JP2016126279A - Optical system and image capturing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system that is of a negative lead type suitable for a bright wide-angle lens with a half view angle of 20° or more, has a compact and light-weight anti-shake group, and can be configured to have a compact lens barrel diameter.SOLUTION: An optical system that clears the above problem comprises a first lens group G1 having negative refractive power and a rear group having positive refractive power as a whole located behind the first lens group G1, in order from the object side, with an aperture stop S disposed on the image side of the first lens group G1. The first lens group G1 comprises a 1A lens group G1A, 1B lens group G1B, and 1C lens group G1C in order from the object side, the 1A lens group G1A having negative refractive power and the 1B lens group being configured as an anti-shake group G1B to move in a direction substantially perpendicular to an optical axis to shift an image.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical system having an image stabilization function for reducing image blur caused by vibration such as camera shake during imaging, and is particularly suitable for an imaging apparatus such as an interchangeable lens camera, a video camera, and 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 having an image stabilization function for reducing image blur caused by vibration during imaging such as camera shake. In general, it is said that the limit value of the shutter speed that is supposed to cause image blur due to vibration during imaging is the reciprocal of the focal length when converted to the screen size of a 35 mm camera. That is, an imaging lens with a long focal length has a smaller limit value compared to an imaging lens with a short focal length, and image blurring due to vibration during imaging tends to occur. For this reason, various proposals have been made for optical systems having a long focal length such as a medium telephoto lens and a telephoto lens having an anti-vibration function.

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

  Similarly, Patent Document 2 includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. Further, there is disclosed a medium telephoto lens in which an anti-vibration group composed of one negative lens is disposed in the first lens group.

  In recent years, imaging devices having a moving image capturing function have become common, and the above-described image blur tends to occur during moving image capturing. For this reason, not only an optical system with a long focal length but also a wide-angle lens with a short focal length has been required to have an anti-vibration function.

  Therefore, in Patent Document 3, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a negative refraction. A wide-angle lens having a focal length of 24 mm to 31 mm has been proposed, which includes a fourth lens group having power, and a vibration-proof group disposed in the first lens group. In a wide-angle lens, the amount of decentered coma aberration and decentered field curvature when the lens is decentered is larger than that of an imaging lens with a long focal length. For this reason, the wide-angle lens has a large aberration fluctuation when the image stabilizing group is decentered during image stabilization, and the imaging performance during image stabilization tends to deteriorate. Therefore, in the optical system described in Patent Document 3, the anti-vibration group is composed of two positive and negative lenses, and aberration correction at the time of anti-vibration is performed favorably to obtain an optical system with high anti-vibration performance.

JP 2012-189637 A JP 2012-242690 A Japanese Patent No. 5196205

  By the way, the optical systems described in Patent Documents 1 to 3 all adopt a positive leading type lens group configuration called a positive lead type, and the image stabilizing group is located near the aperture or closer to the image side than the aperture. It is arranged. In general, in this front-preceding type imaging lens, it is easier to reduce the lens outer diameter of the lens arranged on the image side than the lens arranged on the object side. In order to achieve this, it is effective to dispose the image stabilizing group in the vicinity of the stop or on the image side of the stop. An actuator for driving the image stabilizing group around the image stabilizing group can reduce the outer diameter of the lens constituting the image stabilizing group by disposing the image stabilizing group in the vicinity of the aperture or on the image side of the aperture. This is because it is possible to suppress an increase in the diameter of the lens barrel even when the above are arranged.

  However, a negative leading lens group called a negative lead type in a bright, particularly wide-angle imaging optical system that requires a constant back focus and has a small F-number, such as an interchangeable lens of a single-lens reflex camera. Configuration is adopted. In this case, the outer diameter of the rear lens is increased depending on the image side NA (numerical aperture), and therefore the outer diameter of the lens on the image side is not necessarily smaller in the vicinity of the aperture or the aperture. Therefore, when a vibration-proof group is provided in a bright, particularly wide-angle optical system that is a negative leading type and has a small F value, an image is formed in the first lens group as described in Patent Documents 1 to 3. If the lens disposed on the side and in the vicinity of the stop or on the image side of the stop is set as the anti-vibration group, it may not be possible to reduce the size and weight of the anti-vibration group.

