JP2001311896A - Scanning image-formation lens, scanning image-formation optical system, optical scanner, optical scanning method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce or prevent the bend of a scanning line in an optical scanner including a plastic lens formed by die forming in a scanning image-formation optical system. SOLUTION: A lens 404 constituting at least one part of the scanning image- formation optical system for forming a light spot on a surface to be scanned by condensing deflected luminous flux deflected by a light deflector 403 toward the surface to be scanned is molded by the molding work of transparent resin material, formed to be a strip long in a main scanning direction, and its end face 4041 on a lens side in a subscanning direction has a very small cone angle to a lens optical axis AX, and the lens optical axis AX is deviated by a specified distance in the subscanning direction from the symmetric axis (ax) of refractive index distribution in the subscanning direction made inside the lens during the molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning image forming lens, a scanning image forming optical system, an optical scanning device, an optical scanning method, and an image forming apparatus.

[0002]

2. Description of the Related Art A light beam from a light source is deflected by an "optical deflector that rotates a deflecting and reflecting surface" such as a rotary polygon mirror, and the deflected light beam is collected toward a surface to be scanned by a scanning and imaging optical system. 2. Description of the Related Art An optical scanning device that forms a light spot on a surface to be scanned by light emission and performs optical scanning on the surface to be scanned has been widely known in relation to a digital copying machine, an optical printer, and the like. In such an optical scanning device, a scanning imaging optical system (or a part thereof) is used as a scanning imaging optical system (or a part thereof) by plastic molding for the purpose of improving performance by employing an aspherical surface or the like and reducing the cost of manufacturing a lens. Lenses are being used. A scanning imaging lens formed by plastic molding is formed by heating a resin such as polycarbonate or acrylic into a liquid state and injecting the resin into a mold. At that time, when the plastic cools and solidifies in the mold, the cooling starts from the part in contact with the mold surface,
It gradually reaches the center of the lens. Therefore, a temperature distribution occurs in the lens during cooling, and the liquid plastic has a tendency to flow to a portion that has been cooled and solidified first. Unevenness occurs. That is, the density of the scanning imaging lens manufactured by plastic molding is generally "gradually decreased from near the lens surface to the center of the lens". Since the plastic has "the higher the density, the higher the refractive index", the refractive index in the lens gradually increases from the center of the lens toward the lens surface due to the density distribution. When such a refractive index distribution exists in the lens, the refractive index distribution itself has a lens function in addition to the lens function due to the curvature of the lens surface. Since a plastic lens is designed to have a uniform refractive index inside, if the above-mentioned "refractive index distribution" exists inside the lens, it is not possible to accurately realize the designed optical characteristics. If the scanning image forming optical system includes a plastic lens having a non-uniform refractive index distribution, the image forming position of the light spot shifts from the designed image forming position, and the spot diameter increases.

Since the refractive index increases as it approaches the lens surface, the effect of the refractive index distribution is equivalent to a "concave lens".
Therefore, it has been proposed to adjust the position of the imaging system closer to the light source than the plastic lens to correct the shift of the light spot imaging position due to the refractive index distribution in the plastic lens (Japanese Patent Laid-Open No. 11-2768). No.). When a plastic lens is used for the scanning image forming optical system, there is a problem of "bending of a scanning line" in which a locus of a light spot draws a curve, in addition to the non-uniform refractive index. As previously mentioned,
A plastic lens is molded by injecting a resin that has been heated to a liquid state into a mold, and the lens cooled and solidified in the mold is taken out of the mold. In general, in order to improve the "releasability from the mold", a "taper for die-cutting" is generally provided at a portion where the "lens-side end surface" of the mold is formed. The lens used in the scanning imaging optical system is generally “strip-shaped” which is long in the main scanning direction, and the lens-side end surface along the length direction is “the lens-side end surface in the sub-scanning direction”. Since a "taper for mold release" is also formed on the lens-side end surface of this lens, this side end surface is a straight line connecting the center of the paraxial curvature of the lens optical axis (the paraxial curvature center of the entrance-side lens surface and the exit-side lens surface). ) At a very small angle (about 1 to 3 degrees). In general, the “lens-side end face in the sub-scanning direction” is a reference plane for attachment to the “light-scanning casing” in which each optical system in the optical scanning device is assembled. The optical axis of the lens is inclined in the sub-scanning direction with respect to "deflection scanning surface (in this specification, a plane on which the principal ray of the deflected light beam sweeps with deflection)". For this reason, the direction of the principal ray of the light beam emitted from the plastic lens is tilted with respect to the deflection scanning surface, and the above-described “scanning line bending” occurs.

