  The opacity of spiral galaxy disks, from counts of distant galaxies, is
compared to HI column densities. The opacity measurements are calibrated using
the ``Synthetic Field Method'' from Gonzalez et al (1998) and Holwerda et al.
(2005a).
  When compared for individual disks, the HI column density and dust opacity do
not seem to be correlated as HI and opacity follow different radial profiles.
  To improve statistics, an average radial opacity profile is compared to an
average HI profile. Compared to dust-to-HI estimates from the literature, more
extinction is found in this profile. This difference may be accounted for by an
underestimate of the dust in earlier measurements due to their dependence on
dust temperature. Since the SFM is insensitive to the dust temperature, the
ratio between the SFM opacity and HI could very well be indicative of the true
ratio.
  Earlier claims for a radially extended cold dust disk were based on sub-mm
observations. A comparison between sub-mm observations and counts of distant
galaxies is therefore desirable. We present the best current example of such a
comparison, M51, for which the measurements seem to agree. However, this
remains an area where improved counts of distant galaxies, sub-mm observations
and our understanding of dust emissivity are needed.