  Further, when the outer diameter of the lens constituting the image stabilizing group is increased, the movable range of the image stabilizing group is also increased, and it is difficult to reduce the lens barrel diameter. Furthermore, it is necessary to arrange the actuators etc. around the image stabilization group, but the lens diameter of the image stabilization group is large, and in order to ensure the movable range of the image stabilization group, the lens barrel diameter is increased. There is a need to. Furthermore, it is necessary to arrange an actuator or the like for driving the diaphragm in the lens barrel. For this reason, when the vibration-proof group is arranged in the vicinity of the diaphragm, the actuator for driving the diaphragm interferes with the actuator for driving the vibration-proof group, leading to an increase in the 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 bright wide-angle lens having a half angle of view of 20 ° or more, including a small and lightweight vibration-proof group, and a mirror. It is an object of the present invention to provide an optical system and an imaging apparatus that can be configured to have a compact cylindrical diameter.

  As a result of intensive studies, the present inventors have achieved the above-mentioned problem by employing the following optical system.

  An optical system according to the present invention includes, in order from the object side, a first lens group having negative refractive power and a rear group having positive refractive power as a whole following the first lens group, and an aperture stop The first lens group is arranged on the image side of the first lens group, and 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 a negative refractive power. And the first B lens group is an image stabilization group, and the image is moved by moving the image stabilization 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 represents the focal length of the entire optical system, and f1B represents 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)
However, L1b shows the distance on the optical axis from the most object side lens surface of the optical system to the most object side lens surface of the 1B lens group, and Ym shows 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 most image side lens surface 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-β1b) · βm | <0.9 (5)
Here, β1b represents the lateral magnification of the first B lens group at the time of focusing on infinity, and βm represents the combined lateral magnification of the lens disposed on the image side with respect to the first B lens group at the time of focusing on infinity.

  In the optical system according to the present invention, in the first lens group, the first B lens group has a positive refractive power, the first C lens group has a negative refractive power, and the first B lens group is an object. It is preferable that the side surface is composed 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 a negative refractive power, the first C lens group has a positive refractive power, It is also preferable that the 1B lens unit includes one negative lens having a concave object-side surface.

  In the optical system according to the present invention, it is preferable that the first lens group is fixed in the optical axis direction during focusing.

  An imaging apparatus according to the present invention includes the above-described optical system and an imaging element that is provided on an image side of the optical system and converts an optical image formed by the optical system into an electrical signal. Features.

  According to the present invention, it is possible to reduce the weight and size of the entire optical system including the image stabilizing group, and to provide an optical system that is excellent in imaging performance from infinity to the nearest even during image stabilization.

It is lens sectional drawing which shows the lens structural example of the optical system (single focus wide-angle lens) of Example 1 of this invention. FIG. 4 is a longitudinal aberration diagram of the optical system of Example 1 in a focused state at infinity. FIG. 3 is a lateral aberration diagram of the optical system of Example 1 in a focused state at infinity. It is lens sectional drawing which shows the lens structural example of the optical system (single focus wide-angle lens) of Example 2 of this invention. FIG. 6 is a longitudinal aberration diagram of the optical system of Example 2 in an infinitely focused state. FIG. 6 is a lateral aberration diagram of the optical system of Example 2 in a focused state at infinity. It is lens sectional drawing which shows the lens structural example of the optical system (single focus wide-angle lens) of Example 3 of this invention. FIG. 6 is a longitudinal aberration diagram of the optical system of Example 3 when focusing on infinity. FIG. 6 is a transverse aberration diagram for the optical system of Example 3 when the optical system is in infinity focus. It is lens sectional drawing which shows the lens structural example of the optical system (single focus wide-angle lens) of Example 4 of this invention. FIG. 6 is a longitudinal aberration diagram of the optical system of Example 4 in an infinitely focused state. FIG. 10 is a lateral aberration diagram of the optical system of Example 4 when the optical system is in focus at infinity.

