JP6774537B2 - Wide-angle lens and imaging device - Google Patents

Description

The present invention relates to a wide-angle lens and an image pickup apparatus, and more particularly to a large-diameter wide-angle lens and an image pickup apparatus provided with the wide-angle lens.

Conventionally, a wide-angle lens called a retrofocus type (reverse telescope type) in which a negative lens group precedes is widely known. For example, Patent Document 1 discloses a retrofocus type wide-angle lens having an imaging angle of view of about 100 ° and an F number of 3.5. Such a retrofocus type wide-angle lens has a large back focus with respect to the focal length of the entire lens system. Therefore, it can be suitably used as an image pickup device with interchangeable lenses such as a single-lens reflex camera.

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

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

On the other hand, in a retrofocus type wide-angle lens, we tried to reduce the size of the entire lens system while maintaining an imaging angle of view of about 100 ° and an F number of 2.0 or less while reducing the front lens diameter. In this case, the amount of distortion, astigmatism, etc. generated becomes large. Therefore, in a retrofocus type wide-angle lens, it has been difficult to realize high optical performance while maintaining the required back focus, angle of view, and F number.

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 image pickup apparatus provided with the wide-angle lens.

In order to solve the above problems, 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, and at least a second lens group. 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, and 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 of 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.

Further, the image pickup apparatus of the present invention includes the wide-angle lens according to the present invention and an image pickup element 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 structure example at the time of infinity focusing of the wide-angle lens of Example 1 of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the wide-angle lens of Example 1. However, spherical aberration, astigmatism, and distortion are shown in order from the left when facing the drawing. The same applies to the longitudinal aberration diagram. It is a lateral aberration diagram which shows the coma aberration at the time of infinity focusing of the wide-angle lens of Example 1. FIG. It is a longitudinal aberration diagram at the time of imaging magnification 1:40 of the wide-angle lens of Example 1. FIG. 5 is a lateral aberration diagram showing coma aberration at the time of imaging at an imaging magnification of 1:40 of the wide-angle lens of Example 1. It is sectional drawing which shows the lens structure example at the time of infinity focusing of the wide-angle lens of Example 2 of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the wide-angle lens of Example 2. It is a lateral aberration diagram which shows the coma aberration at the time of infinity focusing of the wide-angle lens of Example 2. FIG. It is a longitudinal aberration diagram at the time of imaging magnification 1:40 of the wide-angle lens of Example 2. FIG. 5 is a lateral aberration diagram showing coma aberration at the time of imaging at an imaging magnification of 1:40 of the wide-angle lens of Example 2. It is sectional drawing which shows the lens structure example at the time of infinity focusing of the wide-angle lens of Example 3 of this invention. It is a longitudinal aberration diagram at the time of infinity focusing of the wide-angle lens of Example 3. It is a lateral aberration diagram which shows the coma aberration at the time of infinity focusing of the wide-angle lens of the practical use 3. FIG. It is a longitudinal aberration diagram at the time of imaging magnification 1:40 of the wide-angle lens of Example 3. FIG. 5 is a lateral aberration diagram showing coma aberration at the time of imaging at an imaging magnification of 1:40 of the wide-angle lens of Example 3.

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

1. 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. Focusing is performed by moving, and the first lens group includes at least three negative lenses and one positive lens, and one of the negative lenses included in the first lens group is negative. When the negative lens L1n is used, the negative lens L1n satisfies a predetermined condition described later. First, the configuration of the wide-angle lens according to the present invention will be described, and then the matters relating to the conditional expression will be described.

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

Further, in general, in a wide-angle lens, the off-axis luminous flux incident at a large incident angle is converged by the first lens group. Therefore, in a wide-angle lens, the incident angle of the off-axis light beam with respect to the lens surface of the lens arranged on the object side in the first lens group is large, aberration is likely to occur, and the amount of the aberration is also likely to be large. Therefore, in the present invention, by configuring 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 luminous flux can be satisfactorily corrected in this way, high optical performance can be realized in the entire screen.

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

(1) First Lens Group The first lens group has a negative 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 is composed of a first A lens group having a negative refractive power and a first B lens group having a positive refractive power in order from the object side, and the first A lens group. Includes two or more negative lens components, and the first B lens group preferably includes a negative lens component with 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 becomes easier to secure a predetermined back focus required for the wide-angle lens.

