Well, I continue posting old pictures as long as I do not have new ones. This one I like to share because it´s something certainly very special within this community: A Schlieren image of a shock configuration on a cone shaped body at Mach 9 in a hypersonic wind tunnel. Due to the blunt body and high Mach number the shock layer is very thin and the shock itself very close to the surface. We used a double amplified high speed camera that was so complex, not even the manufacturer could handle it well. In this kind of blow down tunnel there are only a couple of milliseconds of stationary flow within which all measurement has to be done. So first task was to trigger the camera at the right moment. We had an 18-volts-signal coming from the tunnel control unit and a 5-volts-trigger-input at the camera control unit ... (Some people simply use video cameras and look for the right frames afterwards) Thanks for any comments Hochschulhyperschallkanal HHK-4, TU Dresden, ILR-EAD Schlieren aperture with concave mirrors LaVision Streak Star 3, Nikon-AF object lens DaVis 5.2.2, Corel Photopaint 7 http://tu-dresden.de/ilr