[ATM] Wire spider - er not quite the effect I want

["Roger Chisholm-Batten" <rogecb@tiscali.co.uk>]

I have just finished a small 6inch f7 scope with a wire spider design almost 
identical to Mel's Tridob spider.

The views of the moon at 'first light' two days ago (Wednesday) were 
excellent at 215x.so ' Goodee goodee - Got a good one here Roger'  (The 
finished mirror had only cost me 20GBPounds).

But swivelling round to Vega for an impromptu star test revealed not 4, no 
not even 6 but 16 diffraction spikes...

Each wire crossing over kindly produced 2 definite spikes so it looked like 
a firework going off - pretty but not what I had wanted.  Taking the 
eyepiece out and looking at the moon through the focuser hole showed an 
electrician's nightmare of wires radiating out against the bright moon.

In the design's defence my wires are bare stainless steel and not yet 
blackened - ? use nose grease or sweaty hands ?

The 4 central points (and therefore the wires) are not straight above each 
other as the secondary mirror and attached stalk had to be moved around to 
collimate (which was easy once the knack of correct tension first had been 
independantly discovered).

Have I forgotten or overlooked anything else?  One Luddite friend suggested 
it is a mite overcomplicated (but then he likes curved spiders) but it looks 
real good and has held collimation nicely in spite of two car journeys so I 
am loathe to build a standard spider assembly.

Help gratefully received

Roger

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