Eyepiece design with refractive-diffractive hybrid elements

Eyepieces are a part of visual optical systems. Because of their wide field of view and long eye-relief, it is difficult to further improve the existing eyepieces using all-refractive surfaces. Since diffractive elements demonstrate unique characteristics: negative dispersion and non-field curvature, the eyepiece design can be improved by using refractive-diffractive hybrid surfaces. In this paper, several design examples using refractive-diffractive hybrid surfaces to design moderate field of view (FOV) eyepieces were studied. Firstly, a design example using a diffractive surface to replace the negative piece in the cement doublet of a conventional Kellner type eyepiece is presented. Then a design example is given by employing two diffractive elements to replace the negative elements used in the conventional symmetrical eyepiece. For the above examples the eyepiece aberration correction techniques were also analyzed.