JPH03242608A - Lens for copying machine - Google Patents

Abstract

PURPOSE:To obtain the lens which has various aberrations compensated excel lently although the number of lens elements is extremely small by composing the lens system of two lens elements in two groups and satisfying a specific condition. CONSTITUTION:The lens system is composed of the two lens element in two groups by arraying the positive lenses in a 1st group 1 and a 2nd group 2 in order from the object side to the image side. Then 1<f1/f<3.5 holds, where f1 is the focal length of the 1st group 1 and (f) is the composite focal length of the whole system. When the upper limit of this condition is exceeded, the power of the 1st group 1 becomes too weak and the power of the 2nd group 2 becomes much larger than the power of the 1st group 1, so that a negative distortion aberration increase greatly. Further, when the lower limit of the condition is exceeded, the power of the 1st group 1 becomes too large and the power of the 2nd group 2 becomes much less than the power of the 2nd group 2, so that a positive distortion aberration increase greatly.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a copying machine lens.

[Prior Art] In recent years, as the use of copying machines has become more common, there has been a demand for further downsizing and cost reduction in order to spread the use of copying machines more widely. For this reason, the imaging lenses used in copying machines are also required to be more compact and lower in cost.

In order to realize a copying machine lens compactly and at low cost, it is first necessary to reduce the number of lens elements. Conventionally, the lens for copying machines with the smallest number of lenses has been one with three lenses (Japanese Patent Application Laid-Open No. 180924/1983).

[Problems to be Solved by the Invention] The present invention has been made to solve the problem of further reducing the number of lenses for copying machines than the conventionally known three-element copying machine lens. Moreover, the object of the present invention is to provide a lens for a copying machine in which various aberrations are well corrected.

[Means to solve the problem] The present invention will be explained below.

The copying machine lens of the present invention is "a lens for forming a light image of a document on a photoreceptor surface in a copying machine".

The lens for a copying machine according to claim 1.2 also has a first group 1 and a second group 2 arranged from the object side, that is, the document surface side, toward the image side, that is, the photoreceptor surface side, as shown in FIG. .

Both the first group 1 and the second group 2 are positive lenses, so the overall configuration is two groups with two lenses.

When the focal length of the first group is f1 and the combined focal length of the entire system is f, these satisfy the following conditions: (1-I) 1 <f, /f <3.5.

1st. All the lens surfaces of the second group can also be constructed of spherical surfaces.

In the copying machine lens according to claim 2, in the configuration according to claim 1, one or more lens surfaces are aspherical.

The conic constant of the adopted aspherical surface satisfies the following condition: (2-I) −900<K<300.

[Function] In order for a copying machine to copy a document well, it is necessary that the lens for the copying machine has a distortion aberration of approximately 0 and that the image plane is flat from the vicinity of the optical axis to the outermost periphery.

As mentioned above, the copying machine lens of the present invention is composed of two lenses in two groups, but both of these two lenses are positive lenses, and the conditions (
By satisfying 1(), good correction of distortion aberration and curvature of field was realized.

Condition (1-I) is a condition that defines power distribution between the first group and the second group. If the upper limit of condition (1-I) is exceeded, the power of the first group becomes too weak, and the power of the second group becomes too strong compared to the first group, resulting in a significant increase in negative distortion and aberration. In addition, if the Petzval sum becomes too small, the image plane will tilt extremely in the positive direction and the curvature of field will increase, making it impossible to maintain the flatness of the image over the entire half angle of view of around 20 degrees. The focus position of the lens becomes extremely far apart, making it impossible to obtain good imaging performance over the entire image plane.

If the lower limit of condition (1-I) is exceeded, the power of the first group becomes too strong, and the power of the second group becomes too weak compared to the first group, resulting in a significant increase in positive distortion.

In addition, the Petzval sum becomes too large and the image plane falls extremely in the negative direction, the amount of absolute aberration increases and astigmatism increases, resulting in a decrease in overall contrast and the focus position of the sagittal image plane and meridional image plane. are extremely far apart, making it impossible to obtain good imaging performance over the entire image plane.

As mentioned above, the lens for a copying machine of the present invention may have all lens surfaces made of spherical surfaces.

When all lens surfaces are spherical, if various political differences are well corrected over the entire half-field angle of 20 degrees, the F/No will be 1.
The maximum aperture is about 3, but if one or more lens surfaces are aspherical as in the copying machine lens of claim 2, the F/No can be increased to about 8, compared to the case where it is composed only of spherical surfaces. As a result, the amount of light involved in image formation can be increased approximately 2.6 times.

