  We have carried out extensive VLT-FORS1 observations covering a fair fraction
of the intermediate metallicity globular cluster NGC 6712 in the V and R bands.
We derive accurate colour-magnitude diagrammes (CMD) and luminosity functions
(LFs) of the cluster main sequence (MS) for four overlapping fields extending
from the centre of the cluster out to a radius of ~10', well beyond the nominal
tidal radius, and for a control field at ~42' distance. The LFs extend from the
cluster turn-off (TO) at M_R 4 to the point at which the incompleteness drops
below 50% (corresponding to R 23 or M_R 7.5) for most fields studied. Cluster
stars become indistinguishable from field stars at r 5'. The shape of the
cluster's LF and its variation with distance from the centre in these ranges
are well described by a standard multi-mass static model having the following
parameters: core radius r_c=1', half-light radius r_hl=1.8', tidal radius
r_t=5.2', concentration ratio c=0.7, and a power-law global mass function (MF)
with index alpha 0.9 for masses smaller than 0.8 Msolar, i.e. for all detected
MS stars, and alpha -2.35 for evolved objects. The MF obtained in this way is
consistent with that found in a preliminary investigation of this cluster with
the VLT Test Camera and confirms that this is the only globular cluster known
so far for which the global MF drops with decreasing mass below the TO.
Possible reasons for this unique characteristic are discussed with the most
likely associated with its extreme vulnerability to tidal disruption.
