JP6546076B2 - Wide-angle lens and imaging device - Google Patents

Description

  The present invention relates to a wide-angle lens and an imaging device, and more particularly to a wide-angle lens having a large aperture and an imaging device provided with the wide-angle lens.

  Conventionally, a wide-angle lens called a retrofocus type (reverse telephoto type) preceded by a negative lens group is widely known (see, for example, "Patent Document 1"). A retrofocus wide-angle lens has a large back focus as compared to the focal length of the entire lens system. Therefore, it can be suitably used as a lens interchangeable type imaging device such as a single-lens reflex camera.

  Generally, in a retrofocus wide-angle lens, a negative lens unit is disposed in front (object side), and a positive lens unit is disposed behind (image side). As described above, in the retrofocus wide-angle lens, the arrangement of refractive powers in the entire system is asymmetric in the front-rear direction. For this reason, various aberrations such as spherical aberration, coma, distortion and astigmatism occur in a large amount, and it is very difficult to correct these various aberrations in a well-balanced manner.

  Therefore, a wide-angle lens has been proposed in which the asymmetry of the refractive power arrangement is reconsidered and positive lens groups are arranged in the front group and the rear group, respectively (see, for example, "Patent Document 2"). The wide-angle lens described in Patent Document 2 has an imaging angle of view (2ω) of 83 ° to 84 °, and realizes a bright large-aperture optical system with an F number of about 1.4. Further, by adopting the refractive power arrangement, various aberrations caused by the asymmetric refractive power arrangement, in particular, sagittal coma aberration peculiar to a large aperture wide-angle lens can be corrected well.

JP, 2009-109723, A JP, 2011-59290, A

  However, in the wide-angle lens described in Patent Document 2, the lens configuration of the first lens unit is insufficient. Therefore, in the wide-angle lens, the correction of the axial chromatic aberration and the magnification chromatic aberration peculiar to the large-aperture wide-angle lens is particularly insufficient, and sufficient optical performance is not obtained.

  An object of the present invention is to provide a compact wide-angle lens capable of achieving high optical performance over the entire focus range regardless of the object distance while maintaining the required back focus, angle of view and f-number, and imaging including the wide-angle lens It is in providing an apparatus.

  In order to solve the above problems, the wide-angle lens according to the present invention comprises, in order from the object side, at least a first lens group having positive refractive power and a second lens group having positive refractive power. Focusing is performed by moving a lens group, and the first lens group includes at least three negative lenses and one positive lens, and the most object of the negative lenses included in the first lens group When the negative lens disposed on the side is a negative lens L1n, the negative lens L1n is characterized by satisfying the following conditions.

PgF-(0.6438-0.001682 x vd1n)> 0.006 (1)
d d 1 n <40 (2)
However,
PgF represents a partial dispersion ratio of g-line and F-line of the negative lens L1n,
ν d1 n represents an Abbe number for the d-line of the negative lens L 1 n.

  In addition, the imaging device of the present invention includes the wide-angle lens according to the present invention, and an imaging device for converting an optical image formed by the wide-angle lens into an electrical signal on the image plane side of the wide-angle lens. It is characterized by

  According to the present invention, it is possible to provide a compact wide-angle lens capable of achieving high optical performance while maintaining a predetermined back focus, angle of view, and f-number, and an imaging device provided with the wide-angle lens.

It is sectional drawing which shows the lens structural example at the time of infinity focusing of the wide angle lens of Example 1 of this invention. FIG. 6 is a longitudinal aberration diagram of the wide-angle lens of Example 1 at infinity focusing. However, spherical aberration, astigmatism and distortion are shown sequentially from the left toward the drawing. The same applies to the longitudinal aberration diagrams. 5 is a lateral aberration diagram showing coma aberration at infinity focusing of the wide-angle lens of Example 1. FIG. 5 is a longitudinal aberration diagram at the time of 0.5 m focusing of the wide-angle lens of Example 1. FIG. 5 is a lateral aberration diagram showing coma aberration at the time of 0.5 m focusing of the wide-angle lens of Example 1. FIG. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the wide angle lens of Example 2 of this invention. FIG. 6 is a longitudinal aberration diagram of the wide-angle lens of Example 2 when focused on infinity. FIG. 6 is a lateral aberration diagram representing coma aberration at infinity focusing of the wide-angle lens of Example 2. FIG. 7 is a longitudinal aberration diagram of the wide-angle lens of Example 2 at the time of 0.5 m focusing. FIG. 7 is a lateral aberration diagram representing coma aberration when the wide-angle lens of Example 2 is in focus of 0.5 m. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the wide angle lens of Example 3 of this invention. FIG. 7 is a longitudinal aberration diagram of the wide-angle lens of Example 3 when focused on infinity. FIG. 6 is a lateral aberration diagram representing coma aberration when focusing at infinity of a wide-angle lens according to Implementation 3; FIG. 7 is a longitudinal aberration diagram of the wide-angle lens of Example 3 when in focus of 0.5 m. FIG. 7 is a lateral aberration diagram representing coma aberration when the wide-angle lens of Example 3 is in focus of 0.5 m. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the wide angle lens of Example 4 of this invention. FIG. 7 is a longitudinal aberration diagram of the wide-angle lens of Example 4 when focused on infinity. FIG. 16 is a lateral aberration diagram representing coma aberration at infinity focusing of the wide-angle lens of Example 4. FIG. 7 is a longitudinal aberration diagram of the wide-angle lens of Example 4 when in focus of 0.5 m. FIG. 16 is a lateral aberration diagram showing a coma aberration at the time of 0.5 m focusing of the wide-angle lens of Example 4. It is sectional drawing which shows the lens structural example at the time of infinity focusing of the wide angle lens of Example 5 of this invention. FIG. 16 is a longitudinal aberration diagram of the wide-angle lens of Example 5 when focused on infinity. FIG. 18A is a lateral aberration diagram representing coma aberration at infinity focusing of the wide-angle lens of Example 5. FIG. 16 is a longitudinal aberration diagram at the time of 0.5 m focusing of the wide angle lens of Example 5. FIG. 16 is a lateral aberration diagram representing coma aberration at the time of 0.5 m focusing of the wide-angle lens of Example 5.

