Masking the horizontal branch and giant stars allows unambiguous measurements of mean age and metallicity in simple old stellar populations from metal and hydrogen line strengths. Billion year resolution is possible in the luminous halos of early-type galaxies, constraining formation models. Most of the nuisance parameters in stellar evolution are avoided by isolating the main sequence for analysis. The initial mass function and s-process element diagnostics may also be accessible. Integral field spectrographs have a significant advantage for this work, which is confusion limited by the presence of bright stars in medium to high surface brightness applications.