KR100290097B1 - Reduction lens - Google Patents

Abstract

PURPOSE: A reduction lens is provided to reduce manufacturing costs of a reduction lens by decreasing the number of lens used in the reduction lens. CONSTITUTION: The first lens group is formed with the first lens(1), the second lens(2), and the third lens(3). The first lens(1) has a negative refractive index and a convex face toward an object side. The second lens(2) is adhered to the first lens. The second lens(2) has a positive refractive index. The third lens(3) has the negative refractive index and convex both sides. The second lens group is formed with the fourth lens(4) and the fifth lens(5). The fourth lens(4) has the positive refractive index and the convex face toward the object side. The fifth lens(5) has the positive refractive index and the convex face toward the object side. A fixing iris diaphragm is installed between the first lens group and the second lens group.

Description

Zoom lens

1 (a) is a configuration diagram of the reduction lens according to the first embodiment of the present invention,

1 (b) is an aberration diagram of the reduction lens according to the first embodiment of the present invention,

2 (a) is a configuration diagram of the reduction lens according to the second embodiment of the present invention,

2 (b) is an aberration diagram of the reduction lens according to the second embodiment of the present invention,

3 (a) is a configuration diagram of the reduction lens according to the third embodiment of the present invention,

3 (b) is an aberration diagram of the reduction lens according to the third embodiment of the present invention,

4 (a) is a configuration diagram of the reduction lens according to the fourth embodiment of the present invention,

4 (b) is an aberration diagram of the reduction lens according to the fourth embodiment of the present invention.

The present invention relates to a reduction lens, and more particularly, to a reduction lens having a compact and high resolution of about 0.1 times a reduction factor of about 0.1 times used in office equipment using solid-state image pickup devices such as facsimile, image sensor, and digital copier. .

In recent years, the development of office equipment using a line charge coupled device (line CCD) has been progressing in compactness and high resolution. The compactness is mainly realized by using a contact image sensor (CIS) to directly contact the image plane with the image plane.

However, the method employing the contact type image sensor is still more expensive than the lens adopting method and does not realize high resolution.

Techniques for implementing high resolution lenses have been described in US Pat. Nos. 4,370,032, 4,415,241, 4,671,627, 4,863,251 and 5,040,884.

However, the techniques described in the above-mentioned US Patent Nos. 4,370,032 and 4,415,241 are tesa-type lenses, and the number of lenses is four, which is a relatively inexpensive format but does not realize high contrast in high resolution and high frequency components.

In addition, the US Patent Nos. 4,671,627, 4,863,251, and 5,740,884 are Gaussian lenses that realize high contrast and high contrast at high frequency. However, the number of lenses consists of six to eight lenses, which increases manufacturing costs. have.

Therefore, an object of the present invention is to solve the above-mentioned disadvantages, and it is a reduction lens composed of five pieces as a lens used in office equipment, which can be realized at a relatively low manufacturing cost, and has a high resolution and high contrast in high frequency components. It relates to a reduction lens to be.

The configuration of the present invention, which aims to achieve the above object, comprises a first lens having a convex lens and a negative refractive power from the object side, a second lens bonded to the first lens and having a positive refractive power; , A first lens group composed of a third lens having negative refractive power and having a positive and negative surface, a fourth lens having a concave and positive refractive power on the object side, and a second lens having a fifth lens having convex and positive refractive power on the object side And a fixed diaphragm is mounted between the first lens group and the second lens group, and satisfies the following conditions.

-6.5 <(f-f _II ) / f _I <-2.5

3.5 <(f ₂ f ₃ ) / f ₁ <5.8

0.9 <f ₄ / f ₅ <1.45

F is the combined focal length of the entire optical system, f _I is the focal length of the first lens group, f _II is the focal length of the second lens group, and fi is the focal length of the i-th lens.

When described with reference to the accompanying drawings the most preferred embodiment which can easily implement this invention by the above configuration as follows.

In order to easily understand the structure and operation of the reduction lens according to an embodiment of the present invention, a description of the reduction lens according to the four embodiments of the present invention will be described.

The reduced lens according to the embodiment of the present invention has a brightness of about 4 to 5, a half angle of view of about 17 ° to 19 °, and a magnification of about 0.1 times.

FIG. 1 (a) is a configuration diagram of the reduction lens according to the first embodiment of the present invention, and FIG. 1 (b) is an aberration diagram of the reduction lens according to the first embodiment of the present invention.

As shown in the attached first (a) diagram, the reduction lenses according to the embodiment of the present invention are arranged in order from the side of the object, that is, the object, respectively, and are separated by a predetermined distance from the first lens group I. And the second lens group II.

