JP5082604B2 - Variable-magnification optical system, imaging device, and digital device - Google Patents

Description

  The present invention relates to a variable power optical system that includes a plurality of lens groups and performs zooming by changing the distance between the lens groups in the optical axis direction, an imaging device including the zooming optical system, and a digital apparatus equipped with the imaging device In particular, the present invention relates to a variable magnification optical system suitable for downsizing.

  In recent years, cellular phones and personal digital assistants (PDAs) have become widespread, and specifications for incorporating compact digital still camera units and digital video units into these devices have become common. Since these devices are very strict in size and cost, they have a small number of pixels and a single-focus optical system consisting of 1 to 3 plastic lenses compared to a normal digital still camera. In general, an imaging apparatus including the above is used. As imaging devices mounted on portable information terminals are rapidly increasing in pixel count and functionality, they can support high pixel imaging devices and not only can shoot subjects away from the photographer. In order to enable photographing even when the distance from the subject cannot be separated as in indoor photographing, a small and wide-angle variable magnification optical system that can be mounted on a mobile phone or the like is required.

  As such a variable magnification optical system, for example, Patent Document 1 discloses a variable magnification optical system in which a first lens unit is fixed in a variable magnification optical system having negative, positive and negative three components, and is downsized. Yes. However, the variable magnification optical system proposed there has a narrow angle of view at the wide-angle end and does not satisfy the above-mentioned demand for wide-angle. Patent Document 2 discloses a variable magnification optical system in which a first lens unit is fixed in a variable magnification optical system having negative, positive, and positive four components. However, the zoom ratio is insufficient at 2 times or less, and the angle of view at the wide-angle end is narrow. In Patent Document 3, the first lens unit is movable in a variable magnification optical system with negative positive, negative, positive four components, but this variable magnification optical system also has a narrow angle of view at the wide-angle end.

In Patent Document 4 and Patent Document 5, in a variable magnification optical system with negative, positive, negative, and positive four components, variable power optics that achieves both wide angle of view and back focus by making all four lens groups movable. A system is disclosed. However, in this configuration, the drive system is complicated because there are many movable groups, and the optical total length is long and the diameter of the front lens is also large. Further, Patent Document 6 discloses that in a variable-magnification optical system having negative, positive, negative, positive, and negative five components, a so-called bending optical system is employed to reduce the thickness of the unit. However, since this structure includes a prism, the cost is high and the thickness is reduced. However, since the total optical length is long, the size reduction is insufficient from the viewpoint of unit volume.
JP-A-2005-55725 Japanese Patent No. 3310854 JP 2001-343584 A JP 2005-266181 A JP-A-2005-352428 JP 2005-33834 A

  In the conventionally proposed variable magnification optical systems such as Patent Documents 1 to 6, if a wide angle is to be achieved, the unit volume can be reduced from the large number of variable magnification groups and the amount of variable magnification movement. Is not fully achieved. In addition, there is a problem that aberration correction is insufficient when further compactification is achieved.

  The present invention has been made in view of such a situation, and sufficiently corrects various aberrations such as spherical aberration, chromatic aberration, and astigmatism while achieving compactness while ensuring a wide angle of view at the wide-angle end. An object of the present invention is to provide a variable magnification optical system.

In order to solve the above technical problem, the present invention provides a variable magnification optical system, an imaging apparatus, and a digital apparatus having the following configurations. Note that the terms used in the following description are defined in the present specification as follows.
(A) A refractive index is a refractive index with respect to the wavelength (587.56 nm) of d line | wire.
(B) Abbe number is determined when the refractive index for d line, F line (486.13 nm) and C line (656.28 nm) is nd, nF, nC and Abbe number is νd, respectively.
νd = (nd−1) / (nF−nC)
The Abbe number νd obtained by the definition formula
(C) The notation regarding the surface shape is a notation based on the paraxial curvature.
(D) As a notation method of optical power, for each single lens constituting a cemented lens, the power when both sides of the lens surface are air is defined as optical power.
(E) Since the resin material used for the composite aspheric lens (the lens formed by applying a thin resin material on the spherical glass material to be the substrate) has only an additional function of the substrate glass material, These optical members are not handled, but are handled in the same manner as when the substrate glass material has an aspherical surface, and the number of lenses is considered to be one. At this time, the lens refractive index is also defined as the refractive index of the glass material serving as the substrate.
(F) When the notation “concave”, “convex” or “meniscus” is used for the lens, these represent the lens shape near the optical axis (near the center of the lens) (based on the paraxial curvature) Notation).

A variable magnification optical system according to one aspect of the present invention includes, in order from the object side, a first lens group having a negative optical power, a second lens group having a positive optical power, and a negative optical power. And a fourth lens group having a positive optical power. During zooming, the second lens group and the third lens group move, and the first lens group moves. A variable magnification optical system in which the lens group and the fourth lens group are fixed,
Wherein the first lens group, even without less and having two negative lenses has at least one aspherical surface,
An aperture stop is provided in the second lens group;
Focusing is performed by the third lens group,
A flat glass is disposed on the image side of the fourth lens group,
Below (1), characterized by satisfying the conditional expression (2) and (8).
0.5 <| f1 | / f2 <0.95 (1)
0.7 <T1 / (fw × ft) ^0.5 <1.5 (2)
0.3 <Bfw / fw <0.6 (8)
F1: Composite focal length of the first lens group
f2: Composite focal length of the second lens group
T1: Thickness on the optical axis from the most object side surface to the most image side surface of the first lens unit
fw: Composite focal length of all optical systems at wide angle end
ft: Composite focal length of all optical systems at the telephoto end
Bfw: distance of back focus at the wide-angle end, in which the flat glass from the lens end to the focal plane is converted into air

  According to this configuration, the first lens group located closest to the object side is a so-called negative lead optical system having negative optical power. For this reason, light rays incident at a large angle from the object side can be quickly relaxed by the negative optical power of the first lens group, which is advantageous in terms of reducing the overall optical length and the size of the front lens diameter. Become. Furthermore, the negative lead configuration can suppress an increase in error sensitivity even when the optical system is made compact. In addition, since at least two lenses having negative optical power are arranged in the first lens group, the negative optical power of each lens is dispersed to produce a wide angle of view at the wide angle end. It is possible to correct aberrations satisfactorily while keeping error sensitivity low. Further, by providing at least one aspheric surface in the first lens group, it is possible to satisfactorily correct curvature of field and distortion without using many lenses in the first lens group. Further, by fixing the first lens group at the time of zooming, it is not necessary to arrange a zooming drive device outside the first lens group, and the size in the outer diameter direction can be reduced. In addition, since the second lens group is provided with an aperture stop, the aperture stop moves together with the second lens group having the largest movement amount. For this reason, not only the increase in the effective lens outer diameter of the second lens group is suppressed, but also the aperture stop can be moved away from the image plane, so that the light beam on the image side is telecentric by the most image side lens group. It becomes easy to approach.

  In addition, while satisfying both compactness and obtaining a sufficient angle of view necessary for the wide-angle side, it is necessary to satisfy the conditional expressions (1) and (2) in order to suppress manufacturing difficulty. Yes. If the upper limit of conditional expression (1) is exceeded, the powers of the first lens group and the second lens group will approach, making it difficult to achieve both a wide field angle at the wide-angle end and a reduction in the overall optical length. If the lower limit of conditional expression (1) is not reached, the negative optical power of the first lens group becomes very strong, which is advantageous for ensuring a wide angle of view at the wide-angle end. Becomes too big. On the other hand, if the upper limit of conditional expression (2) is exceeded, the substantial zooming movement amount of the second lens group becomes small when trying to keep the optical total length compact. For this reason, it is necessary to increase the optical power of the second lens group, and the curvature radius of the lens becomes too small, which makes it difficult to manufacture. On the other hand, if the lower limit of conditional expression (2) is not reached, the power of the negative lens in the first lens group becomes weak and the rear principal point moves away from the image plane. It becomes difficult to ensure the back focus, and the tendency to make it difficult to move the exit pupil away from the image plane becomes remarkable.

In addition, since focusing is performed by the third lens group, it is possible to obtain a clear image up to a close object without causing an increase in the total optical length or an increase in the front lens diameter due to the extension.

Further, since the fourth lens group having positive optical power is provided on the image side of the third lens group, the incident angle of the off-axis light beam on the light receiving surface of the image sensor arranged on the image plane is telecentric. Can be approached.

Further, by limiting the movable lens group at the time of zooming to two of the second lens group and the third lens group, the volume occupied by the driving device can be reduced, and the unit volume can be reduced.

When the variable magnification optical system is miniaturized, the lens always occupies a certain space due to manufacturing limitations, so that the lens space occupying ratio with respect to the entire space of the lens unit becomes relatively high. Therefore, it is necessary to reduce the number of groups and the number of lenses as much as possible even if the accuracy of a single lens is improved. Therefore, by adopting a negative, positive, negative, and positive four-component configuration as described above, the balance between compactness and higher performance than other zoom types, focus performance, manufacturing error sensitivity, and telecentricity of the image plane incident angle should be optimized. Can do. On the other hand, if the upper limit of conditional expression (8) is exceeded, the range in which lenses can be arranged becomes narrow with respect to the total optical length, and it is necessary to further reduce the number of groups and the number of lenses, leading to performance degradation. On the other hand, if the lower limit of conditional expression (8) is not reached, when a flat glass such as an infrared cut filter or a sensor cover is disposed between the image sensor and the lens, the image sensor becomes too close to the image sensor. If the distance between the image sensor and the final lens group becomes too short, dust attached to the final lens group becomes conspicuous.

In the above configuration, the first lens group, not to want to meet the following conditional expression (3).
1.3 <| f1 | / fw <2.5 (3)

  If the upper limit of conditional expression (3) is exceeded, the negative optical power of the first lens group becomes too weak, and it becomes difficult to ensure a wide angle of view at the wide-angle end. On the other hand, if the lower limit of conditional expression (3) is not reached, the negative optical power of the first lens group becomes strong and the light beam diverges greatly, so that the decentration error sensitivity of the second lens group becomes high.

In any of the configurations described above, the most object side lens in the first lens group, not to want to meet the following conditional expression (4).
−3.0 <(r12 + r11) / (r12−r11) <− 1.0 (4)
Where r11: radius of curvature of the object side surface of the most object side lens of the first lens unit
r12: radius of curvature of the image side surface of the lens closest to the object side in the first lens group

  Even if the upper limit of conditional expression (4) is exceeded or less than the lower limit, the spherical aberration becomes too large. For this reason, it is difficult to obtain sufficient image quality when trying to obtain a wide angle of view at the wide-angle end.

In any of the configurations described above, the first lens group has at least one positive lens and at least two negative lens, not to want to meet the following conditional expression (5).
20 <Δν1 (5)
However, Δν1: difference between the Abbe number average value of the positive lens and the Abbe number average value of the negative lens for the lenses in the first lens group.

  According to this configuration, the axial chromatic aberration and lateral chromatic aberration generated by the two negative lenses in the first lens group can be corrected by the positive lens, and the Petzval sum can be reduced. For this reason, it is possible to reduce the aberration fluctuation at the time of zooming, and it is possible to reduce the number of lenses arranged from the second lens group to the image plane. On the other hand, if the lower limit of conditional expression (5) is not reached, the tendency of insufficient correction of axial chromatic aberration becomes prominent.

In any of the configurations described above, the first lens group comprises, in order from the object side, a negative meniscus lens element convex to the object side, a negative lens, not to want to be composed by three positive lenses.

  By configuring the first lens group with three lenses, it is possible to prevent an increase in cost while maintaining high aberration correction capability. Further, by arranging a negative meniscus lens convex on the object side closest to the object side of the first lens group, the incident angle of the light beam can be reduced and the spherical aberration can be reduced. Incidentally, in order to maintain the performance and configure the first lens group with two lenses, it is necessary to make all the surfaces aspherical. For this reason, even if it compares with the case where a 1st lens group is comprised with two lenses, cost reduction can be achieved.

In any of the configurations described above, the second lens group, not to want to meet the following conditional expression (6).
1.1 <f2 / fw <2.5 (6)

  If the upper limit of conditional expression (6) is exceeded, the optical power of the second lens group is too weak, and it becomes difficult to obtain a zoom ratio of about 2 to 3 times. On the other hand, if the lower limit of conditional expression (6) is not reached, the optical power of the second lens group is too strong, the error sensitivity of the second lens group becomes very high, and its manufacture becomes difficult.

In this case, the third lens group, not to want to meet the following conditional expression (7).
1.0 <m3t <2.5 (7)
Where m3t: lateral magnification at the telephoto end of the third lens unit

  If the upper limit of conditional expression (7) is exceeded, lateral chromatic aberration that occurs in the third lens group will increase. If the lower limit of conditional expression (7) is not reached, the third lens group moves to the object side during focusing, so the distance between the second lens group and the third lens group needs to be widened. In order to reduce the amount of movement of the lens group, the optical power of the second lens group must be increased. This increases the error sensitivity of the second lens group.

In any of the configurations described above, the third lens group, not to want to be composed only of a single lens. By configuring the third lens group with a single lens, when the third lens group is a movable group, the lens element can be reduced in weight, the load applied to the drive device can be reduced, and the size of the drive device can be reduced. .

