An instrument for moving and positioning of optical elements with nanometric mechanical stability and resolution in synchrotron beamlines, comprising: - a reference structure ; - a mounting structure ; - an optical element mounted to the mounting structure ; - moving means configured to move the mounting structure in relation to the reference structure ; - at least one reaction mass attached in a movable manner to the mounting structure , configured to receive the reaction force resulting from the positioning of the mounting structure in relation to the reference structure , through an actuation of the moving means ; - a means of position measurement configured to measure a position of the mounting structure in relation to the reference structure ; - a main feedback loop including the means of position measurement and the moving means , configured to use information from the means of position measurement to control the position of the mounting structure through the moving means , characterized by including: - a complementary mounting structure rigidly mounted to the reference structure ; - a complementary optical element rigidly mounted to the complementary mounting structure , - a complementary structure attached in a movable manner to the reference structure , - a complementary actuation means configured to move the complementary structure in relation to the reference structure , - a first set of spring means (l 1 ) by which the mounting structure is attached in a movable manner to the complementary structure thereby allowing relative translation or rotation movements along or about one or more axes, - a second set of spring means (l 2 ) by which the reaction mass is attached in a movable manner to the complementary structure thereby allowing relative translation and rotation movements along or about one or more axes, and a third set of spring means (l 3 ) by which the complementary structure is connected to the reference structure . - a reference structure ; - a mounting structure ; - an optical element mounted to the mounting structure ; - moving means configured to move the mounting structure in relation to the reference structure ; - at least one reaction mass attached in a movable manner to the mounting structure , configured to receive the reaction force resulting from the positioning of the mounting structure in relation to the reference structure , through an actuation of the moving means ; - a means of position measurement configured to measure a position of the mounting structure in relation to the reference structure ; - a main feedback loop including the means of position measurement and the moving means , configured to use information from the means of position measurement to control the position of the mounting structure through the moving means , - a complementary mounting structure rigidly mounted to the reference structure ; - a complementary optical element rigidly mounted to the complementary mounting structure , - a complementary structure attached in a movable manner to the reference structure , - a complementary actuation means configured to move the complementary structure in relation to the reference structure , - a first set of spring means (l 1 ) by which the mounting structure is attached in a movable manner to the complementary structure thereby allowing relative translation or rotation movements along or about one or more axes, - a second set of spring means (l 2 ) by which the reaction mass is attached in a movable manner to the complementary structure thereby allowing relative translation and rotation movements along or about one or more axes, and <EOS>