This PL 2x extender/doubler by Schneider/Century Optics uses multi-coated optics to double the effective FoV of many PL mount lenses. For instance, if using a 25-250mm lens, the FoV would become similar to a 50-500mm lens. Please note that because there are optics inside, some PL mount lenses with deeper rear elements are not compatible with this doubler. Most zooms and telephoto primes have shallow enough rear elements to work. Please be extra cautious when attempting to use for the first time and unsure if compatible. This was the go-to doubler for many years at rental houses and provides a good optical result for the price.