Another approach to the problem is the use of a polarizing filter. Light reflected off a smooth surface tends to be strongly polarized, so a filter rotated to a position crossing this direction can greatly reduce the flare from the affected areas. At one time I was working on techniques for auto location of tanks for the military, and built up a sensor which had a rotating polarizing filter. As the filter turned, the pattern of bright spots on the tank would shift around depending on the angle of the component and make them easily identifiable. I found this technique to also be useful in suppressing flares in ordinary photography as well. It seems that years ago such filters were standard items in the photographer's boodle bag, but with the advent of more sophisticated flashes they seem to have been forgotten.