 and 7, and the image plane P are sequentially arranged along the optical axis L from the object side to the image plane side. In the configuration, as shown in FIG. 1, each surface is Si (i = 1 to 14), the radius of curvature of each surface Si is Ri (i = 1 to 14), and the refractive index with respect to the d-line is Ni ( i = 1 to 7), Abbe number is νi (i = 1 to 7), and the distance (thickness, air distance) on each optical axis L from the negative lens 1 to the image plane P is Di (i = 1 to 1). 14).

  Further, the lens system includes the first object group (I) closest to the object side surface (object side surface of the negative lens 1) S1 to image plane P, and the focal lengths at the wide-angle end, the intermediate end, and the telephoto end of the lens system. Fw, fm, ft, the focal length of the second lens group (II) is f2, the distance on the optical axis L of the lens system (lens system total length) is TL, the positive lens 3 and the negative lens of the second lens group (II) The Abbe numbers of the lenses 4 are represented by νs (= ν3) and νf (= ν4), and the focal length of the lens formed of the resin material is represented by fp.

<First lens group (I)>
The negative lens 1 is a plano-concave lens that is formed of a glass material or a resin material and has a negative refractive power and the object-side surface S1 is a flat surface and the image-side surface S2 is concave.
The prism 2 is formed of a glass material or a resin material, and the object side surface S3 is a flat surface and the image surface side surface S4 is a flat surface, or the object side surface S3 or the surface S3 has a positive refractive power. The image side surface S4 is formed to be convexly curved.
Here, since the prism 2 has a positive refractive power, at least one of the surfaces S3 and S4 on the object side and the image surface side is formed to be convexly curved, thereby reducing the number of lenses. It is possible to reduce weight and cost.
Furthermore, the prism 2 is preferably made of a resin material. Thereby, weight reduction, cost reduction, and shortening of an optical path length are attained.

<Second lens group (II)>
The positive lens 3 is a biconvex lens formed of a glass material or a resin material and having a positive refractive power, the object-side surface S5 is convex and the image-side surface S6 is convex. is there.
The negative lens 4 is a meniscus lens formed of a glass material or a resin material and having a negative refractive index, the object-side surface S7 being convex and the image-side surface S8 being concave.

<Third lens group (III)>
The positive lens 5 is formed of a glass material or a resin material, and has a biconvex shape in which the object-side surface S9 is convex or concave and the image-side surface S10 is convex so as to have positive refractive power. This is a meniscus lens.

  In the above configuration, the light rays incident on the first lens group (I) are bent at a substantially right angle by the prism 2 as shown in FIG. 1, and the second lens group (II) and the third lens group (III) are By moving, wide-angle to telephoto zooming and image plane fluctuation correction accompanying zooming are corrected while securing a zooming ratio of about 3 times, and an image is formed on the image plane P of the solid-state imaging device.

In addition to the above configuration, the distance TL on the optical axis L in the lens system from the most object-side surface S1 to the image plane P of the first lens group (I), and the focal length fw at the wide-angle end of the lens system are: The following conditional expression (1),
(1) 4 <TL / fw <10
It is formed to satisfy.
In other words, the lens structure consisting of four lenses 1, 3, 4, 5 and one prism 2 that satisfies the conditional expression (1) as a whole is wide, bright, small, thin, and lightweight. A zoom lens is obtained.

In the above configuration, the Abbe numbers νs and νf of the positive lens 3 and the negative lens 4 of the second lens group (II) are preferably the following conditional expressions (2),
(2) | νf−νs |> 40
It is formed so as to satisfy.
Conditional expression (2) defines the selection of the glass material of the second lens group (II). If this conditional expression (2) is not satisfied, it will be difficult to correct chromatic aberration satisfactorily, resulting in an increase in the number of lenses or a reduction in zoom ratio (magnification). By satisfying this, it is possible to satisfactorily correct chromatic aberration that greatly affects the performance enhancement.

In the above configuration, the first lens group (I), the second lens group (II), and the third lens group (III) preferably each include at least one aspherical lens. Is done.
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 at the apex of the aspheric surface to a point on the aspheric surface whose height from the optical axis L is y, y: height from the optical axis, C: curvature at the apex of the aspheric surface ( 1 / R), ε: conic constant, D, E, F, G: aspheric coefficient.

