Location of Keck optical axis & f/15 focus

The telescope's elevation axis is located 1500 mm above the top of the Nasmyth platform's grating (the grating is 76.2 mm thick).The distance from the telescope's optic axis (i.e. center of the tertiary mirror) to the f/15 focus is 6493 mm. The distance from the optic axis to the center of the elevation bearing journal is 6100 mm. The distance from the optic axis to the inside of the elevation ring is 5125 mm. The distance from the optic axis to the outside of the elevation ring is 6227.5 mm. Therefore the f/15 focus is 265.5 mm beyond the outside of the elevation ring. The dimensions of the Nasmyth platform are 5200 mm along the elevation axis and 9300 mm orthogonal to this axis.