MARKED CARD READER EMPLOYING AFOCAL SPATIAL FILTERING

A marked card reader having a lensless optical detection system with fixed angle illumination and detection, the sensitivity of which is independent of the frequency response associated therewith. The optical detection system includes a radiation source to produce radiation and a radiation detector. A target plane is positioned so that the radiation source directs radiation toward the target plane. The detection source is positioned to sense radiation reflected from the target plane. An optically opaque body is positioned between the optical detector and the radiation source to prevent incident radiation from be sensed by the optical detector.