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Several previous studies of distant clusters have suggested that significant evolution of cluster galaxies, either photometric or spectroscopic, occurs over lookback times of only a few Gyr ({\em e.g.}, Butcher \& Oemler 1984, Dressler \& Gunn 1992). One cluster has proven particularly interesting by appearing to be simultaneously old and young: Cl0016+16 at $z=0.54$ is photometrically unevolved, with galaxies similar in colors to present-day ellipticals (Koo 1981) despite a lookback time of half the age of universe. On the other hand, galaxy spectra indicate 0016+16 has a significant population of ``E+A'' galaxies, leading Dressler to state that ``the population of this extremely rich cluster...is the most unusual we have found.''
We have recently obtained 3 hours of WF/PC 785LP (I) band imaging in the core of Cl0016+16, making this the most distant bona fide cluster studied with HST. The images contain nearly 100 galaxies down to $I\approx24$, reaching $M^*+3$ (for $h=0.5$, $q_0=0.05$). This poster describes the preliminary results from these images, which will allow us to probe the size and surface brightness of early-type galaxies at moderate redshift, determine the morphology of the ``E+A'' population, and search for evidence of arclets produced by gravitationally-lensed background galaxies.
