The invention relates to a grid holder for an X-ray diagnostic system. The grid holder cooperates with a flexible X-ray grid, which in a flat state has a first focus distance/convergence distance of about 120 cm. A flexing means, preferably in the form of an inflatable element, which can exert a pressure on the surface of the grid, is arranged to flex the grid in a first direction to a first position in which it has a second convergence distance of about 180 cm. Another corresponding flexing means is arranged to flex the grid in the opposite direction to a second position in which it has a third convergence distance of about 80 cm. This allows variable convergence distances with minimum flexing of the grid. The invention also relates to grid devices with grid holders and grids as well as X-ray diagnostic systems comprising such grid holders/grid devices.