JP3301579B2 - Inner focusing type zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner focusing type zoom lens suitable for a television camera, and more particularly, to a zoom lens having an F number of about 1.8 and a zoom ratio of 8 to 10.
The present invention relates to a zoom lens having a wide angle of view of about twice.

[0002]

2. Description of the Related Art Conventionally, in a four-group zoom lens, a front lens focusing method in which the entire first lens group is moved during focus adjustment is well known, but the entire first lens group having a positive refractive power as a whole is well known. When the lens is moved to focus on a short-distance object, the first lens group is extended toward the object side, so that the effective diameter of the first lens group is inevitably large in order to secure a light flux around the screen. This becomes remarkable as the angle of view becomes wider. When the effective diameter of the first lens group increases, the lens weight increases, which is inconvenient as a zoom lens mounted on a portable television camera.

As a method for solving this problem, a method of dividing the first lens group into three groups of concave, convex and convex, and moving an intermediate convex lens group to perform focusing is disclosed in JP-B-59-4686 and JP-B-59-4686. This is disclosed in Japanese Unexamined Patent Publication No. Hei 6-242378.

[0004]

However, with the technique described in the above publication, it has been difficult to remove fluctuations in aberrations caused by fluctuations in object distance. The present invention has been made in view of such circumstances, and provides an inner focusing type zoom lens that can reduce the effective diameter of the first lens group and reduce fluctuations in aberrations caused by fluctuations in object distance. It is intended for.

[0005]

An inner focusing type zoom lens according to the present invention comprises, in order from the object side, a first lens unit having a fixed positive refractive power during zooming, and a zoom lens for moving during zooming. A second lens group having a negative refractive power,
A third lens unit having a positive or negative refractive power for correcting a change in an image plane due to zooming, which moves during zooming, and a fourth lens unit having a fixed positive refractive power at zooming, are arranged. In a zoom lens

The first lens group includes, in order from the object side, a first-a lens group having a fixed negative refractive power at the time of focusing;
A first-b lens unit having a positive refractive power that moves to the image side when focusing from an infinity object to a close object, and a positive refractive power that moves to the object side when focusing from an infinite object to a close object Wherein the first c lens group having the following is arranged.

In this inner focusing type zoom lens, it is preferable that the following conditional expression (1) is satisfied. 1.0 <| f1a / f1 | <1.5 (1) where f1 is the composite focal length of the first lens group when focusing on an object at infinity. F1a is the focal length of the first a lens group.

In this inner focusing type zoom lens, it is preferable that the following conditional expression (2) is satisfied. 0.6 <| δ _c · f ₁ / f _1c | <2.0 (2) where f _{1 is} the combined focal length of the first lens group when focusing on an object at infinity f _{1c is} the focal point of the first c lens group Distance δ _c : the amount of movement of the first c lens group from infinity to its closest distance (movement to the image side is defined as positive)

The first b lens group is composed of six lenses, and sequentially from the object side, a meniscus lens 1 _b1 having a positive refractive power with a concave surface facing the object side, a biconcave lens 1 _b2 , and a positive refraction. Lens 1 _b3 having power, lens 1 _b4 having positive refractive power, meniscus lens 1 _b5 having negative refractive power with the convex surface facing the object side, and biconvex lens 1 _b6
And the lens 1 _b3 and the lens 1
Abbe number of _b4 is 35 or less, Abbe number of lens 1 _b6 is 60
It is preferable to set the above. Further, the first b
It is preferable that the moving amount of the lens group and the moving amount of the first c lens group are configured to be proportional to each other.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 to 3 (FIGS. 2 and 3 are each an enlarged view of a part of the zoom lens shown in FIG. 1) show a four-group inner focusing type zoom lens according to an embodiment of the present invention. (A lens configuration of Example 1 described later is shown as a representative). That is, this zoom lens includes, in order from the object side, a first lens group having a fixed positive refractive power when zooming,
A second lens unit having a negative refractive power for zooming, which moves during zooming, and a third lens having positive or negative refractive power, which moves during zooming and corrects a change in the image plane due to zooming. In a zoom lens comprising a group and a fourth lens group having a fixed positive refractive power at the time of zooming, the first lens group has a fixed negative refractive power at the time of focusing, in order from the object side. A 1a lens group, a 1b lens group having a positive refractive power that moves to the image side when focusing from an object at infinity to a close object, and an object side when focusing from an object at infinity to a close object First with positive refractive power
The c lens group is arranged.

