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




Richrad wrote:
> When light travels through glass, it is traveling farther than when it
> travels through free space.   I think that is because the electromagnetic
> wave transfers some of its phlomb to the matter in the glass.   So if you
> put the glass between the paper and the microscope, you have lengthened the
> optical path for that physical distance by a factor of n (the index of
> refraction).   You have to move the microscope closer for it to be in focus.
> The optical path length is still the same.
>
> If the glass thickness is t and the focus shift is x, the index of
> refraction of the glass is
>
> n=1+x/t
>

OK, fine.  Now, will someone explain to me how Schott and Ohara to this to
better than 1 part in 10 million?

                Rick S.

> This is only true if, by accident, I did the math correctly, and the test
> only works if your microscope focal length is greater than n*t (otherwise,
> you bump into the glass before you get close enough to focus through the
> glass).
>
>
>
>

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