An adjustable holder (1) for a concave holographic grating (2) for enabling the correct positioning of the grating vis-à-vis a light entrance port (15) and a light exit port (20), characterized in, that it comprises a grating hinge (10) fixed to said grating, said grating hinge (10) enabling rotational adjustment of the grating position with respect to said holder (1) , the centre point of the rotational adjustment being located at the vertex of said grating (2).