JPH06118302A - Wide-field-angle, large-diameter lens system for copying - Google Patents

Abstract

PURPOSE:To greatly reduce the size of an optical system of the lens system of specific condition by satisfying specific expressions as to focal lengths, radii of curvatures of surfaces, etc. CONSTITUTION:This lens system of six-group, eight-element constitution consists of a 1st positive meniscus lens group 1 which has convex surfaces on the object side, a 2nd negative meniscus lens group 2 which has a convex surface on the object side, and a 3rd cemented lens group 3 of a negative meniscus lens and a positive meniscus lens which have convex surfaces on the object side, and lenses which are arranged completely symmetrically with said lens groups about a center stop S in order from the object side. Then conditional inequalities I, II, and III hold, where (f) is the composite focal length of the whole system, f1 and f6 the focal length of the 1st lens group 1 and 6th lens group 6, f3 and f4 the focal lengths of the 3rd lens group and 4th lens group 4, and ri the radius of curvature of an (i)th surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens system for a copying machine, and more particularly to a lens system having a wide field angle and a bright F number.

[0002]

2. Description of the Related Art A copying lens system used in a copying machine is
For example, as seen in Japanese Patent Laid-Open No. 1-217311 and the like, a lens system arranged in perfect symmetry with respect to a diaphragm has come to be widely used. This is a perfect symmetry with respect to the diaphragm in terms of manufacturing ease and cost.

[0003]

By the way, the copying lens system of the above-mentioned example is a lens system of a complete symmetric type with 8 groups and 8 elements, and has a half angle of view of about 23 degrees and an F number of about 4. The lens system has a large total lens length (Σd). The present invention shortens the overall lens length while having specifications almost equivalent to those of the lens system described in Japanese Patent Laid-Open No. 1-217311, and corrects various aberrations to provide a high contrast from the on-axis to the peripheral portion of the screen. A wide-angle lens system for obtaining a wide-angle lens that has a half-angle of view of about 23 degrees or more even though it has a wide-angle lens. The purpose is to

[0004]

According to the present invention, in order from the object side, a first lens group including a first lens of a positive meniscus lens having a convex surface facing the object side and a negative meniscus having a convex surface facing the object side are provided. The second lens group consisting of the second lens of the lens, the third lens group of the negative meniscus lens with the convex surface facing the object side.
In a lens system of a 6-group 8-element configuration, which is composed of a third lens group of a cemented lens of a lens and a fourth lens of a positive meniscus lens having a convex surface facing the object side, and is arranged in perfect symmetry with respect to the central diaphragm, The combined focal length of the entire system is f, the focal lengths of the first lens group and the sixth lens group are f ₁ and f ₆ , the focal lengths of the third lens group and the fourth lens group are f ₃ ,
When f _{4 is} the radius of curvature r _i of the i-th surface

[0005]

[Equation 8]

[0006]

[Equation 9]

[0007]

[Equation 10]

A wide-angle, large-diameter copying lens system characterized by satisfying the conditional expression (1).

According to a second aspect of the present invention, the first lens group is composed of the first lens of the positive meniscus lens having the convex surface facing the object side, and the convex surface is the object side. Second negative meniscus lens placed toward
A lens group, a third lens group consisting of a third lens of a negative meniscus lens with the convex surface facing the object side, and a fourth lens group of a positive meniscus lens with the convex surface facing the object side,
In a lens system with 8 groups and 8 elements, which are arranged in perfect symmetry with respect to the central diaphragm, the combined focal length of the entire system is f,
The focal length of the lens group is f ₁ , and the radius of curvature r of the i-th surface is r
_When the Abbe number at the d line of the glass material of the i-th and i-th lens is ν _i

[0010]

[Equation 11]

[0011]

[Equation 12]

[0012]

[Equation 13]

[0013]

[Equation 14]

[0014]

[Examples] In recent years, there has been an increasing demand for high speed and high image quality of copying machines.
There has been a demand for a lens system which has a high F-number and a high contrast at all angles of view.
However, generally, when trying to make the lens system brighter, the outer diameter of the lens becomes large, which hinders downsizing of the device. On the other hand, by shortening the overall length of the lens system, it is possible to suppress an increase in the lens outer diameter.

The structure of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the wide-angle-large-aperture copying lens system of the present invention has a first lens group consisting of a positive meniscus first lens with the convex surface facing the object side in order from the object side, and the convex surface facing the object side. A second lens group including a negative meniscus second lens, a third lens group that is a cemented lens of a negative meniscus third lens having a convex surface facing the object side and a positive meniscus fourth lens having a convex surface facing the object side, and an aperture stop S A fourth lens group that is the same as the third lens group, a fifth lens group that is the same as the second lens group, and a sixth lens group that is the same as the first lens group.
This is a lens system composed of eight elements.

