JPH0553052A - Read lens - Google Patents

Abstract

PURPOSE:To obtain the read lens whose focal distance is long such as about 65-85mm (e line), and which can read even a document of size of about A3, and is provided with high resolution of about 400dni by satisfying specific conditions in the read lens constituted of four groups and six pieces. CONSTITUTION:A first lens group consisting of one piece of positive meniscus lens whose convex surface is turned to an object side, a second lens group formed by cementing one piece of positive lens and one piece of negative lens, a third lens group formed by cementing one piece of negative lens and one piece of posi-tive lens, and a fourth lens group consisting of one piece of positive lens are arranged in order from the object side and this lens is constituted of four groups and six pieces as the whole system. Also, conditions of the expression I are satisfied. In the expression I, (di), (f), nuj, fj, and nj denote an interval between an i-th face and an i+l-th face, a focal distance of an (e) line of the whole system, an Abbe number of a (d) line of a j-th lens, a focal distance of an (e) line of a j-th 1-ens, and a refractive index of the (e) line of a j--th lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a reading lens used in an image input device such as a color facsimile and a color scanner.

[0002]

2. Description of the Related Art In recent years, colorization has been promoted in image input devices such as facsimiles and scanners.

In this type of image device, for example, the optical paths of the light flux reflected from the original and transmitted through the reading lens are provided in three primary colors (blue, green,
Red) and three CCDs installed on each optical path
There is a so-called three-color separation system in which a photoelectric conversion signal for each color is obtained by a line sensor. In this method, the three-resolved optical path lengths can be appropriately set for each color, and therefore axial chromatic aberration can be corrected. However, it was necessary to provide three CCD line sensors, which was a factor of cost increase.

There is also a so-called sequential reading system in which one CCD line sensor is provided on the optical path of the reflected light beam and a color separation filter is selectively inserted between the reading lens and the CCD line sensor. .. In this method, an appropriate optical path length can be set for each color according to the switching of the read color. However, in this method, although only one CCD line sensor is required, it is necessary to provide a driving means for setting the optical path length, which also causes a cost increase. Furthermore, since the document needs to be read three times, there is a problem that the image reading time is three times longer than that of the black and white type.

Therefore, a so-called three-line CCD sensor has been used in which three line sensors are arranged in parallel on one substrate at extremely small intervals and a filter for color separation is provided in front of each line sensor. Came. According to this 3-line CCD sensor, each color can be read by one reading, and the image reading time can be shortened.
It is possible to reduce the cost.

[0006]

However, in the 3-line CCD sensor, since reading of each color is performed at the same time,
It is impossible to correct the axial chromatic aberration by changing the optical path length. For example, when a Gaussian lens described in Japanese Patent Laid-Open No. 59-90810 is used as a reading lens, g
The axial chromatic aberration of the line becomes large, and the spherical aberration is not corrected by this lens. In addition, JP-A-62-948
The use of the Gauss-type lens described in Japanese Patent No. 10 has a problem that chromatic aberration of magnification becomes particularly large.

Recently, it is necessary to make the reading lens longer in focus in order to read a large-sized original, a mirror scan system in which the original table is fixed, and a high resolution. If the focal length of the reading lens becomes long, the chromatic aberration thereof tends to increase, and therefore the reading lens itself is required to have improved axial chromatic aberration.

[0008]

SUMMARY OF THE INVENTION In view of the above situation, the present invention has a long focal length of about 65 to 85 mm (e-line), can read an original document of A3 size, and has a high resolution of about 400 dpi. It is intended to provide a reading lens.

[0009]

In order to achieve the above object, a reading lens according to the present invention comprises a first lens group consisting of one positive meniscus lens with a convex surface facing the object side, and one lens. The second lens group consisting of a positive lens and a negative lens cemented together, the third lens group consisting of a negative lens and a positive lens cemented together, and a single positive lens 4th lens group is arranged in order from the object side, and the following (a)
It is characterized by satisfying the condition of (i).

(A) 0.073 <(d1 + d2) / f <0.140 (b) 0.065 <(d8 + d9) / f <0.140 (c) 20 <ν2-ν3 <35 (d) -15 <ν4-ν5 <-10 (e) 5 <ν1 + ν3-ν2 <16 (f) 0.8 <f1 / f <1.05 (g) 0.9 <f6 / f <1.25 (h) 1.7 <(n1 + n2) / 2 <1.8 ( i) 1.75 <(n5 + n6) / 2 <1.8 where di is the distance between the i-th surface and the (i + 1) -th surface, f is the focal length of the e-line of the entire system, and νj is the d-th lens of the j-th lens. Abbe number of the line, fj: focal length of the e-line of the j-th lens, nj: refractive index of the e-line of the j-th lens.

