JP2003222794A - Imaging lens and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform image angle broadening while reducing an effective aperture of a front lens group in an imaging lens by sequentially arranging a plurality of negative lenses and at least two positive lenses in this order from an object side, and constituting the lens arranged at the most focusing surface side of the at least two positive lenses and made of both convex lenses directed at a surface having a storing curvature to the object side. <P>SOLUTION: A negative first lens group G1, a diaphragm 3 and a positive second lens group G2 are arranged. The group G1 has a negative G1a in which a plurality of negative lenses and two positive lenses are sequentially arranged from the object side, a negative G1b having a single negative lens and positive and negative doublets G1bf for focusing, and a group G1c having negative and positive doublets. When a focus is moved from an infinity object point to a close object point, the doublet G1f in the group G1b is moved along the optical axis X to the object side. The positive lens in the G2 and the doublets G1bf in the G1 are respectively constituted of anomalous dispersion materials. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixed-focus image pickup lens suitable for a television camera, and more particularly to a wide-angle image pickup lens having a long back focus and an image pickup apparatus having two groups.

[0002]

2. Description of the Related Art In recent years, there has been known a television broadcast image pickup camera called a so-called E-cinema camera capable of picking up an image for cinema.

The image pickup lens used in this E-cinema camera is required to have a wider angle and higher performance over the entire image forming surface, as compared with an ordinary TV broadcast image pickup camera. When a solid-state image sensor is used in such an E-cinema camera, a low-pass filter or an infrared cut filter is provided between the image pickup lens and the solid-state image sensor, as in a normal television broadcast image-pickup camera. Because
It is necessary to lengthen the back focus of the imaging lens.
Further, in a so-called multi-plate type in which an image pickup device is used for each primary color light, a color separation prism is arranged in front of each solid-state image pickup device, so that the back focus of the image pickup lens needs to be set longer. .

On the other hand, it is preferable to adopt the inner focus system in the above-mentioned television broadcasting image pickup camera in order to suppress the variation of various aberrations and the variation of the angle of view due to focusing.

The one described in Japanese Patent Application Laid-Open No. 4-118612, which has been already disclosed by the applicant of the present invention, is known to satisfy such various requirements. The technology described in this publication is a retrofocus type high-performance imaging lens, and it is possible to obtain sufficiently good performance even if the angle of view is 90 ° or more.

[0006]

However, in the image pickup lens described in the above publication, it is difficult to significantly reduce the effective system of the lens (front lens) forming the front lens group, and recent image pickup cameras have been made compact. The request was not always satisfactory.

For example, in the image pickup lens of Example 1 described in the publication, the focal length is 5.0 mm and the F number is 1.
8 、 angle of view 95.5 degree (image circle φ11.0mm)
The effective diameter of the front lens was φ95.0 mm, and there was a demand to reduce this to about half the size.

The present invention has been made in view of such circumstances, and in a retrofocus type high-performance imaging lens, the effective diameter of the front lens can be significantly reduced, and the imaging camera can be made compact. It is a first object to provide a lens and an image pickup device.

On the other hand, there is known an image pickup lens for an image pickup camera as described above, which employs an inner focus system in order to suppress variations in various aberrations and variations in angle of view due to focusing.

As a wide-angle image pickup lens of this type that employs the inner focus method, there is known an image pickup lens described in Japanese Patent Laid-Open No. 2000-131606, in addition to the one described in the above publication. The one described in this publication is 2
The positive lens group (the first and second groups) on the image plane side of the two lens groups forming the front group is moved forward and backward to perform focusing.

However, in the image pickup lens described in this publication, the ratio of the back focus to the focal length of the entire system (retro ratio) is about 2.6, and the back focus is not always sufficient.

Further, in the above-mentioned Japanese Patent Laid-Open No. 4-118612, the lens group on the image plane side of the two lens groups forming the front group is moved and the rear group is also moved. By doing so, focusing is performed, and the mechanical mechanism for focusing becomes complicated. Further, since the change in the angle of view due to focusing is not small, it may not always be appropriate to mount the camera on the E-cinema or the like.

