  We report the transmission over a wide frequency range (far infrared -
visible) of pristine and hole-doped, free-standing carbon nanotube films at
temperatures between 50 K and 300 K. Optical constants are estimated by
Kramers-Kronig analysis of transmittance. We see evidence in the far infrared
for a gap below 10 meV. Hole doping causes a shift of spectral weight from the
first interband transition into the far infrared. Temperature dependence in
both the doped and undoped samples is restricted to the far-infrared region.
