| 摘要 |
An optical bar code scanner and method which achieves an extended depth of focus by employing a multifocal length collection optical system. A radiation beam is generated for illuminating a field of view, either by a laser or nonlaser source. The embodiments specifically disclosed herein employ nonlaser sources such as LEDs. The multifocal length collection optical system, having at least a near range focal length and a long range focal length, collects radiation reflected from objects in the field of view, and directs it to an optical detector for detection and generation of an electrical output signal indicative thereof. The electrical output signal of the detector is then passed through a high pass filter which filters out a DC background electrical signal, thereby improving the depth of modulation of the signal, and the electrical output signal is directed to electrical processing and decoding circuits. In a first embodiment, the radiation beam is generated by a linear array of light emitting diodes, and the multifocal optical system includes two different lenses, each having a different focal length. The optical detector includes a charge coupled detector having a plurality of charge coupled detection cells, and the field of view is scanned by scanning the electrical outputs of the plurality of charge coupled detection cells. In a second embodiment, the field of view is scanned with an oscillating scanning mirror, and the multifocal optical system includes a first detection mirror having a near range focal length, and a second detection mirror having a far range focal length. 26
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