JP4540387B2 - Zoom lens and imaging device - Google Patents

Description

  The present invention relates to a zoom lens and an imaging apparatus. For example, the present invention relates to a zoom lens suitable for an electronic imaging device such as a digital camera or a video camera.

In recent years, digital cameras have attracted attention as next-generation cameras that replace silver salt 35 mm film cameras. Furthermore, it comes to have a number of categories in a wide range from high-function type for business use to portable popular type. Especially in the category of portable popular types, a camera with a thin depth while securing a high image quality with a wide angle of view with a wide angle of view of about 60 ° with an F value of about 2.8 and a large zoom ratio is desired. ing.
The greatest problem in reducing the depth direction of the camera is the thickness from the most object side surface to the imaging surface of the optical system, particularly the zoom lens system. Recently, it has become the mainstream to adopt a so-called collapsible lens barrel that protrudes the optical system from the camera body during shooting and stores the optical system in the camera body when carried.
In order to reduce the thickness and size of the image sensor, it is only necessary to reduce the size of the image sensor. However, in order to obtain the same number of pixels, it is necessary to reduce the pixel pitch, and the lack of sensitivity must be covered by the optical system. There is also the effect of diffraction. Therefore, an optical system with a bright F value is required.
In order to obtain a camera body with a small depth, it is effective in terms of the drive system layout to move the lens at the time of focusing by the so-called rear focus method instead of the front group extension method. For this reason, it is necessary to select an optical system with less aberration fluctuation when the rear focus method is performed.
For example, Patent Documents 1 and 2 disclose a relatively compact negative-preceding three-group zoom lens having a bright F value, a zoom ratio as large as about 3 times, and a wide angle of view.
Patent Documents 2 and 3 disclose zoom lenses suitable for the rear focus method.
JP 2002-372667 A JP 2002-196240 A Japanese Patent Laid-Open No. 2003-222797

However, the conventional zoom lens as described above has the following problems.
In the techniques described in Patent Documents 1 and 2, off-axis aberrations are not completely removed by the first lens group and the second lens group, and a lens having a large aspheric amount is disposed in the third lens group. By doing so, it is configured to be removed. For this reason, when the third lens group is moved, aberration fluctuations increase, and there is a problem that it is difficult to obtain a stable and good imaging performance from an infinite object point to a short distance object point. Therefore, it is not suitable for the rear focus method.
In the techniques described in Patent Documents 2 and 3, the shortest lens total length at the wide-angle end or the telephoto end is large, and the second lens group movement amount during zooming is large, so the second lens group is driven. The lens barrel portion having the cam mechanism becomes longer. For this reason, it is conceivable that the total length of the lens becomes large even when the lens barrel is retracted, and there is a problem that it cannot be said to be sufficiently compact.

  The present invention has been made in view of the above-described problems, and is compact with a small number of constituent lenses, suitable for a rear focus system that is small and simple in terms of mechanism layout, and has stable connection from infinity to a short distance. An object of the present invention is to provide a zoom lens capable of obtaining image performance.

In order to solve the above problems, the zoom lens of the present invention has, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a positive refractive power. The first lens group includes, in order from the object side, a negative first lens and a positive second lens, and has at least one aspheric surface, and the second lens. The group includes, in order from the object side, a positive first lens, a positive second lens, and a negative third lens, and the positive second lens and the negative third lens are joined to each other, Constructed as a meniscus cemented lens having a convex surface, at least two surfaces excluding the cemented surface of the cemented lens have aspheric surfaces, and the third lens group is composed of a positive single lens consisting only of a spherical surface And zooms from the wide-angle end to the telephoto end when focusing on an object point at infinity. The first lens group moves along a convex locus toward the image side, the second lens group moves only toward the object side, and the third lens group moves and focuses in a different amount from the second lens group. Therefore, the following conditional expressions (1) and (2) are satisfied.
2.3 <L _t / f ₂ <3.7 (1)
1.15 <| f ₁ / f ₂ | <2.0 (2)
Where L _t is the distance from the lens surface closest to the object side to the imaging surface at the telephoto end of the zoom lens, f ₂ is the focal length of the second lens group, and f ₁ is the focal length of the first lens group. is there.

  According to the zoom lens and the imaging apparatus of the present invention, the zoom lens and the imaging device having a small number of lenses, suitable for a rear focus method that is compact and easy to simplify due to a mechanism layout, and that can provide stable imaging performance from infinity to a short distance. There exists an effect that an imaging device can be provided.

Prior to the description of each embodiment, the operation of the present invention will be described based on examples.
The zoom lens of the present invention employs a three-group configuration including a first lens group having negative refractive power from the object side, a second lens group having positive refractive power, and a third lens group having positive refractive power. Therefore, telecentricity is improved, and light can be efficiently incident on an image pickup device such as a CCD. Further, since the back focus can be long, a space for arranging members such as an optical low-pass filter and an infrared cut filter can be secured.

  At the time of zooming from the wide angle end to the telephoto end, the first lens unit moves along a locus convex to the image side, the second lens unit moves only to the object side, and the third lens unit moves to the second lens unit. Since they move by different amounts, the overall length can be made compact while keeping the exit pupil distance appropriate.

  The third lens group is movable and is used for focusing. In such a rear focus method using the third lens group, the moving lens group is lighter than the focus using the first lens group, so the load applied to the drive motor during movement is small, the total length is not increased, and the interior of the lens frame is not increased. Since the drive motor can be disposed in the lens frame, the lens frame has a feature that the radial direction of the lens frame does not increase, which is advantageous for downsizing in terms of layout.

When the third lens group is movable at the time of zooming, or when the third lens group is used for focusing, aberration variation becomes a problem. If an excessive amount of aspherical surface enters the third lens group, the astigmatism remaining in the first and second lens groups is corrected by the third lens group in order to obtain the effect. Here, if the third lens group is moved for focusing or the like, the balance of aberration correction is lost, which is not preferable.
In the zoom lens according to the present invention, since all the lens surfaces of the third lens group are configured as spherical surfaces instead of aspherical surfaces, the total thickness of the lens portion when retracted is reduced, and the third lens group Even when focusing, aberration fluctuations can be suppressed.

On the other hand, if the lens surface of the third lens group is formed of a spherical surface, a load is imposed on correction of astigmatism and the like. For this reason, it is desirable that the first and second lens groups substantially eliminate astigmatism over the entire zoom range. In order to suppress off-axis aberration fluctuations including astigmatism, the aberration correction capability of the second lens group is particularly important.
Therefore, in the zoom lens according to the present invention, the second lens group includes, in order from the object side, the positive first lens, the positive second lens, and the negative third lens, and the positive second lens and the negative third lens. The lenses are cemented together to form a meniscus cemented lens with a convex surface facing the object side, and at least two surfaces excluding the cemented surface of the cemented lens have aspheric surfaces.
According to such a configuration, it is possible to effectively correct astigmatism generated in the third lens group, and to improve the imaging performance. In particular, since aspheric surfaces are provided on at least two surfaces, aberration correction can be performed effectively.
In this case, since at least two aspheric surfaces are provided on the lens surface excluding the cemented surface of the cemented lens, the fabrication of the cemented lens is facilitated.
Further, it is preferable that at least two aspheric surfaces are provided on both surfaces of the positive first lens in the second lens group. In this way, great advantages can be obtained in terms of spherical aberration correction, relaxation of relative decentration sensitivity within the group, and manufacturing costs.

