JP6518067B2 - Optical system and imaging device - Google Patents

Description

  The present invention relates to an optical system having a vibration reduction function for reducing image blurring caused by vibration such as camera shake at the time of imaging, and is particularly suitable for an imaging device such as an interchangeable lens camera, a video camera, or a digital camera. The present invention relates to an imaging optical system and an imaging apparatus including the optical system.

  2. Description of the Related Art Conventionally, there has been known an optical system provided with a vibration reduction function for reducing image blurring caused by vibration during imaging such as camera shake. Generally, it is said that the limit value of the shutter speed which is considered to cause an image blur caused by the vibration at the time of imaging is the reciprocal of the focal length when converted to the screen size of a 35 mm camera. That is, in the imaging lens having a long focal distance, the above-mentioned limit value is small as compared with the imaging lens having a short focal distance, and image blurring due to vibration at the time of imaging tends to occur. From this point of view, various proposals have conventionally been made for optical systems with long focal lengths, such as middle telephoto and telephoto lenses having a vibration reduction function.

  For example, Patent Document 1 includes, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power. There is disclosed a so-called medium telephoto lens having a focal length of 75 mm to 100 mm when converted to the screen size of a 35 mm camera. In this middle telephoto lens, among the four lenses constituting the first lens group, the negative lens disposed closest to the image side is used as a vibration reduction group, and the vibration reduction group is moved in a direction substantially perpendicular to the optical axis By doing this, the image position is displaced, thereby correcting the image blur. By configuring the anti-vibration group with one negative lens, weight reduction of the anti-vibration group is achieved.

  Also in Patent Document 2, similarly in order from the object side, the first lens group having a positive refractive power, the second lens group having a negative refractive power, and the third lens group having a positive refractive power. Discloses a middle telephoto lens in which an anti-vibration group composed of one negative lens is disposed in a first lens group.

  In recent years, an image pickup apparatus having a moving image pickup function is generally used, and the above-described image blurring is likely to occur at the time of moving image pickup. For this reason, not only an optical system having a long focal length but also a wide-angle lens having a short focal length and the like are required to be equipped with a vibration reduction function.

  Therefore, in Patent Document 3, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and negative refractive power There is proposed a wide-angle lens having a focal length of 24 mm to 31 mm, which is composed of a fourth lens group having a force, and in which a vibration reduction group is disposed in the first lens group. In a wide-angle lens, the amount of decentration coma aberration and decentration field curvature generated when the lens is decentered becomes large as compared with an imaging lens with a long focal length. For this reason, in the wide-angle lens, aberration fluctuation is large when the antivibration group is decentered at the time of image stabilization, and the imaging performance at the time of image stabilization is easily deteriorated. Therefore, in the optical system described in Patent Document 3, the anti-vibration group is composed of two lenses, positive and negative, aberration correction at the time of anti-vibration is favorably performed, and an optical system having high anti-vibration performance is obtained.

JP, 2012-189637, A JP 2012-242690 A Patent No. 5196205 gazette

  By the way, all of the optical systems described in Patent Document 1 to Patent Document 3 adopt a positive lead type lens group configuration called positive lead type, and the vibration reduction group is closer to the diaphragm or closer to the image than the diaphragm. It is arranged. In general, in this positive leading type imaging lens, the lens disposed on the image side is easier to make the lens outer diameter smaller than the lens disposed on the object side, and the size and weight of the vibration reduction group are reduced. In order to achieve this, it is effective to dispose the anti-vibration group near the diaphragm or on the image side of the diaphragm. By arranging the anti-vibration group near the aperture or on the image side of the aperture, the outer diameter of the lens constituting the anti-vibration group can be reduced, and an actuator for driving the anti-vibration group around the anti-vibration group This is because the lens barrel diameter can be suppressed from becoming large also when the etc. are arranged.

  However, in a bright, particularly wide-angle imaging optical system requiring a constant back focus, such as an interchangeable lens of a single-lens reflex camera, a negative leading type lens group called a negative lead type. The configuration is adopted. In this case, the outer diameter of the rear lens is also increased depending on the image-side NA (numerical aperture), so the outer diameter of the lens near the aperture or on the image side than the aperture is not necessarily smaller. Therefore, when providing a vibration reduction group to a bright, particularly wide-angle optical system having a negative leading type and a small F value, as described in Patent Documents 1 to 3, an image is formed in the first lens group When a lens disposed on the side of the diaphragm and near the diaphragm or on the image side of the diaphragm is used as a vibration reduction group, the size and weight of the vibration reduction group may not be achieved.

  In addition, when the outer diameter of the lens constituting the antivibration group becomes large, the movable range of the antivibration group also becomes large, and it becomes difficult to reduce the diameter of the lens barrel. Furthermore, although it is necessary to arrange the above-mentioned actuator etc. around the vibration proofing group, the outer diameter of the lens constituting the vibration proofing group is large, and in order to secure the movable range of the vibration proofing group, the lens barrel diameter is large. There is a need to. Furthermore, it is necessary to arrange an actuator or the like for driving the diaphragm in the lens barrel. Therefore, if the anti-vibration group is disposed in the vicinity of the stop, an actuator or the like for driving the stop and an actuator or the like for driving the anti-vibration group interfere with each other, which leads to an increase in lens barrel diameter.

