JP2019168724A - Wide angle lens and imaging apparatus - Google Patents

Abstract

To provide a compact wide angle lens capable of achieving high optical performance while maintaining predetermined back focus, field angle, and F number, and an imaging apparatus including the wide angle lens.SOLUTION: A wide angle lens includes at least, in order from an object side, a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power, and performs focusing by moving at least the second lens group G2. The first lens group G1 includes at least three negative lenses and one positive lens. When one negative lens of negative lenses included in the first lens group G1 is represented as a negative lens L1n, the negative lens L1n satisfies a predetermined condition.SELECTED DRAWING: Figure 1

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 including 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. For example, Patent Document 1 discloses a retrofocus type wide-angle lens having an imaging field angle of about 100 ° and an F number of 3.5. Such a retrofocus type wide-angle lens has a large back focus compared to the focal length of the entire lens system. For this reason, it can be suitably used as an interchangeable lens type imaging apparatus such as a single-lens reflex camera.

  In general, in a retrofocus type wide-angle lens, a negative lens group is arranged in front (object side), and a positive lens group is arranged in rear (image side). As described above, in the retrofocus type wide-angle lens, since the refractive power arrangement in the entire system is asymmetrical in the front-rear direction, various aberrations such as spherical aberration, coma aberration, distortion aberration, and astigmatism are likely to occur. If a larger negative refracting power is disposed in front to ensure a large back focus, the amount of various aberrations generated becomes larger. Therefore, it is very difficult to correct these aberrations in a balanced manner in a retrofocus type wide-angle lens.

  Furthermore, in recent years, there has been a great demand from the market for a wide-angle lens with a large aperture and a small size. Therefore, when an attempt is made to obtain a lens having a smaller F-number in a retrofocus type wide-angle lens, the amount of axial chromatic aberration and lateral chromatic aberration generated increases. Therefore, in addition to the above-mentioned various aberrations, it is necessary to correct axial chromatic aberration and lateral chromatic aberration in a well-balanced manner.

  On the other hand, in a retro-focus wide-angle lens, while attempting to reduce the front lens diameter while maintaining an imaging angle of view of about 100 ° and an F-number of 2.0 or less, it was attempted to reduce the size of the entire lens system. In this case, the amount of distortion, astigmatism, and the like is increased. Therefore, it has been difficult to achieve high optical performance while maintaining the required back focus, angle of view, and F-number in a retrofocus type wide-angle lens.

Japanese Patent No. 4946445

  An object of the present invention is to provide a small wide-angle lens capable of realizing high optical performance while maintaining the required back focus, angle of view, and F-number, and an imaging device including the wide-angle lens.

  In order to solve the above-described problem, the wide-angle lens of the present invention includes at least a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side. Focusing is performed by moving the lens group, and the first lens group includes at least three negative lenses and one positive lens, and is the most object among the negative lenses included in the first lens group. When the negative lens arranged on the side is a negative lens L1n, the negative lens L1n satisfies the following conditions, the lens arranged closest to the image side has a concave surface, and satisfies the following conditions: To do.

PgF− (0.6438−0.001682 × νd1n)> 0.006 (1)
νd1n <40 (2)
D × Y / f ² ≧ 0.528 (4)
However,
PgF represents the partial dispersion ratio between the g-line and the F-line of the negative lens L1n,
νd1n represents the Abbe number of the negative lens L1n with respect to the d-line,
D represents the entrance pupil diameter,
Y represents the maximum image height,
f represents the focal length of the entire wide-angle lens system.

  The imaging device of the present invention includes the wide-angle lens according to the present invention, and an image sensor that converts 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 small wide-angle lens capable of realizing high optical performance while maintaining a predetermined back focus, angle of view, and F number, and an imaging device including 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 when focusing on infinity. However, spherical aberration, astigmatism and distortion are shown in order from the left toward the drawing. The same applies to the longitudinal aberration diagrams. 3 is a lateral aberration diagram illustrating coma aberration when the wide-angle lens of Example 1 is focused at infinity. FIG. FIG. 6 is a longitudinal aberration diagram when the imaging magnification of the wide-angle lens of Example 1 is 1:40. 6 is a lateral aberration diagram illustrating coma aberration at the time of imaging of 1:40 by 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. 6 is a longitudinal aberration diagram of the wide-angle lens of Example 2 when focusing on infinity. FIG. FIG. 6 is a transverse aberration diagram illustrating coma aberration when the wide-angle lens of Example 2 is focused at infinity. It is a longitudinal aberration diagram at the time of imaging magnification 1:40 of the wide-angle lens of Example 2. 6 is a lateral aberration diagram illustrating coma aberration at the time of imaging of 1:40 by the wide-angle lens of Example 2. FIG. 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. 6 is a longitudinal aberration diagram of the wide-angle lens of Example 3 when focusing on infinity. It is a lateral aberration diagram showing the coma aberration at the time of infinity focusing of the wide-angle lens of Example 3. FIG. 6 is a longitudinal aberration diagram when the wide-angle lens of Example 3 has an imaging magnification of 1:40. 6 is a lateral aberration diagram illustrating coma aberration at the time of imaging of 1:40 by the wide-angle lens of Example 3. FIG.

