JP3085823B2 - Aspherical zoom lens and video camera using it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aspherical zoom lens having a high zoom ratio of about 10 times and a long back focus, and a video camera using the same, which is used for a three-panel video camera or the like.

[0002]

2. Description of the Related Art Recent video cameras are required to have high image quality as well as operability and mobility, and in response to this, imaging devices having a small size and a high resolution are becoming mainstream.
Accordingly, there is a strong demand for a high-performance zoom lens with a large aperture ratio, small size and light weight, and high performance. Furthermore, there is a strong demand for cost reduction, and there is a strong demand for a high-magnification zoom lens that reduces the number of components while maintaining high performance.

However, a high-magnification zoom lens not only requires a large lens diameter and a long lens length, but also requires a large number of lenses to achieve more severe aberration correction.
They are large, heavy and expensive, or have a combination of single lenses, so they have tight tolerances, are difficult to assemble, and are not suitable for consumer video cameras.

Hereinafter, an example of the above-mentioned conventional zoom lens for a video camera will be described with reference to the drawings. FIG. 15 shows a configuration diagram of a conventional zoom lens for a video camera. In FIG. 15, reference numeral 21 denotes a first lens group as a light condensing unit, 22 denotes a second lens group as a zooming unit,
Reference numeral 23 denotes a third lens group as a condensing unit, reference numeral 24 denotes a fourth lens group as a focusing unit, reference numeral 25 denotes a color separation optical system, and reference numeral 26 denotes an equivalent glass plate corresponding to a crystal filter or a face plate of an image sensor. And 27 is an image plane.

The operation of the zoom lens for a video camera comprising the above components will be described below. The first lens group 21 fixed to the image plane has an image forming action, and the second lens group 22 moving on the optical axis changes the magnification,
Change the focal length of the whole system. Third lens group that is a fixed group
23 has the function of condensing the divergent light generated by the second lens group 22, and the fourth lens group 24 moving on the optical axis has the focusing action. The second lens group 22 during zooming
Of the image plane position caused by the movement of the fourth lens group
24 by moving it, the image plane position 27
Is kept constant.

[0006]

However, in the above-mentioned conventional zoom lens having a zoom ratio of about 10 times, the fourth lens group 24 is composed of three single lenses. Had the problem of tight tolerances.

The present invention solves the above-mentioned problems, and adopts a new lens type and an optimum aspherical shape, so that a zoom ratio of about 10 times and a color separation optical system can be inserted with a simple structure, It is still another object of the present invention to provide a high-performance aspherical zoom lens having a long back focus that is easy to assemble in a manufacturing process, and to provide a video camera using the aspherical zoom lens.

[0008]

In order to solve the above problem, an aspherical zoom lens according to the present invention comprises, in order from an object side, a first lens group having a positive refractive power and fixed to an image plane; A second lens group having a negative refractive power and performing a zooming action by moving on the optical axis, a third lens group having a positive refractive power fixed to the image plane and having a condensing action, An aspherical zoom lens comprising a fourth lens group having a positive refractive power and moving on the optical axis so as to keep the image plane, which fluctuates due to the movement of the two lens groups and the movement of the object, at a constant position from the reference plane. The third lens group and the fourth lens group have an air gap, the first lens group is composed of a concave lens, a biconvex lens, and a meniscus convex lens in order from the object side, and the second lens group is a meniscus concave lens configuration and from both concave and convex lens The third lens group includes a single lens having at least one aspherical surface, and the fourth lens group includes a lens having at least one aspherical shape, and has a two-element cemented lens and one lens. And satisfies the following conditions . (1) 3.0 <f1 / fW <8.0 (2) 0.5 <| f2 | / fW <1.6 (3) 5.14 <f3 / fW <7.0 (4) 2.0 <F4 / fW <5.0 (5) 1.5 <BF / fW <5.0 (6) 0.02 <d12 / f4 <1.0 (7) 0.3 <r11 / f3 <1.5 (8) 0.3 <| r13 | / f4 <3.0 (9) 0.3 <| r17 | / f4 <1.5 where fW is the focal length at the wide-angle end, and fi (i =
1, 2, 3, 4) are the focal length of the i-th lens group, and BF is empty
The distance from the last lens surface to the imaging surface in the air, d1
2 is an air gap between the third lens unit and the fourth lens unit, r1
1 is the curvature of the object side surface of the convex lens constituting the third lens group
The radius r13 is the maximum value of the cemented lens constituting the fourth lens group.
Is the radius of curvature of the surface from the object, and r17 is the fourth lens group.
Curvature of the image side surface of the convex lens for forming a radius.