Further, according to such a configuration, the negative third lens in the second lens group is generated in the second lens group by canceling the spherical aberration and coma aberration generated in the positive second lens. The amount of aberration can be minimized. Further, by joining the negative third lens to a positive second lens having a lens surface that mainly serves to cancel spherical aberration and coma aberration, the occurrence of aberration due to relative decentration can be suppressed.
In this case, it is preferable to reduce the decentration sensitivity by canceling the aberration in the cemented lens. In this way, it is possible to reduce the relative decentering sensitivity of the second lens group with the positive first lens.
In such a lens configuration, when sufficient imaging performance is obtained by at least two aspheric surfaces, the second lens group is a positive first lens and a meniscus cemented lens with a convex surface facing the object side. Only a positive second lens and a negative third lens may be used. In this case, an inexpensive configuration with a small number of lenses can be obtained.

The zoom lens according to the present invention satisfies the conditional expression (1). Conditional expression (1) prescribes a condition that is suitable for downsizing in the range of L _t / f ₂ .
If L _t / f ₂ exceeds the upper limit of conditional expression (1), the total length becomes too long and it becomes difficult to make it compact. Further, when L _t / f ₂ becomes smaller than the lower limit, the power of the second lens group becomes weak, the zooming action of the second lens group becomes small, and the movement amount during zooming becomes large. For this reason, it is difficult to reduce the size.

Here, the lower limit value of conditional expression (1) is preferably 2.5, and more preferably 2.7. The upper limit is preferably 3.5, and more preferably 3.3.
For example, the following conditional expression (1a) is desirable, and the conditional expression (1b) is more desirable.
2.5 <L _t / f ₂ <3.5 (1a)
2.7 <L _t / f ₂ <3.3 (1b)

The zoom lens according to the present invention satisfies the conditional expression (2).
If | f ₁ / f ₂ | exceeds the upper limit of the conditional expression (2), the power of the second lens group becomes too strong, so that it becomes difficult to ensure telecentricity and shading at the corners of the screen becomes difficult. It tends to occur. If the lower limit is exceeded, the power of the second lens group becomes too weak, the zooming action of the second lens group becomes small, and the lens movement amount increases. Therefore, the entire lens system becomes large.

Here, the lower limit value of conditional expression (2) is preferably 1.2, and more preferably 1.25. The upper limit is preferably 1.75, more preferably 1.5.
For example, the following conditional expression (2a) is desirable, and conditional expression (2b) is more desirable.
1.2 <| f ₁ / f ₂ | <1.75 (2a)
1.25 <| f ₁ / f ₂ | <1.5 (2b)

In the zoom lens according to the present invention, it is preferable that a positive fourth lens is disposed on the image side of the cemented lens of the second lens group.
In this case, when the positive fourth lens is arranged, the positive power in the second lens group is dispersed, so that the relative eccentricity sensitivity in the second lens group can be further reduced. However, in terms of aberration correction, the fourth lens of the second lens group may be a powerless or negative lens.

In addition, when a positive fourth lens is provided in the second lens group, it is more preferable that the lens is a single lens having a convex surface on the image side.
In this case, by directing the convex surface toward the image side, it is possible to reduce performance degradation when the positive fourth lens of the second lens group is decentered. Further, when retracted, mechanical interference with a mechanical member disposed after the second lens group can be avoided, which is advantageous for thinning.

Further, when a positive fourth lens is provided in the second lens group, it is more preferable that the image-side surface is an aspherical surface.
In this case, it is effective for aberration correction. In particular, in order to correct astigmatism and distortion occurring in the first lens group, it is effective to arrange an aspherical surface on the surface where the principal ray height is higher after the stop.
As described above, it is not preferable to provide an aspheric surface on the lens surface of the third lens group in terms of rear focusing. Therefore, it is desirable to dispose an aspheric surface on the most image side surface of the second lens group.
The fourth lens in the second lens group may be a glass lens or a plastic lens. Moreover, it is good also as a compound aspherical lens which formed the aspherical resin on the glass spherical surface.

In the zoom lens according to the present invention, it is preferable that the cemented lens of the second lens group satisfies the following conditional expressions (5) and (6).
0.3 <R _23R / R _22F <1.0 (5)
−0.4 <f ₂ / R _23F <1.4 (6)
Where f ₂ is the focal length of the second lens group, R _22F is the radius of curvature near the optical axis of the object side surface of the positive second lens of the second lens group, and R _23R is the negative radius of the second lens group. A radius of curvature near the optical axis of the surface closest to the image side of the third lens, and R _23F is a radius of curvature near the optical axis of the cemented surface of the cemented lens of the second lens group.

Conditional expression (5) defines a preferable shape range of the cemented lens of the second lens group based on the value of R _23R / R _22F .
When R _23R / R _22F exceeds the upper limit of the conditional expression (5), correction of spherical aberration, coma aberration, and astigmatism within the group is insufficient, and the effect of reducing the decentration sensitivity by joining is reduced. Exceeding the lower limit is advantageous for correcting spherical aberration, coma and astigmatism within the group, and also has an effect of reducing decentration sensitivity. However, since the magnification of the second lens group is increased, it tends to hinder downsizing. .

Here, the lower limit of conditional expression (5) is preferably 0.4, more preferably 0.45. The upper limit is preferably 0.95, and more preferably 0.9.
For example, the following conditional expression (5a) is desirable, and conditional expression (5b) is more desirable.
0.4 <R _23R / R _22F <0.95 (5a)
0.45 <R _23R / R _22F <0.9 (5b)

Conditional expression (6) defines a preferable range of the shape of the cemented surface with respect to the focal length of the second lens group based on the value of f ₂ / R _23F .
If f ₂ / R _23F exceeds the upper limit of conditional expression (6), the longitudinal chromatic aberration and the lateral chromatic aberration are likely to be undercorrected. Exceeding the lower limit is not preferable because the thickness on the optical axis increases in order to secure the edge of the positive second lens in the cemented lens.

Here, the lower limit of conditional expression (6) is desirably 0.4, and more desirably 0.5. The upper limit is preferably 1.2, and more preferably 1.0.
For example, the following conditional expression (6a) is desirable, and conditional expression (6b) is more desirable.
0.4 <f ₂ / R _23F <1.2 (6a)
0.5 <f ₂ / R _23F <1.0 (6b)

In the zoom lens according to the present invention, it is preferable that the negative third lens in the second lens group satisfies the following conditional expression (7).
1.0 <| f ₂ / f ₂₃ | <3.0 (7)
However, f ₂ is the focal length, f ₂₃ of the second lens group is the focal length of the negative third lens in the second lens group.

Conditional expression (7) defines a range of a preferable ratio between the focal length of the negative third lens and the focal length of the second lens group based on the value of | f ₂ / f ₂₃ |. .
If | f ₂ / f ₂₃ | exceeds the upper limit of the conditional expression (7), the principal point of the second lens group is closer to the object side, so that the total length is shortened, but it is difficult to correct astigmatism. Become. If the lower limit is exceeded, the principal point of the second lens group is closer to the image side, and the magnification of the second lens group does not increase, so the amount of movement of the first lens group tends to be large or large. In addition, a dead space tends to occur behind the second lens group in the use state, and the entire length becomes long. As a result, the mechanical structure of the lens frame becomes complicated or enlarged. Alternatively, the entire length of the lens cannot be reduced when retracted.