By providing an aspherical surface in this way, it is possible to satisfactorily correct off-axis aberrations such as on-axis aberrations such as spherical aberration, astigmatism, and distortion, while reducing the number of lenses. A high-performance zoom lens suitable for a solid-state image sensor can be obtained.
That is, generally, axial aberrations such as spherical aberration are likely to occur near the aperture stop SD, and off-axis aberrations such as astigmatism and distortion are likely to occur in a lens located away from the aperture stop SD. If they are corrected with a spherical lens, an increase in the number of components can be considered, which does not meet the purpose. Therefore, by providing an aspheric surface in each lens group, axial aberrations such as spherical aberration and off-axis aberrations such as astigmatism and distortion can be corrected well, and lenses corresponding to recent high-density image sensors. Can be obtained.
For example, by providing aspherical surfaces at least on the negative lens 1 and the positive lens 5, it is possible to effectively correct distortion occurring particularly at the wide-angle end and the telephoto end. Also, by providing an aspherical surface on the lens 3 near the aperture stop SD, axial aberrations such as spherical aberration can be favorably corrected over the entire range from the wide-angle end to the telephoto end.
More specifically, the surface S2 on the image plane side of the negative lens 1, the surface S4 on the image plane side of the prism 2 formed in a convex shape, the surface S5 on the object side of the positive lens 3, and the image plane side of the negative lens 4 Surface S8, and both the object side and image surface side surfaces S9 and S10 of the positive lens 5 are aspherical.

In the above configuration, the first lens group (I), the second lens group (II), and the third lens group (III) are preferably made of a resin material and have different positive and negative refractive powers. A value Σ (1 / fp) including at least two resin lenses and adding the reciprocal of the focal length fp of the resin lens is expressed by the following conditional expression (3):
(3) | Σ (1 / fp) | <0.03
It is formed so as to satisfy.
Conditional expression (3) prescribes measures against the influence of temperature change. When a lens formed of a resin material is biased to one having positive or negative refractive power, back focus due to temperature change is caused. Therefore, the power of the lens must be kept small, and the degree of freedom is reduced. In addition, it becomes difficult to correct the back focus shift.
Therefore, by setting so as to satisfy the conditional expression (3), the influence on the back focus due to the temperature change can be canceled out, the influence can be reduced, and the power of the lens can be set to be appropriately large.

Furthermore, in the above configuration, the relationship between the focal length f2 of the second lens group (II) and the focal length fw at the wide angle end of the lens system is preferably the following conditional expression (4):
(4) 1.5 <| f2 / fw | <3.5
It is formed so as to satisfy.
Conditional expression (2) defines the power of the second lens group (II). By satisfying this conditional expression (4), a zoom ratio of about 3 times can be secured and high optical performance is obtained. be able to.

  Next, specific numerical examples of the zoom lens will be described below as Example 1 and Example 2.

Numerical data of conditional expressions (1) to (4) in Example 1, main specifications of the negative lens 1 to positive lens 5, glass filters 6 and 7, and various numerical data (setting values) are as follows. is there. In the first embodiment, among the negative lens 1, the prism 2, the positive lens 3, the negative lens 4, and the positive lens 5, the positive lens 3 and the negative lens 4 are formed of a glass material. The positive lens 5 is made of a resin material.
<Conditional expression>
(1) TL / fw = 36.37 / 4.84 = 7.514
(2) | νs−νf | = 70.3−20.6 = 49.7
(3) | Σ (1 / fp) | = | (−0.1223 + 0.03067 + 0.07325) | = 0.0184
(4) | f2 / fw | = | 12.1176 / 4.84 | = 2.503

<Specification specifications>
Object distance = ∞ (wide angle end) to ∞ (middle) to ∞ (telephoto end), focal length of lens system (fw, fm, ft) = 4.84 mm (wide angle end) to 8.50 mm (middle) to 14. 16 mm (telephoto end), zoom ratio (magnification) = 2.93, F number = 2.88 (wide angle end) to 4.32 (middle) to 6.09 (telephoto end), field angle (2ω) = 58 .40 ° (wide angle end) to 36.20 ° (middle) to 22.34 ° (telephoto end), emission angle (H = 3.6 mm) = − 7.76 ° (wide angle end) to −0.1 ° (Medium) to 3.97 ° (Telephoto end), lens total length (Air conversion) = 30.30 mm (Wide-angle end) to 32.64 mm (Medium) to 33.87 mm (Telephoto end), lens system total length (Air conversion) = 36.09 mm (wide angle end) to 36.10 mm (middle) to 36.10 mm (telephoto end), back focus (air conversion) = 5 79mm (wide angle end) ~3.46mm (intermediate) ~2.23mm (telephoto end)

