JP2003005072A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a video camera and a digital camera extremely thin by selecting a zoom system and a zoom constitution having stable excellent image formation performance such as the reduced number of constituting pieces and making the total thickness of each group thin. SOLUTION: In a zoom lens which possesses a first group G1 having negative refractive power, a second group G2 having positive refractive power and a third group G3 having positive refractive power and by which variable power from a wide angle end to a telephoto end at the time of focusing at an infinite object point is performed by the monotonous movement of the second group to the object side and the movement of the third group by the amount different from that of the second group, the second group is constituted of a cemented lens consisting of a positive lens and a negative lens in order and a positive lens, and a conditional expression with respect to the shape factor of the positive lens of the second group closest to the object is satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a zoom lens for a video camera or a digital camera, the zoom lens for a video camera or a digital camera, which is thinned in a depth direction by devising an optical system part. It is about lenses. Further, the present invention relates to a zoom lens that enables rear focus.

[0002]

2. Description of the Related Art In recent years, a digital camera (electronic camera) has been attracting attention as a next-generation camera to replace a silver salt 35 mm film (commonly called Leica version) camera. Furthermore, it has come to have several categories in a wide range from high-performance type for business use to portable popular type. In the present invention, attention is particularly paid to the portable popular type category, and an aim is to provide a technique for realizing a video camera and a digital camera with a small depth while ensuring high image quality.

The biggest bottleneck in thinning the depth direction of a camera is the thickness from the most object side surface of the optical system, particularly the zoom lens system, to the image pickup surface. Recently, it has become mainstream to employ a so-called collapsible lens barrel in which the optical system is pushed out of the camera body at the time of photographing and the optical system is housed in the camera body when carrying. However, the thickness of the optical system when retracted greatly varies depending on the lens type and filter used. In particular, a so-called positive-leading type zoom lens in which the lens unit closest to the object side has a positive refractive power is suitable for setting high specifications such as a zoom ratio and an F value, but the thickness and dead space of each lens element It is large and the thickness does not become so thin even when it is collapsed (Japanese Patent Laid-Open No. 11-258507). Negative lead type, especially 2-3
A zoom lens with a group configuration is advantageous in that respect, but the number of elements in the group is large, the element thickness is large,
Even if the lens closest to the object side is a positive lens, the lens does not become thin even when retracted (Japanese Patent Laid-Open No. 11-52246). Suitable for electronic image sensors, zoom ratio, angle of view, F
As an example of the one having good imaging performance including values and the possibility of making the collapsed thickness the thinnest, Japanese Patent Laid-Open No. 11-2879
No. 53, JP-A-2000-267090, JP-A-2000-
There are things such as 275520.

To make the first lens unit thin, it is preferable to make the entrance pupil position shallow, but for that purpose, the magnification of the second lens unit must be increased. On the other hand, this increases the load on the second lens unit, making it difficult to make itself thin, and it is also not preferable because the difficulty of aberration correction and the effect of manufacturing error increase. In order to realize thinning and miniaturization, it is sufficient to make the image pickup device small, but in order to make the number of pixels the same, it is necessary to make the pixel pitch small, and it is necessary to cover the lack of sensitivity with an optical system. The effect of diffraction is no different.

Further, in order to make the camera body with a small depth, so-called rear focus in which the lens movement at the time of focusing is not performed in the front group but in the rear group is effective in the layout of the drive system. For that purpose, it becomes necessary to select an optical system in which the variation in aberration when the rear focus is performed is small.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and an object thereof is to reduce the number of constituents, to make a mechanical layout such as a rear focus type small and easy to simplify, and to approach from infinity. Select a zoom method and zoom configuration that have stable high imaging performance up to the distance, and also consider the selection of filters and the total thickness of each group by thinning each lens element of the zoom lens. The goal is to make video cameras and digital cameras thinner.

[0007]

In order to achieve the above object, the zoom lens of the present invention comprises, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power. And a third lens unit having a positive refracting power, the zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity is performed by moving the second lens unit only to the object side, and the third lens unit. In a zoom lens that is moved by an amount different from that of the second lens group, the second lens group is arranged in order from the object side.
It is characterized in that it is composed of a cemented lens of a positive lens and a negative lens in this order and a single lens of positive refractive power, and satisfies the following conditional expression.

(1) -1.0 <(R ₂₄ + R ₂₅ ) /
(R ₂₄ −R ₂₅ ) <0.6 where R ₂₄ and R ₂₅ are the radii of curvature on the optical axis of the object-side surface and the image-side surface of the most image-side positive lens of the second lens group, respectively. is there. The radius of curvature is positive when the center of curvature is on the image side with respect to the surface, and is negative when the center of curvature is on the object side.

Hereinafter, the reason why the above structure is adopted and the operation thereof will be described.

The zoom lens of the present invention comprises, in order from the object side, a first group having a negative refracting power, a second group having a positive refracting power, and a third group having a positive refracting power. In the zoom lens in which zooming is performed by monotonously moving from the wide-angle end to the telephoto end toward the object side of the second lens unit and by an amount different from that of the second lens unit of the third lens unit when focusing on a point, , A cemented lens in which a positive lens and a negative lens are arranged in this order from the object side, and a positive single lens.

In a negative-positive two-group zoom lens that has been often used as a zoom lens for silver-salt film cameras for a long time, the magnification of the positive rear group (second group) at each focal length is increased in order to miniaturize it. It is better to add one positive lens to the image side of the second lens group as a third lens group, and to change the distance from the second lens group when zooming from the wide-angle end to the telephoto end. The method is well known. Also,
This third group has the possibility of being used for focusing. Then, in order to achieve the object of the present invention, that is, to suppress the fluctuation of off-axis aberrations including astigmatism when the total thickness of the lens portion is reduced when the lens barrel is retracted and the third lens group is focused. In addition, it is an indispensable requirement that the second lens group be composed of, in order from the object side, a cemented lens and a positive lens in order of a positive lens and a negative lens.

When focusing with the third lens group, aberration variation becomes a problem, but if an aspherical surface of an unnecessarily large amount enters the third lens group, it remains in the first and second lens groups in order to exert its effect. Astigmatism will be corrected by the third lens unit, and if the third lens unit moves for focusing, the balance will be lost, which is not desirable. Therefore, when focusing is performed by the third lens group, astigmatism must be almost completely removed by the first and second lens groups over the entire zoom range. Therefore, the third lens unit is composed of a spherical system or a small amount of aspherical surface, the aperture stop is arranged on the object side of the second lens unit, and the lens closest to the image side of the second lens unit is a positive lens. That is, it is preferable to configure the positive lens, the negative lens, and the positive lens in this order. Further, since the front lens diameter is unlikely to be large in this type, it is preferable that the aperture stop is integrated with the second group (in the embodiment of the invention described later, it is arranged immediately before the second group and integrated with the second group). Not only is it mechanically simple, but it is difficult for dead space to occur when the lens barrel is retracted.
The value difference is small. In addition, since the positive lens and the negative lens on the object side of the second lens group have remarkable aberrations due to their relative decentering, it is indispensable to cement them. further,
The following conditional expression should be satisfied for the positive lens closest to the image in the second lens group.

(1) −1.0 <(R ₂₄ + R ₂₅ ) /
(R ₂₄ −R ₂₅ ) <0.6 where R ₂₄ and R ₂₅ are the radiuses of curvature on the optical axis of the object-side surface and the image-side surface of the positive lens closest to the image in the second group, respectively. is there.

Although an aspherical surface is introduced on the air contact surface side of the positive lens (the cemented lens) on the object side of the second lens unit to correct spherical aberration and brighten the F value, the condition (1) is still satisfied. If the lower limit value of -1.0 is exceeded, spherical aberration tends to occur, and if the upper limit value of 0.6 is exceeded, astigmatism cannot be completely corrected even if an aspherical surface is introduced into the first group.

The following is more preferable.

(1 ')-0.7 <(R ₂₄ + R ₂₅ ) /
(R ₂₄ -R ₂₅₎ <0.34 In addition, more desirable if as follows.

(1 ") 0.025 <(R ₂₄ + R ₂₅ ) /
(R ₂₄ −R ₂₅ ) <0.34 Further, the aspherical lens for aberration correction has a first group (distortion aberration / astigmatism / coma aberration correction) and a second group (spherical aberration correction), respectively. It is recommended to make one sheet for each system and a total of two sheets. If you add more than that, the effect will be small and the cost will be high.

When zooming from the wide-angle end to the telephoto end, it is preferable that the third lens unit moves along a locus that is convex toward the image side in order to reduce fluctuations in off-axis aberrations.

For the system satisfying the condition (1), if the following condition is further satisfied, it is good for correction of spherical aberration.

(2) 5 <(R ₂₁ + R ₂₃ ) / (R ₂₁ −R ₂₃ ) <60 Here, R ₂₁ and R ₂₃ are the most object-side surface and the most image-side surface of the cemented lens of the second group, respectively. Is the radius of curvature of the surface of the optical axis.

When the upper limit of 60 of the condition (2) is exceeded, spherical aberration correction tends to be insufficient and the lens thickness tends to increase. Further, the workability of the object-side positive lens also deteriorates. When the lower limit of 5 is exceeded, conversely high-order spherical aberration occurs, and the workability of the deep concave surface on the negative lens side deteriorates.

The following is more preferable.

(2 ′) 7 <(R ₂₁ + R ₂₃ ) / (R ₂₁ −R ₂₃ ) <60 Further, the following is more preferable.