Specifically, it is desirable that the third lens group is a single aspherical lens having a positive refractive power and a convex surface facing the object side. More specifically, it is preferable that the fourth lens group includes, in order from the object side, a cemented lens having two lenses and a convex lens having a convex surface facing the image side, and has at least one aspheric surface.

[0010]

According to another aspect of the present invention, there is provided a video camera including at least the aspherical zoom lens, a color separation optical system, three image sensors, a signal processing circuit, and a viewfinder.

[0012]

According to the present invention, the conventional problem is solved by the above configuration. That is, the first lens group is a concave lens, a biconvex lens, and a meniscus convex lens, the second lens group is a meniscus concave lens, a biconcave lens, and a convex lens, and the third lens group is a lens having a positive refractive power convex toward the object side. By increasing the fourth lens group from the object side to a cemented lens having two lenses, a convex lens having a convex surface facing the image side, and providing at least one or more aspherical shapes in order from the object side, A high-magnification aspherical zoom lens having a moderate zoom ratio and a long back focus can be provided with a simple configuration.

Further, by satisfying the conditions (1) to (9), it is possible to provide a high-performance aspherical zoom lens which has a simple configuration and has good aberration correction. In addition, by using the aspherical zoom lens of the present invention, a compact, lightweight, high-power,
A high-quality three-panel video camera can be realized.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; FIG. 1 shows a configuration diagram of an embodiment of an aspherical zoom lens according to the present invention. In FIG. 1, 1 is a first lens group, 2 is a second lens group, 3 is a third lens group,
Is a fourth lens group, 5 is a flat plate optically equivalent to a color separation optical system, and 6 is a flat plate optically equivalent to a quartz filter, a face plate of an imaging device, or the like.

The aspherical zoom lens has a first lens group 1 which has a positive refractive power and has an image forming action and is a fixed group, and has a negative refractive power and has a zooming action by moving on the optical axis. A second lens group 2 to be performed; a third lens group 3, which is a fixed group composed of an aspheric lens having a positive refractive power and having a light-condensing function, and moving on the optical axis having a positive refractive power to perform focusing. The fourth lens group 4 includes an aspheric lens for adjustment. The third lens group 3 and the fourth lens group 4 have a relatively large air gap, the first lens group 1 is composed of a cemented lens and a meniscus lens having a positive refractive power in order from the object side, and the second lens group 2 is The third lens group 3 is composed of a single lens having at least one aspherical surface, and the fourth lens group 4 is composed of a lens having at least one or more aspherical surfaces. The meniscus lens has a negative refractive power and a cemented lens. It is composed of a cemented lens having two lenses and one convex lens.

The aspherical zoom lens satisfies the following conditions. (1) 3.0 <f1 / fW <8.0 (2) 0.5 <| f2 | / fW <1.6 (3) 2.0 <f3 / fW <7.0 (4) 2.0 <F4 / fW <5.0 (5) 1.5 <BF / fW <5.0 (6) 0.02 <d12 / f4 <1.0 (7) 0.3 <r11 / f3 <1.5 (8) 0.3 <| r13 | / f4 <3.0 (9) 0.3 <| r17 | / f4 <1.5 where fW is the focal length at the wide-angle end, and fi (i =
1, 2, 3, 4) are the focal length of the i-th lens unit, BF is the distance from the last lens surface to the imaging plane in air, and d1
2 is an air gap between the third lens group 3 and the fourth lens group 4,
r11 is the radius of curvature of the object side surface of the convex lens forming the third lens group 3, r13 is the radius of curvature of the surface of the cemented lens forming the fourth lens group 4 closest to the object, and r17 is the fourth lens group 4. This is the radius of curvature of the image side surface of the convex lens.

To make a zoom lens compact, it is necessary to increase the refractive power of each lens group. The above conditions (1), (2), (3), and (4) are conditional expressions that define the refractive power of each lens group. By setting the lens type, surface shape, and the like optimally, it is within the range that satisfactory aberration performance is satisfied.

The condition that the third lens group 3 is an aspherical lens having a convex surface facing the object side is that the third lens group 3 is constituted by a single lens and has various aberrations having a large F-number of about 1.8. It is indispensable to correct. In particular, the aspherical shape of the third lens group 3 has a great effect on correcting spherical aberration.

The condition that the fourth lens group 4 is composed of a cemented lens composed of two lenses and one convex lens and has at least one aspherical shape is that a long back focus is realized and a small number of three lenses is required. The number of pieces is indispensable for correcting on-axis and off-axis chromatic aberrations, correcting monochromatic off-axis aberrations, particularly coma, and relaxing tolerances in the assembly process.

