The invention relates to an optical device for a vehicle with at least one lens comprising an optical axis, an output diopter, and an input diopter. The device including a light source arranged to emit light towards the input diopter of the at least one lens, with the at least one lens having an object focus located substantially on the input diopter of the lens. A section of the output diopter in a vertical plane parallel to the optical axis of the at least one lens includes one or more elliptical or substantially elliptical arcs which are modified relative to a reference elliptical shape, in which all the rays coming from the light source would be emitted parallel to the optical axis of the at least one lens at the output of a reference output diopter.