| 摘要 |
PURPOSE:To prevent dust from sticking to a parabolic reflecting mirror by covering the parabolic reflecting mirror with a dustproof cover which is made of a transparent insulating member and has an external convex surface. CONSTITUTION:The surface of the insulating member is rubbed against wind and charged electrostatically to the positive polarity when planar or concave or to the negative polarity when a convex. Minus charges floating in the air repulse dust charged negatively, so the dust is hard to stick to the convex surface. Consequently, the sticking of the dust to a lens having a planar surface or parabolic reflecting mirror having a concave surface is prevented effectively. |
