JPS59170810A - Ftheta lens system - Google Patents

Abstract

PURPOSE:To scan laser ight which has different wavelength through one ftheta lens by composing the lens of a front group of a negative lens and a rear group of three positive, positive, and negative lenses successively from an entrance pupil, and satisfying specific requirements. CONSTITUTION:This lens system consists of four elements in two groups, i.e. the front group of the 1st negative lens and the rear group of the 2nd positive lens, the 3rd positive lens, and the 4th negative lens in order from the entrance pupil, and is the ftheta lens system which meets requirements shown by inequalities I -III. In the inequalities, (f) is the composite focal length of the whole system and nui the Abbe number of the (i)th lens; and ni is the refractive index of the (i)th lens and d2 is the on-axis air interval between the 1st and the 2nd lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a light emitting device used for scooping in optical racks such as laser printers.

(Background technology) In recent years, laser printers using optical scanning devices that deflect and scan laser beams using polygon mirrors, boroscanners, etc. have come into use. Since gl is constant, the displacement velocity of the spot on the plane is -t VC. When we assume that υ load bearing capacity is Y from the original axis, a lens i+' with a property such that Y=fθ is often 1. Stiff lenses are generally similar to FFJ lenses.
It's been revealed.

'L, FFJ lenses are used for laser light'7) Since the chromaticity may be severe, we need to carefully consider the chromatic aberration, Y = f.
ed '7) Most of the θ lenses satisfy the characteristics.

However, for example, in equipment that uses an f-theta laser to read and print originals (for copying, laser engraving machines, etc.), there is a laser for reading and a laser for reading. However, using a separate f-theta lens for each scan not only increases costs, but also makes it difficult to adjust if there is a difference in performance between the two Df-theta lenses. Ta.

Also, if you try to scan two laser beams with one vfej lens, if there is a wavelength shift for each laser, such as a semiconductor laser, fVcyV will occur for each laser, and 1
This makes it impossible to perform a thorough scan.

(Purpose of Invention V) This invention attempts to make a Kanamachi rudder by scanning laser beams of different wavelengths with one fθ lens by improving the chromatic aberration at the same time when the characteristics of t, Y=, fθ are satisfied. is also υ.

(Invention vm construction) As shown in FIGS. 1 and 2, the lens configuration of the υJfj lens of the present invention includes a front group consisting of a negative lens located in the entrance pupil, a stop υ second lens, and a positive lens. ■4-element configuration O consisting of @ group consisting of the third lens and the negative fourth lens
In the lens system, f: Total system '7) Composite focal length νi: m Amperage of the first lens n1: Refractive index of the i-th lens d2: On-axis air between the 1st lens and the 2nd lens When the interval is 50〈shi, 40〈ν2kuν3ku60 ν4〈35・
... (1) 0.05 <L-21-n, <0.25
-(2) 002 Nora <d2 Ku0.
05f... (3) Satisfies the satisfaction.

The condition (1) is a condition for eliminating chromatic aberration.

When laser beams of different wavelengths are incident, it is necessary to reduce the difference in focal length due to the difference in wavelength, and at the same time to reduce the difference in total curvature aberration V due to the difference in branch length. First, it is necessary to suppress the occurrence of chromatic aberration in each lens group. In other words, if the negative lens fd5 o < , V exceeds the lower limit, the divergence chromatic aberration in the front group will increase, and even if this is stopped in the rear group, a difference in distortion will occur due to the color difference. . In particular, for incident light with a short wavelength, the height is 7. f d
It becomes much smaller.

Regarding f missing 1st place, 40kuν2kushiro 60'D Article f
'l: is necessary, and the divergent chromatic aberration of the front group is suppressed by the converging chromatic aberration in the immediately following positive second lens, but when ν2 exceeds the lower limit t, the converging a■ chromatic aberration The occurrence on the left becomes large, and a focal length k due to color is generated. On the other hand, if the upper limit is exceeded, it will be difficult to obtain high refractive index glass materials. The O father, ν4 (35V) where comaphnoa occurs, is υ to completely eliminate achromatization in the rear group.The rear group has positive second and third lenses and a negative lens for achromatization. Since it is made up of 4 lenses, the 4th lens requires a glass with a small Atbe number.If this upper limit is exceeded, the convergence and chromatic aberrations that occur in the 2nd and 3rd lenses can be completely eliminated. It will no longer be possible to make corrections.

