The figure below shows the telescope limits for the Keck telescopes. In the regions where an elevation limit of ~35° is shown, the telescope hits the Nasmyth deck. Note that this is a problem in the South and West for Keck II, while for Keck I it is more of a problem in the North and East.
Specific limits for the two telescopes:
|Telescope||Azimuth range||Elevations accessible|
|Keck I||5.3° to 146.2°||33.3° to 88.9°|
|Elsewhere||18° to 88.9° (unvignetted), 0° to 18° (vignetted)|
|Keck II||185.3° to 332.8°||36.8° to 89.5°|
|Elsewhere||18° to 89.5° (unvignetted), 0° to 18° (vignetted)|
Stable guiding cannot be guaranteed for targets transiting at elevations higher than ˜85°.