FLAMINGOS-2 has a number of permanent long slits available for long-slit spectroscopy (see the MOS wheel schematic for the locations of these long slits within the wheel). The widths of the long slits are 1, 2, 3, 4, 6, and 8 pixels. They are all ~4.4' (263", 1460 pixels) in length. These long slits can be used with either the moderate or higher resolution grisms. The f/16 and f/32 pixel scales in spectroscopy mode are the same as those in imaging mode.

The available slits are shown in the following table. The slit widths are given in pixels and arcsec projected on the sky. The spectral resolution is lower in a wider slit (see the grism table), even for point sources since under most atmospheric conditions the seeing wings of pointlike objects fill the wider slits.