JP3181944B2 - Copier lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens for a copying machine.

[0002]

2. Description of the Related Art With the miniaturization of copiers, there has been a demand for compact, low-cost and light-weight copier lenses.
As a lens for a copying machine that meets these requirements, a completely symmetrical lens having a four-group, four-element configuration is known. However, this copier lens has a small number of four lenses, and since it is a perfect symmetric type, the number of parameters that can be used for design is small.
There is a problem that it is difficult to increase the diameter.

On the other hand, as an asymmetrical type copying machine lens having a four-group configuration, a lens disclosed in Japanese Patent Publication No. Sho 60-51091 is known.
Has been performed for the purpose of F / N
o: 5.6 and the half angle of view: 19 degrees, and enlargement of the aperture and widening of the angle of view are not always sufficient.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and provides a lens for a copying machine having a four-element structure, a small number of elements, and a wide angle of view and a large aperture. With the goal.

[0005]

As shown in FIG. 1, a lens for a copying machine according to the present invention sequentially moves from an object side (FIG. 1, left side) to an image side (FIG. 1, right side). 1 lens, 2nd
Lens 2, third lens 3, and fourth lens 4,
The first lens 1 is a positive lens, the second lens 2 is a negative lens, the third lens 3 is a biconcave lens, and the fourth lens 4 is a biconvex lens.

As shown in FIG. 1, the lens configuration is a three-group, four-lens configuration in which a first lens 1 and a second lens 2 are joined.

The combined focal length of the entire system is f, the combined focal length of the first and second lenses is f _1,2 , the radius of curvature of the object-side lens surface of the third lens is R _3,1 , and the image-side lens surface is When the radius of curvature is R _3,2 , these conditions (1-1) 0.5f <f _1,2 <1.0f (1-2) 1.0 <| R _3,1 / R _{3, 2} | <1.9 is satisfied. As is clear from the condition (1-2), the third
Comparing the radius of curvature of each lens surface of the lens, the absolute value of the radius of curvature of the object-side lens surface is larger than the radius of curvature of the image-side lens surface.

The combined focal length of the entire system: f, first and second
Lens composite focal length _{of: f 1, 2,} the condition _(2-1) 0.7f <it is desirable to satisfy the f 1,2 <1.0f (claim 2).

[0009]

The condition (1-1) is a condition for determining the basic power distribution of the lens for a copying machine according to the present invention. When the value exceeds the upper limit of the condition (1-1), the Petzval sum becomes too large, and the image surface falls to the negative side, and astigmatism increases. If the lower limit is exceeded, the Petzval sum becomes too small and the image plane falls to the positive side, and the field curvature increases. Therefore, out of the range of the condition (1-1), good imaging performance cannot be obtained over the entire screen.

The condition (1-2) is a condition for correcting coma. When the value exceeds the upper limit of the condition (1-2), the coma of the upper ray when the object height is made negative becomes positive, and the form of the coma becomes convex downward. Above the lower limit, coma flare increases. Therefore, out of the range of the condition (1-2),
MTF deteriorates.

The combined focal length f of the whole system and the combined focal lengths f ₁ and f _{1 of} the first and second lenses are slightly smaller than the condition (1-1) and satisfy the condition (2-1). By doing so, the imaging performance can be further improved.

[0012]

EXAMPLES Four specific examples will be described below. In each embodiment, an "aperture" is provided between the second lens and the third lens.

In each of the embodiments, the i-th position is counted from the object side.
The radius of curvature of the i-th surface (including the stop surface) is r _i , the distance between the i-th surface and the (i + 1) -th surface on the optical axis is d _i , the refractive index of the j-th lens counted from the object side, and Abbe numbers are represented by n _j and v _j , respectively. F is the focal length of the entire system, f
_{1, 2} are the combined focal lengths of the first and second lenses, R _3,1 is the radius of curvature of the object side lens surface of the third lens, R _3,2 is the radius of curvature of the image side lens surface of the third lens, F / No denotes brightness, m denotes magnification, and ω denotes angle of view.

