JPH11174319A - Image forming lens system and optical recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming lens and optical recording device which can be made small-sized and have a large screen size, a large aperture ratio, and high resolution by constituting a 4th lens group of a lens having negative power. SOLUTION: A 1st lens group 2, a 2nd lens group 3, a 3rd lens group 4, and a 4th lens group 5 are arranged in order from a reduction side A. A stop 6 is provided so as to be just placed at the composite focus position 6a of the 1st lens group 2 and 2nd lens group 3. The 1st lens group 2 has positive power, 2nd lens group 3 has negative power, and the 3rd lens group has positive power. Then 4th lens group 5 is composed of a 9th lens 19 which is convex to the enlargement side B and has negative power. Thus, the 4th lens group 5 is composed of the 9th lens 19 having the negative power to obtain a >=20 deg. half field angle and then a large sereen size when compared with the apertures of the lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging lens system suitable for a recording optical device such as a copying machine or a printer using a semiconductor laser array having a plurality of independently controllable light emitting portions, and using the same. The present invention relates to a recording optical device.

[0002]

2. Description of the Related Art Conventional image forming lens systems are disclosed in, for example, Japanese Patent Application Laid-Open No. 62-52516 and Japanese Patent Application Laid-Open No. 3-7231.
No. 0 publication.

A conventional imaging lens system disclosed in Japanese Patent Application Laid-Open No. 62-52516 is used for micrographics for reducing an engineering drawing to a micro-image size, and is arranged at intervals. A first lens group composed of a pair of meniscus lenses, a second lens group composed of a double lens and a biconvex lens cemented to each other, and a third lens group composed of a plano-convex lens and a double lens cemented to each other, A fourth lens group including a double lens, and an aperture stop disposed between the second lens group and the third lens group. According to this imaging lens system, a super-wide-angle lens having a half angle of view of 33 degrees can be provided.

A conventional imaging lens system disclosed in Japanese Patent Application Laid-Open No. 3-72310 is used for an exposure apparatus in the manufacture of a printed circuit board, and is constituted by an image-side telecentric lens system. . That is, the imaging lens system includes a first lens having a positive power with a convex surface facing the object side, and a first lens disposed on the image side of the first lens and having a positive power with a convex surface facing the object side. A front lens group including a second lens, a third lens disposed on the image side of the second lens, and having a negative power with a concave surface facing the image side; and a front lens group disposed on the image side of the front lens group. A fourth lens having a negative power with a concave surface facing the other side, a fifth lens having a positive power having a concave surface facing the image side with the fourth lens disposed on the image side of the fourth lens, and an image of the fifth lens And a sixth power source having a positive power with the convex surface facing the image side.
A rear lens group including a lens, a seventh lens disposed on the image side of the sixth lens, and having a positive power with the convex surface facing the object side, and coincides with the front combined focal position of the rear lens group. And a stop disposed between the front lens group and the rear lens group. According to this imaging lens system, by adopting a telecentric system,
The dimensional accuracy of the image becomes higher, the distance between the object and the image becomes larger than the screen size, and the aperture ratio becomes larger, so that the resolution can be improved.

On the other hand, in recording optical devices such as optical printers and digital copiers of the electrophotographic type, improvement in image quality is required in recent years, and higher precision of print images, that is, improvement in resolution is progressing.

[0006] As such a conventional recording optical device,
For example, there is one disclosed in JP-A-1-152683. This recording optical device is a laser beam scanner using a semiconductor laser array in which semiconductor lasers are arranged one-dimensionally as a light source. Here, since a semiconductor laser array is used as a light source, a sufficient amount of light is obtained, and a light emitting pattern is projected on a recording surface by an optical system, so that a movable portion is not required. In addition, since a semiconductor laser which is monochromatic light is used as a light source, an optical system corresponding to a single wavelength may be used. Therefore, there is an advantage that chromatic aberration correction is not required.