(2 ″) 8 <(R ₂₁ + R ₂₃ ) / (R ₂₁ −R ₂₃ ) <60 For a system satisfying the condition (1) or a system satisfying the condition (2), if the following condition is further satisfied: , The exit pupil position, that is, the shading is advantageous.

[0025] (3) 0.1 <f_{twenty three}  / F₃₀<1.2 (4) 0.01 <d_{twenty three}× R_{twenty three}/ T₂ ²<0.5 Where f_{twenty three}And f₃₀Is a positive lens on the image side of the second group
And the focal length of the third lens group, d _{twenty three}Is the image side of the cemented lens of the second group.
Between the surface and the object side surface of the positive lens, R_{twenty three}Is the junction of the second group
Radius of curvature of the image side of the lens on the optical axis, t₂Is of the second group
It is the distance from the surface closest to the object to the surface closest to the image.

When the upper limit of 1.2 in condition (3) is exceeded,
This is advantageous for the exit pupil position at the wide-angle end, that is, for shading, but the amount of change in the exit pupil position during zooming to the telephoto end is large, which is disadvantageous for shading at the telephoto end. If the lower limit of 0.1 is exceeded, the exit pupil at the wide-angle end will be too close to cause shading, and the amount of movement will be too large when focusing in the third lens group, which is a space disadvantage. There is. In addition, since it is necessary to strengthen the image-side positive lens of the second lens group, which has a paraxially high axial ray height, the position of the principal point of the second lens group moves backward, making it difficult to obtain a high magnification.
The first group tends to become huge. 0.01 as the lower limit of condition (4)
Beyond the range, there is a disadvantage in correction of astigmatism, and in addition, shading is likely to occur due to the position of the exit pupil at the wide-angle end. If the upper limit of 0.5 is exceeded, the thickness of the second group will be large,
It is a shackle to reduce the collapsed thickness.

The following is more preferable.

(3 ′) 0.15 <f ₂₃ / f ₃₀ <1.0 (4 ′) 0.05 <d ₂₃ × R ₂₃ / t ₂ ² <0.3 Further, if the following is performed, desirable.

(3 ″) 0.3 <f ₂₃ / f ₃₀ <0.8 (4 ″) 0.09 <d ₂₃ × R ₂₃ / t ₂ ² <0.2 Apart from this, condition (1) Alternatively, with respect to (2), if the following condition is further satisfied, it is advantageous for downsizing when retracted.

(5) 0.2 <R ₂₂ / f _ce <2 Here, R ₂₂ is the radius of curvature of the cemented surface of the cemented lens of the second group, and f _ce is the focal length of the cemented lens of the second group. .

When the lower limit of 0.2 to condition (5) is not reached, it is easy to reduce the thickness of the cemented lens of the second group, but it becomes difficult to correct axial chromatic aberration. If the upper limit value of 2 is exceeded, it is advantageous for correction of axial chromatic aberration, but the thickness of the cemented lens must be increased, which is a shackle for reducing the collapsed thickness.

The following is more preferable.

(5 ') 0.3 <R ₂₂ / f _ce <1.6 Further, the following is more desirable.

(5 ″) 0.4 <R ₂₂ / f _ce <1.2 For the system satisfying the above condition (1) or the system satisfying the condition (2) or the system satisfying the condition (5), If any one of the conditions or a plurality of the conditions are satisfied at the same time, it is advantageous for miniaturization at the time of collapsing.

(A) 0.0 <f ₂ / f ₂₃ <1.3 (b) 0.04 <t _2N / t ₂ <0.2 (c) 0.5 <t ₂ /L<1.2 Here, f ₂ is the combined focal length of the entire second group, and f ₂₃ is the second focal length.
The single focal length of the positive lens on the image side of the group, t _2N is the distance on the optical axis from the image side surface of the cemented object side positive lens of the second group to the image side surface of the negative lens of the second group. , T ₂ is the thickness on the optical axis from the most object side surface to the most image side surface of the second lens unit, L
Is the diagonal length of the effective image pickup area (substantially rectangular) of the image pickup device.

The condition (a) defines the ratio of the single focal length of the image-side positive lens of the second lens unit to the combined focal length of the entire second lens unit. If the upper limit of 1.3 is exceeded, the second lens unit will not have a high magnification because the principal point of the second lens unit will be closer to the image side, and the amount of movement of the first lens unit tends to increase or the size tends to increase. A dead space is likely to be formed in the rear of the second lens group, the overall length becomes long, and the lens barrel mechanical structure becomes complicated or becomes huge in order to reduce the collapsing thickness. Or it can't be too thin. When the lower limit of 0.0 is exceeded, it becomes difficult to correct astigmatism.

The condition (b) defines the distance t _2N on the optical axis from the image side surface of the cemented object side positive lens of the second group to the image side surface of the negative lens of the second group. is there. Astigmatism cannot be completely corrected unless this portion is made thick to some extent, but this is a shackle for the purpose of reducing the thickness of each element of the optical system. Therefore, the astigmatism is corrected by introducing an aspherical surface into any surface of the first group. Still,
When the lower limit of 0.04 is exceeded, astigmatism cannot be completely corrected. If the upper limit of 0.2 is exceeded, the thickness is unacceptable.

It is more preferable that each of (a), (b) and (c) be individually or simultaneously provided as follows.

(A ′) 0.5 <f ₂ / f ₂₃ <1.2 (b ′) 0.06 <t _2N / t ₂ <0.18 (c ′) 0.55 <t ₂ / L < 1.1 Furthermore, it is more desirable to individually or simultaneously perform each of (a), (b), and (c) as follows.

(A ″) 0.9 <f ₂ / f ₂₃ <1.1 (b ″) 0.08 <t _2N / t ₂ <0.16 (c ″) 0.6 <t ₂ / L < 1.0 By the way, when the zoom ratio is 2.3 times or more, if the following conditions are satisfied, it contributes to reduction in thickness.

(D) 1.2 <-β _2t <2.0 (e) 1.6 <f ₂ / f _W <3.0 where β _2t is the magnification (infinity) at the telephoto end of the second lens unit. Object point), f ₂ is the focal length of the second lens group, and f _W is the focal length of the wide-angle end (infinity object point) of the entire zoom lens system.

The condition (d) defines the magnification β _2t at the object point at infinity at the telephoto end of the second lens unit. As for this, when the absolute value is as large as possible, the entrance pupil position at the wide-angle end can be made shallow, and the diameter of the first group can be easily made small, and thus the thickness can be made small. If the lower limit of 1.2 is exceeded, it will be difficult to satisfy the thickness, and if the upper limit of 2.0 is exceeded, aberration correction (spherical aberration, coma, and astigmatism) will be difficult.

The condition (e) defines the focal length f ₂ of the second lens unit. A shorter focal length is more advantageous for reducing the thickness of the second lens group itself, but the first principal point of the second lens group is closer to the object side than the first focal point.
It is not easy to correct aberrations because it is difficult to arrange the power such that the rear principal point of the group is located on the image side. Lower limit of 1.6
When it exceeds, it becomes difficult to correct spherical aberration, coma aberration, astigmatism and the like. When the upper limit of 3.0 is exceeded, it becomes difficult to reduce the thickness.

It is more preferable to carry out the following steps (d) and (e) individually or simultaneously.

(D ′) 1.25 <−β _2t <1.9 (e ′) 1.8 <f ₂ / f _W <2.7 Furthermore, for (d) and (e), individually or simultaneously. It is more desirable to do the following.

(D ″) 1.3 <−β _2t <1.8 (e ″) 2.0 <f ₂ / f _W <2.5 As described above, thinning and aberration correction are contradictory. To do. Therefore, it is advisable to introduce an aspherical surface into the positive lens closest to the object in the second group. The effect of correcting spherical aberration and coma is great, and astigmatism and axial chromatic aberration can be advantageously corrected accordingly.

It has been described above that, when rear focus is performed by the third lens group, it is preferable that the off-axis aberration correction is substantially completed over the entire zoom range of the first lens group and the second lens group. By devising the selection of the configuration of the first group with respect to the configuration of the second group, it is possible to substantially complete off-axis aberration correction over the entire zoom range in the first group and the second group. The configuration of the first group at that time will be described below. One is, in order from the object side, a negative lens group including two or less negative lenses and a positive lens group including one single lens having a positive refractive power, and at least one of the negative lens groups. The negative lenses include an aspherical surface and satisfy the following conditions (f) and (g).

[0048] (F) -0.03 <f_W/ R₁₁<0.4 (G) 0.15 <d_NP/ F_W<1.0 Where R₁₁Is the first lens surface of the first group from the object side.
Radius of curvature on the optical axis, d _NP Is the air gap between the negative lens group and the positive lens group on the optical axis, f
_WIs the wide-angle end (infinity object point) focal length of the entire zoom lens system
Is.

The condition (f) defines the radius of curvature of the first surface when the configuration of the first group is the first type described above. It is preferable to introduce an aspherical surface into the first lens group to correct distortion and to correct astigmatism with the remaining spherical component. When the upper limit of 0.4 is exceeded, it becomes disadvantageous for the correction of astigmatism, and when the lower limit of -0.03 is exceeded, the distortion cannot be corrected even with an aspherical surface.

The condition (g) defines the air gap d _NP on the optical axis between the negative lens group and the positive lens group when the first group is of the first type described above. When the upper limit of 1.0 is exceeded, it is advantageous for correction of astigmatism, but the thickness of the first lens group increases, which is against the miniaturization. If the lower limit of 0.15 is exceeded, it will be difficult to correct astigmatism.

It is more preferable to carry out the following (f) and (g) individually or simultaneously.

