An optical stack including a periodically varying optical film layer and a grating assembly for reducing moiré is described. The grating assembly includes first and second layers where an interface between the first and second layers define a grating having a peak to valley height and an index contrast. The index contrast multiplied by the peak to valley height may be between 150 nm and 350 nm and the grating has a pitch in the range of 2 micrometers to 50 micrometers. Each of the first and second layers may be viscoelastic or elastomeric adhesive layers, crosslinked resin layers, or soluble resin layers.