The composite focal length of the entire lens system for wide-angle wide-aperture copying is f, the focal lengths of the first lens unit and the sixth lens unit are f ₁ and f ₆ , the third lens unit and the fourth lens unit. Let f ₃ , f _{4 be} the focal lengths of the group and r _{i be the} radius of curvature of the i-th surface.
And when

[0017]

[Equation 15]

[0018]

[Equation 16]

[0019]

[Equation 17]

The following conditions are satisfied.

Conditional expression (1) above is a necessary condition for improving the alignment of the image planes while keeping the overall length of the lens system short. If the lower limit value is exceeded, the meridional image plane will go under and sagittal coma will increase. To do. In addition, the Petzval sum becomes too small and the image quality deteriorates. on the other hand,
When the upper limit is exceeded, the meridional image plane becomes over and the sagittal image plane becomes under. In addition, the total length of the lens system becomes large and it becomes impossible to make it compact.

The above conditional expression (2) is a condition for correcting the flare of coma aberration which affects the MTF performance. When the lower limit value is exceeded, the coma flare of sagittal increases and the MTF in the low frequency region decreases. Resulting in. On the contrary, when the upper limit is exceeded, the meridional frame flare increases and the MTF decreases as in the previous case.

The above conditional expression (3) is a necessary condition for increasing the diameter of the lens system and for flattening the image surface. When the lower limit value is exceeded, the sagittal image surface becomes under and the Petzval sum is reduced. It becomes large, the image surface property becomes poor, and it becomes impossible to increase the aperture. On the other hand, when the upper limit is exceeded, the meridional image plane becomes over, and the image plane becomes poorly aligned as before.

As described above, the wide-viewing-angle large-diameter copying lens system of the present invention has a half field angle of about 23 by arranging a pair of cemented lenses before and after the diaphragm S inside the topogon type.
A wide angle can be achieved at the same time, and at the same time a large aperture can be achieved, and high contrast can be obtained at all angles of view.

Next, the second aspect of the present invention will be described. The wide-angle, large-diameter copying lens system according to the second aspect of the present invention comprises, as shown in FIG. 9, a first group consisting of a positive meniscus first lens with the convex surface facing the object side in order from the object side, and the convex surface facing the object side. Second negative meniscus lens consisting of a second lens
The third group in which the third group including the negative meniscus third lens with the convex surface facing the object side and the fourth group including the positive meniscus fourth lens with the convex surface facing the object side are arranged in perfect symmetry with respect to the diaphragm S. The fourth lens group, which is the same as the lens group, and the second lens group
This is a lens system having a structure of 8 groups of 8 lenses, which includes a fifth lens group that is the same as the lens group and a sixth lens group that is the same as the first lens group.

The composite focal length of the entire lens system for wide-angle wide-aperture copying is f, and the focal lengths of the first and sixth groups are f ₁ and
f ₆ , the refractive index at the d-line of the i-th lens is n _i , the i-th lens
When the radius of curvature of the th surface is r _i ,

[0027]

[Equation 18]

[0028]

[Formula 19]

[0029]

[Equation 20]

[0030]

[Equation 21]

The following conditions are satisfied.

The conditional expression (4) is a necessary condition for improving the alignment of the image planes while keeping the overall length of the lens system short. If the lower limit value is exceeded, the meridional image plane will go under and sagittal coma will increase. To do. In addition, the Petzval sum becomes too small and the image quality deteriorates. on the other hand,
When the upper limit is exceeded, the meridional image plane becomes over and the sagittal image plane becomes under. In addition, the total length of the lens system becomes large and it becomes impossible to make it compact.

The above conditional expression (5) is a condition for correcting flare of coma aberration affecting the MTF performance. When the lower limit value is exceeded, the coma flare of sagittal increases and the MTF in the low frequency region decreases. To do. On the other hand, if the upper limit is exceeded, the meridional frame flare increases and M
TF decreases.

The above conditional expressions (6) and (7) are conditions for correcting the flare of the image surface property and the coma aberration, and
If the lower limit is exceeded, the Petzval sum will increase, the field curvature will worsen, and coma flare will increase and MTF will decrease.

As described above, in the wide-angle, large-diameter copying lens system of the present invention, the third lens group and the fourth lens group each consisting of two lenses are arranged inside and outside the stop S inside the topogon type. By doing so, it is possible to widen the angle of view to about 23 °, at the same time to achieve a large aperture, and to obtain high contrast at all angles of view.

The concrete numerical values of the first and second embodiments of the invention of claim 1 and the third and fourth embodiments of the invention of claim 2 will be described below. The results are shown in Tables 1 to 4. These tables show numerical values on each surface of the radius of curvature r _i of the i-th surface, the axial upper surface distance d _i , the refractive index N _i of the glass material at the d line, and the Abbe number ν _i of the glass material in order from the object side. .

