| 摘要 |
<p>Apparatus for detecting discontinuites in a radiation diffusing surface (10) such as paper comprising means for passing radiation to the surface and radiation collection means (19) for receiving the diffuse radiation (18) from a limited area of the surface (10), the radiation collection means includes means 26 to receive the diffuse radiation from a limited area only and from within predetermined angular limits other than normal to the surface, the radiation collection means (19) including means (26,32) for defining said predetermined angular limits by means of total internal reflection.</p> |