However, in the present invention, the lens component includes a single lens, a composite lens obtained by molding an aspherical resin on one side or both sides of the lens, and the like. The lens component also includes a bonded lens in which two or more lenses are bonded. However, in the case of a bonded lens, the entire bonded lens is referred to as a lens component, and the negative lens component has a negative refractive power when viewed as a whole bonded lens. At this time, when the bonded lens is referred to as a lens component, the object side surface means the surface arranged on the object side most in the bonded lens, and the image side surface means the surface arranged on the image side most in the bonded lens. It shall mean a face.

i) First A lens group In the first A lens group, it is preferable to arrange a meniscus-shaped negative lens having a convex surface facing the object side on the most object side thereof. By arranging such a meniscus-shaped negative lens on the most object side of the first A lens group, even if an off-axis ray is incident on this meniscus-shaped negative lens at a large incident angle, the above aberrations are generated. It can be suppressed, and it becomes easy to realize higher optical performance. It should be noted 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 arranged on the most object side of the first lens group. The same effect as described above can be obtained by using a lens having a meniscus shape with a convex surface facing the object side.

Further, in the first A lens group, the lens surface arranged on the image side most preferably has a concave shape on the image side. By arranging the concave lens surface on the image side on 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 increase the angle and diameter of the lens.

Further, 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 further emphasized, and it becomes easy to further widen the angle and increase the aperture.

ii) 1st B lens group The retrofocus type lens configuration is further emphasized by configuring the 1st B lens group with a negative lens component having a concave surface facing the object side, that is, a negative lens component having a concave surface on the side surface of the object. This makes it easier to secure sufficient back focus even when the wide-angle lens is widened.

In order to obtain 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 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. Further, it is preferable that the curvature of the object side surface of the negative lens component is the largest among the lenses having the concave 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, which is a concave surface having a strong curvature on the side surface of the object, is arranged on the object side of the first B lens group. As a result, the effects described below can be obtained. In general, as 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, when the above configuration is adopted, in the first B lens group, the concave surface arranged closest to the object side has the fluctuations of spherical aberration and astigmatism with respect to the refractive power of the surface acting in opposite directions. That is, when the concave shape of the concave surface becomes stronger, astigmatism acts on the over side, whereas spherical aberration acts on the under side in the opposite direction. Therefore, it is possible to satisfactorily correct spherical aberration and astigmatism by adopting the above configuration and arranging a negative lens component having such a concave surface having a strong curvature on the object side in the first lens group. It becomes.

Further, by forming the first lens group as described above and arranging a negative lens component which is a concave surface having a strong curvature on the side surface of the object on the most object side in the first B lens group, the first A lens group and the first B lens are arranged. It becomes easy to appropriately set the refractive power balance with the group. As a result, in addition to the above-mentioned correction of spherical aberration and astigmatism, correction of distortion aberration becomes easy, various aberrations can be corrected in a well-balanced manner, and higher optical performance can be easily realized.

Further, in the first B lens group, the image side surface of the lens arranged on the image side most, that is, the lens surface arranged on the image side most preferably has a convex shape on the image side. By arranging the convex lens surface on the image side on the most image side of the 1st B lens group, the distortion aberration generated by the negative lens arranged on the 1st A lens group can be satisfactorily corrected, which is higher. It becomes easy to realize the optical performance. Regardless of the specific configuration of the first lens group, the same effect as described above can be obtained by making the lens surface arranged on the most object side of the first lens group convex toward the image side. ..

(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 arranging 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 it is possible to perform good aberration correction over the entire focus range. Become.

(3) Aperture diaphragm In the wide-angle lens according to the present invention, the arrangement of the aperture diaphragm is not particularly limited. However, in order to achieve the object of the present invention, it is preferable that the aperture diaphragm is arranged in the second lens group or on the image side of the second lens group. The luminous flux diameter of the axial luminous flux incident on the second lens group is converged by the second lens group or the second group front group on the object side of the aperture diaphragm. Therefore, if the aperture diaphragm is arranged in the second lens group or on the image side of the second lens group, the aperture diaphragm can be miniaturized. As a result, it is possible to reduce the size and weight of the drive mechanism for driving the aperture diaphragm. Therefore, it becomes easy to reduce the size and weight of the wide-angle lens.

