Shock lube tests were carried out to investigate the influence of the divergent half angle of four planar convergent-divergent nozzles on the incident-shock formation, and on the pressure signature downstream from the nozzle. A diaphragm was mounted in the throat of these nozzles and located at the upstream edge of the test section window of high-quality optical glass through which shadowgraphs and schlieren pictures could be taken. The objectives of this investigation were to obtain optical records of the flow start-up processes in these divergent nozzles immediately after rupturing the diaphragm, and to facilitate comparisons with hydrocode computations. The optical measurements were complemented by measurements of the static pressure at three locations downstream from the nozzles. The test set-up and the results of these experiments are presented and compared with the results of one dimensional hydrocode computations.