JPH09113802A - Reading lens - Google Patents

Abstract

(57) An object of the present invention is to obtain a reading lens having a wide angle of view, a high MTF at a high frequency, and a well-corrected chromatic aberration while maintaining a large aperture. A first group of positive meniscus first lenses 1 having a convex surface facing the object side in order from the object side, a second group of positive second lenses 2 and a negative third lens 3, and a negative first lens. The third lens group includes the fourth lens 4 and the positive fifth lens 5, and the fourth group includes the positive sixth lens 6. The third lens has a refractive index of 1.65412 at d line and an Abbe number of 39. .6
The following conditions are satisfied by using the optical glass of No. 1 and the fourth lens of which the refractive index at the d-line is 1.65412 and the Abbe number is 39.6. (1) 0.72f <f1 <1.02f (2) −0.87f <f23 <−0.73f where f is the combined focal length of the entire system (e line), and f1 is the first
The focal length of the group (first lens) (e line), f23 is the combined focal length of the second and third groups (e line)

Description

Detailed Description of the Invention

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a reading lens which can be used for a facsimile, a digital copying machine, an image scanner and the like.

[0002]

2. Description of the Related Art A reading lens (hereinafter, referred to as a "scanner lens") used in a facsimile, a digital copying machine, an image scanner, etc. Used to read information of

In recent years, for reading color images, 3
Image sensors such as line one-chip CCDs have been developed. In such a color image reading sensor, light receiving elements carrying red, green, and blue filters are arranged on one chip, and an image of a color document is formed on the light receiving surface of the sensor. An image can be separated into three primary colors and signalized. In order to read a color original satisfactorily with such an image sensor, it is necessary to match the image forming positions of red, green, and blue in the optical axis direction. Therefore, in the case of a color original, it is necessary to correct chromatic aberration of the reading lens in a wide wavelength range more favorably than in a monochrome original.

In addition, it is desired that the scanner lens has a wide angle of view in order to reduce the size of the machine body and has a large diameter in order to achieve high-speed reading of a document.

[0005]

As this type of lens, a Gauss-type lens having four groups and six elements has been often used. As a conventional example of a lens having a structure of four groups and six elements,
Japanese Patent Application Laid-Open No. Hei 6-109971 discloses an F-number which is as dark as 5 and cannot meet the demand for high-speed reading. As a conventional example of a lens having four groups and six elements, there is a lens described in JP-A-4-163508.
It is as narrow as 7.5 mm, and cannot cope with downsizing of the machine body.

In view of the above problems of the prior art, the present invention is a Gauss type of four groups and six elements, and has a brightness of F4.
It is an object of the present invention to provide a reading lens having a wide angle of view of 19.9 ° at a half angle of view, a high MTF at a high frequency, and a good correction of chromatic aberration, while maintaining a large aperture of 5.

[0007]

As shown in FIG. 1, a reading lens according to the present invention comprises a first lens unit, a second lens unit, and a third lens unit from the object side to the image side (from left to right in FIG. 1). , And the fourth lens group are sequentially arranged. The first lens 1 forming the first group is a positive meniscus lens having a convex surface facing the object side. The second group includes a second lens 2 and a third lens 3
And a cemented lens. The second lens 2 is a positive lens, and the third lens 3 joined to the image plane side is a negative lens. The third group is a cemented lens of the fourth lens 4 and the fifth lens 5. The fourth lens 4 is a negative lens, and the fifth lens 5 joined to the image plane side is a positive lens. The sixth lens 6 forming the fourth group is a positive lens. Therefore, the whole is composed of six groups in four groups. In FIG. 1, reference numeral 7 denotes a document placing glass, and reference numeral 8 denotes a cover glass of the solid-state imaging device, both of which are made of parallel flat glass.

In the reading lens according to the first aspect, an optical glass having a refractive index at d-line of 1.65412 and an Abbe number of 39.6 is used for the third lens 3, and a d lens is used for the fourth lens 4. An optical glass having a refractive index of 1.65412 and an Abbe number of 39.6 in the line is used, and the combined focal length of the entire system is f, the focal length of the first group is f1, and the second focal length is f1.
When the combined focal length of the group and the third group is f23, the following condition is satisfied: (1-1) 0.72f <f1 <1.02f (1-2) −0.87f <f23 <−0.73f . Focal length under these conditions:
f, f1, and f23 are all for the “e line”.

In the reading lens according to the second aspect, the third lens 3 is made of an optical glass having a refractive index at d-line of 1.65412 and an Abbe number of 39.6, and the fourth lens 4 is made of d glass. An optical glass having a refractive index of 1.613110 and an Abbe number of 44.4 in the line is used. The combined focal length of the entire system is f, the focal length of the first group is f1, and the second group is f1.
Assuming that the combined focal length of the group and the third group is f23, the following condition is satisfied: (2-1) 0.64f <f1 <0.9f (2-2) -1.2f <f23 <-0.38f . Focal length under these conditions:
f, f1, and f23 are all for the “e line”.

