Does anyone know the precise physical explanation for the "starburst" effect you get when shooting into the sun (or other very bright light source) at small apertures? The effect is definitely related to the diaphragm blades as the points of the star are always equal to or a multiple of the number of blades. I believe it is due to diffraction but cannot envisage how the spread of light becomes so wide. Some writers have attributed the effect to reflection off the edges of the diaphragm blades but I cannot envisage how that would work either. Any ideas?