1. An assistance system ( 20 ) for the planning of geometrical imaging parameters that are used during the imaging of an object ( 1 ) with a main imaging system ( 10 ), comprising: a camera ( 21 ) for the generation of an optical image ( 27 ) of the object ( 1 ); an image processing system ( 22 ) with a display unit ( 26 ), wherein said image processing system ( 22 ) is coupled to the camera ( 21 ) and is adapted to display on the display unit ( 26 ) a geometrically registered overlay of an optical image ( 27 ) of the object ( 1 ) and of a representation ( 28 , 29 ) of geometrical imaging parameters.