  Photonic passbands have been derived for the uvby standard system by
convolving the original filter passbands of Str\"omgren and Perry with
atmospheric extinction and the QE of a cooled 1P21 photomultiplier tube. Using
these new passbands, synthetic photometry was calculated for all the stars in
the extensive NGSL and MILES spectrophotometric libraries and compared with the
homogenised b-y, m1 and c1 indices in the Hauck-Mermilliod 1998 catalog and the
derived u - v and v - b colors. Excellent agreement between observed and
synthetic photometry was achieved with regression slopes near unity. Slightly
better fits were obtained by considering stars with b-y < 0.5 and b-y > 0.5,
separately. It is recommended that these new passbands be used together with
the provided transformation equations to generate synthetic photometry from
model atmosphere fluxes and observed spectrophotometry. Synthetic photometry
was also carried out using the natural system of the 4-channel
spectrograph-photometers and those of Cousins and Eggen in order to explore the
systematic dfferences that could be expected between their instrumental systems
and the standard system.
