The Stromgren narrow band filter system was originally designed as a tool for fast surface gravity and metallicity estimations in stars. We use a slightly modified system which consists of four 200A width filters centered on 3500A, 4175A, 4700A and 5500A (called uz,vz,bz,yz).
The bz and yz filters are located on the continuum areas, vz is located on a region sensitive to numerous metallicity lines and uz is located in the near-UV as a measure of hot stars due to recent star formation. For old stellar populations, vz-yz and bz-yz serve as metallicity and age indices. The uz-vz index brackets the 4000A break and is a direct measure of the contribution from massive stars due to recent star formation.