Abstract: A light masking device in accordance with the present invention comprises a support frame adapted to be positioned in front of the screen and an optical filter supported thereby, the optical filter comprising a grating of spaced, elongated planar slats extending horizontally across the width of the screen, the slats being differentially inclined from the horizontal in the directions of their widths so as to converge on a horizontal line at a selected height and a selected distance from the screen. In a preferred embodiment of the invention the slats are pivotally connected to the support frame for pivotal movement about respective horizontal axes, and means are provided for differentially adjusting the inclinations of the slats for selectively adjusting the position of the horizontal line on which the inclined slats converge.