JPH0593857A - Lens for copying - Google Patents

Abstract

PURPOSE:To provide the lens for copying which is compact, low in cost, and usable for X0.5-X20 copying. CONSTITUTION:This lens consists of five elements in five groups which are a 1st positive meniscus lens having a convex surface facing to an object side, a 2nd negative meniscus lens having a concave surface facing to the image side, a 3rd biconvex lens, a 4th negative meniscus lens having a concave surface facing to the object side, and a 5th positive meniscus lens having a convex surface facing to the image side in order from the object side; and the object- side and image-side intervals of the 3rd lens are made slightly asymmetrical and others are made symmetrical.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying lens, and more particularly to a copying lens suitable for use in zooming.

[0002]

2. Description of the Related Art In recent years, it has become common for copying machines to be able to perform variable magnification in a concatenated manner from reduction to enlargement, and as an optical system to be used, there is one that has a wider variation range and is low cost and compact. It has come to be requested. As such an optical system for a copying machine, conventionally, a method using a fixed focus lens, a method for moving a part of the fixed focus lens, and a method using a zoom lens are known. As a method of using a fixed-focus lens, many compact and low-cost copying lenses have been proposed such as Japanese Patent Publication No. 56-49332 and Japanese Patent Publication No. 61-512290. However, the performance of these copying lenses in the vicinity of unity magnification is sufficiently corrected, but as the zooming range expands, the coma aberration in the peripheral area deteriorates, making it difficult to set a large zooming range. It was

Therefore, in order to further increase the zooming range, there has been proposed a lens having asymmetrical lens shapes and intervals.
For example, the one described in JP-A-60-140917 is 6
With a group of 6 lenses, the lens shape is symmetrical, but the lens spacing is asymmetrical, so it can be used up to about 0.64 to 1.4 times, but the total length exceeds 0.3 f and compactness is achieved. Is lacking in. The one disclosed in Japanese Patent Application Laid-Open No. 2-275917 has the same six-group, six-lens configuration. By making the shapes of the third and fourth lenses asymmetric and arranging the intervals asymmetric, it is possible to obtain about 0.5 to 2 times. It has a large zoom range. However, the total length is about 0.28 f, lacking compactness, and a little dark at F6.5. In addition, since the third and fourth lenses are asymmetrical and cannot be shared, the cost is higher than that of a lens having a symmetrical lens shape.

A method of moving a part of the fixed focus lens is disclosed in Japanese Patent Laid-Open Nos. 61-43713 and 1-137217.
It can be found in the official gazette. By moving a part of the lens to make it asymmetric during zooming, good performance can be obtained for reduction and expansion. The one disclosed in JP-A-1-137217 can be used in a composition of 5 elements in 5 groups or 6 elements in 6 groups up to 0.5 to 2 times. However, there is a problem in that a part of the lens is moved, so that the mechanism becomes complicated, the cost becomes high, and the adjustment becomes complicated.

A method using a zoom lens is disclosed in Japanese Patent Laid-Open No. 1-1.
Although many proposals have been made such as Japanese Patent No. 23210, these require a more complicated mechanism and adjustment than the above-mentioned method, resulting in a costly lens.

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to obtain a copying lens which is compact and low in cost and which can be used up to 0.5 to 2.0 times and which does not include the above problems. ..

[0007]

The copying lens of the present invention can be used in a wide zoom range without moving a part of the lens by using a fixed focus lens having a slightly asymmetrical structure. Is becoming Specifically, in order from the object side, a positive meniscus first lens with a convex surface facing the object side,
Second negative-meniscus lens with concave surface facing the image side, biconvex third lens, fourth negative-meniscus lens with concave surface facing the object side
The lens is composed of 5 elements in 5 groups of a positive meniscus fifth lens having a convex surface facing the image side, and the distance between the object side and the image side of the third lens is slightly asymmetric, and the others are symmetrical.
That is, it is characterized in that the following conditions are satisfied. 0.9 <d ₄ / d ₆ <1.0

Further, it is desirable to satisfy the following conditions. 5f <R ₃ (= −R ₈ ) <15f 0.5f <f ₁ (= f ₅ ) <0.6f 1.75 <(n ₁ + n ₃ + n ₅ ) / 3 However, Ri: the first from the object side Radius of curvature of i-th surface di: axial thickness interval of i-th surface counted from the object side ni: refractive index for the i-th d-line counted from the object side fi: i-th counted from the object side Focal length of lens f: Focal length of entire system

[0009]

The function is a condition for correcting the coma aberration at the time of reduction and expansion at a good balance by making the lens configuration slightly asymmetrical as described above. If the lower limit is exceeded, the performance at the time of reduction is improved but at the time of expansion. Performance will deteriorate. On the contrary, if the upper limit is exceeded, the performance at the time of enlargement will improve, but the performance at the time of reduction will deteriorate. If the lower limit of the condition is exceeded, coma flare will increase and the meridional image plane will be undercorrected. In particular, the performance deteriorates when enlarged. On the other hand, if the upper limit is exceeded, the meridional image plane will be overcorrected and the performance at the time of reduction will deteriorate.
If the lower limit of the condition is exceeded, spherical aberration will be overcorrected, but the peripheral meridional image surface will be undercorrected.
It becomes difficult to flatten the image plane. If the upper limit is exceeded, the meridional image plane will be overcorrected and the astigmatic difference will be large. The condition is a condition relating to the refractive index of the positive lens, and if the lower limit is exceeded, the value of Petzval becomes large and it becomes difficult to correct the field curvature. In particular, the performance deteriorates in the vicinity of the same magnification where the angle of view is widest.