The present invention has been made in view of the above circumstances, and in addition to the above-mentioned first object, in an image pickup lens adopting an inner focus system, which is used particularly in an image pickup camera for television broadcasting such as E cinema. , It is possible to suppress the variation of various aberrations associated with focusing without complicating the mechanical mechanism of focusing and without increasing the variation of the angle of view associated with focusing. An object is to provide an imaging lens and an imaging device that can be secured.

Further, in the above-mentioned wide-angle image pickup lens, there is a demand to satisfactorily correct chromatic aberration, and as a response to this demand, one using anomalous dispersion glass as the convex lens in the second lens group. Are known.

However, the anomalous dispersion glass has a characteristic that the change in the refractive index with the temperature change is large.
Therefore, there is a problem that the amount of change in the back focus due to the temperature change becomes large depending on the case where the anomalous dispersion glass is used for the convex lens in the second lens group.

The present invention has been made in view of such circumstances, and in addition to the first object, in the retrofocus type high performance imaging lens, the change amount of the back focus due to the temperature change is not increased. An object of the present invention is to provide an imaging lens and an imaging device capable of satisfactorily correcting chromatic aberration.

[0017]

The image pickup lens according to the present invention comprises, in order from the object side, a first lens group having a negative refracting power as a whole, an aperture stop, and a second lens group having a positive refracting power as a whole. In the arrayed imaging lens,
The first lens group includes, in order from the object side, a plurality of negative lenses arranged on the most object side and at least two positive lenses arranged on the image plane side, and has a negative refracting power as a whole. A first lens group, a single negative lens and a cemented lens of a positive lens and a negative lens arranged in order from the object side and having a negative refracting power as a whole; and at least one positive lens and a negative lens. In addition, the first c lens group is arranged, and among the at least two positive lenses of the first a lens group, the lens arranged closest to the image plane is a biconvex lens having a surface having a strong curvature toward the object side. It is characterized by that.

Further, the cemented lens of the 1b-th lens group is constructed so as to satisfy the following conditional expression (1), and when focusing from an object point at infinity to a near object point, the cemented lens is moved toward the object side. The feature is that it is carried out in a rolling manner. 2.0 <fc / f1b <7.5 (1) where fc: focal length of the cemented lens that moves during focusing f1b: focal length of the entire 1b lens group

The second lens group has at least 1
The negative lens, which includes a positive lens made of one sheet of anomalous dispersion glass and constitutes the cemented lens of the 1b-th lens group, satisfies the following conditional expression (2). dn / dt <-0.000005 (2) However, dn / dt: Change in refractive index with temperature (/ ° C)

Further, the second lens group is formed by arranging the 2a lens group and the 2b lens group in order from the object side, and the combined focal length of the first lens group and the 2a lens group is almost infinite. Configured to be large, the second
It is desirable to adjust the back focus length by moving the b lens group along the optical axis.

An image pickup apparatus according to the present invention is characterized in that any one of the above-mentioned image pickup lenses is housed in a housing.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an imaging lens according to an embodiment of the present invention (the lens configuration of Example 1 described later is shown as a representative).

This image pickup lens is housed in a camera housing as an image pickup lens of an image pickup camera for E cinema, for example, and the first lens group G ₁ having a negative refracting power as a whole in order from the object side. Is a retrofocus type imaging lens including a diaphragm 3 and a second lens group G ₂ arranged on the image plane side of the diaphragm 3 and having a positive refracting power as a whole. The first lens group G ₁ includes a plurality of negative lenses and at least two positive lenses arranged in this order from the object side, and has a negative refracting power as a whole.
Lens group G _1a , a single negative lens, and a first-b lens group G _1b having a cemented lens including a set of positive lens and negative lens and having a negative refracting power as a whole, at least one set of positive lens and negative lens It is configured to include a first c lens group G _{1c including} a cemented lens made of.
The light flux incident on the imaging lens is imaged on the imaging surface 1 of the solid-state imaging device via the three-color separation optical system (including a low-pass filter and the like) 2. Further, among the at least two positive lenses of the 1a lens group, the lens arranged closest to the image forming surface is a biconvex lens having a surface having a strong curvature facing the object side.