1-2. Lens group configuration The wide-angle lens may include the above-mentioned first lens group and second lens group, and may include a subsequent lens group on the image side of the second lens group. For example, a third lens group having a positive or negative refractive power can be arranged 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 during 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 fixation / movement of other lens groups during focusing is particularly limited. Not a thing. 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 at the time of focusing. When the lens group is provided on the image side of the second lens group, the lens group having a positive refractive power may be moved at the time of focusing to perform focusing. At this time, the lens 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, it is preferable that the succeeding lens group is fixed at the time of focusing from the viewpoint of reducing the weight of the focus group.

For example, it is preferable to arrange a third lens group having a positive refractive power on the image side of the second lens group via an aperture diaphragm, and set only the second lens group as the focus group. If this configuration is adopted, the second lens group can be configured with a small number of lenses, and the focus group can be made smaller and lighter. Therefore, a quick focus operation is possible.

1-4. Conditional expression Next, the conditions that the wide-angle lens according to the present invention should be satisfied with, or the conditions that are preferable to be satisfied, will be 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 equations (1) and (2). The conditions represented shall be satisfied.

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

However,
PgF represents the partial dispersion ratio of 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, it is assumed that the refractive indexes of the glass with respect to the g line (435.8 nm), the F line (486.1 nm), the d line (587.6 nm), and the C line (656.3 nm) are Ng, NF, Nd, and NC, respectively. , Abbe number (νd) and 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 the 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). It 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. The conditional expression (1) is an expression that 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, the second-order spectrum of chromatic aberration of magnification can be satisfactorily corrected even when an attempt is made to increase the aperture while maintaining an angle of view of about 100 °. It is possible to realize a compact wide-angle lens with high performance.

On the other hand, when the numerical value of the conditional expression (1) is equal to or less than the lower limit value, it becomes difficult to satisfactorily correct the second-order spectrum of the chromatic aberration of magnification. Therefore, it becomes difficult to realize high optical performance while maintaining a predetermined back focus, angle of view, and F number. Further, 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 more exerted.

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, it is more preferable that the negative lens L1n is a negative lens arranged on the object side most in the first lens group in order to obtain the above effect.

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

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 chromatic aberration of magnification. 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. Further, 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 more exerted.

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 arranged on the image side of the negative lens L1n, and any one of the negative lenses arranged on the image side of the negative lens L1n. When 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.

The conditional expression (3) is an expression that defines the Abbe number of the negative lens L2n with respect to the d line. By constructing the first lens group using the negative lens L2n satisfying the conditional expression (3), it becomes easy to reduce the chromatic aberration of magnification, particularly the width of the F line and the C line, and higher optical performance can be obtained. It will be easier to achieve. On the other hand, if the numerical value of the conditional expression (3) is not more than the lower limit value, it becomes difficult to reduce the chromatic aberration of magnification, particularly the widths of the F line and the C line, which is not preferable. However, the negative lens L2n may be any negative lens other than the negative lens L1n arranged on the object side 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.

The 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 axial chromatic aberration and the magnifying chromatic aberration can be effectively corrected by the negative lens satisfying the conditional expression (1). However, in the conditional expression (4), the focal length of the entire wide-angle lens system refers to the value at the time of focusing at infinity. The focal lengths of the first lens group and the like shown in the conditional expression (5) and the like described later are all values at the time of focusing at infinity.

On the other hand, when the numerical value of the conditional expression (4) becomes less than the lower limit value, the correction of the chromatic aberration of magnification becomes excessive. Therefore, in order to realize high optical performance, it is necessary to increase the number of lenses constituting the wide-angle lens, and it becomes 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 more exerted.

Conditional expression (4)': D x Y / f ² > 0.45
Conditional expression (4)'': D x 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.

The conditional equation (5) is an equation 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 satisfactorily corrected. Further, by satisfying the conditional expression (5), the focal length of the lens group having a positive refractive power arranged on the image side of the first lens group becomes within an appropriate range, and various things when focusing are performed. Fluctuations in aberration can be suppressed, and high optical performance can be obtained over the entire focal length.