(F ′) −0.02 <f _W / R ₁₁ <0.24 (g ′) 0.18 <d _NP / f _W <0.7 Further, for (f) and (g), respectively In addition to or at the same time, the following is more desirable.

(F ″) −0.01 <f _W / R ₁₁ <0.16 (g ″) 0.2 <d _NP / f _W <0.5 On the other hand, in the first group, from the object side, When it is composed of two negative meniscus lenses with a convex surface facing the object side and one positive lens, the aspheric surface has an air gap between the two negative meniscus lenses (the amount along the optical axis is d _NN ). It is advantageous to correct the distortion, astigmatism, and coma aberrations by introducing an aspherical surface into any of the surfaces facing to, and it is advantageous to satisfy the following conditions from the relationship of the principal point positions. .

(H) 0.4 <R ₁₂ / R ₁₃ <1.3 (i) 0.02 <d _NN / f _W <0.25 The condition (h) is that of the first negative meniscus lens from the object side. The ratio of the radius of curvature R ₁₂ on the optical axis of the lens surface on the image side to the radius of curvature R ₁₃ on the optical axis of the lens surface on the object side of the second negative meniscus lens is defined. If the lower limit of 0.4 is not reached, distortion tends to deteriorate, and d _NN must be increased due to lens interference. When the upper limit of 1.3 is exceeded, in addition to being disadvantageous in astigmatism correction, the second negative meniscus lens has a shape that is difficult to process.

Regarding the condition (i), it is preferable to make it as small as possible as long as the lens interference is allowed. However, if the upper limit of 0.25 is exceeded, d _NP will have to be forcibly made small, and astigmatism will be corrected. It will be difficult.

More preferably, (h) and (i) are individually or simultaneously performed as follows.

(H ′) 0.47 <R ₁₂ / R ₁₃ <1.0 (i ′) 0.02 <d _NN / f _W <0.2 Furthermore, (h) and (i) are individually Or at the same time, it is more desirable to do the following.

(H ″) 0.5 <R ₁₂ / R ₁₃ <0.8 (i ″) 0.02 <d _NN / f _W <0.17 Further, the first group is arranged in order from the object side to the object side. In the case of being composed of one negative meniscus lens with one convex surface facing the side and one positive lens, the following conditions may be satisfied for the first group.

(J) −5.0 <(R _1P1 + R _1P2 )
/ (R _1P1 −R _1P2 ) <− 1.3 (k) 1.7 <n _d1N <1.95 where R _1P1 and R _1P2 are the light on the object side and the image side of the positive lens of the first group, respectively. The radius of curvature on the axis, n _d1N, is the medium refractive index of the negative meniscus lens of the first group.

The condition (j) defines the shape factor of the first lens group positive lens. If the lower limit of −5.0 is exceeded, it will be disadvantageous in correction of astigmatism, and it will also be disadvantageous in that an extra distance from the second lens unit will be required to avoid mechanical interference during zooming. . If the upper limit of −1.3 is exceeded, the distortion correction tends to be disadvantageous.

The condition (k) defines the medium refractive index of the first group negative lens. When R ₁₁ has a strong negative curvature in order to secure the strong negative power of the first group with only one lens, even if an aspherical surface is introduced into this lens, the distortion cannot be sufficiently corrected. . Therefore, it is preferable to set the refractive index of the medium as high as possible. If the lower limit of 1.7 is exceeded, distortion tends to occur. The upper limit of 1.95 is set because there is no actual glass including chromatic aberration (Abbe number).

It is more preferable that (j) and (k) be individually or simultaneously performed as follows.

(J ')-5.0 <(R _1P1 + R _1P2 )
/ (R _1P1 −R _1P2 ) <− 1.7 (k ′) 1.74 <n _d1N <1.95 Further, for (j) and (k) individually or at the same time, further: desirable.

(J ") -5.0 <(R _1P1 + R _1P2 )
/ (R _1P1 −R _1P2 ) <− 2.0 (k ″) 1.75 <n _d1N <1.95 Second, the first lens group includes one aspherical surface in order from the object side. It is composed of a single lens having a refractive power, one negative single lens, and one positive single lens, and satisfies the following condition (l).

(L) −0.2 <f _W / f _{1 *} <0.3 where f _{1 *} is the focal length of the lens of weak refractive power including the aspherical surface of the first lens group, and f _W is the zoom lens It is the wide-angle end (infinity object point) focal length of the entire system.

The condition (1) defines the focal length f _{1 *} of the lens having a weak refractive power including the aspherical surface when the first group has the second type. When the upper limit of 0.3 is exceeded, the power of the negative lens in the first lens unit becomes too strong and distortion tends to be deteriorated, and the radius of curvature of the concave surface becomes too small, which makes machining difficult. When the lower limit value of -0.2 is exceeded, the aspherical surface is devoted to distortion correction, which is not preferable in terms of astigmatism correction.

It is more preferable to do the following.

(L ′) −0.15 <f _W / f _{1 *} <0.2 Further, the following is more desirable.

(L ″) −0.1 <f _W / f _{1 *} <0.1 For the third group, one positive single lens composed of substantially spherical surfaces on both sides is preferable. The following conditions should be met in terms of shape.

(M) -1 <(R ₃₁ + R ₃₂ ) / (R ₃₁ −R ₃₂ ) <1 where R ₃₁ and R ₃₂ are the radiuses of curvature of the positive lens of the third group on the object side and the image side, respectively. Is. When the upper limit of 1 of the condition (m) is exceeded, the variation of astigmatism due to rear focus becomes too large, and even if the astigmatism can be satisfactorily corrected at the infinite object point, the astigmatism cannot be corrected at the near object point. Point aberrations tend to get worse. When the value goes below the lower limit of -1, astigmatism fluctuation due to rear focus is small, but it becomes difficult to correct aberration for an infinite object point.

It is more preferable to do the following.

(M ′) −0.45 <(R ₃₁ + R ₃₂ ) /
(R ₃₁ −R ₃₂ ) <0.5 Furthermore, the following is more desirable.

(M ″) −0.25 <(R ₃₁ + R ₃₂ ) /
(R ₃₁ −R ₃₂ ) <0.5 By the way, while optimizing the aberration and paraxial amount,
In order to make the groups thin, it is preferable to balance the thickness relationships of the groups as follows.

(N) 0.5 <t ₂ / t ₁ <1.5 (o) 0.4 <t ₁ /L<1.3 where t ₁ is the lens surface of the first group closest to the object side. To the lens surface closest to the image side on the optical axis. t ₂ represents the thickness on the optical axis from the object side surface of the cemented lens of the second group to the image side surface of the positive lens closest to the image side. L is the diagonal length of the effective image pickup area (substantially rectangular) of the image pickup device.

The condition (n) defines the thickness ratio of each of the first and second groups. In order to correct off-axis aberrations, especially astigmatism, it is effective to increase the surface spacing in any of the groups, but this is not acceptable in reducing the thickness. Therefore, it is the second lens group that the off-axis aberration is less deteriorated due to the effect of the aspherical surface even if the surface distance between the lens groups is reduced. That is, the smaller the value of the condition (n), the better the balance. When the upper limit of 1.5 is exceeded, off-axis aberrations such as astigmatism cannot be sufficiently corrected when each group is made thin. If the lower limit of 0.5 is exceeded, the second lens group cannot be physically constructed, or the first lens group becomes thicker.

The condition (o) defines the total thickness of the first group. When the upper limit of 1.3 is exceeded, it tends to hinder the reduction in thickness, and when the lower limit of 0.4 is exceeded, the radius of curvature of each lens surface is unavoidable, and paraxial relations and various aberrations are inevitable. Correction becomes difficult.

The condition (n) is more preferably set as follows.

(N ') 0.6 <t ₂ / t ₁ <1.4 Furthermore, it is more desirable to do the following.

(N ″) 0.7 <t ₂ / t ₁ <1.3 A more appropriate range under the condition (o) needs to be changed depending on the value of L in order to secure a margin and mechanical space. .

(O ') 0.6 <t ₁ /L<1.3 where L · f _W <6.2 0.5 <t ₁ /L<1.2 where 6.2 <L・ F _W
When <9.2, 0.4 <t ₁ /L<1.1, where 9.2 <L · f _W
At this time, the means for improving the image forming performance while reducing the collapsible thickness of the zoom lens portion is provided. Next, the matter of thinning the filters will be mentioned. In an electronic image pickup device, an infrared absorption filter having a certain thickness is usually inserted closer to the object side than the image pickup element so that infrared light does not enter the image pickup surface. Consider replacing this with a thin coating. Naturally, it will be thinned by that amount, but there is a secondary effect. If a near-infrared sharp cut coat with a transmittance at 600 nm of 80% or more and a transmittance at 700 nm of 10% or less is introduced on the object side of the image sensor behind the zoom lens system, it will be more relative than the absorption type. In addition, the transmittance on the red side becomes high, and the magenta tendency on the blue-violet side, which is a defect of the CCD having the complementary color mosaic filter, is alleviated by the gain adjustment, and color reproduction comparable to that of the CCD having the primary color filter can be obtained. On the other hand, in the case of a complementary color filter, a CCD with a primary color filter is used because of its high transmitted light energy
Compared with the above, since the substantial sensitivity is high and the resolution is also advantageous, the advantage of using a small CCD is great. Also for the optical low-pass filter which is the other filter, it is preferable that the total thickness t _LPF thereof satisfies the following condition.

(P) 0.15 <t _LPF /a<0.45 [mm] where a is the horizontal pixel pitch (unit μ
m).