The embodiments of the present invention will be described below. In the tables, r is the radius of curvature of each refracting surface, d is the refracting surface distance,
n is the refractive index of the lens material for the d line, ν is the same Abbe number, f is the focal length of the entire lens system, F is the F number, and ω
Indicates a half angle of view.

Example 1 f = 235.0 F5.8 ω = 19 ° to 13 ° No. r d n ν 1 52.101 5.79 1.76200 40.2 2 103.738 2.60 3 2110.087 2.80 1.63980 34.5 4 55.017 7.19 5 143.845 5.19 1.77250 49.6 6- 143.845 7.39 7 -55.017 2.80 1.63980 34.5 8 -2110.087 2.60 9 -103.738 5.79 1.76200 40.2 10 -52.101 Total lens length = 0.18f f ₁ = f ₅ = 0.557f R ₃ = -R ₈ = 8.98f d ₄ / d ₆ = 0.97

Example 2 f = 235.0 F5.8 ω = 19 ° to 13 ° No. r d n ν 1 52.834 5.85 1.76200 40.2 2 105.013 2.76 3 3178.627 2.98 1.63980 34.5 4 55.830 7.45 5 142.520 4.97 1.77250 49.6 6- 142.520 7.57 7 -55.830 2.98 1.63980 34.5 8 -3178.627 2.76 9 -105.013 5.85 1.76200 40.2 10 -52.834 lens length _{= 0.18f f 1 = f 5 =} 0.566f R 3 = -R 8 = 13.53f d 4 / d ₆ = 0.98

Example 3 f = 235.0 F5.8 ω = 19 ° to 13 ° No. r d n ν 1 51.333 5.56 1.76200 40.2 2 102.402 2.69 3 1589.709 2.38 1.63980 34.5 4 54.238 6.75 5 145.010 5.15 1.77250 49.6 6- 145.010 7.10 7 -54.238 2.38 1.63980 34.5 8 -1589.709 2.69 9 -102.402 5.56 1.76200 40.2 10 -51.333 lens length _{= 0.17f f 1 = f 5 =} 0.549f R 3 = -R 8 = 6.76f d 4 / d ₆ = 0.95

Example 4 f = 235.0 F5.8 ω = 19 ° to 13 ° No. r d n ν 1 52.623 5.40 1.76200 40.2 2 104.330 3.01 3 1417.089 2.80 1.63980 34.5 4 55.511 6.84 5 146.408 5.28 1.77250 49.6 6- 146.408 7.28 7 -55.511 2.80 1.63980 34.5 8 -1417.089 3.01 9 -104.330 5.40 1.76200 40.2 10 -52.623 Total lens length = 0.18f f ₁ = f ₅ = 0.567f R ₃ = -R ₈ = 6.03f d ₄ / d ₆ = 0.94

[0015]

The copying lens of the present invention is substantially symmetrical as seen in the above-mentioned respective examples and the aberration curves thereof, and mainly by making the lens interval before and after the third lens slightly asymmetrical, It is possible to satisfactorily correct aberrations in a wide zoom range, and it is possible to obtain a low-cost copying lens because it is compact and the shape of the lens itself is symmetrical.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of a copying lens of the present invention.

FIG. 2 is an aberration diagram at 1 × of Example 1 described above.

FIG. 3 is an aberration diagram at 0.5 times that of the first embodiment.

FIG. 4 is an aberration diagram at a magnification of 2 times that of the first embodiment.

FIG. 5 is an aberration diagram at 1 × of Example 2.

FIG. 6 is an aberration diagram at 0.5 × of Example 2.

FIG. 7 is an aberration diagram at double magnification of Example 2.

FIG. 8 is an aberration diagram at 1 × of Example 3.

FIG. 9 is an aberration diagram at 0.5 × of Example 3.

FIG. 10 is an aberration diagram at 2 × of Example 3.

FIG. 11 is an aberration diagram at 1 × of Example 4.

FIG. 12 is an aberration diagram at 0.5 × of Example 4.

FIG. 13 is an aberration diagram at 2 × of Example 4.

Claims (2)

[Claims] 1. A positive meniscus first lens having a convex surface facing the object side, a negative meniscus second lens having a concave surface facing the image side, a biconvex third lens, and a concave surface facing the object side in order from the object side. A negative lens for meniscus, and a fifth lens for positive meniscus with a convex surface facing the image side, 5 elements in 5 groups, satisfying the following conditions: 0.9 <d ₄ / d ₆ <1.0 where di: axial thickness interval of the i-th surface counted from the object side 2. A copying lens according to claim 1, which satisfies the following conditions: 5f <R ₃ (= −R ₈ ) <15f 0.5f <f ₁ (= f ₅ ) <0.6f 1.75 <( n ₁ + n ₃ + n ₅ ) / 3 where Ri: radius of curvature of the i-th surface counted from the object side ni: refractive index for the i-th d-line counted from the object side fi: i-th counted from the object side Focal length of th lens f: Focal length of entire system