The reduced lens according to the embodiment of the present invention includes a first lens 1 having negative refractive power convex from the object side, a second lens 2 bonded to the first lens 1 and having positive refractive power; A first lens group I composed of a third lens 3 having negative refractive power and concave on both sides; And a second lens group (II) composed of a fourth lens (4) having an object side surface convex and positive refractive power, and a fifth lens (5) having an object side surface convex and positive refractive power. A fixed diaphragm between (I) and second lens group II is mounted, and the following conditions are satisfied.

-6.5 <f · f _II / f _I ) <-2.5 (1)

3.5 <(f ₂ · f ₃ ) / f ₁ <5.8 (2)

0.9 <f ₄ / f ₅ <1.45 (3)

F is a compound focal length of the entire optical system, f _I is a compound focal length of the first lens group I, f _II is a compound focal length of the second lens group II, and f _i is I The focal length of the first lens is shown.

Equation (1) relates to the refractive power of the first lens group (I) and the second lens group (II) and the focal length of the entire lens, and is larger than the upper limit of the conditional expression (1). The distance from the vertex to the top surface becomes long, and when the distance becomes smaller than the lower limit of the conditional expression (1), the distortion aberration increases.

The conditional expression (2) relates to the refractive power of each lens of the first lens group (I), and when it is larger than the upper limit of the conditional expression (2), the coma aberration and the Petzval sum increase, which is smaller than the lower limit of the conditional expression (2). When it is lost, spherical and distortion aberration becomes large.

Conditional expression (3) relates to the refractive power of each lens of the second lens group (II), and when the value of the conditional expression (3) becomes larger than the upper limit, the spherical aberration and astigmatism become large, and the conditional expression (3) When smaller than the lower limit, magnification of chromatic aberration becomes large.

In addition, the reduction lens according to the embodiment of the present invention described above must satisfy the following equation.

20 <υ _apI / n _apI <30 Formula (4)

17 <υ _anI / n _anI <23 equation (5)

N _apI is the average refractive index of the lens having positive refractive power of the first lens group I, υ _apI is the average Abbe number of the lenses having positive refractive power in the first lens group I, and n _anI is the first An average refractive index of a lens having negative refractive power of one lens group I, and ν _anI is an average Abbe number of a lens having a negative refractive power of first lens group I.

Equations (4) and (5) above relate to the material of the first lens group I. When the value of the conditional expression (4) becomes larger than the upper limit, spherical aberration and longitudinal chromatic aberration increase. If it is smaller than the lower limit of Conditional Expression (4), an expensive material is used.

When the value of the conditional expression (5) becomes larger than the upper limit, the spherical aberration and the longitudinal chromatic aberration become large, and when the value of the conditional expression (5) becomes smaller than the lower limit of the conditional expression (5), the Petzol synthesis becomes large.

In addition, the reduction lens according to the embodiment of the present invention described above must satisfy the following equation.

1.7 <(r ₁ r ₂ ) / r ₃ <2.7 Formula (6)

-1.5 <r ₆ / r ₈ <-0.9 Formula (7)

Equations (6) and (7) above are related to aberration correction. When the value of the conditional expression (6) becomes larger than the upper limit, the spherical aberration becomes large, and when the value of the conditional expression (6) becomes smaller than the lower limit of the conditional expression (6), the magnification chromatic aberration and coma aberration become It becomes bigger.

When the value of the conditional expression (7) becomes larger than the upper limit value, the astigmatism and Petz's summation become large, and when the value of the conditional expression (7) becomes smaller than the lower limit value, the distortion aberration increases.

Example values according to the first embodiment of the present invention satisfying the above conditions are shown in Table 1 below.

F is the focal length, ri (i = 1-9) is the radius of curvature of each lens surface, di (i = 1-9) is the thickness or air gap of the lens, and N is the d-line of the lens. The refractive index and υ are the Abbe's number of the lens, m is the magnification of the whole lens system, and w is the half angle of view.

The aperture Fno of the reduced lens according to the first embodiment of the present invention is 1: 4.5, the focal length f is 39.506, the half angle of view w is 17.03 °, and the magnification m of the entire lens system is = 0.112.

TABLE 1

The condition values described in the above formulas (1) to (7) according to the first embodiment of the present invention are as follows.