Here, the lower limit value of conditional expression (7) is preferably 1.3, and more preferably 1.6. The upper limit is preferably 2.5, and more preferably 2.0.
For example, the following conditional expression (7a) is desirable, and conditional expression (7b) is more desirable.
1.3 <| f ₂ / f ₂₃ | <2.5 (7a)
1.6 <| f ₂ / f ₂₃ | <2.0 (7b)

In the zoom lens of the present invention, the first lens group includes, in order from the object side, a negative first lens and a positive second lens, and has at least one aspheric surface.
Since the two-lens configuration having at least one aspherical surface can be corrected satisfactorily, chromatic aberration and each off-axis aberration can be corrected well, and the zoom lens can be made thinner.

In the zoom lens according to the present invention, it is preferable to use a glass material having a refractive index of 1.75 or more for the d-line (wavelength 587.56 nm) for the negative first lens in the first lens group. By doing so, a good refractive power can be obtained without increasing the curvature, so that the occurrence of various off-axis aberrations can be minimized.
In the zoom lens according to the present invention, the negative first lens of the first lens group may include a concave surface having a stronger curvature than the object-side surface on the image side, and the image-side concave surface may be an aspherical surface. preferable. By doing so, it is possible to effectively correct distortion and field curvature that occur particularly at the wide-angle end. This lens may be an aspherical lens formed by glass molding, or a composite aspherical lens in which an aspherical resin is formed on a glass spherical surface.

  In the zoom lens of the present invention, it is preferable to use a glass material having a refractive index with respect to d-line of 1.85 or more for the positive second lens in the first lens group. For the same reason as the negative first lens, it is possible to minimize the occurrence of off-axis aberrations. In this case, it is more preferable to use a glass material having a refractive index with respect to d-line of 1.90 or more.

In the zoom lens of the present invention, it is preferable that the positive second lens in the first lens group satisfies the following condition (8).
−2.5 <(R ₁₃ + R ₁₄ ) / (R ₁₃ −R ₁₄ ) <− 0.4 (8)
Here, R ₁₃ is the radius of curvature of the object-side surface of the positive second lens of the first lens group, and R ₁₄ is the radius of curvature of the image-side surface of the positive second lens of the first lens group.

Conditional expression (8) defines a preferable shape of the positive second lens in the first lens group based on the value of (R ₁₃ + R ₁₄ ) / (R ₁₃ −R ₁₄ ).
If (R ₁₃ + R ₁₄ ) / (R ₁₃ −R ₁₄ ) exceeds the upper limit of conditional expression (8), correction of distortion aberration tends to be disadvantageous. Exceeding the lower limit tends to be disadvantageous in correcting astigmatism. In addition, in order to avoid mechanical interference at the time of zooming, an extra space with the second lens group is necessary, which is disadvantageous for downsizing.

Here, the lower limit of conditional expression (8) is preferably −2.4, more preferably −2.3. Further, the upper limit value is desirably −0.45, and more desirably −0.5.
For example, the following conditional expression (8a) is desirable, and conditional expression (8b) is more desirable.
−2.4 <(R ₁₃ + R ₁₄ ) / (R ₁₃ −R ₁₄ ) <− 0.45 (8a)
−2.3 <(R ₁₃ + R ₁₄ ) / (R ₁₃ −R ₁₄ ) <− 0.5 (8b)

In the zoom lens of the present invention, it is preferable that the positive second lens in the first lens group has aspheric surfaces on both sides.
In this case, it is more preferable that the object side surface has an aspherical shape in which positive refractive power is increased at the outer peripheral portion of the lens. In this way, the outer diameter of the negative first lens in the first lens group can be reduced, and distortion and astigmatism at the wide angle end can be effectively corrected. Further, for the same reason, it is more preferable that the surface on the image side has an aspheric shape in which the positive refractive power is increased at the outer peripheral portion of the lens.

In this case, it is preferable that the following conditional expression (9) is satisfied with respect to the aspherical shape.
0.01 <(A _sp12F −A _sp12R ) / f _W <0.05 (9)
However, A _sp12F and A _sp12R are effective diameters with respect to the spherical surface of the curvature radius (paraxial curvature radius) in the vicinity of the optical axis of the object-side and image-side aspheric surfaces of the positive second lens in the first lens group, respectively. aspheric biased amount of, f _W is the focal length of the zoom lens system in the wide-angle end.

Conditional expression (9) defines a preferable range of the aspheric shape by the value of (A _sp12F −A _sp12R ) / f _W.
When (A _sp12F −A _sp12R ) / f _W exceeds the upper limit of the conditional expression (9) and the aspheric amount becomes large, it is difficult to correct off-axis coma. If the lower limit is exceeded, the negative distortion will be insufficiently corrected, and off-axis field curvature and astigmatism cannot be corrected.

Here, the lower limit value of conditional expression (9) is preferably 0.015, more preferably 0.02. The upper limit is preferably 0.04, more preferably 0.03.
For example, the following conditional expression (9a) is desirable, and conditional expression (9b) is more desirable.
0.015 <(A _sp12F −A _sp12R ) / f _W <0.04 (9a)
0.02 <(A _sp12F −A _sp12R ) / f _W <0.03 (9b)

In the zoom lens of the present invention, it is preferable that the third lens group moves along a locus convex toward the image side when zooming from the wide-angle end to the telephoto end.
In this case, it becomes easy to secure an adjustment margin especially at the telephoto end where the variation in the focus position due to the quality error is large.

In the zoom lens of the present invention, the third lens group is composed of one positive lens.
With such a configuration, a practical aberration level can be corrected, and the number of lenses can be reduced to contribute to a reduction in the thickness of the zoom lens.

In the zoom lens according to the present invention, it is preferable that the third lens group satisfies the following conditional expression (3).
0.29 <f _W / f ₃ <0.6 (3)
Here, f _W is the focal length of the entire zoom lens system at the wide angle end, and f ₃ is the focal length of the third lens group.

Conditional expression (3) defines a preferable range of the refractive power of the third lens group based on the range of the value of f _W / f ₃ .
When f _W / f ₃ exceeds the upper limit of conditional expression (3) and the refractive power of the third lens group becomes strong, coma aberration and field curvature generated in the third lens group increase, and rear focusing is performed. Becomes difficult. When the refractive power of the third lens unit becomes weaker beyond the lower limit, the back focus increases or the amount of movement of the third lens unit during focusing becomes large, which makes it difficult to make the system compact. Conditional expression (3) is particularly useful when the lens surface of the third lens group is a spherical surface.

Here, the lower limit value of conditional expression (3) is desirably 0.3, and more desirably 0.31. The upper limit is preferably 0.5, and more preferably 0.45.
For example, the following conditional expression (3a) is desirable, and conditional expression (3b) is more desirable.
0.3 <f _W / f ₃ <0.5 (3a)
0.31 <f _W / f ₃ <0.45 (3b)

In the zoom lens according to the present invention, the position where the aperture stop is disposed is preferably disposed between the first lens group and the second lens group.
In this case, since the entrance pupil position can be made shallow, the diameter of the front lens can be made small, and as a result, the lens thickness on the optical axis can be made thin, which can contribute to downsizing in the thickness direction.
Further, since the exit pupil position can be set far from the imaging position, for example, the angle of the light beam emitted to the image sensor such as a CCD can be reduced, and the occurrence of shading at the edge of the screen can be prevented.
The aperture stop preferably moves integrally with the second lens group at the time of zooming.
In this case, there is an advantage that not only the mechanism is simple but also a dead space at the time of retraction is not easily generated, and the difference in F value between the wide-angle end and the telephoto end is reduced.

