The invention relates to a method for calibrating a sighting system comprising a viewfinder and an optic for detecting the position of an object in space, characterised in that it comprises the determination of a control law to apply to the viewfinder to aim at the object as a function of its position, said position being determined in a frame of reference of the detection optic and the control law comprising two angular controls and a focusing control of the viewfinder, expressed as a function of the relative positions between the object to aim at and an intersection point of all the lines of sight of the viewfinder, the method comprising the steps consisting in: aiming (100), with the viewfinder, at objects found at at least six different known positions in the frame of reference of the sighting system and noting the corresponding controls, from the positions of the object and the corresponding controls, determining (200, 200′) the position of the intersection point of the lines of sight and the control law by the minimisation of a function of the second derivative of the control law.