<Aspherical surface>
Image surface side surface S2 of negative lens 1, image surface side surface S4 of prism 2, object side surface S5 of positive lens 3, image surface side surface S8 of negative lens 4, and both surfaces S9 and S10 of positive lens 5
<Curvature radius>
R1 = ∞, R2 = 4.292 mm (aspherical surface), R3 = ∞, R4 = −19.034 mm (aspherical surface), R5 = 4.386 mm (aspherical surface), R6 = −32.276 mm, R7 = 5. 327 mm, R8 = 3.231 mm (aspherical surface), R9 = −262.368 mm (aspherical surface), R10 = −7.0000 mm (aspherical surface), R11 = ∞, R12 = ∞, R13 = ∞, R14 = ∞
<Spacing on the optical axis>
D1 = 1.00 mm, D2 = 2.00 mm, D3 = 6.95 mm, D4 = variable, D5 = 2.00 mm, D6 = 1.56 mm, D7 = 0.73 mm, D8 = variable, D9 = 2.33 mm, D10 = variable, D11 = 0.30 mm, D12 = 0.15 mm, D13 = 0.50 mm, D14 = 0.50 mm
<Refractive index (Nd)>
N1 = 1.525120, N2 = 1.583850, N3 = 1.518348, N4 = 1.9970701, N5 = 1.525120, N6 = 1.516798, N7 = 1.516798
<Abbe number (νd)>
ν1 = 56.3, ν2 = 30.3, ν3 = 70.3, ν4 = 20.6, ν5 = 56.3, ν6 = 64.2, ν7 = 64.2

<Zoom interval (D4, D8, D10)>
D4 = 11.75 mm (wide angle end) to 6.22 mm (middle) to 1.00 mm (telephoto end),
D8 = 1.98 mm (wide angle end) to 9.85 mm (middle) to 16.30 mm (telephoto end),
D10 = 4.62 mm (wide-angle end) to 2.27 mm (intermediate) to 1.05 mm (telephoto end)

<Numerical data of aspheric coefficient>
<S2>
ε = −0.831755, D = 2.221970 × 10 ⁻⁴ , E = 6.078420 × 10 ⁻⁶ , F = 4.042240 × 10 ⁻⁸ , G = −3.1171650 × 10 ⁻¹⁰
<S4>
ε = 9.7070438, D = −9.668860 × 10 ⁻⁵ , E = 2.364710 × 10 ⁻⁶ , F = 7.564930 × 10 ⁻⁸ , G = 0.0000,
<S5>
ε = −1.155600, D = 5.621040 × 10 ⁻⁴ , E = 8.771330 × 10 ⁻⁶ , F = −9.429230 × 10 ⁻⁷ , G = 0.0000,
<S8>
ε = 0.137403, D = 1.767710 × 10 ⁻⁴ , E = −3.912070 × 10 ⁻⁵ , F = 0.000000, G = 0.000000,
<S9>
ε = −2.698632, D = −9.6677000 × 10 ⁻⁴ , E = −1.103880 × 10 ⁻⁴ , F = −5.309120 × 10 ⁻⁶ , G = 0.0000,
<S10>
ε = 0.000000, D = −9.586520 × 10 ⁻⁴ , E = −1.2234780 × 10 ⁻⁴ , F = 0.000000, G = 0.000000

The aberration diagrams regarding the spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end, the intermediate position, and the telephoto end in Example 1 are as shown in FIG. 3, FIG. 4, and FIG. . 3, 4, and 5, S represents an aberration on the sagittal plane, and M represents an aberration on the meridional plane.
According to the lens specifications according to the first embodiment, the zoom ratio is as high as 2.93, the F-number at the wide-angle end is about 2.88, and a small zoom lens with high optical performance in which various aberrations are well corrected. Is obtained.

