  We present CCD observations of 102 Landolt standard stars obtained with the
R-C spectrograph on the CTIO 1.5 m telescope. Using stellar atmosphere models
we have extended the flux points to our six spectrophotometric secondary
standards, in both the blue and the red, allowing us to produce flux-calibrated
spectra that span a wavelength range from 3050 \AA to 1.1 \micron. Mean
differences between UBVRI spectrophotometry computed using Bessell's standard
passbands and Landolt's published photometry is found to be 1% or less.
Observers in both hemispheres will find these spectra useful for
flux-calibrating spectra and through the use of accurately constructed
instrumental passbands be able to compute accurate corrections to bring
instrumental magnitudes to any desired standard photometric system
(S-corrections). In addition, by combining empirical and modeled spectra of the
Sun, Sirius and Vega, we calculate and compare synthetic photometry to observed
photometry taken from the literature for these three stars.
