  We derive on the level of quantum optics expressions for the uncertainty of
the photocount in a multi-mode multi-frequency setup. The result depends on the
quantum correlations of the individual modes and the frequency spectrum of the
radiation, the latter leading to a frequency beating sometimes referred to as
dynamic laser speckle. When the mode structure of the radiation field is
disturbed between source and detector, another contribution to the photocount
uncertainty referred to as static speckle appears. To predict the size of this
effect, we present a suitable definition of the etendue (or phase space volume)
that links the number of modes of a radiation field to macroscopic quantities.
