For the optical system of the core CXRS port plug several designs were developed in the last years. A survey is given of the three most relevant designs. The first design is based on an off-axis ellipsoid mirror as main imaging component. This design has been the basis of opto-mechanical design as described in previous publications . This design is presented and assessed with regard to the optical properties, the sensitivity to first mirror degradation, the possibility to include a tube to allow replacement of the first mirror (as a possible mitigation of the first mirror degradation) and the manufacturability. Two alternatives are presented that alleviate the issues connected to the optical design. These alternatives may improve both lifetime and manufacturability of the core CXRS port plug. © 2011 Published by Elsevier B.V.