In any of the configurations described above, the second lens group, not to want to be composed of at least one negative lens and at least two positive lenses. In pursuit of downsizing of the variable power optical system, it is necessary to increase the optical power of the positive lens in the second lens group in order to suppress the movement amount of the variable power group. It becomes too high and manufacturing becomes difficult. Therefore, by adopting a configuration in which the second lens group includes two positive lenses, the error sensitivity of each positive lens can be reduced.

In this case, the second lens unit, in order from the object side, a positive lens, a negative lens, not to want to be composed by three positive lenses. By arranging in this order from the object side in the order of positive and negative, the error sensitivity when performing lens adjustment in the second lens group can be optimally balanced.

In any of the configurations described above, it has to desirable to satisfy the conditional expression below SL (9).
1.5 <| EPw / fw | (9)
However, EPw: distance from the exit pupil position of the chief ray at the maximum angle of view to the image plane at the wide angle end

If the lower limit of conditional expression (9), telecentricity of the ray incident angle collapse of the imaging device, even if arranged lens array corresponding to pixels on an imaging surface before, it is difficult to prevent the surrounding illumination intensity .

In any of the configurations described above, an aperture stop is provided on the object side of the second lens group, the aperture stop has to desirable aperture size is fixed. By arranging the aperture stop on the object side of the second lens group, the front lens diameter of the first lens group can be reduced. On the other hand, the distance between the first lens group and the second lens group has a large effect on the optical total length. When the distance is increased, the optical total length is increased by about 2 to 3 times, for example. Therefore, the thickness in the optical axis direction can be reduced by fixing the aperture diameter and simplifying the aperture member.

An imaging apparatus according to another aspect of the present invention includes the above-described zoom optical system and an image sensor that converts an optical image into an electrical signal, and the zoom optical system is on a light receiving surface of the image sensor. it characterized in that it is possible to form an optical image of a subject. According to this configuration, it is possible to realize an imaging apparatus capable of zooming while being ultra-small and high-definition that can be mounted on a mobile phone, a portable information terminal, or the like.

A digital device according to still another aspect of the present invention includes the above- described imaging device, and a control unit that causes the imaging device and the imaging device to perform at least one of photographing a still image and a moving image of a subject, the variable power optical system of the imaging device, characterized by being assembled to allow forms an optical image of a subject on a light receiving surface of the imaging element. Incidentally, the digital equipment has not to demand a portable terminal. According to these configurations, it is possible to realize a digital device equipped with an imaging device capable of scaling while maintaining high definition. The portable terminal is a digital device that is normally carried, such as a cellular phone or a portable information terminal.

  According to the present invention, a variable power optical system that has a variable power ratio of about 2 to 3 times, ensures a wide angle of view at the wide-angle end, achieves a sufficiently compact size, and corrects aberrations well over the entire variable power range. System can be provided. Therefore, it is possible to provide a variable magnification optical system and an imaging apparatus or digital device equipped with the variable magnification optical system in a mode in which high performance and miniaturization are sufficiently achieved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Description of configuration of variable magnification optical system>
FIG. 1 is an optical path diagram (optical path diagram at the wide angle end) showing a configuration example of a variable magnification optical system 1 according to the present invention. The variable magnification optical system 1 forms an optical image of a subject on a light receiving surface (image surface) of an image sensor 16 that converts an optical image into an electrical signal. A first lens group 11 having a positive power, a second lens group 12 having a positive optical power, a third lens group 13 having a negative optical power, and a fourth lens group 14 having a positive optical power. Optical system. In the variable power optical system 1, the second lens group 12 and the third lens group 13 are moved during zooming from the wide-angle end to the telephoto end, and the first lens group 11 and the fourth lens group 14 are fixed. . The variable power optical system 1 illustrated in FIG. 1 has the same configuration as the variable power optical system 1A (see FIG. 4) of Example 1 described later.

  Here, the first lens group 11 includes a negative meniscus lens 111 convex on the object side, a negative meniscus lens 112 concave on the object side, and a biconvex positive lens 113, and the second lens group 12 is biconvex. A positive lens 121, a cemented lens of a biconcave negative lens 122 and a biconvex positive lens 123, the third lens group 13 is composed of only a biconcave negative lens 131, and the fourth lens group 14 is a biconvex lens. An example in which only the positive lens 141 is configured is shown. Here, at least one of the six lens surfaces of the lenses 111, 112, and 113 constituting the first lens group 11 is an aspherical surface. Further, on the object side of the second lens group 12, an optical diaphragm 15 (aperture diaphragm) that moves together with the second lens group 12 at the time of zooming is disposed. An image sensor 16 is disposed on the image side of such a variable magnification optical system 1 via a low-pass filter 17, whereby an object optical image on the object side is aligned along the optical axis AX by the variable magnification optical system 1. The light is guided to the light receiving surface of the image sensor 16 at an appropriate zoom ratio, and an optical image of the subject is captured by the image sensor 16.

  The variable magnification optical system 1 is a negative-positive-negative-positive four-component optical system, and is a negative lead optical system in which the first lens group 11 located closest to the object side has a negative optical power. For this reason, a light beam incident at a large angle from the object side can be quickly relaxed by the negative optical power of the first lens group 11, which is advantageous in terms of downsizing the optical total length and the size of the front lens diameter. It is. Furthermore, the negative lead configuration has an advantage that an increase in error sensitivity can be suppressed even when the optical system is made compact.

  In addition, since the first lens group 11 has two lenses 111 and 112 having negative optical power, the negative optical power of each lens can be dispersed. This makes it possible to correct aberrations satisfactorily while keeping the manufacturing error sensitivity low while maintaining a wide angle of view at the wide-angle end. Further, by providing at least one aspheric surface in the first lens group 11, the curvature of field and distortion can be corrected well in the first lens group 11 with a small number of lenses, such as about three. Furthermore, since the first lens group 11 is fixed at the time of zooming, it is not necessary to arrange a zooming drive device outside the first lens group 11, and the size in the outer diameter direction can be reduced. In addition, since the aperture stop 15 moves together with the second lens group 12 that has the largest movement amount at the time of zooming in the lens group configuration, only an increase in the effective lens outer diameter of the second lens group 12 is suppressed. In addition, the fourth lens group 14 closest to the image side has an advantage that the light rays on the image side can be made close to telecentric.

  There is no particular limitation on which lens surface of the lenses 111, 112, and 113 constituting the first lens group 11 is aspherical, but the lens surface of a lens having negative optical power is aspherical. Is desirable. In the example of FIG. 1, the object side and / or image side lens surfaces of the negative meniscus lenses 111 and 112 are illustrated. In this way, negative distortion occurring in the negative lens can be effectively reduced, and astigmatism can be reduced.

In the variable magnification optical system 1 configured as described above, the focal length of the first lens group 11 is f1, the focal length of the second lens group 12 is f2, and the most object side surface of the first lens group 11 (negative meniscus lens). 111 (object side surface) to the most image surface side surface (image surface side surface of the positive lens 113) on the optical axis is T1, the combined focal length of all optical systems at the wide angle end is fw, and telephoto When the combined focal length of the entire optical system at the end is ft, the following conditional expressions (1) and (2) are satisfied.
0.5 <| f1 | / f2 <0.95 (1)
0.7 <T1 / (fw × ft) ^0.5 <1.5 (2)

  The variable magnification optical system 1 that satisfies the conditional expressions (1) and (2) can achieve both compactness and obtaining a sufficient angle of view necessary for the wide-angle side, and can suppress the difficulty of manufacturing. If the upper limit of conditional expression (1) is exceeded, the powers of the first lens group 11 and the second lens group 12 will approach, making it difficult to achieve both a wide field angle at the wide-angle end and a reduction in the overall optical length. If the lower limit of conditional expression (1) is not reached, the negative optical power of the first lens group 11 becomes very strong, which is advantageous for securing a wide angle of view at the wide-angle end. The diameter becomes too large. On the other hand, if the upper limit of conditional expression (2) is surpassed, the substantial zooming movement amount of the second lens group 12 becomes small when trying to keep the optical total length compact. For this reason, it is necessary to increase the optical power of the second lens group 12, and the radius of curvature of the lens becomes too small, which makes manufacturing difficult. On the other hand, if the lower limit of conditional expression (2) is not reached, the power of the negative lens in the first lens group 11 becomes weak and the rear principal point moves away from the image plane. In particular, it tends to be difficult to ensure the back focus and to make it difficult to move the exit pupil away from the image plane.

Here, it is desirable that the relation | f1 | / f2 of the conditional expression (1) satisfies the following conditional expression (1) ′.
0.60 <| f1 | / f2 <0.95 (1) ′
If the lower limit of (1) ′ in the conditional expression is not reached, the negative power of the first lens group 11 becomes stronger and the error sensitivity tends to be higher than the positive power of the second lens group 12.

Further, it is desirable that the relationship of T1 / (fw × ft) ^0.5 in the conditional expression (2) satisfies the following conditional expression (2) ′.
0.8 <T1 / (fw × ft) ^0.5 <1.5 (2) ′
If the lower limit of conditional expression (2) ′ is not reached, the lens core thicknesses of the lenses 111, 112, and 113 constituting the first lens group 11 having a large lens outer diameter are reduced, so that the manufacturing difficulty of the lens tends to increase. is there.

In the variable magnification optical system 1, it is desirable that the first lens group 11 satisfies the following conditional expression (3).
1.3 <| f1 | / fw <2.5 (3)
If the upper limit of conditional expression (3) is exceeded, the negative optical power of the first lens group 11 becomes too weak, and it becomes difficult to ensure a wide angle of view at the wide-angle end. On the other hand, if the lower limit of conditional expression (3) is not reached, the negative optical power of the first lens group 11 becomes stronger and the light beam diverges greatly, so that the eccentric error sensitivity of the second lens group 12 becomes higher.

The relation of | f1 | / fw in the conditional expression (3) preferably satisfies the following conditional expression (3) ′.
1.4 <| f1 | / fw <1.9 (3) ′
If the upper limit of conditional expression (3) is exceeded, the optical power of the first lens group 11 becomes weak, and the front lens diameter tends to increase by that much, which tends to increase the unit volume. On the other hand, if the lower limit of conditional expression (3) ′ is not reached, the distortion of the first lens group 11 tends to increase.

With respect to the negative meniscus lens 111 which is the most object side lens of the first lens group 11, when the curvature radius of the object side surface is r11 and the curvature radius of the image side surface is r12, the following condition (4) is satisfied. It is desirable to satisfy the formula.
−3.0 <(r12 + r11) / (r12−r11) <− 1.0 (4)
Even if the upper limit of conditional expression (4) is exceeded or below the lower limit, the spherical aberration of the negative meniscus lens 111 becomes too large. For this reason, it is difficult to obtain sufficient image quality when trying to obtain a wide angle of view at the wide-angle end.

As shown in FIG. 1, the first lens group 11 has at least two negative lenses (negative meniscus lenses 111 and 112) and at least one positive lens 113, and the Abbe number of the positive lens 113 (first lens). When the group 11 includes a plurality of positive lenses, the difference between the Abbe number average value) and the Abbe number average value of the negative meniscus lenses 111 and 112 is Δν1, and it is preferable that the following conditional expression (5) is satisfied. .
20 <Δν1 (5)

  With the first lens group 11 having such a lens configuration, axial chromatic aberration and lateral chromatic aberration generated by the negative meniscus lenses 111 and 112 are corrected by the positive lens 113 in the first lens group, and the Petzval sum is corrected. Can be reduced. For this reason, it becomes possible to reduce the aberration fluctuation at the time of zooming, and the number of lenses arranged from the second lens group 12 to the image plane can be reduced. Note that if the lower limit of conditional expression (5) is not reached, the tendency of insufficient correction of axial chromatic aberration becomes prominent.

  As illustrated in FIG. 1, the first lens group 11 includes, in order from the object side, a negative meniscus lens 111 convex toward the object side, a negative meniscus lens 112 (negative lens) concave toward the object side, and a positive lens 113. It is desirable to be composed of three pieces. By configuring the first lens group 11 with three lenses, it is possible to prevent an increase in cost while maintaining high aberration correction capability. Further, by arranging the negative meniscus lens 111 convex on the object side closest to the object side of the first lens group 11, the incident angle of the light beam can be reduced and the spherical aberration can be reduced.

Next, regarding the second lens group 12, it is desirable to satisfy the following conditional expression (6).
1.1 <f2 / fw <2.5 (6)
If the upper limit of conditional expression (6) is exceeded, the optical power of the second lens group 12 is too weak, and it becomes difficult to obtain a zoom ratio of about 2 to 3 times. On the other hand, if the lower limit of conditional expression (6) is not reached, the optical power of the second lens group 12 is too strong, the error sensitivity of the second lens group 12 becomes very high, and its manufacture becomes difficult.

The relation of f2 / fw in the conditional expression (6) preferably satisfies the following conditional expression (6) ′.
1.5 <f2 / fw <1.9 (6) ′
If the upper limit of conditional expression (6) ′ is exceeded, the optical power of the second lens group 12 becomes weak, and the amount of movement at the time of zooming increases, leading to an increase in unit volume. If the lower limit of conditional expression (6) ′ is not reached, the spherical aberration tends to be too large.

