The optical design is driven by the need to feed the large detector array. Although this is new territory for mm-wave design, many concepts can be borrowed from optical telescope design. This design is indeed a hybrid of tradtional radio-wave and visible-wave designs. The system, for instance, is divided between the telescope and camera. The telescope is an off-axis type, used often in radio designs and chosen for it's clear aperture leading to low edge diffration. The camera makes use of lenses to reimage the light from the telescope, similar to visible designs.