JPH0651196A - Telecentric ftheta lens and optical scanning device - Google Patents

Abstract

PURPOSE:To provide the telecentric ftheta lens which is bright and has high performance and the new optical scanning device which excellently correct the surface tilt of an optical deflector by using the ftheta lens. CONSTITUTION:A 1st group is a positive meniscus lens 1, a 2nd group a combined lens of a meniscus lens 3 and a negative lens 2, a 3rd group a positive meniscus lens 4, a 4th group a positive meniscus lens, and a 5th group a positive lens 6; and conditions of (1) -0.9<R2/f1<-0.1, (2) -0.7<f2/f1<-0.1, (3) -0.8<f2/f<-0.3, (4) 0.5<R8/R10<1.0, and (5) 0.4<f3,4/f<1.8 are satisfied, where f is the focal length of the whole system, f1 the focal length of the 1st group, f2 the composite focal length of the 2nd group, f3,4 a the composite focal length of the 3rd and 4th groups, and Ri(i=1-12) a radius of curvature of an (i)th lens surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telecentric f.theta. Lens and an optical scanning device using this f.theta. Lens.

[0002]

2. Description of the Related Art An fθ lens is an imaging lens that makes uniform the speed of light scanning by a deflected light beam that is deflected at a constant angular velocity.
It is widely known in connection with optical scanning devices. In the telecentric fθ lens, the principal ray of the scanning light beam incident on the surface to be scanned becomes orthogonal to the surface to be scanned, so that the surface of the photoconductor to be optically scanned is uniquely the surface to be scanned (uniquely depending on the design conditions of the apparatus). The surface of the photoconductor is arranged so as to match the position of the surface to be scanned), but the fθ characteristic is maintained unchanged even if the surface is displaced in the direction orthogonal to the surface to be scanned. Therefore, f with high accuracy
As an fθ lens for an optical scanning device that requires θ characteristics,
Telecentric fθ lenses have been proposed (JP-A-56-123509, JP-A-62-29992).
7 publication).

However, none of these conventional telecentric f.theta. Lenses is sufficient in terms of brightness, and it is hard to say that the performance is also sufficiently high. In addition, JP-A-62
In the f.theta. Lens disclosed in Japanese Patent Publication No. 299927, the distance between the final surface of the lens and the surface to be scanned is small, and it is difficult to provide a cylinder lens for surface tilt correction. You need a mirror and a pyramidal mirror that doesn't clog.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is a bright and high-performance telecentric fθ lens with FNo = 8.5, and
It is an object of the present invention to provide a novel optical scanning device which can satisfactorily correct the surface tilt of an optical deflector by using this fθ lens.

[0005]

As shown in FIG. 1, a telecentric f.theta. Lens according to the present invention comprises first to fifth groups arranged in order from the object side to the image side. 1). The first group is a positive meniscus lens 1 having a concave surface facing the object side, the second group is a combination lens of a meniscus lens 3 and a negative lens 2, the third group is a positive meniscus lens 4 having a concave surface on the object side, and the fourth group is an object The positive meniscus lens 5 has a concave surface on the side, and the fifth lens group is a positive lens 6 having five groups and six lenses. In FIG. 1, point P indicates the entrance pupil position, that is, the starting point of polarization by the optical deflector, and S indicates the surface to be scanned.

The focal length of the entire system is f, the focal length of the first group is f ₁ , the combined focal length of the second group is f ₂ , the combined focal length of the third and fourth groups is f _3,4 , When the radius of curvature of the i-th lens surface counted from the object side is R _i (i = 1 to 12),
Conditions for this fθ lens are: (1) −0.9 <R ₂ / f ₁ <−0.1 (2) −0.7 <f ₂ / f ₁ <−0.1 (3) −0.8 < f ₂ /f<-0.3 (4) 0.5 <satisfies _{R 8 / R 10 <1.0 (} 5) 0.4 <f 3,4 /f<1.8.

The second group can be constructed as "a combination of a meniscus lens having a concave surface facing the object side and a negative lens having a concave surface on the object side" (claim 2). In this case, as shown in FIG. 1, the negative lens 2 of the two lenses may be arranged on the object side, or as shown in FIG. 2, the meniscus lens 3A having a concave surface facing the object side may be arranged on the object side. The negative lens 2A may be arranged on the image side.

