The standard Gemini peripheral wavefront sensors (PWFS1 and PWFS2), operating in the optical, must be used for guiding at this time. PWFS2 is usually the better choice as its limiting magnitude is fainter than that of PWFS1 and it also has smaller vignetting field. PWFS2 can be used down to 4.7' from the science target. If necessary, a smaller inner radius can be used with PWFS2 - check for vignetting in the OT Position Editor AND please add a note alerting the observer. The outer radius for PWFS2 guide stars can be displayed on the OT position editor and is discussed here. Please ensure that the guide star selected works for ALL offset positions. If guiding is not required in some positions (offsetting to sky), you must change the PWFS entry in the OT offset iterator to "freeze" for those positions. Always check the guide stars "auto-selected" by the Phase I tool, as the GS catalogs have many spurious entries. Reject extended objects and binaries. Guide star problems or mistakes are probably the most common time-waster during acquisition - this time is charged to the program!

There is also an on-instrument wavefront sensor with a HgCdTe detector to allow guiding on near-infrared bright stars; however commissioning of the OIWFS is not complete and it is not available for use.