  Hereinafter, embodiments of a wide-angle lens and an imaging device according to the present invention will be described.

1. Wide-angle lens 1-1. Configuration of Wide-Angle Lens The wide-angle lens according to the present invention comprises at least a first lens group having positive refractive power and a second lens group having positive refractive power in order from the object side, and at least the second lens group The first lens group includes at least three negative lenses and one positive lens, and is disposed closest to the object side among the negative lenses included in the first lens group. When the negative lens L1n is a negative lens, the negative lens L1n is characterized by satisfying a predetermined condition described later. First, after describing the configuration of the wide-angle lens according to the present invention, matters concerning the conditional expression will be described.

  In a wide-angle lens, an off-axis light beam incident at a large incident angle is converged by the first lens group. Therefore, the incident angle of the off-axis light beam with respect to the lens surface of the lens disposed on the object side in the first lens group is large, aberration is apt to occur, and the aberration amount tends to be large. Therefore, in the present invention, by making the first lens group include at least three negative lenses and one positive lens, generation of aberration can be suppressed and high optical performance can be realized. As described above, since the off-axis light flux can be corrected well, high optical performance can be realized over the entire screen.

  Further, by making the first lens group have a positive refractive power, light converged by the first lens group can be made incident on the second lens group. Therefore, it is easy to reduce the diameter of the lens unit disposed closer to the image than the first lens unit. Therefore, by setting the lens unit disposed on the image side of the first lens unit as a moving unit at the time of focusing, the weight of the focus unit can be reduced, and a quick focusing operation can be performed.

  Furthermore, in the present invention, by adopting the above lens group configuration and performing focusing by moving at least the second lens group, it is possible to reduce aberration fluctuation due to focusing from infinity to near distance. Therefore, good optical performance can be realized over the entire focusing range regardless of the object distance. Hereinafter, preferable configuration examples of each lens group will be described.

(1) First Lens Group The first lens group has positive refractive power, and as long as it has the above-mentioned configuration, the specific configuration is not particularly limited. However, it is more preferable to adopt the following configuration.

  In the wide-angle lens according to the present invention, the first lens group includes, in order from the object side, a first A lens group having negative refractive power and a first B lens group having positive refractive power. It is preferable that the first lens unit B includes two or more negative lenses and one or more positive lenses, and the first lens group B includes two or more positive lenses and one or more negative lenses.

  By forming the first lens group having a positive refractive power as a whole from the first A lens group having a negative refractive power and the first B lens group having a positive refractive power in order from the object side, a so-called retro The focus type lens configuration can be emphasized. Therefore, even when the wide-angle lens is made wide-angle, it is easy to secure a predetermined back focus required for the wide-angle lens, such as an interchangeable lens of a single-lens reflex camera.

i) First A lens group In the first A lens group, it is preferable to dispose a meniscus negative lens having a convex surface facing the object side on the most object side. By arranging such a meniscus-shaped negative lens on the most object side of the first lens group A, occurrence of the above-mentioned various aberrations is caused even if an off-axis ray is incident on this meniscus-shaped negative lens at a large incident angle. It can be suppressed and it becomes easy to realize higher optical performance. Note that regardless of the specific configuration of the first lens group, that is, even when the first lens group is not composed of the first A lens group and the first B lens group, it is disposed on the most object side of the first lens group. The same effect as described above can be obtained by using a negative meniscus lens with a convex surface facing the object side.

  Further, in the first lens group A, it is preferable that the lens surface disposed closest to the image side be concave toward the image side. By placing the concave lens surface on the image side closest to the image side of the 1st lens group A, the aberration burden of the negative lens arranged on the object side of the 1st lens group 1 can be reduced, so It is easy to achieve wide angle and large aperture.

  Furthermore, the first lens group A is more preferably composed of three negative lenses and one positive lens. By adopting the configuration, it becomes easy to gently converge the light beam with respect to the off-axis light beam incident at a large incident angle, and correct various aberrations, particularly astigmatism and coma aberration, well with a small number of lenses. It will be easier to do.

ii) First B lens group By configuring the first B lens group to include two or more positive lenses, sagittal coma aberration peculiar to a large aperture optical lens can be corrected well.

  In the first B lens group, it is preferable to dispose a negative lens component that is concave on the object side at the object side on the most object side. By arranging such a negative lens component on the most object side of the 1B lens group, it is possible to further emphasize the retrofocus type lens configuration, and it is sufficient even when the wide angle lens is made wide. It becomes easier to secure the back focus. In order to obtain the effect, when the image side surface of the negative lens component is concave toward the image side, the curvature of the object side surface of the negative lens component is preferably larger than the curvature of the image side surface.

  However, in the present invention, the lens component includes a single lens, a compound lens in which an aspheric resin is formed on one side or both sides of the lens, and the like. The lens component also includes a cemented lens in which two or more lenses are cemented. However, in the case of a cemented lens, the entire cemented lens is referred to as a lens component, and the negative lens component has negative refractive power when viewed in the cemented lens as a whole. At this time, when the cemented lens is referred to as a lens component, the object side surface means the surface disposed closest to the object side in the cemented lens, and the image side surface is disposed most on the image side in the cemented lens. Shall mean the face.

