... Digital systems . ... Standard Stars - CCD Photometry, Transformations and Comparisons . ... Figure 2: A typical sample of transformation relations to the Landolt standard system (1996 Nov. ... 0.006 . ... Landolt's natural GaAs u - b system is not very close to the standard U - B system and so it is likely that, because the transformations were made using a U - B colour term alone, systematic U - B differences exist for some kinds of stars namely, A-F stars, reddened B-A stars and giant A-F stars. ...