  Hereinafter, embodiments of an optical system and an imaging apparatus 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. An optical system according to the present invention includes, in order from the object side, 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. Is disposed on the image side of the first lens group, and 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, and the first A lens group has a negative refractive power. The first B lens group is a vibration-proof group, and the image is moved by moving the vibration-proof 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 arranged closest to the object side in the optical system, and has negative refractive power. That is, the optical system is a negative leading type optical system, which is suitable for a bright optical system requiring a back focus such as an interchangeable lens of a single-lens reflex camera and having a small F value.

  As described above, 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 having negative refractive power, and the aperture stop is the first. Arranged on the image side of the lens group. By adopting this configuration, the height of the on-axis light beam and off-axis light beam incident on the first B lens group from the optical axis can be reduced. For this reason, the outer diameter of the lens which comprises a 1B lens group can be made the smallest in the said optical system. Therefore, by using the 1B lens group as a vibration proof group, the vibration proof group can be reduced in size and weight, and the movable range of the vibration proof group during vibration reduction can be reduced. Further, by reducing the size and weight of the vibration-proof group, the vibration-proof drive mechanism such as an actuator for driving the vibration-proof group can also be reduced in size and weight. For these reasons, the lens barrel diameter can be reduced even if an anti-vibration drive mechanism is disposed around the anti-vibration group. Furthermore, since the aperture stop is disposed on the image side of the first lens group, the arrangement of the image stabilization drive mechanism and the aperture drive mechanism such as an actuator for driving the aperture stop does not interfere with each other in the lens barrel. The lens barrel diameter can be reduced.

  In addition, since the height of the axial light beam incident on the anti-vibration group (the first B lens group) from the optical axis can be reduced, even if the anti-vibration group is decentered at the time of anti-vibration, the variation of the axial coma aberration is It becomes easy to keep it small, and high imaging performance can be maintained even during image stabilization.

  On the other hand, when the lens group arranged in the vicinity of the aperture stop or on the image side from the aperture stop is the anti-vibration lens group, the outer diameter of the lenses constituting the anti-vibration group becomes large, and This is not preferable because the vibration driving mechanism and the barrel diameter are increased. Further, in this case, the axial coma at the time of anti-vibration becomes large, and it is difficult to satisfactorily correct the aberration fluctuation at the time of anti-vibration unless an aspheric surface is introduced into the anti-vibration group.

  The first lens group is preferably fixed to the optical axis during focusing. A focus driving mechanism such as an actuator for driving a focus group that moves along the optical axis during focusing by disposing the image stabilizing group in the first lens group that is a fixed group during focusing; The arrangement with the anti-vibration drive mechanism does not interfere, and the mechanical configuration in the lens barrel can be simplified and the lens barrel diameter 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) 1A lens group As long as the 1A lens group as a whole has negative refractive power, the specific lens configuration is not particularly limited. Depending on the optical performance required for the optical system, an appropriate lens configuration can be obtained as appropriate.

ii) 1C lens group The specific lens configuration of the 1C lens group is not particularly limited, and the refractive power may be positive or negative. However, from the viewpoint of improving the imaging performance during image stabilization, it is preferable to have a refractive power with a sign opposite to the sign of the refractive power of the first B lens group described below. This point will be described later.

iii) 1B lens group The 1B lens group is preferably composed of a single lens component. Here, the single lens component includes a single lens, a cemented lens, and a compound lens, and refers to a lens that does not include an air layer between the most object side surface and the most image side surface. By constructing the first lens group from a single lens component, the configuration of the anti-vibration group can be simplified as compared with the case where the first B lens group is composed of a plurality of lenses including an air layer, and manufacturing errors are increased. It is possible to prevent the deterioration of the imaging performance due to the factor.

  Here, in order to further reduce the size and weight of the vibration-proof group, it is preferable to configure the first B lens group with one single lens. According to the optical configuration of the present invention, as described above, the height from the optical axis of the on-axis light beam incident on the anti-vibration group can be reduced. Therefore, even when the anti-vibration 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 reduce the size and weight of the anti-vibration driving mechanism, and it is also possible to improve the stopping accuracy during the anti-vibration correction.

