An electro-optical technique is described which permits a rapid, non-destructive analysis of defect structures in compound semiconductor materials to be assessed in real time. The instrument operates in the transmission mode and is sensitive to local variations in the stress-birefringence vector produced from the strain field associated with lattice defect structures, including dislocation networks and slip. A macro-zoom optical system allows varying substrate sizes from 5 mm to 75 mm to be imaged at the full aperture of the monitoring system. Materials with transmission windows in the visible and near infrared wavelengths, out to 2 pm, can be assessed and whole wafer stress-birefringence variations mapped. Macrographs of some common semiconductor materials are illustrated including InP and CdTe.