Alternatively, as shown in FIG. 3, the second lens group is composed of "a meniscus lens 3B having a convex surface facing the object side and arranged on the object side, and a negative lens 2 having a concave object side on the image side".
It can also be configured by B "(Claim 3).

In the fθ lens described in claim 2 or 3, the negative lens of the second group can be a "negative meniscus lens or a biconcave lens" (claim 4). Further, in the fθ lens according to any one of claims 2 to 4, the positive lens of the fifth group is configured as "a biconvex lens, or a meniscus lens having a concave surface facing the object side, or a plano-convex lens having a flat object side". (Claim 5).

The optical scanning device of the present invention includes a light source device, a cylinder lens, an optical deflector, an fθ lens, and a surface tilt correction cylinder lens (claim 6). The “light source device” emits a parallel light flux. The "cylinder lens" corresponds to the parallel light beam emitted from the light source device in the sub-scanning corresponding direction (on a virtual optical path that is a linear extension of the optical path from the light source device to the surface to be scanned) To a main scanning direction (a direction corresponding to a direction parallel to the main scanning direction on the virtual optical path) to form a long line image. The “optical deflector” has a deflecting / reflecting surface in the vicinity of the image forming position of the line image, and deflects the reflected light flux at a constant angular velocity. The “fθ lens” is a lens for converging a deflected light beam on a surface to be scanned in the direction corresponding to the main scanning and for making the optical scanning at a constant speed, and the lens according to claim 1 or 2 or 3 or 4 or 5. Is.

"Cylinder lens for correction of surface tilt" is f
It is provided between the θ lens and the surface to be scanned, and cooperates with the fθ lens to focus the deflected light beam on the surface to be scanned in the sub-scanning corresponding direction. Therefore, the fθ lens and the surface tilt correction cylinder lens have a geometrical-optical conjugate relationship between the “line image” and the position of the surface to be scanned in the sub-scanning corresponding direction.

[0012]

The conditions (1) to (6) in the telecentric f.theta. Lens according to claim 1 are bright F of about 8.5.
This is a condition for achieving good performance while achieving No.

The condition (1) is a condition for favorably correcting the field curvature. Outside the range of the condition (1), the residual field curvature is large and cannot be corrected.

The condition (2) is a condition for correcting the coma aberration and the fθ characteristic. Outside the range of the condition (2), uncorrectable coma aberration occurs. The fθ characteristic becomes over when the lower limit of the condition (2) is exceeded and becomes under when it exceeds the upper limit, and cannot be corrected.

The condition (3) is also a condition for correcting the coma aberration and the fθ characteristic. Outside the range of the condition (3), uncorrectable coma aberration occurs. If the lower limit of the condition (3) is exceeded, the fθ characteristic becomes under, and if it exceeds the upper limit, it becomes over and cannot be corrected.

Conditions (4) and (5) are conditions for correcting field curvature, coma and fθ characteristics. Outside the ranges of these conditions (4) and (5), both residual field curvature and coma are large, and good correction cannot be performed. The fθ characteristic becomes under when the lower limit of the conditions (4) and (5) is exceeded, and becomes over when the upper limit is exceeded, and the correction cannot be performed.

Note that the field curvature and other aberrations in the sub-scanning corresponding direction can be easily corrected by using the surface tilt correction cylinder lens, and therefore do not need to be a problem. Therefore, the "field curvature" in the description of the above conditions (1) to (5) means the field curvature in the main scanning corresponding direction.

[0018]

EXAMPLE Seven specific examples of the telecentric f.theta. Lens will be given below. As shown in FIG. 1, in each embodiment, the radius of curvature of the i-th lens surface counted from the object side is R _i (i = 1 to 12), and the light of the i-th and i + 1-th lens surfaces The axial upper surface distance is D _i (i = 1 to 11), the wavelength of 670 n of the material of the j-th lens counted from the object side.
The refractive index for light of m is N _j (j = 1 to 6), and the distance on the optical axis from the deflective reflection surface to the first lens surface at a deflection angle of 0 is D ₀ . Also, the focal length of the whole system:
Normalize f to 100 and set the angle of view (maximum deflection angle) to 2ω
It is represented by. In each example, FNo = 8.5.

