From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


Any obstruction to the view makes a diffraction spike perpendicular to the
direction of the obstruction.  The spike is on both sides of the star.
Thus, if you do a set of supports at 60 deg. rather than the normal 90
deg., there will be the spikes 60 deg. off from each other just like the
supports are but their direction will be rotated by 90 deg. from where you
would initially think.
The above is why the 3 legged spiders have 6 spikes on the bright stars as
the 3 supports are all at different angles and that means each support
makes its spike visible on both sides of the star. The curved spiders do
their job by making the diffraction go all around the star and that
diffraction is extremely weak as there is no real distance that can build
up the diffraction well.  Mostly the curved spiders depend upon the
strength of the material by itself to hold the secondary in place rather
than by tension.
Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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