In this picture, we see that the sun comes out as a hexagon. I am sure it is not arbitrary. What does the hexagon tell us about the instrument that captured the image?
It tells us that the aperture contains either three or six blades and that where these blades meet there is a corner which results in Fraunhofer diffraction. This is discussed mathematically in Physics SE.
It also tells us that the lens was stopped down, as if it were wide open there would be no corners to cause diffraction, regardless of the number of aperture blades.
Incidentally the number of (distinct) points to the star is equal to double the total number of unique orientations* in the sides of the aperture shape i.e. three blades would be six points, six blades would also be six points as a hexagon has only three unique orientations in its sides.
* a hexagonal aperture has six sides but only three unique orientations as there are three pairs of parallel sides.
|show 5 more comments|
The shape of the lens flare is related to the shape of the aperture while the characteristics of the flare as a whole have more to do with the elements used in the lens.
The lens in that image would be using a six blade aperture.
The lens is using an aperture with six blades (or, theoretically, three - see comments); most probably six, since there are very few, if any, lenses with three aperture blades.
The lens is stopped down, and the aperture blades aren't rounded (or not enough for this aperture setting).
OR someone is using a star filter (though probably not, they are not very widely used).