In the reading lens according to the third aspect, the third lens 3 is made of an optical glass having a refractive index at d-line of 1.613110 and an Abbe number of 44.4, and the fourth lens 4 is made of d glass. An optical glass having a refractive index of 1.65412 and an Abbe number of 39.6 in the line is used, and the combined focal length of the entire system is f, the focal length of the first group is f1, and the second focal length is f1.
Assuming that the combined focal length of the group and the third group is f23, the following condition is satisfied: (3-1) 0.86f <f1 <1.12f (3-2) -1.05f <f23 <-0.7f . Focal length under these conditions:
f, f1, and f23 are all for the “e line”.

In the reading lens according to the fourth aspect, the third lens 3 is made of an optical glass having a refractive index at d-line of 1.613110 and an Abbe number of 44.4, and the fourth lens 4 is made of d glass. An optical glass having a refractive index of 1.613110 and an Abbe number of 44.4 in the line is used. The combined focal length of the entire system is f, the focal length of the first group is f1, and the second group is f1.
When the combined focal length of the third group and the third group is f23, the condition of (4-1) 0.79f <f1 <1.12f (4-2) -1.24f <f23 <-0.59f is satisfied. . Focal length under these conditions:
f, f1, and f23 are all for the “e line”.

Next, the conditional expressions in each claim will be described. The conditional expression (1) in each claim defines the power of the first lens unit (first lens) of the reading lens according to the present invention. If the power exceeds the upper limit, the power of the first lens unit becomes too weak. The lens becomes large and causes a cost increase. Exceeding the lower limit is advantageous for making the lens compact, but increases the coma flare.

Conditional expression (2) defines the combined power arrangement of the second group (second and third lenses) and the third group (fourth and fifth lenses) of the present invention, and exceeds the upper limit. In this case, the spherical aberration becomes negative and large. If the lower limit is exceeded, on the contrary, the spherical aberration becomes positive and large, and the coma flare also increases.

[0014]

Next, various embodiments of the present invention will be described. However, the symbols in the examples are as follows. ri: radius of curvature of the i-th surface counted from the object side di: i-th surface interval counted from the object side ni: refractive index of the i-th lens counted from the object side (for d-line) νi: from the object side F / No: F number ω: Half angle of view (unit: degree) Y: Object height (unit: mm) m: Magnification f: Composite focal length of the whole system (Unit: mm) f1: focal length of the first group (unit: mm) f23: composite focal length of the second group and the third group (unit: m)
m)

FIGS. 2 to 13 show aberration curves of the respective embodiments. In the spherical aberration polar diagrams in the respective aberration curve diagrams, the spherical aberration is shown by a solid line and the sine condition is shown by a broken line. In the astigmatism curve, a sagittal ray is shown by a solid line, and a meridional ray is shown by a broken line. Further, in each aberration curve diagram, e represents a curve for the e-line (546.07 nm),
Indicates a curve for the g-line (435.84 nm), and C indicates a curve for the C-line (656.27 nm).

[0016] FIG. 2 shows the spherical aberration, astigmatism, distortion, and coma of the first embodiment.

[0017] FIG. 3 shows the spherical aberration, astigmatism, distortion, and coma of the second embodiment.

[0018] FIG. 4 shows the spherical aberration, astigmatism, distortion, and coma of the third embodiment.

[0019] FIG. 5 shows the spherical aberration, astigmatism, distortion, and coma of the fourth embodiment.

[0020] FIG. 6 shows the spherical aberration, astigmatism, distortion, and coma of the fifth embodiment.

[0021] FIG. 7 shows the spherical aberration, astigmatism, distortion, and coma of the sixth embodiment.

[0022] FIG. 8 shows the spherical aberration, astigmatism, distortion, and coma of the seventh embodiment.

[0023] FIG. 9 shows the spherical aberration, astigmatism, distortion, and coma of the eighth embodiment.

[0024] FIG. 10 shows the spherical aberration, astigmatism, distortion,
Shows coma.

[0025] FIG. 11 shows the spherical aberration, astigmatism, distortion, and coma of the tenth embodiment.

[0026] FIG. 12 shows the spherical aberration, astigmatism, distortion, and coma aberration of the eleventh embodiment.

[0027] FIG. 13 shows the spherical aberration, astigmatism, distortion, and coma aberration of the twelfth embodiment.

The first to third embodiments correspond to the first embodiment, the fourth to sixth embodiments correspond to the second embodiment, and the seventh to ninth embodiments correspond to the third embodiment. Correspondingly, Examples 10 to 12 correspond to the invention described in claim 4.

[0029]

As described above, according to the present invention, a novel reading lens can be provided. Since this reading lens is constructed as described above, it is a Gauss type of 4 groups 6 elements
/No=4.5, half-angle of view = 19.
Since the angle of view is as wide as 9 °, the original can be read at high speed and the size of the machine body can be reduced.
Also, as is clear from the aberration diagrams of the respective embodiments, the on-axis and off-axis aberrations are well-balanced, the coma flare is small despite the aperture efficiency being about 100%, the contrast is high, and the High MTF can be realized. Further, since the chromatic aberration is also good, it is possible to read a document including a color document satisfactorily.

