An optical zoom including a movable pupil that moves according to a movement law, comprises four successive groups of lenses, the first group and the fourth group being fixed, the second group and the third group being movable and placed between the first and fourth groups, the second group being a convergent group and the third group being a divergent group. In a first variant, the diameter of the movable pupil varies according to a variation law, depending on the movement law of the movable pupil. In a second variant, the optical zoom includes a movable stop, the movable stop moving according to a second movement law, the diameter of this stop varying according to a second variation law, depending on the second movement law of the movable stop.