Example 1 f = 100, 2ω = 35.8 i R _i D _i j N _j 0 17.500 1 -117.500 4.844 1 1.67358 2 -48.750 11.625 3 -31 .125 5.000 2 1.83468 4 -275.000 6.875 5 -42.188 8.750 3 1.67358 6 -43.750 3.125 7 -175.625 10.725 4 1.67358 8 -69.500 18.063 9 -186.250 13.125 5 1.67358 10 -78.313 0.625 11 425.000 11.250 6 1.67358 12 -293.750.

Value of condition value R ₂ / f ₁ = -0.405, f ₂ / f ₁ = -0.40, f _{2
/F=-0.481,R 8 / R 10 = 0.887,} f 3,4 /
f = 0.956.

Example 2 f = 100, 2ω = 35.8 i R _i D _i j N _j 0 19.310 1 −32 0.279 9.904 1 1.79465 2 −58.560 8.8.274 3 −38 .847 5.869 2 1.79465 4 25000.000 14.680 5 −31.852 7.500 3 1.61420 6 −38.358 8.475 7 −104.749 8.764 4 1.771962 8- 69.623 2.8709-889.368 13.750 5 1.79465 10-98.411 0.625 11 531.445 10.625 6 1.79465 12-721.747.

Condition value R ₂ / f ₁ = -0.660, f ₂ / f ₁ = -0.525, f
_{2 /f=-0.466,R 8 / R 10 = 0.707} , f 3,4
/F=0.909.

Example 3 f = 100, 2ω = 35.8 i R _i D _i j N _j 0 15.625 1 -66.971 3.385 1 1.79465 2 -40.748 9.9920 3 -27 .240 9.375 2 1.79465 4 -37.964 0.625 5 -56.104 6.250 3 1.52791 6 2500.000 25.489 7 -117.966 9.937 5 4 1.767702 8- 81.787 9.512 9-325.374 10.000 5 1.76702 10-120.097 0.625 11-3963.656 11.250 6 1.76702 12-140.341.

Value of condition value R ₂ / f ₁ = −0.329, f ₂ / f ₁ = −0.499, f
_{2 /f=-0.618,R 8 / R 10 = 0.681} , f 3,4
/F=1.386.

Example 4 f = 100, 2ω = 35.8 i R _i D _i j N _j 0 18.750 1-74.247 4.918 1 1.71962 2-47.539 12.3361 3-33 .619 9.343 2 1.79465 4 -49.413 9.441 5 -45.407 6.189 3 1.68146 6 -19.480 12.2.87 7 -88.937 8.125 4 1.79465 8 -66.497 0.625 9 -239.800 12.500 5 1.79465 10 -82.091 0.625 11 487.039 12.500 6 1.79465 12 224.781.

Value of condition value R ₂ / f ₁ = −0.279, f ₂ / f ₁ = −0.313, f
_{2 /f=-0.535,R 8 / R 10 = 0.810} , f 3,4
/F=0.990.

Example 5 f = 100, 2ω = 35.8 i R _i D _i j N _j 0 15.625 1 −66.875 4.630 1 1.71496 2 −39.244 8.93938 −28 .585 10.068 2 1.79465 4 -40.604 6.729 5 -47.698 5.000 3 1.68146 6 -257.474 24.777 7 -127.193 9.660 4 1.79465 8 -76.080 0.625 9 -331.129 11.250 5 1.79465 10 -121.378 0.625 11 ∞ 12.500 6 1.79465 12 -162.763.

Value of condition value R ₂ / f ₁ = -0.316, f ₂ / f ₁ = -0.427, f
_{2 /f=-0.530,R 8 / R 10 = 0.627} , f 3,4
/F=1.144.

