Abstract: An optical filter comprises a multilayer coating adherent to a substrate, the coating comprising at least four superimposed layer collections. Each layer collection has ordered first, second and third layers of which the first and third layers are made of a first material and are 0.6 quarter wavelengths thick whereas the second layer is made of a second material and is 6.8 quarter wavelengths thick. One of these materials has a high refractive index in the range 1.9 to 2.5 whilst the other of these materials has a low refractive index in the range 1.3 to 1.7. The preferred high index material is zinc sulphide and the preferred low index material is thorium fluoride.The optical filter is generally transmissive except in a number of narrow waveband regions which include respective known laser wavelengths.