Useful transformations between photometric systems

In the course of detailed studies of the long-term variations of particular Be stars, we have practically verified that the non-linear transformations , needed for a reliable transformation between a standard and an instrument al photometric system can also be successfully used to the transformations between two particular standard photometric systems. To demonstrate the imp ortance and power of non-linear transformations and to provide pieces of in formation useful for a broader astronomical community, we summarize the tra nsformation formulae already published (but hidden from the general communi ty in papers dealing with particular Be stars) and present several other us eful transformations derived by us. All transformations formulae presented here are transformations from various photometric systems to Johnson's UBV system. However, the general procedures applied here would allow constructi on of similar transformations between other photometric systems, too.