Measurement of Windscreen Distortion Using Optical Diffraction.
DEPARTMENT OF THE AIR FORCE WASHINGTON DC
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The patent concerns a measurement apparatus and method for detecting, resolving and quantifying the distortion caused by a relatively large region of a distorting optically transparent medium. A precisely defined pattern is viewed through the transparent medium to introduce the distortion effects. The altered pattern is photographically recorded in thin film transparency format. A beam of coherent luminous energy projected through the transparency, once focused, produces a Fraunhofer diffraction pattern which is the Fourier transform of the original pattern. Conventional distortion characteristics in the Fourier domain appear in a form more amenable to quantification and analysis. The character and magnitude of the distortion is readily ascertained by comparing the transforms of distorted and undistored patterns, yielding quantitative data comparable to conventional distortion effects in terms of grid line slop and lens factor.