JPH10260371A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of environmental changes such as, specially, a temperature rise, to form a scanning optical element of plastic and make it lightweight, and to decrease the number of lens elements by composing the scanning optical element of an aspherical cylindrical mirror which has specific refracting power only in a horizontal scanning direction. SOLUTION: The luminous flux emitted by a semiconductor laser 1 is converted by a condenser lens 2 into divergent luminous flux, which is made incident on a cylindrical lens 4 through a stop 3. The luminous flux in vertical scanning section is imaged almost linearly nearby the deflection surface of an optical deflector 5 through an optical path bending mirror 9 and the cylindrical mirror 6. Luminous flux in horizontal scanning section is reflected by the optical path bending mirror 9 while diverged, and converted into nearly parallel luminous flux which has luminous flux width much larger than the deflection surface through the cylindrical mirror 6 to make incident on the deflection surface of the optical deflector 5. Main deflected luminous flux is made incident on the cylindrical mirror 6 again and guided onto a photoreceptor drum surface 8 through a long-sized toric lens 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical apparatus, and more particularly, to an image forming optical system having an f.theta. Characteristic after deflecting a light beam emitted from a light source means and emitted by a light deflector comprising a rotary polygon mirror. The present invention relates to a scanning optical device suitable for an apparatus such as a laser beam printer or a digital copying machine having an electrophotographic process, in which image information is recorded by optically scanning the surface to be scanned through an fθ lens). .

[0002]

2. Description of the Related Art Conventionally, a laser beam printer (L)
In a scanning optical device such as BP), a light beam that has been light-modulated and emitted from a light source means in accordance with an image signal is periodically deflected by an optical deflector composed of, for example, a rotating polygon mirror (polygon mirror), and has a fθ characteristic. An image optical system focuses the light on a photosensitive recording medium (photosensitive drum) surface in the form of a spot and optically scans the surface to record an image.

FIG. 7 is a schematic view of a main part of a conventional scanning optical device. In the figure, a divergent light beam (laser beam) emitted from the light source means 71 after being light-modulated is collimated by a collimator lens 7.
The light is converted into a substantially parallel light beam by 2, and the light beam (light amount) is restricted by a stop 73 and is incident on a cylindrical lens 74. Of the substantially parallel light beams incident on the cylindrical lens 74, they are emitted as they are in the state of substantially parallel light beams in the main scanning plane. In the sub-scanning plane, the light is converged and formed as a substantially linear image on the deflecting surface 75a of the optical deflector 75 composed of a polygon mirror. The light beam deflected and reflected by the deflecting surface of the optical deflector 75 is guided through an imaging optical system (fθ lens) 76 having fθ characteristics onto a photosensitive drum surface 78 as a surface to be scanned. By rotating 5 in the direction of arrow A, the surface of the photosensitive drum is optically scanned in the direction of arrow B (main scanning direction) to record image information.

[0004]

As for such a scanning optical device, a laser beam printer capable of high-speed scanning has been demanded by increasing the speed and definition of the laser beam printer. High-speed scanning is restricted by the number and size of the surfaces of a polygon mirror as a deflecting means.

Therefore, conventionally, as shown in FIG. 8, a light beam having a sufficiently large light beam width (laser beam diameter) is incident on the deflecting surface (polygon surface) of the polygon mirror 85 in the main scanning direction, and the deflecting surface itself is mainly used. A scanning optical system that scans as a pupil in the scanning direction (hereinafter referred to as a “pupil scanning optical system”) has been proposed.

In this pupil scanning optical system, the size (diameter) of the polygon mirror 85 does not increase so much even if the polygon mirror 85 is multifaceted because the deflection surface of the polygon mirror 85 is substantially equal to the size of the pupil. There is an advantage that the load on the polygon motor can be reduced, and the scanning efficiency can be increased, so that the image clock (basic frequency for image ON / OFF) can be set low.

