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Have you realized, that often the photo of a star shows 6 rays spreaded symmetrically around it, independently of the camera chosen? Do you have idea of what kind of optical phenomena is behind it?

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1 Answer 1

Do you have an example of this?

The most common source of 'rays' is diffraction from the spider - the arms that hold the secondary mirror - in the telescope. There are almost always 4 of these.

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If you are using a regular camera there is a weaker effect from the iris - the metal ring that changes size to let more light in. This depends on the number of blades, having more blades keeps the circle more circular as they close and so reduces the effect, expensive lenses will have many more blades - while simple ones may only have 6.

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I've seen cheap cameras with as few as five blades. – dmckee Sep 4 '12 at 17:24
@dmckee - a lot of compact and video cameras only have 2 blades with a v shaped cut-out. Gives horrible bokeh – Martin Beckett Sep 4 '12 at 17:27
Thought (it seems) the phenomena was (is) most complex because even in common reflections it is possible to observe that set of rays surrounding the zone of light. – paritto6 Dec 1 '12 at 13:28

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