Although it is effective to make the optical low-pass filter thin in order to make the collapsible thickness thin, in general, the moire suppressing effect is reduced, which is not preferable. On the other hand, as the pixel pitch becomes smaller, the contrast of frequency components above the Nyquist limit is reduced due to the influence of diffraction of the imaging lens system, and the reduction of the moire suppression effect is allowed to some extent. For example, the azimuth angle when projected on the image plane is horizontal (=
It is known that when three types of filters each having a crystal axis in the directions of 0 °) and ± 45 ° are used in an overlapping manner in the optical axis direction, there is a considerable moire suppressing effect. In this case, the thinnest filter is the horizontal aμ
It is known that the angle is shifted by SQRT (1/2) * aμm in the directions of m and ± 45 °. Here, SQRT is a square root and means a square root. The filter thickness at this time is approximately [1 + 2 * SQRT (1/2)] * a / 5.88.
(Mm).

This is a specification in which the contrast is set to zero at a frequency just corresponding to the Nyquist limit. When the thickness is reduced by several percent to several tens of percent, the contrast of the frequency corresponding to the Nyquist limit is slightly generated, but it can be suppressed by the influence of the diffraction. It is preferable that the condition (p) is satisfied including filter specifications other than the above, for example, a case where two filters are stacked or one filter is used. When the upper limit of 0.45 is exceeded, the optical low-pass filter is too thick, which hinders the reduction in thickness. Lower limit of 0.15
If it exceeds, moire removal will be insufficient. However, the condition of a when this is carried out is 5 μm or less.

When a is 4 μm or less, it is more susceptible to the influence of diffraction, and therefore (p ′) 0.13 <t _LPF /a<0.42 [mm] may be set. Alternatively, the following may be performed.

(P ") 4 μm or more: 0.3 <t _LPF /a<0.4 [mm] (however, when three filters are stacked and a <5 μm) 0.2 <t _LPF / a <0.28 [mm] (However, when two filters are stacked and a <5 μm) 0.1 <t _LPF /a<0.16 [mm] (However, one filter and a <When 5 μm) 4 μm or less: 0.25 <t _LPF /a<0.37 [mm] (However, when three filters are stacked and a <4 μm) 0.16 <t _LPF / a <0 0.25 [mm] (However, when two filters are stacked and a <4 μm) 0.08 <t _LPF /a<0.14 [mm] (However, one filter and a <4 μm When using an image sensor with a small pixel pitch, the effect of diffraction effect due to narrowing down Therefore, the image quality is deteriorated.Therefore, a plurality of apertures having a fixed aperture size are provided, and one of them is used as the image surface side lens surface of the first group and the object side lens surface of the third group. An electronic image pickup device capable of adjusting the image plane illuminance by being inserted into any of the optical paths between them and being exchangeable with another one, and among the plurality of apertures, a part of the apertures is provided. It is advisable to adjust the light amount by providing a medium having different transmittances for 550 nm and less than 80%, or a (μm).
In case of adjusting the light quantity corresponding to the F value such that / F number <0.4, 550n in the opening.
It is preferable that the electronic image pickup device has media having different transmittances for m and less than 80%. For example, if the open value is outside the range of the above conditions, there is no medium or 5
It is preferable to use a dummy medium having a transmittance of 91% or more for 50 nm, and to adjust the light quantity with an ND filter rather than making the aperture stop diameter small enough to cause the influence of diffraction when it is within the range.

Further, the plurality of apertures are made to have diameters that are inversely proportional to the F value and made uniform, and optical low-pass filters having different frequency characteristics are inserted in the apertures instead of the ND filter. But it's okay.
Since the diffraction deterioration increases as the aperture is narrowed down, the frequency characteristic of the optical low pass filter is set higher as the aperture diameter becomes smaller.

[0087]

Embodiments 1 to 7 of the zoom lens of the present invention will be described below. 1 to 3 are lens cross-sectional views of Embodiments 1, 3, and 7 at the wide-angle end (a), the intermediate state (b), and the telephoto end (c) at the time of focusing on an object point at infinity, respectively.
The second, fourth, and sixth embodiments are similar to the first embodiment, and are not shown. 1 to 3, a first group is G1, a second group is G2, a third group is G3, an optical low-pass filter and a parallel flat plate group such as a cover glass of CCD which is an electronic image pickup device are F and CCD. The image plane is indicated by I, and the plane-parallel plate group F
Are fixedly arranged between the third group G3 and the image plane I.

As shown in FIG. 1, the zoom lens of Embodiment 1 has a negative refractive power first group G1, a positive refractive power second group G2,
It consists of a third lens unit G3 having a positive refractive power, and when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then flips to the object side and moves. Then, at the telephoto end, the position becomes substantially the same as the position at the wide-angle end, the second group G2 monotonically moves toward the object side, the distance between the first group G1 and the second group G2 becomes smaller, and the third group G3 becomes an image. Move slightly to the surface side.

The first group G1 of the first embodiment includes two negative meniscus lenses having a convex surface directed toward the object side and a positive meniscus lens having a convex surface directed toward the object side, and the second group G2 includes an aperture stop. It is composed of a cemented lens of a positive meniscus lens having a convex surface directed to the object side and a negative meniscus lens having a convex surface directed to the object side, and a biconvex lens, and the third group G3 is composed of one biconvex lens. The aspherical surfaces are used for the two surfaces, that is, the image-side surface of the negative meniscus lens on the object side of the first group G1 and the object-side surface of the cemented lens of the second group G2.

The zoom lens of the second embodiment is similar to the first embodiment in that the first lens group G1 having negative refractive power, the second lens group G2 having positive refractive power,
It consists of a third lens unit G3 having a positive refractive power, and when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then flips to the object side and moves. Then, at the telephoto end, the position is slightly closer to the image plane side than the wide-angle end, the second group G2 monotonously moves toward the object side, and the distance between the first group G1 and the second group G2 becomes small, and the third group G3. Moves slightly to the image side.

The lens configuration of each of the groups G1 to G3 is the same as that of the first embodiment, but the aspherical surface is the object side surface of the negative meniscus lens on the image side of the first group G1, and the cemented lens of the second group G2. It is used for two surfaces of the object side of the.

As shown in FIG. 2, the zoom lens of Example 3 includes a first group G1 having negative refractive power, a second group G2 having positive refractive power,
It consists of a third lens unit G3 having a positive refractive power, and when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then flips to the object side and moves. Then, at the telephoto end, the position is slightly closer to the image plane side than the wide-angle end, the second group G2 monotonously moves toward the object side, and the distance between the first group G1 and the second group G2 becomes small, and the third group G3. Moves slightly to the image side.

The first group G1 of the third embodiment comprises a negative meniscus lens having a convex surface directed toward the object side, a biconcave negative lens, and a positive meniscus lens having a convex surface directed toward the object side. The second group G2 is composed of , A stop, a cemented lens of a positive meniscus lens having a convex surface directed to the object side and a negative meniscus lens having a convex surface directed to the object side, and a biconvex lens,
The third group G3 is composed of one biconvex lens. The aspherical surface is the first
The object-side surface of the negative meniscus lens of the group G1, the second group G2
It is used for the two surfaces of the cemented lens in the object side.

The zoom lens of the fourth embodiment is similar to the first embodiment in that the first lens group G1 having negative refractive power, the second lens group G2 having positive refractive power,
It consists of a third lens unit G3 having a positive refractive power, and when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then flips to the object side and moves. Then, at the telephoto end, the position becomes substantially the same as the position at the wide-angle end, the second group G2 monotonically moves toward the object side, the distance between the first group G1 and the second group G2 becomes smaller, and the third group G3 becomes an image. Move slightly to the surface side.

The lens construction of each of the groups G1 to G3 is the same as that of the first embodiment, but the aspherical surface is the object side surface of the negative meniscus lens on the image side of the first group G1, and the cemented lens of the second group G2. It is used for two surfaces of the object side of the.

The zoom lenses of Examples 5 and 6 are the same as those of Example 1.
Similarly, the first lens group G1 having negative refractive power and the second lens group G1 having positive refractive power
2. It consists of the third lens group G3 having positive refractive power, and when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens group G1 once moves to the image plane side and then reverses to the object side. The second lens group G2 monotonously moves toward the object side at the telephoto end, and the second lens group G2 monotonously moves toward the object side, and the distance between the first lens group G1 and the second lens group G2 decreases, and The group G3 once moves to the image plane side and then slightly moves to the object side.

The lens construction of each of the groups G1 to G3 is the same as that of the first embodiment, but the aspherical surface is the object side surface of the negative meniscus lens on the image side of the first group G1, and the cemented lens of the second group G2. It is used for two surfaces of the object side of the.

As shown in FIG. 3, the zoom lens of the seventh embodiment has a negative refractive power first group G1, a positive refractive power second group G2,
It consists of a third lens unit G3 having a positive refractive power, and when zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens unit G1 once moves to the image side and then flips to the object side and moves. Then, at the telephoto end, the position is slightly closer to the image plane side than the wide-angle end, the second group G2 monotonously moves toward the object side, and the distance between the first group G1 and the second group G2 becomes small, and the third group G3. Moves once to the object side and then slightly to the image side.

The first group G1 in Example 7 is composed of a biconcave negative lens and a positive meniscus lens having a convex surface directed toward the object side. The second group G2 is provided with an aperture stop and an object side arranged thereafter. It is composed of a cemented lens of a positive meniscus lens having a convex surface facing it and a negative meniscus lens having a convex surface facing the object side, and a biconvex lens, and the third group G3 is composed of one biconvex lens. The aspherical surfaces are used for the two surfaces of the biconcave negative lens of the first group G1 on the image side and the cemented lens of the second group G2 on the object side.