However, on the other hand, the spot diameter and the light amount distribution on the surface to be scanned become non-uniform, and the light beam width of the incident light beam is wider than the deflection surface of the polygon mirror, so that the scanning optical element also serves as a collimating function of the incident light beam. There are problems such as what must be done. In particular, the latter is susceptible to environmental fluctuations (particularly temperature changes), which makes it difficult to use a plastic lens as a scanning optical element. Therefore, there is a major problem in reducing the size, weight, and cost of the entire apparatus. Had become.

The present invention relates to a scanning optical device suitable for high speed and high definition, wherein an aspherical cylindrical mirror having a predetermined refractive power only in the main scanning direction is provided with a scanning optical element which also has a collimating function of a light beam incident on a deflection element. In particular, the present invention aims to provide a compact scanning optical device capable of reducing the influence of environmental fluctuations such as a rise in temperature, making the scanning optical element plastic, lightweight, and reducing the number of lenses. And

[0009]

According to the present invention, there is provided a scanning optical apparatus comprising: (1) converting a state of a light beam emitted from a light source means into another state through a first optical element, and converting the converted light beam; An image is formed on the deflecting surface of the deflecting element via the second optical element and the third optical element in a linear shape elongated in the main scanning direction, and the light beam deflected and reflected by the deflecting element is transmitted to the fourth optical element and the fourth optical element. 5. A scanning optical device which forms an image on the surface to be scanned in the form of a spot on the surface to be scanned via the optical element 5 and scans the surface to be scanned, wherein the third optical element and the fourth optical element are the same. An optical element comprising an aspherical cylindrical mirror having a refractive power only in the main scanning direction, converting a light beam incident on the deflection element into a substantially parallel light beam in a main scanning cross section, and performing main scanning of the substantially parallel light beam; Light beam width in the main scanning direction is wider than the width of the deflecting surface of the deflecting element in the main scanning direction. It has a so that the optical element of the fifth is characterized in that it comprises from long lens having a refractive power in the at least a sub-scanning direction.

In particular, (1-1) when the angular magnification in the sub-scanning direction between the deflection element and the surface to be scanned is rs, the condition of rs <0.5 is satisfied; When the scanning efficiency of the deflection element is Pduty, the condition 0.7 <Pduty <0.95 is satisfied; (1-3) the cylindrical mirror is manufactured by plastic molding; 4) The long lens is manufactured by plastic molding, and (1-5) the substantially parallel light beam incident on the deflecting element via the third optical element is subordinate to the deflecting surface of the deflecting element. (1-6) an optical path bending mirror is provided in an optical path between the second optical element and the third optical element, and the like. I have.

(2) The state of the light beam emitted from the light source means is converted into another state through the first optical element, and the converted light beam is converted by the second optical element through the third optical element. An image is formed on the deflecting surface of the deflecting element in a linear shape elongated in the main scanning direction, and the light beam deflected by the deflecting element is spotted on the surface to be scanned via the fourth optical element and the fifth optical element. In a scanning optical device that forms an image and scans the surface to be scanned, the third optical element and the fourth optical element are the same optical element and have an aspherical shape having refractive power only in the main scanning direction. It is characterized by consisting of a cylindrical mirror.

In particular, (2-1) when the angular magnification in the sub-scanning direction between the deflection element and the surface to be scanned is rs, the condition of rs <0.5 is satisfied; When the scanning efficiency of the deflecting element is Pduty, the condition of 0.7 <Pduty <0.95 is satisfied. (2-3) The cylindrical mirror is manufactured by plastic molding. 4) The fifth optical element is composed of a long lens manufactured by plastic molding having at least a refracting power in the sub-scanning direction, and (2-5) the deflection is performed via the third optical element. The light beam incident on the element is obliquely incident on the deflecting surface of the deflecting element within the sub-scanning cross section, and (2-6) the distance between the second optical element and the third optical element Is characterized in that an optical path bending mirror is provided in the optical path.

[0013]

FIG. 1A shows a first embodiment of the present invention.
1B is a plan view (main scanning cross-sectional view) of a main part of the optical system, and FIG. 1B is a cross-sectional view (sub-scanning cross-sectional view) of a main part perpendicular to the main scanning cross section of FIG.