The image pickup apparatus of the present invention has a configuration in which the zoom lens of the present invention and an image sensor are arranged at the image forming position of the zoom lens.
According to the present invention, an image of a subject can be formed on the image sensor using the zoom lens of the present invention, so that the image pickup apparatus has the same effects as the zoom lens of the present invention.

  It should be noted that a more favorable zoom lens and electronic imaging apparatus can be configured by appropriately combining the above conditional expressions and configurations. In each conditional expression, only the upper limit value or only the lower limit value may be limited by the corresponding upper limit value and lower limit value of the more preferable conditional expression. Moreover, it is good also considering the corresponding value of the conditional expression as described in each below-mentioned Example as an upper limit or a lower limit.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[First Embodiment]
A zoom lens according to the first embodiment of the present invention will be described.
FIGS. 1A, 1B, and 1C show the wide-angle end, the intermediate state, and the telephoto, respectively, at the time of focusing on an object point at infinity of the zoom lens of the first example according to the first embodiment of the present invention. It is lens sectional drawing at an end. In this figure, the symbol I indicates the image plane. These detailed numerical examples will be described later as Example 1.

  As shown in FIG. 1A, the schematic configuration of the zoom lens 100 of the first example of the present embodiment includes a first lens group G1, a second lens group G2, a third lens group G3, and a parallel plate group F. Are arranged in this order from the object side.

The first lens group G1 is composed of, in order from the object side, a negative lens L1 (negative first lens) and a positive lens L2 (positive second lens), thereby forming a lens group having negative refractive power. The
The negative lens L1 includes a concave surface having a stronger curvature than the object-side surface on the image side, and the image-side concave surface is an aspherical lens. And it consists of a glass material whose refractive index with respect to d line | wire is 1.75 or more.
The positive lens L2 is a positive meniscus lens having a convex surface facing the object side .
In the following description, unless there is a possibility of misunderstanding, the negative lens L1, the positive lens L2, and the like are collectively referred to as the lenses L1, L2, etc., omitting the positive and negative signs.

The second lens group G2, in order from the object side, a positive lens L3 (positive first lens) and a cemented lens L4, it from the positive lens L7 (a fourth positive lens), the positive refractive power these A lens group. An aperture stop S that moves integrally with the second lens group G2 at the time of zooming is provided on the object side of the second lens group G2.
The positive lens L3 is composed of a biconvex lens having aspheric surfaces on both sides.
The cemented lens L4, in order from the object side, is a positive lens L5 (positive second lens) composed of a positive meniscus lens having a convex surface facing the object side, and a negative lens L6 (negative) when composed of a negative meniscus lens having a convex surface directed to the object side. 3rd lens). Each of the positive lens L5 and the negative lens L6 has a spherical surface.
The positive lens L7 includes a single lens having a convex surface facing the image side, and has an aspheric surface on the convex surface on the image side.

  The third lens group G3 is composed of a positive lens L8 (positive single lens) composed of a biconvex single lens having only spherical surfaces on both sides.

The parallel plate group F can have an appropriate characteristic depending on the characteristics of the image sensor or the like arranged on the image plane I. In this embodiment, the optical low-pass filter F1 and the cover glass GL are sequentially arranged from the object side. And fixedly arranged between the last lens group and the image plane I.
As the optical low-pass filter F1, a birefringent low-pass filter made of a crystal plate whose crystal axis direction is adjusted, a phase-type low-pass filter that realizes an optical cutoff frequency characteristic using a diffraction effect, and the like are preferably used. can do.
The cover glass GL is a cover glass when an image pickup device such as a CCD is arranged.
In addition, for example, an infrared light cut filter in which vapor deposition for blocking infrared light is performed on a parallel plate may be provided.
In some cases, some or all of these may be omitted.

  As shown in FIGS. 1A, 1B, and 1C, when the zoom lens 100 is zoomed from the wide-angle end to the telephoto end at the time of focusing on an object point at infinity, the first lens group G1 emits light. The second lens group G2 moves along the optical axis along the axis, the second lens group G2 moves together with the aperture stop S along the optical axis only to the object side, and the third lens group G3 moves along the optical axis. The convex locus is moved to the image side by an amount different from that of the second lens group G2. The third lens group G3 is movable for focusing.

Next, a zoom lens according to Example 2 of the present embodiment will be described.
FIGS. 2A, 2B, and 2C are respectively a wide angle end, an intermediate state, and a telephoto when the zoom lens of the second example according to the first embodiment of the present invention is focused on an object point at infinity. It is lens sectional drawing at an end. In this figure, the symbol I indicates the image plane. These detailed numerical examples will be described later as Example 2.

  As shown in FIG. 2A, the schematic configuration of the zoom lens 101 of the second example is the same type in which the positive and negative refractive powers correspond to the lenses L1 to L8 of the first example of the above embodiment. The lenses L10 to L17 having the following lens shape are provided. The aperture stop S and the parallel plate group F are the same as those in the first embodiment.

  As shown in FIGS. 2A, 2B, and 2C, when the zoom lens 101 is zoomed from the wide-angle end to the telephoto end at the time of focusing on an object point at infinity, the first lens group G1 emits light. The second lens group G2 moves along the optical axis along the axis, the second lens group G2 moves together with the aperture stop S along the optical axis only to the object side, and the third lens group G3 moves along the optical axis. It moves to the image plane side by an amount different from that of the second lens group G2. The third lens group G3 is movable for focusing.

Next, a zoom lens according to Example 3 of the present embodiment will be described.
FIGS. 3A, 3B, and 3C show the wide-angle end, the intermediate state, and the telephoto, respectively, at the time of focusing on an object point at infinity of the zoom lens of the third example according to the first embodiment of the present invention. It is lens sectional drawing at an end. In this figure, the symbol I indicates the image plane. These detailed numerical examples will be described later as Example 3.

As shown in FIG. 3A, the schematic configuration of the zoom lens 102 of the third example is such that the refractive power is positive or negative corresponding to the lenses L1, L3 to 6, and L8 of the first example of the above embodiment. Lenses L20, L22 to 25, and L27 having the same lens shape of the same type are provided.
Further, provided in place of the positive lens L 2 of the first embodiment, the positive lens L21 (second positive lens), also in place of the positive lens L7, a positive lens 26 (fourth positive lens).
The positive lens L21 is composed of a single lens having positive refractive power by having aspheric surfaces on both sides. And it consists of a glass material whose refractive index with respect to d line is smaller than 1.85.
The positive lens 26 is a single lens having a convex surface on the image side, and has an aspherical surface on the image side surface.
The aperture stop S and the parallel plate group F are the same as those in the first embodiment.

  As shown in FIGS. 3A, 3B, and 3C, when the zoom lens 102 is zoomed from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens group G1 emits light. The second lens group G2 moves along the optical axis along the axis, the second lens group G2 moves together with the aperture stop S along the optical axis only to the object side, and the third lens group G3 moves along the optical axis. It moves by an amount different from that of the second lens group G2. The third lens group G3 is movable for focusing.