  Furthermore, it is preferable that the curvature of the object side surface of the negative lens component is the largest among the lenses having a concave shape on the object side surface included in the first lens group. As described above, the first lens group is composed of the first A lens group and the first B lens group, and a negative lens component in which the object side surface is a concave having a strong curvature is disposed on the most object side in the first B lens group. Thus, the following effects can be obtained. Generally, as the concave shape of the lens becomes stronger, the negative refractive power becomes stronger, so both spherical aberration and astigmatism act on the over side. However, when the above configuration is adopted, in the first B lens group, the concave surface disposed closest to the object side has variations in spherical aberration and astigmatism with respect to the refractive power of the surface in the opposite directions. That is, when the concave shape of the concave surface becomes strong, astigmatism acts on the over side, while spherical aberration acts on the under side in the reverse direction. Therefore, spherical aberration and astigmatism can be favorably corrected by adopting the above-described configuration and disposing the negative lens component having a concave surface with such a strong curvature on the most object side in the first lens group. It becomes.

Further, the first lens group A and the first B lens are configured by arranging the first lens group in the above configuration and arranging a negative lens component that is a concave surface having a strong curvature on the object side surface on the most object side in the first B lens group. It becomes easy to appropriately set the refractive power balance in the group. As a result, various aberrations can be corrected in a well-balanced manner, and it becomes easy to realize higher optical performance.

Furthermore, in the first B lens group, it is preferable that the image side surface of the lens disposed closest to the image side, that is, the lens surface disposed closest to the image side has a convex shape on the image side. By disposing a convex lens surface on the image side closest to the image side of the 1B lens group, it is possible to satisfactorily correct distortion generated by the negative lens disposed on the 1A lens group, and higher It becomes easy to realize optical performance. In addition, regardless of the specific configuration of the first lens group, the same effect as described above can be obtained by making the lens surface disposed on the most image side of the first lens group convex toward the image side. .

(2) Second lens group The specific lens configuration is not particularly limited as long as the second lens group has positive refractive power as a whole. However, in order to solve the problems according to the present invention, the following configuration is preferable.

  In the second lens group, the lens surface disposed closest to the object side is preferably convex toward the object side. In the wide-angle lens according to the present invention, the first lens group has positive refractive power. Therefore, the luminous flux converged by the first lens group is incident on the second lens group. At this time, by making the lens surface of the second lens group located closest to the object side convex toward the object side, correction of spherical aberration and field curvature becomes easy. Therefore, it is possible to reduce the number of lenses constituting the second lens group, and to miniaturize the wide-angle lens.

  In the wide-angle lens according to the present invention, as described above, at least the second lens group is moved to perform focusing, so by configuring the second lens group with a smaller number of lenses, downsizing and weight reduction of the focusing group can be achieved. It is possible to achieve quick focus operation.

  Further, the second lens group may be divided into two or more partial lens groups, and each partial lens group may be moved at the time of focusing. At this time, even if the moving amounts of the partial lens groups are different, the object of the present invention can be achieved. If each partial lens group is moved by a different moving amount at the time of focusing, it becomes easy to perform better aberration correction over the entire focusing range regardless of the object distance.

(3) Aperture Stop In the wide-angle lens according to the present invention, it is preferable to have an aperture stop in the second lens unit. Since the diameter of the axial luminous flux incident on the second lens group is converged by the first lens group as described above, the aperture stop can be miniaturized, and the drive mechanism for driving the aperture stop Miniaturization and weight reduction can be achieved. Therefore, it is easy to reduce the size and weight of the wide-angle lens. The second lens group may be divided into partial lens groups as described above before and after the aperture stop.

1-2. Lens Group Configuration The wide-angle lens may be provided with the above-described first lens group and second lens group, and the following lens group may be provided on the image side of the second lens group. For example, a third lens group or the like having a positive or negative refractive power can be disposed on the image side of the second lens group. At this time, the specific lens configuration and the like of the subsequent lens unit is not particularly limited.

  Further, the number of lens groups constituting the wide-angle lens is not particularly limited, but from the viewpoint of achieving further downsizing of the wide-angle lens, the wide-angle lens is configured of the first lens group and the second lens group. It is more preferable that

1-3. Operation at the time of focusing In the wide-angle lens according to the present invention, by moving the second lens unit along the optical axis, as long as focusing is performed, the other fixing / moving of the other lens units at the time of focusing is particularly limited. It is not a thing. However, from the viewpoint of reducing the weight of the focus group, it is preferable that the first lens group be fixed in the optical axis direction at the time of focusing. When a lens group is provided on the image side of the second lens group, focusing may be performed by moving the lens group having positive refractive power at the time of focusing. At this time, it may be moved by the same moving amount as the second lens unit, or may be moved by a different moving amount. However, as in the case of the first lens group, from the viewpoint of reducing the weight of the focus group, it is preferable that the subsequent lens group be fixed at the time of focusing.

1-4. Conditional Expressions Next, conditions that the wide-angle lens according to the present invention should satisfy, or conditions that should be satisfied will be described.

  In the wide-angle lens according to the present invention, when the negative lens L1n disposed closest to the object among the negative lenses included in the first lens group is the negative lens L1n, the negative lens L1n has the following conditional expression (1) and It is assumed that the condition expressed by the conditional expression (2) is satisfied.

Conditional Expression (1): PgF− (0.6438−0.001682 × dd1n)> 0.006
Conditional Expression (2): d d 1 n <40

However,
PgF represents the partial dispersion ratio of the g-line to the F-line of the negative lens L1n,
ν d1 n represents the Abbe number for the d-line of the negative lens L 1 n.

