A scan bar assembly includes an illuminating unit including a first length; a photosensor array including a second length; and a first spacer member and a second spacer member, each of the first and second spacer members including: an inner side that is proximate the photosensor array; and an outer side that is distal to the photosensor array, wherein a distance between the inner side of the first spacer member and the inner side of the second spacer member is greater than the second length and less than the first length.