In a lens system of such a recording optical device, a light emission pattern on a semiconductor laser array is enlarged and projected onto a photoreceptor at a relatively small distance at a low magnification of about 1 to 8 times. Therefore, in order to realize high image quality, it is necessary to reduce the size of the semiconductor laser array side to 10
A resolving power of 0 lines / mm or more is required, so that various aberrations of the lens system must be sufficiently corrected. Further, the aperture of the optical system needs to be as large as possible in order to obtain a required beam diameter on the photosensitive member. Specifically, in order to obtain a beam diameter of about 30 μm at a desired screen size of 300 mm or more on the enlargement side, a bright lens system having an effective F-number of 3 or less is desired. Furthermore, in order to meet the demand for obtaining a screen size of 300 mm or more and reducing the distance between an object and an image, the focal length of the lens system is set to 5 mm.
It is as short as 0 mm to about 100 mm, and the angle of view on the enlargement side is 2
It must be able to be widened to 0 degrees or more. To reduce the cost and size of the apparatus, the number of lenses must be 10
The total length of the lens system is 250 mm
The overall length of the lens system must be kept small by shortening it below. Furthermore, since the semiconductor laser array is used as a light source on the reduction side, if the principal ray of the laser light emitted from each laser element of the semiconductor laser array is parallel, the reduction side must be telecentric. No.

[0008]

However, Japanese Patent Application Laid-Open No. Sho 62-62
According to the conventional imaging lens system disclosed in Japanese Patent No. 52516, although the lens system for micrographics has a sufficient screen size, the magnification on the enlargement side is as large as 10 times or more, and the numerical aperture is F / 5. Because of the above, there is a problem that a necessary resolution cannot be obtained. Further, since the reduction side is not a telecentric system, the lens system used here cannot be directly applied to a semiconductor laser array in which the principal rays of laser light emitted from each laser element are parallel. .

Further, according to the conventional imaging lens system disclosed in Japanese Patent Application Laid-Open No. Hei 3-72310, a telecentric system on the reduction side is used. It includes a bright area of about 2 to 4 and seems to have high resolution. However, since the lens system used in this exposure apparatus has a short focal length and a narrow angle of view on the enlargement side, the screen size required in the present recording optical apparatus is considerably larger than the screen size of such an exposure apparatus. In order to satisfy the screen size required for the recording optical device by directly applying the lens system here, a huge lens group is required, and there is a problem that the recording optical device becomes large.

Further, according to the conventional recording optical apparatus disclosed in Japanese Patent Application Laid-Open No. 1-152683, a sufficient amount of light can be obtained because a semiconductor laser array is used as a light source, but the semiconductor lasers are arranged one-dimensionally. Because there is a limit in integration due to thermal interference and fabrication points, there is a limit to high density corresponding to high resolution on the image plane, and even if the magnification is reduced, Due to the limitation of the size of the semiconductor laser array, there is a problem that it has a large screen size and high resolution cannot be obtained.

Accordingly, an object of the present invention is to reduce the size,
It is an object of the present invention to provide an image forming lens system and a recording optical device which have a large screen size, a large aperture ratio, and high resolution.

[0012]

In order to achieve the above object, the present invention provides an imaging lens for enlarging or reducing incident light from a reduction side or an enlargement side to form an image on an imaging surface. And a first lens group having one or more lenses and having a positive power, and a first lens group disposed on an enlarged side of the first lens group and having one or two or more lenses and having a negative power. A second lens group, a third lens group having one or two or more lenses and having a positive power, disposed on an enlarged side of the second lens group, and a third lens group disposed on an enlarged side of the third lens group; A fourth lens group having one or two or more lenses and having a negative power, and a diaphragm arranged so as to coincide with an enlargement side combined focal position formed by the first lens group and the second lens group. Preparation Providing an imaging lens system, characterized in that. In order to achieve the above object, the present invention provides a semiconductor laser array having a plurality of independently controllable light emitting units, and incident light from the plurality of light emitting units of the semiconductor laser array arranged on a reduction side or an enlargement side. An imaging lens system for enlarging or reducing the image on the image plane,
The imaging lens system is arranged on the reduction side, is composed of one or more lenses, has a first lens group having a positive power, and is arranged on an enlargement side of the first lens group, and has one or more lenses. A second lens group having a negative power, and disposed on an enlarged side of the second lens group;
A third lens group having one or two or more lenses and having a positive power; and a fourth lens group having one or two or more lenses and being disposed on the enlarged side of the third lens group and having a negative power. And a stop disposed so as to coincide with an enlarged-side combined focal position formed by the first lens group and the second lens group.