  The present invention has been made in view of the above-described problems, and is a negative leading optical system suitable for a wide angle lens having a half angle of view of 20 ° or more, and is provided with a small and lightweight vibration isolation group, An object of the present invention is to provide an optical system and an imaging device which can be configured to have a compact cylinder diameter.

  As a result of intensive studies, the present inventors have achieved the above object by adopting the following optical system.

  The optical system according to the present invention comprises, in order from the object side, a first lens group having negative refractive power and a rear group having overall positive refractive power following the first lens group, and the aperture stop The first lens group is disposed on the image side of the first lens group, and the first lens group includes, in order from the object side, the first A lens group, the first B lens group, and the first C lens group. The first A lens group has a negative refractive power. The first B lens group is a vibration reduction group, and is characterized in that the image is moved by moving the vibration reduction group in a direction substantially perpendicular to the optical axis.

  The optical system according to the present invention preferably satisfies the following conditional expression (1).

0.1 <f / | f1b | <0.6 (1)
Here, f indicates the focal length of the entire optical system, and f1B indicates the focal length of the first B lens group.

  The optical system according to the present invention preferably satisfies the following conditional expression (2).

0.9 <L1b / Ym <1.6 (2)
Here, L1b indicates the distance on the optical axis from the lens surface closest to the object side of the optical system to the lens surface closest to the object side of the first B lens group, and Ym indicates the maximum image height.

  The optical system according to the present invention preferably satisfies the following conditional expression (3).

0.12 <Ep / D <0.3 ... (3)
Here, Ep indicates the distance on the optical axis from the lens surface closest to the object side to the entrance pupil, and D indicates the total optical length.

  The optical system according to the present invention preferably satisfies the following conditional expression (4).

0.25 <Ls / Ym <1.1 ... (4)
Here, Ls represents the distance on the optical axis from the lens surface closest to the image side of the first B lens group to the aperture stop, and Ym represents the maximum image height.

  The optical system according to the present invention preferably satisfies the following conditional expression (5).

0.2 <| (1-β1 b) · βm | <0.9 ... (5)
Here, β 1 b indicates the lateral magnification of the first B lens group at infinity focusing, and β m indicates the combined lateral magnification of the lens disposed on the image side of the first B lens group at infinity focusing.

  In the optical system according to the present invention, in the first lens group, the first B lens group has positive refractive power, the first C lens group has negative refractive power, and the first B lens group is an object. It is preferable that the side surface is configured of one positive meniscus lens having a concave shape.

  In the optical system according to the present invention, instead of the above, in the first lens group, the first B lens group has negative refractive power, and the first C lens group has positive refractive power; It is also preferable that the 1B lens group be configured of one negative lens having a concave surface on the object side.

  In the optical system according to the present invention, the first lens group is preferably fixed in the optical axis direction at the time of focusing.

  An imaging apparatus according to the present invention includes the optical system described above, and an imaging device provided on the image side of the optical system for converting an optical image formed by the optical system into an electrical signal. It features.

  According to the present invention, it is possible to reduce the weight and size of the entire optical system provided with the vibration reduction group, and to provide an optical system having excellent imaging performance from infinity to close range even during vibration reduction.

It is a lens sectional view showing an example of lens composition of an optical system (single focus wide angle lens) of Example 1 of the present invention. 5 is a longitudinal aberration diagram of an infinity in-focus condition of the optical system of Example 1. FIG. 5 is a lateral aberration diagram of an infinity in-focus condition of the optical system of Example 1. FIG. It is a lens sectional view showing an example of lens composition of an optical system (single focus wide angle lens) of Example 2 of the present invention. 5 is a longitudinal aberration diagram of an infinity in-focus condition of the optical system of Example 2. FIG. FIG. 6 is a lateral aberration diagram of an infinity in-focus condition of the optical system of Example 2; It is a lens sectional view showing an example of lens composition of an optical system (single focus wide angle lens) of Example 3 of the present invention. FIG. 7 is a longitudinal aberration diagram of an infinity in-focus condition of the optical system of Example 3; FIG. 7 is a lateral aberration diagram of an infinity in-focus condition of the optical system of Example 3; It is a lens sectional view showing an example of lens composition of an optical system (single focus wide angle lens) of Example 4 of the present invention. FIG. 16 is a longitudinal aberration diagram of an infinity in-focus condition of the optical system of Example 4; FIG. 16 is a lateral aberration diagram of an infinity in-focus condition of the optical system of Example 4;

  Hereinafter, embodiments of an optical system and an imaging device according to the present invention will be described.

1. Optical system 1-1. Configuration of Optical System First, the configuration of the optical system according to the present invention will be described. The optical system according to the present invention comprises, in order from the object side, a first lens group having negative refractive power, and a rear group having a positive refractive power as a whole following the first lens group, and an aperture stop Is arranged on the image side of the first lens group, and the first lens group comprises, in order from the object side, the first A lens group, the first B lens group, and the first C lens group, and the first A lens group has negative refractive power The first B lens group is a vibration reduction group, and is characterized in that the image is moved by moving the vibration reduction group in a direction substantially perpendicular to the optical axis. Hereinafter, the configuration of the optical system will be described in order of the first lens group, the rear group, and the aperture stop.

(1) First Lens Group The first lens group is a lens group disposed closest to the object side in the optical system, and has negative refractive power. That is, the optical system is a negative leading optical system, which requires a back focus such as an interchangeable lens of a single-lens reflex camera, and is suitable for a bright optical system having a small F value.

