Calibration of theUBVRI High-Speed Photometer of Laboratório Nacional de Astrofísica, Brazil

We describe the characteristics and performance of a high-speed multicolor photometer, FOTRAP, which has been used since 1988 at LNA, Laboratório Nacional de Astrofísica/CNPq, Brazil. The optomechanical concepts, electronics, and software are outlined. We discuss the quality and consistency of the transformations from the natural system to the UBVRI standard system. We give particular attention to the problem of transforming to the standard system observations of objects with blue spectra, like cataclysmic variables. We compare the results of our UBVRI measurements for a few spectrophotometric standards with the values published in the literature.