| 摘要 |
PURPOSE: To provide a device capable of making positions of spots on a plotting surface formed by plotting and focus detecting luminous fluxes in the direction of an optical axis match each other when a wavelength of a plotting luminous flux is different from that of a focus detecting luminous flux and fθlens is subjected to no chromatic aberration correction. CONSTITUTION: The plotting luminous flux generated from a plotting light source 10 is reflected and deflected by a polygon mirror 20, and forms a spot on the plotting surface 30 by the fθlens 40 telecentric to the plotting surface side. The luminous flux emitted from a focus detecting light source 51 is made converged light by a convergence lens 55 to be made incident on the fθlens 40. By making the plotting luminous flux having a short wavelength incident on the plotting surface 30 as parallel luminous fluxes and the focus detecting luminous flux having a long wavelength as the convergence light, positions of spots by both luminous fluxes match each other. The focus detecting luminous flux reflected from the plotting surface 30 returns to the light source side through the same optical path as the time when the light is made incident on the surface 30, and is condensed on a photodetector 58 through an anamorphic condenser lens 57. |