  Here, it is assumed that the refractive index of the glass for g-line (435.8 nm), F-line (486.1 nm), d-line (587.6 nm) and C-line (656.3 nm) is Ng, NF, Nd, NC, respectively. The Abbe number (νd) and the partial dispersion ratio (PgF) can be expressed as follows.

d d = (Nd-1) / (NF-NC)
PgF = (Ng-NF) / (NF-NC)

  The partial dispersion ratio (PgF) is a portion of C7 (glass material) (partial dispersion ratio 0.5393, dd: 60.49) and F2 (glass material) (partial dispersion ratio 0.5829, dd: 36.30) When the straight line passing through the variance ratio and the coordinate of d d is used as a reference line, it means the deviation of the partial dispersion ratio from the reference line.

1-4-1. Conditional expression (1)
First, the conditional expression (1) will be described. Conditional expression (1) defines the so-called anomalous dispersion of the negative lens L1n disposed closest to the object in the first lens group. By satisfying the conditional expression (1), for example, the secondary spectrum of lateral chromatic aberration can be favorably corrected even when attempting to increase the aperture while maintaining the angle of view of about 80 °, A compact, wide-angle lens with high performance can be realized.

  On the other hand, when the numerical value of the conditional expression (1) becomes equal to or less than the lower limit value, it becomes difficult to satisfactorily correct the secondary spectrum of lateral chromatic aberration. Therefore, it becomes difficult to realize high optical performance while maintaining a predetermined back focus, angle of view and F number. In addition, in order to realize good optical performance, the number of lenses for aberration correction increases, and it becomes difficult to miniaturize the wide-angle lens.

  In the wide-angle lens, the negative lens L1 n preferably satisfies the condition represented by the following conditional expression (1) ′, and more preferably satisfies the condition represented by the conditional expression (1) ′ ′. By satisfying these conditions, the effects of the present invention can be exhibited more.

Conditional Expression (1) ′: PgF− (0.6438−0.001682 × νd1n)> 0.01
Conditional Expression (1) ′ ′: PgF− (0.6438−0.001682 × νd1n)> 0.013

1-4-2. Conditional expression (2)
Conditional expression (2) defines the Abbe number of the negative lens L1n for the d-line. By satisfying the conditional expression (2), for example, it is possible to properly correct the chromatic aberration of magnification even when attempting to increase the aperture while maintaining the angle of view of about 80 °, and the small size with high optical performance. Can achieve a wide-angle lens.

  On the other hand, when the numerical value of the conditional expression (2) becomes equal to or more than the upper limit value, it becomes difficult to satisfactorily correct the magnification chromatic aberration. Therefore, as in the case of the conditional expression (1), it becomes difficult to realize high optical performance while maintaining a predetermined back focus, angle of view and F number. In addition, in order to realize good optical performance, the number of lenses for aberration correction increases, and it becomes difficult to miniaturize the wide-angle lens.

  In the wide-angle lens, the negative lens L1 n preferably satisfies the condition represented by the following conditional expression (2) ′, and more preferably satisfies the condition represented by the conditional expression (2) ′ ′. By satisfying these conditions, the effects of the present invention can be exhibited more.

Condition (2) ': d d1 n <35
Condition (2) ′ ′: d d1 n <30

1-4-3. Conditional expression (3)
In the wide-angle lens according to the present invention, when any one of the negative lenses included in the first lens group and disposed on the image side of the negative lens L1n is the negative lens L2n, the negative lens L2n It is preferable to satisfy the condition expressed by the conditional expression (3).

  Conditional Expression (3): d d 2 n> 65

However,
ν d2 n represents an Abbe number for the d-line of the negative lens L 2 n.

  Conditional expression (3) defines the Abbe number of the negative lens L2n with respect to the d-line. By configuring the first lens group using the negative lens L2n that satisfies the conditional expression (3), it becomes easy to reduce the lateral chromatic aberration, particularly the width of the F line and the C line, and higher optical performance can be achieved. It becomes easy to realize. On the other hand, when the numerical value of the conditional expression (3) becomes equal to or less than the lower limit value, it is difficult to reduce the width of the chromatic aberration of magnification, in particular, the F line and the C line. However, the negative lens L2n may be any negative lens other than the negative lens L1n disposed closest to the object among the negative lenses included in the first lens group.

1-4-4. Conditional expression (4)
In the wide-angle lens according to the present invention, when the first lens group is composed of the first A lens group and the first B lens group, in the first B lens group, the negative lens component most disposed on the object side It is preferable that the object side surface satisfies the condition represented by the following conditional expression (4). However, in the first lens group, among negative lenses whose object side surface is concave toward the object side, a negative lens or negative lens component having the largest curvature of the object plane may satisfy the following condition.

  Condition (4): 0.7 <| Cr 1 f | / f <3.0

However,
Cr 1 f represents the radius of curvature of the object side surface of the negative lens component,
f represents the focal length of the whole wide-angle lens system.

  Conditional expression (4) defines the ratio of the curvature of the object side surface of the negative lens component, ie, the curvature radius of the surface closest to the object side of the first lens unit B, to the focal length of the entire wide-angle lens system. . When the first lens group is composed of the first lens group A having negative refractive power and the first lens group B having positive refractive power as described above, the first lens group B is satisfied by satisfying conditional expression (4). The negative refractive power of the concave surface disposed closest to the object side in the lens unit is in an appropriate range, and spherical aberration and astigmatism can be corrected in a well-balanced manner.

  On the other hand, when the value of the conditional expression (4) falls below the lower limit value, the negative refracting power of the concave surface located closest to the object side in the 1st B lens group becomes excessively strong and the spherical aberration becomes under It is not preferable because it becomes difficult to correct the point aberration in a well-balanced manner. On the other hand, when the numerical value of the conditional expression (4) exceeds the upper limit value, the negative refracting power in the concave surface becomes too weak and the spherical aberration becomes over, so also in this case the spherical aberration and the astigmatism It is not preferable because it becomes difficult to make a well-balanced correction.

