A collimator (100) for collimating radiation includes collimator material (150) and at least one collimator hole (110) defined by the surrounding collimator material (150). The collimator hole (110) defines an aperture (112) and a bottom surface (132) through which radiation can leave the collimator (100). The volume of the collimator hole between the aperture (112) and the entrance opening and/or exit opening is shaped such that there is at least one cross-section of the hole between the aperture (112) and the entrance opening and/or exit opening, the cross-section being taken parallel with the aperture, such that the shape of the cross-section of the hole cannot be obtained through an affine transform of the shape of the aperture.