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