Next, each condition will be described in more detail. Condition (1) is a condition relating to the refractive power of the first lens group 1. If the lower limit is exceeded, the refractive power of the first lens group 1 becomes too large, so that it becomes difficult to correct spherical aberration on the long focal length side. If the upper limit is exceeded, the lens length increases, and a compact zoom lens cannot be realized.

Condition (2) is a condition relating to the refracting power of the second lens group 2. When it deviates from the lower limit, it can be formed compact, but the Petzval sum of the whole system becomes largely negative, and the field curvature cannot be corrected only by selecting the glass material. Above the upper limit, aberration correction is easy, but the length of the variable power system becomes longer, making it impossible to achieve a compact system.

Condition (3) is a condition relating to the refractive power of the third lens group 3. If the lower limit is exceeded, the refracting power of the third lens group 3 becomes too large, so that a back focus in which a color separation optical system can be inserted cannot be realized, and it becomes difficult to correct spherical aberration. If the upper limit is exceeded, the combined system of the first lens group 1, the second lens group 2, and the third lens group 3 becomes a divergent system,
The lens outer diameter of the fourth lens group 4 located behind it cannot be reduced, and the Petzval sum of the entire system cannot be reduced.

Condition (4) relates to the refractive power of the fourth lens unit 4. When the value deviates from the lower limit, the comprehensive range of the screen becomes narrower, and it is necessary to increase the lens diameter of the first lens group 1 to obtain a desired range, so that reduction in size and weight cannot be realized. Above the upper limit, aberration correction is easy, but the amount of movement of the fourth lens unit 4 during short-distance shooting increases, so that not only the entire system cannot be made compact, but also short-distance shooting and long-distance shooting. It is difficult to correct the imbalance of off-axis aberrations at the time.

Condition (5) is a conditional expression relating to the back focus length. If the lower limit is exceeded, a color separation optical system having a length as long as sufficient color separation cannot be inserted. If it exceeds the upper limit, it cannot be made compact.

Condition (6) is a conditional expression relating to the air gap between the third lens unit 3 and the fourth lens unit 4. If the lower limit is exceeded, the off-axis ray height becomes small, and it becomes difficult to correct lateral chromatic aberration only by selecting a glass material. In addition, the amount of movement of the fourth lens unit 4 during short-range shooting is restricted, and a sufficient close-up range cannot be realized. Exceeding the upper limit makes it difficult to make the entire system compact. Further, when securing a sufficient light amount around the screen, the lens outer diameter of the fourth lens group 4 cannot be reduced.

The condition (7) relates to the radius of curvature of the object side surface of the aspherical lens constituting the third lens group 3. By introducing an aspherical surface on one or both of the object side surface and the image side surface and optimally setting the shape, various aberrations can be well corrected in spite of a single lens. However, when the value goes below the lower limit of the condition (7), it becomes difficult to correct spherical aberration. When the value goes outside the upper limit, it becomes difficult to correct coma aberration for off-axis rays below the principal ray.

Condition (8) relates to the radius of curvature of the concave surface of the concave lens constituting the fourth lens unit 4 on the object side surface. conditions
Outside the lower limit of (8), the angle of incidence on these surfaces increases, making it difficult to correct coma for off-axis rays below the chief ray, and exceeding the upper limit reduces the refractive power of the concave lens. It cannot be made large, and a sufficient back focus cannot be obtained.

The condition (9) relates to the radius of curvature of the image side surface of the convex lens located on the image side of the two convex lenses constituting the fourth lens group 4. If the lower limit of the condition (9) is not reached, the exit angles from these surfaces become large, and it becomes difficult to correct coma for off-axis rays above the principal ray and to correct distortion on the wide-angle side. If the upper limit is exceeded, the refractive power of the intermediate convex lens increases, so that a sufficient back focus cannot be obtained.

Next, specific numerical examples are shown in Table 1. In this table, r is the radius of curvature of the lens surface, d is the thickness of the lens or the air gap between the lenses, n is the refractive index of each lens for the d-line, and ν is the Abbe number of each lens for the d-line.

The aspheric shape is defined by the following equation.

[0031]

(Equation 1)

Z: distance from the aspherical vertex of a point on the aspheric surface at a height from the optical axis of Y Y: height from the optical axis C: curvature of the aspherical vertex (= 1 / r) D, E , F, G: aspherical surface coefficients

[0033]

[Table 1]

The eleventh, twelfth, and fifteenth surfaces are aspherical surfaces, and the aspherical surface coefficients are shown in Table 2.

