Optical scanner and image forming apparatus

An optical scanner comprising:

• a plurality of light sources;
• a coupling optical system arranged to couple beams emitted from the light sources;
• a line image focusing optical system arranged to focus each beam coupled to a line image extending longer in a main scan direction;
• a deflector that has deflecting reflective surfaces on focused positions of the line image and a common rotary axis for the deflecting reflective surfaces, is shared for all the beams from the light sources, and deflects the beams focused;
• a scanning optical system arranged to guide the beams deflected to a plurality of target surfaces for optical scanning;
• and
• a photodetector arranged to receive the beams deflected at the deflector, wherein
• the beams traveling toward the deflector have an open angle θ in a deflecting rotation plane,
• the scanning optical system includes at least two scanning lenses,
• a scanning lens proximate to the deflector, out of the scanning lenses, passes only the beams traveling toward different target surfaces,
• a scanning lens proximate to the target surface, out of the scanning lenses, passes only the beams traveling toward a same target surface, and
• wherein Pm>0≧PS is satisfied, where Pm is a power of the scanning lens proximate to the deflector in the main scan direction and Ps is a power of the scanning lens proximate to the deflector in the sub scan direction.

An optical scanner comprising:

• a plurality of light sources;
• a coupling optical system arranged to couple beams emitted from the light sources;
• a line image focusing optical system arranged to focus each beam coupled to a line image extending longer in a main scan direction;
• a deflector that has deflecting reflective surfaces on focused positions of the line image and a common rotary axis for the deflecting reflective surfaces, is shared for all the beams from the light sources, and deflects the beams focused;
• a scanning optical system arranged to guide the beams deflected to a plurality of target surfaces for optical scanning;
• and
• a photodetector arranged to receive the beams deflected at the deflector, wherein
• the beams traveling toward the deflector have an open angle θ in a deflecting rotation plane,
• the scanning optical system includes at least two scanning lenses,
• a scanning lens proximate to the deflector, out of the scanning lenses, passes only the beams traveling toward different target surfaces,
• a scanning lens proximate to the target surface, out of the scanning lenses, passes only the beams traveling toward a same target surface, and
• wherein the scanning lens proximate to the target surfaces has a power in the sub scan direction higher than a power in the sub scan direction of the scanning lens proximate to the deflector.

An optical scanner comprising:

• a plurality of light sources;
• a coupling optical system arranged to couple beams emitted from the light sources;
• a line image focusing optical system arranged to focus the beams coupled through the coupling optical system to a line image extending longer in a main scan direction;
• a deflector that has deflecting reflective surfaces in the vicinity of focused positions of the line image and arranged to deflect the beams from the line image focusing optical system;
• and
• a plurality of scanning optical systems arranged to guide the beams deflected at the deflector to different target surfaces to form focused light spots, wherein
• the deflector has a common rotary axis for deflecting reflective surfaces,
• the beams entering a common deflecting reflective surface of the deflector to travel toward different target surfaces has an open angle θ in a deflecting rotation plane,
• each of the scanning optical systems includes at least two scanning lenses and corresponding scanning lenses in the scanning optical systems are identical, and
• wherein at least one specific scanning lens in the scanning optical systems arranged to guide the beams deflected at the common deflecting reflective surface to different target surfaces is located at a position 180 degrees rotated about an optical axis from a corresponding specific scanning lens in another scanning optical system, and
• wherein the specific scanning lens has a sub scan curvature on at least one surface with a shape asymmetrically varying gradually from an optical axis toward both peripheries in the main scan direction.

An image forming apparatus comprising

• an optical scanner that includes
• a plurality of light sources;
• a coupling optical system arranged to couple beams emitted from the light sources;
• a line image focusing optical system arranged to focus each beam coupled to a line image extending longer in a main scan direction;
• a deflector that has deflecting reflective surfaces on focused positions of the line image and a common rotary axis for the deflecting reflective surfaces, is shared for all the beams from the light sources, and deflects the beams focused;
• a scanning optical system arranged to guide the beams deflected to a plurality of photosensitive objects surfaces for optical scanning;
• and
• a photodetector arranged to receive the beams deflected at the deflector, wherein
• the beams traveling toward the deflector have an open angle θ in a deflecting rotation plane,
• the scanning optical system includes at least two scanning lenses,
• a scanning lens proximate to the photosensitive object, out of the scanning lenses, passes only the beams traveling toward a same photosensitive object, and
• wherein scanning lenses proximate to the photosensitive objects for guiding the beams to different photosensitive objects have optical actions different from each other.

