A mounting for optical components, e.g. in spectroscopic apparatus, has a rotatable baseplate 10, on which a plurality of quadrant-shaped mounting plates 12 can be kinematically located. Each mounting plate 12 carries respective optical components, which can be brought into and out of an optical path by rotation of the base plate 10. One or more of the mounting plates 12 carries both a housing 14 for components such as filters 20,22 and also a beam steering mirror 24 on a bracket 16. A gap is provided between the housing 14 and the mirror 24, so that the light beam 30 in the optical path can pass unhindered through the gap when this mounting plate is in an inoperative position.