Patent ID: 8416404

Claim:
A method for measuring and correcting a shift in boresight, effective focal length, and/or focus of an optical system that is caused by temperature variations, said method comprising: (a) providing one or more radiation emitting sources; (b) fixedly attaching radiation emitting sources to a support frame or to a first optical element of said optical system such that they are located in front of and near an outer edge of said first optical element; (c) providing means to limit the size of a footprint of said radiation emitting sources on said first optical element of said optical system when said radiation emitting sources are activated; (d) activating said radiation sources and measuring in a selected coordinate system initial locations of a center and/or initial sizes of images of said radiation emitting sources that are formed on a detector, wherein said measurements are made with said optical system at standard temperature; (e) activating said radiation sources and measuring in said selected coordinate system the shifted locations of the center and/or new sizes of said images of said radiation emitting sources that are formed on said detector, wherein said measurements are made with said optical system at a temperature that is different from said standard temperature; (f) using a processor to calculate shifts dx i and dy i between said initial locations and said shifted locations along X and Y axes of said selected coordinate system and/or to measure changes in size of said images of said radiation emitting sources; (g) measuring and correcting said shift in said boresight and said effective focal length of said optical system that is caused by the change from said standard temperature to said different temperature; and/or (h) correcting said shift of focus of said optical system that is caused by the change from said standard temperature to said different temperature; wherein frequency and duty cycle at which the radiation emitting sources are activated is determined according to one of the following: (a) as a function of time; (b) as a function of temperature; (c) as a function of temperature change; or (d) as a function of image quality.