On the other hand, when the numerical value of the conditional expression (5) becomes equal to or more than the upper limit value, the exit pupil position moves to the image side, and it becomes difficult to form a retrofocus type lens configuration. Therefore, it becomes difficult to secure the required predetermined back focus. Further, in this case, the focal length of the lens group having a positive refractive power arranged on the image side of the first lens group becomes longer, and it becomes difficult to suppress the aberration fluctuation at the time of focusing. In particular, the distortion becomes under, which makes correction difficult.

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

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 is composed of a first A lens group containing two negative lens components in order from the object, and a first B lens group containing a negative lens component with a concave surface facing the object side. At the same time, it is preferable that the first A lens group satisfies the condition represented by the following conditional formula (6), and the first B lens group satisfies the condition represented by the following conditional formula (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 1st A lens group.
f1b represents the focal length of the 1st B lens group.
f1 represents the focal length of the first lens group.

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

On the other hand, when the numerical values of the conditional equations (6) and (7) are equal to or more than the upper limit values, the refractive power of the lens group arranged on the image side of the first lens group becomes relatively too small, resulting in spherical aberration. Since coma aberration worsens, it becomes difficult to correct these. On the other hand, when the numerical values of the conditional equations (6) and (7) are equal to or less than the lower limit, the refractive power of the lens group arranged on the image side of the first lens group becomes relatively large. Since off-axis aberrations such as distortion and astigmatism worsen, it becomes difficult to correct them.

The wide-angle lens preferably satisfies the conditions expressed by the following conditional expression (6)'and conditional expression (7)', and is expressed by the conditional expression (6)'' and the conditional expression (7)''. It is more preferable to satisfy the above conditions. By satisfying these conditions, the effects of the present invention can be more exerted.

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 is composed of the first A lens group and the first B lens group, the negative lens component contained in the first B lens group is the following conditional expression (8). ) Satisfy the conditions.

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

However,
Cr represents the curvature of the side surface of the object 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 contained in the first B lens group satisfies the conditional expression (8), the effect described below is obtained. In general, as 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, when the above configuration is adopted, in the first B lens group, the concave surface arranged closest to the object side has the fluctuations of spherical aberration and astigmatism with respect to the refractive power of the surface acting in opposite directions. That is, when the concave shape of the concave surface becomes stronger, astigmatism acts on the over side, whereas spherical aberration acts on the under side in the opposite direction. Therefore, it is possible to satisfactorily correct spherical aberration and astigmatism by adopting the above configuration and arranging a negative lens component having such a concave surface having a strong curvature on the object side in the first lens group. It becomes.

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

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

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 embodiment listed below 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. Further, in each lens cross-sectional view, the left side is the object side and the right side is the image plane side when viewed from the drawing.

(1) Configuration of Wide-angle Lens FIG. 1 is a cross-sectional view of a lens showing a lens configuration of the wide-angle lens of Example 1 according to the present invention at in-finity focus. The wide-angle lens is composed of 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 in order from the object side. Has been done. When focusing from an infinity object to a short-range object, the second lens group G2 moves toward the object 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 diaphragm S is arranged on the object side of the third lens group G3.

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

The first A lens group G1A includes 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 in order from the object side. It is composed of. The negative meniscus lens L2 is a glass-molded aspherical lens having both sides having an aspherical shape, or an aspherical lens obtained by grinding.

The first B lens group G1B is composed of a bonded lens in which a negative lens L4 having a concave shape and a positive lens L5 having a convex surface facing the image side are joined in order from the object side. The bonded lens is the negative lens component having a concave surface having a stronger curvature on the object side.

The second lens group G2 is composed of a positive meniscus lens L6 having a concave surface facing the object side, and a bonded lens in which a negative meniscus lens L7 having a convex surface facing the object side and a positive lens L8 are joined. The positive meniscus lens L6 is a glass-molded aspherical lens having both sides having an aspherical shape, or an aspherical lens obtained by grinding.

The third lens group L3 is a bonded lens in which an aperture diaphragm S, 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 joined in this order from the object side. It is composed of a negative lens L12, a positive lens L13, and a negative meniscus lens L14 with a concave surface facing the object side. The negative meniscus lens L14 is a glass-molded aspherical lens having both sides having an aspherical shape, or an aspherical lens obtained by grinding.

