100 Times Faster and 3 Times Sharper: Background-Dominated Observations   of Stellar Populations with an 8-meter Optical-UV Space Telescope
  An 8 m successor to the Hubble Space Telescope (HST) would make incredible gains in the study of stellar populations, especially in the Local Group. If diffraction-limited at 0.5 microns, the "Next HST" could produce high-resolution imaging of faint sources over a wide field in 1 percent of the time needed with the HST. With these capabilities, photometry of the ancient main sequence could be obtained for many sight-lines through Local Group galaxies, thus determining directly the ages of their structures and providing a formation history for the Local Group populations. 
Thomas M. Brown (STScI)