Optical scanning device and image forming apparatus using the same
An optical scanning device includes a light source device, a deflector, an input optical system for directing a light beam from the light source device onto the deflector, and an imaging optical system for imaging a light beam scanningly deflected by a deflecting surface of the deflector, upon a scan surface to be scanned, wherein, in a sub-scan section, a light beam directed from the input optical system toward the deflecting surface of the deflector is incident thereon at a finite angle with respect to a plane which is orthogonal to a rotational axis of the deflector, wherein the imaging optical system includes at least one molded imaging lens, and wherein a shape within a sagittal section of at least one lens surface, of lens surfaces of the at least one imaging lens, is non-arcuate, and a sagittal curvature in a light beam passage region has an extreme value.
1. An optical scanning device, comprising:
light source means;
deflecting means;
an input optical system configured to direct a light beam from said light source means onto said deflecting means; and
an imaging optical system configured to image a light beam scanningly deflected by a deflecting surface of said deflecting means, upon a scan surface to be scanned,
wherein, in a sub-scan section, a light beam directed from said input optical system toward the deflecting surface of said deflecting means is incident thereon at a finite angle with respect to a plane which is orthogonal to a rotational axis of said deflecting means,
wherein said imaging optical system includes at least one molded imaging lens,
wherein a shape within a sagittal section of at least one lens surface, of lens surfaces of said at least one imaging lens, is non-arcuate, and a sagittal curvature in a light beam passage region has an extreme value, and
wherein, when N denotes a value which is obtainable by converting a difference between the sagittal curvature at a passage position of a principal ray of a light beam and the sagittal curvature at a central position of the lens surface, into a Newton number with respect to a 3 mm width, within the sagittal section, the shape of said at least one lens surface of said imaging lens in the sagittal section satisfies a condition
0.7 <N< 10
over the whole region in a main-scan direction in which the light beam passes.
2. An optical scanning device according to claim 1 , wherein a shape within the sagittal section of at least one surface of the lens surfaces of said imaging lens is such that a local minimum point of the sagittal curvature is located at a lens center, while a local maximum point of the sagittal curvature is located inside the light beam passage region.
3. An optical scanning device according to claim 1 , wherein a shape within the sagittal section of said at least one lens surface of said imaging lens is such that a local maximum point of the sagittal curvature is located at a lens center, while a local minimum point of the sagittal curvature is located inside the light beam passage region.
4. An optical scanning device according to claim 1 , wherein a shape of said at least one lens surface of said imaging lens in the sagittal section is such that the difference between the sagittal curvature at a passage position of a principal ray of the light beam and the sagittal curvature at a central position of the lens surface increases with a distance in a main-scan direction from an optical axis.
5. An optical scanning device according to claim 1 , wherein a shape of said at least one lens surface of said imaging lens in the sagittal section is such that a central position of the lens surface and a passage position of a principal ray of the light beam are deviated from each other.
6. An optical scanning device according to claim 1 , wherein said at least one lens surface of said imaging lens is a lens surface closest to the scan surface.
7. An optical scanning device according to claim 1 , wherein said at least one lens surface of said imaging lens is a lens surface having a largest refracting power in the sub-scan section.
8. An optical scanning device according to claim 1 , wherein a shape of said at least one lens surface of said imaging lens within the sagittal section has a positive refracting power or a negative refracting power over the whole region in the sagittal section.
9. An image forming apparatus, comprising:
an optical scanning device as recited in claim 1 ;
a photosensitive member disposed at the scan surface to be scanned;
a developing device for developing an electrostatic latent image formed on said photosensitive member with a light beam scanningly deflected by said optical scanning device, to produce a toner image;
a transferring device for transferring the developed toner image onto a transfer material; and
a fixing device for fixing the transferred toner image, on the transfer material.
10. An image forming apparatus, comprising:
an optical scanning device as recited in claim 1 ; and
a printer controller for converting code data supplied from an outside machine into an imagewise signal and for inputting the imagewise signal into said optical scanning device.