possible to make the variations of the degree of hiding proportional to the support displacement a preferred embodiment of said apparatus comprises several sources and the same number of covers moved by motors all the covers and motors are mounted on a single plate and the covers are designed in such a way that the displacements of the support relative to that of the sources bring about different variations of the degree of hiding of each source it is then possible to freely modify the compositions of the deposits made the invention is described in greater detail hereinafter relative to non limitative embodiments and the attached drawings fig1 is a view of a vacuum evaporation coating machine using the apparatus according to the invention the cover being a disk seen by its edge fig2 is a view of an embodiment with two fixed sources the complementary covers seen from the front being mounted on a support performing a translatory movement fig3 is a view of a vacuum evaporation coating machine using the apparatus of fig2 fig4 is a view of an embodiment with two sources the identical covers seen from the front being in each case rotated about a fixed axis and the two sources perform an oscillatory movement on a circular path with reference to fig1 the vacuum evaporation machine comprises an enclosure 1 in which is placed the sample 2 to be covered with a deposit in front of a source 3 subject to an evaporation supplied by an electric cable 4 and a current generator 5.