In a tomosynthesis system a static focal spot is moved in a direction opposite to and generally synchronized with the directional movement of an x-ray source and X-ray collimator blades are moved during each exposure in synchronization with the shifting of the static focal spot. The synchronized movement of the static focal spot, x-ray tube and collimator blades helps keep the effective focal spot fixed in space relative to the breast, detector or both during the entire duration of the exposure and keeps the x-ray field on the detector and breast static. The shifting collimator blades follow an oscillating pattern over the multiple x-ray exposures of a tomosynthesis scan.