  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 an
significant advantage for this work, which is confusion limited by the presence
of bright stars in medium to high surface brightness applications.
