Abstract: The invention concerns a method of producing optical elements, in particular filters, with interference layers comprising alternately slightly refractive and highly refractive dielectric layers deposited on a substrate S. The first layer 1 applied to the substrate is Al.sub.2 O.sub.3, constituting a slightly refractive layer, after which further layers 2 to n of ZnS and Al.sub.2 O.sub.3 are applied in an alternating sequence. The last layer n consists of Al.sub.2 O.sub.3. Such layers can be applied, at low temperatures, on flat substrates and, in particular, on sharply curved substrates. Production costs are reduced, and these layers possess the optical properties of known interference layers however resistance to external influences is greatly increased. In the case of mineral substrates, the coatings also offer considerable resistance to boiling.

Abstract: To permit adhesion of a strain gauge grid applied to a high temperature plastic, such as a polyimide, the side of the strip of polyimide which is to be attached to the support frame, the strain of which is to be measured, has a solderable surface applied thereto which consists, essentially, of three sublayers, as follows:A first sub-layer of from 1 to 8 .mu.m thickness of chromium nickel alloy, containing, for example, about 20% (by weight) of chromium, or an iron chromium nickel alloy containing, for example, about 50% iron, 49% nickel and 1% chromium (by weight);a second sub-layer of at least about 5 .mu.m thickness, preferably about 7.5 .mu.m thickness of nickel and a third outer sub-layer of gold, for example, between about 4 to 10 .mu.m thick, preferably, about 7 .mu.m. The various sub-layers are applied, for example, after cleaning of the element with a volatile hydrocarbon, or toluol, by vapor deposition, for example, vaporization from a tungsten boat of the respective materials.