JPS60123817A - Aspheric zoom lens - Google Patents

Abstract

PURPOSE:To obtain a small-sized, high-performance lens which has a large zoom ratio by providing the 1st positive group, the 2nd group as a negative variator, the 3rd group as a compensator, and the 4th and the 5th groups which have aspherical surface as a relay system. CONSTITUTION:The lens consists of the 1st group 1 as a positive focusing part, the 2nd group 2 as a negative variator, the 3rd group 3 as a compensator for holding an image plane constant, and the 4th group 4 and the 5th group as the relay system. The 4th group 4 consists of a positive single lens and a surface r14 is an aspherical surface. The 5th group 5 consists of a meniscus cemented lens having a concave surface on the object side and a positive single lens, and a surface r18 is an aspherical surface. Those aspherical surfaces compensate large-diameter aperture aberrations and off-axis aberrations. The ranges of the focal lengths of the 2nd - the 5th 2-5, the focal length of the meniscus cemented lens, etc., are limited to obtain a video camera lens which has a 1.4F value and an about x6 zoom ratio.

Description

[Detailed Description of the Invention] (Industrial Application Field) This company provides zoom lenses for video cameras, and in particular, provides high-performance zoom lenses that utilize aspherical surfaces to reduce the number of lenses and achieve smaller size and lighter weight. It is something to do.

(Conventional configuration and its problems) Recent video cameras have placed emphasis on operability and mobility, and in response to these demands, image pickup tubes have also been developed with 1.27 rtta (l/
2 inches), and as a result, there is a strong demand for high-performance zoom lenses with large aperture ratios, large zoom ratios, and small sizes. In addition, the cost-reducing equipment is also strong,
There is a strong need to create a zoom lens that reduces the number of lenses while maintaining high performance.

However, most current lenses with an F number of about 1.4 and a zoom ratio of about 6 times are composed of 14 to 15 elements, and the overall length of the lens cannot be said to be short.

In a zoom lens with an F number of 1.4 and a zoom ratio of about 6, each group that makes up the entire magnification variable unit is often composed of 3 focus cinder parts, 3 variators, and 1 convencator, and the number of lenses can be reduced. It depends on the configuration of the lens system.In the case of a video zoom lens, the color shader's ejection position must be at least a certain distance away from the image plane, and the crystal plate, etc. Since the lens is inserted in front of the image pickup tube, there is a constraint that the back focus length must be long, and a relay lens with a diameter of 11J is required.

The use of aspherical surfaces is effective in reducing the number of lenses. Recent advances in precision resin molding have increased the possibility of mass production of highly aspherical glass lenses.

At the same time, new technology is being developed to create lenses with lath surfaces through press processing.

(Objective of the Invention) Based on this background, the present invention does not struggle with the extremely small number of constituent sheets of 11 sheets, and the F number is 1.4.
The present invention proposes a compact and high-performance zoom lens for a video camera with a zoom ratio of 6.

(Configuration of the Invention) The configuration of the aspherical zoom lens of the present invention is as follows from the object side:
The focusing unit has a positive refractive power, the first group is a dazzling part, the second group has a negative refractive power and is a variator part that changes the magnification by moving on the optical axis, and the movement of the parier part. A compensator part is used to keep the first part 101 which changes depending on the reference plane at a constant position, and the third part, the first part,
A zoom lens consisting of a relay lens system connected to a variable power system formed by the second and third groups, the first group consisting of a cemented lens with positive refractive power and a filler lens, and the second group consisting of a negative lens. h
The relay lens system is composed of a single lens with a positive refractive power and a cemented lens.
It is composed of a meniscus cemented lens with a concave surface facing 111 and a fifth group of positive base lenses, and satisfies the following conditions.

(111, iFW<1f21<16FW(2) 1.8
FW<fR<2.4FW+3+ 1.5 /1< l
r, 1 (season 1.1fR<f4<1.6fR (sL t,2/R<15<1.5fRC6) 3.
5f5< f6 (7) The 4th and 5th groups each move south of the aspherical surface. However, FW is the gold thread focal length at the wide-angle end, /1 * f2
*f4, f5, fB are the 1st group, 2nd N, and
m 1° point distance of the 4th group, 5th group and relay lens, f
6 indicates the focal length of the meniscus-shaped junction/resist in the fifth group, and generally rl is the Jli Kth counting from the object side]
Let us show the radius of curvature of the lk-th surface.