[0004]

SUMMARY OF THE INVENTION According to the present invention, there is provided an optical scanning apparatus including a plastic lens formed by molding in a scanning image forming optical system, wherein the bending of the scanning line is effectively reduced or prevented. It is an object of the present invention to make it possible to perform light scanning with ease.

[0005]

According to the present invention, there is provided a scanning image forming lens for forming a light spot on a surface to be scanned by converging a light beam deflected by an optical deflector toward a surface to be scanned. A lens forming at least a part of the scanning image forming optical system, which is formed by molding a transparent resin material, has a rectangular shape elongated in the main scanning direction, and has a lens-side end surface in the sub-scanning direction which is a lens optical axis. Has a small taper angle. The lens optical axis is "shifted by a predetermined distance in the sub-scanning direction" with respect to "the axis of symmetry of the refractive index distribution in the sub-scanning direction" generated inside the lens due to molding. As described above, since the scanning imaging lens constitutes "at least a part of the scanning imaging optical system", the scanning imaging optical system is referred to as "the scanning imaging lens and another imaging optical element (imaging mirror). And an imaging lens). However, a scanning imaging optical system can also be constituted only by a scanning imaging lens. When the scanning imaging optical system is configured by “the scanning imaging lens and the other imaging optical element”, as one mode of the combination,
A combination of a scanning imaging lens and a toroidal lens is conceivable. In this case, the scanning imaging lens has an fθ function (fθ function).
Lens function) and placed on the optical deflector side,
By disposing the toroidal lens on the surface to be scanned, it is possible to form a scanning image forming optical system having two lenses (claim 2). The scanning image forming optical system according to the present invention is provided for converging a deflected light beam deflected by an optical deflector of a method of rotating a deflecting reflection surface toward a surface to be scanned and forming a light spot on the surface to be scanned. "A scanning image forming optical system", and includes a scanning image forming lens and a toroidal lens according to claim 2. And
This scanning image forming optical system has a function of making the position of the deflecting reflection surface of the optical deflector and the position of the surface to be scanned "a substantially geometrically conjugate relationship" in the sub-scanning direction (claim 3). The optical scanning device according to the present invention is configured such that "a light deflector that rotates a deflecting and reflecting surface deflects a light beam from a light source side, condenses the deflected light beam toward a surface to be scanned by a scanning image forming optical system, 4. An optical scanning device that forms a light spot on a scanning surface and optically scans a scanned surface, wherein the scanning imaging optical system according to claim 3 is used. The scanning image forming lens constituting the unit is "attached to the holding unit with the lens-side end surface in the sub-scanning direction as an attachment surface", but this attachment surface "has a small taper angle with respect to the optical axis in the sub-scanning direction" Accordingly, the lens optical axis is inclined by a small angle in the sub-scanning direction with respect to the deflection scanning surface.

