  Microlensing events are being discovered and alerted by the two survey teams
OGLE and MOA at an increasing rate. Around ten percent of these events involve
binary lenses. Such events potentially contain much information on the physical
properties of the observed binary systems, which can then be used for e.g.
statistical studies on binary objects in the Galactic disk or bulge. However,
such events are usually not straightforward to study, because the model
equations are strongly non-linear and there are many local minima that can fool
the search for the best solution if the parameter space is not inspected with
great care. In this work an alternative parameterisation for the binary lens
fitting problem is proposed, in which the parameters involved are defined to
represent as closely as possible the caustic-crossing features observed in most
binary lens light curves. Furthermore, we work out an extension of the method
in order to make use of the straight line fold caustic approximation, when the
latter applies for both the caustic entry and exit. We introduce an alternative
parameterisation in order to confine the exploration of the parameter space to
regions where the models only involve caustic crossing at the dates seen in the
light curve. We find that the proposed parameterisation provides more
robustness to the light curve fitting process, in particular in avoiding a code
to get stuck in false minima.
