JP3757223B2 - Variable magnification imaging lens - Google Patents

Description

  The present invention relates to an imaging lens device with strict restrictions on the total length such as a digital still camera, a mobile phone mounted camera, and a mobile information terminal mounted camera using an image sensor, and in particular, a suitable lens total length that can be mounted on a mobile phone and the like. The present invention relates to a variable magnification imaging lens having high optical performance.

With the diversification of information, an imaging lens is mounted on a cellular phone or a portable information terminal, and the amount of information of an image is rapidly increasing due to an improvement in information transmission speed. Various types of portable devices that already have a fixed focus lens and a variable power lens have been proposed.
In order to mount a camera module on a mobile phone, a portable information terminal, or the like, which is a portable device of this type, the optical (lens) system needs to be extremely compact.

In response to such a demand, a compact zoom lens having a zooming function that realizes a compact size has been proposed (for example, see Patent Document 1).
The zoom lens described in Patent Document 1 includes a front group having positive power and a rear group having negative power.
The front group is composed of five lenses in four groups of a negative lens from the object side, a meniscus negative lens, a biconvex positive lens, and a biconvex positive lens, and the rear group is a biconvex positive lens, a negative lens, and a meniscus negative lens. It consists of 3 lenses in 3 groups and 8 lenses in total, and by adopting an aspherical surface on at least one surface of the lens in the 3rd group or the 4th group, a compact and high performance optical system is constructed. Yes.
JP-A-9-311275

By the way, it is self-evident when taking into account the thickness of the lens that can be manufactured and the amount of movement of the lens group that accompanies zooming, but conditions for realizing an extremely compact optical system that can be mounted on a portable device. One of them is that the number of lenses constituting the optical system is small.
However, the zoom lens described in Patent Document 1 described above has a relatively large number of lens elements, that is, 8 elements in 7 groups, and there is a limit to downsizing the imaging optical system. It is hard to say that the equipment has been sufficiently downsized.

In an optical system having a zooming function, an example in which the number of lenses is as small as 2 to 5 is generally limited to an imaging lens that targets an imaging device as a small physical size. It is done.
Image sensors used in compact digital still cameras and cameras equipped with mobile phones typically have an extremely small imaging surface size of several to 20% compared to silver halide films, and as a rule, high optical performance can be secured. Must do so.
Accordingly, an imaging optical system using an imaging element is classified into the following two types as lens types in order to emphasize telecentricity.

The first type is a two-group lens type composed of a first lens group having a negative refractive power and a second lens group having a positive refractive power from the object side. This two-group lens type can be configured with a minimum of two lenses.
The first type is a so-called retrofocus type, which is easily applied to widening the angle.
However, the first lens type described above is a so-called retrofocus type, and although it is said that it can be easily applied to widening the angle, it is sufficiently small for a device with a limited overall length, such as a cellular phone. It is hard to say that has been made.

The second type, a first lens unit having a negative refractive power from the object side, a second lens unit having positive refractive power, and is 3 Gun構formed Les Nzutaipu consisting of a positive refractive power third lens group . This three-group lens type can be configured with a minimum of three lenses.
This lens type is excellent in telecentricity, and is often employed in an optical system using an image sensor.
However, although the second lens type is excellent in telecentricity, it is difficult to say that the second lens type is sufficiently miniaturized because it is a retrofocus type like the above-described negative and positive two-group configuration. .

On the other hand, the first lens group having a negative refractive power, the second lens group having a positive refractive power, and the third lens group having a negative refractive power from the object side. So-called negative, positive, and negative lens types have been proposed. Since this lens type can strengthen the action of the telephoto system, it is advantageous in that the total length of the optical system can be shortened, and is suitable for an imaging lens for a silver salt film.
However, in this lens type, the third lens group, which is the lens group closest to the imaging surface, has a negative refracting power, so the exit angle from the optical system tends to jump, and when using the imaging device as a target, There is a concern about vignetting due to the opening of the image sensor.

In an optical system such as a cellular phone that is required to be extremely compact, as described above, it is difficult to achieve compactness with a so-called retrofocus type.
On the other hand, negative, positive, and negative lens types that strengthen the action of the telephoto system are superior in terms of compactness, but tend to jump up the exit angle from the optical system. Further, in recent image pickup devices, in order to promote a reduction in vignetting due to the opening, it has become common to mount a microlens on each pixel and perform correction using the microlens.