  Embodiments of a wide-angle lens and an imaging device according to the present invention will be described below.

1. Wide-angle lens 1-1. Configuration of Wide Angle Lens The wide angle lens according to the present invention includes at least a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side, and includes at least a second lens group. The first lens group includes at least three negative lenses and one positive lens, and any one of the negative lenses included in the first lens group is moved. When the negative lens L1n is used, the negative lens L1n satisfies a predetermined condition described later. First, after describing the configuration of the wide-angle lens according to the present invention, items related to the conditional expression will be described.

  In the present invention, a first lens group having a negative refractive power is disposed on the object side, and a second lens group having a positive refractive power is disposed on the image side, thereby providing a so-called retrofocus type lens configuration. . Therefore, even when the wide-angle lens is widened, it is easy to secure a sufficient back focus, and a predetermined back focus required for an interchangeable lens of an imaging device such as a single-lens reflex camera is ensured. Can do.

  In general, in a wide-angle lens, an off-axis light beam incident at a large incident angle is converged by the first lens group. For this reason, in the wide-angle lens, 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, and aberration is likely to occur, and the amount of aberration is likely to increase. Therefore, in the present invention, by forming the first lens group to include at least three negative lenses and one positive lens, it is possible to suppress the occurrence of aberrations and realize high optical performance. Since the off-axis light beam can be corrected well in this way, high optical performance can be realized over the entire screen.

  Furthermore, in the present invention, the above lens group configuration is adopted, and at least the second lens group is moved to perform focusing, whereby aberration fluctuation due to focusing can be reduced from infinity to a short distance. Therefore, good optical performance can be realized in the entire focus area regardless of the object distance. Hereinafter, a preferable configuration example of each lens group will be described.

(1) First lens group The first lens group has negative refractive power, and its specific configuration is not particularly limited as long as it has the above-described configuration. However, it is more preferable to employ 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 a negative refractive power and a first B lens group having a positive refractive power. Preferably includes two or more negative lens components, and the first B lens group includes a negative lens component having a concave surface facing the object side. By adopting this configuration, the retrofocus type lens configuration can be emphasized. Therefore, even when the wide-angle lens is widened, it is easier to ensure a predetermined back focus required for the wide-angle lens.

  However, in the present invention, the lens component includes a single lens, a compound lens obtained by molding an aspherical resin on one or both surfaces 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 a negative refractive power when viewed from the entire cemented lens. At this time, when referring to the cemented lens and referred to as a lens component, the object side surface means a surface disposed on the most object side in the cemented lens, and the image side surface is disposed on the most image side in the cemented lens. It shall mean a surface.

i) 1A lens group In the 1A lens group, it is preferable to dispose a meniscus negative lens having a convex surface facing the object side closest to the object side. By disposing such a meniscus negative lens on the most object side of the first A lens group, even if off-axis rays are incident on the meniscus negative lens at a large incident angle, the above-mentioned aberrations are generated. It can be suppressed, and it becomes easy to realize higher optical performance. In addition, regardless of the specific configuration of the first lens group, that is, when the first lens group is not configured by the first A lens group and the first B lens group, the first lens group is disposed closest to the object side. By using a negative meniscus lens having a convex surface facing the object side, the same effect as described above can be obtained.

  In the 1A lens group, it is preferable that the lens surface arranged closest to the image side has a concave shape on the image side. By placing the concave lens surface on the image side closest to the image side of the first A lens group, it is possible to reduce the aberration burden of the negative lens arranged on the object side of the first A lens group. It becomes easy to achieve a wide angle and large aperture.

  Furthermore, it is more preferable that the first A lens group is composed of three negative lens components. By adopting this configuration, the retrofocus type lens configuration can be more emphasized, and it becomes easier to further widen the angle and increase the aperture.

ii) 1B lens group The 1B lens group includes a negative lens component having a concave surface directed toward the object side, that is, a negative lens component having a concave surface on the object side surface, thereby further enhancing the retrofocus lens configuration. Therefore, even when the wide-angle lens is widened, it is easier to ensure a sufficient back focus.

