By mounting a camera to rotate with a rotating component to be viewed it is possible to review the whole component illuminated by a light source. Generally the component will be specifically marked with target markings to highlight its profile to allow images produced by the camera to be compared for distortion and displacement. Such in situ monitoring arrangements also allow profiling of the surface, and by projection of a grid or matrix onto a component surface any distortion in that matrix is indicative of variations in the surface or through use of astigmatic techniques variations in the incident image pattern can be utilized in order to determine distance variations.