An image forming apparatus comprising

• an optical scanner that includes
• a plurality of light sources;
• a coupling optical system arranged to couple beams emitted from the light sources;
• a line image focusing optical system arranged to focus each beam coupled to a line image extending longer in a main scan direction;
• a deflector that has deflecting reflective surfaces on focused positions of the line image and a common rotary axis for the deflecting reflective surfaces, is shared for all the beams from the light sources, and deflects the beams focused;
• a scanning optical system arranged to guide the beams deflected to a plurality of photosensitive objects for optical scanning;
• and
• a photodetector arranged to receive the beams deflected at the deflector, wherein
• the beams traveling toward the deflector have an open angle θ in a deflecting rotation plane,
• the scanning optical system includes at least two scanning lenses,
• a scanning lens proximate to the deflector, out of the scanning lenses, passes only the beams traveling toward different photosensitive objects,
• a scanning lens proximate to the photosensitive object, out of the scanning lenses, passes only the beams traveling toward a same photosensitive object, and
• wherein Pm>0≧PS is satisfied, where Pm is a power of the scanning lens proximate to the deflector in the main scan direction and Ps is a power of the scanning lens proximate to the deflector in the sub scan direction.

An image forming apparatus comprising

• an optical scanner that includes
• a plurality of light sources;
• a coupling optical system arranged to couple beams emitted from the light sources;
• a line image focusing optical system arranged to focus each beam coupled to a line image extending longer in a main scan direction;
• a deflector that has deflecting reflective surfaces on focused positions of the line image and a common rotary axis for the deflecting reflective surfaces, is shared for all the beams from the light sources, and deflects the beams focused;
• a scanning optical system arranged to guide the beams deflected to a plurality of photosensitive objects for optical scanning;
• and
• a photodetector arranged to receive the beams deflected at the deflector, wherein
• the beams traveling toward the deflector have an open angle θ in a deflecting rotation plane,
• the scanning optical system includes at least two scanning lenses,
• a scanning lens proximate to the deflector, out of the scanning lenses, passes only the beams traveling toward different photosensitive objects,
• a scanning lens proximate to the photosensitive object, out of the scanning lenses, passes only the beams traveling toward a same photosensitive object, and
• wherein the scanning lens proximate to the photosensitive objects has a power in the sub scan direction higher than a power in the sub scan direction of the scanning lens proximate to the deflector.

An image forming apparatus for multicolor, comprising

• an optical scanner that includes
• a plurality of light sources;
• a coupling optical system arranged to couple beams emitted from the light sources;
• a line image focusing optical system arranged to focus the beams coupled through the coupling optical system to a line image extending longer in a main scan direction;
• a deflector that has deflecting reflective surfaces in the vicinity of focused positions of the line image and arranged to deflect the beams from the line image focusing optical system;
• and
• a plurality of scanning optical systems arranged to guide the beams deflected at the deflector to different photosensitive objects to form focused light spots, wherein
• the deflector has a common rotary axis for deflecting reflective surfaces,
• the beams entering a common deflecting reflective surface of the deflector to travel toward different photosensitive objects has an open angle θ in a deflecting rotation plane,
• each of the scanning optical systems includes at least two scanning lenses and corresponding scanning lenses in the scanning optical systems are identical, and
• wherein at least one specific scanning lens in the scanning optical systems arranged to guide the beams deflected at the common deflecting reflective surface to different photosensitive objects is located at a position 180 degrees rotated about an optical axis from a corresponding specific scanning lens in another scanning optical system, and
• wherein the specific scanning lens has a sub scan curvature on at least one surface with a shape asymmetrically varying gradually from an optical axis toward both peripheries in the main scan direction.