JP2711128B2 - Copier lens - Google Patents

Description

The present invention relates to a lens for a copying machine.

[Related Art] With the miniaturization and high performance of copiers, compact and high performance lenses for copiers are required. In order to reduce the size of the copying machine, it is necessary that the focal length of the copying machine lens be short and the half angle of view be large. It is also desirable that the copier lens itself be compact, and for that purpose, it is desirable that the entire length of the lens be short. Furthermore, in order to minimize the decrease in the amount of light at the periphery of the image plane due to the cosine fourth power rule, it is desirable that the aperture efficiency is 100% up to the periphery, and within a necessary angle of view to obtain a copied image with good contrast. It is necessary to have high contrast.

In addition, it is better if the lens for the copier is made brighter,
Up to F / No.8 is allowed with the improvement of the photoconductor sensitivity.

Conventionally, a compact and low-cost copier lens realized in a three-group, three-element configuration is disclosed in JP-A-63-180924.

[Problems to be Solved by the Invention] The above-mentioned three-group, three-element copier lens has an F / No. 8 and an effective half angle of view of about 21 degrees.

An object of the present invention is to provide a copier lens having a three-group, three-element structure and a brighter and wider angle of view, similarly to the above-mentioned conventional lens.

[Means for Solving the Problems] Hereinafter, the present invention will be described.

As shown in FIG. 1, the copier lens of the present invention has a first lens from the object side (left side in FIG. 1) toward the image side (right side in FIG. 1).
The group 10, the second group 12, and the third group 14 are sequentially arranged.

The first group 10 has a convex meniscus lens having a convex surface facing the object side, the second group 12 has a biconcave lens, and the third group 14 has a three-group three-lens structure.

When the combined focal length of the entire system is f, the radius of curvature of the i-th lens surface from the object side is R _i (i = 1 to 6), and the focal length of the third lens unit is f ₃ , these are (I) 0.32 <f ₃ /f<0.34 (II) 1.6 <−R ₅ / R ₆ <2.5

[Operation] Of the above conditions, the condition (I) is for correcting spherical aberration and distortion. When the value goes below the lower limit of the condition (I), the positive refractive power increases, the negative distortion increases, and it becomes difficult to correct both the spherical aberration and the distortion. When the value exceeds the upper limit of the condition (I), the positive distortion increases, and conversely,
Correction becomes difficult.

Condition (II) is a condition relating to the lens shape of the third group. The third lens unit has a strong positive power. If the upper or lower limit of the condition (II) is exceeded, the load on one surface becomes too large, and it becomes difficult to suppress various aberrations.

Therefore, to properly correct each aberration, the conditions (I),
The range of (II) is appropriate.

[Examples] Hereinafter, three specific examples will be given.

In each example, the radius of curvature of the i-th lens surface from the object side R _i (i = 1 to 6), between the i-th surface distance D _i
(I = 1 to 5), the refractive index and Abbe number of the lens of the j-th group are represented by N _j and ν _j (j = 1 to 3), respectively. Also,
The focal length f of the entire system is normalized to 1, and a quantity having a length dimension represents a ratio to the normalized focal length f. further
F / No is the brightness of the lens, ω is the half angle of view, m is the magnification, and Y is the object height.

Example 1 f = 1, F / No = 7, Y = 0.833, ω = 23 degrees (m = 1) i R _i D _i j N _j v _j 1 0.237 0.086 1 1.713 53.84 2 0.363 0.009 3 −0.462 0.019 2 1.6398 34.48 4 0.287 0.022 5 0.605 0.031 3 1.7 48.08 6 −0.371 Conditional value: f ₃ /f=0.333, −R ₅ / R ₆ = 1.63 FIG. 2 shows an aberration diagram of the first embodiment at the same magnification. Also,
FIG. 3 and FIG. 4 show respective aberration diagrams at the time of reduction and enlargement of the first embodiment.

In the aberration diagrams shown in FIG. 2 and subsequent figures, SA and SC indicate spherical aberration (solid line) and sine condition (dashed line), and DS and DM indicate astigmatism in the radial direction (solid line) and the tangential direction (dashed line). Aberration and DIST indicate distortion (%), COMA indicates tangential coma, and DZ indicates radial coma. Also,
,, Are the d-line (587.56 nm) and c-line (656.27
nm) and F line (486.13 nm).

The magnification at the time of reduction is m = 0.5, and the magnification at the time of enlargement is m = 0.5.
2.

Example 2 f = 1, F / No = 7, Y = 0.834, ω = 23 degrees (m = 1) i R _i D _i j N _j v _j 1 0.244 0.083 1 1.713 53.84 2 0.376 0.015 3 −0.403 0.015 2 1.6398 34.48 4 0.309 0.023 5 0.674 0.03 3 1.7 48.08 6 −0.337 Conditional value: f ₃ /f=0.325, −R ₅ / R ₆ = 2.0 FIG. 5 shows an aberration diagram of the second embodiment at the same magnification. Also,
FIG. 5 and FIG. 7 show aberration diagrams at the time of reduction and enlargement of the second embodiment.

Example 3 f = 1, F / No = 7, Y = 0.834, ω = 23 degrees (m = 1) i R _i D _i j N _j v _j 1 0.252 0.091 1 1.713 53.84 2 0.407 0.013 3 −0.401 0.012 2 1.6398 34.48 4 0.32 0.024 5 0.772 0.027 3 1.7 48.08 6 −0.334 Conditional value: f ₃ /f=0.337, −R ₅ / R ₆ = 2.31 FIG. 8 shows an aberration diagram of the third embodiment at the same magnification. Also,
9 and 10 show aberration diagrams of the third embodiment at the time of reduction and enlargement.

 In each embodiment, various aberrations are satisfactorily corrected.

[Effects of the Invention] As described above, according to the present invention, a novel lens for a copying machine can be provided. This copier lens has a simple structure with three elements in three groups, but can be used in a wide magnification range of, for example, 0.5 to 2.0 times, is brighter than conventional F / No7, and has an aperture efficiency of 100% up to the outermost periphery. While maintaining this, high contrast can be maintained up to a half angle of view of 23 degrees.

[Brief description of the drawings]

FIG. 1 is a view showing a lens configuration of the present invention, FIGS. 2 to 4 are aberration diagrams at the same magnification, reduction, and enlargement of the first embodiment, and FIGS. Aberration diagram at the time of magnification, reduction, enlargement,
8 to 10 are aberration diagrams at the same magnification, reduction, and enlargement of the third embodiment. 10: First group, 12: Second group, 14: Third group

Claims (1)

(57) [Claims] A first group to a third group from an object side to an image side;
The first group is a three-element three-lens configuration in which the first group is a convex meniscus lens with the convex surface facing the object side, the second group is a biconcave lens, and the third group is a biconvex lens. The focal length is f, the radius of curvature of the i-th lens surface from the object side is R _i (i = 1 to 6), and the focal length of the third lens unit is
When the f _3, it is _{(I) 0.32 <f 3 /f<0.34} (II) 1.6 <-R 5 / R 6 < and satisfies 2.5 condition: lens copiers.