  In obtaining the effect, the negative lens component is preferably arranged on the most object side of the first B lens group. Further, when the image side surface of the negative lens component has a shape with a concave surface facing 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. Furthermore, it is preferable that the curvature of the object side surface of the negative lens component is the largest among the concave lenses of the object side surface included in the first lens group. The first lens group is composed of the first A lens group and the first B lens group as described above, and the negative lens component that is a concave surface having a strong curvature on the object side surface is disposed closest to the object side in the first B lens group. Thus, the effects described below can be obtained. In general, when the concave shape of the lens becomes stronger, the negative refractive power becomes stronger, so that both spherical aberration and astigmatism act on the over side. However, in the case where the above configuration is adopted, in the first B lens group, the concave surface arranged closest to the object side has a variation in spherical aberration and astigmatism with respect to the refractive power of the surface in opposite directions. That is, when the concave shape of the concave surface becomes strong, astigmatism acts on the over side, whereas spherical aberration acts on the under side in the reverse direction. Therefore, it is possible to satisfactorily correct spherical aberration and astigmatism by adopting the above configuration and disposing a negative lens component having a concave surface having such a strong curvature on the most object side in the first lens group. It becomes.

  Further, the first lens group and the first B lens are configured by arranging the negative lens component having the above-described configuration and the 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 between the groups. As a result, in addition to the correction of spherical aberration and astigmatism described above, correction of distortion becomes easy, various aberrations can be corrected in a balanced manner, and higher optical performance can be easily realized.

  Furthermore, in the 1B lens group, it is preferable that the image side surface of the lens arranged closest to the image side, that is, the lens surface arranged 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 first B lens group, distortion aberration generated in the negative lens arranged in the first A lens group can be corrected well, and higher. It becomes easy to realize optical performance. Note that, regardless of the specific configuration of the first lens group, the lens surface disposed closest to the object side of the first lens group has a convex shape on the image side, so that the same effect as described above can be obtained. .

(2) Second Lens Group The specific lens configuration of the second lens group is not particularly limited as long as it has a positive refractive power when viewed as a whole. For example, the second lens group preferably includes at least one negative lens. By disposing at least one negative lens in the second lens group having a positive refractive power, it is possible to suppress aberration fluctuations during focusing, and to perform favorable aberration correction throughout the focus. Become.

(3) Aperture stop In the wide-angle lens according to the present invention, the arrangement of the aperture stop is not particularly limited. However, in order to achieve the object of the present invention, the aperture stop is preferably disposed in the second lens group or on the image side of the second lens group. The diameter of the axial light beam incident on the second lens group is converged by the second lens group or the second group front group closer to the object side than the aperture stop. Therefore, if the aperture stop is disposed in the second lens group or on the image side of the second lens group, the aperture stop can be downsized. As a result, the drive mechanism for driving the aperture stop can be reduced in size and weight. Therefore, it becomes easy to reduce the size and weight of the wide-angle lens.

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

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

  For example, it is preferable that a third lens group having a positive refractive power is disposed on the image side of the second lens group via an aperture stop, and only the second lens group is used as a focus group. By adopting this configuration, the second lens group can be configured with a small number of sheets, and the focus group can be reduced in size and weight. Therefore, a quick focus operation is possible.

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

  In the wide-angle lens according to the present invention, when any one of the negative lenses included in the first lens group is the negative lens L1n, the negative lens L1n is represented by the following conditional expressions (1) and (2). It shall satisfy the conditions expressed.

Conditional expression (1): PgF− (0.6438−0.001682 × νd1n)> 0.006
Conditional expression (2): νd1n <40

However,
PgF represents the partial dispersion ratio between the g-line and the F-line of the negative lens L1n,
νd1n represents the Abbe number of the negative lens L1n with respect to the d-line.

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

νd = (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, νd: 60.49) and F2 (glass material) (partial dispersion ratio 0.5829, νd: 36.30). This means the deviation of the partial dispersion ratio from the reference line when the straight line passing through the dispersion ratio and the coordinates of νd is used as 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 dispersibility of any one of the negative lenses L1n among at least three negative lenses included in the first lens group. By satisfying the conditional expression (1), for example, it is possible to satisfactorily correct the secondary spectrum of lateral chromatic aberration even when attempting to increase the aperture while maintaining an angle of view of about 100 °, A high-performance small-sized wide-angle lens can be realized.

