An apparatus is provided for analysing the composition of crop in a crop-conveying machine, such as a harvesting machine. The crop in the machine is conveyed along a crop movement path, whereof a portion is illuminated by a light source (23). A camera (24) captures sequential images of crop in the crop movement path. The apparatus further comprises a control device and a processing device operatively connected to the camera and light source. The intensity and/or the colour of light output by the light source (23) is adjustable in dependence on one or more control commands generated by the control device and determined by optical characteristics generated by the processing device from one or more prior images captured by the camera (24). A portion of the image may include a reference member (26) adjacent the crop movement path.