  As shown in FIG. 1, the second lens group 12 preferably includes at least two positive lenses 121 and 123 and at least one negative lens 122. When the variable magnification optical system 1 is pursued to be compact, it is necessary to increase the optical power of the positive lens in the second lens group 12 in order to suppress the movement amount of the variable magnification group. This increases the error sensitivity of the second lens group 12 and makes its manufacture difficult. Therefore, by adopting a configuration in which the second lens group 12 includes two positive lenses 121 and 123, the error sensitivity of each positive lens can be reduced.

  In particular, as illustrated in FIG. 1, it is desirable that the second lens group 12 is configured by three lenses of a positive lens 121, a negative lens 122, and a positive lens 123 in order from the object side. By arranging in this order from the object side in the order of positive and negative, the error sensitivity when performing lens adjustment in the second lens group 12 can be optimally balanced.

  Further, it is desirable that the second lens group 12 is disposed in order of a biconvex single lens (positive lens 121) and a cemented lens of a negative lens 122 and a positive lens 123 in order from the object side. As a result, it is possible to appropriately distribute the variable magnification burden of the entire second lens group 12 to the lenses 121, 122, and 123, and to reduce error sensitivity. In addition, this arrangement can sufficiently correct axial chromatic aberration.

  In addition, it is desirable that the second lens group 12 includes a lens made of abnormal partial dispersion glass. When the optical system is composed of only lenses having normal partial dispersion, a secondary spectrum of chromatic aberration remains. In order to reduce this secondary spectrum, a large number of lenses are required. Therefore, the secondary spectrum can be reduced with a small number of lenses by using at least one lens made of an anomalous partial dispersion glass in the second lens group 12. By applying such an anomalous partial dispersion glass in the second lens group 12 having a relatively small effective diameter, it is possible to effectively reduce chromatic aberration while maintaining a cost comparable to that of ordinary glass.

  The positive lens included in the second lens group 12 is preferably provided with an aspherical surface. In the example shown in FIG. 1, it is desirable that the positive lens 121 and / or the positive lens 123 have an aspherical surface. Thereby, the spherical aberration and the coma aberration generated due to the power increase of the second lens group 12 accompanying the downsizing can be corrected satisfactorily.

  In the variable magnification optical system 1, it is desirable that focusing is performed by the third lens group 13. By performing focusing with the third lens group 13, it is possible to obtain a clear image up to an object at a short distance without causing an increase in the total optical length or an increase in the front lens diameter due to the extension.

In this case, when the lateral magnification at the telephoto end of the third lens group 13 is m3t, it is desirable that the third lens group 13 satisfies the following conditional expression (7).
1.0 <m3t <2.5 (7)
If the upper limit of conditional expression (7) is exceeded, lateral chromatic aberration that occurs in the third lens group 13 will increase. If the lower limit of conditional expression (7) is not reached, the third lens group 13 moves to the object side during focusing, so it is necessary to widen the distance between the second lens group 12 and the third lens group 13, and as a result. In order to reduce the amount of movement of the second lens group 12, the optical power of the second lens group 12 must be increased. This increases the error sensitivity of the second lens group 12 and is not preferable.

  The third lens group 13 is preferably composed of only one lens (negative lens 131) as illustrated in FIG. By configuring the third lens group 13 with one lens, when the third lens group 13 is a movable group, the lens element can be reduced in weight, the load applied to the drive device can be reduced, and the size of the drive device can be reduced. Can do.

In the variable magnification optical system 1, when the focal length of the third lens group 13 is f3, it is desirable that the third lens group 13 satisfies the following conditional expression (10).
1.5 <| f3 | / fw <5.0 (10)
If the upper limit of conditional expression (10) is exceeded, the optical power of the third lens group 13 becomes very weak. Therefore, it is necessary to increase the amount of movement when correcting the image plane at the time of zooming, and the optical total length is large. turn into. On the other hand, if the lower limit of conditional expression (10) is not reached, the optical power of the second lens group 13 becomes very strong and the error sensitivity of the third lens group 13 becomes high. Accordingly, it is necessary to reduce the error sensitivity of the third lens group 13 by dividing the lens into a plurality of lenses, and the cost and productivity are deteriorated.

The relation of | f3 | / fw in the conditional expression (10) preferably satisfies the following conditional expression (10) ′.
2.5 <| f3 | / fw <5.0 (10) ′
If the lower limit of conditional expression (10) ′ is not reached, the optical power of the third lens group 13 is too strong, and the light beam is strongly bent by the third lens group, so the decentration error sensitivity tends to increase. For this reason, it is necessary to increase not only the lens accuracy of the third lens group, which is a movable group, but also the accuracy of the lens barrel mechanism, and the cost and productivity deteriorate.

  As shown in FIG. 1, it is desirable that a fourth lens group 14 having positive optical power is provided on the image side of the third lens group 13. By providing the fourth lens group 14, the incident angle of the off-axis light beam on the light receiving surface of the image sensor 16 arranged on the image plane can be made close to telecentric.

In this case, the variable magnification optical system 1 includes only four lens groups (first to fourth lens groups 11 to 14), and a flat glass (low-pass filter 17) is disposed on the image side of the fourth lens group 14. Therefore, it is desirable to satisfy the following conditional expression (8). Bfw is a back focus distance at the wide-angle end where the flat glass from the last lens end (image plane of the positive lens 141) to the focal plane is converted into air.
0.3 <Bfw / fw <0.6 (8)

  When the variable magnification optical system 1 is miniaturized, the lens always occupies a certain space due to manufacturing limitations, so that the lens space occupying ratio with respect to the entire space of the lens unit becomes relatively high. Therefore, it is necessary to reduce the number of groups and the number of lenses as much as possible even if the accuracy of a single lens is improved. By adopting a negative, positive, positive, and positive four-component configuration as in this embodiment, the balance between compactness and higher performance, focus performance, manufacturing error sensitivity, and telecentricity of the image plane incident angle than other zoom types is optimized. be able to. On the other hand, if the upper limit of conditional expression (8) is exceeded, the range in which lenses can be arranged becomes narrow with respect to the total optical length, and it is necessary to further reduce the number of groups and the number of lenses, leading to performance degradation. On the other hand, if the lower limit of conditional expression (8) is not reached, the image sensor 16 and the positive lens 141 become too close, and the low-pass filter 17 and the like disposed between the image sensor 16 and the positive lens 141 are replaced with the image sensor 16. Too close to. If the image sensor 16 and the positive lens 141 are too close to each other, dust attached to the positive lens 141 and the low-pass filter 17 is easily noticeable.

The fourth lens group 14 is fixed at the time of zooming from the wide-angle end to the telephoto end, and preferably satisfies the following conditional expression (9). Note that EPw is the distance from the exit pupil position of the principal ray with the maximum field angle to the image plane at the wide angle end.
1.5 <| EPw / fw | (9)

  By fixing the fourth lens group 14 at the time of zooming, the lens barrel mechanism can be simplified and the positional accuracy can be improved. If the lower limit of conditional expression (9) is not reached, the telecentricity of the light incident angle on the image sensor 16 will be lost, and even if a lens array corresponding to the pixels is arranged in front of the imaging surface, it will be difficult to prevent a decrease in ambient illuminance. .

The zoom optical system 1 preferably satisfies the following conditional expression (11), where ωw is the half field angle at the wide-angle end.
30 ° <ωw (11)
If the lower limit of conditional expression (11) is not reached, the angle of view becomes narrow, which is disadvantageous when a sufficient distance from the subject cannot be taken, such as when shooting indoors.

  Although it has been described above that the first and second lens groups 11 and 12 are preferably provided with aspheric surfaces, the other lens groups (third and fourth lens groups 13 and 14) are also provided with aspheric surfaces. It is desirable. In particular, all lens surfaces facing the air are preferably aspheric. This makes it possible to achieve both ultra-compact and high image quality.

  The variable magnification optical system 1 desirably has at least one pair of cemented lenses. FIG. 1 shows an example in which the second lens group 12 includes a cemented lens of a biconcave negative lens 122 and a biconvex positive lens 123. This makes it easy to achieve both compactness of the optical system and reduction in error sensitivity.

  Further, it is desirable that the variable magnification optical system 1 has only two movable lens groups at the time of variable magnification. In FIG. 1, the second lens group 12 and the third lens group 13 are movable lens groups. By limiting the movable lens group to the zooming group and the zooming image plane correction group, the volume occupied by the driving device for moving the lens group can be reduced, and the lens unit volume can be reduced. Can do.

  The optical aperture 15 is preferably provided on the object side of the second lens group 12, and the aperture diameter is preferably fixed. By arranging the optical aperture 15 on the object side of the second lens group 12, the front lens diameter of the first lens group 11 can be reduced. On the other hand, the distance between the first lens group 11 and the second lens group 12 has a great influence on the overall optical length of the variable magnification optical system 1. When the distance is increased, the optical total length is increased by about 2 to 3 times, for example. Therefore, the thickness in the optical axis direction can be reduced by fixing the aperture diameter and simplifying the aperture member.

  In the variable magnification optical system 1, a mechanical shutter having a function of shielding light from the image sensor 16 may be disposed instead of the optical aperture 15. Such a mechanical shutter is effective in preventing smear when, for example, a CCD (Charge Coupled Device) type is used as the image sensor 16.

  Further, it is desirable to arrange a mechanism for adjusting the amount of light on the image side of the second lens group 12. The mechanism for adjusting the amount of light is, for example, an ND filter for suppressing the influence of diffraction by the diaphragm, the mechanical shutter described above, or the like. When arranging these, it is preferable to arrange them at the stop position where all the light beams pass through the same position in order to avoid unevenness in the amount of light around the center and the periphery of the screen. On the other hand, the distance between the first lens group 11 and the second lens group 12 has a large effect on the optical total length, and if the distance is increased, the optical total length is increased by, for example, about 2 to 3 times. It is difficult to arrange the mechanism at the throttle position. Therefore, by providing a light amount adjustment mechanism on the image side of the second lens group 12, light amount unevenness can be suppressed to the same extent as the aperture position, and compactness can be maintained.

  The variable magnification optical system 1 includes, in order from the object side, a first lens group composed of a negative meniscus lens, a negative lens and a positive lens convex to the object side, a second lens group composed of a biconvex lens and a cemented lens of a negative lens and a positive lens. It is desirable to include a third lens group composed of a negative lens and a fourth lens group composed of a positive lens. By arranging the first lens group in the above order, it is easy to secure the back focus at the wide angle end, and it is possible to satisfactorily correct astigmatism and lateral chromatic aberration of off-axis light having a wide field angle. By configuring the second lens group 12 with three positive and negative lenses, the error sensitivity can be reduced with two positive lenses, and the error sensitivity when performing lens adjustment can be optimally balanced. By making the third lens group a negative lens, both shortening of the optical total length and correction of astigmatism can be achieved. Further, by using the fourth lens group as a positive lens, the off-axis ray incident angle on the light receiving surface of the image sensor 16 can be made close to telecentric. The variable magnification optical system 1 shown in FIG. 1 satisfies this requirement, and the variable magnification optical system 1 has a preferable configuration also in the meaning shown here.

  Next, constituent materials of the variable magnification optical system 1 will be described. There is no restriction | limiting in particular about the material of each lens which comprises the said 1st-4th lens group 11-14, The optical material which consists of various glass materials and resin (plastic) material can be used. However, if a resin material is used, it is lightweight and can be mass-produced with an injection mold or the like. Therefore, compared with the case of manufacturing with a glass material, the manufacturing cost can be reduced and the variable magnification optical system 1 can be reduced in weight. Is advantageous. Therefore, it is desirable that the variable magnification optical system 1 includes at least one lens made of a resin material. Of course, two or more lenses made of a resin material may be provided.

  When at least two lenses made of resin material are used, the negative lens in the third lens group 13 (bi-concave negative lens 131 in FIG. 1) and the positive lens in the fourth lens group 14 (positive meniscus). The lens 141) is preferably made of a resin material. In this case, the back focus shift accompanying the environmental temperature change can be suppressed small.

  As this resin material lens, it is desirable to use a lens molded using a material in which particles having a maximum length of 30 nanometers or less, particularly inorganic particles, are dispersed in the resin material. By using such a resin material lens, the refractive index change due to the temperature change of the resin material lens can be made extremely small.

  In general, when fine particles are mixed in a transparent resin material, light scattering occurs and the transmittance decreases, so that it is difficult to use as an optical material. However, by making the size of the microparticles smaller than the wavelength of the transmitted light beam, it is possible to substantially prevent scattering. The refractive index of the resin material decreases as the temperature increases. For example, the refractive index of inorganic fine particles increases as the temperature increases. Therefore, it is possible to make almost no change in the refractive index by using these temperature dependencies so as to cancel each other. Specifically, by dispersing particles having a maximum length of 30 nanometers or less in a resin material serving as a base material, a resin material having extremely low temperature dependency of the refractive index can be obtained. For example, by dispersing fine particles of niobium oxide (Nb2O5) in acrylic, the refractive index change due to temperature change can be reduced. Therefore, by using a resin material in which such particles are dispersed for at least one lens, it is possible to suppress a back focus shift caused by a change in the environmental temperature of the entire zoom optical system 1.

  Here, the temperature change of the refractive index will be described in detail. The temperature change A of the refractive index can be expressed by the following formula (12) by differentiating the refractive index n by the temperature t based on the Lorentz-Lorentz formula.

