Abstract: In the operation of a projection printer (11) photomasks (22), the patterns (21) of which are protected by coverplates (39), are used interchangeably with other photomasks, the patterns of which are located at an open surface thereof. The photomasks (22) feature shims (46) which space the patterns (21) away from a plane of support surfaces (13) of a mounting chuck (12) by a precise distance equal to the shift of the object plane (14) with respect to an image plane (17) because of the presence of the coverplate (39) in the optical path of the projection printer (11).

Abstract: A spacer (52) of an interposer element (51) is placed between support surfaces (27) of a mounting chuck (12) in a projection printer (14) and a photomask (48) which is not protected by a coverplate. The interposer element (51) further features a transparent plate (53) which becomes interposed in the optical path (46) of the projection printer (14) in a position spaced from the photomask (48). The plate (53) shifts the objective focal plane (44) with respect to which the support surfaces (27) are adjusted outward away from an image plane by a distance equal to the shift of the objective focal plane due to the coverplate of a coverplate-protected photomask. Consequently, the spacer (52) features a preferred thickness of a coverplate of such coverplate-protected photomask to position patterns (21) of object features on the unprotected photomask (48) in the plane to which the focal plane is shifted by the interposed plate (53).