Next, a zoom lens according to Example 4 of the present embodiment will be described.
FIGS. 4A, 4B, and 4C show the wide-angle end, the intermediate state, and the telephoto, respectively, when the zoom lens of Example 4 according to the first embodiment of the present invention is focused on an object point at infinity. It is lens sectional drawing at an end. In this figure, the symbol I indicates the image plane. These detailed numerical examples will be described later as Example 4.

As shown in FIG. 4A, the schematic configuration of the zoom lens 103 of the fourth example corresponds to the positive and negative refractive powers corresponding to the lenses L1 to L6 and L8 of the first example of the above embodiment. Lenses L30 to L35 and L37 having the same type of lens shape are provided.
Further, a positive lens 36 (positive fourth lens) is provided instead of the positive lens L7 of the first embodiment.
The positive lens 36 is a single lens having a convex surface on the image side, and has a spherical surface on both surfaces.
The aperture stop S and the parallel plate group F are the same as those in the first embodiment.

  As shown in FIGS. 4A, 4B, and 4C, when the zoom lens 103 zooms from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens group G1 emits light. The second lens group G2 moves along the optical axis along the axis, the second lens group G2 moves together with the aperture stop S along the optical axis only to the object side, and the third lens group G3 moves along the optical axis. It moves by an amount different from that of the second lens group G2. The third lens group G3 is movable for focusing.

Next, a zoom lens according to a reference example of this embodiment will be described.
FIGS. 5A, 5B, and 5C are a wide angle end, an intermediate state, and a telephoto end, respectively, when focusing on an object point at infinity of the zoom lens of the reference example according to the first embodiment of the present invention. FIG. In this figure, the symbol I indicates the image plane. These detailed numerical examples will be described later as reference examples .

As shown in FIG. 5A, the schematic configuration of the zoom lens 104 of the reference example is the same type in which the positive and negative refractive powers correspond to the lenses L1 to L3 and L8 of the first example of the above embodiment. Lens L40-42, L46 which has the following lens shape.
The second lens group G2 includes, in order from the object side, a positive lens L42 (positive first lens) and a cemented lens L43, and is a lens group having positive refractive power. An aperture stop S that moves integrally with the second lens group G2 at the time of zooming is provided on the object side of the second lens group G2.
The cemented lens L43 includes, in order from the object side, a positive lens L44 (positive second lens) made up of a biconvex lens, and a negative lens L45 (negative third lens) made up of a biconcave lens. Each of the positive lens L43 and the negative lens L45 has a spherical surface.
The reference example is an example in which the second lens group does not have a positive fourth lens.
The aperture stop S and the parallel plate group F are the same as those in the first embodiment.

  As shown in FIGS. 5A, 5B, and 5C, when the zoom lens 104 is zoomed from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens group G1 emits light. The second lens group G2 moves along the optical axis along the axis, the second lens group G2 moves together with the aperture stop S along the optical axis only to the object side, and the third lens group G3 moves along the optical axis. A convex locus is moved to the image side along the optical axis by an amount different from that of the second lens group G2. The third lens group G3 is movable for focusing.

  The in-group configuration of the lens described above is an example, and the arrangement of the aspherical surface and the in-group configuration may be changed as long as the positive and negative power of each lens group can be obtained. For example, in the first lens group, the image side surface is an aspherical surface. However, at least one aspheric surface may be an object side surface. In the second lens group, the description has been given on the assumption that both surfaces of the positive first lens are aspherical surfaces. However, at least two aspherical surfaces may be other than the cemented surface of the cemented lens, and the most object of the cemented lens. The surface on the side or the most image side may be an aspherical surface.

  In the first embodiment, it is desirable that the above conditional expressions are appropriately combined to satisfy the configuration.

The configuration parameters of the optical system of the first numerical example corresponding to the zoom lens of the first embodiment are shown below. In the following, in addition to the symbols described above, the following symbols are used (common to each embodiment).
f is the total focal length, FNO is the F number, W is the wide angle end, S is the intermediate state, and T is the telephoto end. r ₁ , r ₂ ,... are the radii of curvature of the lens surfaces, and d ₁ , d ₂ ,... are the intervals between the lens surfaces, and correspond to the reference numerals in FIG. In addition, n _d1 , n _d2 ,... _Are the refractive indexes of each lens at the d-line, and ν _d1 , ν _d2,. These notations are common to all the following reference drawings.
The aspherical shape is represented by the following equation (a) when the optical axis direction is z and the direction orthogonal to the optical axis is y.
z = (y ² / r) / [1 + √ {1- (1 + K) · (y / r) ² }]
+ A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ (a)
Here, r is a paraxial radius of curvature, K is a conical coefficient, and A ₄ , A ₆ , A ₈ , and A ₁₀ are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively.

Surface number Curvature radius Surface spacing Refractive index Abbe number
1 r ₁ = ∞ d ₁ = 1.50 n _d1 = 1.77377 ν _d1 = 47.17
2 r ₂ = 7.265 (aspheric surface) d ₂ = 2.63
3 r ₃ = 12.816 d ₃ = 2.20 n _d2 = 1.80518 ν _d2 = 25.42
4 r ₄ = 39.500 d ₄ = (variable)
S ∞ (aperture) d ₅ = 0.80
5 r ₅ = 14.805 (aspherical surface) d ₆ = 1.82 n _d3 = 1.74330 ν _d3 = 49.33
6 r ₆ = -42.582 (aspherical surface) d ₇ = 0.08
7 r ₇ = 5.519 d ₈ = 2.52 n _d4 = 1.51633 ν _d4 = 64.14
8 r ₈ = 16.682 d ₉ = 0.65 n _d5 = 1.80518 ν _d5 = 25.42
9 r ₉ = 4.631 d ₁₀ = 1.25
10 r ₁₀ = 1148.788 d ₁₁ = 1.38 n _d6 = 1.51633 ν _d6 = 64.14
11 r ₁₁ = -31.519 (aspheric surface) d ₁₂ = (variable)
12 r ₁₂ = 42.164 d ₁₃ = 2.01 n _d7 = 1.74400 ν _d7 = 44.78
13 r ₁₃ = -33.209 d ₁₄ = (variable)
14 r ₁₄ = ∞ d ₁₅ = 0.95 n _d8 = 1.54771 ν _d8 = 62.84
15 r ₁₅ = ∞ d ₁₆ = 0.55
16 r ₁₆ = ∞ d ₁₇ = 0.50 n _d9 = 1.51633 ν _d9 = 64.14
17 r ₁₇ = ∞ d ₁₈ = (variable)
I ∞ (image plane)
[Aspheric coefficient]
Surface number K A ₄ A ₆ A ₈ A ₁₀
2 -0.694 3.79934x10 ^-6 3.02207x10 ^-12 4.80234x10 ^-12 -4.18324x10 ^-11
5 7.272 -5.06557x10 ^-4 -1.23961x10 ^-5 -1.87104x10 ^-9 -1.87517x10 ^-8
6 -43.291 -2.56756x10 ^-4 -4.98807x10 ^-6 7.55902x10 ^-8 -8.45234x10 ^-9
11 0.000 1.68492x10 ^-4 -2.27448x10 ^-6 1.41768x10 ^-6 -6.47233x10 ^-8
[Zoom data]
W S T
f (mm) 8.072 13.438 23.273
FNO 2.87 3.73 5.16
d ₄ 18.51 8.96 1.99
d ₁₂ 6.11 12.81 22.97
d ₁₄ 4.17 3.40 3.83
d ₁₈ 0.80 0.80 0.80

Aberration diagrams in this example are shown in FIGS. 6 (a), (b), and (c). Each figure corresponds to the wide-angle end (W), the intermediate state (S), and the telephoto end (T). Each figure is a spherical aberration diagram, an astigmatism diagram, a distortion diagram, and a lateral chromatic aberration diagram in order from the left. The unit of each horizontal axis is (mm), (mm), (%), (mm).
From these, it can be seen that in this embodiment, each aberration is corrected well.
The calculated values corresponding to the above conditional expressions are collectively described later.

