In Eq. (4), we map the notation of the modified G&L OPD parameters [Eq. (2)] to the notation of the terms in Eq. (3). The specimen is comprised of stratified layers as indicated above, with each layer having RI , where ( and ). The RIs of the immersion medium and coverglass are defined as and , respectively. The thickness of the immersion medium and the coverglass are defined as and , respectively. The thickness of the th (where the point source is located) layer is defined as , while the thickness of all the other specimen layers are defined as , where (; ). The normalized radius () in the back focal plane can be used to determine the terms for .