The invention specifies a radiation collimator, in particular an x-ray collimator, which can be arranged between a radiation source outputting radiation and an object. The radiation collimator includes absorber channels arranged adjacent to one another which form a two-dimensional collimator aperture in the form of a matrix and a first absorber element arranged in the absorber channel. The first absorber element blocks the radiation in a first position and allows the radiation at least partially through the absorber channel in at least one second position. The first absorber element is rod-shaped and can be moved in the absorber channel by a rotation about its longitudinal axis and/or by a longitudinal and/or transverse displacement from the first into the at least one second position. This is advantageous in that the two-dimensional collimator aperture can be modulated easily, rapidly and with high resolution.