  The configuration parameters of the optical system of the second numerical example corresponding to the zoom lens (see FIG. 2) of the second example are shown below.

Surface number Curvature radius Surface spacing Refractive index Abbe number
1 r ₁ = ∞ d ₁ = 1.50 n _d1 = 1.77377 ν _d1 = 47.18
2 r ₂ = 6.812 (aspherical surface) d ₂ = 2.20
3 r ₃ = 12.179 d ₃ = 2.35 n _d2 = 1.90367 ν _d2 = 31.32
4 r ₄ = 40.524 d ₄ = (variable)
S ∞ (aperture) d ₅ = 0.80
5 r ₅ = 14.507 (aspherical surface) d ₆ = 2.12 n _d3 = 1.74330 ν _d3 = 49.33
6 r ₆ = -37.838 (aspherical surface) d ₇ = 0.10
7 r ₇ = 5.549 d ₈ = 2.04 n _d4 = 1.48749 ν _d4 = 70.23
8 r ₈ = 11.872 d ₉ = 1.13 n _d5 = 1.80518 ν _d5 = 25.42
9 r ₉ = 4.276 d ₁₀ = 1.28
10 r ₁₀ = 98.456 d ₁₁ = 1.86 n _d6 = 1.51633 ν _d6 = 64.14
11 r ₁₁ = -27.195 (aspherical surface) d ₁₂ = (variable)
12 r ₁₂ = 27.602 d ₁₃ = 1.97 n _d7 = 1.60311 ν _d7 = 60.70
13 r ₁₃ = -31.375 d ₁₄ = (variable)
14 r ₁₄ = ∞ d ₁₅ = 0.95 n _d8 = 1.54771 ν _d8 = 62.84
15 r ₁₅ = ∞ d ₁₆ = 0.55
16 r ₁₆ = ∞ d ₁₇ = 0.50 n _d9 = 1.51633 ν _d9 = 64.14
17 r ₁₇ = ∞ d ₁₈ = (variable)
I ∞ (image plane)
[Aspheric coefficient]
Surface number K A ₄ A ₆ A ₈ A ₁₀
2 -0.661 -1.18095x10 ^-5 -5.16857x10 ^-7 -8.68102x10 ^-10 -3.63804x10 ^-11
5 7.386 -5.88389x10 ^-4 -1.77024x10 ^-5 2.94038x10 ^-10 -1.44443x10 ^-8
6 -35.173 -3.16877x10 ^-4 -9.12370x10 ^-6 1.33506x10 ^-7 -2.25341x10 ^-10
11 0.000 -1.33259x10 ^-4 -1.89869x10 ^-5 1.62043x10 ^-6 -1.96646x10 ^-7
[Zoom data]
W S T
f (mm) 8.068 13.438 23.275
FNO 2.77 3.59 5.01
d ₄ 18.96 8.95 2.00
d ₁₂ 5.52 12.09 21.96
d ₁₄ 3.79 2.77 2.00
d ₁₈ 0.80 0.80 0.80

Aberration diagrams in this example are shown in FIGS. 6 (a), (b), and (c). Each figure corresponds to the wide-angle end (W), the intermediate state (S), and the telephoto end (T). Each figure is a spherical aberration diagram, an astigmatism diagram, a distortion diagram, and a lateral chromatic aberration diagram in order from the left. The unit of each horizontal axis is (mm), (mm), (%), (mm).
From these, it can be seen that in this embodiment, each aberration is corrected well.
The calculated values corresponding to the above conditional expressions are collectively described later.

  The configuration parameters of the optical system of the third numerical example corresponding to the zoom lens (see FIG. 3) of the third example are shown below.

Surface number Curvature radius Surface spacing Refractive index Abbe number
1 r ₁ = ∞ d ₁ = 1.50 n _d1 = 1.80610 ν _d1 = 40.92
2 r ₂ = 8.753 d ₂ = 2.71
3 r ₃ = 29.169 (aspheric) d ₃ = 2.35 n _d2 = 1.84666 ν _d2 = 23.78
4 r ₄ = -102.659 (aspherical surface) d ₄ = (variable)
S ∞ (aperture) d ₅ = 0.80
5 r ₅ = 14.140 (aspheric) d ₆ = 2.10 n _d3 = 1.58313 ν _d3 = 59.46
6 r ₆ = -24.946 (aspherical surface) d ₇ = 0.10
7 r ₇ = 5.904 d ₈ = 2.08 n _d4 = 1.69100 ν _d4 = 54.82
8 r ₈ = 13.607 d ₉ = 1.37 n _d5 = 1.80518 ν _d5 = 25.42
9 r ₉ = 4.124 d ₁₀ = 1.46
10 r ₁₀ = -131.935 d ₁₁ = 1.47 n _d6 = 1.51633 ν _d6 = 64.14
11 r ₁₁ = -75.520 (aspheric surface) d ₁₂ = (variable)
12 r ₁₂ = 23.098 d ₁₃ = 2.22 n _d7 = 1.60311 ν _d7 = 60.70
13 r ₁₃ = -22.809 d ₁₄ = (variable)
14 r ₁₄ = ∞ d ₁₅ = 0.95 n _d8 = 1.54771 ν _d8 = 62.84
15 r ₁₅ = ∞ d ₁₆ = 0.55
16 r ₁₆ = ∞ d ₁₇ = 0.50 n _d9 = 1.51633 ν _d9 = 64.14
17 r ₁₇ = ∞ d ₁₈ = (variable)
I ∞ (image plane)
[Aspheric coefficient]
Surface number K A ₄ A ₆ A ₈ A ₁₀
3 0.000 5.74375x10 ^-5 -8.37511x10 ^-6 4.11074x10 ^-7 -5.28660x10 ^-9
4 0.000 -6.94729x10 ^-5 -7.63117x10 ^-6 3.77509x10 ^-7 -5.46523x10 ^-9
5 6.643 -6.02020x10 ^-4 -5.51363x10 ^-6 -7.20229x10 ^-7 8.33261x10 ^-9
6 -0.550 -2.31108x10 ^-4 1.70053x10 ^-6 -6.41632x10 ^-7 1.97033x10 ^-8
11 0.000 1.51066x10 ^-4 -5.40629x10 ^-6 4.30502x10 ^-7 -1.15320x10 ^-7
[Zoom data]
W S T
f (mm) 8.068 13.438 23.275
FNO 2.86 3.83 5.29
d ₄ 18.61 9.15 1.24
d ₁₂ 4.60 11.63 20.83
d ₁₄ 3.38 2.00 2.00
d ₁₈ 0.90 0.90 0.90

Aberration diagrams in this example are shown in FIGS. 8A, 8B, and 8C. Each figure corresponds to the wide-angle end (W), the intermediate state (S), and the telephoto end (T). Each figure is a spherical aberration diagram, an astigmatism diagram, a distortion diagram, and a lateral chromatic aberration diagram in order from the left. The unit of each horizontal axis is (mm), (mm), (%), (mm).
From these, it can be seen that in this embodiment, each aberration is corrected well.
The calculated values corresponding to the above conditional expressions are collectively described later.

