Premium
An intercomparison of the modulation transfer functions of square and circular focal spots
Author(s) -
Rao Gopala U. V.,
Soong AnLiang
Publication year - 1974
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1637296
Subject(s) - optics , cardinal point , physics , optical transfer function , magnification , focal length , square (algebra) , spots , geometry , mathematics , chemistry , lens (geology)
In field emission x‐ray tubes, the target is conical in shape and the projection of the focal spot along the central axis a circular disk. To determine the resolution capability of such tubes, a theoretical expression has been derived for the MTF of a circular focal spot. It has been shown that the MTF is given by the equation MTF = 2J 1[πf 0δ(m − 1) / m] / [πf 0 δ(m − 1) / m] where m is the magnification factor, f 0 the spatial frequency in the object plane, and δ the diameter of the focal spot. J 1 stands for the Bessel function of the first order. The above expression has been tested experimentally and used to compare circular focal spots with square focal spots.