Typical set is (CWL FWHM) : CO 4.74 0.18 mkm or (4.67 0.16 mkm), SO2 7.30 0.18 mkm, NO 5.30 0.18mkm, NO2 3.50 0.125mkm (or 6.135 0.19 mkm), CH4 3.33 0.16 mkm, CO2 4.26 0.18 mkm, H2O 6.62 0.17 mkm (or H2O 2.70 0.14 mkm), (optional NF3, SF6, HC ?). Required diameter 21-23 mm (clear aperture 19 mm), this parameter is refined. OD4.