Abstract: A method and apparatus for manipulating the contrast of sine wave gratings and other patterns is disclosed. The apparatus provides an improvement in a projection system for projecting light along an illuminating path to a viewing screen. The improvement is in a form an image forming system which can be manipulated to adjust the contrast between juxtaposed areas of the projected light distribution image. The apparatus comprises a source of substantially unpolarized light arranged to project along an illuminating path and image forming means and a contrast adjustment means. The image forming means has at least two discrete light transmitting zones disposed in the illuminating path to receive and transmit primary and secondary illuminating light beams respectively. The first zone has juxtaposed areas of sharply contrasting translucence whereby the primary illuminating light beam emanating from the first zone forms a primary image which has sharply contrasting image areas.