Abstract: 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.

Abstract: Telescopic ball bar 24 has a male member provided by a sphere 22 at one end and a female member provided by a pair of forks 30 at the other. The ball bar is attached to the spindle 10 of a machine tool by a universal pivotal coupling between the sphere 22 and a magnetic socket 14 retained on the spindle 10. The ball bar 24 is attached to the table by a further universal pivotal coupling between a sphere 28 retained on the table 12 in a clamping device 40, and the forks 30. In use, the spindle is operated to move in a circular path about a center defined by the center of the sphere 28. Any deviation of the spindle movement from such a circular path will be detected by a transducer 36, provided in the bar 24, which bears against the surface of the sphere 28. The position of the center of the sphere 28 is determined by bringing the sphere 28 into engagement with the socket 14, and measuring the position of the spindle 10 at that point.