Method for adjusting a lens for a current image acquisition, comprising the following steps executed in advance of the current image acquisition: - constructing and storing, for each feasible sharpness position (F@) of the lens, a first set of reference criteria obtained for different focusing errors (dfc) of the lens, each reference criterion being obtained by executing the following steps a) to d), for different possible starting positions within the adjustment range of the lens: a) adjusting the lens to a first focusing position and acquiring a first image of a scene through the lens, the first focusing position corresponding to one of said possible starting positions of the lens; b) adjusting the lens to a second focusing position and acquiring a second image of the same scene, the second position being offset from the first position by a first reference interval (Δ) and the difference between the feasible sharpness position and the second position defining the focusing error; c) producing respective power spectra (Vp1, Vp2) of the first and second images; and d) producing the reference criterion representing the ratio of the power spectra, enabling the focusing error of the lens to be estimated; and, during the current image acquisition: e) setting the lens at a first chosen position and capturing a first image; f) offsetting the lens by the first reference interval (Δ); g) capturing a second image in the same window; h) calculating a current reference criterion on the basis of the respective power spectra of the first and second images obtained in steps e) and g); i) comparing the current reference criterion produced by the current image acquisition with the stored reference criteria; and j) correcting the focusing position of the lens by using the sharpness position (F@) associated with the reference criterion closest to the current reference criterion. - constructing and storing, for each feasible sharpness position (F@) of the lens, a first set of reference criteria obtained for different focusing errors (dfc) of the lens, each reference criterion being obtained by executing the following steps a) to d), for different possible starting positions within the adjustment range of the lens: a) adjusting the lens to a first focusing position and acquiring a first image of a scene through the lens, the first focusing position corresponding to one of said possible starting positions of the lens; b) adjusting the lens to a second focusing position and acquiring a second image of the same scene, the second position being offset from the first position by a first reference interval (Δ) and the difference between the feasible sharpness position and the second position defining the focusing error; c) producing respective power spectra (Vp1, Vp2) of the first and second images; and d) producing the reference criterion representing the ratio of the power spectra, enabling the focusing error of the lens to be estimated; and, during the current image acquisition: e) setting the lens at a first chosen position and capturing a first image; f) offsetting the lens by the first reference interval (Δ); g) capturing a second image in the same window; h) calculating a current reference criterion on the basis of the respective power spectra of the first and second images obtained in steps e) and g); i) comparing the current reference criterion produced by the current image acquisition with the stored reference criteria; and j) correcting the focusing position of the lens by using the sharpness position (F@) associated with the reference criterion closest to the current reference criterion. a) adjusting the lens to a first focusing position and acquiring a first image of a scene through the lens, the first focusing position corresponding to one of said possible starting positions of the lens; b) adjusting the lens to a second focusing position and acquiring a second image of the same scene, the second position being offset from the first position by a first reference interval (Δ) and the difference between the feasible sharpness position and the second position defining the focusing error; c) producing respective power spectra (Vp1, Vp2) of the first and second images; and d) producing the reference criterion representing the ratio of the power spectra, enabling the focusing error of the lens to be estimated; e) setting the lens at a first chosen position and capturing a first image; f) offsetting the lens by the first reference interval (Δ); g) capturing a second image in the same window; h) calculating a current reference criterion on the basis of the respective power spectra of the first and second images obtained in steps e) and g); i) comparing the current reference criterion produced by the current image acquisition with the stored reference criteria; and j) correcting the focusing position of the lens by using the sharpness position (F@) associated with the reference criterion closest to the current reference criterion.