[0006] Since the scanning imaging lens is formed by molding a plastic, it has a refractive index distribution inside. However, the deviation of the optical axis of the lens in the sub-scanning direction with respect to the axis of symmetry of the refractive index distribution in the sub-scanning direction. The amount is determined so as to correct the bending of the scanning line due to the inclination of the minute angle of the lens optical axis (claim 4). The “optical deflector of the type that rotates the deflecting reflection surface” includes a rotating single-sided mirror, a rotating two-sided mirror, a rotating polygonal mirror, and the like. 5. The optical scanning device according to claim 4, wherein a "semiconductor laser" is used as a light source, and a divergent light beam emitted from the semiconductor laser is "coupled optical system".
And the coupled light flux is formed as a "long line image in the main scanning direction" near the deflection reflecting surface of the optical deflector by the "line image forming optical system". (Claim 5). The optical scanning method according to the present invention includes a method of deflecting a light beam from a light source side by an optical deflector that rotates a deflecting and reflecting surface, condensing the deflected light beam toward a surface to be scanned by a scanning image forming optical system, and An optical scanning method for forming an optical spot on a scanning surface and optically scanning a surface to be scanned ”, wherein the optical scanning method is performed using the optical scanning device according to claim 4 or 5. Item 6).
The image forming apparatus of the present invention is an “image forming apparatus that forms a latent image by performing optical scanning on a photosensitive surface of a photosensitive medium by an optical scanning device and visualizes the latent image to obtain an image”. According to a fourth aspect of the present invention, there is provided an optical scanning apparatus for performing optical scanning of a surface, the optical scanning apparatus being configured as described above. 8. The image forming apparatus according to claim 7, wherein the photosensitive medium is a photoconductive photoreceptor, and an electrostatic latent image formed by uniform charging of the photosensitive surface and optical scanning of the optical scanning device is visualized as a toner image. It can be configured (claim 8). 8. The image forming apparatus according to claim 7, wherein the toner image is fixed on a sheet-shaped recording medium (transfer paper or "OHP sheet (plastic sheet for an overhead projector)"). In this case, the latent image formed by the optical scanning by the optical scanning device can be visualized by a developing method of a normal silver halide photographic process. Such an image forming device is, for example, an “optical plate making device” or The image forming apparatus according to claim 8 can be specifically implemented as a laser printer, a laser plotter, a digital copying apparatus, a facsimile apparatus, or the like.

[0007]

FIG. 1A is an explanatory view showing an optical scanning device according to the present invention. The light source device 401 is configured such that “a divergent light beam from a semiconductor laser as a light source is converted into a parallel light beam by a coupling lens and emitted”. The parallel light beam emitted from the light source device 401 is applied to a cylinder lens 4 as a “line image forming optical system”.
As a result, the light is condensed in the sub-scanning direction and forms an image as a long line image in the main scanning direction at the position of the deflecting reflection surface of the rotary polygon mirror 403 as an “optical deflector”. The light beam reflected by the deflecting / reflecting surface becomes a deflecting light beam that is deflected at a constant angular velocity as the rotating polygon mirror 403 rotates at a constant speed. The deflected light beams are transmitted through lenses 404 and 4
05 are sequentially transmitted to the surface to be scanned, a light spot is formed on the surface to be scanned, and the scanning line 406 is optically scanned. The lens 404 is an fθ lens and the lens 405 is a toroidal lens, and these constitute a “scanning optical system”. "F
The lens 404 that is the “θ lens” is the “scanning imaging lens” of the present invention, and is manufactured by molding plastic. FIG. 1B shows a state where the scanning imaging lens 404 is viewed from the sub-scanning direction. The upper side in FIG. 1B is the incident side, and the horizontal direction is the main scanning direction. Scanning imaging lens 4
Numeral 04 has a shape as shown in the upper diagram of FIG. Here, reference is made to FIG. FIG.
2 shows a cross section of a molding die (a flat cross section by a plane orthogonal to the main scanning direction). The molding die includes a metal piece 302 for transferring the incident side surface of the lens 404 and a metal piece 30 for transferring the emission side surface.
4. Consisting of fixed dies 305 and 306 and separated dies 307 and 308, resin is injected and filled in a space 309 surrounded by these. After filling, the resin cools rapidly and solidifies,
The separation molds 307 and 308 are separated from each other by the division surface 310, and the molded product is taken out. At that time, the molded product and the separation mold 307, 3
08, so that the separation is smoothly performed.
08 side surfaces 3071 and 3081 are generally referred to as “divided surface 31”.
A taper of 1 to 3 degrees is provided in a direction "from 0 toward the back side of the mold". The “lens-side end surface” formed by the surface 3081 is the lens-side end surface 4041 in the sub-scanning direction in the upper diagram of FIG. 1C, and the lens-side end surface 4041 is a reference surface for attachment to the optical scanning casing. .

