A collimating system (100) for collimating radiation received under different angles for performing tomography is described. The collimating system (100) comprises a static collimator (110) comprising a plurality of collimating apertures (112), shutters (120) for separately and temporarily shutting at least two of said collimating apertures (112), wherein the shutters (120) having a shutting element (122) for blocking said at least two collimating apertures (112), and at least one collimating element (140) distinct from the shutting element (122) for collimating radiation passing through non-shut collimating apertures (112) in a direction so as to control overlap between radiation stemming from different non-shut collimating apertures (112). The invention also relates to an imaging system comprising such a collimating system, a method for collimating and a corresponding controller and software related products.