1. An optical element for focusing a plurality of optical beams deflected by an optical deflector on a scanned surface in a multi-beam optical scanner as a plurality of optical spots wherein said optical beams are emitted by a multi-beam illuminant having a plurality of beam emitting points, comprising:
a lens having a refractive index distribution,
wherein said lens, which serves as one component of an optical system in said multi-beam optical scanner, is designed to correct an optical spot pitch deviation on the scanned surface, which is defined as 1\u2212\u03b2min\u03b2max where \u03b2max (\u03bcm) and \u03b2min (\u03bcm) are a maximal value and a minimal value of pitches of the optical spots on the scanned surface, respectively, due to said refractive index distribution with respect to image heights.
2. The optical element as claimed in claim 1, wherein said optical spot pitch deviation with respect to the image heights is less than or equal to 0.1.
3. The optical element as claimed in claim 1, wherein said lens is formed of plastics.
4. The optical element as claimed in claim 3, wherein said refractive index distribution of the lens is more than or equal to 0.5\xd710\u22126 in an effective range of said lens corresponding to an effective write width W (mm) scanned by each of the optical spots on the scanned surface.
5. The optical element as claimed in claim 1, wherein said optical system has at least one second optical element, and said lens has a maximal value of a lens thickness deviation, which is defined as 1\u2212DminDmax where Dmax (mm) and Dmin (mm) are a maximal lens thickness and a minimal lens thickness, respectively, with respect to an optical axis direction for each position of a main scanning direction among lenses included in said optical system.
6. The optical element as claimed in claim 5, wherein said lens is shaped such that the lens thickness deviation is more than or equal to 0.65 in an effective range of said lens corresponding to an effective write width W (mm) scanned by each of the optical spots on the scanned surface.
7. The optical element as claimed in claim 1, wherein said optical system has at least one second optical element, and said lens has greater power with respect to a sub-scanning direction than any other optical elements included in said optical system.
8. A multi-beam optical scanner for optically scanning a scanned surface, comprising:
a multi-beam illuminant emitting a plurality of optical beams, said multi-beam illuminant having a plurality of beam emitting points;
an optical deflector deflecting said optical beams; and
an optical system focusing said deflected optical beams on the scanned surface as a plurality of optical spots,
wherein said optical system has an optical element comprising: a lens having a refractive index distribution, wherein said lens is designed to correct an optical spot pitch deviation on the scanned surface, which is defined as 1\u2212\u03b2min\u03b2max where \u03b2max (\u03bcm) and \u03b2min (\u03bcm) are a maximal value and a minimal value of pitches of the optical spots on the scanned surface, respectively, due to said refractive index distribution with respect to image heights.
9. An image forming apparatus for forming an image, comprising:
a photosensitive image carrier;
an optical scanning part scanning a scanned surface of said photosensitive image carrier so as to form a latent image; and
a developing part developing said latent image so as to obtain the image,
wherein said optical scanning part is a multi-beam optical scanner, comprising: a multi-beam illuminant emitting a plurality of optical beams, said multi-beam illuminant having a plurality of beam emitting points; an optical deflector deflecting said optical beams; and an optical system focusing said deflected optical beams on the scanned surface as a plurality of optical spots, wherein said optical system has an optical element comprising: a lens having a refractive index distribution, wherein said lens is designed to correct an optical spot pitch deviation on the scanned surface, which is defined as 1\u2212\u03b2min\u03b2max where \u03b2max (\u03bcm) and \u03b2min (\u03bcm) are a maximal value and a minimal value of pitches of the optical spots on the scanned surface, respectively, due to said refractive index distribution with respect to image heights.
10. An optical element for focusing a plurality of optical beams deflected by an optical deflector on a scanned surface in a multi-beam optical scanner as a plurality of optical spots wherein said optical beams are emitted by a multi-beam illuminant having a plurality of beam emitting points, comprising:
means, which serve as one component of an optical system in said multi-beam optical scanner, for correcting an optical spot pitch deviation on the scanned surface, which is defined as 1\u2212\u03b2min\u03b2max where \u03b2max (\u03bcm) and \u03b2min (\u03bcm) are a maximal value and a minimal value of pitches of the optical spots on the scanned surface, respectively, due to a refractive index distribution therein with respect to image heights.
11. The optical element as claimed in claim 10, wherein said optical spot pitch deviation with respect to the image heights is less than or equal to 0.1.
12. The optical element as claimed in claim 10, wherein said means are formed of plastics.
13. The optical element as claimed in claim 12, wherein said refractive index distribution thereof is more than or equal to 0.5\xd710\u22126 in an effective range thereof corresponding to an effective write width W (mm) scanned by each of the optical spots on the scanned surface.
14. The optical element as claimed in claim 10, wherein said optical system has at least one second optical element, and said means achieve a larger lens thickness deviation, which is defined as 1\u2212DminDmax where Dmax (mm) and Dmin (mm) are a maximal lens thickness and a minimal lens thickness, respectively, with respect to an optical axis direction for each position of a main scanning direction than any other optical elements included in said optical system.
15. The optical element as claimed in claim 14, wherein said means have the lens thickness deviation of more than or equal to 0.65 in an effective range thereof corresponding to an effective write width W (mm) scanned by each of the optical spots on the scanned surface.
