JPS62299927A - Telecentric ftheta lens - Google Patents

Abstract

PURPOSE:To improve the linearity of scanning while maintaining telecentric characteristic and to correct excellently chromatic aberration by arranging a front group having negative and positive lens components, and a rear group having positive lens components near an image surface, and satisfying these lenses with specific conditions. CONSTITUTION:The front group GF having a negative lens component LFN and a positive lens component LFP arranged successively from the entrance pupil EP side and the rear group GR consisting of a positive lens component LRP arranged near the image surface constitute the titled lens system. Assuming the Abbe number of the component LFN as nuFN, the Abbe number of the component LFP as nuFP, the Abbe number of the component LRP as nuR, the composite focal distance of the whole system as (f), the focal distance of the front group GF as fF, and the focal distance of the rear group GR as fR, the lens system is satisfied with respective conditions of nuFN<35, nuFP>45, nuR>55, 0.8<fF/f<1.3, 1.8<fR/f<2.8. Consequently, the linearity of scanning can be improved while maintaining the telecentric characteristic and the chromatic aberration can be excellently corrected.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an fθ lens system used in an optical scanning device such as a laser printer.

[Conventional technology]

Many of the fθ lenses used in conventional optical scanning devices do not have a telecentering link, so errors in the position of the scanning spot tend to occur. Also, for example, JP-A-59-19521
Even if it is a telecenter link as in Publication No. 1, f
The deviation from θ was large, and the linearity of scanning was still not sufficient.

Moreover, since chromatic aberration has not been corrected, even if a light source that emits light including multiple spectra is used, it is necessary to select and use only one specific wavelength using a filter or the like.

[Problems that the invention attempts to solve]

For this reason, the conventional telecentric r.theta. lens system as described in 1-C cannot fully utilize the output from the light source, resulting in a scanning device with low efficiency.

Therefore, an eleventh object of the present invention is to provide a telecentric ten lens system that improves scanning linearity while maintaining telecentricity, corrects chromatic aberration well, and can configure an efficient side-by-side scanning device. be.

c Means for Solving Problems The telecentric 10 lens system according to the present invention, as in the first embodiment shown in FIG. Lens component LFN and positive lens component placed on its image side]4. . . , and a rear group GR including a positive lens component LRP disposed near the image plane. Then, the Atsube number of the negative lens component LI in the front group GF is νFN, and the front group G
, the Abbe number of the positive lens component LFP in the rear group is ν12, the Abbe number of the positive lens component as the rear group GR is 1, the composite focal length of the entire system is 1, the focal length of the front group GF is fl, the rear group When the focal length of the G lens is R8, νFN < 35 (1) νFP
> 45 (2) νl >
55 (3) 0.8< f
r/f < 1.3 (4) 1,
H<rl/(< 2.11 (5)
This satisfies Article 4/1.

[Effect]

As mentioned above, the negative lens component and the positive lens component form an 11: eye ff in order from the entrance pupil side, and the rear group is arranged near the image plane to make it telecentric on the image side. , 1- (1) to (3), the chromatic aberration correction is made good (), and the above (4), (
Under the condition 5), L has the ability to maintain the telesend link property in the southern part of the prefecture.

The 1st line of equation (1) is a condition for simultaneously compensating for lateral chromatic aberration and axial chromatic aberration, and if this condition is not met, compensation for axis 1 chromatic aberration is not possible. M even if there is
i+J! It becomes difficult to satisfactorily correct the chromatic aberration of magnification generated from the 11 mm lens component in Y.

The condition of equation (2) is that when the negative lens component in the front group satisfies the condition of equation (1), while maintaining coma aberration well,
This is for correcting chromatic aberration of magnification. If this condition is not met, the refractive powers of the negative lens component and the positive lens component in the front group become too strong, making it difficult to perform good aberration correction.

The condition of equation (3) is that rii
This is to reduce the burden on Group J as much as possible. If this condition ('1) is exceeded, the burden of chromatic aberration correction on the front group increases, and the number of lenses constituting the front group increases, making it difficult to have a simple configuration.

The condition of equation (4) is a condition for arranging the rear group near the image plane to achieve telescend linkage and to lighten the burden of aberration correction on the rear group.

If the lower limit of this condition is exceeded, the power of the front group is negative lf
As i increases, it becomes difficult to correct aberrations in the front group, and the overall length tends to increase. On the other hand, if the upper limit is exceeded,
The increased power burden on the rear group causes coma aberration, making it difficult to construct the rear group from a single lens component. Note that if the upper limit of this condition is 1.1 or less, more favorable correction becomes possible.

Further, the condition of equation (5) is a condition for maintaining good telesend link properties. If the upper limit of this condition is exceeded, the principal ray incident on the image plane will no longer be perpendicular, and the position of the scanning spont will become unstable with respect to displacement of the image plane in the optical axis direction, which may impede accurate scanning. occurs. On the other hand, if the lower limit is exceeded, coma aberration occurs, making it difficult to configure the rear group with a single component.

In the configuration of the present invention as described above, in order to adjust the characteristics of fθ while maintaining the telescend link property by the rear group, the radius of curvature of the entrance pupil side lens surface of the positive lens component as the rear group is set as Ra, and the radius of curvature of the lens surface on the entrance pupil side of the positive lens component as the rear group is When the radius of curvature of the image-side lens surface of the component is R1, it is desirable to satisfy the following condition: IR,l>lRb l (6). If this condition deviates from the
Since the distortion becomes positively large, it deviates from the characteristics of fθ,
The linearity of scanning will deteriorate.