  As described above, the first lens group is composed of, in order from the object side, the first A lens group having negative refractive power, the first B lens group, and the first C lens group, and the aperture stop is the first It is disposed on the image side of the lens unit. By adopting this configuration, it is possible to reduce the height from the optical axis of the on-axis ray and the off-axis ray incident on the first B lens group. For this reason, the outer diameter of the lens which comprises a 1st B lens group can be made smallest in the said optical system. Therefore, by using the first B lens group as the vibration reduction group, the size and weight of the vibration reduction group can be reduced, and the movable range of the vibration reduction group at the time of vibration reduction can also be reduced. Further, by reducing the size and weight of the vibration isolation group, it is possible to reduce the size and weight of the vibration isolation drive mechanism such as an actuator for driving the vibration isolation group. From these things, even if the anti-vibration drive mechanism is disposed around the anti-vibration group, the lens barrel diameter can be reduced. Furthermore, since the aperture stop is disposed closer to the image than the first lens group, the arrangement of the anti-vibration drive mechanism and the aperture drive mechanism such as an actuator for driving the aperture stop does not interfere in the lens barrel. The lens barrel diameter can be reduced.

  In addition, since the height from the optical axis of the axial ray incident on the anti-vibration group (the first B lens group) can be reduced, even if the anti-vibration group is decentered at the time of anti-vibration, fluctuation of on-axis coma aberration It is also easy to reduce the size, and high imaging performance can be maintained even at the time of image stabilization.

  On the other hand, when the lens unit arranged in the vicinity of the aperture stop or on the image side of the aperture stop is used as the vibration reduction lens group, the outer diameter of the lenses constituting the vibration reduction group becomes large. This is not preferable because it leads to an increase in the vibration drive mechanism and the lens barrel diameter. Further, in this case, the axial comatic aberration at the time of vibration isolation becomes large, and it becomes difficult to satisfactorily correct the aberration fluctuation at the time of vibration isolation unless an aspheric surface is introduced into the vibration isolation group.

  The first lens group is preferably fixed to the optical axis during focusing. A focus drive mechanism such as an actuator for driving a focus group which moves along an optical axis by arranging a vibration reduction group in the first lens group which becomes a fixed group at the time of focusing, and the above The arrangement with the anti-vibration drive mechanism does not interfere, and the mechanical configuration in the lens barrel can be simplified and the diameter of the lens barrel can be reduced.

  Next, the first A lens group, the first B lens group, and the first C lens group constituting the first lens group will be described.

i) First A lens group As long as the first A lens group has a negative refractive power as a whole, the specific lens configuration is not particularly limited. Depending on the optical performance required of the optical system, an appropriate lens configuration can be made as appropriate.

ii) First C lens group The specific lens configuration of the first C lens group is not particularly limited, and the refractive power may be positive or negative. However, from the viewpoint of improving the imaging performance at the time of image stabilization, it is preferable to have a refractive power that is the reverse of the sign of the refractive power of the first B lens group described below. This point will be described later.

iii) First B lens group The first B lens group is preferably composed of a single lens component. Here, a single lens component refers to a lens that includes a single lens, a cemented lens, and a compound lens and does not include an air layer between the surface closest to the object and the surface closest to the image. By configuring the first lens group with a single lens component, the configuration of the vibration reduction group can be simplified as compared to the case where the first B lens group is configured with a plurality of lenses including an air layer, and the manufacturing error It is possible to prevent the deterioration of the imaging performance caused by the factors.

  Here, in order to further miniaturize and reduce the weight of the vibration reduction group, it is preferable to configure the first lens group B with a single lens. According to the optical configuration of the present invention, as described above, the height from the optical axis of the axial ray incident on the vibration isolation group can be reduced, so that even when the vibration isolation group is constituted by a single lens, , High imaging performance can be maintained. By configuring the first B lens group with a single lens, it is possible to further miniaturize and reduce the weight of the anti-vibration drive mechanism, and to improve stop accuracy at the time of anti-vibration correction.

  The refractive power of the first B lens group may be positive or negative, but it is preferable that the most object-side surface of the first B lens group has a concave shape. In the optical system according to the present invention, since the first A lens group has negative refractive power, light rays incident on the first B lens group are diverging light. At this time, by making the surface closest to the object side of the 1B lens group concave, the difference between the incident angle of off-axis light at no eccentricity and the incident angle of off-axial light at decentering can be reduced. As a result, it is possible to reduce the amount of astigmatism generated at decentering. At this time, although the sign of the refractive power of the first B lens group may be positive or negative, the refractive power of the first B lens group and the refractive power of the first C lens group are opposite to each other. Is preferred.

  In a wide-angle lens with a short focal length, it may be difficult to suppress fluctuations in astigmatism when the lens is decentered, but the surface on the most object side of the 1B lens group is made concave and the 1B lens By making the refractive power of the group and the refractive power of the first C lens group different from each other, the astigmatism generated in the first B lens group can be immediately canceled by the first C lens group immediately after, so the astigmatism Fluctuations can be suppressed.

  As a specific form, for example, when the refractive power of the first B lens group is positive, the refractive power of the first C lens group is negative, and further, a positive meniscus lens in which the object side surface of the first B lens group is concave. It is preferable to constitute by one sheet. On the other hand, when making the refractive power of the first B lens group negative, it is preferable to make the refractive power of the first C lens group positive. In this case, it is preferable that the first B lens group be configured of one negative lens having a surface on the object side which has a stronger curvature than the surface on the image side.

