  We present initial results of a photometric survey of open star clusters,
primarily in the southern hemisphere, taken in the u'g'r'i'z' filter system.
While our entire observed sample covers more than 100 clusters, here we present
data for NGC2548 (M48) which is a cluster characterized in the UBV and DDO
photometric systems. We compare our results to the published values from other
observers and to the Padova theoretical isochrones and metallicity curves.
These observations demonstrate that the u'g'r'i'z' filters can play an
important role in determining the metallicity of stars and clusters. We begin
this series of papers with a study of NGC2548 because we have obtained data of
this cluster not only with our main program telescope, the CTIO Curtis-Schmidt,
but also with the US Naval Observatory (USNO) 1.0m telescope (the telescope
used to define the u'g'r'i'z' system), and the Sloan Digital Sky Survey (SDSS)
0.5m Photometric Telescope (the photometric monitoring telescope used to
calibrate the SDSS 2.5m telescope imaging data). We have used the data from
this study to validate our ability to transform measurements obtained on other
telescopes to the standard USNO 1.0m u'g'r'i'z' system. This validation is
particularly important for very red stars, for which the original u'g'r'i'z'
standard star network is poorly constrained.