  The refractive power of the first B lens group may be positive or negative, but the most object-side surface of the first B lens group is preferably concave. In the optical system according to the present invention, since the first A lens group has negative refractive power, the light incident on the first B lens group is divergent light. At this time, by making the most object side surface of the 1B lens group concave, the difference between the incident angle of the off-axis light beam at the time of no eccentricity and the incidence angle of the off-axis light beam at the time of decentering can be kept small. As a result, it is possible to reduce the amount of astigmatism at the time of decentering. At this time, the sign of the refractive power of the first B lens group may be positive or negative, but the refractive power of the first B lens group and the refractive power of the first C lens group are opposite to each other. It is preferable.

  In a wide-angle lens with a short focal length, it may be difficult to suppress fluctuations in astigmatism when the lens is decentered. However, the most object-side surface of the first B lens group is concave, and the first B lens Since the refractive power of the first lens group and the refractive power of the first C lens group are different from each other, the astigmatism generated in the first B lens group can be immediately canceled out by the first C lens group immediately after 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, the positive meniscus lens whose surface on the object side is concave is the first B lens group. It is preferable to use a single sheet. On the other hand, when the refractive power of the first B lens group is negative, the refractive power of the first C lens group is preferably positive. In this case, it is preferable that the first B lens group is composed of a single negative lens having a stronger curvature on the object side surface than on the image side surface.

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

(2) Rear Group In the optical system according to the present invention, if the rear group following the first lens group has positive refractive power in the entire rear group, the specific lens group configuration is particularly limited. It is not something. That is, the rear group may be composed of one lens group, or may be composed of a plurality of lens groups, and the specific lens configuration of each lens group is not particularly limited. However, since the first lens group is preferably fixed in the optical axis direction during focusing, it is preferable to provide a focus group that moves along the optical axis direction during focusing in the rear group. For example, when the rear group includes a plurality of lens groups, it is preferable that a lens group other than the lens group disposed closest to the object side in the rear group is the focus group. That is, by making the lens group arranged closer to the image side with respect to the first lens group as the focus group, it becomes easier to avoid interference between the image stabilization drive mechanism and the focus drive mechanism.

(3) Aperture stop In the optical system according to the present invention, the aperture stop only needs to be disposed on the image side of the first lens group. As long as this requirement is satisfied, the aperture stop is disposed between the first lens group and the rear group. It may be arranged in the rear group or in the rear group, and the specific arrangement is not particularly limited. Further, the aperture stop may be fixed in the optical axis direction or may be configured to be movable in the optical axis direction. In any case, the effect according to the present invention can be obtained.

1-2. Conditional Expression Next, each conditional expression will be described. As described above, the optical system preferably employs the above configuration and satisfies the following conditional expressions (1) to (5). Hereinafter, each conditional expression will be described.

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 represents the focal length of the entire optical system, and f1B represents the focal length of the first B lens group.

  Conditional expression (1) is an expression defining the ratio between the focal length of the entire optical system and the focal length of the image stabilizing group (first B lens group). If conditional expression (1) is satisfied, the amount of movement of the image stabilization group during image stabilization is within an appropriate range, aberration fluctuation during image stabilization can be suppressed, and high imaging performance can be maintained during image stabilization. In addition, the vibration-proof drive mechanism can be prevented from becoming large and the lens barrel diameter can be reduced.

  When the numerical value of the conditional expression (1) is less than or equal to the lower limit value, the refractive power of the image stabilizing group is small, which is advantageous in suppressing aberration fluctuations during image stabilizing. However, since the amount of movement of the image stabilizing group during image stabilization, that is, the lens driving amount increases, the driving load of the image stabilization driving mechanism also increases. At the same time, the vibration-proof drive mechanism is increased in size, and the lens barrel diameter is also increased. For these reasons, it is not preferable that the numerical value of conditional expression (1) is less than or equal to the lower limit. On the other hand, if the numerical value of the conditional expression (1) is equal to or greater than the upper limit value, the amount of lens driving during the image stabilization becomes small. It is advantageous. However, the refractive power of the anti-vibration group is large, and fluctuations in astigmatism and coma at the time of anti-vibration become large, and it is difficult to correct these well.