As described above, in the image pickup lens of this embodiment, the first-a lens group G _1a is arranged from the object side with a plurality of (for example, three) negative lenses and at least two positive lenses arranged in this order. , And the lens disposed closest to the image plane is composed of a biconvex lens with a surface having a strong curvature facing the object side. When the ray trace is viewed from the image plane side, at least two of the above Of positive lenses (L ₄ and L _{5 in} the image pickup lens of FIG. 1) are once stopped, and then a plurality of negative lenses (L ₁ , L ₂ and L in the image pickup lens of FIG. 1 are used).
₃ ) because it will be in a state where it is greatly diverged,
It is possible to achieve a wide angle of view while reducing the effective diameter of the front lens, and it is possible to achieve a compact overall lens system.

Further, in this imaging lens, when focusing from an object point at infinity to an object point at a close distance, the cemented lens G _1bf of the 1b-th lens group G _1b is moved to the object side along the optical axis X. When focusing from an object point at infinity to an object point at infinity, the cemented lens G _1bf is an inner focus type in which the cemented lens G _1bf is moved to the image plane side along the optical axis X. Since the focusing is performed by the movement of the chisel, the driving force for performing the focusing can be made small, the mechanical mechanism can be simplified, and the manufacturing cost can be reduced. Further, when focusing is performed, the image plane characteristic associated with the change in the object distance is improved, and the view angle variation associated with the focusing can be suppressed.

The cemented lens G _1bf is constructed so as to satisfy the following conditional expression (1). 2.0 <fc / f1b <7.5 (1) However, fc: cemented lens G that moves during focusing
The focal length of _1BF f1b: focal length of the entire the 1b lens group

As described above, in the image pickup lens of this embodiment, the cemented lens G which moves during focusing is used.
The focal length of 1 _bf is defined, whereby the fluctuation of the tangential image plane and the increase of coma aberration due to focusing can be suppressed, and the lens movement amount at the time of focusing can be suppressed.

That is, when the value goes below the lower limit of the conditional expression (1), the variation of the tangential image plane accompanying focusing becomes large. On the other hand, if the upper limit is exceeded, the amount of movement during focusing becomes large, making it difficult to secure a sufficient distance between the front and rear lenses, and coma also increases.

Furthermore, in the image pickup lens of this embodiment, at least one positive lens made of anomalous dispersion glass is included in the second lens group G ₂ , and the first lens
The negative lens forming the cemented lens in the lens group G ₁ is configured to satisfy the following conditional expression (2). dn / dt <-0.000005 (2) However, dn / dt: Change in refractive index with temperature (/ ° C)

With this configuration, the first
A negative lens formed of anomalous dispersion glass, which is disposed in the lens group G ₁ , causes a back focus change due to a temperature change, and is made of the anomalous dispersion glass in the second lens group G _2. It is possible to cancel the back focus change due to temperature change, which is the opposite direction to the back focus change direction that occurs in the positive lens, so that the chromatic aberration is improved without increasing the back focus change amount due to temperature change. Can be corrected to.

When the upper limit of the conditional expression (2) is exceeded, the above-mentioned back focus change is not sufficiently offset.

The second lens group G ₂ includes, in order from the object side, a 2a lens group G _2a and a 2b lens group G 2.
_2b are arranged so that the combined focal length of the first lens group G ₁ and the second a lens group G _2a is substantially infinite, and the second b lens group G _2b is moved along the optical axis X. The back focus length is adjusted by moving the back focus length.

With this configuration, it is possible to easily adjust the mechanical error in the optical axis direction, which occurs when the image pickup lens is connected to the camera body, without making the mechanism mechanically complicated.

[0034]

EXAMPLES Example 1 The image pickup lens according to Example 1 has the structure shown in FIG. 1 as described above.

The detailed lens structure will be described below. The lens numbers of the lens groups and the lenses are sequentially increased from the object side.

