LWIR IMAGING LENS, IMAGE CAPTURING SYSTEM HAVING THE SAME, AND ASSOCIATED METHOD

An imaging lens for use with an operational waveband over any subset of 7.5-13.5 μm may include a first optical element of a first high-index material and a second optical element of a second high-index material, that may have a refractive index greater than 2.2 in the operational waveband, an absorption per mm of less than 75% in the operational waveband, and an absorption per mm of greater than 75% in a visible waveband of 400-650 nm. Optically powered surfaces of the imaging lens may include a sag across their respective clear apertures that are less than 10% of a largest clear aperture of the imaging lens. Respective maximum peak to peak thicknesses of the first and second optical elements may be similar in size, for example within 15 percent of each other. Ratios of maximum peak to peak thickness to clear aperture and, separately, to sag are also provided.