A thermal imager comprising: a lens assembly; an array of integrated circuit, IC, chips that is arranged in a field of view of the lens assembly, each IC chip comprising an array of thermopile devices; and a filter assembly comprising one or more wavelength filters, wherein the IC chips are arranged in three or more parallel rows of IC chips (15-1, 15-2, 15-3, 15-4) that include a pair of non-adjacent rows of IC chips (15-1, 15-4) and one or more rows of IC chips (15-2, 15-3) other than the pair of non-adjacent rows of IC chips (15-1, 15-4); wherein the filter assembly is arranged between the array of IC chips and the lens assembly and comprises a respective wavelength filter for at least one of the three or more rows of IC chips, wherein the at least one wavelength filter is transparent in a portion of a wavelength range of radiation that can pass through the lens assembly; wherein the filter assembly is further configured such that radiation of the same wavelength range can pass to the rows of IC chips in the pair of non-adjacent rows of IC chips (15-1, 15-4), and such that the wavelength range of radiation that can pass to the rows of IC chips in the pair of non-adjacent rows of IC chips (15-1, 15-4) is different from a wavelength range of radiation that can pass to the one or more rows of IC chips (15-2, 15-3) other than the pair of non-adjacent rows of IC chips (15-1, 15-4); and wherein the wavelength range of radiation that can pass to the rows of IC chips in the pair of non-adjacent rows of IC chips (15-1, 15-4) spans the full wavelength range of radiation that can pass through the lens assembly. a lens assembly; an array of integrated circuit, IC, chips that is arranged in a field of view of the lens assembly, each IC chip comprising an array of thermopile devices; and a filter assembly comprising one or more wavelength filters, wherein the IC chips are arranged in three or more parallel rows of IC chips (15-1, 15-2, 15-3, 15-4) that include a pair of non-adjacent rows of IC chips (15-1, 15-4) and one or more rows of IC chips (15-2, 15-3) other than the pair of non-adjacent rows of IC chips (15-1, 15-4); wherein the filter assembly is arranged between the array of IC chips and the lens assembly and comprises a respective wavelength filter for at least one of the three or more rows of IC chips, wherein the at least one wavelength filter is transparent in a portion of a wavelength range of radiation that can pass through the lens assembly; wherein the filter assembly is further configured such that radiation of the same wavelength range can pass to the rows of IC chips in the pair of non-adjacent rows of IC chips (15-1, 15-4), and such that the wavelength range of radiation that can pass to the rows of IC chips in the pair of non-adjacent rows of IC chips (15-1, 15-4) is different from a wavelength range of radiation that can pass to the one or more rows of IC chips (15-2, 15-3) other than the pair of non-adjacent rows of IC chips (15-1, 15-4); and wherein the wavelength range of radiation that can pass to the rows of IC chips in the pair of non-adjacent rows of IC chips (15-1, 15-4) spans the full wavelength range of radiation that can pass through the lens assembly.