Further, at the time of zooming, the second lens unit and the third lens unit, and at the time of focusing (at the time of focusing), the first lens unit and the first lens unit follow the movement locus shown in FIG. By moving along the optical axis X, the focal length f of the entire system is changed, and further focus adjustment is performed. Note that a parallel light beam incident on the zoom lens in parallel with the optical axis X is imaged at an image forming position P.

As described above, according to the zoom lens of the present embodiment, the first lens group is composed of three concave, convex, and convex lenses in order to suppress the increase in the effective diameter of the first lens group. In addition to adopting an inner focus method in which the lens unit is divided into groups and the concave lens group closest to the object side is fixed,
A so-called floating method in which the remaining two convex lens groups in the lens groups are moved in different directions at the time of focus adjustment, is adopted to greatly reduce aberration fluctuations due to object distance fluctuations.

In the zoom lens according to the above-described embodiment, the following conditional expressions (1) and (2) are satisfied. 1.0 <| f _1a / f ₁ | <1.5 (1) where f _{1 is} the combined focal length of the first lens group when focusing on an object at infinity f _{1a is} the focal length of the first lens group 0.6 < | δ _c · f ₁ / f _1C | <2.0 (2) where f _{1 is} the combined focal length of the first lens group when focusing on an object at infinity f _{1c is} the focal length of the first c lens group δ _c : the amount of movement of the first c lens group from infinity to its closest distance (movement to the image side is defined as positive)

The above conditional expression (1) expresses the absolute value of the ratio of the focal length f _1a of the first-a lens unit to the combined focal length f _{1 of} the first lens unit when focusing on an object at infinity. is there. Below this lower limit, the negative refractive power of the 1a-th lens unit becomes strong,
At the wide-angle end, distortion increases, and field curvature at the telephoto end also increases. On the other hand, when the value exceeds the upper limit, the negative refractive power of the first-a lens unit becomes weak, which leads to an increase in lens diameter, which is not preferable.

The above conditional expression (2) satisfies the ratio f _1c / f ₁ of the refractive power occupied in the first lens group of the first c lens group,
It represents the absolute value of the ratio of the c lens group to the amount of movement Δc from infinity to the closest distance. The amount of movement between the first lens unit b and the first lens unit c for focusing is such that the larger the amount of movement of the first lens unit to the image side, the smaller the amount of movement of the first lens unit c toward the object side. . However, for the main effect of the present embodiment, that is, the effect of overcoming the image plane that has fallen under at the time of short-distance focusing, it is advantageous that the movement amount of the first c lens group is large.

However, moving the first c lens group having a higher refracting power than the first b lens group to the object side leads to increasing the combined focal length of the entire system at the time of focusing, and at the time of short distance focusing. The desired wide effect cannot be obtained. The lower limit of this conditional expression (2) is specified to ensure an effective movement amount for aberration correction, while the upper limit prevents an increase in the combined focal length of the entire system when focusing at a close distance. It is specified in order to do.

In the zoom lens according to the present embodiment, the first b lens group is composed of six lenses, and a meniscus lens 1 _b1 having a positive refractive power with a concave surface facing the object side in order from the object side. , A biconcave lens 1 _b2 , a lens 1 _b3 having a positive refractive power, a lens 1 _b4 having a positive refractive power, a meniscus lens 1 _b5 having a negative refractive power with a convex surface facing the object side, and a biconvex lens 1 are arranged _b6 will be, the lens 1 _b3 and the Abbe number of the lens 1 _b4 35 or less, the Abbe number of the lens 1 _b6 is set to 60 or more.

With this configuration, it is possible to suppress the fluctuation of the axial chromatic aberration due to the fluctuation of the object distance on the telephoto side. Further, the zoom lens according to the present embodiment is configured such that the amount of movement of the first b lens group and the amount of movement of the first c lens group are proportional to each other. This makes it possible to make the rotation angle of the focus ring proportional to the amount of movement of these two lens groups, so that it is only necessary to form a normal helicoid in the cam cylinder, and the cam is specially used for focus adjustment. There is no need to provide them.

The large air gap d in the fourth lens group
_In the part ₃₈ , the focal length of the entire system, consisting of a front group having a positive refractive power as a whole and a rear group having a negative refractive power as a whole, is set from the object side. Or an afocal system in which a so-called extender 3a is inserted or a front group having a negative refractive power as a whole and a rear group as a whole having a positive refractive power are arranged from the object side.
The focal length of the entire system is shifted to the short focal length,
A ratio converter 3b can be inserted.