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

  In the wide-angle lens, the negative lens L1n 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 further exhibited.

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

  Further, among the negative lenses included in the first lens group, the negative lens L1n is more preferably a negative lens arranged closest to the object side in the first lens group in order to obtain the above effect.

1-4-2. Conditional expression (2)
Conditional expression (2) defines the Abbe number for the d-line of the negative lens L1n. By satisfying the conditional expression (2), for example, it is possible to satisfactorily correct lateral chromatic aberration even when attempting to increase the aperture while maintaining an angle of view of about 100 °, and a compact optical device with high optical performance. The wide-angle lens can be realized.

  On the other hand, when the numerical value of conditional expression (2) is equal to or greater than the upper limit value, it is difficult to satisfactorily correct lateral chromatic aberration. Therefore, as in the case of conditional expression (1), it is difficult to achieve high optical performance while maintaining a predetermined back focus, field angle, and F number. In order to realize good optical performance, the number of lenses for correcting aberrations increases, and it becomes difficult to reduce the size of the wide-angle lens.

  In the wide-angle lens, the negative lens L1n 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 further exhibited.

Conditional expression (2) ′: νd1n <35
Conditional expression (2) '': νd1n <30

1-4-3. Conditional expression (3)
In the wide-angle lens according to the present invention, in the first lens group, at least one negative lens is disposed on the image side with respect to the negative lens L1n, and any one negative lens disposed on the image side with respect to the negative lens L1n. Is a negative lens L2n, it is preferable that the negative lens L2n satisfies the condition represented by the following conditional expression (3).

  Conditional expression (3): νd2n> 65

However,
νd2n represents the Abbe number of the negative lens L2n with respect to the d-line.

  Conditional expression (3) defines the Abbe number for the d-line of the negative lens L2n. 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. It becomes easy to realize. On the other hand, if the numerical value of conditional expression (3) is less than or equal to the lower limit value, it is difficult to reduce the lateral chromatic aberration, particularly the widths of the F-line and C-line. However, the negative lens L2n may be any negative lens other than the negative lens L1n arranged closest to the object among the negative lenses included in the first lens group.

1-4-4. Conditional expression (4)
The wide-angle lens according to the present invention preferably satisfies the condition represented by the following conditional expression (4).

Conditional expression (4): D × Y / f ² > 0.4

However,
D represents the entrance pupil diameter,
Y represents the maximum image height,
f represents the focal length of the entire wide-angle lens system.

  Conditional expression (4) is an expression that defines the range of the entrance pupil diameter with respect to the focal length of the entire wide-angle lens system. When the conditional expression (4) is satisfied, the longitudinal chromatic aberration and the lateral chromatic aberration can be effectively corrected by the negative lens that satisfies the conditional expression (1). However, in the conditional expression (4), the focal length of the entire wide-angle lens system is a value at the time of focusing on infinity. The focal lengths of the first lens group and the like shown in conditional expression (5) and the like to be described later are values at the time of focusing on infinity.

  On the other hand, when the numerical value of the conditional expression (4) is less than or equal to the lower limit value, the correction of the lateral chromatic aberration becomes excessive. Therefore, to realize high optical performance, it is necessary to increase the number of lenses constituting the wide-angle lens, and it is difficult to reduce the size of the wide-angle lens.

  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) ″. By satisfying these conditions, the effects of the present invention can be further exhibited.

Conditional expression (4) ′: D × Y / f ² > 0.45
Conditional expression (4) '': D × Y / f ² > 0.50

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

  Conditional expression (5): -f1 / f <7.0

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

  Conditional expression (5) is an expression that defines the ratio between the focal length of the first lens group and the focal length of the entire wide-angle lens system. By satisfying the conditional expression (5), the focal length of the first lens group is within an appropriate range, and various aberrations can be corrected satisfactorily. Further, by satisfying the conditional expression (5), the focal length of the lens unit having positive refractive power arranged on the image side with respect to the first lens unit is within an appropriate range, and various conditions at the time of focusing are set. Variations in aberration can be suppressed, and high optical performance can be obtained over the entire focus range.

  On the other hand, if the numerical value of the conditional expression (5) is greater than or equal to the upper limit value, the exit pupil position moves to the image side, making it difficult to obtain a retrofocus lens configuration. Therefore, it becomes difficult to ensure the required predetermined back focus. In this case, the focal length of the lens unit having a positive refractive power disposed on the image side relative to the first lens unit becomes longer, and it becomes difficult to suppress aberration fluctuations during focusing. In particular, distortion becomes under and correction becomes difficult.