[0013]

FIG. 1 shows an imaging lens system according to an embodiment of the present invention. The imaging lens system 1 uses nine single lenses, for example, to enlarge incident light from the reduction side A to form an image on an image forming surface. 2, second lens group 3, third lens group 4
And the fourth lens group 5, and the first lens group 2 and the second lens group
And a stop 6 arranged to coincide with the combined focal position 6a of the lens group 3.

The first lens group 2 includes a first lens 11 having a negative surface with a convex surface facing the reduction side A, a second lens 12 having a positive surface with a convex surface facing the reduction side A, and a reduction side. A third lens 13 having a positive power and a convex surface facing A
It is composed of

The second lens group 3 includes a fourth lens 14 having a negative power and a convex surface facing the reduction side.

The third lens group 4 includes a fifth lens 15 having a negative power with a concave surface facing the reduction side A, a sixth lens 16 having a negative power with a convex surface facing the enlargement side B, and a magnifying side A seventh lens 17 having a positive power and a convex surface facing B
And an eighth having a positive power with the convex surface facing the enlarged side B side.
And a lens 18.

The fourth lens group 5 is composed of a ninth lens 19 having a negative power and a convex surface facing the enlargement side B.

The imaging lens system 1 has the refractive indices of the first and second lenses 11 and 12 as n ₁ , n ₂ ,
When the total lens length of the first to ninth lenses is OAL and the half angle of view on the enlargement side is θ (degree), each condition of n ₁ <n ₂ (1) 8.5 · θ <OAL (2) It is configured to satisfy (1) and (2).
The above condition (1) regulates the relationship between the refractive indices of the lenses of the front group. The first lens 11 having negative power is given a lower refractive index than the second lens 12 having positive power. I have. The above condition (2) is a condition for regulating the overall length of the lens. A compact lens system is convenient for miniaturization of the device, but as the angle of view becomes wider, the lens surface becomes shorter as the distance between the lenses becomes shorter. Becomes large, and it becomes difficult to correct off-axis aberrations.

According to the above configuration, since the fourth lens group 5 is composed of the lens having the negative power (the ninth lens 19), the half angle of view is 20 ° or more, and the screen size is larger than the diameter of the lens. Is obtained. Further, the third and fourth lens groups 4 and 5 have a plurality of lenses (fourth lens 14, fifth lens 15, and sixth lens 16) having concave surfaces facing the stop 6.
, So the F-number becomes as small as 3 or less,
A bright lens system can be provided. Further, the first lens group 2 is constituted by a lens having a positive power (second lens 12, third lens 13), and the second lens group 3 is constituted by a lens having a negative power (fourth lens 14). Therefore, a telecentric configuration is facilitated, and a semiconductor laser array capable of obtaining a high resolution as a light source can be used. Further, since the number of lenses used can be reduced to nine, the overall length of the lens is reduced to 220 mm or less, and the size can be reduced.