Note that this ratio converter 3b can obtain a wide angle of view similar to that in a normal case even when used in a TV camera having a small image size. Further, in the zoom lens according to the present embodiment, as shown in FIG. 1, a diaphragm 1 is provided between the third lens group and the fourth lens group, and a color separation including an infrared cut filter is provided downstream of the fourth lens group. A prism 2 is provided. Note that the color separation prism 2 is positioned so that the image plane is located on the final surface.

Hereinafter, each embodiment will be described in detail using data. <Embodiment 1> The zoom lens according to Embodiment 1 is configured as shown in FIGS. 1 to 3 as described above. The radius of curvature R (mm) of each lens surface of this zoom lens, Table 1 shows the center thickness, the air gap d (mm) between the lenses, and the refractive index N _d and Abbe number ν _d at the d-line of each lens. The numbers in the table indicate the order from the object side (the same in Tables 3 and 5).

Further, * on the right and left sides of the d value in Table 1
Those marked with a symbol indicate that the d value is variable, and the portions marked with an asterisk on the right indicate that the d value of the first, second, third, and fourth lens groups. It shows the group interval, and the part marked with * on the left side shows the group interval between the 1a group, the 1b group and the 1c group (the same in Tables 3 and 5). Also, in the upper part of Table 2, each lens group (first lens group, second lens group, third lens group, and third lens group) at the wide-angle end (W), the middle (M), and the telephoto end (T) is shown. distance d _20, d _27, d ₃₀ of the fourth lens group), and the focal length at infinity are shown.

The middle part of Table 2 shows the amount of movement of the first b lens unit and the first c lens group, and the focal length at the wide-angle end when focusing on 0.3 m, when the object distance is 0.3 m. 1
Change of the movement amount δc of the c lens group (A when δc = 0, A, δc
= −1.278 mm for B, and δc = −2.555 mm for C). The percentages shown at the right ends of A, B, and C represent percentages of the focal length at the wide-angle end when the object is at infinity. Further, in the lower part of Table 2, the focal length f1 of the first lens group, the focal length f1a of the first a lens group, the focal length f1c of the first c lens group, and the closest distance from infinity of the first c lens group in Example 1 are shown. , The value of | f1a / f1 | (conditional expression (1)) and the value of | δc · f1 / f1c | (conditional expression (2)).

[0024]

[Table 1]

[0025]

[Table 2]

As shown in the lower part of Table 2, | f _1a / f ₁
| = 1.358, | δ _c · f ₁ / f _1c | = 0.71,
Equations (1) and (2) above are all satisfied.

<Embodiment 2> The zoom lens according to Embodiment 2 has the configuration as shown in FIGS. 1 to 3 as described above, and the radius of curvature R of each lens surface of this zoom lens is as follows.
Table 3 shows the values of (mm), the center thickness of each lens, the air gap d (mm) between each lens, and the refractive index N _d and Abbe number ν _d at the d-line of each lens. Further, in the upper part of Table 4, each lens group (first lens group, second lens group, third lens group, and third lens group) at the wide-angle end (W), the middle (M), and the telephoto end (T) is shown. distance d _20, d _27, d ₃₀ of the fourth lens group), and the focal length at infinity are shown.

The middle part of Table 4 shows the amount of movement of the first b lens group and the first c lens group and the focal length at the wide-angle end when focused on 0.3 m, and the focal length at the wide-angle end when the object distance is 0.3 m. 1
Change of the movement amount δc of the c lens group (A when δc = 0, A, δc
= -1.264 mm and C) when δc = -2.529 mm. The percentages shown at the right ends of A, B, and C represent percentages of the focal length at the wide-angle end when the object is at infinity.

Further, in the lower part of Table 4, the focal length f1 of the first lens unit, the focal length f1a of the first a lens unit, the focal length f1c of the first c lens unit, and the infinity of the first c lens unit in Example 2 are shown. The amount of movement δc from far to nearest, | f1a / f1 |
(Conditional expression (1)) and | δc · f1 / f1c | (conditional expression (2)).

[0030]

[Table 3]

[0031]

[Table 4] Amount of focus movement (from object distance infinity to 0.3m from the front of lens) 1b group 1c group 0.3m WIDE end focal length when focusing 0.3m A 6.864 0.0 5.274 (98.97%) B 3.926 -1.264 5.497 (103.15% ) C 1.213 -2.529 5.722 (107.37%) f ₁ : 28.291 f _1a : -40.789 f _1c : 46.456 δ _c : -1.264 (in the case of B) | f _1a / f ₁ |: 1.442 | δ _c · f ₁ / f _1c |: 0.77

As shown in the lower part of Table 4, | f1a / f1
| = 1.442 and | δc · f1 / f1c | = 0.77, and all of the above expressions (1) and (2) are satisfied.

