XCSOURCE 3x Achromatic Barlow Lens 1.25" 31.7mm Metal for Telescope Eyepiece DC623 This Barlow features an air-spaced, three-element, Apo design with fully multicoated optics. The housing is precision machined from aluminum stock and black anodized to a hard finish. The lens edges and inner barrel are blackened to provide maximum contrast. The Barlow body includes a safety undercut on the lower barrel and a brass compression ring so that your eyepiece barrels are not marred by the captive set screw. For those who need a very high quality Barlow for all-round use, the 3x Barlow is a very nice step up from the typical 2x achromatic Barlow commonly found on the market.