KR19980046759A - 2-group zoom lens for cameras - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

camera

2. Technical problem to be solved by the invention

The optical system is composed of a small number of lenses and plastic lenses can be used to maintain good aberration performance.

3. Summary of Solution to Invention

A first meniscus-shaped first lens 11 having a positive refractive power convex on the subject side, a second lens 12 having a negative refractive power concave on the subject side, and a positive refractive power in both directions convex A third lens 13 made of plastic, a meniscus fourth lens 21 made of plastic having a positive refractive power concave on the subject side, and a fifth lens having negative refractive power concave on the subject side It consists of (22).

4. Important uses of the invention

Zoom lens for camera

Description

2-group zoom lens for cameras

Figure 1 is a side cross-sectional view showing the configuration of the optical system of the present invention at a wide-angle end

Figure 2 is a cross-sectional side view showing the configuration of the present invention optical system in the telephoto end

3 is aberration diagrams according to the embodiment in the wide-angle end

4 is aberration diagram according to the embodiment in the telephoto end

5 is a spot diagram according to an embodiment at a wide-angle end;

Figure 6 is a spot diagram according to the embodiment in the telephoto

7 is a view of MTF according to the embodiment in the wide-angle end

8 is an MTF diagram according to an embodiment of a telephoto end.

* Description of the symbols for the main parts of the drawings *

10: first lens optical unit 11: the first lens

12: second lens 13: third lens

20: second lens optical portion 21: fourth lens

22: fifth lens

[Technical Field to which the Invention belongs and Prior Art in the Field]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens of a camera, and more particularly to a zoom lens for a camera, which can simplify the structure of each lens group and maintain a good aberration performance, as well as reduce manufacturing cost by using a plastic lens. will be.

In general, a zoom lens used in a camera is known as a typical configuration of two groups of positive and negative parts and three types of positive and positive parts or negative and positive parts.

The two-group zoom lens adjusts the distance between the two groups to perform shifting. Since the two-group zoom lens is composed of a minimum number of parts for zoom driving, the barrel and the driving mechanism are simplified, and the number of lenses is reduced. Many proposals have been removed so far as they have the potential to be reduced. However, it is known that it is not suitable for high magnification ratios as the aberration fluctuations increase as well as the amount of movement of each component group that is essential to change.

On the other hand, since the three-group type can share the ratio of variation in each lens group, it is possible to limit the amount of movement of each lens group involved in the variation and to correct the aberration fluctuation well, so that it is suitable for high magnification. Will be. However, there is a problem that the barrel structure and the driving mechanism become complicated due to the problems caused by the increase in the number of the lens group, and the number of the lens group also increases.

Accordingly, the present invention allows a lens system suitable for the purpose to be utilized by utilizing the characteristics of the two-group type when using a small number of lenses as described below and using plastic lenses while the ratio of variation is about twice. .

As an example in which the two-group lens type is composed of about six lenses, Japanese Patent Laid-Open No. 62-138818, Japanese Patent Laid-Open No. 63-311224, Japanese Patent Laid-Open No. 2-73322, Japanese Patent Laid-Open No. 2-120714 3-116110, Japanese Patent Laid-Open No. 5-232382, and the like are known.

In Japanese Patent Laid-Open Nos. 62-138818 and 63-311224, a glass aspherical lens is used for aberration correction to improve performance. However, there is a problem that the unit price becomes expensive with respect to the glass aspherical lens.

In addition, Japanese Patent Laid-Open Nos. 2-73322 and 2-120714 are all composed of glass abrasive lenses, and the cost is improved from the above-described prior art, and spherical aberration and coma aberration are not completely corrected.

In addition, Japanese Patent Application No. 3-116110 consists of six elements in five groups, and uses plastic lenses to reduce costs, but consists of a first group of refractive power and a positive lens, a negative lens, and a positive lens of the positive part. As a result, the correction of spherical aberration and coma aberration is not complete.

In addition, Japanese Patent Application Laid-Open No. H5-232382 is composed of six lenses in two groups and aims to reduce costs by using plastic lenses. However, the lens structure is complicated and lengthened by using six lenses. Since the drive mechanism of the complicated, there was a problem that causes a cost increase and failure accordingly.

[Technical problem to be achieved]

Accordingly, the present invention has been made to solve the conventional defects as described above, the object of the camera is to simplify the structure of the optical system while not only suppress the change of the store due to temperature, but also maintain a good aberration performance It is to provide a group 2 zoom lens.

