  We present (V,V-I) VLT-FORS1 observations of the Galactic Globular Cluster
NGC 6397. We derive accurate color--magnitude diagrams and luminosity functions
(LFs) of the cluster Main Sequence (MS) for two fields extending from a region
near the centre of the cluster out to ~ 10 arcmin. The photometry of these
fields produces a narrow MS extending down to V ~ 27, much deeper than any
previous ground based study on this system and comparable to previous HST
photometry. The V, V-I CMD also shows a deep white dwarf cooling sequence
locus, contaminated by many field stars and spurious objects. We concentrate
the present work on the analysis of the MSLFs derived for two annuli at
different radial distance from the center of the cluster. Evidence of a
clear-cut correlation between the slope of the observed LFs before reaching the
turn-over, and the radial position of the observed fields inside the cluster
area is found. We find that the LFs become flatter with decreasing radius (x ~
0.15 for 1'< R1 < 5.5'; x ~ 0.24 for 5.5'< R2 <9.8'; core radius, rc = 0.05'),
a trend that is consistent with the interpretation of NGC 6397 as a dynamically
relaxed system. This trend is also evident in the mass function.
