  We present a modified $8f$ geometry for time domain terahertz (THz)
spectroscopy (TDTS) experiments. We show, through simulations and data, that a
simple rearranging of the off-axis parabolic mirrors, which are typically used
to focus and direct THz radiation in TDTS experiments, results in a nearly 40%
reduction in the THz focal spot diameter. This effect stems from significant
reduction of the principle optical aberrations which are enhanced in the
conventional $8f$ geometry but partially compensated in the modified $8f$
experimental setup. We compare data from our home-built TDTS spectrometer in
the modified $8f$ geometry to that of previous iterations that were designed in
the conventional $8f$ geometry to demonstrate the effect.
