JPS632014A - projection lens - Google Patents

Abstract

PURPOSE:To obtain an excellent projection lens being free from an aberration, by constituting a first group, a third - a fifth groups, of positive meniscus lenses whose concave surfaces have been turned to a light beam incident direction, respectively, and constituting a second group, of a negative lens, and specifying a radius of curvature, a wall thickness, a lens interval, and a refractive index, of each lens. CONSTITUTION:The titled projection lens is constituted of five groups and five pieces, and the first, the third, the fourth, and the fifth groups consist of positive meniscus lenses whose concave surfaces have been turned to a light beam incident direction, respectively, and the second group consists of a negative lens. When r1, r3, r5, r7 and r9, r2, r4, r6, r8 and r10, and d1, d3, d5, d7 and d9, and d2, d4, d6 and d8, and n1-n5, and (f), B.f, and omega, and F are allowed to denote a radius of curvature of a pupil side of each lens, a radius of curvature of the reverse face of each lens, a wall thickness of each lens, an interval between each lens, a refractive index in the vicinity of a wavelength 6,328Angstrom of each lens base material, a composite focal distance of the whole system, a back focus, and an aperture ratio, respectively, this projection lens satisfies the equations.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is applied to facsimile machines and other devices that perform recording or reading using a laser beam subjected to brightness modulation.
・This relates to a projection lens called a θ lens.

Conventional technology The f/theta lens is a laser beam given a deflection angle θ by a deflector, which is focused onto a recording medium by a projection lens with a focal length f, and is then focused on a recording medium with a deflection angle θ that changes at a constant angular velocity. , the projection lens is given a distortion aberration so that the scanning speed on the recording imaging plane y perpendicular to the optical axis is in a proportional relationship,
This refers to a projection lens designed to always obtain a scanning speed of -, and the conditions required for this are as follows.
let

Also, since the distortion at y1=f·θ results in a time lag during scanning, it is corrected to around ±1.0%.

(2) The spot diameter of the laser beam on the imaging plane must be within a predetermined range at the center and periphery.

(3) The pupil position is on the deflection mirror surface and protrudes in front of the lens, so the front diaphragm is small.

Must be a wide-angle lens.

(4) Regarding the aberration correction of the f/θ lens, in order to obtain a -like scanning speed, a predetermined amount of distortion must be satisfied, and regarding the spot diameter, the projected spot on the reference image plane must be To correct the amount of sagittal lateral aberration and meridional lateral aberration, which correspond to the mutually orthogonal inner diameters of the and correcting the amount of coma aberration of both. Conventional lens types that can satisfy these conditions include (1) modified Gauss type, and (2) Ornmeter type.

Problems to be Solved by the Invention However, regarding (1) above, although the spherical aberration is good, 1. Regarding C, (2), the disadvantage is that the sum of P is large and the amount of residual coma aberration is large at intermediate angles of view.
It is characterized by the fact that a flat image surface can be obtained in a wide-angle range, that is, the sum of P is small, so it is somewhat advantageous in order to obtain a spot diameter near the diffraction limit, but the amount of spherical aberration is ( There are many disadvantages compared to 1).

The present invention eliminates the above-mentioned drawbacks, and aims to provide a projection lens that has small spherical aberration, astigmatism, and distortion, and is capable of obtaining good spot imaging.

Means for Solving the Problems The present invention achieves the above object, and the technical means thereof include five elements in five groups. 3rd゜4th. The fifth group is a positive meniscus lens with a concave surface facing the light beam incident direction, and the second group is a negative lens, r1. rs
p r s , r 7 F r g is the radius of curvature on the pupil side of each lens, r21 r4F"61 r8"10 is the radius of curvature on the opposite surface of each lens, dll ct31 ci5
t ci7t ci9 is the thickness of each lens, d2. d4.
d6. d8 is the distance between each lens, n 1p n 2 F
When n 3 p n 4 + n 5 is the refractive index of each lens material near the wavelength of 6328 Å, f is the composite focal length of the entire system, B-f is the back focus, ω is the angle of view, and F is the aperture ratio, r1= -0,216016 d 5=0.01706n 1=1.63561r
2 ” -0-15531 2d2=0.o19o4 r s =-0-149974 d5=0.01624fi2=: 1-56996
r4=+11.664 d4=0.01376 r s =-6-9800 d3=0.0286 n3=1.63561 r e
=-0-61226 d6=O,0O07B r -r =-〇 -971242 d3=0.0398 n4=1.62001r8=
-0,343526 d =0.00078 r9=-1-29623 d=0.0380 n5=1.62001r10=
−043180 f=1. OB, f=1.190332a+=67.64
The projection lens satisfies °F/33.3.