〔Example〕

In the first embodiment according to the present invention, as shown in the optical path H in FIG. This is a telecentric fθ lens system in which the front group GF is made up of +14, and the rear RY cm is made up of a positive lens component 158. placed near the image plane I.The positive lens component as the rear group is made up of +14. It is a plano-convex lens with a flat pupil side.

Note that the optical path diagram shows only the optical paths of the axial light flux (solid line) and the light flux at the JiJ angle of view (broken line).

The second embodiment is a front group G, as shown in FIG.

is a negative lens component 17 consisting of two negative lenses. N and a positive lens component 1-FP consisting of two positive lenses.

In the third embodiment, as shown in FIG.
It has almost the same configuration as the embodiment, and the rear Iff is composed of a biconvex positive lens component.

In each of the above embodiments, the center wavelength λ+ = 488 nm, the short wavelength side λm = 476.5 nm, and the long wavelength side λ2-44.
Chromatic aberration has been corrected for 16.5 nm.

Tables 1, 2, and 3 below list the sources of distortion for the first, second, and third h embodiments, respectively.

In the table, the leftmost number represents the order from the object side, the refractive index is the value for the wavelength of 41111 nm, and the refractive index is the value for the d-line (λ-587.6 nm). Also, d,
is the distance from the entrance pupil to the tip of the lens surface.

f, /f = 1.02 f, /f = 2.48 f * / f = 2.42 Various aberration diagrams for the above first, second and third embodiments are shown below.
They are shown in FIGS. 4, 5 and 6, respectively.

Each aberration diagram shows λ1・-48)Inf as the reference wavelength.
Indicates spherical aberration, astigmatism, and distortion for fI,
Short wavelength light λz -476,5 nm and long wavelength light λ,,
In order to show the correction state of chromatic aberration for =496°5n+a, spherical aberration, astigmatism, and lateral chromatic aberration for each wavelength are shown. Note that the distortion aberration is expressed as a percentage of the amount of displacement with respect to 0 in order to express the linearity of the scanning spot.

From each aberration diagram, it is clear that various aberrations are well corrected in each example, and in particular, chromatic aberration and distortion aberration are well corrected.

Generally, when using an optical system that has not been corrected for chromatic aberration, even if a laser that can emit light at multiple wavelengths simultaneously, such as an argon laser, is used as a light source, it is necessary to emit light at a single wavelength or use a filter, etc. to only emit light at a single wavelength. had to choose, and could only utilize the energy of the conflict wavelength. When using an optical system in which chromatic aberration has been corrected, it is possible to effectively utilize the wavelength range within the correction range. The wavelength range for which chromatic aberration correction is to be performed is determined by the output of each oscillation wavelength from the light source, the sensitivity characteristics of the photosensitive material, the light receiver, etc. FIG. 7 shows an example of each spectrum intensity in simultaneous multi-wavelength oscillation of an argon laser and the relative sensitivity ratio of the photosensitive material. In each of the above embodiments, an argon laser having the characteristics as shown in FIG. 7 is used as a light source, and a photosensitive material having the characteristics shown is used. Therefore, the center wavelength λ11-4
The energy from the light source can be used approximately twice as effectively as compared to the case where only 88n is used.

Incidentally, the method of correcting this chromatic aberration according to the present invention is as follows:
This is also effective when taking into consideration the chromatic aberration that occurs in the optical system up to the fθ lens system.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to achieve a telecentric rθ lens system that maintains telecenter linkability, has excellent scanning linearity, and has chromatic aberrations well corrected. Since chromatic aberration occurs over a relatively wide wavelength range, light in a wide wavelength range from the light source can be efficiently focused and scanned, improving the efficiency of the scanning device! It's something you get.

[Brief explanation of the drawing]

FIG. 1 is an optical path diagram showing the lens configuration of the first embodiment according to the present invention, FIG. 2 is an optical path diagram showing the lens configuration of the second embodiment according to the invention, and FIG. 3 is an optical path diagram showing the lens configuration of the second embodiment according to the present invention. An optical path diagram showing the lens configuration, FIG. 4 is a diagram of various aberrations for the first embodiment, FIG. 5 is a diagram of various aberrations for the second embodiment, and FIG. 6 is a diagram of various aberrations for the third embodiment. FIG. 7 is a diagram illustrating the emission spectrum from the laser light source and the sensitivity characteristics of the photosensitive material used in the use of each embodiment according to the present invention. [Explanation of symbols of main parts] EP... Entrance pupil GF... Front group Gll... Rear group LFN... Negative lens component in the front group LFP... Positive lens component in the front group LIIP. ...Positive lens component in the rear group Applicant Nippon Kogaku Kogyo Co., Ltd. Agent Patent attorney Takashi Watanabe No. 8 Figure Spherical aberration Astigmatism No. 1 ---48; in/I+ ---d76,, ';ytttt --4'? 6. , 'l' II 111 Spherical aberration
Astigmatism Distortion Lateral Chromatic Aberration Distortion Lateral Chromatic Aberration

Claims (1)

[Scope of Claims] In order from the entrance pupil side, a front group includes a negative lens component with a concave surface facing the entrance pupil side and a positive lens component located on the image side thereof, and a positive lens located near the image plane. The Abbe number of the negative lens component in the front group is ν_F_N, the Abbe number of the positive lens component in the front group is ν_F_P, and the Abbe number of the positive lens component in the rear group is ν.
_R, the combined focal length of the entire system is f, the focal length of the front group is f_F, and the focal length of the rear group is f_R, then ν_F_N<35(1) ν_F_P>45(2) ν_R>55(3) A telecentric fθ lens system that satisfies the following conditions: 0.8<f_F/f<1.3(4) 1.8<f_R/f<2.8(5).