[0011]

Embodiments of the reading lens according to the present invention will be described below with reference to the drawings.

The reading lens of this embodiment is formed by bonding a first lens group consisting of one positive meniscus lens with a convex surface facing the object side, one positive lens and one negative lens. A second lens group, a third lens group formed by bonding one negative lens and one positive lens together, and a fourth lens group consisting of one positive lens are arranged in order from the object side, and all The system consists of 6 elements in 4 groups. Also, the following conditions (a) to (i) are satisfied.

(A) 0.073 <(d1 + d2) / f <0.140 (b) 0.065 <(d8 + d9) / f <0.140 (c) 20 <ν2-ν3 <35 (d) -15 <ν4-ν5 <-10 (e) 5 <ν1 + ν3-ν2 <16 (f) 0.8 <f1 / f <1.05 (g) 0.9 <f6 / f <1.25 (h) 1.7 <(n1 + n2) / 2 <1.8 ( i) 1.75 <(n5 + n6) / 2 <1.8 where di is the distance between the i-th surface and the (i + 1) -th surface, f is the focal length of the e-line of the entire system, and νj is the d-th lens of the j-th lens. Abbe number of the line, fj: focal length of the e-line of the j-th lens, nj: refractive index of the e-line of the j-th lens.

The conditions (a) and (b) are conditions for suppressing the coma aberration of the reading lens. Both conditions
If it is out of that range, coma will be large.

The conditions (c), (d) and (e) are conditions for limiting the range in which the axial chromatic aberration of the reading lens can be corrected. If any of the conditions is out of the range, it becomes difficult to correct the axial chromatic aberration, and it cannot be applied to a color image input device.

The conditions (f) and (g) are conditions for the reading lens to have an appropriate power. If any of these conditions is out of the range, it is difficult to properly arrange the power of the reading lens, which is not preferable.

The conditions (h) and (i) are conditions that limit the range in which the field curvature and lateral chromatic aberration of the reading lens can be corrected. If any of these conditions is out of the range, the field curvature and the chromatic aberration of magnification are deteriorated, which is not preferable.

Next, numerical configuration examples 1 to 5 of the reading lens according to the present invention will be described. Here, f is the focal length in the e-line, r is the radius of curvature of each lens surface, d is the lens thickness or lens surface spacing (above, unit is mm), Fno. Is the F number, and n is the e-line of each lens. Refractive index, ν is the Abbe number at the d-line of each lens.

[0019]

Example 1 FIG. 1 is a lens system configuration diagram of Example 1. As shown in FIG. The specific configuration is as shown in Table 1. The various aberrations are as shown in FIG.

[0020]

[Table 1] FNo. = 1: 4.5, f = 85.16, use magnification: -0.2205, document size: A3, resolution: 400dpi, sensor density: 1
4μ, platen glass thickness: 3.0mm, platen glass refractive index: 1.51825 (e-line), CCD cover glass thickness: 1.0mm, CC
D cover glass refractive index: 1.51825 (e-line)

[0021]

Second Embodiment FIG. 3 is a lens system configuration diagram of a second embodiment. The specific configuration is as shown in Table 2. The various aberrations are as shown in FIG.

[0022]

[Table 2] FNo. = 1: 4.0, f = 84.47, use magnification: -0.2205, document size: A3, resolution: 400dpi, sensor density: 1
4μ, platen glass thickness: 3.0mm, platen glass refractive index: 1.51825 (e-line), CCD cover glass thickness: 1.0mm, CC
D cover glass refractive index: 1.51825 (e-line)

[0023]

Third Embodiment FIG. 5 is a lens system configuration diagram of the third embodiment. The specific structure is shown in Table 3. Also, various aberrations are as shown in FIG.

[0024]

[Table 3] FNo. = 1: 4.0, f = 67.92, use magnification: -0.1575, document size: A3, resolution: 400dpi, sensor density: 1
0μ, Platen glass thickness: 3.0mm, Platen glass refractive index: 1.51825 (e-line), CCD cover glass thickness: 0.8mm, CC
D cover glass refractive index: 1.53188 (e-line)

[0025]

Fourth Embodiment FIG. 7 is a lens system configuration diagram of the fourth embodiment. The specific structure is shown in Table 4. Further, various aberrations are as shown in FIG.

