be filtered by a corresponding slit aperture filter 108 while the portion illuminating the position detector would not the position detector 117 produces a signal corresponding to the position of the illumination line image 122 in the scanning direction x direction in some embodiments similar image sensor 116 position detector 117 pairs are used for each collection channel referring to fig2 a close up representation of wafer light scattered in a moving wafer inspection system is shown in a wafer inspection process a wafer is illuminated by a line illumination source having an illumination profile 206 as the wafer moves in a direction of travel 200 primary light 210 is scattered by the wafer to be received and focused by one or more collection channels furthermore secondary light 212 may be scattered by undesirable structures 202 referring to fig3 a close up of a portion of the wafer inspection system of fig1 is shown in at least one embodiment of the present disclosure a first slit aperture filter 108 is associated with a first collection channel the first slit aperture filter 108 is positioned and oriented in the confocal plane as defined by the first collection channel optics the first slit aperture filter 108 transmits a primary beam 300 associated with the primary light scattered by the wafer by the line illumination source and filters out incidental beams 302 associated with the secondary light or sidelobes of the line illumination beam scattered by the wafer in at least one embodiment the first slit aperture filter 108 comprises a mechanical filter the mechanical filter may be replaceable with mechanical filters having larger slit apertures to allow more light where increased sensitivity is required alternatively in at least one embodiment the first slit aperture filter 108 comprises an electronic.