From: "Mel Bartels" 
To: 
Reply-To: "Mel Bartels" 


>>>
And for those who think it is not caused by the edge explain why curved, or
as a previous post suggest, little circles on the vanes spread the
diffraction.
<<<

One of the best ways to think of diffraction effects that I've found is to
consider the inverted image.  That is, allow the light only through the
spider/diagonal/obstruction, then look at the star pattern/light pattern
that results.  The diffraction coming off of the pattern is correlated to
the diffraction in the otherwise normal image.  The one rule that can be
formed is that diffraction roughly follows area obscured.  I don't think
that the pattern of diffraction matters that much - if it is sharply
defined into bright narrow spikes or spread out unnoticed at first glance
through the image thanks to curved spiders - the contrast in the image, the
ability to resolve detail is largely limited to the same degree - roughly
following the area of the obscuration.

Mel Bartels

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