In FIG. 1, reference numeral 1 denotes a light source means, for example, a semiconductor laser. Reference numeral 2 denotes a condenser lens serving as a first optical element, which converts a light beam (laser beam) emitted from the light source unit 1 into a divergent light beam. Reference numeral 3 denotes a stop, which restricts a passing light beam (light amount). Reference numeral 4 denotes a cylindrical lens as a second optical element, which has a predetermined refractive power only in the sub-scanning direction, and converts a light beam passing through the stop 3 into an optical path bending mirror 9 and a third optical element 6, which will be described later. An image is formed as a substantially linear image in the vicinity of the deflecting surface of the optical deflector 5 in the sub-scanning section through the sub-scanning section. Reference numeral 9 denotes an optical path bending mirror (reflection mirror), and the cylindrical lens 4
Are reflected to the third optical element 6 side.

Numeral 6 denotes a cylindrical mirror acting as a third optical element and a fourth optical element, which is manufactured by plastic molding and has a predetermined refractive power only in the main scanning direction. The mirror surface 6 in the main scanning direction is formed of an aspherical shape.

The function of the cylindrical mirror 6 in the present embodiment as a third optical element is to convert a divergent light beam via the optical path bending mirror 9 into a substantially parallel light beam in a main scanning section, and to perform the main scanning of the substantially parallel light beam. The light beam width (laser beam diameter) in the direction is set to be wider than the width in the main scanning direction of the deflecting surface of the optical deflector 5 described later. That is, in the present embodiment, a pupil scanning optical system is used in which a light beam having a sufficiently large light beam width is incident on the deflection surface of the optical deflector 5 in the main scanning direction, and the deflection surface itself is used as a pupil in the main scanning direction. I have. The function of the cylindrical mirror 6 as a fourth optical element is to condense the light beam (main deflection light beam) deflected and reflected by the optical deflector 5 and to scan with the fifth optical element 7 the scanning surface 8 in the main scanning section. An image is formed in a spot shape on the top.

Reference numeral 5 denotes an optical deflector as a deflecting element, which comprises, for example, a rotating polygon mirror (polygon mirror), and is rotated at a constant speed in a predetermined direction by a driving means (not shown) such as a motor. Reference numeral 7 denotes a long toric lens (long lens) serving as a fifth optical element, which is manufactured by plastic molding and has a predetermined refractive power only in the sub-scanning direction. Each element of the cylindrical mirror 6 and the long toric lens 7 constitutes one element of the imaging optical system (fθ lens system) 10. Reference numeral 8 denotes a photosensitive drum surface as a surface to be scanned.

In this embodiment, the light beam emitted from the semiconductor laser 1 after being modulated is converted into a divergent light beam by the condenser lens 2, and the light beam (light amount) is limited by the stop 3 and is incident on the cylindrical lens 4. Of the light beams incident on the cylindrical lens 4, the light beams in the sub-scanning cross section are converged and incident on the deflection surface of the optical deflector 5 obliquely via the optical path bending mirror 9 and the cylindrical mirror 6, and near the deflection surface. The image is formed substantially as a line image (a line image elongated in the main scanning direction). The luminous flux in the main scanning section is reflected by the optical path bending mirror 9 in a divergent state, converted into a substantially parallel luminous flux by passing through the cylindrical mirror 6, and is incident on the deflection surface of the optical deflector 5.
At this time, the light beam width (laser beam diameter) of the substantially parallel light beam is sufficiently wider than the deflecting surface of the light deflector 5 in the main scanning direction as described above.
It is split into (n / 2) deflection light beams. However, only one light beam (mainly deflected light beam) deflected and reflected toward the cylindrical mirror 6 is used as a scanning light beam, and the other light beams are shielded by a light shielding member (not shown) as a flare light beam. .

