  We present V and I photometry for a field 5' from the center of 47 Tuc. The
field was imaged with the HST WFPC2 as part of the Medium Deep Survey project.
The luminosity function (LF) continually rises in the domain $5 < M_I < 9$ with
a slope $\Delta log \Phi (M) / \Delta M \sim 0.15$ and then drops off sharply.
We compare our LF with that derived by De Marchi \& Paresce for a neighbouring
HST field. The two independent LFs are very similar in the entire range of
luminosities probed ($M_I < 10$). Comparisons are also made to other HST LFs
derived by several authors for different clusters in the Galaxy. We use the KS
test to assess the significance of the differences found. The LFs obtained with
HST are consistent with being derived from the same population down to $M_I
\sim 9.0$. Beyond that, statistically significant variations arise. Globular
cluster LFs also differ according to the prominence of a plateau in the bright
end ($5 < M_I < 6.5$). Mass functions are sensitive to the mass-luminosity
relation. Different approaches to deriving the 47 Tuc mass function from its LF
lead to markedly different results at the low mass end. For $M > 0.4 M_\odot$,
the 47 Tuc mass function is significantly different from that of \wcen. The
calibrated HST $M_V(V-I)$ colour-magnitude diagrams (CMDs) show a trend with
metallicity in the sense of metal richer systems having redder CMDs for a fixed
absolute magnitude. The main-sequence becomes shallower with increasing
metallicity. For metal-rich systems, the CMDs derived from HST are in general
agreement with previous ground-based studies. However, the CMDs of metal poor
subdwarfs observed from the ground are shallower than those of globular
clusters observed with HST.
