title: Focal spots: III. Field characteristics.
abstract: Experimental results for focal spot field characteristics are presented. These results do not agree completely with results published by Moores and Roeck but are in agreement with Doi's theory as applied to separable focal spots. A new image plane origin called the principal ray is proposed. The variation of the star test pattern image for separable, symmetric focal spots is described. The equation for the field variation of the RMS equivalent rectangle is presented.
mesh_terms: D013679:Technology, Radiologic