The main deflection light beam deflected and reflected by the light deflector 5 re-enters the cylindrical mirror 6 and is guided onto the photosensitive drum surface 8 via the long toric lens 7 to move the light deflector 5 to a predetermined position. By rotating the photosensitive drum 8 in the main scanning direction, optical scanning is performed on the photosensitive drum surface 8 in the main scanning direction. Thus, an image is recorded on the photosensitive drum surface 8 as a recording medium.

In this embodiment, the fθ characteristic is compensated for by the cylindrical mirror 6 and the long toric lens 7.
Conformal scanning on the photosensitive drum surface 8 is realized. Further, the cylindrical mirror 6 mainly corrects the image forming operation in the main scanning direction, and the long toric lens 7 mainly corrects the image forming operation in the sub-scanning direction and the tilt of the deflecting surface of the optical deflector 5. It is manufactured by plastic molding.

In the present embodiment, when the angular magnification in the sub-scanning direction between the optical deflector 5 and the photosensitive drum surface 8 is rs, the condition of rs <0.5 ‥‥‥‥ (1) is satisfied. I have. The conditional expression (1) relates to the angular magnification of the scanning optical device in the sub-scanning direction. If the conditional expression (1) is not satisfied, the light beam is obliquely incident on the deflection surface of the optical deflector 5 within the sub-scanning section. In the scanning optical system, it is difficult to reduce the bending of the scanning line, the rotation of the spot, and the like, which is not preferable.

Note that the angular magnification rs is u when the inclination angle of the paraxial ray in the sub-scanning direction on the deflection surface of the deflecting element in the sub-scanning direction is u '

[0023]

(Equation 1) Is defined by

In this embodiment, when the scanning efficiency of the optical deflector 5 is Pduty, the following condition is satisfied: 0.7 <Pduty <0.95 (2) Conditional expression (2) is an optical deflector 5
If the conditional expression (2) is not satisfied, it is difficult to reduce the size of the conventional scanning optical device, and it is difficult to set a low image clock.

The scanning efficiency Pduty is given by n when the number of surfaces of the deflection element is n and θy is the maximum exit angle of the light beam from the deflection element with respect to the optical axis of the fourth optical element.

[0026]

(Equation 2) Is defined by

In this embodiment, the lens shape of the cylindrical mirror 6 and the long toric lens 7 in the main scanning direction is an aspherical shape that can be expressed by a function up to the tenth order, and the lens of the long toric lens 7 in the sub-scanning direction. The shape is a spherical surface that changes continuously in the image height direction. The lens shape is
For example, the origin is the intersection of the optical surface and the optical axis, and the optical axis direction is X
Axis, the axis orthogonal to the optical axis in the main scanning section is the Y axis, and the axis orthogonal to the optical axis in the sub-scanning section is the Z axis, the generatrix direction corresponding to the main scanning direction is

[0028]

(Equation 3) Here, R is the radius of curvature, and K, B ₄ , B ₆ , B ₈ , and B ₁₀ are aspherical coefficients. The sagittal direction corresponding to the sub-scanning direction (the direction orthogonal to the main scanning direction including the optical axis) is:

[0029]

(Equation 4) Where 1 / r '= 1 / r + D ₂ Y ² + D ₄ Y ⁴ + D ₆ Y ⁶ + D ₈ Y ⁸ + D ₁₀
Y becomes ¹⁰ is expressed as in Equation.

Table 1 shows the optical arrangement and the surface shape of each optical element (cylindrical mirror and long toric lens) in this embodiment.

[0031]

[Table 1] In this embodiment, a plastic molded cylindrical mirror 6 having a predetermined refractive power only in the main scanning direction is used instead of a conventional glass lens as an optical element having both a collimating function and an imaging scanning function in the main scanning direction. . As a result, it is possible to enjoy the advantages of cost reduction and compactness due to the reduction in the number of lens components due to plasticization without being substantially affected by aberration fluctuations due to environmental fluctuations (particularly temperature changes).

