  Estimating accurate bolometric fluxes for stars requires reliable photometry
to absolutely flux calibrate the spectra. This is a significant problem for
studies of very bright stars, which are generally saturated in modern
photometric surveys. Instead we must rely on photometry with less precise
calibration. We utilize precisely flux-calibrated spectra to derive improved
filter bandpasses and zero points for the most common sources of photometry for
bright stars. In total we test 40 different filters in the General Catalog of
Photometric Data as well as those from Tycho-2 and Hipparcos. We show that
utilizing inaccurate filter profiles from the literature can create significant
color terms resulting in fluxes that deviate by >10% from actual values. To
remedy this we employ an empirical approach; we iteratively adjust the
literature filter profile and zero point, convolve it with catalog spectra, and
compare to the corresponding flux from the photometry. We adopt the passband
values that produces the best agreement between photometry and spectroscopy and
is independent of stellar color. We find that while most zero points change by
<5%, a few systems change by 10-15%. Our final profiles and zero points are
similar to recent estimates from the literature. Based on determinations of
systematic errors in our selected spectroscopic libraries, we estimate that
most of our improved zero points are accurate to 0.5-1% or better.