  The present invention has been made in view of such circumstances, and an object of the present invention is to realize an extremely compact optical system capable of suppressing an emission angle while being a negative, positive, and negative lens type. An object of the present invention is to provide a variable magnification imaging lens capable of satisfying the requirements.

In order to achieve the above object, an aspect of the present invention is a variable magnification imaging lens having an imaging optical system having a variable magnification function for an imaging element, wherein the imaging optical system is arranged in order from the object side. It is composed of five lenses, the zoom ratio is about 2.5 or less, and the following conditional expression (1) is satisfied.
0.17 <y ′ / L (1)
However, y ′ is the maximum image height on the imaging surface of the imaging device, and L is from the forefront of the optical system when the distance from the top of the lens surface of the optical system on the most object side to the imaging surface on the optical axis is maximum. Each distance to the imaging surface is shown.

  Preferably, the imaging optical system includes a first lens group having a negative refracting power and a three-lens structure having positive and negative refracting power, which are arranged in order from the object side. A second lens group having a positive refractive power and a single lens third lens group having a negative refractive power, and at the time of zooming, at least the second lens group and the third lens group. The lens group moves on the optical axis.

Preferably, the focal lengths of the first lens group, the second lens group, and the third lens group satisfy the following conditional expressions (2), (3), and (4), respectively.
2.0 <| f1 | / fw <3.0 (2)
0.74 <f2 / fw <0.86 (3)
1.0 <| f3 | / fw <1.42 (4)
Here, f1 represents the focal length of the first lens group, f2 represents the focal length of the second lens group, f3 represents the focal length of the third lens group, and fw represents the focal length of the optical system at the wide angle end. .

  Preferably, the second lens group has at least one aspheric surface, and the third lens group has at least one aspheric surface.

Preferably, the third lens group is a negative lens having a concave surface facing the image side, and satisfies the following conditional expression (5).
tan ω × fst / Lst <0.35 (5)
Here, ω represents the maximum incident angle at the wide-angle end, fst represents the combined focal length of the optical system on the image side from the stop at the wide-angle end, and Lst represents the distance from the stop to the imaging surface at the wide-angle end.

  Preferably, the second lens group is composed of three plastic lenses.

  Preferably, the first lens group is a negative meniscus lens having a convex surface on the object side on the first surface.

  Preferably, the three lenses of the second lens group include a positive meniscus lens, a negative meniscus lens, and a positive biconvex lens from the object side.

ADVANTAGE OF THE INVENTION According to this invention, the compact variable magnification imaging lens which can be mounted in an information terminal, a mobile telephone, etc. is realizable.
Further, it can be applied to a digital still camera, and can realize an ultra-thin camera equipped with a variable magnification lens, and can realize a variable magnification imaging lens with a wide application range.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIGS. 1A and 1B are diagrams showing a basic configuration of a variable magnification imaging lens. FIG. 1A shows a lens configuration at the wide-angle end, and FIG. 1B shows a lens configuration at the telephoto end. Is shown.

As shown in FIG. 1, the variable magnification imaging lens 100 includes a first lens group 110 that is arranged in order from the object side OBJS and that has a single refractive power, and has three positive and negative refractive powers. A second lens group 120 having a positive refracting power as a whole, a single lens structure having a negative refracting power, a third lens group 130 having a negative refracting power, an imaging unit 140, and an object side of the second lens group 120 (first It is constituted by a diaphragm 150 arranged on the lens group 110 side.
When zooming is performed in the zoom imaging lens 100, for example, the second lens group 120 and the third lens group 130 out of the first lens group 110, the second lens group 120, and the third lens group 130 are light beams. Move on axis AX.
Regarding the zooming function, the first lens group 110 can be fixed, but the first lens group 110 can be changed (movable ) and used. It can respond according to the purpose.

Among these components, a first lens group 110 having a single lens structure having a negative refractive power, and a second lens group 120 having a positive power as a whole consisting of a three-lens structure having positive and negative refractive powers. The imaging optical system of the variable magnification imaging lens 100 is constituted by the third lens group 130 having a negative refractive power and a single lens configuration.
In other words, in the present embodiment, the imaging optical system includes a first lens group 110 arranged in order from the object side OBJS, a second lens group 120, a third lens group 130, and a third lens group 130. It consists of a total of 5 lenses.