(Description of Embodiments) An embodiment of the present invention will be described below with reference to the drawings. - Figure 1 shows the structure of the aspherical zoom lens of the present invention.
The figure is shown below. In Figure 1, IFi 1st group, 2r1 1st group, 3 is 3rd group, 4 is 4th group, 5 is 5th group, 6 is isometric glass corresponding to the crystal filter or the face plate of the image pickup tube. It is a board.

In order to configure a zoom lens in a compact manner, it is necessary to strengthen the power of each group, especially the variator that changes magnification.
It is crucial to make the power fully strong. The above conditions (11,
(2) Variator and relay lens system, respectively.
This is a condition that gives P-war. When the zoom ratio is Iz, the variator can be made most compact when the variable magnification range is from 11 m to 1 σ, but since there is a constraint that the groups do not collide during zooming, conditions (1) and (2) are satisfied. There is a potential problem with the focal length of the focusing section and convencator section. Condition (1).

(2) gives strong power, but is within the range in which all good aberrations can be realized by balancing the shapes of each group.

When the condition deviates from the lower limit, concave holes can be used, but the radii of curvature of the opposing concave surfaces in the variator and some surfaces in the relay lens are small, making it difficult to correct aberrations. If the upper limit is exceeded, aberrations can be easily corrected, but the lens system becomes larger, which is not preferable.

Condition (3) is @1 group of objects i11! The shape of the l cemented lens and the radius of curvature of the cemented surface are also indirectly defined. 1r31
Due to the achromatic condition, the radius of curvature of the bonding surface also becomes smaller. These conditions are effective for correcting the spherical aberration of the first group lens.

Condition (4) is a condition regarding .91 NO of the fourth group 4 in the relay lens. If the lower limit is exceeded, the back focus will be short and the focal point distance f5 of the fifth group 5 will be large, so that the necessary injection position IIIA can be secured.

It becomes. When f4 exceeds the upper limit, the light beam exiting the fourth group 4 becomes a diverging light beam, so that the spherical aberration of the fifth group 5, which has a large refraction direction and a high ray height, worsens.

Sakae) 'I' (5) defines the power of the fifth group 5 and the appropriate distance from the fourth group 4 in conjunction with condition (4), and the necessary injection 1
This is to get 15 IU. f5 is 1.5
When the angle is larger than fR, the exit pupil position becomes close to the image pickup tube, which is not desirable as a lens for a video camera. When f5 exceeds the lower limit, the refractive power of the optical lens group 5 becomes too strong, resulting in overcorrection of spherical aberration.

One of the features of the present invention is that the fifth group 5 is made up of a meniscus cemented lens with a concave surface facing the object side and a single lens with positive refractive power. For this reason, No. 51j ¥5
The principal point of the lens is advantageous in ensuring a clear focus and exit pupil position regardless of the image plane elevation, and is also preferable for aberrations other than 1IQ11 and chromatic aberration. for that purpose,
It is desirable that the pores of the meniscus cemented lens are not large, and if condition (6) is not met, the effect of @ is not sufficient.

The condition (7) that the fourth group 4 and the fifth group 5 each have an aspherical surface is extremely rare (aperture aberration of a large aperture with an F number of 1.4 and 'Flit This is essential for completely correcting external aberrations. By arranging aspherical surfaces a with large air gaps, aberration correction can be performed very effectively.

The aperture is placed immediately before or after the whistle 4 group 4.

Therefore, the fourth group 4 is the position where the luminous flux is the thickest in the relay lens system, and the aspheric surface here is effective for correcting aperture aberration. However, this alone is not enough, and when combined with the aspheric surface of the fifth lens group, the effect becomes even more pronounced. The fifth group is a relay lens system and corresponds to the part where the off-axis chief ray becomes high, so it is effective in abstracting off-axis aberrations.

Under the lens configuration and conditions based on the present invention, we were able to realize a high-performance zoom lens for a video camera with an 11-element configuration with an F number of approximately 1.4 and a zoom ratio of approximately 6 times. .

