From: "Richrad" 
To: 
Reply-To: "Richrad" 


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

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).

. . . Richard

----- Original Message -----
From: "John Sherman" 
To: "Richrad" 
Sent: Wednesday, January 15, 2003 7:21 PM Subject: Re: ATM Corning optical glass


>
>
>
>
> Richrad,
>
> >Put a piece of paper under the glass, and focus on it.
> >Then put the glass on the paper, and focus again.
>
> Come again?
>
> John
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>

--- BBBS/NT v4.00 MP