Function: Since the present invention has the above-mentioned specifications, it is possible to obtain an excellent projection lens free of aberrations.

Example An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view of the f/θ lens according to the present invention. The f/θ lens according to the present invention has a configuration of five elements in five groups: four positive meniscus lenses and one negative biconcave lens. Third. Fourth
．． The fifth lens group is a positive meniscus lens with a concave surface facing the direction of light incidence, that is, the pupil side, and the second group is a negative lens with a concave surface facing the direction of light incidence.

The fourth one near the pupil of the positive meniscus with the concave surface facing the pupil.
The radius of curvature of the lens 4 is rl from the pupil e side.

τ2. Negative second lens 20 has the same radius of curvature r3°τ4
．． The third lens 30 of the positive meniscus has the same radius of curvature <
r s t r s The radius of curvature of the fourth lens 4 with a positive meniscus is the same (r7. r8. The radius of curvature of the fifth lens 5 with a positive meniscus is the same (r9. rl.

The thickness on the optical axis of the first lens/lens 1 is d1, the refractive index near the wavelength of 6328 Å is n1p, the same thickness of the second lens, the refractive index d3r n2, and the same thickness of the third lens.

The refractive index is d5 I n31 The same thickness of the 4th lens, the refractive index is ct71 ``41 The same thickness of the 5th lens, the refractive index is d9'' 51 The distance on the optical axis from the pupil position to the rl curvature surface of the 51st lens d. , the distance on the optical axis between the first lens and the second lens is d2, and the distance on the optical axis between the second lens and the third lens is d4.
The distance between the third lens and the fourth lens on the optical axis is d6. When the distance between the fourth lens and the fifth lens on the optical axis is d8, each surface and the distance satisfy the following conditions.

(1) -0,48f(rlo<-0,38f(2)
72.0f(r9(-0,8f(3) -0.1
7fkr and r3k-0,13f(4) 0.01
2f d4 0. o16f(6) 6.85f<l
r41 The above conditions will be explained below.

First, the first condition is 10, 48f<rl. <-0.38
Regarding the relationship f, when the value of the rearmost surface r1° is outside the upper limit value, the meridional field curvature increases, and when it is outside the lower limit value, the sagittal field curvature increases, and the astigmatism difference worsens. Both methods result in spot-shaped diffuse length measurement.

For the second condition, -2-Of<r9<0-Bf,
Regarding the concave surface 'rs of the fifth lens, when it is outside the upper limit value, even if the tilt of the image plane is compensated for by r6, the distortion aberration moves in the positive direction, and in the opposite case, when it is outside the lower limit value, the distortion aberration moves in the positive direction. , and it becomes difficult to provide a predetermined amount of aberration.

Third condition, -0-17f(r2.r3(-0.1sf, r2+r3 is related to spherical aberration, and in order to maintain the image plane, even if it is set in a canceling relationship with rl, the upper limit value When it is outside the lower limit, it is under-corrected, and when it is outside the lower limit, it is over-corrected.If these are replaced with lateral aberrations, the spot diameter at the center becomes unbalanced with the periphery.

In the fourth case, 0.012f x d4 x 0.016f, d is the adjustment point for the unbalance of the upper and lower ray transverse aberrations regarding the asymmetry of comatic aberration, and when it is set outside the lower limit, the meridional image plane The curvature is corrected, while the sagittal field curvature is worsened. Also, when it is outside the upper limit,
However, if this is replaced with a spot shape, the edges converge or diverge in the sagittal and meridional directions, making it impossible to obtain a clear edge.