  In the wide-angle lens, it is preferable to satisfy the condition represented by the following conditional expression (4) ′, and it is more preferable to satisfy the condition represented by the conditional expression (4) ′ ′, the conditional expression (4) It is further preferable to satisfy the condition represented by '' '. By satisfying these conditions, the effects of the present invention can be exhibited more.

Condition (4) ': 0.8 <| Cr 1 f | / f <2.5
Conditional Expression (4) ′ ′: 0.9 <| Cr 1 f | / f <2.0
Condition (4) ′ ′ ′: 0.9 <| Cr 1 f | / f <1.5

1-4-5. Conditional expression (5)
In the wide-angle lens according to the present invention, it is preferable that the first lens unit satisfies the following conditions.

  Conditional Expression (5): 3.5 <f1 / f <30

However,
f1 represents the focal length of the first lens group,
f represents the focal length of the whole wide-angle lens system.

  Conditional expression (5) defines the ratio of the focal length of the first lens unit to the focal length of the entire wide-angle lens. By satisfying the conditional expression (5), it becomes easy to form a retrofocus lens configuration, and it becomes easy to secure a required predetermined back focus. Further, by satisfying the conditional expression (5), the focal length of the lens unit having a positive refractive power, which is disposed on the image side of the first lens unit, becomes within the appropriate range, and the spherical surface when focusing is performed. Aberration variation can be suppressed.

  On the other hand, when the numerical value of the conditional expression (5) becomes equal to or less than the lower limit value, it becomes difficult to form a retrofocus lens configuration, and it becomes difficult to secure a required predetermined back focus. Also, in this case, the focal length of the lens unit having a positive refractive power, which is disposed closer to the image than the first lens unit, becomes long, and it becomes difficult to suppress the variation of the spherical aberration at the time of focusing. In particular, the spherical aberration at the time of focusing on a short distance object is over, and the correction becomes difficult. On the other hand, when the numerical value of the conditional expression (5) becomes equal to or more than the upper limit, it becomes difficult to achieve reduction in diameter and weight of the lens unit disposed on the image side of the first lens unit. It becomes difficult to perform the focus operation.

  In the wide-angle lens, it is preferable to satisfy the condition represented by the following conditional expression (5) ′, and it is more preferable to satisfy the condition represented by the conditional expression (5) ′ ′, the conditional expression (5) It is further preferable to satisfy the condition represented by '' '. By satisfying these conditions, the effects of the present invention can be exhibited more.

Conditional Expression (5) ': 4.5 <f1 / f <25
Conditional Expression (5) ′ ′: 5.2 <f1 / f <20
Conditional Expression (5) ''': 5.2 <f1 / f <15

2. Imaging Device Next, an imaging device according to the present invention will be described. An imaging apparatus according to the present invention includes the wide-angle lens according to the present invention, and an imaging device provided on the image plane side of the wide-angle lens for converting an optical image formed by the wide-angle lens into an electrical signal. It is characterized by Here, the imaging device or the like is not particularly limited, and a solid-state imaging device or the like such as a CCD sensor or a CMOS sensor can also be used. The imaging device according to the present invention is suitable for an imaging device using such a solid-state imaging device such as a digital camera or a video camera. In addition, the imaging device may be a lens-fixed imaging device in which a lens is fixed to a housing. The wide-angle lens according to the present invention can ensure the back focus required for lens-interchangeable imaging devices such as single-lens reflex cameras and mirrorless single-lens cameras. Therefore, as a interchangeable lens of these lens-interchangeable imaging devices It is suitable.

  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 wide-angle lens in each of the following examples is an imaging wide-angle lens used in an imaging device (optical device) such as a digital camera, a video camera, or a silver-halide film camera. In each lens sectional view, the left side is the object side and the right side is the image plane side.

(1) Configuration of Wide-Angle Lens FIG. 1 is a lens sectional view showing a lens configuration at the time of infinity focusing of a wide-angle lens according to a first embodiment of the present invention. The wide-angle lens is composed of, in order from the object side, a first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power. At the time of focusing from an infinite distance object to a near distance object, the second lens group G2 moves to the object side along the optical axis with the first lens group G1 fixed in the optical axis direction. The aperture stop S is disposed inside the second lens group G2.

  The first lens group G1 is composed of, in order from the object side, a first A lens group G1A of negative refractive power and a first B lens group G1B of positive refractive power.

  The first lens group G1A includes, in order from the object side, 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, a biconvex positive lens L3, and a biconcave shape And the negative lens L4. The negative meniscus lens L2 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The first B lens group G1B is composed of, in order from the object side, a biconcave negative lens L5, a positive meniscus lens L6 with a convex surface facing the image side, and a biconvex positive lens L7. The most object-side lens (negative lens L5) of the 1B lens group G1B is the negative lens component having a concave surface with a stronger curvature on the object side with respect to the image side.

  The second lens group G2 includes a biconvex positive lens L8, a negative meniscus lens L9 having a convex surface facing the object side, an aperture stop S, a biconcave negative lens L10, and a biconvex positive lens L11 And a cemented lens of positive refractive power in which a negative meniscus lens L12 having a convex surface directed to the image side is cemented, and a biconvex positive lens L13. The negative meniscus lens L12 is a glass mold type aspheric lens whose image side surface is aspheric, or an aspheric lens by grinding.

