We describe an extensive observational project that has obtained high-quality and homogeneous photometry for a number of different Galactic star clusters ( including M 92 , M 13 , M 3 , M 71 , and NGC 6791 ) spanning a wide range in metallicity ( -2.3 \lesssim [ Fe / H ] \lesssim + 0.4 ) , as observed in the u ^ { \prime } g ^ { \prime } r ^ { \prime } i ^ { \prime } z ^ { \prime } passbands with the MegaCam wide-field imager on the Canada-France-Hawaii Telescope .
By employing these purest of stellar populations , fiducial sequences have been defined from color-magnitude diagrams that extend from the tip of the red-giant branch down to approximately 4 magnitudes below the turnoff : these sequences have been accurately calibrated to the standard u ^ { \prime } g ^ { \prime } r ^ { \prime } i ^ { \prime } z ^ { \prime } system via a set of secondary photometric standards located within these same clusters .
Consequently , they can serve as a valuable set of empirical fiducials for the interpretation of stellar populations data in the u ^ { \prime } g ^ { \prime } r ^ { \prime } i ^ { \prime } z ^ { \prime } system .