FIG. 2 shows a recording optical device according to an embodiment of the present invention. The recording optical device 100 includes a semiconductor laser array 101 in which nxm laser light sources are arranged in an array, and a laser beam from each laser light source can be emitted in parallel and independently at the same time. After converging a plurality of laser beams emitted in parallel from the light source to the combined focal position 6a, the photosensitive drum 102 is enlarged at a predetermined angle of view and rotated by a driving device (not shown).
An image forming lens system 1 for forming an image thereon, an image memory 103 storing an image signal, reading an image signal from the image memory 103, processing the image signal, and inputting and outputting a recording signal corresponding to a recording pattern. A signal processing circuit 104,
A laser driving circuit 105 that inputs a recording signal from the signal processing circuit 104 and drives the semiconductor laser array 101;
And a control circuit 106 that outputs a control signal to the laser drive circuit 105 to control the drive by the laser drive circuit 105. Although not shown, the recording optical apparatus 100 is provided with image forming means such as a charging device, a developing device, and a transfer device around the photoreceptor drum 102. A fixing unit for fixing the toner image transferred to the recording paper, and a paper discharge unit for discharging the recording paper on which the toner image is fixed are provided at the subsequent stage of the transfer device. I have.

According to this configuration, the total optical path length is shortened, the size is reduced, and the aperture ratio is increased with a large screen size. Further, since the semiconductor laser array 101 can be used on the reduction side, high resolution can be obtained.

[0022]

Embodiment 1 Table 1 shows lens data of the imaging lens system of the first embodiment.

[Table 1]

In Table 1, r _i indicates the radius of curvature of the lens, and d _i indicates the distance between adjacent surfaces of each lens and the distance between the lens surface and the diaphragm. Further, n _j is the refractive index of each lens at d-line, and ν shows the dispersion value (Abbe number) of each lens.

The effective focal length f, magnification M, image-side half angle of view θ, image-side F-number F _no , object-image distance (total optical path length) TT, and total lens length OAL of the imaging lens system having the above lens data are as follows. Are set as follows. f = 70 mm, M = 6, θ = 20 °, F _no = 17.75 TT = 575.918 mm, OAL = 170 mm

Here, the image side F number is an F number in a finite conjugate system, and the F number for an infinite image of the lens system is 2.5. Further, the focal length and the image-side half angle of view are set so that the image height becomes a screen size of 150 mm or more.

FIGS. 3 (a), (b), (c) and FIG. 4 show the spherical aberration, astigmatism, distortion and lateral aberration on the enlargement side of the imaging lens system configured as described above, respectively. Show. Each of the figures is for 780 nm, which is the wavelength of a semiconductor laser used as a light source on the reduction side. In the astigmatism of FIG. 3 and the lateral aberration of FIG.
S represents a sagittal image plane, and T represents a tangential image plane. In the embodiments described later, the same reference numerals are used and the description is omitted.

<Embodiment 2> Table 2 shows lens data of the imaging lens system of the second embodiment.

[Table 2]

The effective focal length f, magnification M, image-side half angle of view θ, image-side F-number F _no , object-image distance (total optical path length) TT, and total lens length OAL of the imaging lens system having the above lens data are as follows. Are set as follows. f = 70 mm, M = 6, θ = 20 °, F _no = 17.75 TT = 602.589 mm, OAL = 200 mm

FIGS. 5 (a), 5 (b), 5 (c) and 6 show the spherical aberration, astigmatism, distortion and lateral aberration on the enlargement side of the imaging lens system constructed as described above, respectively. Show. In this embodiment, in order to keep the focal length and the half angle of view the same as those in the first embodiment, and to increase the resolution, the total lens length is set to 200.
mm.

<Embodiment 3> Table 3 shows lens data of the imaging lens system of the third embodiment.

[Table 3]

The effective focal length f, magnification M, image-side half angle of view θ, image-side F-number F _no , object-image distance (total optical path length) TT, and total lens length OAL of the imaging lens system having the above lens data are as follows. Are set as follows. f = 70 mm, M = 6, θ = 20 °, F _no = 17.75 TT = 621.408 mm, OAL = 220 mm

FIGS. 7 (a), 7 (b), 7 (c) and 8 show the spherical aberration, astigmatism, distortion and lateral aberration on the magnifying side of the imaging lens system constructed as described above. Show. In the present embodiment, the focal length and the half angle of view are kept the same as in the first and second embodiments, and the total lens length is increased to 220 mm in order to further increase the resolution.

<Embodiment 4> Table 4 shows lens data of the imaging lens system of the fourth embodiment.

