normal density in the middle of the radiograph and decreased density on the sides.
result in image forming xrays being absorbed all across the radiographic field, with cuttoff ( decreased density) visible over the entire radiograph. the grids must be perpendicular to the grids to avoid this.
central ray does not strike the grid in the center, cuttoff visible more to one side of the radiograph
grid focus decentering
ciolation of the grid radius when a focused grid is used, normal density in the middle of the radiograph with cutoff visible on the sides