Technical means of the present invention for achieving this object, the first lens of the meniscus shape having a positive refractive power convex on the subject side, the second lens having a negative refractive power concave on the subject side, both sides A third lens made of a plastic material having a positive refractive power in the convex direction, a meniscus fourth lens made of a plastic material having a positive refractive power concave on the subject side, and a fifth lens having a negative refractive power concave on the subject side It is characterized by consisting of a lens.

[Configuration and Function of Invention]

Hereinafter, the configuration of an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 1 is a side cross-sectional view showing the configuration of the optical system of the present invention in a wide-angle end, Figure 2 is a side cross-sectional view showing the configuration of the optical system of the present invention in a telephoto end.

The zoom lens of the camera to which the present invention is applied is composed of a first lens group having a forward refractive power and a second lens group having a negative refractive power so that a change of a predetermined ratio can be performed by changing the distance between the two lens groups. Will be.

In the zoom lens of the camera configured as described above, the present invention, as shown in Figs. 1 and 2, has a meniscus-shaped first lens 11 having a forward refractive power convex on the subject side and a concave on the subject side. A first lens optical portion 10 including a second lens 12 having a refractive power in the negative direction, a third lens 13 having a positive refractive power in both directions, and a positive concave on the subject side. The second lens optical unit 20 includes a meniscus-shaped fourth lens 21 having a refractive power and a fifth lens 22 having a negative refractive power concave on the subject side. At this time, left and right surface numbers of each lens are indicated by s and film surface is indicated by F.

In this configuration, the present invention provides a focal length of the first lens optical unit 10 as f ₁ , a rear focal length at the telephoto end and a wide-angle end, respectively, f _bt , f _bw , and a first lens optical unit at the telephoto end ( When the distance between 10) and the second lens optical unit 20 is D _t , and the refractive index of the lens having negative refractive power in the first lens optical unit 10 is N _a1 , 45f ₁ · f _bt / D _t · f _bw 55, 1.1D _t / N _a1 1.3.

In addition, when the average refractive index of all the lens systems is N _r and the average Abbe number of all the lens systems is V _r , N _r 1.7 and V _r 42 are satisfied.

In addition, the average refractive index of the lens having a _positive refractive power in the first lens optical unit 10 is N _ap1 , and the average Abbe number of the lens having a negative refractive power in the first lens optical unit 10 is V _a1 , When the average Abbe number of a lens having forward refractive power in the one lens optical unit 10 is V _ap1 , N _a1 1.45, N _ap1 1.9, 30 V _ap1 / N _ap1 33, 15 V _a1 / N _a1 18 are satisfied. It is.

In addition, the average refractive index of the lens having the positive refractive power in the second lens optical unit 20 is N _p2 , and the average refractive index of the lens having the negative refractive power in the second lens optical unit 20 is N _n2 and the second lens. When the average Abbe number of lenses having negative refractive power in the optical part 20 is V _n2 and the average Abbe number of lenses having positive refractive power in the second lens optical part 20 is V _p2 , N _p2 1.65 , N _n2 1.85, 0.55V _p2 / V _n2 0.75 is to be satisfied.

The following describes the effects of the present invention configured as described above.

When the user wants to photograph the camera having the above-described configuration by selectively adjusting the zoom magnification appropriately, the first lens optical unit 10 having the positive refractive power configured in the camera and the negative refractive power By varying the mutual spacing of the second lens optical unit 20 to have a predetermined ratio change, it is possible to obtain a picture of the magnification desired by the user.

That is, the camera having the above-described configuration allows the aberration to be corrected well from the wide end to the telephoto end. In addition, since the plastic lens has a very small change in the shop due to temperature, the lens of the plastic material has the refractive power in the forward direction of the second lens optical unit 20 as well as the third lens 13 having the forward refractive power of the first lens optical unit 10. By manufacturing the fourth lens 21 having a meniscus shape having a plastic material, it is possible to reduce manufacturing costs and to suppress aberration correction and changes in store location due to changes in temperature. When the focal length of the third lens 13 of the unit 10 is f _p1 and the focal length of the second lens optical unit 20 is f _p2 , it is set to satisfy 0.5 | f _p1 / f _p2 | 0.6. Therefore, the effects of temperature and humidity can be further reduced.

In addition, the present invention for the purpose of reducing the production cost and miniaturization of the product includes a reduction in the amount of movement of each lens group due to the shortening of the front of the optical system, the displacement and the reduction of the diameter of each lens. Accordingly, in order to shorten the front of the optical system, the components of the optical system are reduced, and the positive and negative refractive power lenses are appropriately combined to reduce the movement amount of the lens group and reduce the diameter of the lens. The focal length of the lens optical unit 10 is f ₁ , and the rear focal lengths at the telephoto end and the wide-angle end are respectively f _bt , f _bw , and the first lens optical unit 10 and the second lens optical unit at the telephoto end ( When the distance between 20) is D _t and the refractive index of the lens having the negative refractive power in the first lens optical unit 10 is N _a1 , 45f ₁ · f _bt / D _t · f _bw 55, 1.1D _t / N _a1 is configured to satisfy 1.3.