  Furthermore, it is preferable that the curvature of the surface on the most object side of the first C lens group and the curvature of the surface on the most image side of the first B lens group have the same sign. By adopting such a configuration, various aberrations (spherical aberration, astigmatism, coma aberration) generated on the image side surface of the 1B lens group are immediately obtained on the object side surface of the 1C lens group immediately after that. As a result, it becomes easy to correct various aberrations (spherical aberration, astigmatism, coma) at decentering.

(2) Rear group In the optical system according to the present invention, the specific lens group configuration is particularly limited as long as the rear group following the first lens group has positive refractive power in the entire rear group. It is not a thing. That is, the rear group may be configured of one lens group, or may be configured of a plurality of lens groups, and the specific lens configuration of each lens group is not particularly limited. However, since it is preferable that the first lens group be fixed in the optical axis direction at the time of focusing, it is preferable that a focusing group which moves along the optical axis direction at the time of focusing be provided in the rear group. For example, when the rear group is composed of a plurality of lens groups, it is preferable to set a lens group other than the lens group disposed closest to the object side in the rear group as the focus group. That is, by setting the lens group disposed closer to the image side to the first lens group as the focus group, it is easier to avoid the interference between the anti-vibration drive mechanism and the focus drive mechanism.

(3) Aperture Stop In the optical system according to the present invention, the aperture stop may be disposed closer to the image than the first lens group, and as long as this requirement is satisfied, the aperture stop is between the first lens group and the rear group. , And may be arranged in the rear group, and the specific arrangement is not particularly limited. The aperture stop may be fixed in the optical axis direction or may be movable in the optical axis direction. In any case, the effects of the present invention can be obtained.

1-2. Conditional Expressions Next, each conditional expression will be described. As described above, it is preferable that the optical system adopt the above configuration and satisfy the following conditional expression (1) to conditional expression (5). Each conditional expression will be described below.

1-2-1. Conditional expression (1)
The optical system according to the present invention preferably satisfies the following conditional expression (1).

0.1 <f / | f1b | <0.6 (1)
Here, f indicates the focal length of the entire optical system, and f1B indicates the focal length of the first B lens group.

  Conditional expression (1) defines the ratio between the focal length of the entire optical system and the focal length of the anti-vibration group (the first B lens group). If conditional expression (1) is satisfied, the moving amount of the image stabilizing unit at the time of image stabilization will be within the appropriate range, aberration fluctuation at the time of image stabilization can be suppressed, and high imaging performance can be maintained even at the time of image stabilization. And, the enlargement of the anti-vibration drive mechanism can be prevented, and the diameter of the lens barrel can be reduced.

  When the numerical value of the conditional expression (1) becomes equal to or less than the lower limit value, the refractive power of the vibration reduction group is small, which is advantageous in suppressing aberration fluctuation during vibration reduction. However, since the amount by which the anti-vibration group is moved at the time of anti-vibration, that is, the lens driving amount becomes large, the driving load of the anti-vibration driving mechanism also becomes large. At the same time, the size of the antivibration drive mechanism is increased, and the diameter of the lens barrel is also increased. From these things, it is not preferable that the numerical value of conditional expression (1) becomes less than or equal to the lower limit value. On the other hand, when the numerical value of the conditional expression (1) becomes equal to or more than the upper limit, the lens drive amount at the time of image stabilization becomes smaller, so the drive load of the image stabilization drive mechanism becomes smaller. It is advantageous. However, the refracting power of the anti-vibration group is large, and fluctuations of astigmatism and coma at the time of anti-vibration become large, and it becomes difficult to correct them well.

  In order to make these effects more reliable, the lower limit value of conditional expression (1) is more preferably 0.13, and the upper limit value is more preferably 0.35.

1-2-2. Conditional expression (2)
The optical system according to the present invention preferably satisfies the following conditional expression (2).

0.9 <L1b / Ym <1.6 (2)
Here, L1b indicates the distance on the optical axis from the lens surface closest to the object side of the optical system to the lens surface closest to the object side of the first B lens group, and Ym indicates the maximum image height.

  Conditional expression (2) is a condition which indicates the optimum position of the first B lens group on the optical axis. By satisfying conditional expression (2), the height from the optical axis when the off-axis light beam enters the first B lens group, and the height from the optical axis when the axial light beam enters the first B lens group Any of the heights can be lowered. As a result, it is possible to reduce the outer diameter of the lens constituting the 1B lens group, and accordingly to reduce the drive load of the antivibration drive mechanism, and to achieve the miniaturization of the antivibration drive mechanism. .

  If the numerical value of the conditional expression (2) for this becomes less than the lower limit value, the height from the optical axis when the off-axis ray enters the first B lens group becomes high, so the lenses constituting the anti-vibration group This is not preferable because the outside diameter of the drive mechanism increases, the drive load of the vibration control drive mechanism increases, and the vibration control mechanism also increases. Also, in this case, it is difficult to suppress the fluctuation of astigmatism at the time of decentering. On the other hand, when the numerical value of the conditional expression (2) exceeds the upper limit, the height from the optical axis when the off-axis ray enters the first B lens group decreases, but the on-axis ray entering the first B lens group Height from the optical axis of the Therefore, in this case as well, the outer diameter of the lens constituting the anti-vibration group can not be made sufficiently small, the drive load of the anti-vibration drive mechanism becomes large, and the size of the anti-vibration drive mechanism also increases.

