Monroe L. King Jr. wrote: > Schlieren photography Well, yeah, that's an example of the sort of "specialized optical system" I was envisioning: I remain curious regarding the larger point... assuming the success of such an imaging campaign, what is thereby revealed that would be of interest from an engineering point of view? (I recognize that capturing pretty pictures of schlieren-visualized shock wave effects is not an uninteresting act in itself, of course, but presumably there's some object to the exercise beyond the mere image?) Keeping a schlieren optical system correctly aligned while in proximity to an operating shock tube tunnel might be ... interesting! (At least electronic imaging -probably- makes life easier than some of the stories I've heard about the old high-speed film cameras...) -dave w