| 摘要 |
PURPOSE:To effectively eliminate ununiformity of the diameter of a light spot in the sub- scanning direction which remains behind after eliminating a curvature of image and to execute a high density optical scan by controlling a very small oscillation of a cylindrical lens executed by an oscillating means by a second control means, and equalizing the diameter in the sub-scanning direction of the light spot by synchronizing with an optical scan executed by a deflection luminous flux. CONSTITUTION:A relation of an image forming position in the main scanning direction and the diameter of a light spot in the sub-scanning direction by a residual fluctuation is checked in advance, and an aperture, etc. are designed so that the maximum light spot diameter in the sub-scanning direction in the residual fluctuation becomes a target spot diameter 2W3. In this state, a cylindrical lens 2 is brought to very small oscillation by an oscillating means 9 so as to eliminate a fluctuation of the light spot diameter in the sub-scanning direction caused by the residual fluctuation. The oscillation quantity is related in advance to a synchronizing clock and stored in advance in a second control means 11, and the residual fluctuation is eliminated by controlling the oscillation of the cylindrical lens 2 by synchronizing with an optical scan by the oscillating means 9 in accordance with its storage contents. In such a way, since the light spot diameter in the sub-scanning direction can be equalized with high accuracy, the optical scan of a good quality can be executed. |
