| 摘要 |
PURPOSE:To perform the conversion of picture element density with low cost by setting the diameter of a scan spot at the constant value in the main scan direction in response to the main scan direction of the minimum picture element and increasing gradually said diameter in the subscan direction in response to reduction of the picture element density. CONSTITUTION:The diameter of a scan spot is decided constant in the main scan direction in response to the size of a picture element with the maximum picture element density. While the spot diameter is gradually increased in the subscan direction as the picture element density is reduced. That is, an optical system consists of a spherical lens 1, an optical modulator 2, a cylindrical lens 3, spherical lens 4, an ftheta lens 5 and a cylindrical lens 6. In this case, the position of a deflecting start point P is conjugate to the position of a main scan line in the subscan direction. Therefore the scan spot in the subscan direction is equal to a reduced image of the section of aluminous flux at the point P. Thus the spot diameter can be changed just by changing the diameter of the luminous flux section in the subscan direction at the point P. For this purpose, the lens 3 is replaced with another one having a proper focal distance in response to the picture element density.
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