| 摘要 |
In an optical scanner, an image-forming optical system approximately sets the position of a deflecting/reflecting face of a rotary polygon mirror and the position of a scanned face in a conjugate relation in geometrical optics in a cross scan-corresponding direction. This optical system has a function for converging a deflected light beam onto the scanned face in a main scan-corresponding direction. The optical system is set such that the following condition, W0/k2<R/D<W0/k1 is satisfied, where R designates a distance between the position of a real image and the position of an image of a light emitting section formed by an image-forming element between a laser diode light source and the scanned face; D designates a diameter of an opening image in the cross scan-corresponding direction with respect to the real image; W0 designates a waist diameter of the deflected light beam to be obtained between the real image position and the image position of the light emitting section; lambda designates a light emitting wavelength of the light source; a wavelength lambda is set to 780 nm; k1 is equal to 0.67 lambda / lambda 0; and k2 is equal to 1.1 lambda / lambda 0.
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