  We report on the redshift of the lensing galaxy and of the quasar QJ
0158-4325 and on the lens model of the system. A deep VLT/FORS2 spectrum and
HST/NICMOS-F160W images are deconvolved. From the images we derive the light
profile of the lensing galaxy and an accurate relative astrometry for the
system. In addition we measure the flux ratio between the quasar images in the
MgII emission line to constrain the mass model. From the spectrum we measure
the redshift of the lensing galaxy (z=0.317+/-0.001) and of the quasar
(z=1.294+/-0.008). Using the flux ratio in the lens model allows to discard the
SIE as a suitable approximation of the lens potential. On the contrary the
truncated-PIEMD gives a good fit to the lens and leads to a time delay of
t(A-B)=-14.5+/-0.1 days, with H0=73 km/s/Mpc. Using the flux ratio to constrain
the mass model favors the truncated-PIEMD over the SIE, while ignoring this
constraint leaves the choice open.