Numerical data of conditional expressions (1) to (4) in Example 2, main specifications of the negative lens 1 to positive lens 5, glass filters 6 and 7, and various numerical data (setting values) are as follows. is there. In the first embodiment, among the negative lens 1, the prism 2, the positive lens 3, the negative lens 4, and the positive lens 5, the positive lens 3 and the negative lens 4 are formed of a glass material. The positive lens 5 is made of a resin material.
<Conditional expression>
(1) TL / fw = 35.255 / 4.84 = 7.284
(2) | νs−νf | = 70.3−20.6 = 49.7
(3) | Σ (1 / fp) | = | (−0.1222 + 0.02585 + 0.07197) | = 0.024
(4) | f2 / fw | = | 10.708 / 4.84 | = 2.212

<Specification specifications>
Object distance = ∞ (wide angle end) to ∞ (middle) to ∞ (telephoto end), focal length of lens system (fw, fm, ft) = 4.84 mm (wide angle end) to 8.50 mm (middle) to 14. 20 mm (telephoto end), zoom ratio (magnification) = 2.93, F-number = 2.90 (wide-angle end) to 4.40 (middle) to 6.07 (telephoto end), field angle (2ω) = 59 .94 ° (wide angle end) to 36.44 ° (middle) to 22.48 ° (telephoto end), emission angle (H = 3.6 mm) = 9.4 ° (wide angle end) to 0.76 ° (middle) ) To -3.24 ° (telephoto end), lens total length (air conversion) = 30.07 mm (wide angle end) to 32.8 mm (intermediate) to 33.0 mm (telephoto end), lens system total length (air conversion) = 34.98 mm to 34.97 mm (intermediate) to 34.98 mm (telephoto end), back focus (air conversion) = 4.91 mm (wide angle) ) ～2.17Mm (Intermediate) ～1.98Mm (telephoto end)

<Aspherical surface>
Image surface side surface S2 of negative lens 1, image surface side surface S4 of prism 2, object side surface S5 of positive lens 3, image surface side surface S8 of negative lens 4, and both surfaces S9 and S10 of positive lens 5
<Curvature radius>
R1 = ∞, R2 = 4.296 mm (aspheric), R3 = ∞, R4 = −22.586 mm (aspheric), R5 = 4.465 mm (aspheric), R6 = −19.468 mm, R7 = 7. 473 mm, R8 = 3.626 mm (aspherical), R9 = 65.474 mm (aspherical), R10 = −8.118 mm (aspherical), R11 = ∞, R12 = ∞, R13 = ∞, R14 = ∞
<Spacing on the optical axis>
D1 = 1.00 mm, D2 = 2.00 mm, D3 = 6.89 mm, D4 = variable, D5 = 2.02 mm, D6 = 1.60 mm, D7 = 1.41 mm, D8 = variable, D9 = 2.16 mm, D10 = variable, D11 = 0.30 mm, D12 = 0.15 mm, D13 = 0.50 mm, D14 = 0.50 mm
<Refractive index (Nd)>
N1 = 1.525120, N2 = 1.583850, N3 = 1.518348, N4 = 1.9970701, N5 = 1.525120, N6 = 1.516798, N7 = 1.516798
<Abbe number (νd)>
ν1 = 56.3, ν2 = 30.3, ν3 = 70.3, ν4 = 20.6, ν5 = 56.3, ν6 = 64.2, ν7 = 64.2

<Zoom interval (D4, D8, D10)>
D4 = 11.02 mm (wide angle end) to 6.41 mm (middle) to 1.00 mm (telephoto end),
D8 = 1.97 mm (wide angle end) to 9.31 mm (middle) to 14.92 mm (telephoto end),
D10 = 3.74 mm (wide angle end) to 1.00 mm (middle) to 0.80 mm (telephoto end)

<Numerical data of aspheric coefficient>
<S2>
ε = 0.2798928, D = 2.538260 × 10 ⁻⁴ , E = 1.924420 × 10 ⁻⁵ , F = −1.794750 × 10 ⁻⁶ , G = 4.814660 × 10 ⁻⁸
<S4>
ε = 27.393960, D = 6.593390 × 10 -7, E = 2.333820 × 10 -6, F = 9.370910 × 10 -7, G = 0.000000
<S5>
ε = −0.196466, D = 5.270810 × 10 ⁻⁴ , E = −3.3341370 × 10 ⁻⁶ , F = −2.195800 × 10 ⁻⁷ , G = 0.000000
<S8>
ε = 1.301132, D = 8.669290 × 10 ⁻⁴ , E = 6.881620 × 10 ⁻⁵ , F = 2.404530 × 10 ⁻⁶ , G = 0.0000
<S9>
ε = 1.00000, D = −1.43740 × 10 ⁻³ , E = 0.0000, F = 0.0000, G = 0.0000
<S10>
ε = -17.932650, D = -4.700900 × 10 ⁻³ , E = 1.947960 × 10 ⁻⁴ , F = −4.584930 × 10 ⁻⁶ , G = 0.0000

