Bucky diaphragm?
Potter Bucky grid is a type of moving grid. These devices reduce the amount of scattered radiation reaching the film while still allowing the patterns containing the primary beams to reach the film.
The image of radiolucent grid lines on the film can be deleted by moving the grid perpendicular to the direction of grid lines, this has the effect of blurring out the radiolucent line and allowing a more uniform exposure. This movement doesn't interfere with absorption of scattered photons.
Reduces scattered radiation
Reduces response time
Decreases long wavelength rays
Decreases kVp and mA requirement