Patent ID: 7568808

Claim:
An optical observation instrument having a device for protecting against incoming flare having a wavelength, said device being arranged within a beam path of said instrument having an input directed to a source of said flare and having an output directed to an observation means, said device comprising a narrowband filter tuned to the wavelength of said flare for selectively absorbing said flare, wherein said filter is configured and arranged within said beam path such that said flare transits said filter at least two times on its way between said input and said output, said device comprising a prism provided with a filter layer on a first surface thereof, said flare entering said device through said filter layer provided on said first surface and being reflected within said prism on a second surface and on a third surface of said prism and then exiting from said prism towards said output through said filter layer provided on said first surface, and further wherein the flare entering said device transits said filter layer at a first transit and transits said filter layer when exiting from said prism toward said output at a second transit distant from said first transit.