A set of glass filters is described, which when used with a GaAs photomultiplier, enables good transformations to be made to the existing UBV and VRI systems of photometry.
Good representations of the passbands for the Johnson-Cousins UBVRI system have been devised by comparing synthetic photometry with the actual observations and with standard system magnitudes. Small adjustements 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 filters combinations are discussed.
The current consensus regarding the absolute calibration of the spectra of alpha Lyrae and some subdwarfs has led us to revise the calibration of the Geneva photometric system's passbands. The alteration made to the earlier version by Rufener and meader (1971) are smaller than +-5%. The new response functions are presented in tabular form for an equiphotonic flux. An absolute spectrophotometric adjustement allows to obtain for each entry of the Geneva catalogue (now ~29400 stars) a corresponding spectrophotometric description in SI units. The definition and the means of computing the necessary quasi-isophotal frequencies or wavelengths are given. The coherence of the Geneva catalogue with several sets of absolute spectrophotometric data is examined. In particular, a correction is proposed for the entire Gunn and Stryker (1983) catalogue.