  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) ″. By satisfying these conditions, the effects of the present invention can be further exhibited.

Conditional expression (5) ′: −f1 / f <6.5
Conditional expression (5) '': -f1 / f <6.0

1-4-6. Conditional expression (6) and conditional expression (7)
In the wide-angle lens according to the present invention, the first lens group includes, in order from the object, a first A lens group that includes two negative lens components, and a first B lens group that includes a negative lens component with a concave surface facing the object side. In addition, it is preferable that the first A lens group satisfies the condition represented by the following conditional expression (6), and the first B lens group satisfies the condition represented by the following conditional expression (7).

Conditional expression (6): 3.0> f1a / f1> 0.15
Conditional expression (7): 10.0> f1b / f1> −1.0

However,
f1a represents the focal length of the 1A lens group,
f1b represents the focal length of the first B lens group,
f1 represents the focal length of the first lens group.

  Conditional expression (6) and conditional expression (7) are preferably satisfied when the first lens group is composed of the first A lens group and the first B lens group described above. Conditional expression (6) and conditional expression (7) are expressions that respectively define the combined focal length of each lens group with respect to the focal length of the first lens group. When the first A lens group and the first B lens group satisfy the conditional expressions (6) and (7), respectively, the refractive power arrangement in the first lens group as the front group becomes appropriate, and the retrofocus type The lens configuration can be further emphasized, and various aberrations can be corrected satisfactorily.

  On the other hand, when the numerical values of the conditional expressions (6) and (7) are equal to or higher than the upper limit value, the refractive power of the lens group disposed on the image side relative to the first lens group becomes relatively small, and spherical aberration and Since coma becomes worse, it is difficult to correct these. On the other hand, when the numerical values of the conditional expression (6) and the conditional expression (7) are equal to or lower than the lower limit value, the refractive power of the lens group disposed on the image side relative to the first lens group becomes relatively large, Since off-axis aberrations such as distortion and astigmatism deteriorate, these corrections are difficult.

  In the wide-angle lens, it is preferable that the conditions expressed by the following conditional expressions (6) ′ and (7) ′ are satisfied, and are expressed by the conditional expressions (6) ″ and (7) ″. It is more preferable to satisfy the following conditions. By satisfying these conditions, the effects of the present invention can be further exhibited.

Conditional expression (6) ′: 2.5> f1a / f1> 0.17
Conditional expression (7) ′: 9.0> f1b / f1> −0.8

Conditional expression (6) '': 2.0> f1a / f1> 0.19
Conditional expression (7) '': 8.0> f1b / f1> −0.6

1-4-7. Conditional expression (8)
In the wide-angle lens according to the present invention, when the first lens group includes the first A lens group and the first B lens group, the negative lens component included in the first B lens group has the following conditional expression (8 It is preferable that the conditions represented by

  Conditional expression (8): Cr / f> −1.5

However,
Cr represents the curvature of the object side surface of the negative lens component included in the first B lens group,
f represents the focal length of the entire wide-angle lens system.

  When the negative lens component included in the first B lens group satisfies the conditional expression (8), the following effects can be obtained. In general, when the concave shape of the lens becomes stronger, the negative refractive power becomes stronger, so that both spherical aberration and astigmatism act on the over side. However, in the case where the above configuration is adopted, in the first B lens group, the concave surface arranged closest to the object side has a variation in spherical aberration and astigmatism with respect to the refractive power of the surface in opposite directions. That is, when the concave shape of the concave surface becomes strong, astigmatism acts on the over side, whereas spherical aberration acts on the under side in the reverse direction. Therefore, it is possible to satisfactorily correct spherical aberration and astigmatism by adopting the above configuration and disposing a negative lens component having a concave surface having such a strong curvature on the most object side in the first lens group. It becomes.

  According to the wide-angle lens having the above-described configuration, the entire lens system is realized while achieving high optical performance and reducing the front lens diameter while maintaining an angle of view of about 100 ° and an F-number of 2.0 or less. Can be miniaturized.

2. Next, an imaging apparatus 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 element that is provided on the image plane side of the wide-angle lens and converts an optical image formed by the wide-angle lens into an electrical signal. It is characterized by that. Here, there is no limitation in particular in an image pick-up element etc., Solid-state image pick-up elements, such as a CCD sensor and a CMOS sensor, etc. can be used. The imaging device according to the present invention is suitable for an imaging device using these solid-state imaging devices such as a digital camera and a video camera. The imaging device may be a lens-fixed imaging device in which a lens is fixed to a housing. Since the wide-angle lens according to the present invention can ensure the back focus required for the interchangeable lens imaging device such as a single-lens reflex camera or a mirrorless single-lens camera, the interchangeable lens of these interchangeable lens imaging devices. Is preferred.