The first lens group 110 includes, for example, a meniscus lens 111 having a negative refractive power and having a convex surface on the object side on the first surface.
As described above, by configuring the first lens group 110 with the meniscus lens 111 having negative refractive power, it becomes easy to suppress distortion.

Since the second lens group 120 is the only group having a positive refractive power, a three-lens configuration is employed to correct various aberrations. Further, if a glass lens is used for the second lens group 120, it is smaller and therefore more expensive than a normal lens. Therefore, in order to achieve cost reduction, the three lenses constituting the second lens group 120 are constituted by plastic lenses.
The three plastic lenses constituting the second lens group 120 include, for example, a positive meniscus lens 121, a negative meniscus lens 122, and a positive biconvex lens 123 from the first lens group 110 side (object side). Is done.
The positive meniscus lens 121 performs spherical aberration correction satisfactorily, and the negative meniscus lens 122 is used as the lens located at the center of the three lenses while suppressing overcorrection of the ellipsoidal curvature that occurs in the positive lens. By suppressing the occurrence of coma aberration, the performance balance is achieved. By these, aberration fluctuations associated with zooming are suppressed, and high-performance zooming is possible.

Since the third lens group 130 has a single lens configuration, various aberrations need to be corrected here, spherical aberration, coma aberration, astigmatism, distortion correction, and correction of the exit angle at the wide angle end are performed. It is also necessary for.
The third lens group 130 is constituted by, for example, a negative lens 131 having a concave surface on the image surface side.
In the present embodiment, focus adjustment (focus adjustment) is performed by the third lens group 130, and moves from the infinity toward the imaging surface side .
When the third lens group is a positive lens, the distance between the second lens group and the third lens group at the telephoto end must be ensured in order to move toward the object side.
In the present embodiment, since the lens moves to the image plane side, the distance between the second lens group 120 and the third lens group 130 at the telephoto end can be reduced.
This is one of the factors that make it possible to reduce the size of the variable magnification optical system, and if it is the same size, it is possible to arrange the power without difficulty, enabling higher performance and lowering the eccentricity sensitivity. Yes.

In the imaging unit 140, a parallel plane plate (cover glass) 141 made of glass and an imaging element 142 made of, for example, a CCD or a CMOS sensor are sequentially arranged from the third lens group 130 side.
Light from the subject (object) via the imaging optical system is imaged on the imaging surface 142 a of the imaging element 142.

  The imaging optical system having the first lens group 110, the second lens group 120, and the third lens group 130 described above has a telephoto function because the entire optical system has negative, positive, and negative lens configurations. Therefore, the overall length can be shortened.

The variable magnification imaging lens 100 according to the present embodiment having the above-described configuration is made compact so that it can be mounted on a mobile phone or the like, and the restriction of the exit pupil of the incident angle to the imaging element is relaxed. Various conditions as described below are set.
Hereinafter, each condition set in the variable magnification imaging lens 100 according to the present embodiment will be described.

The variable magnification imaging lens 100 has a magnification ratio of about 2.5 or less, the maximum image height on the imaging surface 142a of the imaging element 142 is y ', and the top of the most object side lens 111 of the imaging optical system. When the distance from the forefront of the optical system to the imaging surface when the distance to the imaging surface 142a on the optical axis AX is maximum is expressed as L, the following (Condition 1) is satisfied. ing.
0.17 <y ′ / L (Condition 1)

The imaging optical system can change the magnification by about 2.5 times or less while shortening the total length by reducing the number of lenses and the number of lenses. Furthermore, although the size of the optical system depends on the size of the sensor used, in order to achieve compactness, even if it is a variable magnification lens, the total length exceeds the lower limit (0.17) of conditional expression 1. Since it becomes longer and the diameter of the lens constituting the first lens group 110 becomes larger, it cannot be said to be a compact optical system.
In the present embodiment, the overall length of the imaging optical system is shortened, which makes it possible to reduce the diameter of the lens in the first lens group 110 having the largest diameter.