  In order to ensure these effects, 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)
However, L1b shows the distance on the optical axis from the most object side lens surface of the optical system to the most object side lens surface of the 1B lens group, and Ym shows the maximum image height.

  Conditional expression (2) is a condition indicating 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 is incident on the first B lens group, and the height from the optical axis when the on-axis light beam is incident on the first B lens group. Any of the heights can be lowered. As a result, the outer diameter of the lenses constituting the 1B lens group can be reduced, and accordingly, the driving load of the image stabilization drive mechanism can be reduced, and the image stabilization drive mechanism can be downsized. .

  On the other hand, when the numerical value of the conditional expression (2) is less than or equal to the lower limit value, the height from the optical axis when the off-axis light beam enters the first B lens group increases, so that the lens constituting the image stabilization group This increases the outer diameter of the lens, increases the driving load of the image stabilization drive mechanism, and increases the size of the image stabilization drive mechanism. In this case, it is difficult to suppress the fluctuation of astigmatism at the time of decentration. On the other hand, when the numerical value of the conditional expression (2) is equal to or greater than the upper limit value, the height from the optical axis when the off-axis light beam enters the first B lens group decreases, but the on-axis light beam that enters the first B lens group. The height from the optical axis increases. Therefore, also in this case, the outer diameter of the lens constituting the image stabilizing group cannot be made sufficiently small, the driving load of the image stabilizing drive mechanism is increased, and the image stabilizing drive mechanism is also increased in size, which is not preferable.

  In order to ensure these effects, 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 indicating the ratio of the entrance pupil position to the total optical length. By satisfying conditional expression (3), the position of the entrance pupil on the optical axis becomes appropriate, the image stabilizing group can be downsized, and high imaging performance can be maintained even during image stabilization. .

  On the other hand, when the numerical value of the conditional expression (3) is equal to or lower 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 diameter of the filter and reducing the outer diameter of the lens constituting the vibration isolation group. However, in the rear group on the image side from the first lens group, it is necessary to arrange a group having a strong positive refractive power, and each lens group alone has insufficient aberration correction, and coma aberration and field curvature are improved. It becomes difficult to correct. On the other hand, when the numerical value of conditional expression (3) is equal to or greater than the upper limit value, the height from the optical axis of the off-axis light beam passing through the first lens group increases, so the outer diameter of the lens constituting the image stabilizing group is increased. This is not preferable.

  In order to ensure these effects, the lower limit value of conditional expression (2) 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)
However, Ls indicates the distance on the optical axis from the most image side lens surface 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 first B lens group and the aperture stop on the optical axis becomes appropriate, and the image stabilization drive mechanism and the aperture drive mechanism are not interfered with each other in the lens barrel. These can be arranged. Further, when the conditional expression (4) is satisfied, the height from the optical axis of the off-axis light beam passing through the first B lens group is within an appropriate range, and the outer diameter of the lens constituting the first B lens group is increased. Can be suppressed.

  On the other hand, when the numerical value of the conditional expression (4) is less than or equal to the lower limit value, the distance between the first B lens group and the aperture stop on the optical axis becomes shorter than an appropriate range, and the vibration-proof drive mechanism The diaphragm drive mechanism interferes, making it difficult to dispose the mechanism in the lens barrel and increasing the lens barrel diameter. On the other hand, if the upper limit is exceeded, the height of the off-axis light beam passing through the first B lens group from the optical axis becomes high, and therefore it is necessary to configure the first B lens group with a lens having a large outer diameter. Increases in size and weight, which increases the driving load of the vibration-proof drive mechanism. For this reason, it leads to the enlargement of an anti-vibration drive mechanism, and 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-β1b) · βm | <0.9 (5)
However, β1b is the lateral magnification of the first B lens group at the time of focusing on infinity, βm is the combined lateral magnification of the lens disposed on the image side of the first B lens group at the time of focusing on infinity, that is, the first C lens. The composite lateral magnification of the group and the rear group is shown.