[0035]

[Table 2]

Next, as an example of the air spacing that can be changed by zooming, the value at an object point at infinity is shown in (Table 3), and the value at an object point at 2 m from the lens tip is shown in (Table 4). )
Table 5 shows the values at the time of an object point at a position 1 m from the lens tip. In these tables, the standard position is a zoom position where the fourth lens group 4 comes closest to the third lens group 3 at each object point position. Note that f and F / NO
Are the focal length and the F-number at the wide-angle end and the telephoto end, respectively.

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

Each condition (1) to (9) for the first embodiment
Is shown in (Equation 2).

[0041]

(Equation 2)

A second embodiment in which each numerical value is different from the above is shown in (Table 6).

[0043]

[Table 6]

The eleventh, twelfth, and fifteenth surfaces are aspherical surfaces, and the aspherical surface coefficients are shown in (Table 7).

[0045]

[Table 7]

Next, as an example of the air gap that can be changed by zooming, the values at an object point at a position 2 m from the lens tip are shown in Table 8 below.

[0047]

[Table 8]

Each condition (1) to (9) for the second embodiment
Is shown in (Equation 3).

[0049]

(Equation 3)

A third embodiment in which each numerical value is different from the above is shown in (Table 9).

[0051]

[Table 9]

The eleventh, twelfth, and fifteenth surfaces are aspherical surfaces, and the aspherical surface coefficients are shown in Table 10.

[0053]

[Table 10]

Next, as an example of the air gap which can be changed by zooming, the value at the time of an object point at a position 2 m from the front end of the lens is shown in (Table 11).

[0055]

[Table 11]

Each condition (1) to (9) for the third embodiment
Is shown in (Equation 4).

[0057]

(Equation 4)

Next, FIG. 11 shows a configuration diagram of the fourth embodiment, and numerical values are shown in (Table 12).

[0059]

[Table 12]

The eleventh, twelfth, and fifteenth surfaces are aspherical surfaces, and the aspherical surface coefficients are shown in Table 13.

[0061]

[Table 13]

Next, as an example of the air gap that can be changed by zooming, the value at the time of an object point at a position 2 m from the lens tip is shown in (Table 14).

[0063]

[Table 14]

Each condition (1) to (9) for the fourth embodiment
Is shown in (Equation 5).

[0065]

(Equation 5)

Here, (a), (b), (c), (d),
(e) is an aberration diagram at a wide-angle end, a standard, and a telephoto end of the aspherical zoom lens of the first example shown in (Table 1). Similarly, (a), (b), (c), (d), and (e) of FIGS. 5 to 7 show aberration performance of the aspherical zoom lens of the second embodiment shown in (Table 6). (A), (b), (c), (d), and (e) of FIGS. 8 to 10 are aberration performances of the aspherical zoom lens of the third embodiment shown in (Table 9), and FIGS. (A), (b), (c), (d), and (e) show the aberration performance of the aspherical zoom lens of the fourth embodiment shown in (Table 12). From these figures, it can be seen that each of the examples has good optical performance.

In the spherical aberration diagram, the solid line indicates the value for the d-line, and the dotted line indicates the sine condition. In the figure of astigmatism, a solid line indicates sagittal field curvature, and a dotted line indicates meridional field curvature. In the axial chromatic aberration diagram, the solid line is d
Lines and dotted lines indicate values for the F line, and wavy lines indicate values for the C line. In the diagram of the chromatic aberration of magnification, a dotted line indicates a value with respect to the F line, and a wavy line indicates a value with respect to the C line.

Further, the three-panel video camera of the present invention includes at least the high-magnification zoom lens of the above-described embodiment of the present invention,
It is composed of an optical system such as a color separation prism, three image pickup devices, a signal processing circuit, and a viewfinder, thereby realizing a compact, lightweight, and high-performance video camera.

In the above description, the case where the cemented lens of the fourth lens group 4 is a combination of a lens having a negative power and a lens having a positive power in order from the object side has been described. Of course, it can be applied to the case of a combination of lenses having negative power. Further, in the above description, the case where the image-side convex surface of the cemented lens of the fourth lens group 4 has an aspherical shape among the cemented lens and the convex lens has been described. Needless to say, the present invention can be applied to a case where the concave lens constituting the lens has an aspherical shape.