-Note (2) is the condition that requires the image surface to be used as a carrier.

It is well known that one way to reduce the Veravar sum of a lens system is to use a glass with a low refractive index for the negative lens and a glass with a high refractive index for the positive lens.
In the lens system of the invention, condition (1) is particularly necessary for correcting chromatic aberration and for using a high refractive index lens with a relatively small Abbe number for the negative fourth lens. KoO
If S exceeds the lower limit of condition O, the Veravar sum or the positive large straight υ image surface will be undervalued, and a clear one-zone surface cannot be obtained. There is a method of increasing the curvature of each lens surface in order to reduce Benvar+row, but with this S-shape, coma flare occurs and the spot i becomes larger. On the other hand, when the upper limit is exceeded, the number of drops for the stop V second and third lenses Km will greatly deteriorate [rate 7] How to obtain a crow? [ilJ distortion occurs, it becomes difficult to correct chromatic aberration, and glass f with a low refractive index
, #+3, the divergent coma flare of the first run is not large and the spot size is increased.

(3) Due to astigmatism k and distortion q difference, V
When the lower limit is exceeded, the light flux emitted from the entrance pupil on the lens group υ111 passes through the bending υ negative lens, and then
When entering the V rear group, it approaches the optical axis direction,
Rear group ■Converging force is insufficient, and the spot 1u is located outside of the position corresponding to f-&. Father, this time the luminous flux υ is more insufficient in the outer part, resulting in excessive oil stoppage and 7) test surface.

On the other hand, the light flux that exceeds the upper limit and enters the center and stop hu from the optical axis '7) The fusion L becomes unobtrusive, and convergent distortion aberration occurs. Especially since the original axis has an O-share-) ＃'L
? Depth 1'
θreren? I can't get it.

(People relax) The following is an example of 1/this invention//1ffj lens.

In the above, the refractive index n indicates the value for light of 632,8 rim, fk3 is the bank focus, υ distance s from the rear surface of the lens to the travel plane, (i:'Example f=100 jB''ll'o.80F'50
2W=500n2+n3 2-”j=0.15405 Example f=100 fB=113.75 F25 2w=
44゜n2-1-Hello I-Published 1-0, 15405 (Effect of the invention) This υinvented Qfθ lens, as described above, and also in Fig. 3,
As seen in the aberration curve shown in Figure 4, the aberrations are well extracted and the inclusion cancellation is also performed.One laser beam with a different wavelength 7) is imaged and scanned using an fθ lens. This is what made it possible. At this time, on the other hand, the manuscript is illuminated with a set beam, the image color removal number of the manuscript is transmitted by a sensor, and the ability Q beam is modulated by a Koka Junki etc. to create an image (#i
■ Used for giving. In addition, even if the light source is changed for some reason, the condensation vomiting will hardly change, so the lens O
The effect is that changing the settings and adjusting the optical system is a breeze.

[Brief explanation of the drawing]

1 and 42 are cross-sectional views of the first and second implementation rows of the fθ relen V of the invention, and FIGS. 3 and 4 are cross-sectional views of the first and second implementation rows of the fθ
It is a red convergence curve diagram of the practical, second implementation area. % Applicant Rokuyo Konishi, NI Ei Closing Ceremony Tsuji No. 1
Figure 2 [tsu 1 3rd shi 1 : r - / convergence g knee' 4711 m Spherical aberration Astigmatism Distortion aberration Figure 4 □ (Pi 2.8 nm

Claims (1)

[Claims] A villa consisting of a negative lunus II' (from the entrance pupil) and 5.
It is a four-element lens system consisting of a second lens, a negative third lens, and a negative fourth lens. ：Tan yi Can-eye υ Lens Atsube number n1: First lens refractive index d2: When the distance between the first lens and the second lens is the air distance above the track, 5 (j (, ν140<1]2) ν, ku60 ν4ku35o, o5<uni” n+ <0.250.0
2f < d2 < 0.05 fθ relen yarn with special ridges that satisfy the fυ condition