[Brief description of the drawings]

FIG. 1 is an optical layout diagram showing a configuration of a reading lens according to the present invention.

FIG. 2 is an aberration curve diagram for Example 1.

FIG. 3 is an aberration curve diagram for Example 2.

FIG. 4 is an aberration curve diagram of the third embodiment.

FIG. 5 is an aberration curve diagram of the fourth embodiment.

FIG. 6 is an aberration curve diagram of the fifth embodiment.

FIG. 7 is an aberration curve diagram of the sixth embodiment.

FIG. 8 is an aberration curve diagram of the seventh embodiment.

FIG. 9 is an aberration curve diagram of the eighth embodiment.

FIG. 10 is an aberration curve diagram of the ninth embodiment.

FIG. 11 is an aberration curve diagram of the tenth embodiment.

FIG. 12 is an aberration curve diagram for Example 11.

FIG. 13 is an aberration curve diagram of the twelfth embodiment.

[Explanation of symbols]

1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens 6 6th lens 7 Contact glass 8 CCD cover glass ri Counted from the object side Curvature radius of the i-th surface di Counted from the object side i-th surface interval ni Refractive index (d) of the i-th lens counted from the object side (d
Νi Abbe number of the i-th lens counted from the object side (for the d-line)

Claims (4)

[Claims] 1. A first group consisting of a first meniscus lens having a convex surface facing the object side in order from the object side, a second lens of the positive lens, and a negative lens joined to the second lens. A second group consisting of a third lens, a fourth group consisting of a fourth lens of a negative lens and a fifth lens of a positive lens joined to the fourth lens, and a fourth group consisting of a sixth lens of a positive lens. In the four-group, six-lens reading lens, the third lens has a refractive index of 1.65412 at d-line,
Using an optical glass having an Abbe number of 39.6, the fourth lens has a refractive index of 1.65412 at d-line,
A reading lens comprising four elements and six elements, comprising optical glass having an Abbe number of 39.6, and satisfying the following conditions. (1) 0.72f <f1 <1.02f (2) −0.87f <f23 <−0.73f where f: combined focal length of the entire system (e-line) f1: first group (first lens) F23: second group (second and third lenses) and third group (fourth and fourth lenses)
Fifth lens) combined focal length (e-line) 2. A first group consisting of a first meniscus lens having a convex surface facing the object side in order from the object side, a second lens of the positive lens, and a negative lens joined to the second lens. A second group consisting of a third lens, a fourth group consisting of a fourth lens of a negative lens and a fifth lens of a positive lens joined to the fourth lens, and a fourth group consisting of a sixth lens of a positive lens. In the four-group, six-lens reading lens, the third lens has a refractive index of 1.65412 at d-line,
An optical glass having an Abbe number of 39.6 is used, and the fourth lens has a refractive index of 1.613110 at d-line,
A reading lens comprising four groups and six elements, which uses an optical glass having an Abbe number of 44.4 and satisfies the following conditions. (1) 0.64f <f1 <0.9f (2) -1.2f <f23 <-0.38f where f: combined focal length of the entire system (e-line) f1: first group (first lens) F23: second group (second and third lenses) and third group (fourth and fourth lenses)
Fifth lens) combined focal length (e-line) 3. A first group consisting of a first meniscus lens having a convex surface facing the object side in order from the object side, a second lens of the positive lens, and a negative lens joined to the second lens. A second group consisting of a third lens, a fourth group consisting of a fourth lens of a negative lens and a fifth lens of a positive lens joined to the fourth lens, and a fourth group consisting of a sixth lens of a positive lens. In the constructed four-group, six-lens reading lens, the third lens has a refractive index at d-line of 1.61310,
Using an optical glass having an Abbe number of 44.4, the fourth lens has a refractive index of 1.65412 at d-line,
A reading lens comprising four elements and six elements, comprising optical glass having an Abbe number of 39.6, and satisfying the following conditions. (1) 0.86f <f1 <1.12f (2) -1.05f <f23 <-0.7f where f: combined focal length of the entire system (e-line) f1: first group (first lens) F23: second group (second and third lenses) and third group (fourth and fourth lenses)
Fifth lens) combined focal length (e-line) 4. A first group consisting of a first meniscus lens having a convex surface facing the object side in order from the object side, a second lens of the positive lens, and a negative lens joined to the second lens. A second group consisting of a third lens, a fourth group consisting of a fourth lens of a negative lens and a fifth lens of a positive lens joined to the fourth lens, and a fourth group consisting of a sixth lens of a positive lens. In the constructed four-group, six-lens reading lens, the third lens has a refractive index at d-line of 1.61310,
An optical glass having an Abbe number of 44.4 was used, and the fourth lens had a refractive index of 1.613110 at d-line.
A reading lens comprising four groups and six elements, which uses an optical glass having an Abbe number of 44.4 and satisfies the following conditions. (1) 0.79f <f1 <1.12f (2) −1.24f <f23 <−0.59f where f: combined focal length of the entire system (e-line) f1: first group (first lens) F23: second group (second and third lenses) and third group (fourth and fourth lenses)
Fifth lens) combined focal length (e-line)