Nikon Granted New Patent For 24-70mm f/2.8E PF ED (Phase Fresnel)
Nikon was first granted a patent for a 24-70 f/2.8 PF lens back in September of 2014, but since then the only PF lens to come to market was the 300mm f/4E PF ED VR PF.
PF Lenses feature what Nikon is calling a Phase Fresnel lens element, or Diffractive Optics as others like Canon are calling it. If you’re not familiar with the technology, you can read our knowledge base article entitled: What are Diffractive Optics?
Although new developments around the technology seem to be slow, as they have been with Canon DO lenses, it’s no surprise to see Nikon continuing the development of these lenses after the good reception that the first PF lens, the 300mm, received from reviewers.
Proof of continued development in lenses with this technology can be found in the form of a new patent that was granted to Nikon just a few weeks ago in early January 2017. The patent is a continuation of the one from 2014, but it contains a few additional details. As is often the case with lens patents, the document contains several variations on the lens’ optical formula. It’s no surprise that several versions of a lens get tested during development, and presumably this patent application method means they will be covered for whichever one they decide to bring to market, whenever that might be.
Problems to be Solved by the Invention
Generally it is desirable for an optical system, such as a digital camera and a video camera, to have a total lens length (total optical length, that is, the length from the lens surface closest to the object (first surface) to the image surface) that is short and an entire optical system that is compact. However as the total lens length becomes shorter, various aberrations, including chromatic aberration, tend to increase and optical performance tends to deteriorate. Even if a diffractive optical element alone is installed in such an optical system, it is difficult to correct the chromatic aberration well in the entire zoom range unless the installed position and the refractive power are set appropriately. If a diffractive optical element is used inappropriately, chromatic aberration correction becomes insufficient. If the refractive power of the diffractive optical element is high, the grating pitch of the diffractive optical element becomes small, which makes manufacturing difficult and productivity deteriorates.