Note that the relationship constraint between y ′ and L in conditional expression 1 depends on the size of the imaging system 142a and the size of the optical system.
However, in the present embodiment, a compact optical system having a short overall length is possible in spite of the negative, positive, and negative three-group configuration.
In addition, the present embodiment achieves compactness with a five-sheet configuration and a small number of sheets. If the number of sheets is reduced, it becomes difficult to shorten L in order to perform aberration correction, and in this embodiment, y ′ / L <0.23.

In the variable magnification imaging lens 100 of the present embodiment, the focal length f1 of the first lens group 110, the focal length f2 of the second lens group 120, and the focal length f3 of the third lens group 130 are wide-angle ends where the combined power becomes strong. The following (conditional expression 2), (conditional expression 3), and (conditional expression 4) are satisfied using the focal length fw of the imaging optical system in FIG.
2.0 <| f1 | / fw <3.0 (conditional expression 2)
0.74 <f2 / fw <0.86 (conditional expression 3)
1.0 <| f3 | / fw <1.42 (conditional expression 4)

  Conditional Expression 2, Conditional Expression 3, and Conditional Expression 4 are the power conditions of each group for achieving the compactness of the variable magnification imaging lens 100, in other words, by taking the power balance of each lens group, The conditions for enabling a compact variable magnification imaging lens in terms of performance are shown.

Conditional expression 2 indicates the power condition of the first lens group 110. When the upper limit is exceeded, negative distortion correction becomes severe, and further, aberration deterioration due to the power of the second lens group 120 increasing occurs. On the other hand, if the lower limit is exceeded, the total length becomes large and compactness cannot be achieved, and the power of the first lens group 110 increases, and astigmatism and distortion become worse.
Conditional expression 3 indicates the power condition of the second lens group 120. If the upper limit is exceeded, the total length becomes large, and it becomes difficult to correct spherical aberration. If the lower limit is exceeded, spherical aberration, astigmatism and coma will deteriorate.
Conditional expression 4 shows the power condition of the third lens group 130. When the upper limit is raised, it becomes difficult to perform negative distortion correction. When the upper limit is exceeded, coma aberration and positive distortion are increased, and the total length is increased. Become.

In addition, the variable magnification imaging lens 100 of the present embodiment is configured such that the second lens group 120 has at least one aspheric surface and the third lens group 130 has at least one aspheric surface.
Specifically, as described above, the variable magnification imaging lens 100 of the present embodiment achieves compactness by optimizing the power arrangement of each group in aberration correction, and further, the second lens group 120. Further, by further appropriately arranging an aspheric surface in the third lens group 130, further downsizing is realized. By optimizing these conditions, the distortion can be further reduced with high performance despite a compact variable power lens.

That is, in the present embodiment, it is difficult to correct aberrations of a compact variable magnification imaging lens with only a spherical system, and various aberrations are corrected by arranging an aspherical surface in place.
In the imaging optical system according to the present embodiment, the second lens group 120 has only one positive refracting power, inevitably increases its power, and increases the occurrence of aberrations, so that at least one aspheric surface is required. This corrects spherical aberration, coma and astigmatism.
Further, since the third lens group 130 has a single lens configuration, various aberrations need to be corrected here, and spherical aberration, coma aberration, astigmatism, and distortion correction are performed, and the exit angle is corrected at the wide angle end. Is also necessary for.

As described above, in the present embodiment, the spherical aberration, astigmatism, and coma generated in the second lens group 120 are corrected by disposing an appropriate aspheric surface in the second lens group 120. Further, by disposing an aspheric surface in the third lens group 130, distortion aberration correction, coma aberration, and astigmatism correction are performed, and spherical aberration correction at the telephoto end is also performed.
Further, the exit pupil position at the wide angle (wide) end is relaxed. In the present embodiment, the performance correction is performed by applying at least one aspheric surface to each lens.

The aspherical surface used in this embodiment is given by the following equation.
Z = (h ² / r) / [1+ {1− (1 + k) (h / r) ² } ^1/2 ]
+ Ah ⁴ + Bh ⁶ + Ch ⁸ + Dh ¹⁰

  Where Z is the depth from the tangent plane to the surface vertex, r is the radius of curvature, h is the height from the optical axis, k is the conic constant, A is the fourth-order aspheric coefficient, and B is 6 The next aspherical coefficient, C represents the 8th-order aspherical coefficient, and D represents the 10th-order aspherical coefficient.