In this embodiment, the scanning efficiency is defined as Pduty =
The optical deflector 5 is set at a high scanning efficiency of 0.89 to further reduce the size of the scanning optical device and reduce the image clock, and by setting the angular magnification in the sub-scanning direction to rs = 0.15. Also, in a scanning optical system in which a light beam is incident on the deflection surface in an oblique direction within the sub-scanning section, the bending of the scanning line and the rotation of the spot are reduced.

FIG. 2 is a diagram showing various aberrations showing paraxial aberrations (field curvature, scanning line bending, distortion) of the scanning optical apparatus according to the present embodiment.
The dotted line indicates the main scanning direction. As can be seen from the various aberration diagrams, in the present embodiment, paraxial aberration is corrected very well, and a scanning optical device suitable for high-definition printing is realized.

As described above, in this embodiment, in the scanning optical device suitable for high speed and high definition as described above, the scanning optical element (the third and fourth optical elements) which also has the function of collimating the light beam incident on the optical deflector. Element) is constituted by an aspherical cylindrical mirror formed of a plastic material having a predetermined refractive power only in the main scanning direction, thereby reducing the influence of environmental changes such as a temperature rise, and making the scanning optical element plastic. The weight and the number of lens components are reduced. In the present embodiment, the scanning optical system is constituted by the pupil scanning optical system. However, the present invention is not limited to this, and may be an ordinary scanning optical system.

FIG. 3A is a plan view (main scanning sectional view) of a main part of an optical system according to a second embodiment of the present invention, and FIG.
FIG. 3A is a vertical sectional view (sub-scan sectional view) of a main part in the main scanning section. 3A and 3B, FIG.
Elements that are the same as those shown in (A) and (B) are given the same reference numerals.

The present embodiment is different from the above-described first embodiment in that the deflection surface (polygon surface), which is the pupil in the main scanning direction, is reduced in order to reduce the spot diameter of the scanning optical device so as to cope with higher definition printing. The difference from the first embodiment is that the shapes of the cylindrical mirrors as the third and fourth optical elements are set accordingly. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

That is, in the figure, reference numeral 35 denotes an optical deflector (polygon mirror), which comprises a deflecting surface larger than the deflecting surface of the optical deflector 5 of the first embodiment shown in FIG. 3
Numeral 0 denotes an imaging optical system (fθ lens system), which comprises a cylindrical mirror 36 as third and fourth optical elements having a shape to be described later and a long toric lens 37 as a fifth optical element. .

Table 2 shows the optical arrangement and the surface shape of each optical element (cylindrical mirror and long toric lens) in this embodiment.

[0039]

[Table 2] In this embodiment, as in the first embodiment, a plastic molding having a predetermined refractive power only in the main scanning direction is used as an optical element having both a collimating function and an imaging scanning function in the main scanning direction, instead of a conventional glass lens. Is used. As a result, it is possible to enjoy the advantages of cost reduction and compactness due to the reduction in the number of lens components due to plasticization without being substantially affected by aberration fluctuations due to environmental fluctuations (particularly temperature changes).

Also in this embodiment, the scanning efficiency is Pdu
By setting a high scanning efficiency of ty = 0.89 to further reduce the size of the scanning optical device and reducing the image clock, and by setting the angular magnification in the sub-scanning direction to rs = 0.15, light deflection is achieved. In a scanning optical system in which a light beam is incident on the deflection surface of the device 35 in an oblique direction in the sub-scanning cross section, the bending of the scanning line and the rotation of the spot are reduced.

FIG. 4 is a diagram showing various aberrations showing paraxial aberrations (field curvature, scanning line bending, and distortion) of the scanning optical device according to the present embodiment.
The dotted line indicates the main scanning direction. As can be seen from these aberration diagrams, paraxial aberration is corrected very well in the present embodiment.

Further, in the present embodiment, the pupil (corresponding to the deflecting surface) in the main scanning direction is set to be about 20% larger than in the first embodiment, so that the spot diameter on the surface to be scanned is reduced. Smaller (main × sub = 50 μm × in this embodiment)
60 μm), thereby realizing a scanning optical device suitable for higher definition printing.