Numerical data of each of the above-mentioned examples is shown below, but the symbols are not the above, f is the focal length of the entire system, F _NO is the F number, ω is the half angle of view, WE is the wide angle end, and ST is the middle. State, T
E is the telephoto end, r ₁ , r ₂ ... Is the radius of curvature of each lens surface, d
₁ , d ₂ ... Intervals between lens surfaces, n _d1 , n _d2 ..., Refractive index of d line of each lens, ν _d1 , ν _d2, ... Abbe number of each lens. The aspherical shape is represented by the following formula, where x is an optical axis with the traveling direction of light being positive and y is a direction orthogonal to the optical axis.

X = (y ² / r) / [1+ {1- (K +
1) (y / r) ² } ^1/2 ] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ +
A ₁₀ y ¹⁰ However, r is a paraxial radius of curvature, K is a conic coefficient, A ₄ , A ₆ ,
A ₈ and A ₁₀ are aspherical coefficients of the 4th, 6th, 8th and 10th orders, respectively.

Example 1 r ₁ = 7.022 d ₁ = 0.22 n _d1 = 1.74320 ν _d1 = 49.34 r ₂ = 1.616 (aspherical surface) d ₂ = 0.14 r ₃ = 2.913 d ₃ = 0.15 n _d2 = 1.77250 ν _d2 = 49.60 r ₄ = 1.304 d ₄ = 0.33 r ₅ = 1.814 d ₅ = 0.43 n _d3 = 1.84666 ν _d3 = 23.78 r ₆ = 4.242 d ₆ = D6 r ₇ = ∞ (aperture) d ₇ = 0.15 r ₈ = 0.926 ( _{aspherical) d 8 = 0.40 n d4 =} 1.80610 ν d4 = 40.92 r 9 = 5.825 d 9 = 0.15 n d5 = 1.84666 ν d5 = 23.78 r 10 = 0.830 d 10 = 0.31 r 11 = 4.641 d 11 = 0.28 n d6 = 1.72916 ν _d6 = 54.68 r ₁₂ = -2.815 d ₁₂ = D12 r ₁₃ = 3.532 d ₁₃ = 0.31 n _d7 = 1.69680 ν _d7 = 55.53 r ₁₄ = -32.824 d ₁₄ = D14 r ₁₅ = ∞ d ₁₅ = 0.27 n _d8 = 1.54771 ν _d8 = 62.84 r ₁₆ = ∞ d ₁₆ = 0.15 r ₁₇ = ∞ d ₁₇ = 0.15 n _d9 = 1.51633 ν _d9 = 64.14 r ₁₈ = ∞ d ₁₈ = 0.19 r ₁₉ = ∞ (image plane) aspherical coefficient second Surface K = 0.000 A ₄ = -4.00774 × 10 ^-2 A ₆ = -6.32914 × 10 ^-3 A ₈ = -8.21616 × 10 ^-3 A ₁₀ = 6.420 64 × 10 ^-4 8th surface K = 0 .000 A ₄ = -6.45705 × 10 ^-2 A ₆ = -1.92709 × 10 ^-2 A ₈ = -1.10326 × 10 ^-1 A ₁₀ = 0 Zoom data (∞) WE ST TE f (mm) 1.000 1.732 3.000 F _NO 2.50 3.30 4.51 Ω (°) 32.51 19.97 11.69 D6 3.03 1.43 0.34 D12 0.40 1.87 3.62 D14 0.88 0.56 0.34 Zoom data (close to) D6 3.03 1.43 0.34 D12 0.32 1.60 2.86 D14 0.96 0.84 1.09.

Example 2 r ₁ = 17.447 d ₁ = 0.19 n _d1 = 1.78590 ν _d1 = 44.20 r ₂ = 1.843 d ₂ = 0.11 r ₃ = 3.105 (aspherical surface) d ₃ = 0.24 n _d2 = 1.74320 ν _d2 = 49.34 r ₄ = 1.330 d ₄ = 0.28 r ₅ = 1.814 d ₅ = 0.51 n _d3 = 1.80518 ν _d3 = 25.42 r ₆ = 5.663 d ₆ = D6 r ₇ = ∞ (aperture) d ₇ = 0.15 r ₈ = 0.918 ( Aspherical surface) d ₈ = 0.40 n _d4 = 1.80610 ν _d4 = 40.92 r ₉ = 5.480 d ₉ = 0.15 n _d5 = 1.84666 ν _d5 = 23.78 r ₁₀ = 0.826 d ₁₀ = 0.22 r ₁₁ = 4.528 d ₁₁ = 0.27 n _d6 = 1.69350 ν _d6 = 53.21 r ₁₂ = -2.567 d ₁₂ = D12 r ₁₃ = 4.061 d ₁₃ = 0.35 n _d7 = 1.48749 ν _d7 = 70.23 r ₁₄ = -4.932 d ₁₄ = D14 r ₁₅ = ∞ d ₁₅ = 0.27 n _d8 = 1.54771 ν _d8 = 62.84 r ₁₆ = ∞ d ₁₆ = 0.15 r ₁₇ = ∞ d ₁₇ = 0.15 n _d9 = 1.51633 ν _d9 = 64.14 r ₁₈ = ∞ d ₁₈ = 0.19 r ₁₉ = ∞ (image plane) aspherical coefficient third Surface K = 0.000 A ₄ = 3.86501 × 10 ^-2 A ₆ = -3.71941 × 10 ^-3 A ₈ = 8.72 100 × 10 ^-3 A ₁₀ = 4.61 180 × 10 ^-5 8th surface K = 0 .000 A ₄ = -6.63342 x 10 ^-2 A ₆ = -5.508 21 x 10 ^-2 A ₈ = -4.32431 x 10 ^-2 A ₁₀ = 0 Zoom data (∞) WE ST TE f (mm) 1.000 1.732 3.000 F _NO 2.50 3.14 4.50 Ω (°) 33.08 20.12 11.73 D6 3.03 1.17 0.27 D12 0.38 1.38 3.35 D14 0.83 0.78 0.32 Zoom data (at close range) D6 3.03 1.17 0.27 D12 0.33 1.24 2.89 D14 0.87 0.91 0.78.

(Example 3) r ₁ = 14.219 (aspherical surface) d ₁ = 0.24 n _d1 = 1.74320 ν _d1 = 49.34 r ₂ = 6.139 d ₂ = 0.22 r ₃ = -26.932 d ₃ = 0.15 n _d2 = 1.77250 ν _d2 = 49.60 r ₄ = 1.259 d ₄ = 0.37 r ₅ = 1.956 d ₅ = 0.39 n _d3 = 1.84666 ν _d3 = 23.78 r ₆ = 5.308 d ₆ = D6 r ₇ = ∞ (aperture) d ₇ = 0.15 r ₈ = 0.963 _{(aspherical) d 8 = 0.42 n d4 =} 1.80610 ν d4 = 40.92 r 9 = 7.612 d 9 = 0.15 n d5 = 1.84666 ν d5 = 23.78 r 10 = 0.873 d 10 = 0.25 r 11 = 4.528 d 11 = 0.27 n d6 = 1.69680 ν _d6 = 55.53 r ₁₂ = -2.502 d ₁₂ = D12 r ₁₃ = 3.409 d ₁₃ = 0.30 n _d7 = 1.58913 ν _d7 = 61.14 r ₁₄ = -34.710 d ₁₄ = D14 r ₁₅ = ∞ d ₁₅ = 0.27 n _d8 = 1.54771 ν _d8 = 62.84 r ₁₆ = ∞ d ₁₆ = 0.15 r ₁₇ = ∞ d ₁₇ = 0.15 n _d9 = 1.51633 ν _d9 = 64.14 r ₁₈ = ∞ d ₁₈ = 0.19 r ₁₉ = ∞ (image plane) aspheric coefficient 1st surface K = 0.000 A ₄ = 2.93055 × 10 ^-2 A ₆ = -3.1977 ₈ × 10 ^-3 A ₈ = 2.11980 × 10 ^-3 A ₁₀ = -5.70 506 × 10 ^-5 8th surface K = 0.000 A ₄ = -6.255 64 × 10 ^-2 A ₆ = -2.68 400 × 10 ^-2 A ₈ = -6.508 20 × 10 ^-2 A ₁₀ = 0 Zoom data (∞) WE ST TE f (mm) 1.000 1.732 3.000 F _NO 2.51 3.29 4.50 ω (°) 32.55 20.08 11.71 D6 2.96 1.36 0.31 D12 0.40 1.81 3.54 D14 0.91 0.58 0.34 Zoom data (at close) D6 2.96 1.36 0.31 D12 0.35 1.65 3.05 D14 0.96 0.75 0.83.