[Table 4]

The effective focal length f, magnification M, image-side half angle of view θ, image-side F number F _no , object-image distance (total optical path length) TT, and total lens length OAL of the imaging lens system having the above-mentioned lens data are as follows. Are set as follows. f = 65 mm, M = 6, θ = 21 °, F _no = 17.75 TT = 546.144 mm, OAL = 170 mm

FIGS. 9 (a), 9 (b), 9 (c) and 10 show the spherical aberration, astigmatism, distortion and lateral aberration on the magnification side of the imaging lens system configured as described above. Show. In the present embodiment, the focal length is shortened and the half angle of view is widened in order to shorten the total optical path length so as to obtain an image height of 150 mm or more while maintaining the entire lens length as in the first embodiment.

<Embodiment 5> Table 5 shows lens data of the imaging lens system of the fifth embodiment.

[Table 5]

The effective focal length f, magnification M, image-side half angle of view θ, image-side F number F _no , object-image distance (total optical path length) TT, and total lens length OAL of the imaging lens system having the above lens data are as follows. Are set as follows. f = 65 mm, M = 6, θ = 21 °, F _no = 17.75 TT = 575.077 mm, OAL = 200 mm

FIGS. 11 (a), (b) and (c) and FIG.
The spherical aberration, astigmatism, distortion, and lateral aberration on the magnification side of the imaging lens system configured as described above are respectively shown. In this embodiment, the focal length and the half angle of view are the same as those in the fourth embodiment, and the total lens length is increased to 200 mm in order to further increase the resolution.

<Embodiment 6> Table 6 shows lens data of the imaging lens system of the sixth embodiment.

[Table 6]

The effective focal length f, the magnification M, the image side half angle of view θ, the image side F number F _no , the object-image distance (total optical path length) TT, and the total lens length OAL of the imaging lens system having the above lens data are as follows. Are set as follows. f = 65 mm, M = 6, θ = 21 °, F _no = 17.75 TT = 595.085 mm, OAL = 220 mm

FIGS. 13 (a), (b) and (c) and FIG.
The spherical aberration, astigmatism, distortion, and lateral aberration on the magnification side of the imaging lens system configured as described above are respectively shown. In this embodiment, the focal length and the half angle of view are the same as those in Embodiments 4 and 5, and the total lens length is increased to 220 mm in order to further increase the resolution.

[0042]

As described above, according to the present invention, since the fourth lens group is constituted by a lens having a negative power, a screen size larger than the diameter of the lens can be obtained.
Further, since the third and fourth lens groups are constituted by a plurality of lenses having concave surfaces facing the stop, a bright lens system having a small F number can be obtained. In addition, since the first lens group is constituted by a lens having a positive power and the second lens group is constituted by a lens having a negative power, a telecentric construction becomes easy and a semiconductor laser array capable of obtaining a high resolution light source. Can be used. Also,
Since the number of lenses used can be reduced, the overall length of the lens is shortened, and the size can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an imaging lens system according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a recording optical device according to an embodiment of the present invention.

3A and 3B are graphs showing various aberrations in Example 1, (a) is a spherical aberration diagram, (b) is an astigmatism diagram, and (c) is a distortion diagram.

FIG. 4 is a lateral aberration diagram in the first embodiment.

5A and 5B are diagrams illustrating various aberrations in Example 2, in which FIG. 5A is a spherical aberration diagram, FIG. 5B is an astigmatism diagram, and FIG. 5C is a distortion diagram.

FIG. 6 is a lateral aberration diagram in the second embodiment.

7A and 7B are diagrams showing various aberrations in Example 3, (a) a spherical aberration diagram, (b) an astigmatism diagram, and (c) a distortion diagram.

FIG. 8 is a lateral aberration diagram in the third embodiment.

9A and 9B are graphs showing various aberrations in Example 4, in which FIG. 9A is a spherical aberration diagram, FIG. 9B is an astigmatism diagram, and FIG. 9C is a distortion aberration diagram.

