A small scale rocket combustion chamber has been developed for investigations on atomization and breakup of a coaxial injected liquid oxygen jet under hot-fire conditions by the means of optical diagnostics. Two large flat windows allow optical access to the whole chamber. Different injector heads with one, three or seven injectors can be mounted. Liquid oxygen and gaseous hydrogen as propellants are precooled by liquid nitrogen. Different optical diagnostic methods like flash lamp photography and UV imaging with an intensified CCD camera have been used. The flash lamp photos are compared with the images of the ultraviolett radiation. Different flow conditions are compared relative to their spray patterns.