A new approach to high speed combustion photography consists in viewing the fuel injection and combustion process through specially designed endoscopes. Compared to conventional film techniques, the use of an endoscope as a photography system requires that very small windows be fitted into the cylinder head of the engine, thus causing minimal interference with the combustion process. The windows are made of fused silica to withstand the high gas temperature and pressure inside the combustion chamber of a diesel engine. The outcoming image from the endoscope is transmitted to the camera through several rigid optical relay systems, interconnected with rotating optical joints. A flash bulb located behind a second window is used to illuminate the nonluminous process of fuel spray formation during the ignition delay period.