FIG. 1D shows a state in which a scanning image forming lens 404 is attached to a lens installation portion 50 of an optical scanning casing, and
A state of attachment 41 is shown. Lens installation part 5
Since the upper surface of the scanning imaging lens 404 is attached parallel to the deflection scanning surface as shown in FIG. 1D, when the scanning imaging lens 404 is attached as shown in FIG. The axis AX is in the sub-scanning direction (vertical direction in the figure)
To lean on. Returning to FIG. 1C, the scanning imaging lens 404 has a substantially symmetrical shape with a plane including the axis ax and orthogonal to the drawing as a “symmetric plane”. Accordingly, the distribution of the refractive index: n generated upon cooling of the lens forming process (FIG. 1)
((C) below) has a shape symmetrical with respect to the above-mentioned symmetry plane. The “symmetric axis ax of the refractive index distribution” is shifted from the optical axis AX of the scanning imaging lens 404 (the axis of symmetry with respect to the lens surface shape) by a shift amount Δ in the sub-scanning direction. In other words, in the scanning imaging lens 404, the optical axis AX is shifted in the sub-scanning direction with respect to the symmetric axis ax in the sub-scanning direction (that is, the axis of symmetry of the refractive index distribution in the sub-scanning direction). Only ". If the scanning imaging lens is molded under the same material and under the same conditions using a mold having the same shape, the “refractive index distribution” in each mass-produced scanning imaging lens also has the same distribution. Please refer to FIG. In FIG. 2B, reference numeral 404 ′ indicates “a lens having substantially the same shape as the scanning imaging lens 404”. In this lens 404 ', the refractive index inside the lens is uniform,
The optical axis AX ′ matches the axis of symmetry of the lens shape in the sub-scanning direction. Such a lens 404 'is attached to the optical scanning casing as shown in FIG. 1D, and the optical axis AX' has an angle α 'with respect to the polarization scanning surface (due to the taper of the mounting surface).
When a deflected light beam is incident in a state where the light beam is only inclined, the principal ray PL ′ (incident at the height of the optical axis on the incident side surface of the lens 404 ′) is refracted as shown in the drawing (the refraction state is emphasized). ), The principal ray PL ′ of the deflected light beam emitted from the lens 404 ′ is inclined by an angle β ′ with respect to the deflection scanning surface. Considering the state in which the deflected light beam thus emitted enters the toroidal lens 405 in FIG. 1A, the distance that the beam emitted from the lens 404 ′ reaches the toroidal lens 405 increases as the deflection angle increases. Toroidal lens 4
The trajectory of the incident position on the plane of incidence to 05 curves with the deflection angle into an "upward convex" shape, which causes the scanning line to bend on the surface to be scanned.