  In the case of a plastic material, the contribution of the second term is generally smaller than that of the first term in the equation (12) and can be almost ignored. For example, in the case of PMMA resin, the linear expansion coefficient α is 7 × 10 −5, and when it is substituted into the above equation (12), A = −1.2 × 10 −4 [/ ° C.], which is almost the same as the actually measured value. To do. Specifically, it is preferable to suppress the temperature change A of the refractive index, which was conventionally about −1.2 × 10 −4 [/ ° C.], to an absolute value of less than 8 × 10 −5 [/ ° C.]. The absolute value is preferably less than 6 × 10 −5 [/ ° C.]. By making it less than 6 × 10 −5 [/ ° C.], it is possible to suppress the back focus fluctuation amount when the environmental temperature changes to about half. The temperature change A (= dn / dT) of the refractive index of the plastic material applicable to the variable magnification optical system 1 is shown in Table 1.

  In the variable magnification optical system 1, when an aspheric glass lens is used, the aspheric glass lens may be molded by a mold, or may of course be a composite type of a glass material and a resin material. The mold type is suitable for mass production, but the glass material is limited. On the other hand, the composite type has the advantage that there are many glass materials that can be used as a substrate and the degree of freedom in design is high. Since an aspherical lens using a high refractive material is generally difficult to mold, in the case of a single-sided aspherical surface, the advantages of the composite type can be maximized.

  A conventionally known cam mechanism or stepping motor can be used as a drive source for driving each lens group, diaphragm, shutter, and the like provided in the variable magnification optical system 1. In addition, when the amount of movement is small or the weight of the drive group is light, it is possible to drive each group independently while suppressing the increase in volume and power consumption of the drive unit by using an ultra-small piezoelectric actuator. Thus, the imaging lens device including the variable magnification optical system 1 can be further downsized.

  The image sensor 16 photoelectrically converts the R, G, and B component image signals into a predetermined image processing circuit according to the amount of light of the subject image formed by the variable magnification optical system 1 and outputs the image signal to a predetermined image processing circuit. It is. For example, as the imaging device 16, R (red), G (green), and B (blue) color filters are pasted in a checkered pattern on the surface of each CCD of an area sensor in which the CCD is two-dimensionally arranged. In addition, it is possible to use a so-called Bayer type single-chip color area sensor. In addition to such a CCD image sensor, a CMOS image sensor, a VMIS image sensor, or the like can also be used.

  The low-pass filter 17 is a parallel plate-like optical component that is disposed on the light receiving surface of the image sensor 16 and removes noise components. As this low-pass filter 17, for example, a birefringence low-pass filter made of quartz or the like whose predetermined crystal axis direction is adjusted, a phase-type low-pass filter that realizes a required optical cutoff frequency characteristic by a diffraction effect, etc. Is applicable. Note that the low-pass filter 17 is not necessarily provided, and an infrared cut filter may be used to reduce noise included in the image signal of the image sensor 16 instead of the optical low-pass filter 17 described above. Good. Further, an infrared reflection coating may be applied to the surface of the optical low-pass filter 17 so that both filter functions can be realized by one.

<Description of digital equipment incorporating variable magnification optical system>
Next, a digital apparatus incorporating the variable magnification optical system 1 as described above will be described. FIG. 2 is an external configuration diagram of the camera-equipped mobile phone 2 showing an embodiment of the digital device according to the present invention. In the present invention, the digital device includes a digital still camera, a video camera, a digital video unit, a personal digital assistant (PDA), a personal computer, a mobile computer, or peripheral devices (mouse, scanner, printer). Etc.).

  2A shows the operation surface of the mobile phone 2, and FIG. 2B shows the back surface of the operation surface, that is, the back surface. The mobile phone 2 has an antenna 21 at the top, a rectangular display 22 on the operation surface, an image switching button 23 for starting an image shooting mode and switching between still image and moving image shooting, and a variable for controlling zooming. A double button 24, a shutter button 25, and a dial button 26 are provided. The enlargement / reduction button 24 is printed with “T” representing telephoto at the upper end portion and “W” representing wide angle at the lower end portion, and each enlargement operation is instructed by pressing the print position. It consists of possible two-contact type switches. Further, the mobile phone 2 incorporates an imaging device 27 constituted by the variable magnification optical system 1 described above.

  FIG. 3 is a functional block diagram showing an electrical functional configuration related to imaging of the mobile phone 2. The cellular phone 2 includes an imaging unit 30, an image generation unit 31, an image data buffer 32, an image processing unit 33, a driving unit 34, a control unit 35, a storage unit 36, and an I / F unit 37 for the imaging function. It is prepared for.

  The imaging unit 30 includes an imaging device 27 and an imaging element 16. The imaging device 27 includes a variable magnification optical system 1 as shown in FIG. 1 and a lens drive device (not shown) for driving the lens in the optical axis direction to perform variable magnification and focusing. Light rays from the subject are imaged on the light receiving surface of the image sensor 16 by the variable magnification optical system 1 and become an optical image of the subject.

  The image sensor 16 converts the optical image of the subject imaged by the variable magnification optical system 1 into electrical signals (image signals) of R (red), G (green), and B (blue) color components. It outputs to the image generation part 31 as an image signal of each color of G and B. The imaging device 16 controls imaging operations such as imaging of either a still image or a moving image or reading of output signals of each pixel (horizontal synchronization, vertical synchronization, transfer) in the imaging device 16 under the control of the control unit 35. Is done.

  The image generation unit 31 performs amplification processing, digital conversion processing, and the like on the analog output signal from the image sensor 16 and determines an appropriate black level, γ correction, and white balance adjustment (WB adjustment) for the entire image. Then, well-known image processing such as contour correction and color unevenness correction is performed to generate image data of each pixel from the image signal. The image data generated by the image generation unit 31 is output to the image data buffer 32.

  The image data buffer 32 is a memory that temporarily stores image data and is used as a work area for performing processing described later on the image data by the image processing unit 33. For example, a RAM (Random Access Memory) is used. Etc.

  The image processing unit 33 is a circuit that performs image processing such as resolution conversion on the image data in the image data buffer 32. It is also possible to configure the image processing unit 33 to correct aberrations that could not be corrected by the variable magnification optical system 1 as necessary.

  The drive unit 34 drives a plurality of lens groups of the variable magnification optical system 1 so as to perform desired variable magnification and focusing by a control signal output from the control unit 35.

  The control unit 35 includes, for example, a microprocessor and the like. The control unit 35 includes an imaging unit 30, an image generation unit 31, an image data buffer 32, an image processing unit 33, a drive unit 34, a storage unit 36, and an I / F unit 37. Control the behavior. That is, the control unit 35 controls the imaging device 27 and the imaging device 16 to perform at least one of the still image shooting and the moving image shooting of the subject.

  The storage unit 36 is a storage circuit that stores image data generated by still image shooting or moving image shooting of a subject, and includes, for example, a ROM (Read Only Memory) and a RAM. That is, the storage unit 36 has a function as a still image memory and a moving image memory.

  The I / F unit 37 is an interface that transmits / receives image data to / from an external device. For example, the I / F unit 37 is an interface that conforms to a standard such as USB or IEEE1394.

  An imaging operation of the mobile phone 2 configured as described above will be described. When shooting a still image, first, the image switching mode 23 is pressed to activate the image shooting mode. Here, the still image shooting mode is activated by pressing the image switching button 23 once, and the video switching mode is switched by pressing the image switching button 23 again in this state. That is, the control unit 35 of the main body of the mobile phone 2 that has received an instruction from the image switching button 23 causes the imaging device 27 and the imaging device 16 to perform at least one of still image shooting and moving image shooting of the object on the object side.

  When the still image capturing mode is activated, the control unit 35 controls the image capturing device 27 and the image sensor 16 to capture a still image, and drives a lens driving device (not shown) of the image capturing device 27 to perform focusing. Do. As a result, the focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor 16, converted into R, G, and B color component image signals, and then output to the image generation unit 31. . The image signal is temporarily stored in the image data buffer 32, subjected to image processing by the image processing unit 33, transferred to a display memory (not shown), and guided to the display 22. Then, the photographer can adjust the main subject to fit in a desired position on the screen by looking at the display 22. By pressing the shutter button 25 in this state, a still image can be obtained. That is, the image data is stored in the storage unit 36 as a still image memory.

  At this time, when zoom shooting is performed because the subject is at a position away from the photographer or a close subject is desired to be enlarged, the state is detected by pressing the printing portion of the upper end “T” of the scaling button 24, The control unit 35 executes lens driving for zooming according to the pressing time, and causes the zooming optical system 1 to perform zooming continuously. Further, when it is desired to reduce the enlargement ratio of the subject such as when zooming is excessive, the state is detected by pressing the lower end “W” of the scaling button 24, and the control unit 35 performs scaling optics. By controlling the system 1, zooming is continuously performed according to the pressing time. In this way, the enlargement ratio can be adjusted using the scaling button 24 even for a subject far from the photographer. Then, as in normal normal shooting, an enlarged still image can be obtained by adjusting the main subject to be in a desired position on the screen and pressing the shutter button 25.

  When moving image shooting is performed, the image switching button 23 is pressed once to activate the still image shooting mode, and then the image switching button 23 is pressed again to switch to the movie shooting mode. As a result, the control unit 35 controls the imaging device 27 and the imaging device 16 to take a moving image. Thereafter, in the same manner as in the case of still image shooting, the photographer looks into the display 22 and adjusts so that the image of the subject obtained through the imaging device 27 is within a desired position on the screen. At this time, similarly to the still image shooting, the enlargement ratio of the subject image can be adjusted by using the scaling button 24. By pressing the shutter button 25 in this state, moving image shooting is started. During the photographing, the enlargement ratio of the subject can be changed at any time by the scaling button 24.

  At the time of moving image shooting, the control unit 35 controls the image pickup device 27 and the image sensor 16 to take a moving image, and drives a lens driving device (not shown) of the image pickup device 27 to perform focusing. As a result, the focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor 16, converted into R, G, and B color component image signals, and then output to the image generation unit 31. . The image signal is temporarily stored in the image data buffer 32, subjected to image processing by the image processing unit 33, transferred to the display memory, and guided to the display 22. Here, when the shutter button 25 is pressed again, the moving image shooting is completed. The captured moving image is guided to and stored in the storage unit 36 as a moving image memory.

<Description of More Specific Embodiment of Variable-Magnification Optical System>
A specific configuration of the variable power optical system 1 constituting the imaging device 27 mounted on the variable power optical system 1 as shown in FIG. Will be described with reference to FIG.

  FIG. 4 is a cross-sectional view (optical path diagram) in which the optical axis (AX) is cut longitudinally and shows the arrangement of lens groups in the variable magnification optical system 1A of Example 1. In FIG. 4 and the following three optical path diagrams shown in FIGS. 5 to 13, the lens arrangement at the wide-angle end [W], the middle stage at the middle point [M], and the lower stage at the telephoto end [T]. Respectively. In addition, the arrows in the figure indicate the movement trajectory of each lens group during zooming.

  The lens group of Example 1 includes a first lens group (Gr1) having negative optical power as a whole and a second lens group having positive optical power (in order from the object side (left side in FIG. 4)). Gr2), a third lens group (Gr3) having negative optical power, and a fourth lens group (Gr4) having positive optical power.

  Specifically, in the variable magnification optical system 1A of Example 1, each lens group is configured as follows in order from the object side. The first lens group (Gr1) includes a negative meniscus lens convex to the object side (first lens L1), a negative meniscus lens concave to the object side (second lens L2), and a biconvex positive lens (third lens L3). ). The second lens group (Gr2) includes a biconvex positive lens (fourth lens L4) and a cemented lens of a biconcave negative lens (fifth lens L5) and a biconvex positive lens (sixth lens L6). . On the object side of the second lens group (Gr2), an optical stop (ST) that moves together with the second lens group (Gr2) at the time of zooming is provided. The third lens group (Gr3) is composed of one biconcave negative lens (seventh lens L7). The fourth lens group (Gr4) is composed of one biconvex positive lens (eighth lens L8). On the image side of the fourth lens group (Gr4), the light receiving surface of the image sensor (SR) is arranged via a parallel plate (FT). The parallel plate (FT) corresponds to an optical low-pass filter, an infrared cut filter, a cover glass of an image sensor, or the like. It should be noted that a mechanical shutter may be disposed in place of the optical diaphragm (ST) (the same applies to Examples 2 to 10). In this embodiment, only a continuous variable magnification optical system is shown. However, a bifocal switching variable magnification optical system with the same optical configuration may be used as a matter of course in order to achieve a more compact size.

  The number ri (i = 1, 2, 3,...) Given to each lens surface in the optical path diagram at the wide-angle end [W] in FIG. 4 is the i-th lens surface (when counted from the object side). However, the cemented surface of the lens is counted as one surface.), And the surface marked with “*” in ri indicates that it is an aspherical surface. The optical diaphragm (ST), both surfaces of the parallel plate (FT), and the light receiving surface of the image sensor (SR) are also handled as one surface. Such a treatment is the same in the optical path diagrams (FIGS. 5 to 13) for other embodiments to be described later, and the meanings of the reference numerals in the drawings are basically the same as those in FIG. However, it does not mean that they are exactly the same. For example, the lens surface closest to the object is denoted by the same reference numeral (r1) throughout the drawings, but these curvatures are the same throughout the embodiments. It does not mean that.

