Re: [ATM] wire spider, and regular spider, reason not to blacken

["Mel Bartels" <mbartels@bbastrodesigns.com>]

> Nils is completely right (as usual!):
> In Jean Marc Lecleire's  "A Manual for Amateur Telescope Makers, pg 
> 272-3",
> the translation of Couder's 1949 article is not correct:
> Couder explain that the spider LOOSE its heat by radiation and that it is
> the tiny layer of cool air around spider vanes that makes the spikes 
> bigger
> than what we would expect theoriticaly. He made the calculation and 
> Ireally
> think that he is right : painting should be avoided...
> A big part of couder article is vailable here
> http://astrosurf.com/altaz/effetthermique.htm
> I think a translator like http://trans.voila.fr/ or other could help for 
> the
> non french speakers.


What I found in exposed upper ends is that the same thickness traditional 
vane caused more diffraction at the eyepiece than the same thickness wire 
spider.  It's a pretty easy experience.  Just add a faked spider to your 
current setup, such that you add the faked 4 vanes at 45 degrees to the 
current vanes holding the spider.  You can switch between metal vanes and 
wire pretty easy with a little wooden frame over the end of the scope.

Mel Bartels 

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