RE: ATM 3-Vane or 4-Vane Spiders

["Jim Fitch" <jf@arn.net>]

>
> > The mass of the vanes radiates to the sky and is a bit
> > cooler than ambient air and consequently the vanes are
> optically much
> > "thicker" than their physical thickness.
>
> Anyone seen this in reality?
> Nils Olof
>
 I insulated two vanes of a four vane spider with Black Flocked Paper to
see if I could demonstrate any thermal effects on the diffraction
spikes. Even though the insulated vanes had a thicker profile the
corresponding spikes appeared dimmer and were thinner and longer. Unless
I looked at the wrong spikes (I don't think so) I think the temperature
difference of the vanes does effect the size of the diffraction spikes.

Any other findings?

Jim Fitch
Amarillo, TX