FIG. 5A is a plan view (main scanning sectional view) of a main part of an optical system according to Embodiment 3 of the present invention, and FIG.
FIG. 3A is a vertical sectional view (sub-scan sectional view) of a main part in the main scanning section. 5A and 5B, FIG.
Elements that are the same as those shown in (A) and (B) are given the same reference numerals.

The difference between the first embodiment and the first embodiment is that the angular magnification in the sub-scanning direction is reduced in the sub-scanning direction in order to reduce the bending of the scanning line of the scanning optical device and the rotation of the spot so as to cope with higher definition printing. The point is that the shape of the cylindrical mirror as the third and fourth optical elements is set accordingly. Other configurations and optical functions are substantially the same as those in the first embodiment,
Thereby, a similar effect is obtained.

That is, in the figure, reference numeral 50 denotes an imaging optical system (f
lens system), and has third and fourth
And a long toric lens 57 as a fifth optical element.

Table 3 shows the optical arrangement and the surface shape of each optical element (cylindrical mirror and long toric lens) in the present embodiment.

[0047]

[Table 3] Also in the present embodiment, as in the first embodiment, as an optical element having both a collimating function and an imaging scanning function in the main scanning direction, not a conventional glass lens but a plastic molding having a predetermined refractive power only in the main scanning direction. A cylindrical mirror 56 is used. As a result, it is possible to enjoy the advantages of cost reduction and compactness due to the reduction in the number of lens components due to plasticization without being substantially affected by aberration fluctuations due to environmental fluctuations (particularly temperature changes).

Also in this embodiment, the scanning efficiency is Pdu
By setting a high scanning efficiency of ty = 0.89, further reducing the size of the scanning optical device and reducing the image clock, and setting the angular magnification in the sub-scanning direction as rs = 0.05 lower. Also, in a scanning optical system in which a light beam is incident on a deflection surface of an optical deflector in an oblique direction in a sub-scanning cross section, scanning line bending and spot rotation are reduced.

FIG. 6 is a diagram showing various aberrations showing paraxial aberrations (field curvature, scanning line bending, and distortion) of the scanning optical apparatus according to the present embodiment.
The dotted line indicates the main scanning direction. As can be seen from these aberration diagrams, paraxial aberration is corrected very well in the present embodiment. In particular, the scanning line bending is reduced to about し て as compared with the first embodiment, thereby realizing a scanning optical device more suitable for high-definition printing.

[0050]

According to the present invention, as described above, in a scanning optical device suitable for high speed and high definition, a scanning optical element (third, third) having a function of collimating a light beam incident on a deflection element is provided.
(Fourth optical element) is constituted by an aspherical cylindrical mirror having a predetermined refractive power only in the main scanning direction, thereby reducing the effects of environmental fluctuations such as a temperature rise, and making the scanning optical element plastic and lightweight. Thus, it is possible to achieve a compact scanning optical device capable of reducing the number of lens components.

Further, the angular magnification r of the scanning optical device in the sub-scanning direction
By setting s to an appropriate value, even in a scanning optical system in which a light beam is incident on the deflection surface of the deflection element in an oblique direction in the sub-scanning cross section, it is possible to reduce scanning line bending and spot rotation. An optical device can be achieved.

Further, by setting the scanning efficiency Pduty of the deflecting element to an appropriate value, it is possible to realize a scanning optical device which can be made more compact than the conventional scanning optical device and can set the image clock lower. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part in a main scanning direction and a sub-scanning direction according to a first embodiment of the present invention.

FIG. 2 shows a paraxial aberration (field curvature,
Diagram showing scanning line bending and distortion)

FIG. 3 is a cross-sectional view of a main part in a main scanning direction and a sub scanning direction according to a second embodiment of the present invention.

FIG. 4 shows paraxial aberrations (field curvature,
Diagram showing scanning line bending and distortion)

FIG. 5 is a sectional view of a main part in a main scanning direction and a sub scanning direction according to a third embodiment of the present invention.