However, in the wide-angle lens of the first embodiment, the third lens group may be moved along the optical axis together with the second lens group for focusing. 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 image pickup surface of a solid-state image sensor such as a CCD sensor or a CMOS sensor, or a film surface of a silver salt film. Further, a cover glass (reference numeral omitted) is provided on the object side of the IP. This point is the same in the cross-sectional views of the lenses 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 the lens data of the wide-angle lens. In Table 1, "NS" is the order (plane number) of the lens surface 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) and "ABV" indicate the Abbe number for the d line. Further, "ASPH" displayed in the column next to the surface number indicates that the lens surface is an aspherical surface, and "STOP" indicates an aperture diaphragm.

Table 2 shows aspherical data and variable intervals when the lens surface is aspherical.
The aspherical data shows the aspherical coefficient when the aspherical shape is defined by the following formula. However, in the table, " ^Ea " indicates " ^x10 -a". In the following equation, "x" is the amount of displacement from the reference plane in the optical axis direction, "r" is the radius of curvature of the near axis, "H" is the height from the optical axis in the direction perpendicular to the optical axis, and "k". Is a cone coefficient, and "An" is an nth-order aspherical coefficient.

The variable interval indicates the interval between the lens surfaces at the time of focusing at infinity, the image magnification of 1:40 times (40 times), and the closest object distance image (MOD).

In addition, Table 7 shows the numerical values of each conditional expression (1) to (7) and the numerical values required for obtaining them. In Table 7, "Fno" is an 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, respectively, and "Y". "Is the maximum image height," D "is the entrance pupil diameter, and" Cr "is the curvature of the side surface of the object 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 matters related to these tables are the same in each of the tables shown in Examples 2 to 5, the description thereof will be omitted below.

2 and 3 show a longitudinal aberration diagram and a transverse aberration diagram when the wide-angle lens is in focus at infinity. Further, FIGS. 4 and 5 show a longitudinal aberration diagram and a transverse aberration diagram when an image is taken with the wide-angle lens at an imaging magnification of 1:40.

In each longitudinal aberration diagram, spherical aberration, astigmatism, and distortion are shown in order from the left when facing the drawing. In the diagram 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). Shows the spherical aberration in. In the figure showing astigmatism, the vertical axis shows the image height and the horizontal axis shows the defocus, the solid line shows the sagittal image plane (ds) with respect to the d line, and the dotted line shows the meridional image plane (dm) with respect to the d line. In the figure showing the distortion, the vertical axis represents the image height and the horizontal axis represents%, and the distortion is represented.

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

Since the matters related to each of these figures are the same in the longitudinal aberration diagram and the transverse aberration diagram shown in the second and third embodiments, the description thereof will be omitted below.

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

(1) Configuration of Wide-angle Lens FIG. 6 is a cross-sectional view of a lens showing a lens configuration of the wide-angle lens of the second embodiment according to the present invention when the lens is in focus at infinity. The wide-angle lens is composed of 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 in order from the object side. Has been done. When focusing from an infinity object to a short-range object, the second lens group G2 moves toward the object 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 diaphragm S is arranged on the object side of the third lens group G3.

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

The first A lens group G1A includes 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 in order from the object side. It is composed of. The negative meniscus lens L2 is a glass-molded aspherical lens having both sides having an aspherical shape, or an aspherical lens obtained by grinding.

The first B lens group G1B is composed of a bonded lens in which a negative lens L4 having a concave shape and a positive lens L5 having a convex surface facing the image side are joined in order from the object side. The bonded lens is the negative lens component having a concave surface having a stronger curvature on the object side.

The second lens group G2 is composed of a positive meniscus lens L6 having a concave surface facing the object side, and a bonded lens in which a negative meniscus lens L7 having a convex surface facing the object side and a positive lens L8 are joined. The positive meniscus lens L6 is a glass-molded aspherical lens having both sides having an aspherical shape, or an aspherical lens obtained by grinding.