  In FIG. 1, “IP” is an image plane, and specifically, indicates an imaging surface of a solid-state imaging device such as a CCD sensor or a CMOS sensor, a film surface of a silver salt film, or the like. Further, a cover glass or the like (symbols omitted) are provided on the object side of the IP. This point is the same as in the lens cross-sectional views shown in Example 2 to Example 5.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the wide-angle lens is applied will be described. Table 1 shows lens data of the wide-angle lens. In Table 1, "surface number" is the order of the lens surface counted from the object side, "r" is the curvature radius of the lens surface, "d" is the distance on the optical axis of the lens surface, "nd" is the d line (wavelength The refractive index for λ = 587.6 nm), and “νd” indicates the Abbe number for the d-line. Further, "ASP" displayed in the column next to the surface number indicates that the lens surface is aspheric, and represents the "S" aperture stop.

  Table 2 shows an outline table of the wide-angle lens, aspheric surface data, variable intervals on the optical axis, and focal lengths of the respective lens units. The front table shows the focal length “f”, the F number “Fno.”, The half angle of view “ω”, and the image height “Ym” of the whole wide-angle lens at the time of infinity object focusing.

The aspheric surface data indicates an aspheric coefficient when the aspheric surface shape is defined by the following equation. However, in the table, "E-a" indicates "x 10 ^-a ". In the following equation, “x” is the displacement from the reference plane in the optical axis direction, “r” is the paraxial radius of curvature, “H” is the height from the optical axis in the direction perpendicular to the optical axis, “k” "Is a conic coefficient, and" An "is an n-th order aspheric coefficient.

  The variable distance indicates the distance between the lens surfaces at infinity focusing and at 0.5 m focusing. Further, numerical values of each of the conditional expressions (1) to (5) are shown in Table 11. The unit of length in each table is all "mm" and the unit of angle of view is all "°". The matters relating to these tables are the same as in each of the tables shown in the second to fifth embodiments, and therefore the description thereof will be omitted below.

  FIG. 2 and FIG. 3 show longitudinal aberration diagrams and lateral aberration diagrams of the wide-angle lens, respectively, at infinity focusing. Further, FIG. 4 and FIG. 5 show longitudinal aberration diagrams and lateral aberration diagrams, respectively, when the wide-angle lens is in focus of 0.5 m.

  In each longitudinal aberration diagram, spherical aberration, astigmatism, and distortion are represented in order from the left toward the drawing. In the figure representing spherical aberration, the vertical axis represents the ratio to the open F value, the horizontal axis represents defocus, the solid line represents d line (wavelength λ = 587.6 nm), and the dotted line represents g line (wavelength λ = 435.8 nm) Spherical aberration at In the diagram showing astigmatism, the vertical axis represents image height, the horizontal axis is defocused, the solid line represents the sagittal image plane (ds) for the d-line, and the dotted line represents the meridional image plane (dm) for the d-line. In a diagram showing distortion, the vertical axis represents image height, and the horizontal axis represents%, which represents distortion.

  In each lateral aberration diagram, an image point of 100% of the maximum image height (1.0 ω), an image point of 90% (0.9 ω), an image point of 70% (0.7 ω), and an image of 50% The lateral aberration at the point (0.5ω) and the on-axis point (0.0ω) is shown. In each lateral aberration diagram, the horizontal axis represents the distance from the chief ray on the pupil plane, and the solid line indicates the d-line and the dotted line indicates the coma at the g-line.

  The matters relating to these figures are the same as in the longitudinal aberration diagrams and the lateral aberration diagrams shown in Example 2 to Example 5, and therefore the description thereof will be omitted below.

The back focus “BF” at the time of infinity focusing of the wide-angle lens is as follows. However, the following values are values including a cover glass having a thickness of 2 mm, and the same applies to the back focus shown in the other embodiments.
BF = 39.0567

(1) Configuration of Wide-Angle Lens FIG. 6 is a lens cross-sectional view showing a lens configuration at the time of infinity focusing of a wide-angle lens according to a second embodiment of the present invention. The wide-angle lens is composed of, in order from the object side, a first lens group G1 of positive refractive power and a second lens group G2 of positive refractive power. At the time of focusing from an infinite distance object to a near distance object, the second lens group G2 moves to the object side along the optical axis with the first lens group G1 fixed in the optical axis direction. The aperture stop S is disposed inside the second lens group G2.

  The first lens group G1 is composed of, in order from the object side, a first A lens group G1A of negative refractive power and a first B lens group G1B of positive refractive power.

  The first lens group G1A includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconvex positive lens L2, a negative meniscus lens L3 having a convex surface facing the object side, and the object side It is composed of a negative meniscus lens L4 having a convex surface. The negative meniscus lens L4 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The first B lens group G1B includes, in order from the object side, a negative meniscus lens L5 having a convex surface facing the image, a biconvex positive lens L6, a biconvex positive lens L7, and a positive lens having the convex surface facing the image And a cemented lens of positive refractive power in which a meniscus lens L8 is cemented. The most object side lens (negative meniscus lens L5) of the 1B lens group G1B is the negative lens component having the strongest concave surface on the object side in the first lens group.

  The second lens group G2 includes a biconvex positive lens L9, a biconvex positive lens L10, and a biconcave negative lens L11, which is a cemented lens of negative refractive power, an aperture stop S, and an image side. A positive meniscus lens L12 having a convex surface and a negative meniscus lens L13 having a convex surface facing the image side are cemented, a positive lens L14 having a biconvex shape, and a positive lens having a convex surface facing the image side And a meniscus lens L15. The positive meniscus lens L15 is a glass mold type aspheric lens whose surface on the object side is aspheric, or an aspheric lens by grinding.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the wide-angle lens is applied will be described. Table 3 shows lens data of the optical system, and Table 4 shows an outline table of the wide-angle lens, aspheric surface data, variable intervals on the optical axis, and focal lengths of the respective lens units. Table 11 shows numerical values of conditional expression (1) to conditional expression (5). Further, FIGS. 7 to 10 are longitudinal aberration diagrams and lateral aberration diagrams of the wide-angle lens when in infinity focusing and 0.5 m focusing, respectively.