FIG. 2A shows the height of the optical axis of the incident surface when the optical axis AX of the scanning image forming lens 404 is inclined with respect to the deflection scanning surface by an angle α (due to the taper of the lens-side end surface). Further, a state where a deflected light beam is incident is schematically shown. The principal ray PL of the deflected light beam is refracted on the incident side surface, but the optical axis AX is shifted with respect to the axis of symmetry ax in the sub-scanning direction of the refractive index distribution. And therefore the refraction angle also increases. The refractive index of the scanning image forming lens 404 is as shown in FIG.
The trajectory of the chief ray PL in the scanning imaging lens is “upward” as shown in the figure, since the light beam that propagates through the medium has a property of “bending to a direction having a larger refractive index” since it gradually increases upward from the axis ax. And the principal ray PL of the light beam emitted from the scanning imaging lens 404 can be substantially matched with the polarization scanning plane. Of course, for this, it is necessary to adjust the shift amount Δ between the axis ax and the optical axis AX according to the distribution of the refractive index. The condition for "matching the chief ray substantially to the polarization scanning plane" can be determined experimentally. In the above embodiment, the cooling condition of the scanning imaging lens in the sub-scanning direction is symmetrical with respect to the center of the lens, so that the central axis ax of the refractive index distribution in the sub-scanning direction is obtained.
Is matched with the center position of the scanning imaging lens in the sub-scanning direction, but conversely, `` the optical axis position is matched with the symmetric axis position in the sub-scanning direction '', and there is a temperature difference in the mold during cooling. By doing so, the axis of symmetry of the refractive index distribution may be shifted with respect to the optical axis.

In the embodiment described above with reference to FIGS. 1 to 3, the "scanning imaging lens" converges the deflected light beam deflected by the optical deflector 403 toward the surface to be scanned, and A lens 404 constituting at least a part of a scanning image forming optical system for forming a light spot on a scanning surface, which is formed by a molding process of a transparent resin material, has a strip shape long in the main scanning direction, Lens-side end surface 4041 in scanning direction
Has a small taper angle with respect to the lens optical axis, and sets the lens optical axis AX in the sub-scanning direction with respect to the symmetry axis ax of the refractive index distribution in the sub-scanning direction generated inside the lens due to molding. Distance: Δ shifted (claim 1), and a scanning image forming optical system having a two-element configuration together with the toroidal lens 405 disposed on the optical deflector 403 side and having the fθ function and disposed on the scanning surface side. A system is constituted (claim 2). Further, the “scanning optical system” in the above embodiment condenses the deflected light beam deflected by the optical deflector 403 of the type that rotates the deflecting reflection surface toward the surface to be scanned, and forms the light beam on the surface to be scanned. 3. A scanning image forming optical system for forming a light spot, comprising: a scanning image forming lens 404 and a toroidal lens 40 according to claim 2.
5 and has a function of making the position of the deflecting reflection surface of the optical deflector 403 and the position of the surface to be scanned substantially geometrically optically conjugate with respect to the sub-scanning direction. In the “optical scanning device” of the above embodiment, the light deflector 403 that rotates the deflecting / reflecting surface deflects the light beam from the light source side, and deflects the deflecting light beam onto the surface to be scanned by the scanning image forming optical system. 4. An optical scanning apparatus for converging light toward the surface to be scanned, forming a light spot on the surface to be scanned, and optically scanning the surface to be scanned, wherein the scanning and imaging optical systems 404 and 405 are those according to claim 3. The image lens 404 is attached to the holder 50 with the “lens side end surface 4041 in the sub-scanning direction” having a small taper angle with respect to the optical axis in the sub-scanning direction, so that the lens optical axis AX is deflected. The axis of symmetry of the refractive index distribution in the sub-scanning direction of the scanning imaging lens so as to correct the scan line bending caused by the small angle tilt in the sub-scanning direction with respect to the scanning surface and the slight angle tilt of the lens optical axis. ax Sub-scanning direction shift amount of's optical axis AX: delta
(Claim 4). And
The light source is a "semiconductor laser", which has a coupling optical system (coupling lens) for coupling a divergent light beam emitted from the semiconductor laser to a subsequent optical system, and the coupled light beam forms a line image. By the image optical system 402,
An image is formed near the deflection reflection surface of the optical deflector as a linear image long in the main scanning direction.

