Doppler imaging sensitivity analyses for three representative cases: an L0 dwarf observed with a 3.5 m telescope (left), a T0 with an 8 m telescope (center), and a T8 with a 30 m telescope (right), all located 4 pc away. From bottom to top, the plots show (in 0.02λ bins) the median S/N, total equivalent width of absorption lines, and the normalized product of these quantities. The root sum square of this last quantity over observable wavelengths determines the final Doppler imaging sensitivity of a given instrument. The gray regions indicate the wavelength regions used to calculate the magnitude limits shown in Fig. 4.