Quote:
Originally Posted by Merlin66
Bert,
I think this is wrong:
"difference is actally 1.5x0.050 = 0.075mm or 75 micron in optical path difference as the refractive index of the silica is 1.5."
The effect on the focus position "in a converging beam" would be 0.5 x 50 micron = 25 micron.
The focus "difference".......
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The speed of light is slower in a medium of higher refractive index than one ie a vacuum. The optical path length is then therefore longer and this factor is a measure of refractive index.
A 3mm filter that has a refractive index of 1.5 has an optical path that is 1.5 times longer than a vacuum or air to a first approximation. In other words the 3mm filter increases your optical path length by a factor of 1.5 that is by 1.5mm to 4.5mm.
Bert