Device for observing test-piece surfaces by the speckle-shearing-method for the measurement of deformations

A device for observing an illuminated test-piece surface for deformation measurement in accordance with a speckle-shearing method, comprising:

• lens means for receiving light reflected from said illuminated test-piece surface and for providing an optical output;
• splitter means for splitting said optical output into two output beams traveling in substantially perpendicular paths;
• first mirror means for receiving and reflecting a first one of said two output beams to produce a first reflected beam;
• second mirror means for receiving and reflecting a second one of said two output beams to produce a second reflected beam;
• and
• sensing means for receiving and sensing said first and second reflected beams;
• wherein said lens means comprises an objective lens disposed between said test-piece surface and said splitter means for converging and diverging the light reflected from said illuminated test-piece surface to produce an intermediate image of the illuminated test-piece surface, said intermediate image forming the optical output of said lens means, said intermediate image being split by said splitter means and reflected by said first and second mirror means, whereupon it is imaged onto said sensing means;
• and
• wherein said first and second mirror means comprise concave mirrors of equal focal length, said device further comprising adjusting means for longitudinally and transversely adjusting the position of said concave mirrors.