Optical method for measuring contour slopes of an object.

This paper presents a new coherent optical method whereby the partial derivatives of the contour of an object are measured. The object to be studied is immersed in a refractive medium and is imaged by a camera with a shearing device. The processed photographic plate which has been doubly exposed in the image plane with the refractive medium changed between the exposures can be Fourier filtered to yield a fringe pattern depicting derivatives of the surface contour with respect to the direction of shearing. This new method enjoys the advantages of being simple and less demanding in vibration isolation, coherence of light source, and film resolution.