  The configuration parameters of the optical system of the fourth numerical example corresponding to the zoom lens (see FIG. 4) of the fourth example are shown below.

Surface number Curvature radius Surface spacing Refractive index Abbe number
1 r ₁ = ∞ d ₁ = 1.50 n _d1 = 1.77377 ν _d1 = 47.17
2 r ₂ = 7.490 (aspherical surface) d ₂ = 2.72
3 r ₃ = 13.222 d ₃ = 2.11 n _d2 = 1.80518 ν _d2 = 25.42
4 r ₄ = 38.308 d ₄ = (variable)
S ∞ (aperture) d ₅ = 0.80
5 r ₅ = 16.536 (aspherical surface) d ₆ = 1.77 n _d3 = 1.74330 ν _d3 = 49.33
6 r ₆ = -41.171 (aspherical surface) d ₇ = 0.02
7 r ₇ = 5.596 d ₈ = 2.48 n _d4 = 1.51633 ν _d4 = 64.14
8 r ₈ = 16.030 d ₉ = 1.02 n _d5 = 1.80518 ν _d5 = 25.42
9 r ₉ = 4.623 d ₁₀ = 1.02
10 r ₁₀ = 1319.760 d ₁₁ = 1.43 n _d6 = 1.51633 ν _d6 = 64.14
11 r ₁₁ = -24.853 d ₁₂ = (variable)
12 r ₁₂ = 37.064 d ₁₃ = 2.07 n _d7 = 1.74400 ν _d7 = 44.78
13 r ₁₃ = -36.893 d ₁₄ = (variable)
14 r ₁₄ = ∞ d ₁₅ = 0.95 n _d8 = 1.54771 ν _d8 = 62.84
15 r ₁₅ = ∞ d ₁₆ = 0.55
16 r ₁₆ = ∞ d ₁₇ = 0.50 n _d9 = 1.51633 ν _d9 = 64.14
17 r ₁₇ = ∞ d ₁₈ = (variable)
I ∞ (image plane)
[Aspheric coefficient]
Surface number K A ₄ A ₆ A ₈ A ₁₀
2 -0.697 7.65750x10 ^-6 -1.68254x10 ^-12 -1.42325x10 ^-15 -8.49690x10 ^-12
5 9.778 -4.32998x10 ^-4 -5.71365x10 ^-6 -4.70780x10 ^-8 -6.55631x10 ^-9
6 -29.058 -1.46704x10 ^-4 1.20833x10 ^-6 7.61198x10 ^-8 2.82407x10 ^-9
[Zoom data]
W S T
f (mm) 8.119 13.436 23.244
FNO 2.87 3.70 5.15
d ₄ 18.31 8.63 1.99
d ₁₂ 6.21 12.49 23.05
d ₁₄ 4.16 3.76 3.87
d ₁₈ 0.79 0.80 0.79

Aberration diagrams in this example are shown in FIGS. 9A, 9B, and 9C. Each figure corresponds to the wide-angle end (W), the intermediate state (S), and the telephoto end (T). Each figure is a spherical aberration diagram, an astigmatism diagram, a distortion diagram, and a lateral chromatic aberration diagram in order from the left. The unit of each horizontal axis is (mm), (mm), (%), (mm).
From these, it can be seen that in this embodiment, each aberration is corrected well.
The calculated values corresponding to the above conditional expressions are collectively described later.
[Reference example]
The following shows the construction parameters of the optical system of Numerical Example that corresponds to the reference example of the zoom lens (see Fig. 5).
Surface number Curvature radius Surface spacing Refractive index Abbe number
1 r ₁ = ∞ d ₁ = 1.50 n _d1 = 1.77377 ν _d1 = 47.18
2 r ₂ = 8.155 (aspheric surface) d ₂ = 3.36
3 r ₃ = 15.204 d ₃ = 1.65 n _d2 = 1.84666 ν _d2 = 23.78
4 r ₄ = 38.711 d ₄ = (variable)
S ∞ (aperture) d ₅ = 0.80
5 r ₅ = 8.232 (aspheric) d ₆ = 2.99 n _d3 = 1.51633 ν _d3 = 64.14
6 r ₆ = -15.571 (aspherical surface) d ₇ = 0.10
7 r ₇ = 9.472 d ₈ = 2.09 n _d4 = 1.69680 ν _d4 = 55.53
8 r ₈ = -50.000 d ₉ = 1.00 n _d5 = 1.68893 ν _d5 = 31.16
9 r ₉ = 4.569 d ₁₀ = (variable)
10 r ₁₀ = 40.201 d ₁₁ = 2.50 n _d6 = 1.76802 ν _d6 = 49.23
11 r ₁₁ = -33.383 d ₁₂ = (variable)
12 r ₁₂ = ∞ d ₁₃ = 0.95 n _d7 = 1.54771 ν _d7 = 62.84
13 r ₁₃ = ∞ d ₁₄ = 0.55
14 r ₁₄ = ∞ d ₁₅ = 0.50 n _d8 = 1.51633 ν _d8 = 64.14
15 r ₁₅ = ∞ d ₁₆ = (variable)
I ∞ (image plane)
[Aspheric coefficient]
Surface number K A ₄ A ₆ A ₈ A ₁₀
2 -1.224 1.15285x10 ^-4 8.39751x10 ^-7 -2.79967x10 ^-8 3.18923x10 ^-10
5 -0.726 -3.47679x10 ^-4 -2.49225x10 ^-5 6.50686x10 ^-7 -7.77039x10 ^-8
6 1.958 -1.35093x10 ^-4 -2.32879x10 ^-5 2.62867x10 ^-7 -4.12333x10 ^-8
[Zoom data]
W S T
f (mm) 8.068 13.986 23.274
FNO 2.90 3.87 5.20
d ₄ 18.78 8.34 1.54
d ₁₀ 7.45 14.41 23.06
d ₁₂ 3.29 2.34 3.00
d ₁₆ 0.90 0.90 0.90

The following table shows the values of the conditional expressions in Examples 1 to 4 and the reference example .

[Second Embodiment]
Next, a camera according to a second embodiment of the present invention will be described.
The zoom lens according to the first embodiment of the present invention as described above is an imaging device, particularly a digital camera or video, which forms an object image with the zoom lens and receives the image with an electronic image sensor such as a CCD. It can be used for a camera, a personal computer which is an example of an information processing device, a telephone, particularly a mobile phone which is convenient to carry. The embodiment is illustrated below.
11 to 13 are conceptual diagrams of a configuration in which the zoom lens according to the present invention is incorporated in a photographing optical system 41 of a digital camera. 11 is a front perspective view showing the appearance of the digital camera 40, FIG. 12 is a rear perspective view thereof, and FIG. 13 is a cross-sectional view showing the configuration of the digital camera 40.