Further, the back focus at the time of infinity focusing of the wide-angle lens is as follows.
BF = 39.0331

(1) Configuration of Optical System FIG. 11 is a lens sectional view showing a lens configuration at the time of infinity focusing of the wide-angle lens of Embodiment 3 according to the present invention. The wide-angle lens is composed of, in order from the object side, a first lens group G1 of positive refractive power and a second lens group G2 of positive refractive power. At the time of focusing from an infinite distance object to a near distance object, the second lens group G2 moves to the object side along the optical axis with the first lens group G1 fixed in the optical axis direction. The aperture stop S is disposed inside the second lens group G2.

  The first lens group G1 is composed of, in order from the object side, a first A lens group G1A of negative refractive power and a first B lens group G1B of positive refractive power.

  The first lens group G1A includes, in order from the object side, 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, a biconvex positive lens L3 and a biconcave shape And a cemented lens of negative refractive power in which a negative lens L4 is cemented. The negative meniscus lens L2 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The 1st B lens group G1B is composed of, in order from the object side, a cemented lens of negative refractive power formed by cementing a biconcave negative lens L5 and a biconvex positive lens L6, a biconvex positive lens L7, and a biconvex It is composed of a cemented lens of negative refractive power in which a positive lens L8 of a shape and a negative lens L9 of a biconcave shape are cemented. The most object-side lens component of the 1B lens group G1B (the cemented lens of the negative lens L5 and the positive lens L6) is a cemented lens having a negative refractive power and a concave surface having a stronger concave surface on the object side with respect to the image side It is an ingredient.

  The second lens group G2 includes a biconvex positive lens L10, a negative meniscus lens L11 having a convex surface facing the object side, an aperture stop S, a biconcave negative lens L12, and a biconvex positive lens L13. And it is comprised from the cemented lens of the positive refractive power which joined the positive meniscus lens L14 which orient | assigned the convex surface to the object side, and the biconvex positive lens L15. The positive meniscus lens L14 is a glass mold type aspheric lens whose surface on the image side is aspheric, or an aspheric lens by grinding.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the wide-angle lens is applied will be described. Table 5 shows lens data of the optical system, and Table 6 shows an outline table of the wide-angle lens, aspheric surface data, variable intervals on the optical axis, and focal lengths of the respective lens units. Table 11 shows numerical values of conditional expression (1) to conditional expression (5). Further, FIGS. 12 to 15 are longitudinal aberration diagrams and lateral aberration diagrams of the wide-angle lens at infinity focus and at 0.5 m focus, respectively.

Further, the back focus at the time of infinity focusing of the wide-angle lens is as follows.
BF = 39.0353

(1) Configuration of Wide-Angle Lens FIG. 16 is a lens sectional view showing a lens configuration at the time of infinity focusing of an optical system according to a fourth embodiment of the present invention. The wide-angle lens is composed of, in order from the object side, a first lens group G1 of positive refractive power and a second lens group G2 of positive refractive power. At the time of focusing from an infinite distance object to a near distance object, the second lens group G2 moves to the object side along the optical axis with the first lens group G1 fixed in the optical axis direction. The aperture stop S is disposed inside the second lens group G2.

  The first lens group G1 is composed of, in order from the object side, a first A lens group G1A of negative refractive power and a first B lens group G1B of positive refractive power.

  The first lens group G1A includes, in order from the object side, 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, a biconvex positive lens L3, and a biconcave shape And the negative lens L4. The negative meniscus lens L2 is a glass mold type aspheric lens whose surface on the image side is aspheric, or an aspheric lens by grinding.

  The first B lens group G1B is composed of, in order from the object side, a biconcave negative lens L5, a positive meniscus lens L6 having a convex surface facing the image side, and a biconvex positive lens L7. The most object side lens (negative lens L5) of the 1B lens group G1B is the negative lens component having a concave surface that is stronger on the object side with respect to the image side.

  The second lens group G2 has a positive meniscus lens L8 having a convex surface on the object side, a negative meniscus lens L9 having a convex surface on the object side, an aperture stop S, a biconcave negative lens L10, and a biconvex shape. It is composed of a triple cemented lens of negative refractive power in which a positive lens L11 and a negative meniscus lens L12 having a convex surface facing the image side are cemented, and a biconvex positive lens L13. The negative meniscus lens L12 is a glass mold type aspheric lens whose surface on the image side is aspheric, or an aspheric lens by grinding.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the wide-angle lens is applied will be described. Table 7 shows lens data of the optical system, and Table 8 shows an outline table of the wide-angle lens, aspheric surface data, variable intervals on the optical axis, and focal lengths of the respective lens units. Table 11 shows numerical values of conditional expression (1) to conditional expression (5). Furthermore, FIGS. 17 to 20 are longitudinal aberration diagrams and lateral aberration diagrams of the wide-angle lens at infinity focus and at 0.5 m focus, respectively.

Further, the back focus at the time of infinity focusing of the wide-angle lens is as follows.
BF = 39.0465

(1) Configuration of Wide-Angle Lens FIG. 21 is a lens sectional view showing a lens configuration at the time of infinity focusing of an optical system according to a fifth embodiment of the present invention. The wide-angle lens is composed of, in order from the object side, a first lens group G1 of positive refractive power and a second lens group G2 of positive refractive power. At the time of focusing from an infinite distance object to a near distance object, the second lens group G2 moves to the object side along the optical axis with the first lens group G1 fixed in the optical axis direction. The aperture stop S is disposed inside the second lens group G2.

  The first lens group G1 is composed of, in order from the object side, a first A lens group G1A of negative refractive power and a first B lens group G1B of positive refractive power.