The first-a lens group G _1a includes a first lens L ₁ which is a negative meniscus lens having a concave surface facing the image plane.
And a second lens L ₂ , a third lens L ₃ composed of a biconcave lens, a fourth lens L ₄ composed of a positive meniscus lens having a convex surface facing the image forming surface side, and a biconvex lens having a surface having a strong curvature facing the object side. And a fifth lens L ₅ .

The first-b lens group G _1b includes a cemented lens G _1bf for focusing, and includes a sixth lens L ₆ including a negative meniscus lens having a concave surface facing the image-forming surface side, and the image-forming surface side. It is composed of a cemented lens of a seventh lens L _{7 made of} a positive meniscus lens having a convex surface facing to and an eighth lens L _{8 made} of a negative meniscus lens having a concave surface facing to the object side.

The first-c lens group G _1c is composed of a ninth lens L ₉ which is a biconcave lens having a surface of strong curvature facing the image plane side and a biconvex lens which is a biconvex lens having a surface of strong curvature facing the object side. 10 lens L _{10 is} a cemented lens.

The second-a lens group G _2a is composed of a cemented lens of an eleventh lens L ₁₁ which is a biconvex lens, a twelfth lens L _{12 which is a} biconcave lens and a thirteenth lens L _{13 which is} a biconvex lens.

The 2b-th lens group G _2b is a back focus adjustment group, and includes a 14th lens L ₁₄ consisting of a negative meniscus lens with a concave surface facing the image forming surface and a surface having a strong curvature toward the object side. The 15th consisting of a biconvex lens
It is composed of a cemented lens of the lens L _{15 and} a 16th lens L ₁₆ which is a biconvex lens with a surface having a strong curvature facing the object side.

The radius of curvature R (mm) of each lens surface of the image pickup lens according to the first embodiment, the center thickness of each lens and the air gap D (mm) between the lenses, and the refractive index N at the d-line of each lens. The values of Abbe number ν are shown in Table 1. The numbers in the table represent the order from the object side (same in Tables 2, 3, and 4).

[0042]

[Table 1]

The values relating to the focal length f '(mm) of the entire system, the back focus Bf' (mm) and the F number Fno, and the conditional expressions (1) and (2) in Example 1 are shown. It is shown in the lower part of 1. As shown in Table 1, the conditional expressions (1) and (2) are both satisfied. Here, in Example 1, the lens made of the glass material with anomalous dispersion is the negative eighth lens L ₈ and the positive thirteenth lens L.
₁₃ and the positive fifteenth lens L ₁₅ . Further, the effective diameter of the front lens of the first embodiment is φ46.0 mm, so that the wide-angle lens can be made compact.

Further, FIG. 2 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, chromatic aberration of magnification, coma aberration) in the first embodiment when the focus is adjusted to infinity and infinity. As is clear from FIG. 2, the image pickup lens of Example 1 has good aberrations.

Example 2 The structure and operation of the image pickup lens according to Example 2 are almost the same as those in Example 1. The radius of curvature R (m of each lens surface of the imaging lens according to Example 2
m), the center thickness of each lens and the air gap D between each lens
Table 2 shows the values of the refractive index N and the Abbe number ν (mm), d line of each lens.

[0046]

[Table 2]

The values relating to the focal length f '(mm) of the entire system, the back focus Bf' (mm) and the F number Fno, and the conditional expressions (1) and (2) in Example 2 are shown. It is shown in the lower part of 2. As shown in Table 2, the conditional expressions (1) and (2) are both satisfied. The lens made of anomalous dispersion glass materials in Example 2 is the negative of the eighth lens L ₈ and positive fifteenth lens L _15. The effective diameter of the front lens of Example 2 is φ46.0m.
Therefore, the wide-angle lens can be made compact.

Further, FIG. 3 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, chromatic aberration of magnification, coma aberration) in the second embodiment when the focus is adjusted to infinity and infinity. As is clear from FIG. 3, the image pickup lens of Example 2 has various aberrations.

