Nikon filed a patent for a 70-300mm f/4.5-6 VR CX lens with Phase Fresnel (PF) element for Nikon 1 mirrorless system:
Now the diffraction optical surface will be described. Well known methods for deflecting a ray are refraction and reflection, but diffraction is also known as a third such method. A diffraction optical element is an optical element using the diffraction phenomena of light, and presents a behavior that is different from refraction and reflection. In concrete terms, a diffraction grating and a Fresnel’s zone plate have been known (conventionally known). Even in the case of natural light, coherence length is normally several λ (nm), hence if a structure in a wavelength order is created, obvious diffraction phenomena can be generated as a result of the interference of light waves. The surface which plays the function of deflecting a ray like this using a diffraction phenomenon is called “diffraction optical surface”. An optical element having such as surface is normally called a “diffraction optical element”.
The diffraction optical surface has the nature of having a negative dispersion value while the refractive power is positive, which is very effective for correcting chromatic aberration. Therefore good chromatic aberration correction at a level which normal glass cannot reach becomes possible, or good chromatic Aberration which can be implemented only by using an expensive special low dispersion glass becomes possible.
Therefore in the zoom lens ZL according to this embodiment, a diffraction optical surface that has a function to deflect a ray, utilizing the diffracting phenomena of diffraction grating or Fresnel’s zone plate, is created on the surface of an optical member, such as glass or plastic, so that good optical performance is acquired by this function.
