A monochromator has at least one optical grating which is rotatable in relation to incident light of a source of light, a drive unit to rotate the optical grating by a connected drive rod around a longitudinal axis, and a control unit to control the drive unit and thereby the rotation of the optical grating. The drive unit further has a first damping element with at least one electrical conductive surface, and a second damping element which provides at least one magnetic field having a magnetic axis which penetrates the electrical conductive surface. One of the first and second damping elements is fixed to the drive rod and is rotatable along with the drive rod around the longitudinal axis thereof in relation to the other one of the second or first damping element.