Example 6 f = 100, 2ω = 35.8 i R _i D _i j N _j 0 23.750 1 -180.889 6.250 1 1.79465 2 -93.207 0.625 3 58. 446 5.625 2 1.79465 4 51.245 17.0785 -32.818 4.375 3 1.61420 6 -223.727 9.954 7 -77.545 10.643 4 1.79465 8-59 .585 0.625 9 -273.786 13.125 5 1.79465 10 -90.187 0.625 11 43224.140 13.750 6 1.79465 12 -115.905.

Condition value R ₂ / f ₁ = -0.397, f ₂ / f ₁ = -0.255, f
_{2 /f=-0.598,R 8 / R 10 = 0.661} , f 3,4
/F=0.990.

Example 7 f = 100, 2ω = 35.8 i R _i D _i j N _j 0 17.987 1 -222.996 8.750 1 1.79465 2 -100.009 8.531 3 54. 481 5.168 2 1.61420 4 50.300 10.625 5 -35.554 4.375 3 1.61420 6 5000.000 8.0887 -79.347 9.213 4 1.794465 8-62. 287 6.908 9-312.014 13.125 5 1.79465 10-90.647 0.625 11 1680.373 13.750 6 1.79465 12-113.389.

Value of condition value R ₂ / f ₁ = -0.452, f ₂ / f ₁ = -0.260, f
₂ / f = −0.576, R ₈ / R ₁₀ = 0.687, f _3,4
/F=1.026.

FIGS. 5 to 11 show, in order, the field curvature, coma aberration, and f.theta. Characteristics of the first to seventh embodiments. As described above, since the field curvature in the sub-scanning corresponding direction can be corrected by using the surface tilt correcting cylinder lens, only the field curvature in the main scanning corresponding direction is shown in FIGS. Θ in the figure represents the deflection angle. As is well known, the fθ characteristic is an amount defined by {(H−fθ) / fθ} × 100% where fθ is the ideal image height and H is the actual image height with respect to the deflection angle θ. In each of the examples, the aberration and the fθ characteristic are well corrected.

FIG. 4 shows an embodiment of the optical scanning device of the present invention. The light source device shown by reference numeral 10 is configured to have a light source such as a semiconductor laser or an LED and a collimating lens, and emits a substantially parallel light flux. The parallel light flux emitted from the light source device 10 is converged by the cylinder lens 12 only in the sub-scanning corresponding direction, and is formed as a long line image I in the main scanning direction at the position of the deflecting / reflecting surface 14 of the rotary polygon mirror 13 which is a light deflecting device. An image is formed and is deflected at a constant angular velocity as the rotary polygon mirror 13 rotates.

The deflected light beam is condensed as a light spot on the surface 17 to be scanned by the action of the telecentric fθ lens 15 and the cylinder lens 16 for correcting surface tilt, and scans the surface 17 to be scanned at a constant speed. That is, the deflected light flux is condensed on the surface 17 to be scanned by the fθ lens 15 in the main scanning corresponding direction, and the fθ lens 15 in the sub scanning corresponding direction.
And the surface tilt correction cylinder lens 16 collects the light on the scanned surface 17. Example 1 as the fθ lens 15
The telecentric fθ lens shown in FIGS. The fθ lens 15 and the surface tilt correction cylinder lens 16 have a geometrical-optical conjugate relationship between the line image I and the position of the surface to be scanned 17 in the sub-scanning corresponding direction, and the image forming position of the line image I is deflected and reflected. Since it is the position of the surface 14, the tilt of the deflective reflection surface 14 does not affect the image forming position of the light spot in the sub scanning corresponding direction.

The surface tilt correction cylinder lens 16 is set so as to favorably correct field curvature and other aberrations in the sub-scanning corresponding direction.

[0037]

As described above, according to the present invention, a novel telecentric fθ lens and an optical scanning device using this fθ lens can be provided. Since the telecentric fθ lens of the present invention is configured as described above, while realizing a bright FNo of about 8.5, the field curvature and the coma aberration in the main scanning corresponding direction are satisfactorily corrected,
In addition, a high performance with excellent fθ characteristic can be realized. Further, since the optical scanning device of the present invention is configured as described above, it is possible to correct the surface tilt and realize good optical scanning in which the fθ characteristic does not change regardless of the positional error between the photoconductor and the surface to be scanned. .