<Example 3> The configuration and operation of the imaging lens according to Example 3 are almost the same as those of Example 1, but mainly the third lens which is the third lens from the object side of the 1a-th lens group G _1a . The lens L ₃ is composed of a negative meniscus lens with the concave surface facing the image plane side, and the eighth lens L ₈ which is the third lens from the object side of the 1b-th lens group G _1b has a surface having a strong curvature on the object side. made of a biconcave lens having, ninth lens L ₉ is different in that a negative meniscus lens having a concave surface facing the image plane side is the first lens from the object side of the 1c lens group G _1c.

The radius of curvature R (mm) of each lens surface of the image pickup lens according to the third embodiment, the center thickness of each lens and the air gap D (mm) between each lens, and the refractive index N at the d-line of each lens. The values of Abbe number ν are shown in Table 3.

[0051]

[Table 3]

The values relating to the focal length f '(mm) of the entire system, the back focus Bf' (mm) and the F number Fno, and the conditional expressions (1) and (2) in Example 3 are shown. It is shown in the lower part of 3. As shown in Table 3, both conditional expressions (1) and (2) are satisfied. Here, in Example 3, the lens made of the anomalous dispersion glass material is the negative eighth lens L ₈ and the positive thirteenth lens L.
₁₃ and the positive fifteenth lens L ₁₅ . In addition, the effective diameter of the front lens of the third embodiment is φ45.5 mm, and the wide-angle lens can be made compact.

Further, FIG. 4 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, chromatic aberration of magnification, coma) in the third embodiment when the focus is adjusted to infinity and infinity. As is clear from FIG. 4, the image pickup lens of Example 3 has various aberrations.

Example 4 The structure and operation of the image pickup lens of Example 4 are almost the same as those of Example 1, but mainly the eighth lens which is the third lens from the object side of the 1b-th lens group G _1b . The lens L ₈ is composed of a biconcave lens with a surface having a strong curvature facing the object side, and the ninth lens L ₉ which is the first lens from the object side of the 1c-th lens group G _{1 c} has a concave surface on the image formation side. The difference is that it consists of a negative meniscus lens aimed at.

The radius of curvature R (mm) of each lens surface of the image pickup lens according to the fourth embodiment, the center thickness of each lens and the air gap D (mm) between each lens, and the refractive index N at the d-line of each lens. The values of Abbe number ν are shown in Table 4.

[0056]

[Table 4]

The values relating to the focal length f '(mm) of the entire system, the back focus Bf' (mm) and the F number Fno, and the conditional expressions (1) and (2) in Example 4 are shown. It is shown in the lower part of No. 4. As shown in Table 4, the conditional expressions (1) and (2) are both satisfied. Here, in Example 4, the lens made of the glass material with anomalous dispersion is the negative eighth lens L ₈ and the positive thirteenth lens L.
₁₃ and the positive fifteenth lens L ₁₅ . Further, the effective diameter of the front lens of the fourth embodiment is φ43.3 mm, and the wide-angle lens can be made compact.

Further, FIG. 5 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, chromatic aberration of magnification, coma) in the fourth embodiment when the focus is adjusted to infinity and infinity. As is clear from FIG. 5, the image pickup lens of Example 4 has various aberrations.

The image pickup lens of the present invention is not limited to the above-mentioned embodiment, but various modifications can be made. For example, the shape of the lenses forming each lens group and the number of lenses are It can be selected appropriately.

Further, the image pickup apparatus of the present invention can be applied to various image pickup apparatuses other than the image pickup camera for television broadcasting described above.

[0061]

As described above, according to the image pickup lens and the image pickup apparatus of the present invention, in the first lens group, a plurality of negative lenses and at least two positive lenses are arranged in this order from the object side. Of the at least two positive lenses, the lens arranged closest to the image plane is composed of a biconvex lens with a surface having a strong curvature facing the object side.
When the ray trace is viewed from the image plane side, it is once narrowed down by the at least two positive lenses and then largely diverged by a plurality of negative lenses. Therefore, the effective diameter of the front lens is made small and wide. The angle of view can be achieved, and the entire lens system can be made compact.

