There are many ways to make photographic lenses as we all know, some more efficient than others, some better suited to particular use cases.  One of the greater challenges in creating longer focal length telephoto lenses has always been balancing focal length with physical size and weight.  Canon embarked on a limited series of lenses several years ago using a technology that they call Diffractive Optics.  You can recognize a Canon DO lens by the distinct green line.  Recently, the folks at Nikon have done something similar and released their own design using a new element mode called Phase Fresnel or PF.  At the outset, it looks and sounds like DO.  Since I am a huge fan of DO, I wanted to check out Nikon's Phase Fresnel system and they graciously loaned me one to try.