[0026]

[Table 4] FNo. = 1: 4.5, f = 66.42, use magnification: -0.1575, document size: A3, resolution: 400dpi, sensor density: 1
0μ, Platen glass thickness: 3.0mm, Platen glass refractive index: 1.51825 (e-line), CCD cover glass thickness: 0.8mm, CC
D cover glass refractive index: 1.53188 (e-line)

[0027]

Fifth Embodiment FIG. 9 is a lens system configuration diagram of the fifth embodiment. The specific configuration is as shown in Table 5. Also, various aberrations are shown in Fig. 10.
As shown in.

[0028]

[Table 5] FNo. = 1: 4.0, f = 70.00, Use magnification: -0.4252, Document size: 4 (inch) x5 (inch), Resolution: 1200dpi,
Sensor density: 9μ, Platen glass thickness: 3.0mm, Platen glass refractive index: 1.51825 (e line), CCD cover glass thickness: 0.7mm, CCD cover glass refractive index: 1.53188 (e line)

Table 6 shows values corresponding to various conditions of each of the above embodiments. Here, each calculation is based on the focal length at the e-line, the refractive index, and the Abbe number at the d-line.

[0030]

[Table 6] Conditional Example Example 1 Example 2 Example 3 Example 4 Example 5 (d1 + d2) / f 0.085 0.078 0.081 0.074 0.131 (d8 + d9) / f 0.129 0.072 0.126 0.083 0.138 ν2-ν3 29.6 28.7 30.2 29.6 29.6 ν4-ν5 -11.6 -11.6 -14.7 -11.6 -11.6 ν1 + ν3-ν2 7.6 15.5 7.0 7.6 7.6 f1 / f 0.884 0.971 0.859 0.976 0.894 f6 / f 0.961 0.936 1.024 1.239 1.033 (n1 + n2) / 2 1.722 1.705 1.731 1.722 1.722 (n5 + n6) / 2 1.778 1.778 1.779 1.789 1.778

[0031]

As described above, according to the present invention, the focal length is as long as about 65 to 85 mm (e-line), and it is possible to read an original document of about A3 size and about 400 dpi. It is possible to obtain a reading lens having a high resolution and a structure of 6 elements in 4 groups.

[Brief description of drawings]

FIG. 1 is a lens system configuration diagram of a reading lens according to Example 1 of the present invention.

FIG. 2 is a diagram of various types of aberration of the reading lens according to the first example of the present invention.

FIG. 3 is a lens system configuration diagram of a reading lens according to Example 2 of the present invention.

FIG. 4 is a diagram of various types of aberration of the reading lens according to the second example of the present invention.

FIG. 5 is a lens system configuration diagram of a reading lens according to Example 3 of the present invention.

FIG. 6 is a diagram of various types of aberration of the reading lens according to the third example of the present invention.

FIG. 7 is a lens system configuration diagram of a reading lens according to Example 4 of the present invention.

FIG. 8 is a diagram of various types of aberration of the reading lens according to Example 4 of the present invention.

FIG. 9 is a lens system configuration diagram of a reading lens according to Example 5 of the present invention.

FIG. 10 is a diagram of various types of aberration of the reading lens according to the fifth example of the present invention.

Claims (1)

[Claims] 1. A first lens group consisting of one positive meniscus lens having a convex surface directed toward the object side, and a second lens group consisting of one positive lens and one negative lens cemented together. A third lens group consisting of one negative lens and one positive lens cemented together and a fourth lens group consisting of one positive lens are arranged in order from the object side, and the following (a) to (i ) A reading lens characterized by satisfying the condition (1). (a) 0.073 <(d1 + d2) / f <0.140 (b) 0.065 <(d8 + d9) / f <0.140 (c) 20 <ν2-ν3 <35 (d) -15 <ν4-ν5 <-10 (e) 5 <ν1 + ν3-ν2 <16 (f) 0.8 <f1 / f <1.05 (g) 0.9 <f6 / f <1.25 (h) 1.7 <(n1 + n2) / 2 <1.8 (i) 1.75 <(N5 + n6) / 2 <1.8 where di is the distance between the i-th surface and the (i + 1) -th surface, f is the focal length of the e-line of the entire system, and νj is the Abbe of the d-line of the j-th lens. Let fj be the focal length of the j-th lens in the e-line, and nj be the refractive index of the j-th lens in the e-line.