As is well known, an aspheric surface has X in the optical axis direction and H in the direction orthogonal to the optical axis, C is the reciprocal of the center of curvature on the axis, K is the conic constant, and A21 A3? is the higher-order aspheric coefficient. A4g -----+
A1゜, A□□, A12. , and then
1T7°)+A2H2+A3H3+,,,10A1211
2+,.

This is a curved surface obtained by rotating the curve represented by around the optical axis.

Condition (2-I) is for obtaining good imaging performance when the aperture of a copying machine lens is increased by employing an aspherical surface on one or more lens surfaces.

When the aperture of the lens is increased, the peripheral rays of the imaging light beam are incident on the periphery of the lens, so that the angle of incidence of the peripheral rays becomes larger than the angle of incidence near the optical axis. For this reason, the refraction angle of peripheral rays is larger than that of rays near the optical axis, making coma flare more likely to occur.

In order to correct coma flare, it is sufficient to reduce the difference in the angle of incidence between the peripheral rays and the rays near the optical axis, and this can be done by employing an aspheric surface.

Conditioning the range of the conic constant of the adopted aspheric surface (2-I)
By setting the value within the range of , it is possible to increase the diameter of the lens and realize a copying machine lens with high contrast.

[Examples] Eight specific examples are listed below. Examples 1 to 3 are examples in which all lens surfaces are spherical, and Examples 4 to 8 are examples in which aspheric surfaces are used.

As illustrated in FIG. 2 showing the lens configuration of Example 1,
Counting from the object side (left side of the figure), the radius of curvature of the first lens surface (on-axis radius of curvature for an aspherical surface) is r8, the surface spacing is d1, and the j-th lens surface counting from the object side is Let the refractive index and Abbe number of the lens for the e-line be nj and ν, respectively.

Also, the composite focal length of the entire system and the focal lengths of the first group f, f
, gives the value for e-line (546,07 nm).

m is the magnification, Y is the object height, F/No is the brightness, and ω is the half angle of view (unit: twice).

Example 1 r:180. F/No=16. ω:16.3. Y:10
5.01m: 1.0°fl=260.45. fl/f
=1.447i ri ci, j
nj v.

1 50.128 10.000 1 1.
75844 52.302 61.395 10
．． 000 3 -48.497 10.000 2 1
．． 88814 40.804 -47.040 The lens configuration of Example 1 is shown in FIG. 2, and the aberration diagram is shown in FIG. 3. The broken line in the diagram of spherical aberration indicates the sine condition. In addition, the solid line in astigmatism is related to sagittal aberration, and the broken line is related to meridional.

Example 2 f=180. F/No=13. ω:16.3. Y=10
5.09m: 1.0°fl=235.76, f1/f
=1.3101r t d 1J n=
ν.

1 441.249 2.205 1 1.888
14 40.802 -397.550 30.479 3 -36.695 17.316 2 1.88
814 40.804 -40.655 The lens configuration of Example 2 is shown in FIG. 4, and the aberration diagram is shown in FIG. 5.

Example 3 r=180. F/No=13. ω:22.4. Y=14
8.59m=1.0°fl=345.26. H/f=
1.968i ri d□ J
nj ν.

1 40.603 16.996 1 1.
88814 40.802 37.440 30
．． 353 3 393.337 2.651 2 1
．． 84963 43.364 -510.007 The lens configuration of Example 3 is shown in FIG. 6, and the aberration diagram is shown in FIG. 7.

In Examples 4 to 8 listed below, one or more lens surfaces are aspherical.

The aspheric surfaces adopted in the following examples are marked with * to indicate that they are aspheric surfaces, and each aspheric surface has a conic constant and a higher-order aspheric surface A 4 * in addition to the axial curvature radius. A 6 +A,
, AIO is given to specify the aspherical shape.

Furthermore, in the representation of high-order aspherical coefficients, E and the number following it represent a power of 10. For example, E-13 means that the number before E is multiplied by 10-1.3.

Example 4 f=180. F/No=lO9ω:16.3. Y=10
5.09m: 1.0°fl=370.11. H/f=
2.0651 r, d, J nj
ν.

1 41.150 17.500 1 1
．． 88814 40. ．． 802 37.629
29.800 3 243.386 2.700 2 1
．． 88814 40.804" -2766,88
6 Aspherical 4th surface: K = -835, 267606°A4” 1.
19904E-7,AS”-9,14138E-11°A8=-1,56023E-13,AI.=6.31
The lens configuration of 137E-16 Example 4 is shown in FIG. 8, and the aberration diagram is shown in FIG. 9.

Example 5 f=180. F/No=10. m=16.3,
Y=105.0. m=1.0°fl=550.5,
fl/f=3.0581rid, ,
) nJ ν.

