A Survey of Open Clusters in the u'g'r'i'z' Filter System: III. Results   for the Cluster NGC 188
  We continue our series of papers describing the results of a photometric survey of open star clusters, primarily in the southern hemisphere, taken in the u'g'r'i'z' filter system. The entire observed sample covered more than 100 clusters, but here we present data only on NGC 188, which is one of the oldest open clusters known in the Milky Way. We fit the Padova theoretical isochrones to our data. Assuming a solar metallicity for NGC 188, we find a distance of 1700+/-100 pc, an age of 7.5+/-0.7 Gyr, and a reddening E(B-V) of 0.025+/-0.005. This yields a distance modulus of 11.23+/-0.14. 
Bartosz Fornal, Douglas L. Tucker, J. Allyn Smith, Sahar S. Allam,   Cristin J. Rider, and Hwankyung Sung