  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. The wide-angle lens of each example given below is an imaging wide-angle lens used for an imaging device (optical device) such as a digital camera, a video camera, and a silver salt film camera. In each lens cross-sectional view, the left side is the object side and the right side is the image plane side in the drawing.

(1) Configuration of Wide Angle Lens FIG. 1 is a lens cross-sectional view showing the lens configuration of the wide angle lens of Example 1 according to the present invention when focusing on infinity. The wide-angle lens 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. Has been. When focusing from an object at infinity to an object at a short distance, the second lens group G2 moves toward the object side along the optical axis while the first lens group G1 and the third lens group G3 are fixed in the optical axis direction. Moving. The aperture stop S is disposed on the object side of the third lens group G3.

  The first lens group G1 includes, in order from the object side, a first A lens group G1A having a negative refractive power and a first B lens group G1B having a negative refractive power.

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

  The first B lens group G1B includes, in order from the object side, a cemented lens in which a biconcave negative lens L4 and a positive lens L5 having a convex surface facing the image side are cemented. The cemented lens is the negative lens component having a concave surface with a stronger curvature on the object side.

  The second lens group G2 includes a positive meniscus lens L6 having a concave surface facing the object side, and a cemented lens in which a negative meniscus lens L7 and a positive lens L8 having a convex surface facing the object side are cemented. The positive meniscus lens L6 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The third lens unit L3 includes, in order from the object side, an aperture stop S, a cemented lens in which a negative meniscus lens L9 having a convex surface facing the object side, a positive lens L10, and a negative meniscus lens L11 having a concave surface facing the object side are cemented. , A negative lens L12, a positive lens L13, and a negative meniscus lens L14 having a concave surface facing the object side. The negative meniscus lens L14 is a glass mold type aspherical lens whose both surfaces are aspherical, or an aspherical lens by grinding.

  However, in the wide-angle lens of the first embodiment, focusing may be performed by moving the third lens group along with the second lens group along the optical axis. Even in that case, the effect of the present invention can be obtained.

  In FIG. 1, “IP” is an image plane, and specifically indicates an imaging plane of a solid-state imaging device such as a CCD sensor or a CMOS sensor, or a film plane of a silver salt film. Further, a cover glass (reference number omitted) is provided on the object side of the IP. This also applies to the lens cross-sectional views shown in the second and third embodiments.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the wide-angle lens are applied will be described. Table 1 shows lens data of the wide-angle lens. In Table 1, “NS” is the lens surface order (surface number) counted from the object side, “R” is the radius of curvature of the lens surface, “D” is the distance on the optical axis of the lens surface, and “Nd” is d. The refractive index for the line (wavelength λ = 587.6 nm), “ABV”, indicates the Abbe number for the d line. “ASPH” displayed in the column next to the surface number indicates that the lens surface is an aspheric surface, and “STOP” indicates an aperture stop.

Table 2 shows aspheric data and variable intervals when the lens surface is aspheric.
The aspheric surface data indicates an aspheric coefficient when the aspheric shape is defined by the following equation. However, in the table, “E−a” indicates “× 10 ^−a ”. In the following equation, “x” is the amount of 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-order aspheric coefficient.

  The variable interval indicates the interval between the lens surfaces when focusing on infinity, imaging magnification 1: 40 times (40 times), and closest object distance (MOD).

  Table 7 shows the numerical values of the conditional expressions (1) to (7) and the numerical values necessary for obtaining them. In Table 7, “Fno” is the F number, “f1” is the focal length of the first lens group, “f1a” and “f1b” are the focal lengths of the first A lens group and the first B lens group, and “Y "Represents the maximum image height," D "represents the entrance pupil diameter, and" Cr "represents the curvature of the object side surface of the negative lens component included in the first B lens group. The unit of length in each table is “mm”, and the unit of angle of view is “°”. Since the items related to these tables are the same in the tables shown in Examples 2 to 5, the description thereof will be omitted below.

  2 and 3 are longitudinal aberration diagrams and lateral aberration diagrams when the wide-angle lens is focused at infinity. 4 and 5 show longitudinal aberration diagrams and lateral aberration diagrams when the wide-angle lens is imaged at an imaging magnification of 1:40.