Do 35.664 17.500 1 1.743
32 53.062 30.895 24.930 3 168.813 7.569 2 1.723
17 54.124” -955,210 Aspherical first surface: ni=-0,101638° A4=-2,33120E-7, A6=-1,1394
4E-9.

A,=4.73079E-12,A,. =-7,44
729E-15 Aspherical 4th surface: 209.299635°A4”-5,58994E-8,A6” 1.9324
4E-10°A8=-1,52228E-13,A,
. =-7,43593E-16 The lens configuration of Practical Example 5 is shown in FIG. 10, and the aberration diagram is shown in FIG. 11.

Example 6 f=180. F/No.40. m=16.3, Y
:105. O, m-1, 0°fl=407.1, f
l/f=2.2621 r + d, J
n = ν, do 34.484 17.
500 1 1.71309 54.702'
30.866 29.5273" 225.572
2.973 2 1.73930 53.204”
-698,661 Aspherical first surface 2 = -0,039289°A, = -7,27793E-8, A6 = -5,3525
7E~10°As” 2.41450E 12.A□.

=-1,59091E-15 2nd side: to = 0.188
215゜A4" 5.25741E-7, As" 3.9321
8E-9.

Aa” 1.08384E 11.At.=-3,67
487E-13 3rd side: = 7.877021゜A4" 3.04518E-8, As"-8,5604
1E-11゜Aa"1.17983E43.Ato"
3.18992E-16 4th side: to = 72.976
744°A4=-5,02527E-8,A6=1.0840
0E-10゜As”4.44225E-14, At o
"-2,75989E-16 The lens configuration of Example 6 is shown in FIG. 12, and the aberration diagram is shown in FIG. 13.

Example 7 f480. F/No. 28, ω46.3, Y:
105.0. m=1.0°fl=522.54. f1
/f=2.9031rid,
j nj ν.

Do 36.379 17.500 1 1.758
44 52.302 31.745 26.425 3 174.875 6.075 2 1.758
44 52.304 -1293.948 Aspherical first surface: ni = -0,103262°A4"-5,14329E-9,Aa"-4,4393
9E～9゜As" 2.44999E-11, Ato"
-4,54495E-14 The lens configuration of Example 7 is
FIG. 4 shows an aberration diagram, and FIG. 15 shows an aberration diagram.

Example 8 f=180. F/No=10. m=22.4. Y:14
8.59m=1.0°fl=335.73. fl/f
=1.8651 r= d; j
nj ν.

1 34.378 14.808 1 1.758
44 52.302" 32.360 32.04
73 243.817 3.145 2 1.86
584 42.214-24313.276 Aspherical second surface: ni = 0.178133° A4 = -1,55356E-7, A6 = 4.3111
1E-8.

As”-5,89179E-10,A□.=2.77
The lens configuration of Example 8 of 158E-12 is shown in FIG. 16, and the aberration diagram is shown in FIG. 17.

The performance of each example is good.

[Effects of the Invention] As described above, according to the present invention, a novel lens for a copying machine can be provided.

Although this lens has two elements in two groups, which is an extremely small number of lenses, it has extremely good performance.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the configuration of a lens for a copying machine according to the present invention, and FIGS. 2 to 17 are lens configuration diagrams and aberration diagrams related to each embodiment. Chi 7 -43 of both Kuni and Z-phantom Otogo 8 - Coma aberration F/Molθ Y= is 5θ γ□m5.0 Distortion aberration (”/-) Coma aberration 0 F/No/θ Y=/θ5θ Y= 〃5θ Spherical aberration Astigmatism Distortion qK1 and (“〉(Comma aberration F/N0 Y= 10f, θ Y= 105.θ gfD Aberration Astigmatism Base S aberration ('/-Comma aberration F//% Jty, g Y=lρ5θ Y=lθδθ 46- Comatic aberration F/N010 Y=#5 Y-44flJ Beady aberration Astigmatism Distortion tIB

Claims (1)

[Claims] 1. A lens for forming a light image of a document on a photoreceptor surface in a copying machine, the lens having first and second groups arranged sequentially from the object side to the image side. Therefore, the first group and the second group are both positive lenses, and when the focal length of the first group is f_1 and the combined focal length of the entire system is f_1, (1-I)1 A lens for a copying machine, characterized in that it satisfies the following condition: <f_1/f<3.5. 2. Claim 1 is characterized in that at least one lens surface is an aspherical surface, and the conic constant K of the adopted aspherical surface satisfies the following condition: (2-I)-900<K<300. Copying machine lens.