An aberration curve at the same magnification as in Example 1 is shown in FIG. 2 together with lateral aberration. Further, the aberration curve at the time of reduction of 0.61 × is shown in FIG. 3 together with the lateral aberration curve.
Furthermore, the aberration curve at the time of expansion of 1.64 × is shown in FIG. 4 together with the lateral aberration curve. Similarly, FIG. 6 to FIG. 8 show each aberration curve at the same magnification of the second embodiment, at the time of reduction (0.61 ×), and at the time of enlargement (1.64 ×), and at the same magnification of the third embodiment. The aberration curves at the time of reduction (0.61 ×) and at the time of enlargement (1.64 ×) are shown in FIGS. 10 to 12 at the same magnification of the fourth embodiment, at the time of reduction (0.61 ×), and at the time of enlargement (0.61 ×). The respective aberration curves for 1.64 ×) are shown in order in FIGS. 14 to 16.
The value of K in each lateral aberration curve diagram indicates the object height.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

[0042]

As described above, in the high angle-of-view copying lens system of the present invention, by arranging the two cemented lens groups close to the central diaphragm S so as to sandwich the diaphragm S symmetrically, Despite maintaining the advantages of the Topogon type, the angle of view (2ω) is 45.6 degrees, which is a very high angle of view, but there is little curvature of the image surface, and astigmatism is very good over the entire image surface. It is a corrected lens system for copying. Further, also in zooming, various aberrations are satisfactorily corrected in the zooming range of 0.5 × to 2.0 ×, high contrast is achieved in the low spatial frequency region, and high image quality is achieved, thus making a compact lens system. Has become.

[Brief description of drawings]

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

FIG. 2 is an aberration curve diagram at the same magnification of Example 1 of the copying lens of the present invention,

FIG. 3 is an aberration curve diagram at the time of reduction (−0.61 ×) in Example 1 of the copying lens of the present invention,

FIG. 4 is an aberration curve diagram of Example 1 of the copying lens of the present invention at the time of enlargement (−1.64 ×);

FIG. 5 is a sectional view showing the structure of a second embodiment of the copying lens of the present invention,

6 is an aberration curve diagram of Example 2 of the copying lens of the present invention at the same magnification, FIG.

FIG. 7 is an aberration curve diagram at the time of reduction (−0.61 ×) of Example 2 of the copying lens of the present invention,

FIG. 8 is an aberration curve diagram of Example 2 of the copying lens of the present invention at the time of expansion (−1.64 ×);

FIG. 9 is a cross-sectional view showing the configuration of Embodiment 3 of the copying lens of the present invention,

FIG. 10 is an aberration curve diagram of Example 3 of the copying lens of the present invention at the same magnification,

FIG. 11 is an aberration curve diagram at the time of reduction (−0.61 ×) in Example 3 of the copying lens of the present invention,

FIG. 12 is an aberration curve diagram of Example 3 of the copying lens of the present invention at the time of enlargement (−1.64 ×),

FIG. 13 is a sectional view showing the structure of Embodiment 4 of the copying lens of the present invention;

FIG. 14 is an aberration curve diagram of Example 4 of the copying lens of the present invention at the same magnification,

FIG. 15 is an aberration curve diagram at the time of reduction (−0.61 ×) in Example 4 of the copying lens of the present invention,

FIG. 16 is an aberration curve diagram of Example 4 of the copying lens of the present invention at the time of enlargement (−1.64 ×).

Claims (2)

[Claims] 1. A first lens group consisting of a first lens of a positive meniscus lens with a convex surface facing the object side, and a second lens of a negative meniscus lens with a convex surface facing the object side, in order from the object side.
A second lens group consisting of a lens, and a third lens group of a cemented lens of a negative meniscus lens third lens having a convex surface facing the object side and a positive meniscus lens fourth lens having a convex surface facing the object side. , In a lens system of 8 elements in 6 groups, which are arranged in perfect symmetry with respect to the central diaphragm, the combined focal length of the entire system is f, and the focal lengths of the first lens group and the sixth lens group are f ₁ and f ₆ , The focal lengths of the third lens group and the fourth lens group are f ₃ and f ₄ , and the radius of curvature r of the i-th surface is r
_{Let i} be [Equation 1] [Equation 2] [Equation 3] A wide-angle, large-diameter copying lens system characterized by satisfying the conditional expression of. 2. A first lens group consisting of a first lens of a positive meniscus lens having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side, in order from the object side. Two lens groups, a third lens group consisting of a third lens of a negative meniscus lens with the convex surface facing the object side,
In a lens system of 8 groups and 8 elements, which is composed of a fourth lens unit of a positive meniscus lens having a convex surface facing the object side and is arranged symmetrically with respect to the central diaphragm, the combined focal length of the entire system is f, The focal length of the first lens unit is f ₁ , the radius of curvature r _i of the i-th surface, and d of the glass material of the i-th lens.
When the Abbe number on the line is ν _i , [Equation 5] [Equation 6] [Equation 7] A wide-angle, large-diameter copying lens system characterized by satisfying the conditional expression of.