  In order to make these effects more reliable, the lower limit value of conditional expression (2) is more preferably 1.0, and the upper limit value is more preferably 1.4.

1-2-3. Conditional expression (3)
The optical system according to the present invention preferably satisfies the following conditional expression (3).

0.12 <Ep / D <0.3 ... (3)
Here, Ep indicates the distance on the optical axis from the lens surface closest to the object side to the entrance pupil, and D indicates the total optical length.

  Conditional expression (3) is an expression showing the ratio of the entrance pupil position to the total optical length. By satisfying the conditional expression (3), the position of the entrance pupil on the optical axis becomes appropriate, and the size of the vibration isolation group can be reduced, and high imaging performance can be maintained even at the time of vibration isolation. .

  On the other hand, when the numerical value of the conditional expression (3) becomes equal to or less than the lower limit value, the entrance pupil position with respect to the entire optical length becomes shorter than the appropriate range. In this case, it is advantageous in reducing the filter diameter and in reducing the outer diameter of the lens constituting the vibration reduction group. However, in the rear group on the image side of the first lens group, it is necessary to arrange a group having strong positive refractive power, aberration correction becomes insufficient with each lens group alone, and coma and field curvature are favorably made. It becomes difficult to correct. On the other hand, when the numerical value of the conditional expression (3) exceeds the upper limit value, the height from the optical axis of the off-axis ray passing through the first lens group becomes high, so the outer diameter of the lenses constituting the vibration reduction group becomes large. It is not necessary to

In order to make these effects more reliable, the lower limit value of conditional expression (3) is preferably 0.14, and the upper limit value is preferably 0.22.

1-2-4. Conditional expression (4)
The optical system according to the present invention preferably satisfies the following conditional expression (4).

0.25 <Ls / Ym <1.1 ... (4)
Here, Ls indicates the distance on the optical axis from the lens surface closest to the image side of the first B lens group to the aperture stop, and Ym indicates the maximum image height.

  Conditional expression (4) defines the distance between the first B lens group and the aperture stop on the optical axis. By satisfying the conditional expression (4), the distance between the 1st lens group B and the aperture stop on the optical axis becomes appropriate, and the interference between the anti-vibration drive mechanism and the stop drive mechanism can be prevented. These can be arranged. In addition, when conditional expression (4) is satisfied, the height from the optical axis of the off-axis ray passing through the first B lens group falls within an appropriate range, and the outer diameter of the lenses constituting the first B lens group becomes large. Can be suppressed.

  On the other hand, when the numerical value of the conditional expression (4) becomes equal to or less than the lower limit value, the distance between the 1st B lens group and the aperture stop on the optical axis becomes shorter than the appropriate range, This is not preferable because it interferes with the diaphragm driving mechanism, which makes it difficult to arrange the mechanism in the lens barrel, and the diameter of the lens barrel becomes large. On the other hand, if the value exceeds the upper limit, the height from the optical axis of the off-axis ray passing through the first B lens group becomes high, so it is necessary to configure the first B lens group by a lens with a large outer diameter. The drive load of the anti-vibration drive mechanism is increased because the This leads to an increase in the size of the vibration isolation drive mechanism, which is not preferable.

1-2-5. Conditional expression (5)
The optical system according to the present invention preferably satisfies the following conditional expression (5).

0.2 <| (1-β1 b) · βm | <0.9 ... (5)
However, β 1 b is the lateral magnification of the first B lens group at infinity focusing, and β m is the combined lateral magnification of the lens disposed on the image side of the first B lens group at infinity focusing, ie, the first C lens The combined lateral magnification of groups and rear groups is shown.

  Conditional expression (5) defines the ratio of the amount of movement of the first lens subunit B in the direction substantially perpendicular to the optical axis and the amount of movement of the image position on the image forming surface generated thereby. When the numerical value of the conditional expression (5) exceeds the upper limit value, the movement amount of the vibration control group required to move the image position by a predetermined amount becomes too small, and the movement amount of the vibration control group is high. Control of accuracy is required, and in practice, position control of the vibration isolation group becomes difficult. On the other hand, when the numerical value of the conditional expression (5) becomes equal to or less than the lower limit, the moving amount of the vibration reduction group required to move the image position by a predetermined amount becomes large. For this reason, the drive load of the anti-vibration drive mechanism becomes large, which causes the enlargement of the anti-vibration drive mechanism, which is not preferable.

  In order to further ensure these effects, it is preferable to set the lower limit value of conditional expression (4) to 0.25 and the upper limit value to 0.7.

2. Imaging Device Next, an imaging device according to the present invention will be described. An imaging device according to the present invention includes the optical system according to the present invention, and an imaging device provided on the image side of the optical system for converting an optical image formed by the optical system into an electrical signal. It is characterized by Here, the imaging device and the like are not particularly limited, and a solid-state imaging device such as a CCD sensor or a CMOS sensor can also be used, and the imaging device according to the present invention is a solid-state imaging device such as a digital camera or a video camera. It is suitable for the used imaging device. Further, the imaging device may be a lens fixed imaging device in which a lens is fixed to a housing, or may be a lens interchangeable imaging device such as a single-lens reflex camera or a mirrorless single-lens camera. Of course. However, the optical system according to the present invention can be a negative optical system in which the first lens group has a negative refractive power, and can be a bright optical system with a small F value, and the back focus is relatively long. Therefore, the imaging device according to the present invention is preferably an imaging device with a relatively long back focus, such as a single-lens reflex camera.