Further, as described above, the third lens group 130 can be constituted by, for example, the negative lens 131 having a concave surface directed toward the image plane side. In this case, the maximum incident angle ω at the wide-angle end and the wide-angle end are used. Using the combined focal length fst of the optical system on the image side from the stop and the distance Lst from the stop to the imaging surface at the wide angle end, the following (Condition 5) is satisfied.
tan ω × fst / Lst <0.35 (Condition 5)

In recent image pickup devices with finer pixels, the light toward the light receiving portion is more likely to be blocked by the aperture, and therefore the peripheral light amount is corrected using a microlens.
Therefore, an optical system using an image sensor does not necessarily require telecentricity.
However, in order to secure the amount of light to the image sensor, there is a limit on the incident angle, and this limit angle is regulated. If the upper limit is exceeded, the angle to the light receiving unit becomes strict and abrupt at the periphery of the screen. A decrease in light intensity occurs.

Conditional expression 5 represents the condition of the exit pupil position with respect to the restriction of the incident angle to the image sensor 142, and is a conditional expression at the wide-angle end where conditions are severe.
It is a relational expression of the aperture position and the focal length (power) of the optical system on the imaging surface 142a side from the aperture with respect to the exit pupil distance with respect to the angle (both angles) incident on the optical system. In the present embodiment, the restriction of the exit pupil is relaxed while having a wide angle of view and compactness, and the conditional expression achieved is shown.

Examples 1-4 according to specific numerical values of the variable magnification imaging lens are shown below.
In each of the first to fourth embodiments, the lens constituting each lens group of the variable magnification imaging lens 100, the diaphragm 150, and the cover glass 141 constituting the imaging unit 140 are as shown in FIG. A face number was assigned.
Specifically, the object side surface (convex surface) of the negative meniscus lens 111 constituting the first lens group 110 is No. 1, the opposite concave surface is No. 2, the diaphragm 150 is No. 3, and the second lens group. No. 4 of the diaphragm side surface (convex surface) of the positive meniscus lens 121 constituting 120, No. 5 of the concave surface on the opposite side of the lens 121, No. 6 of the surface (concave surface) of the negative meniscus lens 122 on the lens 121 side, The convex surface on the opposite side of the lens 122 is No. 7, the convex surface on the lens 122 side of the biconvex lens 123 is No. 8, the convex surface on the opposite side of the lens 123 is No. 9, and the negative lens 131 constituting the third lens group 130 The surface (convex surface) on the second lens group 120 side is No. 10, the surface (concave surface) on the opposite side of the lens 131 is No. 11, and the surface on the third lens group 130 side of the cover glass 141 is No. 12. The surface on the element 142 side is number 13 .

Example 1
Tables 1 to 4 show the numerical values of Example 1.
Table 1 shows the curvature radii (r: mm) and intervals (d: mm) of the lenses, the diaphragm, and the cover glass corresponding to the surface numbers of the variable magnification imaging lens in Example 1.

  Table 2 shows aspheric coefficients of predetermined surfaces of the second lens group 120 and the third lens group 130 including the aspheric surface in the first embodiment. In Table 2, K is the conic constant, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, C is the eighth-order aspheric coefficient, and D is the tenth-order aspheric coefficient. Represents.

  Table 3 shows the numerical values of the variable interval, the aperture diameter, the focal length, and the F number (Fno) at the wide-angle end and the telephoto end of the surfaces 2, 9, 11, and 13 whose intervals change with zooming. Yes.

  Table 4 shows numerical values of the conditional expressions 1 to 5. In Example 1, (y ′ / L) in conditional expression 1 is 0.221 (0.17 <0.221 <0.23), and (f1 / fw) in conditional expression 2 is 2.946 (2. 0 <2.946 <3.0), (f2 / fw) in conditional expression 3 is 0.772 (0.74 <0.772 <0.86), and (f3 / fw) in conditional expression 4 is 1. 224 (1.0 <1.224 <1.42) and (tan ω × fst / Lst) of conditional expression 5 is 0.329 (0.329 <0.35).

FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 1. FIG. 4 shows spherical aberration, astigmatism, and distortion at the telephoto end in Example 1. It is an aberration diagram showing aberration. 3A and 3B, spherical aberration is shown, (B) is astigmatism, and (C) is distortion. In FIG. 3 and FIG. 3B, the solid line indicates the value of the d line on the meridional image plane, and the broken line indicates the value of the d line on the sagittal image plane.
As can be seen from FIGS. 3 and 4, according to Example 1, the spherical, astigmatism, and distortion aberrations are well corrected at the focal position distance from the wide-angle end to the telephoto end, and the imaging performance is excellent. A variable magnification imaging lens is obtained.

(Example 2)
Tables 5 to 8 show numerical values of Example 2.
Table 5 shows the radius of curvature (r: mm) and the interval (d: mm) of each lens, diaphragm, and cover glass corresponding to each surface number of the variable magnification imaging lens in Example 2.

  Table 6 shows aspheric coefficients of predetermined surfaces of the second lens group 120 and the third lens group 130 including the aspheric surface in the second embodiment. In Table 6, K is a conic constant, A is a fourth-order aspheric coefficient, B is a sixth-order aspheric coefficient, C is an eighth-order aspheric coefficient, and D is a tenth-order aspheric coefficient. Represents.

  Table 7 shows the numerical values of the variable distance, the aperture diameter, the focal length, and the F number (Fno) at the wide-angle end and the telephoto end of the surfaces 2, 9, 11, and 13 whose intervals change with zooming. Yes.

  Table 8 shows numerical values of the conditional expressions 1 to 5. In Example 2, (y ′ / L) in conditional expression 1 is 0.215 (0.17 <0.215 <0.23), and (f1 / fw) in conditional expression 2 is 2.608 (2. 0 <2.608 <3.0), (f2 / fw) in conditional expression 3 is 0.746 (0.74 <0.746 <0.86), and (f3 / fw) in conditional expression 4 is 1. 173 (1.0 <1.173 <1.42) and (tan ω × fst / Lst) in conditional expression 5 is 0.323 (0.323 <0.35).

FIG. 5 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 2. FIG. 6 shows spherical aberration, astigmatism, and distortion at the telephoto end in Example 2. It is an aberration diagram showing aberration. In FIGS. 5 and 6, (A) shows spherical aberration, (B) shows astigmatism, and (C) shows distortion. In FIG. 5 and FIG. 6B, the solid line indicates the value of the d line on the meridional image plane, and the broken line indicates the value of the d line on the sagittal image plane.
As can be seen from FIGS. 5 and 6, according to Example 2, spherical, astigmatism, and distortion aberrations are well corrected at the focal position distance from the wide-angle end to the telephoto end, and the imaging performance is excellent. A variable magnification imaging lens is obtained.

Example 3
Tables 9 to 12 show numerical values of Example 3.
Table 9 shows the radius of curvature (r: mm) and interval (d: mm) of each lens, diaphragm, and cover glass corresponding to each surface number of the variable magnification imaging lens in Example 3.

  Table 10 shows aspherical coefficients of predetermined surfaces of the second lens group 120 and the third lens group 130 including the aspherical surface in Example 3. In Table 10, K is a conic constant, A is a fourth-order aspheric coefficient, B is a sixth-order aspheric coefficient, C is an eighth-order aspheric coefficient, and D is a tenth-order aspheric coefficient. Represents.

  Table 11 shows the numerical values of the variable interval, the aperture diameter, the focal length, and the F number (Fno) at the wide-angle end and the telephoto end of the surfaces 2, 9, 11, and 13 whose intervals change with zooming. Yes.

  Table 12 shows the numerical values of Conditional Expression 1 to Conditional Expression 5. In Example 3, (y ′ / L) of conditional expression 1 is 0.188 (0.17 <0.188 <0.23), and (f1 / fw) of conditional expression 2 is 2.075 (2. 0 <2.075 <3.0), (f2 / fw) in conditional expression 3 is 0.854 (0.74 <0.854 <0.86), and (f3 / fw) in conditional expression 4 is 1. 417 (1.0 <1.417 <1.42), and (tan ω × fst / Lst) of conditional expression 5 is 0.325 (0.325 <0.35).

FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 3. FIG. 8 shows spherical aberration, astigmatism, and distortion at the telephoto end in Example 3. It is an aberration diagram showing aberration. 7A and 7A show spherical aberration, FIG. 7B shows astigmatism, and FIG. 7C shows distortion. 7B and 8B, the solid line indicates the value of the d line on the meridional image plane, and the broken line indicates the value of the d line on the sagittal image plane.
As can be seen from FIGS. 7 and 8, according to Example 3, spherical, astigmatism, and distortion aberrations are well corrected at the focal position distance from the wide-angle end to the telephoto end, and the imaging performance is excellent. A variable magnification imaging lens is obtained.

(Example 4)
Tables 13 to 16 show the numerical values of Example 4.
Table 13 shows the radius of curvature (r: mm) and the interval (d: mm) of each lens, diaphragm, and cover glass corresponding to each surface number of the variable magnification imaging lens in Example 4.

  Table 14 shows the aspheric coefficients of the predetermined surfaces of the second lens group 120 and the third lens group 130 including the aspheric surface in Example 4. In Table 14, K is a conic constant, A is a fourth-order aspheric coefficient, B is a sixth-order aspheric coefficient, C is an eighth-order aspheric coefficient, and D is a tenth-order aspheric coefficient. Represents.

  Table 15 shows the numerical values of the variable distance, the aperture diameter, the focal length, and the F number (Fno) at the wide-angle end and the telephoto end of the surfaces 2, 9, 11, and 13 whose intervals change with zooming. Yes.

  Table 16 shows the numerical values of conditional expression 1 to conditional expression 5. In Example 4, (y ′ / L) in conditional expression 1 is 0.178 (0.17 <0.178 <0.23), and (f1 / fw) in conditional expression 2 is 2.358 (2. 0 <2.358 <3.0), (f2 / fw) in conditional expression 3 is 0.791 (0.74 <0.791 <0.86), and (f3 / fw) in conditional expression 4 is 1. 058 (1.0 <1.058 <1.42), and (tan ω × fst / Lst) of conditional expression 5 is 0.341 (0.341 <0.35).

FIG. 9 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end in Example 4. FIG. 10 shows spherical aberration, astigmatism, and distortion at the telephoto end in Example 4. It is an aberration diagram showing aberration. 9A and 9B, spherical aberration is shown, (B) is astigmatism, and (C) is distortion. In FIG. 9 and FIG. 10B, the solid line indicates the value of the d line on the meridional image plane, and the broken line indicates the value of the d line on the sagittal image plane.
As can be seen from FIGS. 9 and 10, according to Example 4, spherical, astigmatism, and distortion aberrations are well corrected at the focal position distance from the wide-angle end to the telephoto end, and the imaging performance is excellent. A variable magnification imaging lens is obtained.

As described above, according to the present embodiment, the imaging optical system is a variable power lens having a three-group configuration. The first lens group 110 includes one lens, the second lens group 120 includes three lenses, Since the three lens groups 130 are configured as a single lens and all the second lens groups 120 are made of plastic, the entire length of the optical system can be shortened. The diameter of the lens can be reduced, and the cost can be reduced.
During zooming, the first lens group 110 can be fixed or varied, and can be handled according to the purpose of use.
In the aberration correction, the lens arrangement is optimized by optimizing the power arrangement of each lens group. Further, the lens arrangement is further reduced by appropriately arranging aspheric surfaces in the second lens group 120 and the third lens group 130. realizable. By optimizing these conditions, there is an advantage that the distortion can be further reduced with high performance in spite of a compact variable power lens.
Further, in the present embodiment, the focus adjustment is performed by the third lens group 130 and moves to the imaging surface measurement from infinity to the closest distance. Therefore, the second lens group 120 and the third lens group 130 at the telephoto end are moved. The distance can be reduced. As a result, the variable magnification optical system can be made compact, and if it is the same size, it is possible to arrange the power without difficulty, and it is possible to achieve higher performance and lower decentration sensitivity.

  In addition, since the three plastic second lens groups 120 have a positive meniscus lens, a negative meniscus lens, and a positive biconvex lens configuration, spherical aberration correction can be favorably performed with a positive meniscus lens. In the negative meniscus lens, it is possible to suppress overcorrection of the ellipsoidal curvature generated in the positive lens, and to suppress the occurrence of coma aberration in parallel with this. Accordingly, it is possible to balance the performance, and there is an advantage that high-performance zooming is possible by suppressing aberration fluctuations accompanying zooming.