16. The optical element as claimed in claim 10, wherein said optical system has at least one second optical element, and said means have greater power with respect to a sub-scanning direction than any other optical elements included in said optical system.
17. A multi-beam optical scanner for optically scanning a scanned surface, comprising:
means for emitting a plurality of optical beams, said means for emitting the optical beams having a plurality of beam emitting points;
means for deflecting said optical beams;
means for focusing said deflected optical beams on the scanned surface as a plurality of optical spots,
wherein said means for focusing the deflected optical beams have an optical element, comprising: means for correcting an optical spot pitch deviation on the scanned surface, which is defined as 1\u2212\u03b2min\u03b2max where \u03b2max (\u03bcm) and \u03b2min (\u03bcm) are a maximal value and a minimal value of pitches of the optical spots on the scanned surface, respectively, due to a refractive index distribution therein with respect to image heights.
18. An image forming apparatus for forming an image, comprising:
means for carrying the image photosensitively;
means for scanning a scanned surface of said means for carrying the image photosensitively so as to form a latent image; and
means for developing said latent image so as to form the image,
wherein said means for scanning the scanned surface are a multi-beam optical scanner, comprising: means for emitting a plurality of optical beams, said means for emitting the optical beams having a plurality of beam emitting points; means for deflecting said optical beams; means for focusing said deflected optical beams on the scanned surface as a plurality of optical spots, wherein said means for focusing the deflected optical beams have an optical element, comprising: means for correcting an optical spot pitch deviation on the scanned surface, which is defined as 1\u2212\u03b2min\u03b2max where \u03b2max (\u03bcm) and \u03b2min (\u03bcm) are a maximal value and a minimal value of pitches of the optical spots on the scanned surface, respectively, due to a refractive index distribution therein with respect to image heights.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A glass filler for a polycarbonate resin, which comprises, as inorganic components in the entire glass filler, from 50 to 60 mass % of silicon dioxide (SiO2), from 7 to 15 mass % of aluminum oxide (Al2O3), from 10 to 20 mass % of calcium oxide (CaO), from 0 to 5 mass % of magnesium oxide (MgO), from 2 to 8 mass % of zirconium oxide (ZrO2), from 0 to 10 mass % of zinc oxide (ZnO), from 0 to 10 mass % of strontium oxide (SrO), from 0 to 18 mass % of barium oxide (BaO), from 0 to 2 mass % of lithium oxide (Li2O), from 0 to 2 mass % of sodium oxide (Na2O), and from 0 to 2 mass % of potassium oxide (K20), provided that the total content of the lithium oxide (Li2O), the sodium oxide (Na2O) and the potassium oxide (K2O) is from 0 to 2 mass % based on the entire glass filler.
2. The glass filler for a polycarbonate resin according to claim 1, which has a refractive index of from 1.581 to 1.587 to a light with a wavelength of 589 nm.
3. The glass filler for a polycarbonate resin according to claim 1, which contains substantially no boron oxide (B2O3).
4. The glass filler for a polycarbonate resin according to claim 1, which contains substantially no titanium oxide (TiO2).
5. The glass filler for a polycarbonate resin according to claim 1, wherein the content of the zirconium oxide (ZrO2) is from 3 to 6 mass %.
6. The glass filler for a polycarbonate resin according to claim 1, wherein the total content of the silicon oxide (SiO2) and the aluminum oxide (Al2O3) is from 57 to 70 mass % based on the entire glass filler.
7. The glass filler for a polycarbonate resin according to claim 1, wherein the total content of the lithium oxide (Li2O), the sodium oxide (Na2O) and the potassium oxide (K2O) is from 0 to 1.5 mass % based on the entire glass filler.
8. The glass filler for a polycarbonate resin according to claim 1, wherein the total content of the zinc oxide (ZnO), the strontium oxide (SrO) and the barium oxide (BaO) is from 5 to 20 mass % based on the entire glass filler.
9. The glass filler for a polycarbonate resin according to claim 1, wherein the total content of the calcium oxide (CaO), the zinc oxide (ZnO), the strontium oxide (SrO) and barium oxide (BaO) is from 25 to 35 mass % based on the entire glass filler.
10. The glass filler for a polycarbonate resin according to claim 1, wherein the content of the barium oxide (BaO) is from 7 to 14 mass % based on the entire glass filler.
11. The glass filler for a polycarbonate resin according to claim 1, which is in the form of fiber, milled fiber, powder or flakes.
12. The glass filler for a polycarbonate resin according to claim 11, which is in the form of fiber.
13. A polycarbonate resin composition comprising the glass filler as defined in claim 1 and a polycarbonate resin.
14. The polycarbonate resin composition according to claim 13, wherein the content of the glass filler is from 5 to 60 mass %.
15. The polycarbonate resin composition according to claim 13, wherein the difference between the refractive index of the polycarbonate resin and the refractive index of the glass filler is not more than 0.001 to a light with a wavelength of 589 nm.
16. The polycarbonate resin composition according to claim 13, which, when formed into a flat plate having a thickness of from 0.1 to 5 mm, has a parallel light transmittance of at least 65%.