  Conditional expression (5) is a condition that defines the ratio of the amount of movement of the first B lens group in the direction substantially perpendicular to the optical axis and the amount of movement of the image position on the image plane that occurs in association therewith. If the numerical value of the conditional expression (5) is equal to or greater than the upper limit value, the amount of movement of the image stabilizing group required to move the image position by a predetermined amount becomes too small, and it is too high to move the image stabilizing group to the required position. Accuracy control is required, and in reality, it is difficult to control the position of the vibration isolation group. On the other hand, when the numerical value of the conditional expression (5) is less than or equal to the lower limit, the amount of movement of the image stabilizing group required for moving the image position by a predetermined amount increases. For this reason, the driving load of the vibration proof drive mechanism is increased, which increases the size of the vibration proof drive mechanism.

  In order to 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. Next, an imaging apparatus according to the present invention will be described. An imaging apparatus according to the present invention includes the optical system according to the present invention, and an imaging element that is provided on an image side of the optical system and converts an optical image formed by the optical system into an electrical signal. It is characterized by that. Here, there is no particular limitation on the image sensor and the like, and a solid-state image sensor such as a CCD sensor or a CMOS sensor can also be used. The image pickup apparatus according to the present invention uses these solid-state image sensors such as a digital camera and 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-exchangeable 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 is a negative leading type in which the first lens unit has a negative refractive power, can be a bright optical system with a small F value, and has a relatively long back focus. For this reason, the imaging device according to the present invention is particularly 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 with reference to examples and comparative examples. However, the present invention is not limited to the following examples. An optical system of each embodiment described below is a photographing optical system used for an imaging apparatus (optical apparatus) such as a digital camera, a video camera, and a silver salt film camera, and is configured as a single-focus wide-angle lens. In the lens cross-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 the optical system of an imaging lens (single focus wide angle lens) of Example 1 according to the present invention. The imaging lens includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, and includes the first lens group G1 and the second lens group G2. Has been.

  The first lens group G1, in order from the object side, includes a negative meniscus lens L1 having a convex surface on the object side, a biconvex lens L2, a negative meniscus lens L3 having a concave surface on the object side, a biconcave lens L4, and a biconvex lens L5. It is comprised from the cemented lens which consists of. In the first lens group G1, the negative meniscus lens L1 located closest to the object side is a composite aspherical lens in which an aspherical surface is formed by providing a resin layer on the image side surface. In the first lens group G1, the first A lens group G1A is composed of the negative meniscus lens L1 and the biconvex lens L2, and the first B lens group G1B is composed of the negative meniscus lens L3, and the first C lens group G1C. Is composed of the above cemented lens. The negative meniscus lens L3 having a concave object-side surface constituting the 1B lens group is a vibration-proof group. By moving the vibration-proof group in the direction perpendicular to the optical axis, vibrations such as camera shake are generated during imaging. When it occurs, the image position is moved to correct the image blur. 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 during focusing.

  The second lens group G2, in order from the object side, includes a biconvex lens L6, a cemented lens composed of 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. 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 infinity to a close 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, specifically, an imaging plane of a solid-state imaging device such as a CCD sensor or a CMOS sensor, or a silver salt film. The film surface etc. are shown. These symbols and the like are the same 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 surfaces counted from the object side, “r” is the radius of curvature of the lens surface, “d” is the interval (surface interval) on the optical axis of the lens surface, and “nd” is the d line. The refractive index with respect to (wavelength λ = 587.6 nm), “vd”, indicates the Abbe number with respect to the d-line. When the lens surface is an aspherical surface, * (asterisk) is attached after the surface number, and the paraxial radius of curvature is shown in the column of the radius of curvature r. The unit of length in the table is all “mm”, and the unit of angle of view is “°”.

  Table 2 (2-1) shows the aspheric coefficient 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 ] + A4h ⁴ + A6h ⁶ + A8h ⁸ + A10h ¹⁰ ...
(Where c is the curvature (1 / r), h is the height from the optical axis, k is the conic coefficient, A4, A6, A8, A10... Are the aspheric coefficients of the respective orders.)