  In this example, the digital camera 40 (camera) includes a photographing optical system 41 (zoom lens) having a photographing optical path 42, a finder optical system 43 having a finder optical path 44, a shutter 45, a flash 46, a liquid crystal display monitor 47, and the like. When the shutter 45 disposed on the upper part of the digital camera 40 is pressed, photographing is performed through the photographing optical system 41, for example, the zoom lenses 100, 101, 102, 103, 104 of the first embodiment. Is called. An object image formed by the photographing optical system 41 is formed on the imaging surface of the CCD 49 (imaging device) via the optical low-pass filter F1 and the cover glass GL. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera via the processing means 51. Further, the processing means 51 is connected to a recording means 52 so that a photographed electronic image can be recorded. The recording unit 52 may be provided separately from the processing unit 51, or may be configured to perform recording and writing electronically using a floppy (registered trademark) disk, a memory card, an MO, or the like. Further, it may be configured as a silver salt camera in which a silver salt film is arranged in place of the CCD 49.

  Further, a finder objective optical system 53 is disposed 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 this polyprism 55 is an eyepiece optical system 59 that guides the erect image to the observer eyeball E. Note that cover members 50 are disposed on the incident side of the photographing optical system 41 and the finder objective optical system 53 and on the exit side of the eyepiece optical system 59, respectively.

  The digital camera 40 configured in this manner is a zoom lens with a large back focus, a photographing optical system 41 having a wide angle of view and a high zoom ratio, good aberration, bright, and a filter that can be arranged with a high back focus. Performance and cost reduction can be realized.

  In the example of FIG. 13, a parallel plane plate is disposed as the cover member 50, but a lens having power may be used.

1 is a lens cross-sectional view at a wide-angle end, an intermediate state, and a telephoto end during focusing on an object point at infinity of a zoom lens according to a first example of the first embodiment of the present invention. FIG. 6 is a lens cross-sectional view at the wide-angle end, an intermediate state, and a telephoto end when the zoom lens of the second embodiment is in focus at infinity. FIG. 6 is a lens cross-sectional view at the wide-angle end, an intermediate state, and a telephoto end when the zoom lens of the third embodiment is in focus at infinity. FIG. 6 is a lens cross-sectional view at the wide-angle end, an intermediate state, and a telephoto end when the zoom lens of the fourth embodiment is in focus at infinity. FIG. 6 is a lens cross-sectional view at the wide-angle end, in the intermediate state, and at the telephoto end when the zoom lens of the reference example is in focus at the same time. FIG. 4 is an aberration diagram corresponding to a wide angle end, an intermediate state, and a telephoto end in Example 1. FIG. 6 is an aberration diagram corresponding to a wide-angle end, an intermediate state, and a telephoto end in Example 2. FIG. 6 is an aberration diagram corresponding to a wide-angle end, an intermediate state, and a telephoto end in Example 3. FIG. 6 is an aberration diagram corresponding to a wide angle end, an intermediate state, and a telephoto end in Example 4. FIG. 6 is an aberration diagram corresponding to a wide angle end, an intermediate state, and a telephoto end in a reference example . It is a conceptual diagram of a front perspective view showing an appearance of a digital camera incorporating a zoom lens according to the present invention. It is a conceptual diagram of back perspective similarly. 1 is a conceptual cross-sectional view illustrating a configuration of a digital camera incorporating a zoom lens according to the present invention.

Explanation of symbols

100, 101, 102, 103, 104 Zoom lens G1 First lens group G2 Second lens group G3 Third lens group S Aperture stop F Parallel plate group F1 Optical low-pass filter I Image planes L1, L10, L20, L30, L40 Negative lens (negative first lens in the first lens group)
L2, L11, L21, L31, L41 Positive lens (positive second lens in the first lens group)
L3, L12, L22, L32, L42 Positive lens (positive first lens in the second lens group)
L4, L13, L23, L33, L43 Joint lens L5, L14, L24, L34, L44 Positive lens (positive second lens in the second lens group)
L6, L15, L25, L35, L45 Negative lens (negative third lens of the second lens group)
L7, L16, L26, L36 Positive lens (positive fourth lens in the second lens group)
L8, L17, L27, L37, L46 Positive lens (positive single lens in the third lens group)
40 Digital camera (camera)
41 Imaging optical system (zoom lens)
49 CCD (imaging device)

Claims (10)

In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power,
The first lens group includes, in order from the object side, a negative first lens and a positive second lens, and has at least one aspheric surface.
The second lens group includes, in order from the object side, a positive first lens, a positive second lens, and a negative third lens, and the positive second lens and the negative third lens are cemented with each other. A meniscus cemented lens having a convex surface facing the object side, and has at least two surfaces other than the cemented surface of the cemented lens, and has an aspheric surface,
The third lens group is composed of a positive single lens consisting only of a spherical surface,
When zooming from the wide-angle end to the telephoto end when focusing on an object point at infinity, the first lens group moves along a locus convex toward the image side, the second lens group moves only toward the object side, and the third The lens group moves by a different amount than the second lens group and is movable for focusing;
A zoom lens characterized by satisfying the following conditional expressions (1), (2) , (5), (6) ′, and (7) ′ .
2.3 <L _t / f ₂ <3.7 (1)
1.15 <| f ₁ / f ₂ | <2.0 (2)
0.3 <R _23R / R _22F <1.0 (5)
0.9 ≦ f ₂ / R _23F <1.4 (6) ′
1.69 ≦ | f ₂ / f ₂₃ | <3.0 (7) ′
Where L _t is the distance from the lens surface closest to the object side to the imaging surface at the telephoto end of the zoom lens, f ₂ is the focal length of the second lens group, f ₁ is the focal length of the first lens group , R _22F is a radius of curvature in the vicinity of the optical axis of the object side surface of the positive second lens in the second lens group, and R _23R is in the vicinity of the optical axis of the most image side surface of the negative third lens in the second lens group. R _23F is the radius of curvature near the optical axis of the cemented surface of the cemented lens of the second lens group , and f ₂₃ is the focal length of the negative third lens of the second lens group . The zoom lens according to claim 1, wherein the following conditional expression (3) is satisfied.
0.29 <f _W / f ₃ <0.6 (3)
Here, f _W is the focal length of the entire zoom lens system at the wide angle end, and f ₃ is the focal length of the third lens group. Wherein said positive first lens in the second lens group, the zoom lens according to claim 1 or 2, characterized in that it has an aspherical surface on both sides. Wherein the image side of the cemented lens in the second lens group, a positive zoom lens according to any one of claims 1 to 3, characterized in that the fourth lens arranged. The zoom lens according to claim 4 , wherein the positive fourth lens of the second lens group is a single lens having a convex surface on the image side. Claim 4 or zoom lens according to 5, wherein the positive image-side surface of the fourth lens in the second lens group is an aspherical surface. 2. The negative first lens of the first lens group includes a concave surface on the image side having a stronger curvature than the object-side surface, and the concave surface on the image side is an aspheric surface. The zoom lens according to any one of items 1 to 6 . The zoom lens according to any one of claims 1 to 7 , wherein the positive second lens of the first lens group has aspheric surfaces on both sides. The zoom lens according to any one of claims 1 to 8 , wherein the positive second lens of the first lens group is made of a glass material having a refractive index with respect to d-line of 1.85 or more. A zoom lens according to any one of claims 1 9, the imaging apparatus characterized in that a capturing device at the imaging position of the zoom lens.

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