The general field of the invention is that of optical systems comprising a zoom lens (Z) and an optical detection unit with depth estimation, said optical detection unit with depth estimation comprising a microlens array (MML) and a matrix detector (DM), the microlens array being arranged in such a way that the image of the focal plane of the zoom is focused by the microlens array in the plane ofthe matrix detector. The optical system according to the invention comprises calculation means for calculating, for a first focal length of the zoom and for a determined object, the estimated distance(DE) of said object and the measurement uncertainty (I) for said estimation, as a function of said first focal length and said estimated distance and, said estimated distance being known, optimisation means for determining at least one second focal length of the zoom having a measurement uncertainty which is less than that for said estimation.