The third lens group L3 is a bonded lens in which an aperture diaphragm S, 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 joined in this order from the object side. , A positive lens L12 and a negative meniscus lens L13 with a concave surface facing the object side. The negative meniscus lens L13 is a glass-molded aspherical lens having both sides having an aspherical shape, or an aspherical lens obtained by grinding.

However, in the wide-angle lens of the second embodiment, the third lens group may be moved along the optical axis together with the second lens group for focusing. 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 the lens data of the optical system, and Table 4 shows the aspherical data and the variable interval on the optical axis. Table 7 shows the numerical values of the conditional expressions (1) to (7). Further, FIGS. 7 to 10 are a longitudinal aberration diagram and a transverse aberration diagram when the wide-angle lens is in focus at infinity and when an image is taken at an imaging magnification of 1:40.

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

(1) Configuration of Optical System FIG. 11 is a cross-sectional view of a lens showing a lens configuration of a wide-angle lens according to the present invention according to the third embodiment at infinity focusing. The wide-angle lens is composed of a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power in order from the object side. When focusing from an infinity object to a short-range object, the second lens group G2 moves toward the object along the optical axis while the first lens group G1 is fixed in the optical axis direction. The aperture diaphragm S is arranged in the second lens group G2.

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

The first A lens group G1A includes 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 in order from the object side. It is composed of. The negative meniscus lens L2 is a glass-molded aspherical lens having both sides having an aspherical shape, or an aspherical lens obtained by grinding.

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

The second lens group G2 includes a junction lens in which a negative meniscus lens L7 having a convex surface facing the object side and a positive lens L8 are joined, an aperture aperture S, a negative meniscus lens L9 having a convex surface facing the object side, a positive lens L10, and the like. It is composed of a junction lens in which a negative meniscus lens L11 with a concave surface facing the object side is joined, a biconcave negative lens L12, a biconvex positive lens L13, and a negative lens L14. The negative lens L14 is a glass-molded aspherical lens having both sides having an aspherical shape, or an aspherical lens obtained 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 the lens data of the optical system, and Table 6 shows the aspherical data and the variable interval on the optical axis. Table 7 shows the numerical values of the conditional expressions (1) to (7). Further, FIGS. 12 to 15 are a longitudinal aberration diagram and a lateral aberration diagram when the wide-angle lens is in focus at infinity and when an image is taken at an imaging magnification of 1:40.

The back focus of the wide-angle lens at infinity focusing 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 ・ ・ ・ 1st A lens group G1B ・ ・ ・ 1st B lens group G2 ・ ・ ・ 2nd lens group S ・ ・ ・ Aperture aperture IP ・ ・ ・ Image plane

Claims (11)

In order from the object side, a negative first lens group having a refractive power, positive at least with Ru wide-angle lens and a second lens group having a refractive power,
Focusing is performed by moving at least the second lens group.
The first lens group includes at least three negative lenses and one positive lens, and when 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 on the image side of the wide-angle lens has a concave surface at least on the object side or the image side .
A wide-angle lens characterized by satisfying 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 of 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 arranged on the image side of the negative lens L1n, and any one negative lens arranged on the image side of the negative lens L1n is designated as the negative lens L2n. The wide-angle lens according to claim 1, wherein the negative lens L2n satisfies the following conditions.
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 or 2, 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 is composed of a first A lens group containing two negative lens components in order from the object, and a first B lens group containing a negative lens component having a concave surface facing the object side.
The optical system according to any one of claims 1 to 3, which satisfies the following conditions.
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. The wide-angle lens according to claim 4 , wherein among the negative lens components having a concave surface facing the object side included in the first lens group, the curvature of the surface of the negative lens component included in the first B lens group on the object side is the largest. lens. The wide-angle lens according to claim 4, wherein the negative lens component included in the first B lens group satisfies the following conditions.
Cr / f> −1.5 ・ ・ ・ (8)
However,
Cr represents the curvature of the side surface of the object 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 4 to 6, wherein the first B lens group is composed of one negative lens component. The wide-angle lens according to any one of claims 4 to 6, wherein the first B lens group is composed of 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, wherein an aperture diaphragm is provided 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 pickup element that converts an optical image formed by the wide-angle lens into an electrical signal are provided on the image plane side of the wide-angle lens. An image pickup device characterized by this.

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