The X-ray Multi-Mirror (XMM) Telescope
was launched by ESA on December 10th, 1999 and carries two distinct
types of telescope: three Wolter type-1 X-ray telescopes, with different
X-ray detectors in their foci,
and a 30-cm optical/UV telescope with a microchannel-plate pre-amplified
CCD detector in its focal plane.
The Optical Monitor can provide spectral resolution by the use of broad-
and narrow-band filters contained within a filter wheel, plus there are also
two grisms in the filter wheel for low resolution spectroscopy. The spatial pixel
size in normal operation is 1 arc second and the limiting sensitivity is B=24
for a star viewed with the detector in unfiltered light.