| 摘要 |
The invention has application in the field of non contacting probes, and also in connection with the reading of video discs. Conventional means usually involve the movement of optical components of appreciable mass and hence relatively slow response. The present invention permits very substantial reduction of mass of optical components, and in some embodiments change of focus can be effected without mechanical movement. The invention provides apparatus to focus light onto a given surface, (10), the focussing means (30) having appreciable chromatic aberration. A variable wavelength light source (12) supplies light through the focussing means (30) to said surface, and focus detecting means (36) senses when the light so supplied is in focus at the surface. Control means (50) responsive to the wavelength of the light source, and to the focus detecting means, can actuate the light source to maintain the light in focus if the surface moves. In a preferred embodiment the focussing means (30) is a zone plate. |