(1) f · f _II / f _I = -2.852

(2) f ₂ f ₃ / f ₁ = 5.372

(3) f ₄ / f ₅ = 1.320

(4) υ _apI / n _apI = 23.422

(5) υ _anI / n _anI = 18.387

_{(6) r 1 · r 2} / r 3 = 1.887

(7) r ₆ / r ₈ = -0.978

FIG. 2 (a) is a configuration diagram of the reduction lens according to the second embodiment of the present invention, and FIG. 2 (b) is an aberration diagram of the reduction lens according to the second embodiment of the present invention.

Example values according to the second embodiment of the present invention are shown in Table 2 below. The aperture Fno of the reduction lens according to the second embodiment of the present invention is 1: 4.8, the focal length f is 39.487, and the half angle of view w is 17.38. And the magnification m of the whole lens system is = -0.112.

TABLE 2

The condition values described in the above formulas (1) to (7) according to the second embodiment of the present invention are as follows.

(1) f-f _II / f _I = -4.075

(2) f ₂ f ₃ / f ₁ = 3.912

(3) f ₄ / f ₅ = 1.363

(4) υ _apI / n _apI = 27.994

(5) υ _anI / n _anI = 20.609

_{(6) r 1 · r 2} / r 3 = 2.356

(7) r ₆ / r ₈ = -1.113

FIG. 3 (a) is a configuration diagram of the reduction lens according to the third embodiment of the present invention, and FIG. 3 (b) is a reduction lens aberration diagram according to the third embodiment of the present invention.

Example values according to the third embodiment of the present invention are shown in Table 3 below. The aperture Fno of the reduction lens according to the third embodiment of the present invention is 1: 5.0, the focal length f is 39.561, and the half angle of view w is 18.95. And the magnification m of the whole lens system is = -0.126.

TABLE 3

The condition values described in the above formulas (1) to (7) according to the third embodiment of the present invention are as follows.

(1) f · f _II / f _I = -5.901

(2) f ₂ f ₃ / f ₁ = 4.642

(3) f ₄ / f ₅ = 1.173

(4) υ _apI / n _apI = 28.234

(5) υ _anI / n _anI = 21.428

_{(6) r 1 · r 2} / r 3 = 2.441

(7) r ₆ / r ₈ = -1.207

4A is a configuration diagram of the reduction lens according to the fourth embodiment of the present invention, and FIG. 4B is an aberration diagram of the reduction lens according to the fourth embodiment of the present invention.

Example values according to the fourth embodiment of the present invention are shown in Table 4 below. The aperture Fno of the reduction lens according to the fourth embodiment of the present invention is 1: 4.8, the focal length f is 41.035, and the half angle of view w is 18.77. And the magnification m of the whole lens system is = -0.126.

TABLE 4

The condition values described in the above formulas (1) to (7) according to the fourth embodiment of the present invention are as follows.

(1) f · f _II / f _I = -4.132

(2) f ₂ f ₃ / f ₁ = 4.453

(3) f ₄ / f ₅ = 0.957

(4) υ _apI / n _apI = 25.773

(5) υ _anI / n _anI = 18.540

_{(6) r 1 · r 2} / r 3 = 2.560

(7) r ₆ / r ₈ = -1.407

As described above, in the embodiment of the present invention, it is possible to provide a reduced-lens lens having a relatively low price by consisting of five lenses.

In addition, it is possible to provide a reduction lens having the effect of maintaining a high contrast and high contrast at high frequency components.

Claims (3)

From the object side, a first lens group consisting of a first lens having a convex and negative refractive power on the object side, a second lens bonded to the first lens and having positive refractive power, and a third lens having negative refractive power and concave on both sides and; A second lens group consisting of a fourth lens having a convex and positive refractive power on an object side, and a fifth lens having a convex and positive refractive power on an object side, and having a fixed aperture between the first lens group and the second lens group. And a reduction lens, which satisfies the following conditions. -6.5 <f · f _II / f _I ) <-2.5 3.5 <(f ₂ · f ₃ ) / f ₁ <5.8 0.9 <f ₄ / f ₅ <1.45 f: composite focal length of the whole optical system f _I : Composite focal length of the first lens group I _II : Composite focal length of the second lens group The reduction lens of claim 1, wherein the following expression is further satisfied. 20 <υ _apI / n _apI <30 17 <υ _anI / n _apI <23 n _apI : Average refractive index of the lens having positive refractive power of the first lens group υ _apI : average Abbe number of the lens having positive refractive power of the first lens group n _anI : Average refractive index of the lens having negative refractive power of the first lens group υ _anI : average Abbe number of lenses having negative refractive power of the first lens group The reduction lens of claim 1, wherein the following expression is further satisfied. 1.7 <(r ₁ r ₂ ) / r ₃ <2.7 -1.5 <r ₆ / r ₈ <-0.9