  Next, the present invention will be specifically described by showing Examples and Comparative Examples. However, the present invention is not limited to the following examples. The optical system of each of the following examples is a photographing optical system used for an imaging apparatus (optical apparatus) such as a digital camera, a video camera, a silver halide film camera, etc., and is configured as a single focus wide-angle lens. In the lens sectional views (FIGS. 1, 4, 7 and 10), the left side is the object side and the right side is the image side in the drawings.

(1) Configuration of Optical System FIG. 1 is a lens cross-sectional view showing the configuration of an optical system of an imaging lens (single focal wide-angle lens) according to a first embodiment of the present invention. The imaging lens includes, in order from the object side, a first lens group G1 of negative refractive power and a second lens group G2 of positive refractive power, and is configured of the first lens group G1 and the second lens group G2 It is done.

  The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface, a biconvex lens L2, a negative meniscus lens L3 having a concave surface at the object side, a biconcave lens L4 and a biconvex lens L5. And a cemented lens made of In the first lens group G1, the negative meniscus lens L1 located closest to the object side is a composite aspheric lens in which a resin layer is provided on the surface on the image side to form an aspheric surface. In the first lens group G1, the first A lens group G1A includes the negative meniscus lens L1 and the biconvex lens L2, and the first B lens group G1B includes the negative meniscus lens L3. The first C lens group G1C Is composed of the above cemented lens. The negative meniscus lens L3, which has a concave surface on the object side of the 1B lens group, is a vibration reduction group, and vibration such as camera shake occurs at the time of imaging by moving the vibration reduction group in a direction perpendicular to the optical axis. When it occurs, the image position is moved to perform image blur correction. The first lens group G1 is fixed in the optical axis direction during focusing.

  The aperture stop S is disposed adjacent to the image side of the first lens group G1, and is fixed at the time of focusing.

  The second lens group G2, in order from the object side, is a cemented lens consisting of a biconvex lens L6, a biconvex lens L7 and a biconcave lens L8, a biconcave lens L9, a biconvex lens L10, and a negative meniscus lens having a concave surface on the object side And L11. In the second lens group G2, the negative meniscus lens L11 located closest to the image side is a glass mold type aspheric lens having an aspheric surface on the object side. Focusing from an infinity point to a near distance object is performed by moving the second lens group G2 to the object side.

  In FIG. 1, “IP” shown on the image side of the second moving group G2 is an image plane, and specifically, an imaging surface of a solid-state imaging device such as a CCD sensor or a CMOS sensor, or a silver salt film Indicates the film surface etc. These reference numerals and the like are the same as in FIGS. 4, 7 and 10 shown in the second to fourth embodiments.

(2) Numerical Examples Next, numerical examples in which specific numerical values are applied to the imaging lens will be described. Table 1 shows lens data of the imaging lens. In Table 1, the surface number is the order of the lens surface counted from the object side, "r" is the radius of curvature of the lens surface, "d" is the distance (surface distance) on the optical axis of the lens surface, and "nd" is the d-line The refractive index for (wavelength λ = 587.6 nm), and “vd” indicates the Abbe number for the d-line. When the lens surface is aspheric, the surface number is followed by * (asterisk), and the column of radius of curvature r indicates the paraxial radius of curvature. The unit of length in the table is all "mm" and the unit of angle of view is all "°".

  Table 2 (2-1) shows the aspheric coefficients and the conic constant when the shape of the aspheric surface shown in Table 1 is expressed by the following equation.

Here, the aspheric surface is defined by the following equation.
z = ch ² / [1+ {1- (1 + k) c ² h ² } ^1/2 ] + A ⁴ h ⁴ + A ⁶ h ⁶ + A ⁸ h ⁸ + A ¹⁰ h ¹⁰ ...
(Where c is curvature (1 / r), h is height from the optical axis, k is conical coefficient, A4, A6, A8, A10,... Are aspheric coefficients of each order).

  Further, Table 2 (2-2) shows the focal lengths of the first lens group and the second lens group, respectively, and Table 2 (2-3) shows the variable distances on the optical axis of the lens surface shown in Table 1 Indicates

  In the following, “f” is the focal length of the entire optical system, “FNo.” Is the F value, “ω” is the half angle of view, and “Ym” is the maximum image height. These notations are the same in Examples 2 to 4 below.

f = 34.00
F No. = 1.83
ω = 32.81
Ym = 21.633

  FIG. 2 shows a longitudinal aberration diagram at the time of infinity focusing of the imaging lens. The respective longitudinal aberration diagrams represent spherical aberration, astigmatism and distortion in order from the left toward the drawing. Further, FIG. 3 shows a lateral aberration diagram at the time of infinity focusing of the imaging lens. The respective lateral aberration diagrams show coma at the time of 0.0 Ym to 1.0 Ym. Ym is the maximum image height. Further, in the spherical aberration diagram, distortion aberration diagram, and lateral aberration diagram, the solid line indicates the aberration at the d-line (λ = 587.6 nm), and the alternate long and short dash line indicates the aberration at the g-line (λ = 435.8 nm). In the astigmatism diagram, the solid line (ds) indicates the aberration of the sagittal image plane at the d-line, and the broken line (dm) indicates the aberration of the meridional image plane at the d-line. Since these are the same in the respective drawings shown in the second to fourth embodiments, the description will be omitted in the following.