Example 4 r ₁ = 8.732 d ₁ = 0.14 n _d1 = 1.79952 ν _d1 = 42.22 r ₂ = 1.591 d ₂ = 0.14 r ₃ = 2.927 (aspherical surface) d ₃ = 0.22 n _d2 = 1.80610 ν _d2 = 40.92 r ₄ = 1.218 d ₄ = 0.23 r ₅ = 1.615 d ₅ = 0.38 n _d3 = 1.84666 ν _d3 = 23.78 r ₆ = 4.774 d ₆ = D6 r ₇ = ∞ (aperture) d ₇ = 0.14 r ₈ = 0.932 ( Aspherical surface) d ₈ = 0.48 n _d4 = 1.80610 ν _d4 = 40.92 r ₉ = 7.556 d ₉ = 0.14 n _d5 = 1.84666 ν _d5 = 23.78 r ₁₀ = 0.824 d ₁₀ = 0.18 r ₁₁ = 3.445 d ₁₁ = 0.24 n _d6 = 1.72916 ν _d6 = 54.68 r ₁₂ = -2.680 d ₁₂ = D12 r ₁₃ = 5.006 d ₁₃ = 0.31 n _d7 = 1.58913 ν _d7 = 61.14 r ₁₄ = -7.258 d ₁₄ = D14 r ₁₅ = ∞ d ₁₅ = 0.25 n _d8 = 1.54771 ν _d8 = 62.84 r ₁₆ = ∞ d ₁₆ = 0.14 r ₁₇ = ∞ d ₁₇ = 0.14 n _d9 = 1.51633 ν _d9 = 64.14 r ₁₈ = ∞ d ₁₈ = 0.17 r ₁₉ = ∞ (image plane) aspheric coefficient third Surface K = 0.000 A ₄ = 3.85367 × 10 ^-2 A ₆ = 1.14007 × 10 ^-2 A ₈ = -6.888670 × 10 ^-4 A ₁₀ = 5.90038 × 10 ^-3 Eighth surface K = 0. 000 A ₄ = -6.72801 × 10 ^-2 A ₆ = -4.58387 × 10 ^-2 A ₈ = -7.41050 × 10 ^-2 A ₁₀ = -2.205 26 × 10 ^-18 Zoom data (∞) WE ST TE f (mm) 1.000 1.733 3.000 F _NO 2.50 3.31 4.50 ω (°) 30.79 18.50 10.79 D6 2.70 1.28 0.29 D12 0.42 1.76 3.27 D14 0.81 0.46 0.31 Zoom data (when close) D6 2.70 1.28 0.29 D12 0.36 1.56 2.72 D14 0.87 0.65 0.86.

(Example 5) r ₁ = 7.848 d ₁ = 0.17 n _d1 = 1.77250 ν _d1 = 49.60 r ₂ = 1.894 d ₂ = 0.08 r ₃ = 2.942 (aspherical surface) d ₃ = 0.22 n _d2 = 1.80610 ν _d2 = 40.74 r ₄ = 1.250 d ₄ = 0.34 r ₅ = 1.735 d ₅ = 0.35 n _d3 = 1.84666 ν _d3 = 23.78 r ₆ = 3.718 d ₆ = D6 r ₇ = ∞ (aperture) d ₇ = 0.14 r ₈ = 0.881 ( Aspherical surface) d ₈ = 0.39 n _d4 = 1.80610 ν _d4 = 40.74 r ₉ = 3.976 d ₉ = 0.14 n _d5 = 1.84666 ν _d5 = 23.78 r ₁₀ = 0.784 d ₁₀ = 0.14 r ₁₁ = 3.751 d ₁₁ = 0.27 n _d6 = 1.72916 ν _d6 = 54.68 r ₁₂ = -2.716 d ₁₂ = D12 r ₁₃ = 3.953 d ₁₃ = 0.32 n _d7 = 1.48749 ν _d7 = 70.23 r ₁₄ = -5.192 d ₁₄ = D14 r ₁₅ = ∞ d ₁₅ = 0.25 n _d8 = 1.54771 ν _d8 = 62.84 r ₁₆ = ∞ d ₁₆ = 0.14 r ₁₇ = ∞ d ₁₇ = 0.14 n _d9 = 1.51633 ν _d9 = 64.14 r ₁₈ = ∞ d ₁₈ = 0.17 r ₁₉ = ∞ (image plane) aspheric coefficient third Surface K = 0.000 A ₄ = 2.50462 × 10 ^-2 A ₆ = 1.63662 × 10 ^-2 A ₈ = -1.006286 × 10 ^-2 A ₁₀ = 6.52447 × 10 ^-3 8th surface K = 0. 000 A ₄ = -7.41926 × 10 ^-2 A ₆ = -3.23268 × 10 ^-2 A ₈ = -1.508 37 × 10 ^-1 A ₁₀ = 0 Zoom data (∞) WE ST TE f (mm) 1.000 1.733 3.000 F _NO 2.55 3.42 4.50 ω (°) 30.75 18.49 10.80 D6 2.96 1.49 0.28 D12 0.54 1.95 3.18 D14 0.70 0.26 0.31 Zoom data (close to) D6 2.96 1.49 0.28 D12 0.49 1.74 2.67 D14 0.76 0.47 0.82.

(Example 6) r ₁ = 9.732 d ₁ = 0.17 n _d1 = 1.77250 ν _d1 = 49.60 r ₂ = 1.974 d ₂ = 0.09 r ₃ = 2.976 (aspherical surface) d ₃ = 0.22 n _d2 = 1.80610 ν _d2 = 40.74 r ₄ = 1.250 d ₄ = 0.33 r ₅ = 1.747 d ₅ = 0.36 n _d3 = 1.84666 ν _d3 = 23.78 r ₆ = 3.910 d ₆ = D6 r ₇ = ∞ (aperture) d ₇ = 0.14 r ₈ = 0.878 ( Aspherical surface) d ₈ = 0.39 n _d4 = 1.80610 ν _d4 = 40.74 r ₉ = 4.472 d ₉ = 0.14 n _d5 = 1.84666 ν _d5 = 23.78 r ₁₀ = 0.784 d ₁₀ = 0.14 r ₁₁ = 4.127 d ₁₁ = 0.26 n _d6 = 1.72916 ν _d6 = 54.68 r ₁₂ = -2.569 d ₁₂ = D12 r ₁₃ = 4.461 d ₁₃ = 0.32 n _d7 = 1.48749 ν _d7 = 70.23 r ₁₄ = -4.461 d ₁₄ = D14 r ₁₅ = ∞ d ₁₅ = 0.25 n _d8 = 1.54771 ν _d8 = 62.84 r ₁₆ = ∞ d ₁₆ = 0.14 r ₁₇ = ∞ d ₁₇ = 0.14 n _d9 = 1.51633 ν _d9 = 64.14 r ₁₈ = ∞ d ₁₈ = 0.17 r ₁₉ = ∞ (image plane) aspheric coefficient third Surface K = 0.000 A ₄ = 2.92 391 × 10 ^-2 A ₆ = 5.50087 × 10 ^-3 A ₈ = 2.35202 × 10 ^-3 A ₁₀ = 1.37638 × 10 ^-3 8th surface K = 0. 000 A ₄ = -7.56772 × 10 ^-2 A ₆ = -5.169 16 × 10 ^-2 A ₈ = -1.05324 × 10 ^-1 A ₁₀ = 0 Zoom data (∞) WE ST TE f (mm) 1.000 1.733 3.000 F _NO 2.55 3.42 4.50 ω (°) 30.78 18.49 10.81 D6 2.94 1.48 0.25 D12 0.53 1.95 3.16 D14 0.72 0.25 0.31 Zoom data (when close) D6 2.94 1.48 0.25 D12 0.48 1.74 2.65 D14 0.77 0.46 0.82.

(Example 7) r ₁ = -220.166 d ₁ = 0.15 n _d1 = 1.77250 ν _d1 = 49.60 r ₂ = 1.244 (aspherical surface) d ₂ = 0.44 r ₃ = 2.559 d ₃ = 0.40 n _d2 = 1.84666 ν _d2 = 23.78 r ₄ = 6.846 d ₄ = D4 r ₅ = ∞ (aperture) d ₅ = 0.27 r ₆ = 0.889 (aspherical surface) d ₆ = 0.55 n _d3 = 1.80610 ν _d3 = 40.92 r ₇ = 4.149 d ₇ = 0.15 n _d4 = 1.84666 ν _d4 = 23.78 r ₈ = 0.719 d ₈ = 0.11 r ₉ = 2.170 d ₉ = 0.40 n _d5 = 1.77250 ν _d5 = 49.60 r ₁₀ = -8.691 d ₁₀ = D10 r ₁₁ = 2.917 d ₁₁ = 0.40 n _d6 = 1.48749 ν _d6 = 70.23 r ₁₂ = -3.604 d ₁₂ = D12 r ₁₃ = ∞ d ₁₃ = 0.18 n _d7 = 1.51633 ν _d7 = 64.14 r ₁₄ = ∞ d ₁₄ = 0.33 n _d8 = 1.54771 ν _d8 = 62.84 r ₁₅ = ∞ d ₁₅ = 0.18 r ₁₆ = ∞ d ₁₆ = 0.17 n _d9 = 1.51633 ν _d9 = 64.14 r ₁₇ = ∞ d ₁₇ = 0.27 r ₁₈ = ∞ (image surface) Aspherical coefficient second surface K = 0.000 A ₄ = -7.5590 × 10 ^-2 A ₆ = 1.8175 × 10 ^-2 A ₈ = -4.1479 × 10 ^-2 A ₁₀ = 0 6th surface K = 0.000 A ₄ = -7.6156 × 10 ^-2 A ₆ = 1.3955 × 10 ^-2 A ₈ = -2.3422 × 10 ^-1 A ₁₀ = 0 Zoom data (∞) WE ST TE f (mm) 1.000 1.923 2.851 F _NO 2.65 3.50 4.51 ω (°) 35.55 20.00 13.75 D4 2.98 0.93 0.33 D10 0.56 1.68 3.07 D12 0.20 0.30 0.22 Zoom data (when close) D4 2.98 0.93 0.33 D10 0.52 1.56 2.80 D12 0.24 0.42 0.48.

FIG. 4 is an aberration diagram of Example 1 in the case of focusing to infinity, and FIG. 5 is an aberration diagram in the case of focusing to a shooting distance of 10 cm by moving the third lens group G3. 6 to 11 are aberration diagrams of Examples 2 to 7 when focusing to infinity.
Shown in. In these aberration charts, (a) is the wide-angle end, (b) is the intermediate state, (c) is the telephoto end, "SA" is spherical aberration, "AS" is astigmatism, and "DT" is distortion. Aberration, "C
C "indicates lateral chromatic aberration. Also, in each aberration diagram," FI "
Y "indicates the image height.

