JPH05181062A - High-power zoom lens and video camera using the same - Google Patents

Abstract

PURPOSE:To provide about X10 zoom lens of about 1.4 in F number while decreasing the number of lens elements and maintaining high performance by employing specific lens constitution and satisfying specific conditions. CONSTITUTION:This zoom lens has three lenses in a 1st group G1 as a focusing part, three lenses in a 2nd group G2 as a variator part, one lens in a 3rd group G3 as a compensator part, a single aspherical lens in a 4th group G4 as a relay lens system, and three lenses arranged in a 5th group G5 at relatively large air intervals. Then inequalities I-IV hold. Here, fw is the total focal length at the wide-angle and f4, f5, and fr the focal lengths of the 4th group, 5th group, and relay lens system, f6 the focal length of the single lens with positive refracting power in the 5th group, and rB the radius of curvature of the cemented lens surface in the 5th group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens for a video camera, and more particularly to a high performance zoom lens and a video camera in which the number of lenses is reduced by utilizing an aspherical surface and an appropriate relay lens system.

[0002]

2. Description of the Related Art Recently, operability and functionality have been emphasized in video cameras, and image pickup devices have been reduced in size in response to the demands, and accordingly, a large aperture ratio, a large zoom ratio, a small size and a light weight and high performance. There is a strong demand for zoom lenses. Further, there is a strong demand for cost reduction, and there is a strong pressing to realize a zoom lens that reduces the number of constituent elements while maintaining high performance.

The F number is about 1.4 and the zoom ratio is about 10.
Many of the current double lenses use four lenses for the focusing part, three lenses for the variator part, two lenses for the compensator part, and nine lenses for the relay lens system, and the entire configuration. The number of sheets is also 18 (for example, JP-A-61-10051).

[0004]

In such a conventional zoom lens having a high-magnification spherical lens system, it is difficult to significantly reduce the number of components.

The present invention solves the above-mentioned drawbacks, the number of constituent elements is as small as 11, the zoom lens has an F number of about 1.4 and a zoom ratio of about 10 times, and a compact and high-performance video using the zoom lens. The purpose is to provide a camera.

[0006]

In order to solve the above problems, the present invention focuses on reducing the number of relay lens system components, and uses a zoom lens having a small number of components by utilizing an aspherical surface and creating an appropriate relay lens type. I will get it. The relay lens system is composed of a biconvex single lens having a positive refracting power, a cemented lens arranged with a relatively large air gap from the single lens, and a biconvex single lens having a positive refracting power.

[0007]

With the above-described structure, the present invention creates a new relay lens type using an aspherical surface, and maintains the high performance by the function of properly selecting its optical parameters, and has a small number of lenses and a compact zoom lens. Realized a high-performance video camera.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A lens configuration diagram of an embodiment of the present invention will be described below with reference to the drawings. (FIG. 1) is a configuration diagram corresponding to Example 1 of the zoom lens of the present invention (FIG. 2)
A configuration diagram corresponding to the second embodiment is shown in FIG.

However, in the figure, r1, r2, ... Are the radii of curvature of each lens surface counted from the object side, and d1, d2 ,.

Regarding each of (FIG. 1) and (FIG. 2), G1 is a first group as a focusing portion having a positive refractive power, and G2 has a negative refractive power and is moved by moving along the optical axis. Second group, G as a variator unit that changes the
Reference numeral 3 denotes a third group as a compensator unit that keeps the image plane that fluctuates due to the movement of the second group G2 from the reference plane at a fixed position.
G4 and G5 are the 4th which comprises a relay lens system, respectively.
The fifth group, the fifth group, and G6 represent the sixth group of flat plates corresponding to the crystal filter and the face plate of the imaging device.

The first group G1 has a negative refractive power of 1 in order from the object side.
It consists of one lens and two lenses with positive refracting power.
The group G2 is composed of a single lens having a negative refractive power and a cemented lens, and the third group G3 is composed of a single lens having a negative refractive power.
The fourth group G4 is composed of a biconvex single lens having a positive refracting power, and the fifth group G5 is arranged with a relatively large air space from G4, and has a negative refracting power lens and a positive refracting power lens. It consists of a cemented lens and a biconvex single lens with positive refracting power. In the zoom lens of the present invention, the following conditions must be satisfied in order to reduce the number of sheets while maintaining high performance.

(1) 3.5fw <fr <5.5fw (2) 0.5fr <f4 <1.0fr (3) 0.5fr <f5 <1.2fr (4) 0.5f5 <f6 <1.5f5 (5) 0.4f5 <rB <1.0f5 (6) The fourth group has an aspherical surface, where fw is the focal length of the entire system at the wide-angle end, f4, f5, and fr are the focal lengths of the fourth, fifth, and relay lens systems, respectively. f6
Is the focal length of the single lens of positive refracting power in the fifth group, and rB is the fifth
The curvature radius of the cemented surface of the cemented lens in a group is shown.