(1) Configuration of Optical System FIG. 4 is a lens cross-sectional view showing the configuration of the optical system of the imaging lens (single focus wide angle lens) of Example 2. As shown in FIG. The imaging lens of Example 2 includes, in order from the object side, a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power.

  The first lens group G1 is composed of, in order from the object side, a negative meniscus lens L1 having a convex surface, a positive meniscus lens L2 having a convex surface, a biconcave lens L3, and a biconvex lens L4. Ru. In the first lens group G1, the negative meniscus lens L1 located closest to the object side is a composite aspheric lens in which a resin layer is provided on the surface on the image side to form an aspheric surface. In the first lens group G1, the first A lens group G1A comprises the negative meniscus lens L1 and the positive meniscus lens L2, the first B lens group G1B comprises a biconcave lens L3, and the first C lens group G1C comprises It comprises the biconvex lens L4. The biconcave lens L3 constituting the first B lens group is a vibration reduction group, and the image blur correction is performed by moving the vibration reduction group in a direction perpendicular to the optical axis. Further, the first lens group G1 is fixed in the optical axis direction during focusing.

  The aperture stop S is disposed adjacent to the image side of the first lens group G1, and is fixed at the time of focusing.

  The second lens group G2, in order from the object side, is a cemented lens of a biconvex lens L5, a biconvex lens L6 and a biconcave lens L7, a biconcave lens L8, a biconvex lens L9, and a negative meniscus lens having a concave object side surface And L10. In the second lens group, the negative meniscus lens L10 located closest to the image side is a glass mold type aspheric lens having an aspheric surface on the object side. Focusing from an infinity point to a near distance object is performed by moving the second lens group G2 to the object side.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the imaging lens is applied will be described. Table 3 shows lens data of the imaging lens. Table 4 (4-1) is the aspherical coefficient and the conical constant of the aspheric surface shown in Table 3, Table 4 (4-2) is the focal length of each lens group, and Table 4 (4-3) is the It is a variable interval on the optical axis of the lens surface shown in Table 3. In addition, the focal length, the F-number, the half angle of view, and the maximum image height of the optical system are shown below. Further, FIG. 4 and FIG. 5 show longitudinal aberration diagrams and lateral aberration diagrams, respectively, at infinity focusing of the optical system.

f = 34.00
F No. = 1.85
ω = 32.74
Ym = 21.633

(1) Configuration of Optical System FIG. 7 is a lens sectional view showing the configuration of the optical system of the imaging lens (single-focus wide-angle lens) of Example 3. As shown in FIG. The imaging lens of Example 3 includes, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. And consists of

  The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface, a negative meniscus lens L2 having a convex surface, and a positive meniscus lens L3 having a convex surface. The surface on the image side is composed of a convex negative meniscus lens L4. The negative meniscus lens L2 disposed second from the object side is a glass mold type aspheric lens having an aspheric surface on the image side. In the first lens group G1, the first A lens group G1A includes the negative meniscus lens L1 and the negative meniscus lens L2, and the first B lens group G1B includes the positive meniscus lens L3. The first C lens group G1C is composed of the negative meniscus lens L4. The positive meniscus lens L3 constituting the first B lens group G1B is a vibration reduction group, and the image blur correction is performed by moving the vibration reduction group in a direction perpendicular to the optical axis. The first lens group is fixed in the optical axis direction during focusing.

  The second lens group G2 is composed of, in order from the object side, a cemented lens including a negative meniscus lens L5 having a convex surface and a biconvex lens L6, and a biconvex lens L7. Focusing from infinity to a near distance object is performed by moving the second lens group G2 to the image side.

  The aperture stop is disposed adjacent to the image side of the second lens group G2, and is fixed at the time of focusing.

  The third lens group G3 includes, in order from the object side, a three-piece cemented lens in which a biconcave lens L8, a biconvex lens L9, and a negative meniscus lens L10 having a convex surface are cemented, and a biconvex lens L11. It comprises a cemented lens consisting of a negative meniscus lens L12 having a convex surface, and a biconvex lens L13, and a biconcave lens L14. In the third lens group G3, the biconcave lens L14 located closest to the image side is a glass mold type aspheric lens having an aspheric surface on the object side.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the imaging lens is applied will be described. Table 5 is lens data of the imaging lens. Table 6 (6-1) is the aspheric coefficient and the conical constant of the aspheric surface shown in Table 5, Table 6 (6-2) is the focal length of each lens group, and Table 6 (6-3) is It is a variable interval on the optical axis of the lens surface shown in Table 5. In addition, the focal length, the F-number, the half angle of view, and the maximum image height of the optical system are shown below. Further, FIG. 8 and FIG. 9 show longitudinal aberration diagrams and lateral aberration diagrams, respectively, at infinity focusing of the optical system.

f = 20.60
F No. = 2.05
ω = 46.81
Ym = 21.633

(1) Configuration of Optical System FIG. 10 is a lens cross-sectional view showing the configuration of the optical system of the imaging lens (single focus wide angle lens) of Example 4. As shown in FIG. The imaging lens of Example 4 includes, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. And consists of

