Published online by Cambridge University Press: 07 August 2017
CCD photometry is capable of high internal precision, however there are several important requirements necessary to attain high precision in standardized photometry. Firstly, the CCD passbands must match as closely as possible the standard passbands; secondly, new faint standards must be set up in several declination zones and thirdly, for convenience a sufficient number of standards covering a good range in color should be obtained on a single CCD frame so that several different frames should suffice for standardization. Landolt has taken the first steps in defining several such fields. The small systematic differences between different UBVRI systems have been examined and transformations can be applied to the photometry of Landolt and Bessell to place it on the Cape — SAAO system.