Therefore, by using the optical scanning device of the above-described embodiment, the light deflector 403 that rotates the deflecting / reflecting surface deflects the light beam from the light source side, and converts the deflected light beam into a scanning image forming optical system 404. , 405 converge toward the surface to be scanned, form an optical spot on the surface to be scanned, and perform an optical scanning method for optically scanning the surface to be scanned (claim 6). Finally, referring to FIG. 4, the first embodiment of the image forming apparatus will be described.
The form will be described. This image forming apparatus is a “laser printer”. The laser printer 100 includes a photosensitive medium 111
As a photoconductive photoconductor formed in a cylindrical shape. Around the photosensitive medium 111, a charging roller 112 as a charging unit, a developing device 113, a transfer roller 11
4. A cleaning device 115 is provided. A well-known "corona charger" can be used as the charging means. Further, the optical scanning device 117 using the laser beam LB
Is provided, and “exposure by optical writing” is performed between the charging roller 112 and the developing device 113. FIG.
, Reference numeral 116 denotes a fixing device, reference numeral 118 denotes a cassette, reference numeral 119 denotes a pair of registration rollers, reference numeral 120 denotes a paper feed roller, reference numeral 121 denotes a conveyance path, reference numeral 122 denotes a pair of discharge rollers, reference numeral 123 denotes a tray, and reference numeral P denotes recording. The transfer paper is shown as a medium. When performing image formation, the photosensitive medium 111, which is a photoconductive photoconductor, is rotated clockwise at a constant speed, and the surface thereof is uniformly charged by the charging roller 112.
An electrostatic latent image is formed by exposure of the laser beam LB of the optical scanning device 117 by optical writing. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.
This electrostatic latent image is reversely developed by the developing device 113,
A toner image is formed on the image carrier 111. Transfer paper P
Is detachable from the main body of the image forming apparatus 100. When the cassette 118 is mounted as shown in FIG.
0 is fed. The fed transfer paper P has its leading end held by a pair of registration rollers 119. The registration roller pair 119 sends the transfer paper P to the transfer portion in synchronization with the timing at which the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer section, and the toner image is electrostatically transferred by the operation of the transfer roller 114. The transfer paper P on which the toner image has been transferred is sent to the fixing device 116 and the fixing device 1
At 16, the toner image is fixed, and is discharged onto a tray 123 by a discharge roller pair 122 through a conveyance path 121. The surface of the image carrier 111 after the transfer of the toner image is cleaned by the cleaning device 115 to remove residual toner, paper dust, and the like. The above-described OHP sheet or the like can be used instead of the transfer paper, and the transfer of the toner image is performed by using an “intermediate transfer medium” such as an intermediate transfer belt.
Can also be performed via Optical scanning device 11
As 7, good image formation can be performed by using an optical scanning device as shown in FIG.

Accordingly, the image forming apparatus is provided with the photosensitive medium 1
11. An image forming apparatus for forming a latent image by performing optical scanning on a photosensitive surface of an optical scanning device 117 and visualizing the latent image to obtain an image, wherein the optical scanning device performs optical scanning of a photosensitive surface of a photosensitive medium. As the 117, the one described in claim 4 or 5 is used (claim 7), the photosensitive medium 111 is a photoconductive photoconductor, and the photosensitive surface is uniformly charged and the optical scanning of the optical scanning device is performed. Is visualized as a toner image (claim 8).

[0013]

As described above, according to the present invention, a novel scanning imaging lens, scanning imaging optical system, optical scanning device, optical scanning method, and image forming apparatus can be realized. Since the present invention is as described above, the scanning line bending caused by the taper of the mounting surface of the “scanning imaging lens formed by plastic molding” included in the scanning imaging optical system is effectively reduced or prevented. It is possible.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of an optical scanning device of the present invention.

FIG. 2 is a diagram for explaining an effect of preventing scanning line bending.

FIG. 3 is a view for explaining a mold for a scanning image forming lens.

