| 摘要 |
PURPOSE:To enable the easy formation of an interference thin film by the film forming method such as vapor deposition and to eliminate intricate masking techniques by forming a thin film for which an interference effect is utilized and which has an approximately uniform prescribed thickness. CONSTITUTION:The illuminance correcting film 6 has such prescribed film thickness at which the thin film interference is caused by a light beam 1A for scanning. The film thickness thereof is set at such a value at which the thin film transmittance increases with an increase in the incident angle on this thin film 6 nearer the peripheral position from the neighborhood of the optical axis position of a lens 4 and at which the difference in this transmittance can correct the difference in the exit light quantity of the lens 4. Then, both of the incident light beam 1A on the neighborhood of the optical axis position of the lens 4 and the incident light beam 1A on the peripheral part can be so formed that the illuminances when a surface to be scanned is irradiated with these beams after the passage through the illuminance correcting film 6 are approximately equaled. As a result, the illuminance correcting film 6 is easily and inexpensively produced. |
