source-film distance

tar·get-film dis·tance

(TFD) (tahrgĕt-film distăns)
The space measured from the focal point of an x-ray tube to the film.
Synonym(s): source-film distance.

source-film distance (SFD),

n distance from the focal spot of a radiograph tube to the radiographic film. Also known as
target-film distance.
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