| 摘要 |
<p>An electro-optical reader for, and method of, reading a symbol, utilize a light source (64) for emitting a light beam along a path, an optical assembly- including a variable focusing element (10) for focusing a major light fraction of the light beam between a range of working distances in which the symbol to be read is located along the path, and a controller (70) for controlling the variable focusing element to have different focusing states. One of the focusing states is a reference focusing state in which the variable focusing element is operative for focusing the major light fraction at a reference focal plane. A detector assembly, including a detector aperture (86) located at the reference focal plane, is operative for detecting an amount of a minor light fraction of the light beam, and for generating a self-calibration signal indicative of the reference focusing state when a predetermined amount of the minor light fraction has been detected. The controller is operative for processing the self-calibration signal to determine the reference focusing state for the variable focusing element during reading.</p> |
