The tables give the above-atmosphere AB apparent magnitudes which yield 1 detected photon/sec for an observation made at the zenith in clear conditions. (Number of photons = number of counts CCD gain; gain typically 1.) The response curves of the Harris filters are given in La Palma technical note 96 (note that the throughput of the Harris B filter is believed to be about 30% lower than that of the older KPNO B filters).
Table: Imaging Instruments with broadband filters
Count rates for the JKT Peoples' Photometer were given in Gemini 35 (March 1992).