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° others |
33.3° to 88.9° 18° to 88.9° (unvignetted), or 0° to 18° (vignetted) |
| Keck II | 185.3° to 332.8° others |
36.8° to 89.5° 18° to 89.5° (unvignetted), or 0° to 18° (vignetted) |
The lower limit at other azimuths is shown as zero degrees, but in reality there is usually a software limit set at some positive elevation. In certain circumstances this limit may be decreased, to allow access to objects too far south to observe otherwise.