The mechanism of and a solution to the problem of vertical banding in projection systems (100) is disclosed. An offset lens array (306, 308) includes a plurality of lens elements (312, 313) arranged in a plurality of rows that are offset with respect to one another. The offset lens array (306, 308) is incorporated in an illuminator (102) for a projection system (100). The asymmetrical arrangement of the rows of lens elements (312, 313) in the array (306, 308) with respect to a seam (126) in a color separation element (106) of the projection system (100) substantially reduces the vertical banding in the projected image (Fig. 7).