European Community Represented by Commision of the European Communities

Colin Forno

Maurice Whelan

An interferometer ( ) is arranged to form a first interference fringe pattern comprising at least ten interference fringes; recording an image of said first interference fringe pattern; perturbing an optical path in the interferometer ( ) to form a second interference fringe pattern comprising at least ten interference fringes; and combining an image of said second interference fringe pattern with the recorded image of the first interference fringe pattern to produce a further image comprising a moir&eacute; fringe pattern arising from a difference or differences between the first and second interference fringe patterns. The combining step involves subtraction ( ) of digital images. Different wavelengths and interferometers are used: Michelson, Mach-Zehnder, Fizeau, Twyman-Green. In this new approach, all the errors of a poor quality, misaligned system are accepted and then eliminated by the combination process, producing a moir&eacute; fringe pattern. The method enables very large aperture optical systems for traditional and engineering interferometers to be constructed from inexpensive and basic components.

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Ispra, Italy

Colin Forno