Further, this imaging lens is of an inner focus type in which only the cemented lens of the 1b-th lens group is moved toward the object side along the optical axis when focusing from an object point at infinity to a near object point. By doing so, the driving force is small, the mechanical mechanism for performing focusing becomes simple, and the manufacturing cost becomes low. Further, when focusing is performed, the image plane characteristic associated with the change in the object distance is improved, and it becomes possible to suppress the variation in the angle of view associated with the focusing.

Further, at least 1 is included in the second lens group G _2.
When the negative lens that includes the convex lens made of one sheet of anomalous dispersion glass and that constitutes the cemented lens in the first lens group G ₁ satisfies the predetermined conditional expression expressing the anomalous dispersion, the second lens group G 1 Since it is possible to cancel the change in the back focus due to the temperature change that occurs in the convex lens made of anomalous dispersion glass in ₂ , it is possible to satisfactorily correct the chromatic aberration without increasing the change amount of the back focus due to the temperature change. You can

[Brief description of drawings]

FIG. 1 is a configuration diagram of an imaging lens according to a first embodiment of the present invention.

FIG. 2 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, lateral chromatic aberration, coma aberration) in Example 1 when focus adjustment is performed at infinity and close distance.

FIG. 3 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, lateral chromatic aberration, coma aberration) in the second embodiment when focus adjustment is performed at infinity and close distance.

FIG. 4 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, lateral chromatic aberration, coma aberration) in Example 3 when the focus is adjusted to infinity and close distance.

FIG. 5 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, lateral chromatic aberration, coma aberration) in Example 4 when focus adjustment is performed at infinity and infinity.

[Explanation of symbols]

L _{1 to} L ₁₆ lens R _{1 to} R ₃₂ surface radius of curvature of lens D _{1 to} D ₃₁ surface spacing of lens (lens thickness) X optical axis 1 image forming surface 2 3 color separation optical system 3 diaphragm

Continued front page    F term (reference) 2H087 KA03 LA03 MA07 NA02 NA08                       NA09 NA14 PA12 PA16 PB16                       QA02 QA07 QA17 QA22 QA26                       QA34 QA41 QA46 RA32 RA41                       RA43 UA06

Claims (5)

[Claims] 1. An imaging lens comprising a first lens group having a negative refracting power as a whole, an aperture stop, and a second lens group having a positive refracting power as a whole arranged in order from the object side. A first lens group having a negative refracting power as a whole, in which a lens group includes, in order from the object side, a plurality of negative lenses arranged closest to the object side and at least two positive lenses arranged on the image plane side. Group, a first negative lens group having a single negative lens and a cemented lens composed of a positive lens and a negative lens arranged in order from the object side and having a negative refractive power as a whole, and a first lens group including at least one positive lens and negative lens 1c lens group is arranged, and among the at least two positive lenses of the 1a lens group, the lens arranged closest to the image forming surface side is a biconvex lens with a surface having a strong curvature facing the object side. An imaging lens according to claim. 2. The cemented lens of the 1b-th lens group is configured to satisfy the following conditional expression (1), and when focusing from an object point at infinity to a near object point, the cemented lens is moved toward the object side. 2. The method according to claim 1, wherein the operation is carried out in a rolling manner.
The imaging lens described. 2.0 <fc / f1b <7.5 (1) where fc: focal length of the cemented lens that moves during focusing f1b: focal length of the entire 1b lens group 3. The second lens group includes at least one positive lens made of anomalous dispersion glass, and the negative lens forming the cemented lens of the 1bth lens group satisfies the following conditional expression (2). The imaging lens according to claim 1, wherein: dn / dt <-0.000005 (2) However, dn / dt: Change in refractive index with temperature (/ ° C) 4. The second lens group, in order from the object side,
The second-a lens group and the second-b lens group are arranged so that the combined focal length of the first-lens group and the second-a lens group is substantially infinite.
The back focus length is adjusted by moving the lens group along the optical axis.
The imaging lens according to claim 1. 5. An image pickup apparatus comprising the image pickup lens according to claim 1 housed in a housing.