Next, the conditional expression will be described. conditions
(1) is a condition that gives the power of the relay lens system, and if it deviates from the lower limit, it can be made compact, but the radius of curvature of some surfaces in the relay lens system becomes small, and it becomes difficult to correct aberrations.

When the upper limit of the condition (1) is exceeded, aberration correction is easy, but the lens system becomes large, which is not preferable.

The condition (2) relates to the power of the fourth lens group G4 in the relay lens system. When the lower limit is exceeded, the back focus becomes short, and when the upper limit is exceeded, the luminous flux exiting the fourth lens group G4. Becomes a divergent light beam, so that the refracting power and the ray height of the fifth lens group G5 increase and the spherical aberration deteriorates.

The condition (3) is a condition for defining an appropriate distance from the fourth lens unit G4 together with the power of the fifth lens unit G5 and the condition (2). When the upper limit is exceeded, the exit pupil position is close to the image pickup device. It is not suitable as a lens for video cameras. conditions
If the value goes below the lower limit of (3), the refracting power of the fifth lens unit G5 becomes too strong, and the spherical aberration is overcorrected.

The condition (4) is a condition relating to the power of the biconvex lens in the fifth group G5, and if the upper limit is exceeded, the back focus becomes long and the lens system cannot be made compact. Condition (4)
If the value deviates from the lower limit, the back focus becomes short and the exit pupil position becomes close to the image pickup device, which is not preferable as a lens for a video camera.

The condition (5) defines the radius of curvature of the cemented surface of the cemented lens in the fifth lens group G5. If the lower limit is not reached, the curvature becomes too tight and high-order spherical aberration occurs. If the upper limit of condition (5) is exceeded, it will be difficult to correct chromatic aberration.

The condition (6) that the fourth lens group G4 has an aspherical surface is to correct aperture aberrations and off-axis aberrations with a large aperture ratio of F-number of about 1.4 even with a very small number of components. It is indispensable to do. Aberration correction is effectively performed by disposing aspherical surfaces with a large air gap. The diaphragm is arranged immediately before or after the fourth group G4. Therefore, the fourth lens group G4 is the position where the luminous flux becomes thickest in the relay lens system, and the aspherical surface is effective for correcting the aperture aberration. In order to make the lens compact, it is desirable that the focal length f2 of the second lens unit G2 satisfy the following condition. (7) 0.7fw <| f2 | <2.0fw In order to make the zoom lens compact, it is crucial to increase the power of the second lens group G2 for zooming. When the value exceeds the upper limit of the condition (7), aberration correction is ready, but the lens system becomes large, which is not preferable. Condition (7)
If the value goes below the lower limit of, it can be made compact, but the second group G2
The curvature of some of the inner surfaces becomes too tight, which makes it difficult to correct aberrations.

Under the lens construction and conditions according to the present invention, the F number is about 1.4 to 1.8 and the zoom ratio is about 10.
It was possible to realize a zoom lens for a video camera that is twice as compact and has good performance with an 11-element configuration.

An image pickup device is arranged on the image plane of the zoom lens, the image pickup device is driven and controlled by a drive circuit, and an output signal is processed by a signal processing circuit.
Further, by sending this signal to the image output device and the focus detection circuit and feeding back the output from the focus detection circuit to the focusing and zooming mechanism section, a high performance video camera can be realized.

An embodiment satisfying these conditions will be shown below. In the table, r is the radius of curvature of each surface of the lens, d is the wall thickness or air gap between the lens surfaces, n is the refractive index of each lens with respect to the d-line, and ν is the Abbe number. Also, di is the first from the object side.
The i-th lens thickness and air gap. A surface having an aspherical shape (indicated by *) is defined by the expression of (Equation 1).

[0023]

[Equation 1]

Where Z: distance from the tangent plane of the aspherical vertex of the aspherical surface whose height from the optical axis is y, y: height from the optical axis c: curvature of the aspherical vertex (= 1 / r) k: conic constant D, E, F, G: aspherical coefficient (Example 1)

[0025]

[Table 1]

The 14th and 15th surfaces marked with * are aspherical surfaces and are shown by the constants in Table 2.

[0027]

[Table 2]

(Example 2)

[0029]

[Table 3]

The thirteenth surface and the fourteenth surface marked with * are aspherical surfaces and are shown by the constants in (Table 4).

[0031]

[Table 4]

(Example 3)

[0033]

[Table 5]

The 14th and 15th surfaces marked with * are aspherical surfaces and are shown by the constants in (Table 6).

