The development of high-speed cameras has made significant advances in the last two decades, and the resulting large variety of commercially available camera systems has substantially simplified the high-speed imaging of transient events. This has opened up many new avenues of investigation, in particular when these cameras are combined with suitable visualization techniques for the investigation of shock wave interactions and high-speed compressible flows. Compared to earlier film-based cameras, most of the new developments have very few if any mechanically moving parts (other than a capping shutter) which makes them compact and generally easy to use. The new generations of cameras avoid most of the complexity of film-based systems and have become a more "mainstream" piece of instrumentation than their often highly specialized and customized film-based predecessors. In spite of these improvements, current systems still suffer from the primary shortcoming that had already characterized most early high-speed cameras, namely reduced image quality when compared to single-shot imaging, albeit for different reasons. In most film-based high-speed cameras, the observed reduction in image quality is a consequence of the optomechanical image separation process and largely caused by motion blur and/or light diffraction. These effects are generally absent when the image is recorded on a stationary CCD chip, but the requirement to expose it at high repetition rates limits the spatial resolution of the chip. At frame rates above approximately 100,000 frames per second (fps), the image resolution is considerably below one megapixel and thus only a small fraction of the resolution offered by standard single-image digital cameras. While the currently available high-speed camera systems have contributed much to recent successes in the investigation of transient processes, there is a continuing need for further improvement of camera technology, as will be outlined below.
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