  Microlensing of multiply imaged quasars is a unique probe of quasar
structure, down to the size of the accretion disc and the central black hole.
Flux ratios between close pairs of images of lensed quasars can be used to
constrain the accretion disc size and temperature profile. The starting point
of any microlensing model is the macromodel of the lens, which provides the
convergence and shear values at the location of the multiple images. Here I
present a new approach of microlensing modelling independently of the
macromodel of the lens. The technique is applied to the close pair of images A1
and A2 of MG 0414+0534, for a set of flux ratios with large variation with
respect to wavelength. The inferred accretion disc size and temperature profile
measurements, as well as the smooth matter fraction at the location of the
images, are quite robust under a wide range of macromodel variations. A case of
using purely microlensing data (flux ratios) to constrain the macromodel is
also presented. This is a first application of the technique on a fiducial
system and set of flux ratios; the method is readily applicable to collections
of such objects and can be extended to light curve and/or imaging data.
