Since the first optical detection of RX J0720.4-3125 various observations have been performed to determine astrometric and photometric data .
We present the first detection of the isolated neutron star in the V Bessel filter to study the spectral energy distribution and derive a new astrometric position .
At ESO Paranal we obtained very deep images with FORS 1 ( three hours exposure time ) of RX J0720.4-3125 in V Bessel filter in January 2008 .
We derive the visual magnitude by standard star aperture photometry.Using sophisticated resampling software we correct the images for field distortions .
Then we derive an updated position and proper motion value by comparing its position with FORS 1 observations of December 2000 .
We calculate a visual magnitude of V = 26.81 \pm 0.09 mag , which is seven times in excess of what is expected from X-ray data , but consistent with the extant U , B and R data .
Over about a seven year epoch difference we measured a proper motion of \mu = 105.1 \pm 7.4 mas yr ^ { -1 } towards \theta = 296.951 ^ { \circ } \pm 0.0063 ^ { \circ } ( NW ) , consistent with previous data .