Patent ID: 7110035

Claim:
An image analysing focusing device for an infrared optical apparatus ( 10 ) comprising: a controllable optical convergence element ( 20 ); an image detector ( 30 ) arranged so as to receive an image of an object projected by the optical convergence element; and a processor arranged so as to receive signals from the image detector and to generate control signals to control the optical convergence element ( 20 ) to focus the image of the object onto the image detector ( 30 ); wherein the processor comprises a search element constructed and arranged so as to analyze the image on the image detector ( 30 ) to select at least one image window in the image in connection with which a focusing operation is to be performed in accordance with predetermined conditions; and wherein the processor further comprises a focusing element ( 150 ) in the processing means ( 40 ) constructed and arranged so as to control the optical convergence element so as to focus a portion of the image within the at least one image window using an iterative process; wherein the iterative process comprises the steps of: performing a coarse focusing using only a first range of spatial frequency components of the image; and after the coarse focusing step, performing a fine focusing using only a second range of spatial frequency components of the image, the second range being higher than the first range; wherein the predetermined conditions comprise estimation of a distance from the apparatus ( 10 ) to a viewed object based on information on temperature and/or position of the optical convergence means ( 20 ).