  In each longitudinal aberration diagram, spherical aberration, astigmatism, and distortion aberration are shown in order from the left toward the drawing. In the graph showing spherical aberration, the vertical axis is the ratio to the open F value, the horizontal axis is defocused, the solid line is the d line (wavelength λ = 587.6 nm), and the dotted line is the g line (wavelength λ = 435.8 nm). The spherical aberration at is shown. In the diagram showing astigmatism, the vertical axis represents the image height, the horizontal axis 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 the diagram showing distortion aberration, the vertical axis represents image height and the horizontal axis represents%, and represents distortion aberration.

  In each lateral aberration diagram, 100% image point (1.0Ω), 90% image point (0.9Ω), 70% image point (0.7Ω), and 50% image of the maximum image height in order from the top. Lateral aberrations are shown at point (0.5Ω) and on-axis point (0.0Ω). In each lateral aberration diagram, the horizontal axis represents the distance from the principal ray on the pupil plane, the solid line indicates the d-line and the dotted line indicates the coma aberration at the g-line.

  Since the matters relating to these drawings are the same in the longitudinal aberration diagram and the lateral aberration diagram shown in Example 2 and Example 3, the description thereof will be omitted below.

The back focus “BF” when the wide-angle lens is focused at infinity is as follows. However, the following values are values that do not include the cover glass having a thickness of 2 mm, and the same applies to the back focus shown in the other examples.
BF = 38.31867

(1) Configuration of Wide Angle Lens FIG. 6 is a lens cross-sectional view showing the lens configuration of the wide angle lens of Example 2 according to the present invention when focusing on infinity. The wide-angle lens 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. Has been. When focusing from an object at infinity to an object at a short distance, the second lens group G2 moves toward the object side along the optical axis while the first lens group G1 and the third lens group G3 are fixed in the optical axis direction. Moving. The aperture stop S is disposed on the object side of the third lens group G3.

  The first lens group G1 includes, in order from the object side, a first A lens group G1A having a negative refractive power and a first B lens group G1B having a negative refractive power.

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

  The first B lens group G1B includes, in order from the object side, a cemented lens in which a biconcave negative lens L4 and a positive lens L5 having a convex surface facing the image side are cemented. The cemented lens is the negative lens component having a concave surface with a stronger curvature on the object side.

  The second lens group G2 includes a positive meniscus lens L6 having a concave surface facing the object side, and a cemented lens in which a negative meniscus lens L7 and a positive lens L8 having a convex surface facing the object side are cemented. The positive meniscus lens L6 is a glass mold type aspheric lens whose both surfaces are aspheric, or an aspheric lens by grinding.

  The third lens unit L3 includes, in order from the object side, an aperture stop S, a cemented lens in which a negative meniscus lens L9 having a convex surface facing the object side, a positive lens L10, and a negative meniscus lens L11 having a concave surface facing the object side are cemented. And a positive lens L12 and a negative meniscus lens L13 having a concave surface facing the object side. The negative meniscus lens L13 is a glass mold type aspherical lens whose both surfaces are aspherical, or an aspherical lens by grinding.

  However, in the wide-angle lens of the second embodiment, focusing may be performed by moving the third lens group along with the second lens group along the optical axis. Even in that case, the effect of the present invention can be obtained.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the wide-angle lens are applied will be described. Table 3 shows lens data of the optical system, and Table 4 shows aspheric data and variable intervals on the optical axis. Table 7 shows numerical values of the conditional expressions (1) to (7). Further, FIGS. 7 to 10 are longitudinal aberration diagrams and lateral aberration diagrams when the wide-angle lens is focused at infinity and when imaging is performed at an imaging magnification of 1:40.

The back focus when the wide-angle lens is focused at infinity is as follows.
BF = 38.31987

(1) Configuration of Optical System FIG. 11 is a lens cross-sectional view showing a lens configuration at the time of focusing on infinity of the wide-angle lens of Example 3 according to the present invention. The wide-angle 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. When focusing from an object at infinity to an object at a short distance, the second lens group G2 moves to the object side along the optical axis while the first lens group G1 is fixed in the optical axis direction. The aperture stop S is disposed in the second lens group G2.

  The first lens group G1 includes, in order from the object side, a first A lens group G1A having a negative refractive power and a first B lens group G1B having a negative refractive power.

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

  The first B lens group G1B includes, in order from the object side, a cemented lens in which a biconcave negative lens L4 and a positive lens L5 having a convex surface facing the image side are cemented, and a biconvex positive lens L6. Yes. The cemented lens composed of the negative lens L4 and the positive lens L15 is the negative lens component having a concave surface with a stronger curvature on the object side.

