Photometric Calibration: lessons from CFHTLS

For about a decade, photometric calibration has been identified as a potential limitation of current and future imaging surveys. Uncertainties on the relative (band to band) flux scale are currently the dominant contribution to the systematic error budget affecting SNIa distances. Non-uniformities of the imager response may introduce spurious correlations in the LSS analyses, via the photometric redshifts. In this talk, I review the lessons learnt from the analysis of the CFHTLS survey, and I discuss related topics of the LSST-DESC roadmap.