The optical axis of a Nasmyth telescope should be perpendicular to the Elevation axis and pass through the rotational center of the Tertiary mirror turret rotator. Realized by aligning a laser beam to the rotational center of the two field derotators. A high precision Pentaprism mounted on the Tertiary mirror rotator deviates the laser beam by 90 degrees defining the optical axis onto which the Primary and Secondary mirrors are mounted and aligned. We present method, procedure, tools and results for two examples of Nasmyth Telescopes; the 4.1m SOAR and the LSST's 1.2m Auxiliary Telescope.