for a motor vehicle the optical system performing at least one main optical function and including in particular a diffusion screen at least one light source of the led type each led of the optical system producing a set of rays of light to be propagated in the diffusion screen wherein the screen is in the form of a curved sheet with an upper lateral flange and a lower lateral flange which meet at a periphery which has in particular a rear face and a front edge and the principal function is performed essentially via an output face constituted by the front edge of the diffusion screen application_number US 201213656970 A description the different elements appearing in several figures unless otherwise stated have retained the same reference numbers fig1 a 1 b and 1 c show a first embodiment of an optical system according to the invention in respectively a first position a second position and a third position a three dimensional orthogonal marker is shown in these figures with an axis of abscissas x corresponding to the axis of displacement of the reversing vehicle and a normal z axis corresponding to the vertical in these figures the optical system 100 according to the invention consists of a diffusion screen 113 and of a.