The spectral efficiency of NIRSPEC operated in low-resolution mode is demonstrated in this image pair of the lensed young galaxy
MS1512-cB58. This object is the brightest object in the "Lyman Break Galaxy" class of high-Z star-forming galaxies. It has a K-prime
magnitude of 17.8, and a redshift of Z=2.72.

The direct image (top) displays the difference of a 20s exposure and a median sky constructed from other exposures on the same field.
The object is marked with a circle, and the very long 42 arcsec slit is nearly removed in the subtraction. The bottom image is a reduced spectrum from 2.1 microns to 2.45 microns.  The emission line is a redshifted Halpha, which was the goal of the observation.