RE: ATM 3-Vane or 4-Vane Spiders

["William Thornley" <billt051@hotmail.com>]

G'day All,

Any subjective test needs to be done 'double blind' (so to speak). ie. More 
than two observers looking thru more than two scopes, with at least one 
placebo and none of the observers nor the recorder knowing which two vanes 
were flocked (so to speak). Even better, how about a range of flocked vanes 
None, 1, 2, 3 and 4?

Also, not having bothered to use an off-axis mask yet, what do to the spikes 
look like then? One would assume no spike at all!

Regards,

Bill Thornley
Sydney, Aus.

>FWIW - John Dobson has long recommended three-vane spiders made from wood
>(e.g., cedar shingles), rather than metal.  He likes three vanes largely
>because it gives you options for the largest possible unobstructed aperture
>when you use an off-axis mask.  As best I recall, one of the reasons he
>likes using wood is so as to minimize thermal effects.  It does seem like
>the extra thickness is a down side to using wood, though.
>-- Andrew Bell


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