From: "Richard F.L.R. Snashall" 
To:  atm{at}shore.net
Reply-To: "Richard F.L.R. Snashall" 




mdholm{at}telerama.com wrote:
> Dwight Elvey wrote,
>
>
>
> It is the temperature gradients in air that cause bad "tube
currents".  Small
> temperature differences make fairly large refractive index changes in air.
> These gradients can be simply blown out of the optical path.  The air,
> turbulent or not, that replaces them will be much more thermally uniform,
> unless the air is coming from a source with strong temperature differences.
>

I never could get over the gross differences in the Schott catalog between
the absolute thermal coefficient of refractive index and the relative
thermal coefficient of refractive index... after all, it's just air vs. a
vacuum... right?  Now you you have said this it make more sense.

                Rick S.

>
> Mark Holm
> mdholm{at}telerama.com
>
>

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