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Name: Craig
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Question:
I am having a debate with a friend. Were are discussing the photo effect of star bursts around a point light source in photos. I have done empirical tests that show the bladed aperture diaphragm is the root cause of star bursts in photos. My test started with by taking a photo with the aperture closed and seeing the resulting image shows a star burst. Taking the same photo after opening the aperture to wide open shows a photo with no star burst, thus my claim that the root cause is the bladed aperture diaphragm. My friend says I am wrong. He says the ultimate cause of star bursts in photos is light interference. I do not deny that light interference is a part of the process of producing a star burst in a photo. I disagree that it is the ultimate cause for the reason that many more causes and effects exist in the chain to the finished photo. Clearly the star bursts could never happen without the mechanical interference caused by the bladed aperture diaphragm, and the diffraction that occurs where the blades intersect.



Replies:
It is difficult to resolve your argument without knowing the details of your experimental setup and the quality of your optical components. There are a number of aberrations that could produce the effects you observe. See:

http://hyperphysics.phy-astr.gsu.edu/Hbase/geoopt/aberrcon.html#c2

Any of these could produce the distortions you observe.

Vince Calder



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