Four techniques are compared for the geometric calibration of flash light positions in a dome illumination device for digital photography: (1) the shadow cast by a vertical pin onto graph paper; (2) the illuminance distribution on white paper; (3) the reflections from a billiard ball; (4) a multi-image photogrammetric technique. The precision of the coordinates obtained by the four techniques is analysed, and the consequent effect on the accuracy with which surface normals can be determined. Calibrated test objects are used to guide the metrology of the 3D digitisation of cultural heritage objects. A case study is included for the performance of the dome with an object from ancient Egypt in the Petrie Museum.