  The first lens group G1A includes, in order from the object side, a positive 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 negative meniscus lens L3 having a convex surface on the object side It is composed of a positive meniscus lens L4 having a convex surface facing the image side and a cemented lens having negative refractive power in which a biconcave negative lens L5 is cemented. The negative meniscus lens L3 is a glass mold type aspheric lens in which both surfaces are aspheric, or an aspheric lens by grinding.

  The first B lens group G1B is composed of, in order from the object side, a cemented lens having negative refractive power in which a biconcave negative lens L6 and a biconvex positive lens L7 are cemented, and a biconvex positive lens L8. It is done. The lens closest to the object side (the cemented lens of the negative lens L6 and the positive lens L7) of the 1B lens group G1B is a negative cemented lens having a more concave surface on the object side than the image side having a more concave surface on the object side It is a lens, that is, the negative lens component.

  The second lens group G2 includes a biconvex positive lens L9, a negative meniscus lens L10 having a convex surface facing the object side, an aperture stop S, a biconcave negative lens L11, and a biconvex positive lens L12. And a cemented lens of positive refractive power in which a negative meniscus lens L13 having a convex surface directed to the image side is cemented, and a biconvex positive lens L14. The negative meniscus lens L13 constituting the cemented lens is a glass mold type aspheric lens whose surface on the image side is aspheric, or an aspheric lens by grinding.

(2) Numerical Example Next, a numerical example to which a specific numerical value of the wide-angle lens is applied will be described. Table 9 shows lens data of the optical system, and Table 10 shows an outline table of the wide-angle lens, aspheric surface data, variable intervals on the optical axis, and focal lengths of the respective lens groups. Table 11 shows numerical values of conditional expression (1) to conditional expression (5). Further, FIG. 21 to FIG. 25 are longitudinal aberration diagrams and lateral aberration diagrams of the wide-angle lens when in infinity focusing and 0.5 m focusing, respectively.

Further, the back focus at the time of infinity focusing of the wide-angle lens is as follows.
BF = 39.0376

  According to the present invention, it is possible to provide a compact wide-angle lens capable of achieving high optical performance while maintaining a predetermined back focus, angle of view, and f-number, and an imaging device provided with the wide-angle lens.

G1 ··· First lens group G1A ··· First lens group G1B ··· First lens group G2 ··· Second lens group S ··· Aperture stop IP ··· Image plane

Claims (15)

In order from the object side, a first lens group having a positive refractive power and a second lens group having positive refractive power,
Focusing is performed by moving the second lens group along the optical axis ,
The first lens group includes, in order from the object side, a first A lens group having negative refractive power, and a first B lens group having positive refractive power.
The first lens group A includes two or more negative lenses and one or more positive lenses.
The first B lens group is composed of two or more positive lenses and one or more negative lenses.
Among the negative lenses included in the first lens group A, when the negative lens L1n disposed closest to the object side is a negative lens L1n, the negative lens L1n satisfies the following condition.
PgF-(0.6438-0.001682 x vd1n)> 0.006 (1)
d d 1 n <40 (2)
However,
PgF represents a partial dispersion ratio of g-line and F-line of the negative lens L1n,
ν d1 n represents an Abbe number for the d-line of the negative lens L 1 n. Among negative lenses included in the first lens group, when one of the negative lenses disposed on the image side of the negative lens L1n is a negative lens L2n, the negative lens L2n satisfies the following condition. The wide-angle lens described in 1.
d d 2 n> 65 (3)
However,
ν d2 n represents an Abbe number for the d-line of the negative lens L 2 n. The wide-angle lens according to claim 1 or 2 , wherein the lens disposed on the most object side in the first B lens group is a negative lens component whose object side surface is concave on the object side. The optical system according to claim 3 , wherein the curvature of the object side surface of the negative lens component is the largest among the lenses having a concave shape toward the object side, in the object side surface included in the first lens group. 5. The wide-angle lens according to claim 3 , wherein an object side surface of the negative lens component in the first B lens group satisfies the following condition.
0.7 <| Cr 1 f | / f <3.0 ... (4)
However,
Cr 1 f represents the radius of curvature of the object side surface of the negative lens component,
f represents the focal length of the whole wide-angle lens system. The wide-angle lens according to any one of claims 1 to 5 , wherein a lens surface disposed closest to the image in the first lens group A is concave toward the image. The wide-angle lens according to any one of claims 1 to 6 , wherein the first lens group satisfies the following condition.
3.5 <f1 / f <30 (5)
However,
f1 represents the focal length of the first lens group,
f represents the focal length of the whole wide-angle lens system. The wide-angle lens according to any one of claims 1 to 7, wherein the first B lens group includes, in order from the object side, a negative lens, a positive lens, and a positive lens.   The wide-angle lens according to any one of claims 1 to 7, wherein the first B lens group includes, in order from the object side, a negative lens, a positive lens, a positive lens, and a negative lens.   The said 1st B lens group is a negative lens, a positive lens, a positive lens, a positive lens, and a negative lens in any one of Claim 1 to 7 comprised in an order from an object side. Wide-angle lens. The wide-angle lens according to any one of claims 1 to 10 , wherein the first lens group is fixed in the optical axis direction. The wide-angle lens according to any one of claims 1 to 11 , further comprising an aperture stop in the second lens group. The wide-angle lens according to any one of claims 1 to 12 , wherein the lens surface arranged closest to the object in the second lens group has a convex shape on the object side. The wide-angle lens according to any one of claims 1 to 13 , wherein a lens surface disposed closest to the image in the first lens group has a convex shape on the image side. A wide-angle lens according to any one of claims 1 to 14, on the image plane side of the wide-angle lens, with an imaging device that converts an optical image formed by the wide-angle lens into an electrical signal An imaging device characterized by

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