[0035]

[Table 6]

(Example 4)

[0037]

[Table 7]

The thirteenth and fourteenth surfaces marked with * are aspherical surfaces and are shown by the constants in (Table 8).

[0039]

[Table 8]

(FIGS. 3 (a) (b) (c)), (FIG. 4)
(A), (b), (c), and (FIGS. 5 (a), (b), and (c)) show the aberration performances at the wide-angle, standard, and telephoto ends of Example 1, respectively (see FIGS. ) (C)), (FIG. 7 (a))
(B) (c)) and (FIGS. 8 (a) (b) (c)) show aberration performances at the wide-angle, standard, and telephoto ends of Example 2, respectively (FIGS. 9 (a) (b) (c)). )), (Fig. 10 (a))
(B) (c)) and (FIGS. 11 (a) (b) (c)) show the aberration performances at the wide-angle, standard, and telephoto ends of the third embodiment, respectively (see FIGS. 12 (a) (b) (c)). )), (FIG. 13A)
(B), (c), and (FIGS. 14 (a), (b), and (c)) show aberration performances at the wide-angle, standard, and telephoto ends of the fourth embodiment, respectively.

In the spherical aberration diagram, d, F and C are d
The spherical aberrations for the line, the F line, and the C line are shown. In the diagram of astigmatism, m indicates the field curvature in the meridional direction, and s indicates the field curvature in the sagittal direction. It can be seen from the drawings that all of the examples 1, 2, 3, and 4 have good optical performance.

[0042]

As is apparent from the above description, under the lens configuration and conditions of the present invention, the number of F is about 1.4 and the zoom ratio is about 10 times as small as 11 lenses. With that, we were able to realize a high-performance zoom lens and video camera.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a zoom lens according to a second embodiment of the present invention.

FIG. 3 is a diagram of various types of aberration in Example 1.

FIG. 4 is a diagram showing various types of aberration in Example 1.

FIG. 5 is a diagram of various types of aberration in Example 1.

FIG. 6 is a diagram showing various aberrations of Example 2.

FIG. 7 is a diagram of various types of aberration of the second embodiment.

FIG. 8 is a diagram showing various aberrations of Example 2.

FIG. 9 is a diagram showing various types of aberration in Example 3.

FIG. 10 is a diagram showing various types of aberration in Example 3.

FIG. 11 is a diagram showing various types of aberration in Example 3.

FIG. 12 is a diagram showing various aberration diagrams of Example 4.

FIG. 13 is a diagram showing various aberration diagrams of Example 4.

FIG. 14 is a diagram showing various aberration diagrams of Example 4.

[Explanation of symbols]

 G1 first group as focusing section G2 second group as variator section G3 third group as compensator section G4 fourth group forming part of relay lens G5 fifth group G6 forming part of relay lens flat plate Crystal filter m Field curvature in meridional direction s Field curvature in sagittal direction

Claims (3)

[Claims] 1. From the object side, a first group as a focusing section having a positive refractive power, and a second group as a variator section having a negative refractive power and changing the magnification by moving on the optical axis. , A third as a compensator unit that keeps the image plane that fluctuates due to the movement of the second group from the reference plane at a fixed position.
A zoom lens comprising a group and a relay lens system connected to a variable power system formed by the first group, the second group, and the third group,
The first group is composed of one negative refractive index lens and two lenses of positive refractive power, the second group is composed of a single lens of negative refractive power and a cemented lens, and the third group is of negative refractive power. The relay lens system consists of a biconvex single lens having a positive refracting power and a biconvex lens having a positive refracting power with a relatively large air gap from the fourth group. A zoom lens comprising a single lens and a fifth lens group including a cemented lens of a lens having a negative refractive power and a lens having a positive refractive power, and satisfying the following conditions (1) to (6): lens. (1) 3.5fw <fr <5.5fw (2) 0.5fr <f4 <1.0fr (3) 0.5fr <f5 <1.2fr (4) 0.5f5 <f6 <1.5f5 (5) 0.4f5 <rB <1.0f5 (6) The fourth lens group has an aspherical surface, where fw is the total focal length at the wide-angle end, f4, f5, and fr are the fourth lens group, the fifth lens group, the focal length of the relay lens system, and f6 is the fifth lens group. The focal length of a single lens having a positive refracting power, rB, indicates the radius of curvature of the cemented lens surface in the fifth group. 2. The zoom lens according to claim 1, wherein the following condition (7) is satisfied when the focal length of the second lens unit is f2. (7) 0.7fw <| f2 | <2.0fw 3. A video camera configured using the zoom lens according to claim 1.