FIG. 10 is a lateral aberration diagram in the fourth embodiment.

11A and 11B are diagrams illustrating various aberrations in Example 5, in which FIG. 11A is a spherical aberration diagram, FIG. 11B is an astigmatism diagram, and FIG. 11C is a distortion aberration diagram.

FIG. 12 is a lateral aberration diagram in Example 5.

13A and 13B are diagrams showing various aberrations in Example 6, in which FIG. 13A is a spherical aberration diagram, FIG. 13B is an astigmatism diagram, and FIG. 13C is a distortion diagram.

FIG. 14 is a lateral aberration diagram in Example 6.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Imaging lens system 2 1st lens group 3 2nd lens group 4 3rd lens group 5 4th lens group 6 Aperture 6a Synthetic focal point 11 1st lens 12 2nd lens 13 3rd lens 14 4th lens 15 5th Lens 16 Sixth lens 17 Seventh lens 18 Eighth lens 19 Ninth lens 100 Recording optical device 101 Semiconductor laser array 102 Photoconductor drum 103 Image memory 104 Signal processing circuit 105 Laser drive circuit 106 Control circuit

Claims (6)

[Claims] 1. An imaging lens for enlarging or reducing incident light from a reduction side or an enlargement side to form an image on an imaging surface, comprising: one or two or more lenses disposed on the reduction side; A first lens group having power; a second lens group having one or two or more lenses disposed on the enlargement side of the first lens group and having a negative power; and a second lens group having negative power on the enlargement side of the second lens group. A third lens group having one or two or more lenses and having a positive power; and a third lens group having one or two or more lenses and being disposed on the enlarged side of the third lens group and having a negative power. An imaging lens system comprising: four lens groups; and a stop arranged so as to coincide with an enlarged-side combined focal position formed by the first lens group and the second lens group. 2. The first lens group includes a first lens having a negative power with a convex surface facing the reduction side, a second lens having a positive power with a convex surface facing the reduction side, and the reduction lens. A third lens group having a positive power with a convex surface facing the side; and the second lens group including a fourth lens having a negative power with a convex surface facing the reduction side. A fifth lens having a negative power with a concave surface facing the reduction side, a sixth lens having a negative power with a convex surface facing the enlargement side, and a positive lens having a convex surface facing the enlargement side. A fourth lens group including a seventh lens and an eighth lens having a positive power with a convex surface facing the magnifying side; the fourth lens group including a ninth lens having a negative power with a convex surface facing the magnifying side The aperture is located between the fourth lens and the fifth lens. The imaging lens system according to claim 1, wherein: 3. The first lens and the second lens have refractive indices of n ₁ and n ₂ , respectively, the total length of the first to ninth lenses is OAL, and the half angle of view on the enlarged side is θ (degree).
3. The imaging lens according to claim 2, wherein each of the conditions (1) and (2) of n ₁ <n ₂ (1) 8.5 · θ <OAL (2) is satisfied. system. 4. A semiconductor laser array having a plurality of independently controllable light emitting portions, and an incident light from the plurality of light emitting portions of the semiconductor laser array arranged on a reduction side or an enlargement side is enlarged or reduced. An imaging lens system that forms an image on an imaging surface, wherein the imaging lens system is disposed on the reduction side, includes a first lens group having one or two or more lenses, and has a positive power; A second lens group having one or two or more lenses and having a negative power, disposed on an enlarged side of the first lens group, and disposed on an enlarged side of the second lens group;
A third lens group having one or two or more lenses and having a positive power; and a fourth lens group having one or two or more lenses and being disposed on the enlarged side of the third lens group and having a negative power. A recording optical device, comprising: a stop disposed so as to coincide with an enlarged-side combined focal position formed by the first lens group and the second lens group. 5. The recording optical device according to claim 4, wherein said plurality of light emitting portions of said semiconductor laser array are arranged two-dimensionally. 6. The recording optical apparatus according to claim 4, wherein said image forming surface is a surface of an image carrier on which an electrostatic latent image is formed.