In a first aspect, there is described an optical system for monitoring a ball play volume of a roulette wheel. The optical system comprises an electronic image detector and a reflector arranged to reflect light from a ball play volume of a roulette wheel onto the electronic image detector. The electronic image detector is configured to form an image of the ball play volume from the reflected light. In a second aspect, there is described a method of monitoring a ball play volume of a roulette wheel. The method comprises the steps of using a reflector to reflect light from the ball play volume, and forming an image of the ball play volume from the reflected light. In a third aspect, there is described a method of manufacturing an optical system for monitoring a ball play volume of a roulette wheel. The method comprises the steps of providing an electronic image detector, and providing a reflector arranged to reflect light from a ball play volume of a roulette wheel onto the electronic image detector.