ABSTRACT
A diffractive optical element can be considered as a very thin device that changes the phase of the emerging wavefront. The simplest type is a binary optic that has a discrete number of these phase altering steps. These steps either add zero or π phase difference to the wavefront. Such diffractive surfaces may be applied to a lens to aid in color and other aberration correction (O’Shea et al. 2004). The paraxial power of such surfaces is a linear function of wavelength, i.e.: v = λ 0 λ short − λ long ; https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315222295/bd2ad0d9-a48e-40ac-8986-c51474069cbd/content/eq196.tif"/> consequently, this value is negative and its absolute value is much smaller than “flint” glasses (Buralli 1994). This, therefore, is very effective for correcting chromatic aberration. It also does not increase the Petzval sum.