FIG. 6 shows paraxial aberrations (field curvature,
Diagram showing scanning line bending and distortion)

FIG. 7 is a perspective view of a main part of a conventional scanning optical device.

FIG. 8 is a sectional view of a main part of a conventional pupil scanning optical device in a main scanning direction.

[Explanation of symbols]

Reference Signs List 1 light source means (semiconductor laser) 2 first optical element (condensing lens) 3 aperture 4 second optical element (cylindrical lens) 5,35 optical deflector (polygon mirror) 6,36,56 third, fourth Optical element (cylindrical mirror) 7, 37, 57 Fifth optical element (long toric lens) 8 Scanned surface (photosensitive drum surface) 9 Optical path bending mirror 10, 20, 30 Imaging optical system (fθ lens system)

Claims (14)

[Claims] 1. A state of a light beam emitted from a light source means is set to a first state.
Is converted into another state through the optical element, and the converted light beam is imaged on the deflection surface of the deflection element as a linear line elongated in the main scanning direction via the second optical element and the third optical element. Let
A scanning optical device that scans the surface to be scanned by forming a light beam deflected and reflected by the deflecting element into a spot on the surface to be scanned via a fourth optical element and a fifth optical element. The third optical element and the fourth optical element are the same optical element, and are formed of aspherical cylindrical mirrors having refractive power only in the main scanning direction. And the light beam width of the substantially parallel light beam in the main scanning direction is made larger than the width of the deflecting surface of the deflecting element in the main scanning direction. A scanning optical device comprising a long lens having a refractive power at least in a sub-scanning direction. 2. The scanning optical system according to claim 1, wherein when an angular magnification between the deflection element and the surface to be scanned in the sub-scanning direction is rs, a condition of rs <0.5 is satisfied. apparatus. 3. The scanning optical device according to claim 1, wherein a condition of 0.7 <Pduty <0.95 is satisfied when the scanning efficiency of the deflection element is Pduty. 4. The cylindrical mirror according to claim 1, wherein said cylindrical mirror is manufactured by plastic molding.
The scanning optical device according to claim 1. 5. The scanning optical device according to claim 1, wherein said long lens is manufactured by plastic molding. 6. A substantially parallel light beam incident on the deflection element via the third optical element is obliquely incident on a deflection surface of the deflection element in a sub-scan section. Item 2. The scanning optical device according to Item 1. 7. The scanning optical apparatus according to claim 1, wherein an optical path bending mirror is provided in an optical path between the second optical element and the third optical element. 8. The state of a light beam emitted from the light source means is set to a first state.
Is converted into another state through the optical element, and the converted light flux is imaged by the second optical element via the third optical element on the deflecting surface of the deflecting element in a linear shape elongated in the main scanning direction. And a light beam deflected by the deflecting element is formed into a spot image on a surface to be scanned via a fourth optical element and a fifth optical element, thereby scanning the surface to be scanned. A scanning optical device, wherein the third optical element and the fourth optical element are the same optical element and are each formed of an aspheric cylindrical mirror having refractive power only in the main scanning direction. 9. The scanning optical system according to claim 8, wherein a condition of rs <0.5 is satisfied when an angular magnification between the deflection element and the surface to be scanned in the sub-scanning direction is rs. apparatus. 10. The scanning optical apparatus according to claim 8, wherein, when the scanning efficiency of the deflection element is Pduty, a condition of 0.7 <Pduty <0.95 is satisfied. 11. The scanning optical device according to claim 8, wherein the cylindrical mirror is manufactured by plastic molding. 12. The scanning optical device according to claim 8, wherein said fifth optical element is formed of a long lens manufactured by plastic molding having a refractive power at least in a sub-scanning direction. 13. The light beam incident on the deflecting element via the third optical element is incident on the deflecting surface of the deflecting element from an oblique direction in a sub-scan section. The scanning optical device according to claim 1. 14. The scanning optical apparatus according to claim 8, wherein an optical path bending mirror is provided in an optical path between said second optical element and said third optical element.