This standard describes a method for the determination of the modulation transfer function (MTF) of electro-optical X-ray image intensifiers. The method is based on fourier-analysing a line spread function in terms of its spatial frequency spectrum. The X-ray image of a test slit is imaged by the X-ray image intensifier, and the brightness distribution of the optical slit image, formed on the output screen of the image intensifier and broadened in accordance with the MTF, is determined.*Alternatively to a test slit, a test grid comprising various spatial frequencies can be used for determining the MTF.