A fast and reliable optical setup is here presented for in-focus imaging of objects in the macro range. The setup uses a camera equipped with an objective embedding a liquid lens, whose focal length is voltage-controlled. The defocus condition of the image is controlled by means of two indexes, both suitable for coarse and for fine adjustments. A purposely designed algorithm makes use of the two indexes, switching from one to the other to position the image in focus by adequately controlling the liquid lens focal length. The setup has been calibrated by means of target planes of known contrasts, and applied to process biomedical images such as fingerprints.
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