  Under such a configuration, light rays incident from the object side sequentially pass through the first, second, third and fourth (Gr1, Gr2, Gr3, Gr4) and parallel plate (FT) along the optical axis AX. Passes and forms an optical image of the object on the light receiving surface of the image sensor (SR). In the image sensor (SR), the optical image corrected in the parallel plate (FT) is converted into an electrical signal. This electric signal is subjected to predetermined digital image processing, image compression processing, and the like as necessary, and is recorded as a digital video signal in a memory of a mobile phone, a portable information terminal, or other digital device by wire or wirelessly Or transmitted to.

  As shown in FIG. 4, in Example 1, the first lens group (Gr1) and the fourth lens group (Gr4) are fixed at the time of zooming, and the second lens group (Gr2) and the third lens group (Gr3) are fixed. ) Is movable when zooming. Specifically, at the time of zooming from the wide angle end (W) to the telephoto end (T), the second lens group (Gr2) is linearly moved in the direction approaching the object, and the third lens group (Gr3) is moved to the object. It is moved to draw a convex trajectory. However, including the following embodiments, the direction and amount of movement of these lens groups can vary depending on the optical power of the lens group, the lens configuration, and the like. For example, in FIG. 4, even if it is drawn so as to move linearly like the second lens group (Gr2), it includes a case where it is a convex curve on the object side or the image side, etc. This includes the case of a U-turn shape.

  The construction data of each lens in the variable magnification optical system 1A of Example 1 is shown below. In Example 1, the fourth, seventh, and eighth lenses (L4, L7, and L8) are double-sided aspherical lenses, and the first and second lenses (L1, L2) are single-sided aspherical lenses. The second, seventh, and eighth lenses (L2, L7, and L8) are resin lenses, and the other lenses are glass lenses.

Numerical example 1
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 * 15.930 0.900 1.77250 49.78
2 4.234 3.601
3 * -7.550 0.800 1.53048 55.72
4 -3.50220E + 07 0.100
5 20.037 1.388 1.84666 23.78
6 -51.713 Variable 7 (Aperture) ∞ 0.000
8 * 7.145 2.795 1.58913 61.24
9 * -10.637 1.118
10 -32.916 0.600 1.83400 37.35
11 5.311 2.242 1.49700 81.61
12 -5.876 Variable 13 * -24.738 0.800 1.53048 55.72
14 * 11.006 Variable 15 * 8.544 3.500 1.53048 55.72
16 * -138.459 1.225
17 ∞ 0.300 1.51680 64.20
18 ∞ 0.500
19 (image plane) ∞ 0.000

Aspheric data first surface
K = 0, A = 6.3941E-04, B = -3.66009E-06, C = 4.7293E-08, D = 2.3216E-09, E = 0.000, F = 0.000
Third side
K = 0, A = -2.4284E-04, B = -3.8734E-06, C = 1.1136E-06, D = -7.2951E-08, E = 0.000, F = 0.000
8th page
K = 0, A = -7.0798E-04, B = -3.5119E-06, C = 3.1337E-06, D = -2.3466E-06, E = 3.5675E-07, F = -1.8390E-08
9th page
K = 0, A = 5.1490E-04, B = 3.5555E-05, C = -1.7170E-05, D = 2.2520E-06, E = -1.5928E-07, F = 3.7241E-09
13th page
K = 0, A = -2.7173E-03, B = 5.6175E-04, C = -6.5730E-05, D = -1.7276E-07, E = 1.1373E-06, F = -9.0463E-08
14th page
K = 0, A = -2.5154E-03, B = 5.6214E-04, C = -6.6982E-05, D = 1.7465E-06, E = 6.2264E-07, F = -5.1052E-08
15th page
K = 0, A = 2.0378E-04, B = 8.1441E-06, C = -1.8058E-07, D = -1.2721E-10, E = 0.000, F = 0.000
16th page
K = 0, A = 1.1058E-03, B = 2.4558E-05, C = -2.3292E-06, D = 1.3531E-08, E = 0.000, F = 0.000

Various data Zoom ratio 2.88
Wide angle Medium telephoto Focal length 4.690 8.674 13.520
F number 3.55 4.94 6.00
Half angle of view 38.34 22.15 14.42
Statue height 3.57 3.57 3.57
Total lens length 36.4 36.4 36.4
BF 1.94 1.92 1.94
d6 9.956 4.300 0.500
d12 3.464 4.494 8.579
d14 3.211 7.836 7.551

Zoom lens group data Group Start surface Focal length 1 1 -7.365
2 8 8.526
3 13 -14.248
4 15 15.296

  In the above surface data, the surface number corresponds to the number i of the symbol ri (i = 1, 2, 3,...) Given to each lens surface shown in FIG. The surface marked with * in the number i indicates an aspherical surface (aspherical refractive optical surface or a surface having a refractive action equivalent to an aspherical surface). “R” is the radius of curvature of each surface (unit is mm), “d” is the distance between the lens surfaces on the optical axis in the infinite focus state (axis upper surface distance), and “nd” is the distance between each lens. The refractive index, “νd”, indicates the Abbe number. Since each surface of the optical diaphragm (ST), the plane parallel plate (FT) and the cover glass (CG), and the light receiving surface of the image sensor (SR) are flat surfaces, their curvature radii are ∞.

  The above-mentioned aspheric surface data includes the conical coefficient K and the aspheric surface coefficients A, B, C, D, E, F, and G of the surface that is an aspheric surface (the surface that is marked with * in the surface data). Each value. The aspherical shape of the optical surface uses a local orthogonal coordinate system (x, y, z) in which the vertex of the surface is the origin and the direction from the object toward the image sensor is the positive direction of the z-axis. It is defined by an expression.

However, z: displacement in the z-axis direction at the position of height h (based on the surface vertex)
h: Height in the direction perpendicular to the z-axis (h ² = x ² + y ² )
c: Paraxial curvature (= 1 / radius of curvature)
A, B, C, D, E, F, G: 4th, 6th, 8th, 10th, 12th, 14th, and 16th order aspheric coefficients
k: Conical coefficient

  From the left side of FIG. 14, spherical aberration (LONGITUDINAL SPHERICAL ABERRATION), astigmatism (ASTIGMATISM), and distortion (DISTORTION) of the entire optical system in Example 1 under the lens arrangement and configuration as described above are shown. Shown in order. In this figure, the upper part represents the aberration at the wide-angle end (W), the middle part represents the aberration at the intermediate point (M), and the lower part represents the aberration at the telephoto end (T). Further, the horizontal axis of spherical aberration and astigmatism represents the focal position shift in mm, and the horizontal axis of distortion aberration represents the amount of distortion as a percentage (%) of the total. The vertical axis of spherical aberration is indicated by a value normalized by the incident height, while the vertical axis of astigmatism and distortion is indicated by the height of the image (image height) (unit: mm).

  Further, the spherical aberration diagram shows three different wavelengths: red (dashed wavelength 656.28 nm) with a dashed line, yellow (so-called d-line; wavelength 587.56 nm) with a solid line, and blue (wavelength 435.84 nm) with a broken line. The aberrations when using light are shown respectively. In the figure of astigmatism, symbols s and t represent results on the sagittal (radial) plane and the tangential (meridional) plane, respectively. Further, the diagrams of astigmatism and distortion are the results when the yellow line (d line) is used. As can be seen from FIG. 14, the lens group of Example 1 has excellent optical characteristics with distortion within approximately 5% at any of the wide-angle end (W), intermediate point (M), and telephoto end (T). Is shown. Further, the focal length (unit: mm) and the F value at the wide angle end (W), the intermediate point (M), and the telephoto end (T) in Example 1 are shown in Tables 2 and 3 below. From these tables, it can be seen that the variable magnification optical system 1A of Example 1 can realize a bright optical system with a short focus.

  FIG. 5 is a cross-sectional view of the lens group in the variable magnification optical system 1B of Example 2 with the optical axis (AX) cut longitudinally. The variable magnification optical system 1B includes a first lens group (Gr1) having a negative optical power as a whole, an optical aperture stop (ST), and a second optical power having a positive optical power as a whole. It consists of a lens group (Gr2), a third lens group (Gr3) having negative optical power, and a fourth lens group (Gr4) having positive optical power.

  More specifically, the first lens group (Gr1) includes, in order from the object side, a negative meniscus lens (L1) convex toward the object side, a negative meniscus lens (L2) concave toward the object side, and a biconvex positive lens (L3). Become. The second lens group (Gr2) is composed of, in order from the object side, a biconvex positive lens (L4) and a cemented lens of a biconcave negative lens (L5) and a biconvex positive lens (L6). The third lens group (Gr3) is composed of one biconcave negative lens (L7). The fourth lens group (Gr4) is composed of one biconvex positive lens (L8).

  In the zoom optical system 1B having such a lens configuration, the second lens group (Gr2) approaches the object as shown in FIG. 5 when zooming from the wide angle end (W) to the telephoto end (T). The third lens group (Gr3) is moved linearly so as to draw a convex trajectory on the object side. The first lens group (Gr1) and the fourth lens group (Gr4) are fixed during zooming. The optical diaphragm (ST) moves together with the second lens group (Gr2) at the time of zooming.

  The construction data of each lens in the variable magnification optical system 1B according to Example 2 is shown below. In Example 2, the first, fourth, seventh, and eighth lenses (L1, L4, L7, and L8) are double-sided aspheric lenses. The second, seventh, and eighth lenses (L2, L7, and L8) are resin lenses, and the other lenses are glass lenses.

Numerical example 2
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 * 14.906 0.900 1.68980 52.82
2 * 4.093 3.909
3 -6.601 0.800 1.53048 55.72
4 -207.892 0.127
5 35.271 1.465 1.84666 23.78
6 -26.664 Variable 7 (Aperture) ∞ 0.000
8 * 7.144 2.565 1.58913 61.24
9 * -10.716 1.053
10 -965.282 0.600 1.83400 37.35
11 4.600 2.198 1.49700 81.61
12 -7.251 Variable 13 * -31.583 0.800 1.53048 55.72
14 * 10.688 Variable 15 * 8.482 3.500 1.53048 55.72
16 * -348.025 1.168
17 ∞ 0.300 1.51680 64.20
18 ∞ 0.500
19 (image plane) ∞ 0.000

Aspheric data first surface
K = 0, A = 5.4436E-04, B = -4.0253E-06, C = 2.6379E-07, D = -8.8755E-10, E = 0.000, F = 0.000
Second side
K = 0, A = -1.2997E-04, B = -9.6459E-06, C = 0.000, D = 0.000, E = 0.000, F = 0.000
8th page
K = 0, A = -1.1557E-03, B = -8.8498E-06, C = -8.9361E-06, D = -2.2483E-07, E = 1.7478E-07, F = -1.8390E-08
9th page
K = 0, A = -2.1832E-04, B = 7.8469E-06, C = -2.0120E-05, D = 2.6254E-06, E = -1.9709E-07, F = 3.7241E-09
13th page
K = 0, A = -2.6625E-03, B = 5.3150E-04, C = -6.5193E-05, D = 1.5041E-07, E = 1.1143E-06, F = -9.0463E-08
14th page
K = 0, A = -2.5046E-03, B = 5.4960E-04, C = -7.0120E-05, D = 2.5589E-06, E = 5.7323E-07, F = -5.1052E-08
15th page
K = 0, A = -2.5114E-06, B = 1.5202E-05, C = -4.7659E-07, D = 6.0784E-09, E = 0.000, F = 0.000
16th page
K = 0, A = 5.8768E-04, B = 3.1967E-05, C = -1.6867E-06, D = -4.2615E-10, E = 0.000, F = 0.000

Various data Zoom ratio 2.88
Wide angle Medium telephoto Focal length 4.690 8.674 13.521
F number 3.52 4.91 6.00
Half angle of view 38.45 22.15 14.40
Statue height 3.57 3.57 3.57
Total lens length 36.4 36.4 36.4
BF 1.87 1.85 1.88
d6 9.883 4.257 0.500
d12 3.269 4.313 8.579
d14 3.463 8.046 7.536

Zoom lens group data Start surface Focal length 1 1 -7.340
2 8 8.454
3 13 -14.956
4 15 15.662

  FIG. 6 is a cross-sectional view of the lens group in the variable magnification optical system 1C according to the third embodiment, taken along the optical axis (AX). The variable magnification optical system 1C includes a first lens group (Gr1) having a negative optical power as a whole, an optical stop (ST), and a second optical power having a positive optical power as a whole. It consists of a lens group (Gr2), a third lens group (Gr3) having negative optical power, and a fourth lens group (Gr4) having positive optical power.

  More specifically, the first lens group (Gr1) includes, in order from the object side, a negative meniscus lens (L1) convex toward the object side, a negative meniscus lens (L2) concave toward the object side, and a biconvex positive lens (L3). Become. The second lens group (Gr2) is composed of, in order from the object side, a biconvex positive lens (L4) and a cemented lens of a negative meniscus lens (L5) convex to the object side and a biconvex positive lens (L6). The third lens group (Gr3) is composed of one biconcave negative lens (L7). The fourth lens group (Gr4) is composed of one biconvex positive lens (L8).

  In the zoom optical system 1C having such a lens configuration, as shown in FIG. 6, the second lens group (Gr2) approaches the object when zooming from the wide-angle end (W) to the telephoto end (T). The third lens group (Gr3) is moved linearly so as to draw a convex trajectory on the object side. The first lens group (Gr1) and the fourth lens group (Gr4) are fixed during zooming. The optical diaphragm (ST) moves together with the second lens group (Gr2) at the time of zooming.

