| 摘要 |
PURPOSE:To prolong the service life of an optical system by setting the width of incident light in a predetermined direction narrower than the effective width of a selected optical element in the predetermined direction and gradually shifting the region on the selected optical element, being irradiated with the incident light, in the predetermined direction. CONSTITUTION:In an optical system 4 receiving an incident light having wavelength of 450nm or less and delivering a light through one or a plurality of optical elements 5A, 5B, the width of a incident light to at least one selected optical element 5A is set narrower, in a predetermined direction, than the effective width of the selected optical element 5A in the predetermined direction. When a plurality of optical elements 5A, 5B are selected, they are classified into a plurality of optical element groups which are then provided individually with rotary means 7A, 7B for rotating the optical elements in each group synchronously. |
