The Cassegrain Nasmyth telescope has the same optical design as the classical Cassegrain telescope except for a smalltertiar mirror which send the light out on the side of the telescope tube instead of through a hole in the primary mirror. This design is common in large telescopes: ex. the W. M. Keck Observatory. 410x Figure 1 shows the light-path from a star based on the 0.61m telescope in Oslo. Figures 2 and 3 show the use of a focal reducer, flip mirror unit, ocular and CCD Camera.See also: Nasmyth telescope.