Next, the values of the conditional expressions (1) to (5) and (a) to (p) in each of the above Examples 1 to 7 and L (m
The values of m) and a (μm) are shown below.

Example 1 2 3 4 5 6 7 (1) 0.24492 0.27629 0.28816 0.12488 0.16002 0.23271 -0.60048 (2) 18.28796 19.10338 20.29713 16.18615 17.17668 17.6776 9.44392 (3) 0.53146 0.51842 0.44472 0.41401 0.47203 0.47681 0.67688 (4) 0.1571 0.1296 0.1413 0.1060 0.0938 0.09348 0.0540 (5) 0.72519 0.71345 0.97105 1.07385 0.52802 0.60735 0.63366 (a) 1.01086 0.99296 1.01047 1.03140 1.00641 1.00032 1.02977 (b) 0.13080 0.14473 0.13513 0.13293 0.14680 0.14762 0.12723 1.c723 0.8364 0.75761 0.81068 0.82927 0.72 1.362 (d) 1.40568 1.35430 1.42694 1.46599 1.37508 1.36830 1.66044 (e) 2.4674 2.3824 2.3749 2.1680 2.2125 2.2086 2.3520 (f) 0.14242 0.05732 *** 0.11452 0.12742 0.10275 -0.0045 (g) 0.3309 0.2789 *** 0.2298 0.3442 0.3339 0.4421 (h) 0.55475 0.59356 *** 0.54356 0.64378 0.66331 *** (i) 0.14 0.11 *** 0.14 0.08 0.09 *** (j) *** *** *** *** *** *** -2.19 417 (k) *** *** *** *** *** *** 1.77250 (l) *** *** -0.06792 *** *** *** *** (m)- 0.80570 -0.09685 -0.82114 -0.18363 -0.13548 0.00000 -0.10531 (n) 0.89306 0.77586 0.79914 0.92584 0.80029 0.79008 1.22222 (o) 0.93783 0.97647 1.01445 0.89085 0.93318 0.94003 0.73040 (p) 0.36 0.36 0.36 0.36 0.36 0.36 0.3604 (a = 0.75) (a = 0.75) 0.75) (a = 0.75) (a = 0.75) (a = 0.75) (a = 0.75) (a = 0.92) Although a = 0.75 is set in each example, 0.4 <a <in each example. It can be used in the range of 1.0 [μm].

By the way, the zoom lens of the present invention as described above is a photographing device for forming an image of an object by the zoom lens and receiving the image by an image pickup device such as a CCD or a silver salt film for photographing, particularly a digital camera or a video camera. It can be used for a camera, a personal computer, a telephone, especially a mobile phone which is convenient to carry. Below, the case where it is used for a digital camera is illustrated.

12 to 14 are conceptual diagrams showing the construction in which the zoom lens according to the present invention is incorporated in the photographing optical system 41 of a digital camera. 12 is a front perspective view showing the appearance of the digital camera 40, FIG. 13 is a rear perspective view of the same, and FIG. 14 is a sectional view showing the configuration of the digital camera 40. In this example, the digital camera 40 includes a photographing optical system 41 having a photographing optical path 42, a finder optical system 43 having a finder optical path 44, a shutter 45, and a flash 4.
6. When the shutter 45, which includes the liquid crystal display monitor 47 and the like and is arranged above the camera 40, is pressed, the photographing is performed through the photographing optical system 41, for example, the zoom lens of the first embodiment in conjunction with the shutter 45. The object image formed by the photographing optical system 41 is formed on the image pickup surface of the CCD 49 through the filters F such as an optical low pass filter. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the rear surface of the camera via the processing means 51. Further, the recording means 52 is connected to the processing means 51, and the captured electronic image can be recorded. The recording means 52 is the processing means 5.
It may be provided separately from 1, or may be configured to record and write electronically by a floppy (registered trademark) disk, memory card, MO, or the like. Further, it may be configured as a silver salt camera in which a silver salt film is arranged instead of the CCD 49.

Further, a finder objective optical system 53 is arranged on the finder optical path 44. The object image formed by the finder objective optical system 53 is formed on the field frame 57 of the Porro prism 55 which is an image erecting member. Behind the poly prism 55, an eyepiece optical system 59 for guiding an erect image to the observer's eye E is arranged. A cover member 50 is arranged on each of the incident side of the photographing optical system 41 and the objective optical system 53 for the finder, and the exit side of the eyepiece optical system 59.

The digital camera 40 configured as described above
Since the photographic optical system 41 is a zoom lens having a wide angle of view, a high zoom ratio, good aberrations, a high brightness, and a large back focus in which filters and the like can be arranged, high performance and low cost can be realized.

In the example of FIG. 14, a plane parallel plate is arranged as the cover member 50, but a lens having power may be used.

The zoom lens of the present invention described above can be constructed, for example, as follows.

[1] In order from the object side, the first lens group having negative refracting power, the second lens group having positive refracting power, and the third lens group having positive refracting power, A zoom lens that performs zooming from a wide-angle end to a telephoto end during focusing by moving only the object side of the second lens unit and moving the third lens unit by a different amount from that of the second lens unit. The second lens group comprises, in order from the object side, a cemented lens of a positive lens and a negative lens in this order, and a single lens having a positive refractive power, and satisfies the following conditional expression.

(1) −1.0 <(R ₂₄ + R ₂₅ ) /
(R ₂₄ −R ₂₅ ) <0.6 where R ₂₄ and R ₂₅ are respectively on the optical axes of the object-side surface and the image-side surface of the single lens having the positive refractive power closest to the image side in the second lens group. Is the radius of curvature of.

[2] The zoom lens described in the item 1, which satisfies the following condition.

(2) 5 <(R ₂₁ + R ₂₃ ) / (R ₂₁ −R ₂₃ ) <60 where R ₂₁ and R ₂₃ are the object-side surface and the image-side surface of the cemented lens of the second lens group, respectively. Is the radius of curvature of the surface of the optical axis.

[3] The zoom lens described in 1 or 2 above, which satisfies the following condition.

(3) 0.1 <f ₂₃ / f ₃₀ <1.2 (4) 0.01 <d ₂₃ × R ₂₃ / t ₂ ² <0.5 where f ₂₃ and f ₃₀ are the second single lens and the focal length of the third lens group on the image side of the positive refractive power of the lens group, d ₂₃ the distance between the object side surface of the image side surface and a positive lens of the cemented lens in the second lens group, the R ₂₃ second lens The radius of curvature on the optical axis of the image side surface of the cemented lens of the group, t ₂ is the distance from the most object side surface to the most image side surface of the second lens group.

[4] The zoom lens described in any one of 1 to 3 above, which satisfies the following condition.

(5) 0.2 <R ₂₂ / f _ce <2 where R ₂₂ is the radius of curvature of the cemented surface of the cemented lens of the second lens group, and f _ce is the focal length of the cemented lens of the second lens group. is there.

[5] When zooming from the wide-angle end to the telephoto end,
5. The zoom lens according to any one of 1 to 4 above, wherein the third lens group moves along a locus that is convex toward the image side.

[6] The zoom lens described in any one of 1 to 5 above, wherein focusing is performed by moving the third lens group.

[7] The zoom lens described in any one of 1 to 6 above, which has a diaphragm that moves integrally with the second lens group.

[8] The zoom lens described in any one of the above items 1 to 7, wherein the lens surface closest to the object in the second lens unit is an aspherical surface.

[0130]

[9] The zoom lens described in any one of 1 to 8 above, which satisfies the following condition (1 ′) instead of the condition (1).

(1 ′) −0.7 <(R ₂₄ + R ₂₅ ) /
(R ₂₄ -R ₂₅₎ <0.34 [10] the first lens group aspherical has only one plane,
10. The zoom lens according to any one of 1 to 9 above, wherein the second lens group has only one aspherical surface, and the third lens group includes only spherical lenses.

[11] The zoom lens described in the above item 2, wherein the following condition (2 ′) is satisfied instead of the condition (2).

(2 ′) 7 <(R ₂₁ + R ₂₃ ) / (R ₂₁ −R ₂₃ ) <60 [12] In place of the condition (3), the following condition (3 ′) is satisfied. The zoom lens described in 3 above.

(3 ′) 0.15 <f ₂₃ / f ₃₀ <1.0 [13] The zoom according to the above 3, wherein the following condition (4 ′) is satisfied instead of the condition (4). lens.

(4 ′) 0.05 <d ₂₃ × R ₂₃ / t ₂ ² <0.3 [14] In place of the condition (5), the following condition (5 ′) is satisfied, 4. The zoom lens according to 4.

(5 ′) 0.3 <R ₂₂ / f _ce <1.6 [15] The zoom lens described in any one of 1 to 14 above, which satisfies the following condition (a): .

(A) 0.0 <f ₂ / f ₂₃ <1.3 where f ₂ is the combined focal length of the entire second lens group, and f ₂₃
Is a single focal length of a single lens having a positive refractive power on the image side of the second lens group.

[16] The zoom lens described in any one of 1 to 15 above, which satisfies the following condition (b):

(B) 0.04 <t _2N / t ₂ <0.2 where t _2N is the image of the negative lens of the second lens group from the image side surface of the object side positive lens of the cemented lens of the second lens group The distance on the optical axis to the side surface, t ₂ is the distance from the most object side surface to the most image side surface of the second lens group.

