The computedMTF of a radiographic screen-film system may eibit erroneus oscillations resulting from the necessary truncation of the measured line spread function. The slit method was extended to permit evaluation of the LSF to approximately 0.001 of its maximum value. This reduces the MTF oscillations to a negligible level. The maximum MTF deviation was determined as a function of the truncation. Resultx show that for LSF's measured in the usual manner (0.01 truncation) the maxumum MTF deviatian is from 0.04 to 0.07, depending on the screen-film system. A theoretical analysis to estimate the error due to truncation is described, and a correction procedure is developed.

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