An optical system with an optical beam propagation extension, having an input and an output for the optical beam. The system includes at least two optical reflection elements for reflection of the beam, arranged to extend the propagation of the beam by reflection on the reflection elements, and at least one optical beam transmission element arranged to be traversed at least twice by the optical beam in different directions during propagation of the optical beam in the optical system. The optical transmission element ensures an optical transformation of the optical beam each time the optical beam passes through so as to correct the divergence thereof.