  We have used deep high-resolution Hubble Space Telescope ACS observations to
image the cluster NGC 1978 in the Large Magellanic Cloud. This high-quality
photometric data set allowed us to confirm the high ellipticity (~0.30+-0.02)
of this stellar system. The derived Color Magnitude Diagram allowed a detailed
study of the main evolutionary sequences: in particular we have detected the so
called Bump along the Red Giant Branch (at V_{555}=19.10+-0.10). This is the
first detection of this feature in an intermediate-age cluster. Moreover the
morphology of the evolutionary sequence and their population ratios have been
compared with the expectations of different theoretical models (namely BaSTI,
PEL and Padua) in order to quantify the effect of convective overshooting. The
best agreement (both in terms of morphology and star counts) has been found the
PEL (Pisa Evolutionary Library) isochrone with Z=0.008 (consistenly with the
most recent determination of the cluster metallicity, [M/H]=-0.37 dex) and a
mild overshooting efficiency (Lambda_{os}=0.1). By adopting this theoretical
set an age of 1.9+-0.1 Gyr has been obtained.
