The present invention is an improvement in a method of screening a line screen slit mask color picture tube that includes coating a faceplate panel of the tube with a photosensitive material, inserting a slit shadow mask into the panel and exposing the photosensitive material by passing light from a line light source through a misregister correction lens and through the slits of the mask. The improvement comprises positioning a skew correction lens between the line light source and the misregister correction lens during exposure of the photosensitive material. The skew correction lens has a surface with a general overall cylindrical shape with deviations from the cylindrical shape being in the four corners of the skew correction lens.