  The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface, a negative meniscus lens L2 having a convex surface, and a negative meniscus lens L3 having a convex surface. A positive meniscus lens L4 having a convex surface on the image side and a negative meniscus lens L5 having a convex surface on the image side are provided. The negative meniscus lens L3 disposed third from the object side is a glass mold aspheric lens having an aspheric surface on both sides. In the first lens group G1, the first A lens group G1A includes the negative meniscus lens L1, the negative meniscus lens L2, and the negative meniscus lens L3, and the first B lens group G1B includes the positive meniscus lens L4. The first C lens group G1C is composed of the negative meniscus lens L5. The positive meniscus lens L4 constituting the first B lens group G1B is a vibration reduction group, and the image blur correction is performed by moving the vibration reduction group in a direction perpendicular to the optical axis. The first lens group is fixed in the optical axis direction during focusing.

  The second lens group G2 is composed of, in order from the object side, a cemented lens including a negative meniscus lens L6 having a convex surface and a biconvex lens L7, and a biconvex lens L8. Focusing from infinity to a near distance object is performed by moving the second lens group G2 to the image side.

  The aperture stop is disposed adjacent to the image side of the second lens group G2 and is fixed at the time of focusing.

  The third lens group G3 includes, in order from the object side, a cemented lens including a biconcave lens L9 and a positive meniscus lens L10 having a convex surface on the object side, a biconvex lens L11, and a negative meniscus lens L12 having a convex surface on the object side It comprises a cemented lens consisting of a biconvex lens L13 and a biconcave lens L14. In the third lens group G3, the biconcave lens L14 disposed closest to the image side is a glass mold type aspheric lens in which the object side surface is aspheric.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the imaging lens is applied will be described. Table 7 shows lens data of the imaging lens. Table 8 (8-1) is the aspheric coefficient and the conical constant of the aspheric surface shown in Table 7, Table 8 (8-2) is the focal length of each lens group, and Table 8 (8-3) is the It is a variable interval on the optical axis of the lens surface shown in Table 5. In addition, the focal length, the F-number, the half angle of view, and the maximum image height of the optical system are shown below. Furthermore, FIG. 11 and FIG. 12 show longitudinal aberration diagrams and lateral aberration diagrams, respectively, at infinity focusing of the optical system.

f = 18.50
F No. = 2.89
ω = 49.85
Ym = 21.633

The numerical values of conditional expression (1) to conditional expression (5) in each example are shown in Table 9.

  According to the present invention, it is a negative leading optical system suitable for a bright wide-angle lens having a half angle of view of 20 ° or more, preferably 25 ° or more, more preferably 30 ° or more, Accordingly, it is possible to provide an optical system and an imaging device which can be configured to have a compact lens barrel diameter.

Claims (9)

From the object side, it comprises a first lens group having a negative refractive power and a rear group having a positive refractive power as a whole following the first lens group,
An aperture stop is disposed on the image side of the first lens group,
The first lens group includes, in order from the object side, a first A lens group, a first B lens group, and a first C lens group, the first A lens group has negative refractive power, and the first B lens group A vibration group, and the image is moved by moving the vibration reduction group in a direction substantially perpendicular to the optical axis ,
An optical system characterized by satisfying the following conditional expression (4) .
0.25 <Ls / Ym <1.1 ... (4)
Here, Ls represents the distance on the optical axis from the lens surface closest to the image to the first B lens group to the aperture stop, and Ym represents the maximum image height. The optical system according to claim 1, wherein the following conditional expression (1) is satisfied.
0.1 <f / | f1b | <0.6 (1)
Here, f indicates the focal length of the entire optical system, and f1B indicates the focal length of the first B lens group. The optical system according to claim 1, wherein the following conditional expression (2) is satisfied.
0.9 <L1b / Ym <1.6 (2)
Here, L1b indicates the distance on the optical axis from the lens surface closest to the object side of the optical system to the lens surface closest to the object side of the first B lens group, and Ym indicates the maximum image height. The optical system according to any one of claims 1 to 3, wherein the following conditional expression (3) is satisfied.
0.12 <Ep / D <0.3 ... (3)
Here, Ep indicates the distance on the optical axis from the lens surface closest to the object side to the entrance pupil, and D indicates the total optical length. The optical system according to any one of claims 1 to 4 , wherein the following conditional expression (5) is satisfied.
0.2 <| (1-β1 b) · βm | <0.9 ... (5)
Here, β 1 b indicates the lateral magnification of the first B lens group at infinity focusing, and β m indicates the combined lateral magnification of the lens disposed on the image side of the first B lens group at infinity focusing. In the first lens group, the first B lens group has positive refractive power, and the first C lens group has negative refractive power.
The optical system according to any one of claims 1 to 5 , wherein the first B lens group includes one positive meniscus lens having a concave surface on the object side. In the first lens group, the first B lens group has negative refractive power, and the first C lens group has positive refractive power.
The optical system according to any one of claims 1 to 5 , wherein the first B lens group includes one negative lens having a concave surface on the object side. The optical system according to any one of claims 1 to 7 , wherein the first lens group is fixed in the optical axis direction during focusing. An optical system according to any one of claims 1 to 8 and an imaging device provided on the image side of the optical system for converting an optical image formed by the optical system into an electrical signal. An imaging apparatus characterized by comprising.

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