PURPOSE: To obtain a good thin film pattern with high accuracy without being bothered with generation of light interference fringes by forming waste patterns of the same material as the desird pattern and by the same process to the part except the part to be provided with disired pattern on the bare plate to be worked as well so that the envelope of the surface of the photosensitive film coated over the entire pattern parallels with the plane of the base plate to be worked.

CONSTITUTION: Desired pattern groups 1, 1' are provided on base plate glass 8 for a filter and waste patterns 7 are simultaneously formed of the same material by the same process on the ineffective parts 6, 6', 6" between said groups in the stage of forming the groups 1, 1' so that the envelope of the plate of a photosensitive film 9 for the 2nd exposure parallels with the plane of the base plate to be worked, i.e., the glass 8. Therefore the surface of the film 9 and the surface of an original plate 4 for photoetching are brought into tight contact with each other over the entire surface and the parellellism beteeen both surfaces is extremely satisfactorily maintained when the plate 4 is pressed to the work side for the purpose of 2nd exposure. The chance for generating light interference fringes is thus decreased. There are practically no restrictions for the design of the waste patterns and any design which makes the waste patterns hardly strippable and removable and makes the envelope on the surface of the photosensitive film on the base plate side supposing the tight contact of the original plate for photoetching with said film for the purpose of the 2nd exposure parallel with the surface of the base plate to be worked is satisfactorily usable.