  In addition, in the relationship between the focal lengths (fl, f2, f3) of each lens unit and the focal length fw at the wide-angle end where the combined power is strong, by taking the power balance of each lens unit, high-performance and compact zooming A lens can be realized.

  By defining the condition of the exit pupil position with respect to the restriction of the incident angle to the image sensor 142 as a desired condition, it is possible to relax the restriction of the exit pupil while being wide-angle and compact.

2A and 2B are diagrams illustrating a basic configuration of a variable magnification imaging lens, in which FIG. 1A illustrates a lens configuration at a wide angle end, and FIG. 2B illustrates a lens configuration at a telephoto end. In Examples 1-4, it is a figure which shows the surface number provided with respect to each lens which comprises each lens group of a variable magnification imaging lens, a stop, and the cover glass which comprises an imaging part. In Example 1, it is an aberrational figure which shows the spherical aberration, astigmatism, and distortion aberration in a wide angle end. FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end in Example 1. In Example 2, it is an aberrational figure which shows the spherical aberration, astigmatism, and distortion aberration in a wide angle end. In Example 2, it is an aberrational figure which shows the spherical aberration, astigmatism, and distortion aberration in a telephoto end. In Example 3, it is an aberrational figure which shows the spherical aberration, astigmatism, and a distortion aberration in a wide angle end. In Example 3, it is an aberrational figure which shows the spherical aberration, astigmatism, and distortion aberration in a telephoto end. In Example 4, it is an aberrational figure which shows the spherical aberration, astigmatism, and distortion aberration in a wide angle end. In Example 4, it is an aberrational figure which shows the spherical aberration, astigmatism, and distortion aberration in a telephoto end.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Variable magnification imaging lens 110 ... 1st lens group 111 ... Negative meniscus lens 120 ... 2nd lens group 121 ... Positive meniscus lens 122 ... Negative meniscus lens 123 ... Biconvex lens 130 ... 3rd lens group 131 ... Negative Lens 140 ... Imaging unit 141 ... Parallel plane plate made of glass (cover glass)
142: Imaging element 142a: Imaging surface

Claims (6)

A zoom lens having an imaging optical system having a zoom function for an image sensor,
The imaging optical system is arranged in order from the object side,
A first lens group having a single lens structure having negative refractive power;
A second lens group having a positive refractive power as a whole, comprising a three-lens configuration having positive and negative refractive powers;
And a third lens group having a single refractive power having a negative refractive power,
When zooming, the second lens group and the third lens group move on the optical axis,
A zoom ratio of about 2.5 or less, and
The following conditional expression (1) is satisfied ,
The focal lengths of the first lens group, the second lens group, and the third lens group satisfy the following conditional expressions (2), (3), and (4), respectively: Imaging lens.
0.17 <y ′ / L (1)
However, y ′ is the maximum image height on the imaging surface of the imaging device, and L is from the forefront of the optical system when the distance from the top of the lens surface of the optical system on the most object side to the imaging surface on the optical axis is maximum. Each distance to the imaging surface is shown.
2.0 <| f1 | / fw <3.0 (2)
0.74 <f2 / fw <0.86 (3)
1.0 <| f3 | / fw <1.42 (4)
Here, f1 represents the focal length of the first lens group, f2 represents the focal length of the second lens group, f3 represents the focal length of the third lens group, and fw represents the focal length of the optical system at the wide angle end. . 2. The variable magnification imaging lens according to claim 1, wherein the second lens group has at least one aspheric surface, and the third lens group has a one-surface aspheric surface . 3. The variable magnification imaging lens according to claim 2, wherein the third lens group is a negative lens having a concave surface directed toward the image side, and satisfies the following conditional expression (5) .
tan ω × fst / Lst <0.35 (5)
Here, ω represents the maximum incident angle at the wide-angle end, fst represents the combined focal length of the optical system on the image side from the stop at the wide-angle end, and Lst represents the distance from the stop to the imaging surface at the wide-angle end. The second lens group, zooming imaging lens as claimed in any one of the three that are configured by three plastic lenses. The first lens group, zooming imaging lens as claimed in any one of the 4 is a negative meniscus lens the object side and a convex surface facing the first surface. The three lenses of the second lens group, a positive meniscus lens from the object side, a negative meniscus lens, a positive zooming imaging lens according to claims 1, which is configured in any one of 5 biconvex lens .

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