unused camera pixel locations are recovered when shifting from photographing an x - ray scintillation image of a larger subject to that of a substantially smaller one by using a suitably shorter optical path combined with appropriate changes in focus . the optical path for large subjects involves a first mirror followed by a second mirror . the camera receives light from the second mirror , and is in a fixed and unchanging physical relationship to that second mirror , forming a unitary mirror - camera assembly . to shorten the optical path that unitary assembly is rotated about an axis from a position where it was in the optical path downstream from the first mirror to one where the second mirror is interposed between the scintillation screen and the first mirror , and also such that the camera looks in a different direction along the shortened optical path length . focus adjustment to accommodate the different optical paths may be accomplished by changing the spacing of elements internal to the lens , or , the entire lens assembly can be moved a bit closer to or further away from the camera body . the scintillation image may be replaced with a glass plate carrying a document illuminated from within a housing carrying the unitary mirror - camera assembly .