The optimal constant for the colored version of Tverberg''s theorem

Disclosed is a method and apparatus for holding and detecting correct placement of a photosensitive film on a carrier in a photographic reproduction apparatus for imaging the film. The carrier has an alignment surface against which the film is firmly held when imaged. Vacuum means are provided which are operably connected to the alignment surface for holding the film securely to the alignment surface. Air passageway means operably connected to the vacuum means are provided in the alignment surface, the air passageway means being of a size and in a position to form a closed vacuum system which permits a high vacuum level only when the film is correctly placed on the carrier. Vacuum level detecting means operably connected to the vacuum means are provided for detecting the level of the vacuum, and therefore, correct placement of the film on the carrier. The carrier is preferably provided with reciprocating means for moving the carrier to and from a load position outside of the enclosure of the photographic reproduction apparatus and an imaging position within the enclosure. The vacuum detecting means is preferably operably connected to control means which prevent the carrier from moving into an imaging position unless the film is correctly placed upon the carrier with the photosensitive surface facing the imaging means within the apparatus, and the control means is also preferably operably connected to the reciprocating means to return the carrier to the load position if the film moves from its securely held position against the alignment surface.