[17] The zoom lens described in any one of 1 to 16 above, which has a zoom ratio of 2.3 or more and satisfies the following conditions (d) and (e).

(D) 1.2 <-β _2t <2.0 (e) 1.6 <f ₂ / f _W <3.0 where β _2t is when the second lens group is focused on the object point at infinity. At the telephoto end, f ₂ is the focal length of the second lens group, and f _W
Is the focal length at the wide-angle end when focusing on an object point at infinity of the entire zoom lens system.

[18] The first lens group includes, in order from the object side, a negative lens group composed of two or less negative lenses and a positive lens group composed of one single lens having a positive refractive power, 18. The zoom lens or the imaging device according to any one of 1 to 17 above, wherein the negative lens group includes an aspherical surface.

[19] The zoom lens described in the item 18, wherein the first lens group satisfies the following conditions (f) and (g).

(F) −0.03 <f _W / R ₁₁ <0.4 (g) 0.15 <d _NP / f _W <1.0 However, R ₁₁ is 1 from the object side of the first lens group. The radius of curvature of the second lens surface on the optical axis, d _NP is the air space between the negative lens group and the positive lens group of the first lens on the optical axis, and f _W is the infinity object point focus of the entire zoom lens It is the focal length at the wide-angle end at the time.

[20] The first lens group comprises, in order from the object side, two negative meniscus lenses each having a convex surface facing the object side and one single lens having a positive refracting power. Any one of the above items 1 to 17, characterized in that one of the surfaces facing the air space of the lens is an aspherical surface.
The zoom lens described in the item.

[21] The zoom lens described in 20 above, wherein the first lens group satisfies the following conditions (h) and (i).

(H) 0.4 <R ₁₂ / R ₁₃ <1.3 (i) 0.02 <d _NN / f _W <0.25 where R ₁₂ is a negative meniscus on the object side of the first lens group. The radius of curvature on the optical axis of the lens surface on the image side of the lens, R ₁₃ is the radius of curvature on the optical axis of the lens surface on the object side of the second negative meniscus lens from the object side of the first lens group, d _NN Is the amount of air gap between the two negative meniscus lenses along the optical axis, f _W
Is the focal length at the wide-angle end when focusing on an object point at infinity of the entire zoom lens system.

[22] The first lens group comprises, in order from the object side, one negative meniscus lens having a convex surface facing the object side and one single lens having a positive refractive power, and the following condition (j) , (K) is satisfied, The zoom lens according to any one of 1 to 17 above.

(J) −5.0 <(R _1P1 + R _1P2 )
/ (R _1P1 −R _1P2 ) <− 1.3 (k) 1.7 <n _d1N <1.95 where R _1P1 and R _1P2 are the object side of the single lens of positive refractive power of the first lens group, respectively. The radius of curvature of the image-side lens surface on the optical axis, n _d1N, is the refractive index of the medium of the negative meniscus lens of the first lens group.

[23] The first lens group includes, in order from the object side, a single lens having a weak refractive power that satisfies the following condition (l), one negative single lens, and one positive single lens. 18. The zoom lens according to any one of 1 to 17 above, which comprises a lens.

(L) −0.2 <f _W / f _{1 *} <0.3 where f _{1 *} is the focal length of the single lens having a weak refractive power in the first lens group, and f _W is the zoom lens system as a whole. It is the focal length at the wide-angle end when focusing on an object point at infinity.

[24] The third lens group is composed of only a positive single lens having a shape satisfying the following condition (m):
24. The zoom lens according to any one of 1 to 23, wherein the positive single lens has spherical surfaces on both sides.

(M) −1 <(R ₃₁ + R ₃₂ ) / (R ₃₁ −R ₃₂ ) <1 where R ₃₁ and R ₃₂ are the object side and the image side of the positive single lens of the third lens group, respectively. It is the radius of curvature of the lens surface on the optical axis.

[25] An image pickup apparatus comprising the zoom lens described in any one of 1 to 24 above, and an image pickup element arranged on the image side thereof.

[26] The image pickup device described in 25 above, wherein the zoom lens satisfies the following condition (c).

(C) 0.5 <t ₂ /L<1.2 where t ₂ is the distance from the most object side surface to the most image side surface of the second lens group, and L is the effective image pickup of the image pickup device. The diagonal length of the area.

[27] The image pickup apparatus described in 25 or 26, wherein the zoom lens satisfies the following conditions (n) and (o).

(N) 0.5 <t ₂ / t ₁ <1.5 (o) 0.4 <t ₁ /L<1.3 where t ₁ is the lens surface of the first lens group closest to the object side. To the image-side lens surface on the optical axis, t ₂ is the optical axis from the object-side lens surface of the cemented lens of the second lens group to the image-side lens surface of the image-side positive lens Thickness of L
Is the diagonal length of the effective imaging area of the image sensor.

[0159]

According to the present invention, it is possible to obtain a zoom lens which has a thin collapsible thickness, is excellent in storability, has a high magnification, and is excellent in image forming performance even in rear focus. It becomes possible to reduce the thickness.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of a zoom lens according to a first exemplary embodiment of the present invention at a wide-angle end (a), an intermediate state (b), and a telephoto end (c).

FIG. 2 is a lens cross-sectional view similar to FIG. 1 of a zoom lens according to Example 3 of the present invention.

FIG. 3 is a lens cross-sectional view similar to FIG. 1 of a zoom lens according to Example 7 of the present invention.

FIG. 4 is an aberration diagram of a wide-angle end (a), an intermediate state (b), and a telephoto end (c) when focusing on infinity according to the first exemplary embodiment.

FIG. 5 is an aberration diagram at a wide-angle end (a), an intermediate state (b), and a telephoto end (c) when focusing is performed at a shooting distance of 10 cm according to the first exemplary embodiment.

6 is an aberration diagram similar to FIG. 4 of Example 2. FIG.

FIG. 7 is an aberration diagram similar to FIG. 4 of Example 3;

FIG. 8 is an aberration diagram similar to FIG. 4 of Example 4;

FIG. 9 is an aberration diagram similar to FIG. 4 of Example 5;

FIG. 10 is an aberration diagram similar to FIG. 4 of Example 6;

FIG. 11 is an aberration diagram similar to FIG. 4 of Example 7.

FIG. 12 is a front perspective view showing the external appearance of a digital camera incorporating the zoom lens according to the present invention.

13 is a rear perspective view of the digital camera shown in FIG.

14 is a cross-sectional view of the digital camera shown in FIG.

[Explanation of symbols]

G1 ... 1st group G2 ... Second group G3 ... Group 3 F: Parallel plane plate group I ... CCD image plane 40 ... Digital camera 41 ... Shooting optical system 42 ... Optical path for photography 43 ... Finder optical system 44 ... Optical path for finder 45 ... Shutter 46 ... Flash 47 ... LCD monitor 49 ... CCD 50 ... Cover member 51 ... Processing means 52 ... Recording means 53 ... Objective optical system for viewfinder 55 ... Porro prism 57 ... Field of view frame 59 ... Eyepiece optical system

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H087 KA02 KA03 PA05 PA06 PA18                       PB06 PB07 QA02 QA07 QA12                       QA21 QA22 QA25 QA33 QA41                       QA46 RA05 RA12 RA13 RA32                       RA42 RA43 SA14 SA16 SA19                       SA62 SA63 SA64 SB03 SB04                       SB14 SB22                 5C022 AA00 AB23 AB44 CA00

Claims (5)

[Claims] 1. An infinite object point combination comprising a first lens group having negative refracting power, a second lens group having positive refracting power, and a third lens group having positive refracting power in order from the object side. A zoom lens that performs zooming from the wide-angle end to the telephoto end during focusing by moving only the object side of the second lens unit and moving the third lens unit by a different amount from that of the second lens unit, A zoom lens characterized in that the second lens group comprises, in order from the object side, a cemented lens having a positive lens and a negative lens in that order and a single lens having a positive refractive power, and satisfies the following conditional expression. _{(1) -1.0 <(R 24} + R 25) / (R 24 -R 25)
<0.6 where R ₂₄ and R ₂₅ are the radii of curvature on the optical axis of the object-side surface and the image-side surface, respectively, of the single lens having the most image-side positive refractive power of the second lens group. 2. The zoom lens according to claim 1, wherein the following condition is satisfied. (2) 5 <(R ₂₁ + R ₂₃ ) / (R ₂₁ −R ₂₃ ) <60 where R ₂₁ and R ₂₃ are respectively the object-side surface and the image-side surface of the cemented lens of the second lens group. It is the radius of curvature on the optical axis. 3. The zoom lens according to claim 1, which satisfies the following condition. (3) 0.1 <f ₂₃ / f ₃₀ <1.2 (4) 0.01 <d ₂₃ × R ₂₃ / t ₂ ² <0.5 where f ₂₃ and f ₃₀ are respectively in the second lens group. single lens and the focal length of the third lens unit having a positive refractive power on the image side, d ₂₃ the distance between the object side surface of the image side surface and a positive lens of the cemented lens in the second lens group, R ₂₃ is bonded to the second lens group The radius of curvature of the image side surface of the lens on the optical axis, t ₂ is the distance from the most object side surface to the most image side surface of the second lens group. 4. The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditions. (5) 0.2 <R ₂₂ / f _ce <2 where R ₂₂ is the radius of curvature of the cemented surface of the cemented lens of the second lens group, and f _ce is the focal length of the cemented lens of the second lens group. 5. The zoom lens according to claim 1, wherein the third lens group moves along a locus convex toward the image side when zooming from the wide-angle end to the telephoto end.