[Brief description of drawings]

FIG. 1 is a diagram for explaining an example of a lens configuration of a telecentric fθ lens according to the present invention.

FIG. 2 is a diagram for explaining another example of the lens configuration of the telecentric fθ lens of the present invention.

FIG. 3 is a diagram for explaining another example of the lens configuration of the telecentric fθ lens of the present invention.

FIG. 4 is a perspective view showing an embodiment of the optical scanning device of the present invention.

FIG. 5 is a diagram of aberration and fθ characteristics regarding Example 1 relating to a telecentric fθ lens.

FIG. 6 is a diagram of aberration and fθ characteristics with respect to Example 2 relating to a telecentric fθ lens.

FIG. 7 is a diagram of aberration and fθ characteristics regarding Example 3 relating to a telecentric fθ lens.

FIG. 8 is a diagram of aberrations and fθ characteristics regarding Example 4 relating to a telecentric fθ lens.

FIG. 9 is a diagram of aberration and fθ characteristics with respect to Example 5 relating to a telecentric fθ lens.

FIG. 10 is a diagram of aberration and fθ characteristics regarding Example 6 relating to the telecentric fθ lens.

FIG. 11 is a diagram of aberration and fθ characteristics with respect to Example 7 regarding the telecentric fθ lens.

[Explanation of symbols]

 1 1st group (positive meniscus lens) 2 2nd group negative lens 3 2nd group meniscus lens 4 3rd group (positive meniscus lens) 5 4th group (positive meniscus lens) 6 5th group (positive lens)

Claims (6)

[Claims] 1. A positive meniscus lens having a concave surface facing the object side, a second group consisting of a meniscus lens and a negative lens. The third lens group is a positive meniscus lens having a concave surface on the object side, the fourth lens group is a positive meniscus lens having a concave surface on the object side, and the fifth lens group is a positive lens in the fifth lens group. The focal length is f, the focal length of the first lens group is f ₁ , the combined focal length of the second lens group is f ₂ , the combined focal length of the third lens group and the fourth lens group is f _3,4 , and the first focal point is counted from the object side. When the radius of curvature of the i-th lens surface is R _i (i = 1 to 12), the condition: (1) −0.9 <R ₂ / f ₁ <−0.1 (2) −0.7 < _{f 2 / f 1 <-0.1 (} 3) -0.8 <f 2 /f<-0.3 (4) 0.5 <R 8 / R 10 <1.0 (5) 0.4 < f _3,4 Telecentric fθ lens satisfies the f <1.8. 2. The telecentric f.theta. Lens according to claim 1, wherein the second group is a combination lens of a meniscus lens having a concave surface on the object side and a negative lens having a concave surface on the object side. . 3. The fθ lens according to claim 1, wherein the second group is a combination of a meniscus lens having a convex surface directed toward the object side and arranged on the object side, and a negative lens arranged on the image side with a concave surface on the object side. A telecentric fθ lens that is a lens. 4. The telecentric f.theta. Lens according to claim 2 or 3, wherein the second group of negative lenses is a negative meniscus lens or a biconcave lens. 5. The fθ lens according to claim 2, 3 or 4, wherein the fifth group is a biconvex lens, a meniscus lens having a concave surface facing the object side, or a plano-convex lens having a flat object side. Telecentric fθ lens. 6. A light source device that emits a parallel light beam, a cylinder lens that converges the parallel light beam emitted from the light source device in a direction corresponding to sub-scanning, and forms a long line image in a direction corresponding to main scanning, and the line image. , Which has a deflecting / reflecting surface in the vicinity of the image forming position, deflects the reflected light beam at a constant angular velocity, and collects the deflected light beam on the surface to be scanned in the direction corresponding to the main scanning, and makes the optical scanning at a constant speed. An fθ lens for converting the light beam, and a surface tilt correction cylinder lens that is provided between the fθ lens and the surface to be scanned and that cooperates with the fθ lens to collect a deflected light beam on the surface to be scanned in the sub-scanning corresponding direction. And the fθ lens has a structure according to claim 1 or 2 or 3 or 4.
Alternatively, the optical scanning device is the telecentric fθ lens described in item 5.