The invention relates to an optical system comprising: at least one source of illumination designed to produce an illuminating beam; and at least one imager able to produce an imaging beam when illuminated by the said illuminating beam; the said system being characterized in that it further comprises: collimating means for collimating the said illuminating beam; and at least one optical element comprising, on a first surface, means for redirecting part of the said illuminating beam towards the said imager, so as to illuminate the said imager and for adapting the shape of the said beam to suit the said imager.