  The charge radii of Sigma^- and pi^- have been determined by direct elastic
scttering on shell electrons. The measurement was performed in the framework of
the SELEX (E781) charm hadroproduction experiment at Fermilab which employs a
600 GeV/c high-intensity Sigma^-/pi^- beam and a 3-stage magnetic spectrometer
covering 0.1 <= x_F <= 1.0. Scattering angles and momenta of both hadron and
electron were measured with high precision using silicon microstrip detectors,
thus allowing for a segmented solid target. Two TRDs provided full particle
identification. A preliminary result for the Sigma^- charge radius for a
four-momentum transfer squared of 0.03 GeV^2/c^2 <= Q^2 <= 0.16 GeV^2/c^2 will
be reported. In a parallel analysis the pi^- charge radius has been determined
for 0.03 GeV^2/c^2 <= Q^2 <= 0.2 GeV^2/c^2, and is found to be consistent with
previous experiments.
