The adjustment system comprises at least one pair of adjustment apparatuses. For each optical assembly, one adjustment apparatus is adapted to turn the optical assembly around the turning axis (α; β) independently of the other optical assembly. The adjustment system further comprises an additional adjustment apparatus connected to a first adjustment apparatus and adapted to transfer its movement to the movement of this adjustment apparatus; and a connecting member connected to the additional adjustment apparatus and to a second adjustment apparatus at the same time, and adapted to transfer the movement of the additional adjustment apparatus to the movement of the second adjustment apparatus (. If the additional adjustment apparatus is connected to the first adjustment apparatus and the connecting member is connected between the additional adjustment apparatus and the second adjustment apparatus, turning movement of one optical assembly will automatically induce a turning movement of the other optical assembly.