  The second lens group G2 includes a cemented lens obtained by cementing a negative meniscus lens L7 and a positive lens L8 having a convex surface facing the object side, an aperture stop S, a negative meniscus lens L9 having a convex surface facing the object side, a positive lens L10, and the like. The lens includes a cemented lens in which a negative meniscus lens L11 having a concave surface facing the object side is cemented, a biconcave negative lens L12, a biconvex positive lens L13, and a negative lens L14. The negative lens L14 is a glass mold type aspherical lens whose both surfaces are aspherical or an aspherical lens by grinding.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the wide-angle lens are applied will be described. Table 5 shows lens data of the optical system, and Table 6 shows aspheric data and variable intervals on the optical axis. Table 7 shows numerical values of the conditional expressions (1) to (7). Further, FIGS. 12 to 15 are longitudinal aberration diagrams and lateral aberration diagrams when the wide-angle lens is focused at infinity and when imaging is performed at an imaging magnification of 1:40.

The back focus when the wide-angle lens is focused at infinity is as follows.
BF = 38.75137

  According to the present invention, it is possible to provide a small wide-angle lens capable of realizing high optical performance while maintaining a predetermined back focus, angle of view, and F number, and an imaging device including the wide-angle lens.

G1 ... 1st lens group G1A ... 1A lens group G1B ... 1B lens group G2 ... 2nd lens group S ... Aperture stop IP ... Image plane

Claims (11)

In order from the object side, at least a first lens group having a negative refractive power and a second lens group having a positive refractive power are provided,
Focus by moving at least the second lens group;
When the first lens group includes at least three negative lenses and one positive lens, and any one of the negative lenses included in the first lens group is a negative lens L1n, The negative lens L1n satisfies the following conditions:
The lens arranged closest to the image side has a concave surface,
A wide-angle lens that satisfies the following conditions.
PgF− (0.6438−0.001682 × νd1n)> 0.006 (1)
νd1n <40 (2)
D × Y / f ² ≧ 0.528 (4)
However,
PgF represents the partial dispersion ratio between the g-line and the F-line of the negative lens L1n,
νd1n represents the Abbe number of the negative lens L1n with respect to the d-line,
D represents the entrance pupil diameter,
Y represents the maximum image height,
f represents the focal length of the entire wide-angle lens system. In the first lens group, at least one negative lens is disposed on the image side of the negative lens L1n, and any one negative lens disposed on the image side of the negative lens L1n is defined as the negative lens L2n. The wide-angle lens according to claim 1, wherein the negative lens L2n satisfies the following condition.
νd2n> 65 (3)
However,
νd2n represents the Abbe number of the negative lens L2n with respect to the d-line. The wide-angle lens according to claim 1, wherein the first lens group satisfies the following conditions.
-F1 / f <6.0 (5)
However,
f1 represents the focal length of the first lens group,
f represents the focal length of the entire wide-angle lens system. The first lens group includes, in order from the object, a first A lens group including two negative lens components and a first B lens group including a negative lens component having a concave surface facing the object side,
The optical system according to any one of claims 1 to 3, wherein the following condition is satisfied.
3.0> f1a / f1> 0.15 (6)
10.0> f1b / f1> −1.0 (7)
However,
f1a represents the focal length of the first A lens group,
f1b represents the focal length of the first B lens group,
f1 represents the focal length of the first lens group.   5. The curvature of the object side surface of the negative lens component included in the first B lens group is the largest among negative lens components including a concave surface facing the object side included in the first lens group. A wide-angle lens according to any one of the above. The wide-angle lens according to any one of claims 1 to 5, wherein a negative lens component included in the first B lens group satisfies the following condition.
Cr / f> −1.5 (8)
However,
Cr represents the curvature of the object side surface of the negative lens component included in the first B lens group,
f represents the focal length of the entire wide-angle lens system.   The wide-angle lens according to any one of claims 1 to 6, wherein the first B lens group includes one negative lens component.   The wide-angle lens according to any one of claims 1 to 6, wherein the first B lens group includes a negative lens component and a positive lens component in order from the object side.   The wide-angle lens according to any one of claims 1 to 8, wherein the first lens group is fixed in the optical axis direction.   The wide angle lens according to any one of claims 1 to 9, further comprising an aperture stop on the image side of the second lens group.   The wide-angle lens according to any one of claims 1 to 10, and an image sensor that converts an optical image formed by the wide-angle lens into an electrical signal on an image plane side of the wide-angle lens. An imaging apparatus characterized by that.

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