The aberration diagrams regarding the spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end, the intermediate position, and the telephoto end in Example 2 are as shown in FIG. 6, FIG. 7, and FIG. . 6, 7, and 8, S represents an aberration on the sagittal plane, and M represents an aberration on the meridional plane.
According to the lens specifications according to the second embodiment, the zoom ratio is as high as 2.93, the F-number at the wide-angle end is about 2.90, and a small zoom lens with high optical performance in which various aberrations are well corrected. Is obtained.

  As described above, the zoom lens of the present invention adopts a very simple lens configuration of four lenses and one prism, and appropriately sets the shape of the lens, the position where the aspheric surface is applied, the glass material, and the like. Therefore, it has optical performance compatible with recent high-density image sensors, has a wide angle of view, is bright, is cheaper, and is compact, so it can be applied to digital still cameras, mobile cameras mounted on mobile phones, etc. Of course, it is also useful as a zoom lens of a camera used for other purposes.

It is a schematic block diagram which shows one Embodiment of the zoom lens which concerns on this invention. (A), (b), (c) is an optical path diagram at the wide-angle end, middle, and telephoto end of the zoom lens shown in FIG. FIG. 3 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end in Example 1. FIG. 3 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at an intermediate position in Example 1. FIG. 3 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end in Example 1. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide angle end in Example 2. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at an intermediate position in Example 2. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end in Example 2.

Explanation of symbols

L Optical axis I First lens group II Second lens group III Third lens group 1 Negative lens 2 Prism 3 Positive lens 4 Negative lens 5 Positive lens 6, 7 Glass filter SD Aperture stop TL The most object side of the first lens group Distance fw on optical axis in lens system from surface to image plane Focal length νs at wide-angle end of lens system Abbe number of positive lens in second lens group νf Abbe number of negative lens in second lens group f2 Second lens group Focal length fp The focal length of a lens formed of a resin material

Claims (7)

A first lens group, a second lens group having a positive refractive power as a whole, and a third lens group having a positive refractive power as a whole, in order from the object side toward the image plane, the second lens group and the second lens group A zoom lens that corrects image plane variation accompanying zooming and zooming from the wide-angle end to the telephoto end by moving three lens groups,
The first lens group includes a negative lens having negative refractive power and a prism that bends the optical path.
The second lens group includes an aperture stop having a predetermined aperture, a positive lens having a positive refractive power, and a negative lens having a negative refractive power,
The third lens group includes a positive lens having a positive refractive power,
When the distance on the optical axis in the lens system from the most object side surface of the first lens group to the image plane is TL and the focal length at the wide-angle end of the lens system is fw, the following conditional expression (1) is satisfied. A zoom lens characterized by that.
(1) 4 <TL / fw <10 The prism of the first lens group is formed such that at least one of the object side and the image plane side is curved in a convex shape so as to have a positive refractive power.
The zoom lens according to claim 1. The prism of the first lens group is formed of a resin material.
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. 4. The zoom lens according to claim 1, wherein the following conditional expression (2) is satisfied when the Abbe numbers of the positive lens and the negative lens of the second lens group are νs and νf, respectively.
(2) | νf−νs |> 40 Each of the first lens group, the second lens group, and the third lens group includes a lens having at least one aspheric surface;
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The first lens group, the second lens group, and the third lens group include at least two resin lenses that are formed of a resin material and have different positive and negative refractive powers,
When a value obtained by adding the reciprocal of the focal length fp of the resin lens is Σ (1 / fp),
The zoom lens according to claim 1, wherein the following conditional expression (3) is satisfied.
(3) | Σ (1 / fp) | <0.03 The following conditional expression (4) is satisfied, where f2 is a focal length of the second lens group and fw is a focal length at the wide angle end of the lens system. Zoom lens.
(4) 1.5 <| f2 / fw | <3.5

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