ATM 3-Vane or 4-Vane Spiders

[Scot Radowski <scot@vquill.com>]

When taking diffraction patterns and general light interruption into 
account, is there a good, better, best when it comes to spiders?

I've seen designs where there is but a single arm for the spider, or 
2 even.  Standards seem to be 3 and 4.  Is there a trade-off? 
Triangles are supposed to be more stable than squares, but does this 
really count when talking about vanes on a spider?

Then there is the question of material and thickness.  I would 
imagine that its important to obstruct the view as little as 
possible.  Is there a good formula to consider?  Percentage of light 
loss or whatnot?

Any help is appreciated.
Scot
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