  The construction data of each lens in the variable magnification optical system 1C according to Example 3 is shown below. In Example 3, the first, fourth, seventh, and eighth lenses (L1, L4, L7, and L8) are double-sided aspheric lenses. The first, seventh, and eighth lenses (L1, L7, and L8) are resin lenses, and the other lenses are glass lenses.

Numerical Example 3
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 * 24.867 0.900 1.53048 55.72
2 * 3.978 4.107
3 -6.665 0.800 1.58913 61.25
4 -45.599 0.100
5 46.140 1.277 1.84666 23.78
6 -26.660 Variable 7 (Aperture) ∞ 0.000
8 * 7.208 2.601 1.58913 61.24
9 * -10.808 1.017
10 819.753 0.600 1.83400 37.35
11 4.615 2.188 1.49700 81.61
12 -7.356 Variable 13 * -30.170 0.800 1.53048 55.72
14 * 10.938 Variable 15 * 8.169 3.500 1.53048 55.72
16 * -436.268 1.259
17 ∞ 0.300 1.51680 64.20
18 ∞ 0.500
19 (image plane) ∞ 0.000

Aspheric data first surface
K = 0, A = 7.5002E-04, B = -5.2259E-06, C = -1.1931E-07, D = 7.5347E-09, E = 0.000, F = 0.000
Second side
K = 0, A = -1.5802E-04, B = -2.3994E-06, C = -6.5082E-08, D = -1.7909E-07, E = 0.000, F = 0.000
8th page
K = 0, A = -1.1417E-03, B = -2.1116E-05, C = -2.8218E-06, D = -1.4748E-06, E = 2.7680E-07, F = -1.8390E-08
9th page
K = 0, A = -2.3237E-04, B = 7.8995E-06, C = -2.0411E-05, D = 2.7827E-06, E = -2.0702E-07, F = 3.7241E-09
13th page
K = 0, A = -2.6644E-03, B = 5.5276E-04, C = -6.3339E-05, D = -8.4566E-07, E = 1.2116E-06, F = -9.0463E-08
14th page
K = 0, A = -2.5155E-03, B = 5.5470E-04, C = -6.4427E-05, D = 1.1765E-06, E = 6.7825E-07, F = -5.1052E-08
15th page
K = 0, A = 1.1268E-04, B = 1.4979E-05, C = -5.9022E-07, D = 1.0667E-08, E = 0.000, F = 0.000
16th page
K = 0, A = 1.0694E-03, B = 2.5213E-05, C = -2.1603E-06, D = 1.2084E-08, E = 0.000, F = 0.000

Various data Zoom ratio 2.88
Wide angle Medium telephoto Focal length 4.690 8.674 13.520
F number 3.52 4.91 6.00
Half angle of view 38.45 22.15 14.40
Statue height 3.57 3.57 3.57
Total lens length 36.4 36.4 36.4
BF 1.96 1.95 1.97
d6 9.910 4.261 0.500
d12 3.272 4.346 8.646
d14 3.370 7.945 7.405

Zoom lens group data Group Start surface Focal length 1 1 -7.456
2 8 8.467
3 13 -15.032
4 15 15.157

  FIG. 7 is a cross-sectional view of the lens group in the variable magnification optical system 1 </ b> D according to the fourth embodiment, taken along the optical axis (AX). The variable magnification optical system 1D includes a first lens group (Gr1) having a negative optical power as a whole, an optical stop (ST), and a second optical power having a positive optical power as a whole. It consists of a lens group (Gr2), a third lens group (Gr3) having negative optical power, and a fourth lens group (Gr4) having positive optical power.

  More specifically, the first lens group (Gr1) includes, in order from the object side, a negative meniscus lens (L1) convex toward the object side, a negative meniscus lens (L2) convex toward the object side, and a positive meniscus lens convex toward the object side ( L3). The second lens group (Gr2) is composed of, in order from the object side, a biconvex positive lens (L4) and a cemented lens of a biconcave negative lens (L5) and a biconvex positive lens (L6). The third lens group (Gr3) is composed of one biconcave negative lens (L7). The fourth lens group (Gr4) is composed of one biconvex positive lens (L8).

  In the zoom optical system 1D having such a lens configuration, when zooming from the wide angle end (W) to the telephoto end (T), as shown in FIG. 7, the second lens group (Gr2) approaches the object. The third lens group (Gr3) is moved linearly so as to draw a convex trajectory on the object side. The first lens group (Gr1) and the fourth lens group (Gr4) are fixed during zooming. The optical diaphragm (ST) moves together with the second lens group (Gr2) at the time of zooming.

  The construction data of each lens in the variable magnification optical system 1D according to Example 4 is shown below. In Example 4, the fourth, seventh, and eighth lenses (L4, L7, and L8) are double-sided aspherical lenses, and the second lens (L2) is a single-sided aspherical lens. The second, seventh, and eighth lenses (L2, L7, and L8) are resin lenses, and the other lenses are glass lenses.

Numerical Example 4
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 12.360 0.900 1.74330 49.22
2 4.302 2.178
3 72.324 0.800 1.53048 55.72
4 * 5.448 1.488
5 10.842 1.748 1.84666 23.78
6 43.029 Variable 7 (Aperture) ∞ 0.000
8 * 7.824 2.119 1.58913 61.24
9 * -11.737 1.133
10 -57.545 0.774 1.83400 37.35
11 5.259 2.265 1.49700 81.61
12 -5.634 Variable 13 * -18.326 0.800 1.53048 55.72
14 * 10.650 Variable 15 * 9.662 3.500 1.53048 55.72
16 * -37.543 1.600
17 ∞ 0.300 1.51680 64.20
18 ∞ 0.500
19 (image plane) ∞ 0.000

Aspheric data 4th surface
K = 0, A = -1.4325E-03, B = -5.3095E-05, C = 1.0037E-06, D = -1.1654E-07
8th page
K = 0, A = -1.0157E-03, B = -4.5599E-06, C = -1.1236E-05, D = 2.2567E-07
9th page
K = 0, A = 6.0256E-05, B = 1.1308E-05, C = -1.6303E-05, D = 7.6457E-07
13th page
K = 0, A = -2.8354E-03, B = 4.4000E-04mC = -2.5861E-05, D = 6.0849E-07
14th page
K = 0, A = -2.3541E-03, B = 4.4842E-04, C = -2.9190E-05, D = 9.3393E-07
15th page
K = 0, A = 1.1196E-04, B = 9.8257E-06, C = 1.4795E-07, D = 8.0934E-09
16th page
K = 0, A = 3.6577E-04, B = 3.2946E-05, C = -1.4689E-06, D = 6.4734E-08

Various data Zoom ratio 2.88
Wide angle Medium telephoto Focal length 4.755 8.794 13.708
F number 3.50 4.91 6.00
Half angle of view 38.26 22.05 14.31
Statue height 3.57 3.57 3.57
Total lens length 36.4 36.4 36.4
BF 2.32 2.29 2.28
d6 10.094 4.472 0.652
d12 4.071 4.910 8.230
d14 2.229 7.012 7.511

Zoom lens group data Group Start surface Focal length 1 1 -7.694
2 8 8.459
3 13 -12.577
4 15 14.867

  FIG. 8 is a cross-sectional view of the lens group in the variable magnification optical system 1E according to Example 5 taken along the optical axis (AX). The variable magnification optical system 1E includes, in order from the object side, a first lens group (Gr1) having a negative optical power as a whole, an optical stop (ST), and a second lens having a positive optical power as a whole. It consists of a lens group (Gr2), a third lens group (Gr3) having negative optical power, and a fourth lens group (Gr4) having positive optical power.

  More specifically, the first lens group (Gr1) includes, in order from the object side, a negative meniscus lens (L1) convex toward the object side, a negative meniscus lens (L2) convex toward the object side, and a positive meniscus lens convex toward the object side ( L3). The second lens group (Gr2) is composed of, in order from the object side, a biconvex positive lens (L4) and a cemented lens of a biconcave negative lens (L5) and a biconvex positive lens (L6). The third lens group (Gr3) is composed of one biconcave negative lens (L7). The fourth lens group (Gr4) is composed of one biconvex positive lens (L8).

  In the zoom optical system 1E having such a lens configuration, as shown in FIG. 8, the second lens group (Gr2) approaches the object when zooming from the wide-angle end (W) to the telephoto end (T). The third lens group (Gr3) is moved linearly so as to draw a convex trajectory on the object side. The first lens group (Gr1) and the fourth lens group (Gr4) are fixed during zooming. The optical diaphragm (ST) moves together with the second lens group (Gr2) at the time of zooming.

  The construction data of each lens in the variable magnification optical system 1E according to Example 5 is shown below. In Example 5, the second, fourth, seventh, and eighth lenses (L2, L4, L7, and L8) are double-sided aspheric lenses. The seventh and eighth lenses (L7, L8) are resin lenses, and the other lenses are glass lenses.

Numerical Example 5
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 10.109 0.900 1.74330 49.22
2 4.328 2.134
3 * 43.554 0.800 1.68980 52.82
4 * 5.481 1.490
5 10.219 1.309 1.84666 23.78
6 40.495 Variable 7 (Aperture) ∞ 0.000
8 * 7.272 2.625 1.58913 61.24
9 * -10.908 1.113
10 -30.422 0.600 1.83400 37.35
11 5.362 2.277 1.49700 81.61
12 -5.804 Variable 13 * -63.376 0.800 1.53048 55.72
14 * 9.644 Variable 15 * 8.073 3.500 1.53048 55.72
16 * -3344.509 1.600
17 ∞ 0.300 1.51680 64.20
18 ∞ 0.500
19 (image plane) ∞ 0.000

Aspheric data 3rd surface
K = 0, A = -5.9068E-05, B = 2.8485E-06, C = 9.2582E-08, D = -1.4202E-09
4th page
K = 0, A = -1.2667E-03, B = -2.9252E-05, C = 4.0636E-07, D = -8.4368E-08
8th page
K = 0, A = -7.4378E-04, B = 1.2941E-06, C = -3.8689E-06, D = 2.9357E-08
9th page
K = 0, A = 4.2215E-04, B = 7.7049E-06, C = -5.9697E-06, D = 1.7474E-07
13th page
K = 0, A = -3.1850E-03, B = 3.5270E-04, C = -1.0169E-05, D = -4.6541E-08
14th page
K = 0, A = -3.1295E-03, B = 3.7690E-04, C = -1.5651E-05, D = 3.8859E-07
15th page
K = 0, A = 3.0278E-04, B = -1.0410E-05, C = 9.8902E-08, D = -3.0292E-09
16th page
K = 0, A = 1.6436E-03, B = -1.7142E-05, C = -3.2198E-06, D = 6.6957E-08

Various data Zoom ratio 2.88
Wide angle Medium telephoto Focal length 4.689 8.673 13.519
F number 2.88 3.99 4.92
Half angle of view 38.45 22.17 14.39
Statue height 3.57 3.57 3.57
Total lens length 36.4 36.4 36.4
BF 2.33 2.30 2.27
d6 10.250 4.512 0.659
d12 3.510 4.735 9.641
d14 2.790 7.304 6.250

Zoom lens group data Group Start surface Focal length 1 1 -7.670
2 8 8.680
3 13 -15.719
4 15 15.188

  FIG. 9 is a cross-sectional view of the lens group in the variable magnification optical system 1F of Example 6 taken along the optical axis (AX). The variable magnification optical system 1F includes a first lens group (Gr1) having a negative optical power as a whole, an optical stop (ST), and a second optical power having a positive optical power as a whole. It consists of a lens group (Gr2), a third lens group (Gr3) having negative optical power, and a fourth lens group (Gr4) having positive optical power.

  More specifically, the first lens group (Gr1) includes, in order from the object side, a negative meniscus lens (L1) convex toward the object side, a negative biconcave lens (L2), and a positive meniscus lens (L3) convex toward the object side. Become. The second lens group (Gr2) is composed of, in order from the object side, a biconvex positive lens (L4) and a cemented lens of a biconcave negative lens (L5) and a biconvex positive lens (L6). The third lens group (Gr3) is composed of one biconcave negative lens (L7). The fourth lens group (Gr4) is composed of one biconvex positive lens (L8).

  In the zoom optical system 1F having such a lens configuration, the second lens group (Gr2) approaches the object as shown in FIG. 9 when zooming from the wide-angle end (W) to the telephoto end (T). The third lens group (Gr3) is moved linearly so as to draw a convex trajectory on the object side. The first lens group (Gr1) and the fourth lens group (Gr4) are fixed during zooming. The optical diaphragm (ST) moves together with the second lens group (Gr2) at the time of zooming.

  The construction data of each lens in the variable magnification optical system 1F according to Example 6 is shown below. In Example 6, the first, fourth, seventh, and eighth lenses (L1, L4, L7, and L8) are double-sided aspherical lenses, and the second lens (L2) is a single-sided aspherical lens. The seventh and eighth lenses (L7, L8) are resin lenses, and the other lenses are glass lenses.