In addition, for the first lens optical unit 10, the average refractive index of the lens having the forward refractive power in the first lens optical unit 10 is N _ap1 , and the first lens optical unit 10 has the negative refractive power in the first lens optical unit 10. When the average Abbe number of the lens is V _a1 , and the average Abbe number of the lens having forward refractive power in the first lens optical unit 10 is V _ap1 , N _a1 1.45, N _ap1 1.9, 30V _ap1 / N _ap1 33, 15V _a1 / N _a1 18, and for the second lens optical unit 20, the average refractive index of the lens having forward refractive power in the second lens optical unit 20 is N _p2 and the second lens optical unit. The average refractive index of the lens having the refractive power in the qn direction at the portion 20 is N _n2 , and the average Abbe number of the lens having the refractive power in the negative direction at the second lens optical portion 20 is V _n2 and the second lens optical portion 20. ) configuration when said average of the Abbe number V _p2 of the lens, N _p2 1.65, N 1.85 _n2, to satisfy the 0.55V _p2 / V _n2 0.75 having a refractive power in the forward direction Since it is standing had a good performance of the aberration correction and optical system as shown in the examples.

In addition, when the average refractive index of the entire lens system is N _r and the average Abbe number of the entire lens system is V _r , N _r 1.7 and V _r 42 can be satisfied so as to reduce dispersion in chromatic aberration correction.

EXAMPLE

t1

Aspherical surface coefficient

Page 7

A2 = -0.548E-04

A4 = -0.228E-07

A6 = -0.94E-08

A8 = -0.19E-09

K = -49.80

Page 11

A2 = -0.519E-04

A4 = -0.444E-06

A6 = -0.785E-09

A8 = -0.468E-10

K = 1.64

[Effects of the Invention]

In addition to maintaining a good aberration performance while simplifying the structure of each lens group, the plastic lens is used to simplify the reworking process to improve productivity as well as to reduce manufacturing costs.

Claims (5)

A zoom lens of a camera, comprising a first lens group having a forward refractive power and a second lens group having a negative refractive power, thereby allowing a predetermined ratio to be varied by changing a distance between the two lens groups. Meniscus-shaped first lens 11 having a positive refractive power convex on the subject side, a second lens 12 having a negative refractive power concave on the subject side, and positive refractive power in both directions convex A first lens optical unit 10 composed of a third lens 13 having; The second lens optical unit 20 includes a meniscus fourth lens 21 having a forward refractive power concave on the subject side and a fifth lens 22 having a negative refractive power concave on the subject side. Zoom lens, characterized in that consisting of). The method of claim 1, The focal length of the first lens optical unit 10 is f ₁ , and the rear focal lengths at the telephoto end and the wide-angle end are respectively f _bt , f _bw , and the first lens optical unit 10 and the second lens optical at the telephoto end, respectively. When the distance between the portions 20 is D _t , the refractive index of the lens having the negative refractive power in the first lens optical portion 10 is N _a1 . _{45f 1 · f bt / D t} · f bw 55, 1.1D t / N a1 1.3 Zoom lens, characterized in that configured to satisfy. The method of claim 1, When the average refractive index of all lens systems is N _r and the average Abbe number of all lens systems is V _r N _r 1.7, V _r 42 Zoom lens, characterized in that configured to satisfy. The method of claim 1, The average refractive index of the lens having the forward refractive power in the first lens optical unit 10 is N _ap1 , and the average Abbe number of the lens having the negative refractive power in the first lens optical unit 10 is V _a1 , the first lens optical When the average Abbe number of the lens having the forward refractive power in the unit 10 is V _ap1 N _a1 1.45, N _ap1 1.9, 30V _ap1 / N _ap1 33, 15V _a1 / N _a1 18 Zoom lens, characterized in that configured to satisfy. The method of claim 1, The average refractive index of the lens having positive refractive power in the second lens optical part 20 is N _p2 , and the average refractive index of the lens having negative refractive power in the second lens optical part 20 is N _n2 and the second lens optical part When the average Abbe number of the lens having a negative refractive power at (20) is V _n2 , and the average Abbe number of the lens having a positive refractive power at the second lens optical unit 20 is V _p2 . N _p2 1.65, N _n2 1.85, 0.55 V _p2 / V _n2 0.75 Zoom lens, characterized in that configured to satisfy.