Re: ATM Optical Path Lengths For Star Diagonals

[astillma@nit.AirTouch.COM (Anthony Stillman)]

Bob,

Regarding the distance light travels through glass:

I think we are saying the same thing in different ways.

Specifically I am saying that if you have a ten inch length of glass rod,
the optical path length along the axis of the rod is 15 inches (ish) or
n=1.5 times 10" (physical). As the speed of light is 1.5 (ish) times slower
in glass relative to air.

Hence, if you take a simple lens with a 15 inch focal length in air,
and push it up against the end of the rod the focal plane will be 
coincident with the end of the rod.  That is you divide the optical path
length by the index to obtain the physical path length.

Anthony