UBVRI passbands

Good representations of the passbands for the Johnson-Cousins UBVRI system have been devised by comparing synthetic photometry with actual observations and with standard system magnitudes. Small adjustments have been made to previously published passbands. Users are urged to match these passbands so that better photometry and calibration are ensured. Mismatched B bands are shown to be a major source of recent (U - B) transformation problems. The nature of systematic differences between the natural colors of the most widely used sets of standard star photometry is investigated and suggested CCD filter combinations are discussed.