  Further, Table 2 (2-2) shows the focal lengths of the first lens group and the second lens group, respectively. Table 2 (2-3) shows the variable distance 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 field angle, and “Ym” is the maximum image height. These notations are the same in the following Examples 2 to 4.

f = 34.00
FNo. = 1.83
ω = 32.81
Ym = 21.633

  FIG. 2 is a longitudinal aberration diagram when the imaging lens is focused at infinity. Each longitudinal aberration diagram represents spherical aberration, astigmatism, and distortion aberration in order from the left toward the drawing. FIG. 3 shows a lateral aberration diagram of the imaging lens when focused at infinity. Each lateral aberration diagram shows coma when 0.0Ym to 1.0Ym. Ym is the maximum image height. In the spherical aberration diagram, the distortion diagram, and the 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 sagittal image plane aberration at the d line, and the broken line (dm) indicates the meridional image plane aberration at the d line. Since these are the same in each figure shown in Example 2-Example 4, description is abbreviate | omitted below.

(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. The imaging lens of Example 2 includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex object side surface, a positive meniscus lens L2 having a convex object side surface, a biconcave lens L3, and a biconvex lens L4. The In the first lens group G1, the negative meniscus lens L1 located closest to the object side is a composite aspherical lens in which an aspherical surface is formed by providing a resin layer on the image side surface. In the first lens group G1, the first A lens group G1A is composed of the negative meniscus lens L1 and the positive meniscus lens L2, the first B lens group G1B is composed of a biconcave lens L3, and the first C lens group G1C is The biconvex lens L4 is used. The biconcave lens L3 constituting the first B lens group is a vibration-proof group, and the image blur correction is performed by moving the vibration-proof group in a direction perpendicular to the optical axis. 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 during focusing.

  The second lens group G2 includes, in order from the object side, a biconvex lens L5, a cemented lens of 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 surface on the object side. 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 infinity to a close object is performed by moving the second lens group G2 to the object side.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging lens are applied will be described. Table 3 shows lens data of the imaging lens. Table 4 (4-1) shows the aspherical coefficients and conic constants of the aspheric surfaces shown in Table 3, Table 4 (4-2) shows the focal length of each lens group, and Table 4 (4-3) shows It is a variable interval on the optical axis of the lens surface shown in Table 3. The focal length, F value, half field angle, and maximum image height of the optical system are shown below. Further, FIG. 4 and FIG. 5 show longitudinal aberration diagrams and lateral aberration diagrams of the optical system when focusing on infinity, respectively.

f = 34.00
FNo. = 1.85
ω = 32.74
Ym = 21.633

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

  The first lens group G1, in order from the object side, includes a negative meniscus lens L1 having a convex surface on the object side, a negative meniscus lens L2 having a convex surface on the object side, and a positive meniscus lens L3 having a convex surface on the image side. The negative meniscus lens L4 having a convex surface on the image side. The negative meniscus lens L2 arranged 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 is composed of the negative meniscus lens L1 and the negative meniscus lens L2, and the first B lens group G1B is composed of the positive meniscus lens L3, and the first C lens group. G1C includes the negative meniscus lens L4. The positive meniscus lens L3 constituting the first B lens group G1B is an image stabilization group, and the image blur correction is performed by moving the image stabilization 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 includes, in order from the object side, a cemented lens including a negative meniscus lens L5 and a biconvex lens L6 whose surface on the object side is convex, and a biconvex lens L7. Focusing from an infinite distance to a short 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 during focusing.

  The third lens group G3 includes, in order from the object side, a three-piece cemented lens obtained by cementing three lenses, a biconcave lens L8, a biconvex lens L9, and a negative meniscus lens L10 having a convex surface on the image side, a biconvex lens L11, The object side surface includes a cemented lens including 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 Examples Next, numerical examples to which specific numerical values of the imaging lens are applied will be described. Table 5 shows lens data of the imaging lens. Table 6 (6-1) shows the aspherical coefficients and conic constants of the aspheric surfaces shown in Table 5, Table 6 (6-2) shows the focal length of each lens group, and Table 6 (6-3) shows It is a variable interval on the optical axis of the lens surface shown in Table 5. The focal length, F value, half field angle, and maximum image height of the optical system are shown below. Further, FIG. 8 and FIG. 9 show a longitudinal aberration diagram and a lateral aberration diagram of the optical system when focusing on infinity, respectively.

f = 20.60
FNo. = 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. The imaging lens of Embodiment 4 includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. It consists of.