Numerical Example 6
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 * 13.974 0.900 1.68980 52.82
2 * 4.006 2.578
3 -15.816 0.800 1.68980 52.82
4 * 9.459 1.137
5 10.068 1.182 1.84666 23.78
6 39.447 Variable 7 (Aperture) ∞ 0.000
8 * 7.242 3.030 1.58913 61.24
9 * -10.862 1.083
10 -53.924 0.600 1.83400 37.35
11 5.054 2.260 1.49700 81.61
12 -5.763 Variable 13 * -22.348 0.800 1.53048 55.72
14 * 10.930 Variable 15 * 8.319 2.615 1.53048 55.72
16 * -60.901 1.200
17 ∞ 0.300 1.51680 64.20
18 ∞ 0.500
19 (image plane) ∞ 0.000

Aspheric data first surface
K = 0, A = 9.0901E-04, B = 9.8762E-07, C = 0.000, D = 0.000
Second side
K = 0, A = 1.0409E-04, B = 2.6956E-05, C = 2.7251E-06, D = 5.2070E-08
4th page
K = 0, A = 6.7858E-04, B = -4.5137E-05, C = 1.1365E-06, D = 3.2477E-08
8th page
K = 0, A = -8.1459E-04, B = -1.5389E-05, C = -1.9961E-06, D = -1.8855E-07
9th page
K = 0, A = 3.6095E-04, B = 1.9442E-05, C = -1.2197E-05, D = 7.4714E-07
13th page
K = 0, A = -3.8902E-03, B = 3.5456E-04, C = -1.2919E-05, D = 1.6618E-07
14th page
K = 0, A = -3.5017E-03, B = 3.4542E-04, C = -1.4617E-05, D = 3.1137E-07
15th page
K = 0, A = 3.5903E-04, B = -2.3535E-06, C = 2.5711E-07, D = -3.3699E-10
16th page
K = 0, A = 6.3896E-04, B = 2.9328E-05, C = -1.8486E-06, D = 1.9576E-08

Various data Zoom ratio 2.88
Wide angle Medium telephoto Focal length 4.224 7.814 12.181
F number 3.79 5.21 6.02
Half angle of view 41.30 24.36 15.95
Statue height 3.57 3.57 3.57
Total lens length 36.4 36.4 36.4
BF 1.91 1.93 1.87
d6 9.930 4.635 0.686
d12 3.958 5.719 13.185
d14 3.626 7.160 3.644

Zoom lens group data Group Start surface Focal length 1 1 -5.860
2 8 8.330
3 13 -13.664
4 15 13.921

  FIG. 10 is a cross-sectional view of the lens group in the variable magnification optical system 1 </ b> G according to Example 7 with the optical axis (AX) cut longitudinally. In the variable magnification optical system 1G, each lens group in order from the object side is a first lens group (Gr1) having a negative optical power as a whole, an optical stop (ST), and a second lens having a positive optical power as a whole. It consists of a lens group (Gr2), a third lens group (Gr3) having negative optical power, and a fourth lens group (Gr4) having positive optical power.

  More specifically, the first lens group (Gr1) includes, in order from the object side, a negative meniscus lens (L1) convex toward the object side, a negative biconcave lens (L2), and a positive meniscus lens (L3) convex toward the object side. Become. The second lens group (Gr2) is composed of, in order from the object side, a biconvex positive lens (L4) and a cemented lens of a biconcave negative lens (L5) and a biconvex positive lens (L6). The third lens group (Gr3) is composed of one biconcave negative lens (L7). The fourth lens group (Gr4) is composed of one biconvex positive lens (L8).

  In the zoom optical system 1G having such a lens configuration, when zooming from the wide angle end (W) to the telephoto end (T), as shown in FIG. 10, the second lens group (Gr2) approaches the object. The third lens group (Gr3) is moved linearly so as to draw a convex trajectory on the object side. The first lens group (Gr1) and the fourth lens group (Gr4) are fixed during zooming. The optical diaphragm (ST) moves together with the second lens group (Gr2) at the time of zooming.

  The construction data of each lens in the variable magnification optical system 1G according to Example 7 is shown below. In Example 7, the first, fourth, seventh, and eighth lenses (L1, L4, L7, and L8) are double-sided aspherical lenses, and the second lens (L2) is a single-sided aspherical lens. The seventh and eighth lenses (L7, L8) are resin lenses, and the other lenses are glass lenses.

Numerical Example 7
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 * 1090.975 0.900 1.68980 52.82
2 * 5.065 3.809
3 -23.828 0.800 1.68980 52.82
4 * 5.734 0.529
5 5.931 2.036 1.84666 23.78
6 15.750 Variable 7 (Aperture) ∞ 0.000
8 * 6.817 2.282 1.58913 61.24
9 * -10.225 0.777
10 -40.638 0.600 1.83400 37.35
11 4.969 2.267 1.49700 81.61
12 -5.187 Variable 13 * -39.362 0.800 1.53048 55.72
14 * 10.129 Variable 15 * 8.387 2.500 1.53048 55.72
16 * -35.737 1.139
17 ∞ 0.300 1.51680 64.20
18 ∞ 0.500
19 (image plane) ∞ 0.000

Aspheric data first surface
K = 0, A = 1.3328E-03, B = -4.8496E-07, C = -3.0913E-07, D = 3.8300E-09
Second side
K = 0, A = 1.3924E-04, B = 6.0490E-05, C = 5.9121E-06, D = -1.0115E-07
4th page
K = 0, A = 1.6293E-03, B = -1.1625E-04, C = 7.8464E-06, D = -1.1167E-07
8th page
K = 0, A = -1.0821E-03, B = -8.0052E-05, C = 1.4806E-05, D = -3.9464E-06
9th page
K = 0, A = 3.5743E-04, B = 4.2762E-05, C = -2.7061E-05, D = 1.3456E-06
13th page
K = 0, A = -3.7659E-03, B = 3.0505E-04, C = -1.4484E-05, D = 3.7222E-07
14th page
K = 0, A = -3.3036E-03, B = 3.1926E-04, C = -1.6476E-05, D = 4.5646E-07
15th page
K = 0, A = 4.7071E-04, B = 3.2153E-06, C = 6.7799E-07, D = -1.2033E-08
16th page
K = 0, A = 9.0896E-04, B = 4.4387E-05, C = -1.4545E-06, D = -1.9078E-08

Various data Zoom ratio 2.88
Wide angle Medium telephoto Focal length 3.332 6.163 9.599
F number 3.88 5.25 6.00
Half angle of view 47.90 30.11 19.86
Statue height 3.57 3.57 3.57
Total lens length 36.4 36.4 36.4
BF 1.84 1.87 1.82
d6 9.500 4.525 0.935
d12 3.152 4.994 13.104
d14 4.609 7.742 3.222

Zoom lens group data Group Start surface Focal length 1 1 -4.566
2 8 7.623
3 13 -15.037
4 15 13.007

  FIG. 11 is a cross-sectional view of the lens group in the variable magnification optical system 1H according to Example 8 taken along the optical axis (AX). The variable magnification optical system 1H includes a first lens group (Gr1) having a negative optical power as a whole, an optical stop (ST), and a second optical power having a positive optical power as a whole. It consists of a lens group (Gr2) and a third lens group (Gr3) having negative optical power.

  More specifically, the first lens group (Gr1) includes, in order from the object side, a negative meniscus lens (L1) convex toward the object side, a negative biconcave lens (L2), and a positive meniscus lens (L3) convex toward the object side. Become. The second lens group (Gr2) is composed of, in order from the object side, a biconvex positive lens (L4) and a cemented lens of a negative meniscus lens (L5) convex to the object side and a biconvex positive lens (L6). The third lens group (Gr3) is composed of one biconcave negative lens (L7).

  In the zoom optical system 1H having such a lens configuration, as shown in FIG. 11, the second lens group (Gr2) approaches the object when zooming from the wide angle end (W) to the telephoto end (T). The third lens group (Gr3) is moved linearly so as to draw a convex trajectory on the object side. The first lens group (Gr1) is fixed during zooming. The optical diaphragm (ST) moves together with the second lens group (Gr2) at the time of zooming.

  The construction data of each lens in the variable magnification optical system 1H according to Example 8 is shown below. In Example 8, the second, fourth, and seventh lenses (L2, L4, and L7) are double-sided aspherical lenses, and the first lens (L1) is a single-sided aspherical lens. The seventh (L7) is a resin lens, and the other lenses are glass lenses.

Numerical Example 8
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 13.539 0.900 1.74330 49.22
2 * 5.917 3.369
3 * -64.403 1.443 1.68980 52.82
4 * 5.334 1.560
5 7.855 1.168 1.84666 23.78
6 14.576 Variable 7 (Aperture) ∞ 0.000
8 * 6.081 2.501 1.58913 61.24
9 * -28.575 1.228
10 70.348 0.600 1.83400 37.35
11 4.777 2.329 1.49700 81.61
12 -5.773 Variable 13 * -26.972 0.800 1.53048 55.72
14 * 20.440 Variable 15 ∞ 0.300 1.51680 64.20
16 ∞ 0.500
17 (image plane) ∞ 0.000

Aspheric data 2nd surface
K = 0, A = -6.7215E-04, B = -1.3356E-05, C = -4.7567E-07, D = -1.2906E-08
Third side
K = 0, A = -6.7457E-04, B = -2.8015E-05, C = 3.1073E-07, D = 2.8004E-08
4th page
K = 0, A = 3.3420E-05, B = -4.2514E-05, C = -4.3916E-07, D = 1.7175E-07
8th page
K = 0, A = -2.5115E-04, B = 4.4607E-06, C = -1.4917E-06, D = -1.1620E-08
9th page
K = 0, A = 9.9445E-04, B = 6.0888E-05, C = -1.3474E-05, D = 1.0430E-06
13th page
K = 0, A = -2.7186E-03, B = 2.6061E-04, C = -3.2537E-05, D = 2.5157E-06
14th page
K = 0, A = -2.0837E-03, B = 2.4945E-04, C = -3.0067E-05, D = 2.1196E-06

Various data Zoom ratio 2.88
Wide angle Medium telephoto Focal length 4.759 8.791 13.693
F number 4.15 5.67 6.70
Half angle of view 38.10 22.06 14.35
Statue height 3.57 3.57 3.57
Total lens length 36.4 36.4 36.4
BF 7.65 12.23 9.31
d6 9.840 4.530 0.880
d12 3.058 3.723 10.272
d14 6.904 11.549 8.650

Zoom lens group data group Start surface Focal length 1 1 -6.084
2 8 8.132
3 13 -21.792

  FIG. 12 is a cross-sectional view of the lens group in the variable magnification optical system 1I according to the ninth example, taken along the optical axis (AX). The variable magnification optical system 1I includes a first lens group (Gr1) having a negative optical power as a whole, an optical stop (ST), and a second optical power having a positive optical power as a whole. It consists of a lens group (Gr2), a third lens group (Gr3) having negative optical power, and a fourth lens group (Gr4) having positive optical power.

  More specifically, the first lens group (Gr1) includes, in order from the object side, a negative meniscus lens (L1) convex toward the object side and a negative meniscus lens (L2) concave toward the object side. The second lens group (Gr2) includes, in order from the object side, a biconvex positive lens (L3) and a cemented lens of a negative meniscus lens (L4) convex to the object side and a biconvex positive lens (L5). The third lens group (Gr3) is composed of one biconcave negative lens (L6). The fourth lens group (Gr4) is composed of one biconvex positive lens (L7).

  In the variable power optical system 1I having such a lens configuration, as shown in FIG. 12, the second lens group (Gr2) approaches the object when zooming from the wide angle end (W) to the telephoto end (T). The third lens group (Gr3) is moved linearly so as to draw a convex trajectory on the object side. The first lens group (Gr1) and the fourth lens group (Gr4) are fixed during zooming. The optical diaphragm (ST) moves together with the second lens group (Gr2) at the time of zooming.

  The construction data of each lens in the variable magnification optical system 1I according to Example 9 is shown below. In Example 9, the first, second, third, sixth, and seventh lenses (L1, L2, L3, L6, and L7) are double-sided aspheric lenses. The sixth and seventh lenses (L6, L7) are resin lenses, and the other lenses are glass lenses.

