| 摘要 |
<p>In a system for scanning a document (43), a light source (22) illuminates the document; an imager (24, 41, 41', 61, 62) receives light from the document and directs it toward a detector array (25) which produces a corresponding array of electrical signals. The imager has several optical properties that are useful either individually or in combination. The imager is telecentric and thereby ensures that image size and magnification are insensitive to object displacement along the optical axis (46, 46') and image brightness is uniform independent of object off-axis distance. An aspheric element (33) within the imager balances focus variation (82-81-83) within the depth of field with spherical aberration and thereby provide nearly uniform image resolution. A diffraction pattern (33'), carried by the imager, corrects for spectral dispersion which occurs when light passes (63) from air into a refractive material (61, 62). An imager with a reflecting surface (32, 33) provides a system that is subject to little or no chromatic aberration. A solid imager (61, 62) with multiple internal reflecting surfaces (32, 33, 42) in optical series (32-33-32-42), configured to include the previously mentioned optical properties, also provides for highly stable alignment of reflecting surfaces. <IMAGE></p> |
