Friendly Bob
):-{])) <---- madden@netcom.com madden@svpal.org Remember amateur astronomers: "keep looking for the next Universe"
On Wed, 2 Aug 1995, Stephen Tonkin wrote:
> Some months ago, we were discussing, somewhat theoretically, the pro's
> and cons of attempting to improve the transmissivity of air-spaced
> doublets by putting oil between the elements.
>
> Some weeks ago I bought, at auction, a 60mm refractor c/w a
> sturdy-looking equatorial -- it looked like it had been run over by a
> tractor, but I paid what I think a 60mm refractor is worth --UKP5
> (about $8). Having straightened and cleaned things, I decided to try
> to improve the transmissivity of the unbloomed objective by replacing
> the air (& 3 spacers) with thickened cedar oil.
>
> The first attempt was a disaster -- owing entirely to my attempt to
> mate the crown (biconvex) with the flat surface of the flint
> (plano-concave). Having eventually realised why the oil was refusing
> to stay near the edge of the doublet, I cleaned the flint and tried
> again.
>
> The result is better than I had dared hope -- everything is _so_ much
> brighter. We'll have to see what transpires over a couple of seasons
> -- it's blissful unremitting heat-wave (in UK terms) at present --
> winter should show if it's going to do anything untoward.
>
> I realise 60mm is not exactly representative, but it has given me
> enought confidence to try it with the 112mm I am working on at the
> moment.
>
> Clear Skies,
> Steve <sft@aegis1.demon.co.uk>
>
>