For sensitivities of ALTAIR with NIRI and NIFS, use the NIRI and NIFS Integration Time Calculators, but see here for some restrictions regarding use of the NIRI ITC, including use at L'. The NIRI ITC also estimates FWHM and Strehl ratios of point sources.

The observing overhead due to Altair/NGS is small. If the coordinates are accurate the guide star generally falls within or very close to the WFS field stop, and the loop can be closed in a few minutes. The overhead including slew time is typically from 5 to 20 minutes, depending on distance from the previous target, the field crowdedness, and the accuracy of the observer's estimate of the guide star magnitude / spectral type. After that, everything behaves as in regular operation with NIRI or NIFS, and the overhead associated with those instruments applies (see the NIRI and NIFS overheads sections). More time is required for LGS, in order to close the additional control loops (and if the open loop focus model is used).