ETC and pysynphot
The ETC relies heavily on the synthetic photometry packages pysynphot. This package simulates photometric data and spectra as they are observed by the HST instruments. For this, it relies on the information about the HST instrument throughputs that are included in the Calibraton Data Base System (CDBS) at STScI. Pysynphot is intended as a modern-language successor to the IRAF/STSDAS SYNPHOT package, and is developed and maintained by the Science Software Branch (SSB) at STScI.
Except for the details of the SYNPHOT call descriptions and parameters, the ETC documentation describing SYNPHOT applies equally well to pysynphot.
The diagram below depicts the relationship between the ETC and pysynphot. Each instance of the ETC contains its own pysynphot implementation, but refers to an external CDBS collection for the appropriate reference files. This allows the CDBS reference files to be updated without changing the ETC codebase. The ETC handles the conversion between the ETC request and the pysynphot request internally.
