An optical arrangement 1, wherein four directional mirrors are provided, each of said four mirrors being mounted for rotation on an edge thereof to form a quadrangle around the optical axis of the concave mirror, {HEAD ~ each} of {TAIL ~ said mirrors} creating an optical effective curtain coacting to surround the space being mounted 
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An optical arrangement 1 , wherein four directional mirrors are provided , each of said four mirrors being mounted for rotation on an edge thereof to form a quadrangle around the optical axis of the concave mirror , { HEAD ~ each } of { TAIL ~ said mirrors } creating an optical effective curtain coacting to surround the space being mounted
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