Numerical Example 9
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 * 19.549 0.900 1.68980 52.82
2 * 3.552 2.586
3 * -13.218 3.600 1.80542 26.13
4 * -17.712 Variable 5 (Aperture) ∞ 0.000
6 * 9.110 1.324 1.58913 61.24
7 * -15.320 3.137
8 16.607 0.600 1.83400 37.35
9 4.867 2.198 1.49700 81.61
10 -8.259 Variable 11 * -11.505 0.800 1.53048 55.72
12 * 17.068 Variable 13 * 10.956 3.500 1.53048 55.72
14 * -26.138 0.907
15 ∞ 0.300 1.51680 64.20
16 ∞ 0.500
17 (image plane) ∞ 0.000

Aspheric data first surface
K = 0, A = 2.7141E-03, B = -1.7806E-04, C = 4.9376E-06, D = -7.9272E-08, E = 0.000, F
= 0.000
Second side
K = 0, A = 3.3213E-03, B = -3.0482E-05, C = -3.3343E-06, D = -1.3096E-06, E = -9.5004E-08, F = -1.2736E-08
Third side
K = 0, A = 1.4777E-04, B = 1.2983E-05, C = 2.0039E-07, D = -1.0083E-06, E = 0.000, F = 0.000
4th page
K = 0, A = -3.0445E-04, B = -5.6089E-06, C = -3.7320E-06, D = 2.9010E-07, E = 0.000, F = 0.000
6th page
K = 0, A = -5.3950E-04, B = 5.5666E-05, C = -1.2006E-05, D = 2.9209E-07, E = 2.3617E-07, F = -1.8558E-08
7th page
K = 0, A = 2.2860E-05, B = 5.1397E-05, C = -1.4882E-05, D = 2.5140E-06, E = -2.0495E-07, F = 1.0036E-08
11th page
K = 0, A = -5.2940E-04, B = 6.9803E-04, C = -4.6783E-05, D = -1.2601E-06, E = 3.2679E-08, F = 4.3692E-08
12th page
K = 0, A = -2.1552E-04, B = 7.3135E-04, C = -7.0988E-05, D = 5.9242E-06, E = -7.2365E-07, F = 7.0493E-08
13th page
K = 0, A = -3.3687E-04, B = 5.4626E-05, C = -1.1412E-06, D = 4.6528E-09, E = 0.000, F = 0.000
14th page
K = 0, A = 4.5263E-04, B = 3.6561E-05, C = 1.6871E-06, D = -1.5352E-07, E = 0.000, F = 0.000

Various data Zoom ratio 2.40
Wide angle Medium telephoto Focal length 4.699 8.644 11.260
F number 3.59 4.94 5.57
Half angle of view 38.15 21.95 17.01
Statue height 3.52 3.52 3.52
Total lens length 37.1 37.1 37.1
BF 1.61 1.60 1.56
d4 9.835 4.268 2.008
d10 2.500 3.740 5.601
d12 4.493 8.819 9.218

Zoom lens group data Group Start surface Focal length 1 1 -6.455
2 6 8.389
3 11 -12.831
4 13 15.045

  FIG. 13 is a cross-sectional view of the lens group in the variable magnification optical system 1J of Example 10 taken along the optical axis (AX). In the variable magnification optical system 1G, each lens group in order from the object side is a first lens group (Gr1) having a negative optical power as a whole, an optical stop (ST), and a second lens having a positive optical power as a whole. It consists of a lens group (Gr2), a third lens group (Gr3) having negative optical power, and a fourth lens group (Gr4) having positive optical power.

  More specifically, the first lens group (Gr1) includes, in order from the object side, a negative meniscus lens (L1) convex toward the object side, a negative meniscus lens (L2) convex toward the object side, and a positive bilens lens (L3). Become. The second lens group (Gr2) is composed of, in order from the object side, a biconvex positive lens (L4) and a cemented lens of a biconcave negative lens (L5) and a biconvex positive lens (L6). The third lens group (Gr3) is composed of one biconcave negative lens (L7). The fourth lens group (Gr4) is composed of one biconvex positive lens (L8).

  In the zoom optical system 1J having such a lens configuration, the second lens group (Gr2) approaches the object as shown in FIG. 13 when zooming from the wide-angle end (W) to the telephoto end (T). The third lens group (Gr3) is moved linearly so as to draw a convex trajectory on the object side. The first lens group (Gr1) and the fourth lens group (Gr4) are fixed during zooming. The optical diaphragm (ST) moves together with the second lens group (Gr2) at the time of zooming.

  The construction data of each lens in the variable magnification optical system 1J according to Example 10 is shown below. In Example 10, the third, fourth, seventh, and eighth lenses (L3, L4, L7, and L8) are double-sided aspheric lenses. The seventh and eighth lenses (L7, L8) are resin lenses, and the other lenses are glass lenses.

Numerical Example 10
Unit mm
Surface data Surface number r d nd νd
Object ∞ ∞
1 10.556 0.900 1.74330 49.22
2 4.671 2.048
3 33.679 0.800 1.72916 54.67
4 5.242 1.202
5 * 20.931 2.196 1.80542 26.13
6 * -36.014 Variable 7 (Aperture) ∞ 0.000
8 * 8.084 2.445 1.58913 61.24
9 * -12.126 1.163
10 -52.297 0.600 1.83400 37.35
11 5.866 2.197 1.49700 81.61
12 -5.635 Variable 13 * -20.900 0.800 1.53048 55.72
14 * 10.772 Variable 15 * 8.571 3.500 1.53048 55.72
16 * -136.411 1.600
17 ∞ 0.300 1.51680 64.20
18 ∞ 0.500
19 (image plane) ∞ 0.000

Aspheric data 5th surface
K = 0, A = 4.3301E-04, B = -7.2908E-07, C = 4.0218E-07, D = 3.4843E-08, E = -6.4078E-10
6th page
K = 0, A = -3.5147E-04, B = -2.1785E-05, C = 4.1711E-07, D = -5.4667E-09, E = -2.5968E-09
8th page
K = 0, A = -7.6759E-04, B = 1.7113E-05, C = -8.3040E-06, D = 4.8816E-07, E = 0.000
9th page
K = 0, A = 3.7470E-04, B = 2.5159E-05, C = -9.2438E-06, D = 5.2595E-07, E = 0.000
13th page
K = 0, A = -2.6833E-03, B = 4.0464E-04, C = -1.0763E-05, D = 8.5966E-08, E = 0.000
14th page
K = 0, A = -2.4717E-03, B = 4.2353E-04, C = -1.7319E-05, D = 7.5200E-07, E = 0.000
15th page
K = 0, A = 1.5535E-04, B = -5.6365E-06, C = -1.3912E-07, D = 1.4416E-08, E = 0.000
16th page
K = 0, A = 1.2053E-03, B = -1.2275E-05, C = -2.8565E-06, D = 8.8087E-08, E = 0.000

Various data Zoom ratio 2.88
Wide angle Medium telephoto Focal length 4.758 8.798 13.712
F number 3.548 4.939 5.997
Half angle of view 39.473 22.843 14.805
Image height 3.720 3.720 3.720
Total lens length 36.4 36.4 36.4
BF 2.32 2.29 2.27
d6 9.949 4.305 0.500
d12 3.996 4.922 8.548
d14 2.304 7.022 7.201

Zoom lens group data Group Start surface Focal length 1 1 -7.773
2 8 8.475
3 13 -13.284
4 15 15.330

  The spherical aberration, astigmatism, and distortion aberration of the variable magnification optical systems 1B to 1J of Examples 2 to 10 under the lens arrangement and configuration as described above are shown in FIGS. In these figures, the spherical aberration diagrams show the aberrations when three lights having different wavelengths are used, as in FIG. 14, red with a dashed line, yellow with a solid line, and blue with a broken line. . The lens groups in any of the examples show excellent optical characteristics with distortion within approximately 5% at any of the wide-angle end (W), the midpoint (M), and the telephoto end (T).

  In addition, the focal lengths (unit: mm) and F values at the wide angle end (W), the intermediate point (M), and the telephoto end (T) in the variable magnification optical systems 1B to 1J of Examples 2 to 10 are shown in Table 2. And Table 3 respectively. From these tables, it can be seen that, similarly to Example 1, a bright optical system with a short focal point can be realized.

  Table 4 shows numerical values obtained when the above-described conditional expressions (1) to (11) are applied to the variable magnification optical systems 1A to 1J of Examples 1 to 10, respectively.

  As described above, according to the variable magnification optical systems 1A to 1J according to Examples 1 to 10, the zoom ratio is about 2 to 3 times, a wide angle of view is secured at the wide angle end, and sufficient compactness is achieved. While achieving this, it is possible to provide a variable magnification optical system in which aberrations are well corrected over the entire variable magnification range. Therefore, it is possible to provide a variable magnification optical system and an imaging apparatus or digital device equipped with the variable magnification optical system in a mode in which high performance and miniaturization are sufficiently achieved.

It is a figure which shows typically the structure of the variable magnification optical system which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is an external appearance block diagram of the camera-equipped mobile telephone which mounts the variable magnification optical system based on this invention, Comprising: (a) is an external appearance block diagram which shows the operation surface, (b) is an external appearance structure which shows the back surface of an operation surface. FIG. It is a functional block diagram which shows the structure of the function part which concerns on the imaging of the mobile telephone as an example of the digital apparatus which comprises the variable magnification optical system which concerns on this invention. It is sectional drawing which shows the wide angle end optical path figure of the variable magnification optical system which concerns on Example 1 of this invention. 6 is a cross-sectional view illustrating an optical path diagram of a variable magnification optical system according to Example 2. FIG. 6 is a cross-sectional view illustrating an optical path diagram of a variable magnification optical system according to Example 3. FIG. 6 is a cross-sectional view illustrating an optical path diagram of a variable magnification optical system according to Example 4. FIG. 10 is a cross-sectional view illustrating an optical path diagram of a variable magnification optical system according to Example 5. FIG. 10 is a cross-sectional view illustrating an optical path diagram of a variable magnification optical system according to Example 6. FIG. 10 is a cross-sectional view illustrating an optical path diagram of a variable magnification optical system according to Example 7. FIG. 10 is a cross-sectional view illustrating an optical path diagram of a variable magnification optical system according to Example 8. FIG. 10 is a cross-sectional view illustrating an optical path diagram of a variable magnification optical system according to Example 9. FIG. FIG. 10 is a cross-sectional view illustrating an optical path diagram of a variable magnification optical system according to Example 10. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 1. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 2. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 3. FIG. 9 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 4. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 5. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 6. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 7. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 8. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 9. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the variable magnification optical system according to Example 10.

DESCRIPTION OF SYMBOLS 1, 1A-1J Variable magnification optical system 11, Gr1 1st lens group 12, Gr2 2nd lens group 13, Gr3 3rd lens group 14, Gr4 4th lens group 15, ST Optical aperture 16, SR image pick-up element AX Optical axis 2 Mobile phones (digital devices)
27 Imaging device

Claims (15)

In order from the object side, a first lens group having a negative optical power, a second lens group having a positive optical power, a third lens group having a negative optical power, and a positive optical power. The fourth lens group includes four lens groups, and the second lens group and the third lens group move during zooming, and the first lens group and the fourth lens group are fixed. A variable magnification optical system,
Wherein the first lens group, even without less and having two negative lenses has at least one aspherical surface,
An aperture stop is provided in the second lens group;
Focusing is performed by the third lens group,
A flat glass is disposed on the image side of the fourth lens group,
A variable magnification optical system characterized by satisfying the following conditional expressions (1), (2) and (8) :
0.5 <| f1 | / f2 <0.95 (1)
0.7 <T1 / (fw × ft) ^0.5 <1.5 (2)
0.3 <Bfw / fw <0.6 (8)
F1: Composite focal length of the first lens group
f2: Composite focal length of the second lens group
T1: Thickness on the optical axis from the most object side surface to the most image side surface of the first lens unit
fw: Composite focal length of all optical systems at the wide-angle end
ft: Composite focal length of all optical systems at the telephoto end
Bfw: distance of back focus at the wide-angle end, in which the flat glass from the lens end to the focal plane is converted into air The variable power optical system according to claim 1, wherein the first lens group satisfies the following conditional expression (3).
1.3 <| f1 | / fw <2.5 (3) 3. The zoom optical system according to claim 1, wherein a lens closest to the object side of the first lens group satisfies the following conditional expression (4): 3.
−3.0 <(r12 + r11) / (r12−r11) <− 1.0 (4)
Where r11: radius of curvature of the object side surface of the most object side lens of the first lens unit
r12: radius of curvature of the image side surface of the lens closest to the object side in the first lens group 4. The variable according to claim 1, wherein the first lens group includes at least two negative lenses and at least one positive lens, and satisfies the following conditional expression (5): Double optical system.
20 <Δν1 (5)
However, Δν1: difference between the Abbe number average value of the positive lens and the Abbe number average value of the negative lens for the lenses in the first lens group.   5. The first lens group includes three elements, a negative meniscus lens convex to the object side, a negative lens, and a positive lens in order from the object side. Variable magnification optical system. The variable power optical system according to claim 1, wherein the second lens group satisfies the following conditional expression (6).
1.1 <f2 / fw <2.5 (6) The variable power optical system according to claim 1 , wherein the third lens group satisfies the following conditional expression (7).
1.0 <m3t <2.5 (7)
Where m3t: lateral magnification at the telephoto end of the third lens unit The variable power optical system according to claim 1 , wherein the third lens group includes only one lens. The variable power optical system according to claim 1 , wherein the second lens group includes at least two positive lenses and at least one negative lens. 10. The variable magnification optical system according to claim 9 , wherein the second lens group includes a positive lens, a negative lens, and a positive lens in order from the object side. Variable-power optical system according to any one of claims 1 to 10, characterized by satisfying the conditional expression below SL (9).
1.5 <| EPw / fw | (9)
However, EPw: distance from the exit pupil position of the chief ray at the maximum angle of view to the image plane at the wide angle end The variable magnification optical system according to claim 1 , wherein an aperture stop is provided on the object side of the second lens group, and the aperture stop has a fixed aperture diameter. A variable magnification optical system according to any one of claims 1 to 12 , and an image sensor that converts an optical image into an electrical signal,
An image pickup apparatus, wherein the variable magnification optical system is capable of forming an optical image of a subject on a light receiving surface of the image pickup device. An imaging device according to claim 13 ,
A controller that causes the imaging device and the imaging device to perform at least one of still image shooting and moving image shooting of a subject,
A digital apparatus, wherein the variable magnification optical system of the imaging device is assembled so as to form an optical image of a subject on a light receiving surface of the imaging device. The digital device according to claim 14 , wherein the digital device is a mobile terminal.

Images