[0014] Example 1 f = 190.0mm, F / No = 5.4, m = 1.0, ω = 21.5 ( _{degrees) i r i d i j n} j ν j 1 55.284 15. 0 1 1.72000 46.03 2 -1134.553 4.838 2 1.6258 35.7 3 73.256 1.766 4 (Aperture) 1.644 5 -73.368 3.465 3 1.63636 35 .38 6 66.1 2.922 7 112.929 10.365 4 1.72000 46.038 -69.605

R _3,1 = r ₅ , R _3,2 = r ₆ Value of conditional expression f _1,2 = 0.899f, | R _3,1 / R _{3,2 |} = 1.110

[0016] Example 2 f = 190.0mm, F / No = 5.4, m = 1.0, ω = 21.5 ( _{degrees) i r i d i j n} j ν j 1 52.293 15. 0 1 1.69700 48.51 2 -449.805 4.5 2 1.60342 38.01 3 71.494 1.74 (aperture) 1.55 -80.001 2.53 1.62004 36 .26 6 61.25 3.5 7 111.887 11.24 1.69700 48.518-8-73.4

R _3,1 = r ₅ , R _3,2 = r ₆ Values of conditional expressions f _1,2 = 0.824f, | R _3,1 / R _3,2 | = 1.306

[0018] Example 3 f = 190.0mm, F / No = 5.4, m = 1.0, ω = 21.5 ( _{degrees) i r i d i j n} j ν j 1 52.621 15. 0 1 1.74400 44.79 2 724.589 4.768 2 1.69803 34.48 3 70.599 1.798 4 (aperture) 1.145 5 -105.708 4.115 3 1.66680 33. 05 6 59.088 3.175 7 100.917 15.0 4 1.74400 44.79 8 -90.819

R _3,1 = r ₅ , R _3,2 = r ₆ Value of conditional expression f _1,2 = 0.820f, | R _3,1 / R _3,2 | = 1.789

[0020] Example 4 f = 190.0mm, F / No = 5.4, m = 1.0, ω = 21.5 ( _{degrees) i r i d i j n} j ν j 1 55.443 15. 0 1 1.67790 50.722 2-126.025 6.699 2 1.55951 39.21 3 81.514 1.357 4 (Aperture) 1.513 5 -73.209 3.03 1.595551 39 .21 6 65.061 4.422 7 132.734 9.546 4 1.67790 50.72 8 -70.399

R _3,1 = r ₅ , R _3,2 = r ₆ Values of conditional expressions f _1,2 = 0.786f, | R _3,1 / R _3,2 | = 1.125

The aberration diagrams for the first to fourth embodiments are shown sequentially in FIGS. In these aberration diagrams,
Indicates that it relates to the d, C, and F lines, respectively. In the diagram of spherical aberration, a solid line indicates spherical aberration, and a broken line indicates a sine condition. The solid line in the figure of astigmatism represents a sagittal ray, and the broken line represents a meridional ray. Y represents the image height. In each embodiment, on-axis and off-axis aberrations are well-balanced, and coma has a small coma flare and achieves high contrast despite the aperture efficiency of about 100%.

[0023]

As described above, according to the present invention, a novel lens for a copying machine can be provided. Although this lens has a four-element configuration and a small number of components, it is asymmetrical and has a large degree of freedom in aberration correction parameters. Therefore, a relatively inexpensive glass material is used, and a large aperture, a wide angle of view, and approximately 100% Aperture efficiency can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a lens configuration according to the present invention.

FIG. 2 is an aberration diagram relating to Example 1.

FIG. 3 is an aberration diagram relating to Example 2.

FIG. 4 is an aberration diagram relating to Example 3.

FIG. 5 is an aberration diagram relating to Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-81316 (JP, A) JP-A-57-6820 (JP, A) JP-A-57-161823 (JP, A) JP-A-58-81 9118 (JP, A) JP-A-58-220116 (JP, A) JP-A-59-211013 (JP, A) JP-A-61-277914 (JP, A) JP-A-61-292119 (JP, A) JP-A-62-9310 (JP, A) JP-A-62-25719 (JP, A) JP-A-1-261615 (JP, A) JP-A-3-100512 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (2)

(57) [Claims] A first lens, a second lens, a second lens, a third lens, a biconcave lens, a fourth lens, lens is biconvex lens, the first,
It is a three-group, four-element configuration in which the second lens is cemented. The combined focal length of the entire system is f, and the combined focal length of the first and second lenses is f.
₁ , ₂ , the radius of curvature of the object side lens surface of the third lens is R
_3,1, when the radius of curvature of the image side lens surface and _{R 3,2,} these are conditions _{(1-1) 0.5f <f 1,2 <} 1.0f (1-2) 1.0 < | R _3,1 / R _3,2 | <1.9. 2. A copying lens according to claim 1, wherein f, f ₁ , ₂ satisfy the condition (2-1) 0.7f <f _1,2 <1.0f. Lens for copier.