Re: [ATM] Re: ATM Digest, Vol 11, Issue 10

[Jim Burrows <burrjaw@earthlink.net>]

At 2004-11-13 07:59 -0500, Art Bianconi wrote:

>I am unclear how spiders cause diffraction stars so I am
>uncertain if attempting to use super thin material like this help
>eliminate them.
>
>Can anyone shed some light (sic!) on this? Thanks

You can't eliminate the diffraction spikes, but you can reduce the amount 
of light in 'em.  Here's how thin spiders help:

Imagine the light waves impinging on the spider.  The way the waves get to 
be zero amplitude (absorbed) by the spider is to generate Huygens wavelets 
of opposite phase at the spider.  These wavelets spread out, interfering 
with the incoming light, and produce the spikes on the image plane.  Less 
light in the wavelets means dimmer spikes, and thinner spiders mean less 
light in the wavelets.  Also, some thought on this senario will explain how 
curved spiders spread out the spikes.

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84) 

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