  The first lens group G1, in order from the object side, includes a negative meniscus lens L1 having a convex object side surface, a negative meniscus lens L2 having a convex object side surface, and a negative meniscus lens L3 having a convex object side surface. The positive meniscus lens L4 having a convex surface on the image side and the negative meniscus lens L5 having a convex surface on the image side. The negative meniscus lens L3 arranged third from the object side is a glass mold type aspheric lens having both aspheric surfaces. 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. The first B lens group G1B includes the positive meniscus lens L4. The first C lens group G1C is configured by the negative meniscus lens L5. The positive meniscus lens L4 constituting the first B lens group G1B is an image stabilization group, and the image blur correction is performed by moving the image stabilization 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 includes, in order from the object side, a cemented lens including a negative meniscus lens L6 and a biconvex lens L7 whose surface on the object side is convex, and a biconvex lens L8. Focusing from an infinite distance to a short 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 during focusing.

  The third lens group G3 includes, in order from the object side, a biconcave lens L9, a cemented lens including 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 is composed of a cemented lens made up of a biconvex lens L13 and a biconcave lens L14. In the third lens group G3, the biconcave lens L14 arranged closest to the image side is a glass mold type aspheric lens having an aspheric surface on the object side.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the imaging lens are applied will be described. Table 7 shows lens data of the imaging lens. Table 8 (8-1) shows the aspheric coefficients and conic constants of the aspheric surfaces shown in Table 7, Table 8 (8-2) shows the focal length of each lens group, and Table 8 (8-3) shows It is a variable interval on the optical axis of the lens surface shown in Table 5. The focal length, F value, half field angle, and maximum image height of the optical system are shown below. Furthermore, FIG.11 and FIG.12 shows the longitudinal aberration figure and lateral aberration figure at the time of infinity focusing of the said optical system, respectively.

f = 18.50
FNo. = 2.89
ω = 49.85
Ym = 21.633

Table 9 shows numerical values of the conditional expressions (1) to (5) in the respective examples.

  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. It is possible to provide an optical system and an imaging apparatus that can be provided with a compact barrel diameter.

Claims (10)

In order from the object side, the 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 closer to the image side than 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 a negative refractive power, and the first B lens group An optical system which is a vibration group and moves an image by moving the vibration isolation group in a direction substantially perpendicular to the optical axis. The optical system according to claim 1, wherein the following conditional expression (1) is satisfied.
0.1 <f / | f1b | <0.6 (1)
Here, f represents the focal length of the entire optical system, and f1B represents the focal length of the first B lens group. The optical system according to claim 1 or 2, wherein the following conditional expression (2) is satisfied.
0.9 <L1b / Ym <1.6 (2)
However, L1b shows the distance on the optical axis from the most object side lens surface of the optical system to the most object side lens surface of the 1B lens group, and Ym shows 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 (4) is satisfied.
0.25 <Ls / Ym <1.1 (4)
Here, Ls represents the distance on the optical axis from the most image side lens surface of 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 (5) is satisfied.
0.2 <| (1-β1b) · βm | <0.9 (5)
Here, β1b represents the lateral magnification of the first B lens group when focused at infinity, and βm represents the combined lateral magnification of the lens disposed on the image side of the first B lens group when focused at infinity. In the first lens group, the first B lens group has a positive refractive power, the first C lens group has a negative refractive power,
The optical system according to any one of claims 1 to 6, wherein the first B lens group includes a single positive meniscus lens having a concave object-side surface. In the first lens group, the first B lens group has a negative refractive power, the first C lens group has a positive refractive power,
The optical system according to any one of claims 1 to 6, wherein the first B lens group includes one negative lens having a concave object-side surface.   The optical system according to any one of claims 1 to 8, wherein the first lens group is fixed in an optical axis direction during focusing.   An optical system according to any one of claims 1 to 9, and an image pickup device that is provided on an image side of the optical system and converts an optical image formed by the optical system into an electrical signal. An image pickup apparatus comprising:

Images