Compatible Machines: AF2440;AF4063;AF3555;AF5070;ZF3551 Cutting Edge Features: HIGH-QUALITY CVD ZnSe: OMTech's powerful focus lenses are manufactured from premium zinc selenium via chemical vapor deposition for superior optical properties. HIGH TRANSMITTANCE: Both sides of each lens are covered with strongly antireflective coatings to achieve at least 99.5% transmittance rate for infrared light at a wavelength of 10.6 microns. LASTING DURABILITY: Our laser engraver focus lenses' double-sided coating process also ensures outstanding scratch resistance for longer service life. WIDE COMPATIBILITY: This 20mm laser focus lens fits OMTech 100W-130W CO2 laser engravers. Please check the focal lens diameter in your machine’s manual before purchasing. EASY TO USE: The plano-convex shape of OMTech's engraver focal lens lets you install it easily and correctly onto your machine in the proper orientation. Detailed cleaning instructions also help you take proper care of your lens. Specifications: Material: Zinc Selenium Color: Yellow Diameter: 20mm (0.79") Thickness: 2mm (0.08") Focal Length: 1.5" (38.1mm)/ 2" (50.8mm)/ 2.5" (63.5mm)/ 3" (76.2mm)/ 4" (101.6mm) Rec. Wavelength: 10.6 microns (10600 nm) Min. Light Transmittance: 99.5% Net Weight: 0.2 oz (5g)  Summary: It is all smoke and mirrors! As you engrave, debris such as smoke and dust land on your focal lens, building up a layer of residue over time that absorbs laser beam power and can stain the lens permanently. Eventually, this lost power will affect your machine’s precision and throw off your laser settings. To keep your device running at its full potential, we recommend inspecting and cleaning the optics system once a week and replacing the mirrors or focal lens as soon they get damaged. Package Includes: 1 x CVD ZnSe Focus Lens Warranty: No need to worry! We offer a 1-year warranty on all focal lenses. Certifications: FDA Compliant CE Certification ISO9001 Quality Certification