| 摘要 |
PURPOSE:To stabilize picture quality without any increase in cost by moving a plastic lens in a predtermined direction by a specific value, and calculating the proper amount of displacement of the plastic lens from the variation in beam diameter about the movement point. CONSTITUTION:A laser beam 3 before being modulated with a video signal X is incident to a CCD9 near a no-image area on a photosensitive body 8 and the CCD9 outputs a beam diameter signal D1 corresponding to the beam diameter of the laser beam 3 perpendicular to a deflection direction. Then, a collimator lens 5 is moved along an optical axis toward a rotary polygon mirror 6 by the specificl value, and when the CCD9 is irradiated with the next laser beam 3, a beam diameter signal D2 corresponding to the beam diameter is detected and a control part 11 performs arithmetic D1-D2. The control part 11 compares the arithmetic result with a beam diameter signal DC corresponding to a specific beam diameter and a moving device 10 moves the collimator lens 5 to correct the laser beam diameter to the specific beam diameter. |