Examples that meet these conditions are shown below. r1 in the table.
r2... is the lens saved to 111α from the object side (0 radius in each direction), dt r dz... is the thickness between the lens surfaces 11J-', f fc 41 space, n, r n2
... is for the d-line of each lens.

Refractive index, C4. C2... is the Atsube number for the d-line, which is 2.
1 degree. In addition, objects having an aspherical shape (indicated by sain) are defined by the following indications.

However, 2: The height of the aspheric surface with a height of y from the optical axis 1 Distance from the tangential plane of the spherical apex y: Height from the optical axis C: Curvature of the aspheric apex (= 1/R) : conic constant, E, F, G: aspherical surface, coefficient +n'CQ 6.ゝ 0 ゝII') () () F) () u') O NLO, CD Ln (RiC', I (DII II
11 1 II II IIυ ■ oo O pus size Qko0 ■ IIJLI layer )) ) 1 IO's ω ■ ト's ト+n O6% 6 (A 6 evil RO Q's Q evil C 1111II II till II ω −-0 − of − x x w x k k k k k k k il Φ
000 pus size ■ 0 Φ ￥ RO RO - C5 uj )M Figures 2, 3, and 4 show the aberration performance of Example 1 at the wide-angle, standard, and telephoto ends, respectively, and Figure 5, sugar Figure 6 and Figure 17 respectively show the aberration performance of Example 2 at the wide-angle, standard, and telephoto ends. Note that Example 2 is an example in which a lens having an aspherical shape is made of 4-trimethyl methacrylate resin. It can be seen from the figure that both Example 1 and Example 2 have good array optical performance.

(Effects of the Invention) As is clear from the above explanation, under the lens configuration and conditions of the present invention, a connoduct with a very small number of lenses, 11, has an F number of about 1.4 and a zoom ratio of about 6 times. This enabled us to create a zoom lens with good performance.

Furthermore, if a glass lens is introduced, it is easy to form an aspherical surface and can be produced at low cost.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an aspherical zoom lens according to an embodiment of the present invention, Figs. 2, 3, and 4 are various aberration diagrams of embodiment 1, Fig. 5, Fig. 6, and Fig. 7. shows various aberration diagrams of Example 2. In the diagram of spherical aberration, the solid line shows the spherical aberration for the d-ray, and the dashed line shows the spherical aberration for the g-line. 1... 1st group, 2...) 2nd group, 3... 3rd group,
4...Fourth group, 5...Fifth group, 6...Crystal filter. Patent applicant: Matsushita Electric Industrial Co., Ltd. Representative: Hisashi Hoshino Figure 1

Claims (1)

[Scope of Claims] (1) In order from the object side, the first group as a focus cinder part having a positive refractive power and the light -1' having a negative refractive power.
a second ring group as a variator section that changes the magnification by moving above; a third ring group as a convencator section that keeps the image plane, which changes due to the movement of the variator section, at a constant position from the reference plane; A zoom lens consisting of a relay lens system connected to a variable magnification system formed by the second and third groups, the first group consisting of a cemented lens with positive Jfli refracting power and a single lens, and the second group Negative 11] A single lens with a single fold and a cemented lens form a 4/f4 system, the third group consists of a single lens with negative refractive power, and the relay lens system consists of a single lens with positive refractive power. It consists of a meniscus-shaped cemented lens with a concave surface facing the object side with a relatively large air gap from the fourth group, and a positive single lens in the fifth group, and it satisfies the following conditions. Characteristic aspherical zoom lens (131, 1fw < 1121 < 1-6 fvi
(2) 1.8 fw < fn < 2-4 fw (
3) 15 fl < It, 1 (4) 1. i fB < f4 < ” f, R(
5) 1.21R<f5< 1.5 fR (6) 3.
5f5〈f6 (7) The fourth group and the fifth group are each valve inr Th
However, FW is the focal length of the entire system at the wide-angle end, fl, f2.
f4. f5. fR is the focal length of the first group, second group, fourth group, fifth group, and relay lens, respectively; f6 is the focal length of the meniscus cemented lens in the fifth group; r3 is the distance counted in order from the object 1il+. The radius of curvature of the third surface is shown. (2) The aspherical zoom lens according to claim (1), wherein the single positive lens in the M4 group and the four positive lenses in the fifth group are made of plastic lenses.