FIG. 4 is a diagram illustrating an example of an embodiment of an image forming apparatus.

[Explanation of symbols]

401 Light source device 402 Cylinder lens (line image forming optical system) 403 Rotating polygon mirror (optical deflector) 404 Scanning lens 405 Toroidal lens 406 Scan line ax Symmetry axis of refractive index distribution AX Lens optical axis Δ Symmetry axis ax Amount of displacement of lens optical axis AX in the sub-scanning direction

Claims (8)

[Claims] 1. A scanning image forming optical system for converging a deflecting light beam deflected by an optical deflector toward a surface to be scanned and forming a light spot on the surface to be scanned. The lens is formed by molding a transparent resin material, has a strip shape that is long in the main scanning direction, and the lens side end surface in the sub-scanning direction has a small taper angle with respect to the lens optical axis. A scanning imaging lens, wherein the optical axis of the lens is shifted by a predetermined distance in the sub-scanning direction with respect to the axis of symmetry of the refractive index distribution in the sub-scanning direction generated inside the lens. 2. The scanning image forming optical system according to claim 1, wherein the scanning image forming optical system has an fθ function disposed on the optical deflector side and a toroidal lens disposed on the scanning surface side. A scanning imaging lens comprising a system. 3. A deflected light beam deflected by an optical deflector that rotates a deflective reflection surface is converged toward a surface to be scanned.
3. A scanning image forming optical system for forming a light spot on the surface to be scanned, comprising a scanning image forming lens according to claim 2 and a toroidal lens, wherein a position of a deflecting reflection surface of an optical deflector and a position of a scanning object. A scanning image forming optical system having a function of making a surface position substantially geometrically conjugate with respect to a sub-scanning direction. 4. An optical deflector for rotating a deflecting / reflecting surface, deflecting a light beam from a light source side, and condensing the deflecting light beam toward a surface to be scanned by a scanning image forming optical system. 4. An optical scanning device which forms a light spot thereon and optically scans the surface to be scanned, wherein the scanning image forming optical system is the one according to claim 3, wherein the scanning image forming lens is configured to emit light in a sub-scanning direction. With the lens side end surface in the sub-scanning direction having a small taper angle with respect to the axis as a mounting surface, the lens optical axis is tilted in the sub-scanning direction by a small angle with respect to the deflection scanning surface by being attached to the holding portion. In the scanning image forming lens, the amount of deviation of the lens optical axis in the sub-scanning direction with respect to the axis of symmetry of the refractive index distribution in the sub-scanning direction is corrected so as to correct the bending of the scanning line due to the inclination of the small angle of the lens optical axis. It is characterized by being decided That the optical scanning device. 5. The optical scanning device according to claim 4, wherein the light source is a semiconductor laser, and has a coupling optical system for coupling a divergent light beam emitted from the semiconductor laser to a subsequent optical system. An optical scanning device, wherein a ringed light beam is imaged by a line image imaging optical system as a long line image in a main scanning direction near a deflection reflecting surface of an optical deflector. 6. An optical deflector for rotating a deflecting / reflecting surface, deflects a light beam from a light source side, and condenses the deflecting light beam toward a surface to be scanned by a scanning image forming optical system. An optical scanning method for forming an optical spot thereon and optically scanning the surface to be scanned, wherein the optical scanning method is performed using the optical scanning device according to claim 4 or 5. 7. An image forming apparatus for forming a latent image by performing optical scanning on a photosensitive surface of a photosensitive medium by an optical scanning device and visualizing the latent image to obtain an image, wherein the light on the photosensitive surface of the photosensitive medium is obtained. An image forming apparatus comprising: an optical scanning device that performs scanning; 8. The image forming apparatus according to claim 7, wherein the photosensitive medium is a photoconductive photoreceptor, and the electrostatic latent image formed by uniform charging of the photosensitive surface and optical scanning of the optical scanning device is:
An image forming apparatus which is visualized as a toner image.