In the sixth condition, s, 56f (lr41), if the surface r4 on the ray exit side of the second lens becomes a convex surface larger than -6,86f and smaller than 0, the image plane tilts in the positive direction and convergence occurs. If coma aberration occurs and concave surfaces are smaller than e and 85f and larger than o, negative distortion increases and a predetermined amount of aberration cannot be obtained.

From the above, the aspect ratio of the spot diameter is the field curvature in the sagittal and meridional directions, that is, the amount of comatic aberration in both directions, and these tend to increase and decrease in opposition to each other, and the scanning direction of the spot is , is a meridional surface, so the line width of the scanning line is the amount of comatic aberration in the sagittal direction. Therefore, by keeping the sagittal direction within a specified amount and adjusting the meridional coma amount, it is possible to make the scanning spot elongated and minimize the line width of the scanning spot.

Next, specific examples are shown below.

<Example> r 1 = -0-215016 d = 0.01706 n1 = 1.63561 r 2
=-〇-155312 d2=0.01904 r3=-0-149974 d=0.01624 n2=1.56996τ4=
+11.664 d =0.01376 r6=-6,980 d5=0.0286 n3=1.63561r6=
-○, 61226 d6=0.00078 r -r =-0-971242 d7;0.0398 n4=1.62001τ8=
-0,343526 d8=0. ooo78 r9=-1,29623 d9=0.0380 n5=1.62001r, o
=-043180 f=1. OB, f=1.190332ω=67.64°
F/33, 3, where f is the composite focal length of the entire system, B,
f is the bank focus.

FIG. 2A shows each aberration of the projection lens according to this example.

Shown in B and C. SA and SC are spherical aberration and sine conditions, respectively, and SA is shown by a solid line and SC is shown by a dotted line. As is astigmatism, S is shown as a solid line in the sagittal direction, and M is shown as a dotted line in the meridional direction. ω indicates the angle of view of parallel rays incident on the lens.

fθ indicates the ratio of deviation from the fθ characteristic, and if the image height at the imaging position is Y, then fθ=l×10o(a), then f・
ω Yes.

Each aberration is well corrected, and good spot imaging can be obtained.

Effects of the Invention In summary, the present invention has the following advantages. Third. 4th. The fifth group is a positive meniscus lens with a concave surface facing the light incident direction, and the second group is a negative lens, and the radius of curvature of each lens is
By specifying the wall thickness, lens spacing, and refractive index, it is possible to obtain an excellent projection lens without aberrations.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a projection lens according to an embodiment of the present invention, and FIGS. 2A and 2C are diagrams showing aberrations of the projection lens. 1 to 6... Name of lens agent Patent attorney Toshio Nakao and 1 other person 1st
Figure 2 SA, 5C (A)

Claims (1)

[Claims] From a five-element structure in which the first, third, fourth, and fifth groups are positive meniscus lenses each having a concave surface facing the light incident direction, and the second group is a negative lens. A projection lens having the following specifications. r_1=-0.215016 d_1=0.01706 n_1=1.63561 r_2=-0.155312 d_2=0.01904 r_3=-0.149974 d_3=0.01624 n_2=1.56996 r_4=+11.664 d_4= 0.01376 r_5=-6.9800 d_5=0.0286 n_3=1.63561 r_6=-0.61226 d_6=0.00078 r_7=-0.971242 d_7=0.0398 n_4=1.62001 r_8=-0 .343526 d_8=0.00078 r_9=-1.29623 d_9=0.0380 n_5=1.62001 r_1_0=-043180 f=1.0 B. f=1.19033 2ω=67.6
4°F/33.3 However, r_1, r_3, r_5, r_7, r_9 are the radius of curvature of each lens on the pupil side, r_2, r_4, r_6, r_8
, r_1_0 is the radius of curvature of the opposite surface of each lens, d_1,
d_3, d_5, d_7, d_9 are the thicknesses of each lens, d
_2, d_4, d_6, d_8 are the distances between each lens, n
_1, n_2, n_3, n_4, n_5 are the refractive indexes of each lens material near the wavelength of 6329 Å, f is the composite focal length of the entire system, and B. f is the back focus, ω is the angle of view, and F is the aperture ratio.