<Embodiment 3> The zoom lens according to Embodiment 3 has the configuration as shown in FIGS. 1 to 3 as described above. The radius of curvature R of each lens surface of this zoom lens is as follows.
Table 5 shows the values of (mm), the center thickness of each lens, the air gap d (mm) between each lens, and the refractive index N _d and Abbe number ν _d at the d-line of each lens. Further, in the upper part of Table 6, each lens group (the first lens group, the second lens group, the third lens group, and the second lens group) at each position of the wide-angle end (W), the middle (M), and the telephoto end (T) is shown. distance d _20, d _27, d ₃₀ of the fourth lens group), and the focal length at infinity are shown.

In the middle part of Table 6, the 1b lens unit and the 1c
Changes in the amount of movement of the lens unit and the amount of movement δc of the first c lens group when the object distance is 0.3 m (the case where δc = 0, A, δc =-
The case of 1.399 mm is shown according to B, and the case of δc = -2.799 mm is shown according to C). The percentages shown at the right ends of A, B, and C represent percentages of the focal length at the wide-angle end when the object is at infinity.

Further, in the lower part of Table 6, the focal length f1 of the first lens group, the focal length f1a of the first-a lens group, the focal length f1c of the first-c lens group, and the infinity of the first-c lens group in Example 3 are shown. The amount of movement δc from far to nearest, | f1a / f1 |
(Conditional expression (1)) and | δc · f1 / f1c | (conditional expression (2)).

[0036]

[Table 5]

[0037]

[Table 6]

As shown in the lower part of Table 6, | f _1a / f ₁
| = 1.327 and | δ _c · f ₁ / f _1c | = 1.78, and all of the above expressions (1) and (2) are satisfied.

FIGS. 4 to 7 show the zoom lens of the first embodiment, FIGS. 8 to 11 show the zoom lens of the second embodiment, and FIGS. 12 to 15 show the zoom lens of the third embodiment. When the object is at infinity (FIGS. 4, 8, and 12), the object distance is 0.3 m and the moving distance of the first lens unit is 0 (FIGS. 5, 9, and 13).
When the moving distance of the first c lens group to the object side is medium at 0.3 m (FIGS. 6, 10, and 14), and when the moving distance of the first c lens group to the object side is 0.3 m and the object distance is 0.3 m (FIG. 7, 1
FIG. 3 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, and distortion) in (1, 15).

That is, in each of the embodiments, the aberration diagram at infinity and the 1c
Each aberration diagram is shown when the lens group is not moved, when the amount of movement of the first c lens group is medium, and when the amount of movement of the first c lens group is large. Comparing the aberration diagrams in each of the examples A, B, and C in which the moving distance of the first c lens group is changed, the spherical aberration and the astigmatism particularly increase as the movement toward the telephoto end side. Obviously, they differ greatly from each other.

That is, if an appropriate amount of movement is set for the first c lens group, and the amount of movement of the first b lens group is set to be proportional to the amount of movement of the first c lens group, and the amount of movement is set in the opposite direction, the entire lens is set. It is possible to perform appropriate aberration correction in the system. In the first and second embodiments, B is in an appropriate state, and in C, the amount of movement of the first c lens group is excessively large, so that the state is excessively corrected.

On the other hand, in the third embodiment, C is in an appropriate state, and in B, correction is insufficient because the movement amount of the first c lens group is still small. Note that the zoom lens of the present invention is not limited to those in the above-described embodiments, and for example, the shape of the lens constituting each lens group and the number of lenses can be appropriately selected.

[0043]

As described above, according to the inner focusing type zoom lens of the present invention, in order to suppress an increase in the effective diameter of the first lens unit, the first lens unit is divided into three groups, concave, convex and convex. And a so-called floating method of moving the remaining two convex lens groups in the first lens group in directions different from each other at the time of focus adjustment while adopting an inner focus method of fixing the concave lens group closest to the object side. This is used to greatly reduce the variation in aberration due to the variation in object distance. This makes it possible to reduce the effective diameter of the first lens group and to reduce the fluctuation of aberration due to the fluctuation of the object distance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a basic configuration of a zoom lens according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a part of the zoom lens shown in FIG. 1;

FIG. 3 is a schematic view showing a part of the zoom lens shown in FIG. 1;

FIG. 4 is an aberration diagram of the zoom lens according to the first embodiment when focused on an object at infinity.

