DFT independent variable as fraction of sampling rate
The DFT calculates spectral components up to $f_\mathrm{s}/2$, no matter what the input signal is. If the input signal to the DFT contains (absolutely) no spectral components between $0.33 f_\mathrm{s}$ and $0.5 f_\mathrm{s}$ the corresponding DFT outputs are zero (assuming that there is no spectral leakage).