The future large telescope for the Observatorio del Roque de los Muchachos will have a 10 m diameter segmented primary made of hexagonal elements (similar to the Keck I primary). The telescope optical configuration is being selected to achieve excellent image quality and low emissivity out to the mid-IR. The design includes provision for two exchangeable secondary mirrors, one of which is to be an adaptive secondary. In order to perform an independent optical calibration of the segmented primary and the adaptive secondary mirrors, the telescope with the adaptive secondary will be of the Gregorian type, whereas with the conventional secondary it will have a Ritchey- Chretien configuration. Current work to define both telescope configurations and to make them compatible is presented in this poster.