FIG. 5 illustrates an object distance of 0.3 of the zoom lens according to the first embodiment.
m, aberration diagram when the moving distance of the first c lens group is 0

FIG. 6 illustrates an object distance of 0.3 of the zoom lens according to the first embodiment.
m, Aberration diagram when the moving distance of the 1st c lens group is medium

FIG. 7 shows an object distance of 0.3 of the zoom lens according to the first embodiment.
Aberration diagram when the moving distance of the m, 1c lens group is large

FIG. 8 is an aberration diagram of the zoom lens according to Example 2 upon focusing on an object at infinity.

FIG. 9 illustrates an object distance of 0.3 of the zoom lens according to the second embodiment.
m, aberration diagram when the moving distance of the first c lens group is 0

FIG. 10 is a diagram illustrating an example in which the object distance of the zoom lens according to the second embodiment is 0.
Aberration diagram when the moving distance of the 1m lens group is 3m

FIG. 11 is a view illustrating an example in which the object distance of the zoom lens according to the second embodiment is 0.
Aberration diagram when the moving distance of the 3m, 1c lens group is large

FIG. 12 is an aberration diagram of the zoom lens according to the third embodiment when focused on an object at infinity.

FIG. 13 illustrates an example in which the zoom lens according to the third embodiment has an object distance of 0.
Aberration diagram when the moving distance of the 3m, 1c lens group is 0

FIG. 14 is a diagram illustrating an example in which the zoom lens according to the third embodiment has an object distance of 0.
Aberration diagram when the moving distance of the 1m lens group is 3m

FIG. 15 is a diagram illustrating an example in which the object distance of the zoom lens according to the third embodiment is 0.
Aberration diagram when the moving distance of the 3m, 1c lens group is large

[Explanation of symbols]

L1 to L27 lenses R1 to R53 Curvature radii of surfaces such as lenses d1 to d52 Surface spacing (lens thickness) of lenses etc. X Optical axis P Image forming position 1 Aperture 2 Color separation prism including infrared cut filter 3a Extender 3b Ratio converter

Claims (5)

(57) [Claims] 1. A first lens group having a fixed positive refractive power at the time of zooming, a second lens group having a negative refractive power for zooming which moves at the time of zooming, and moving at the time of zooming in order from the object side. Do
In a zoom lens in which a third lens group having a positive or negative refractive power for correcting a change in an image plane due to zooming and a fourth lens group having a fixed positive refractive power at the time of zooming are arranged. The first lens group includes, in order from the object side, a first a lens group having a fixed negative refractive power at the time of focus adjustment, and a positive refractive power moving to the image side at the time of focus adjustment from an object at infinity to a close object. And a first b lens group having a positive refractive power, which moves toward the object side during focusing from an object at infinity to a close object, and an inner focusing type zoom. lens. 2. The inner focusing type zoom lens according to claim 1, wherein the following conditional expression (1) is satisfied. 1.0 <| f _1a / f ₁ | <1.5 (1) where f _{1 is} the combined focal length of the first lens group when focusing on an object at infinity f _{1a is} the focal length of the first a lens group 3. The zoom lens of the inner focusing type according to claim 1, wherein the following conditional expression (2) is satisfied. 0.6 <| δ _c · f ₁ / f _1c | <2.0 (2) where f _{1 is} the combined focal length of the first lens group when focusing on an object at infinity f _{1c is} the focal point of the first c lens group Distance δ _c : the amount of movement of the first c lens group from infinity to the closest distance (movement to the image side is defined as positive) 4. A first meniscus lens 1 _b1 and a biconcave lens 1 having a positive refractive power with a concave surface facing the object side in order from the object side.
_b2 , a lens 1 _b3 having a positive refractive power, a lens 1 _b4 having a positive refractive power, a meniscus lens 1 _b5 having a negative refractive power with a convex surface facing the object side, and a biconvex lens 1 _b6 are arranged. The Abbe number of the lens 1 _b3 and the lens 1 _b4 is set to 35 or less, and the Abbe number of the lens 1 _b6 is set to 60 or more. The described inner focusing type zoom lens. 5. The moving amount of the first b lens group and the first c lens
The inner focusing type zoom lens according to any one of claims 1 to 4, wherein movement amounts of the lens groups are proportional to each other.