[0070]

As is apparent from the above description, according to the present invention, in order from the object side, the first lens unit having a positive refractive power and fixed to the image plane, and the negative lens unit having a negative refractive power. A second lens group that performs a zooming action by moving on the optical axis;
A third lens group having a positive refractive power fixed to the image plane and having a condensing function, and an image plane that fluctuates due to the movement of the second lens group and the movement of the object is kept at a fixed position from the reference plane. An aspherical zoom lens comprising: a fourth lens group having a positive refractive power that moves on the optical axis; wherein the third lens group and the fourth lens group have an air gap; The second lens group is composed of a concave meniscus lens, a biconcave lens, and a convex lens, and the third lens group is composed of a single lens having at least one aspheric surface. The fourth lens group includes a lens having at least one or more aspherical surfaces, and is constituted by a two-element cemented lens and one convex lens, so that the F-number is about 1 8, about 10-fold zoom ratio, the back focus is long high-performance aspherical zoom lens 1
It can be realized with a small number of components such as 0, and by using this aspherical zoom lens, a compact, lightweight and high-performance 3
A plate-type video camera can be realized.

[Brief description of the drawings]

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

FIG. 2 is an aberration diagram showing aberration performance of the aspherical zoom lens of the first example shown in (Table 1).

FIG. 3 is an aberration diagram showing aberration performance of the aspherical zoom lens of the first example shown in (Table 1).

FIG. 4 is an aberration diagram showing an aberration performance of the aspherical zoom lens of the first example shown in (Table 1).

FIG. 5 is an aberration diagram showing aberration performance of the aspherical zoom lens of the second example shown in (Table 6).

FIG. 6 is an aberration diagram showing aberration performance of the aspherical zoom lens of the second example shown in (Table 6).

FIG. 7 is an aberration diagram showing aberration performance of the aspherical zoom lens of the second example shown in (Table 6).

FIG. 8 is an aberration diagram showing aberration performance of the aspherical zoom lens of the third example shown in (Table 9).

FIG. 9 is an aberration diagram showing aberration performance of the aspherical zoom lens of the third example shown in (Table 9).

FIG. 10 is an aberration diagram showing aberration performance of the aspherical zoom lens of the third example shown in (Table 9).

FIG. 11 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 12 is an aberration diagram showing aberration performance of the aspherical zoom lens of the fourth example shown in (Table 12).

FIG. 13 is an aberration diagram showing aberration performance of the aspherical zoom lens of the fourth example shown in (Table 12).

FIG. 14 is an aberration diagram showing aberration performance of the aspherical zoom lens of the fourth example shown in (Table 12).

FIG. 15 is a configuration diagram of a conventional aspherical zoom lens.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st lens group 2 2nd lens group 3 3rd lens group 4 4th lens group 5,6 flat plate 7 imaging surface

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (4)

(57) [Claims] 1. A first lens unit having a positive refractive power and fixed with respect to an image plane, and a first lens unit having a negative refractive power and performing a zooming operation by moving on an optical axis in order from an object side. A second lens group, a third lens group having a positive refractive power fixed to the image plane and having a condensing action, and an image plane that fluctuates due to the movement of the second lens group and the movement of the object are fixed from the reference plane. And a fourth lens group having a positive refractive power that moves on the optical axis so as to maintain the third lens position.
The lens group and the fourth lens group have an air gap, the first lens group is composed of a concave lens, a biconvex lens, and a meniscus convex lens in order from the object side, and the second lens group is a meniscus concave lens . The third lens group is composed of a single lens having at least one aspheric surface, and the fourth lens group is composed of a single lens having at least one aspheric surface. It consists of a cemented lens and one convex lens .
Aspherical zoom lens that satisfies the conditions . (1) 3.0 <f1 / fW <8.0 (2) 0.5 <| f2 | / fW <1.6 (3) 5.14 <f3 / fW <7.0 (4) 2.0 <F4 / fW <5.0 (5) 1.5 <BF / fW <5.0 (6) 0.02 <d12 / f4 <1.0 (7) 0.3 <r11 / f3 <1.5 (8) 0.3 <| r13 | / f4 <3.0 (9) 0.3 <| r17 | / f4 <1.5 where fW is the focal length at the wide-angle end, and fi (i =
1, 2, 3, 4) are the focal length of the i-th lens group, and BF is empty
The distance from the last lens surface to the imaging surface in the air, d1
2 is an air gap between the third lens unit and the fourth lens unit, r1
1 is the curvature of the object side surface of the convex lens constituting the third lens group
The radius r13 is the maximum value of the cemented lens constituting the fourth lens group.
Is the radius of curvature of the surface from the object, and r17 is the fourth lens group.
This is the radius of curvature of the image side surface of the resulting convex lens. 2. The aspherical zoom lens according to claim 1, wherein the third lens group is an aspherical single lens having a positive refractive power and a convex surface facing the object side. 3. The fourth lens group includes, in order from the object side, a cemented lens having a two-element configuration and a convex lens having a convex surface facing the image side.
The aspherical zoom lens according to claim 1. 4. A video camera having a non-spherical zoom lens of claim 1, wherein.