CD's as parabolic mirrors?

From: Andreas Meyer <ahm_at_spies.com>
Date: Sun Dec 10 21:31:58 2000

John Tinker writes:
> I just noticed that sunlight reflecting off the top side of a CD focuses
> somewhat, maybe with a focal length of about 20 feet. Off of the data side, it
> spreads. I've tried it with several different types, and so far they all show
> the same effect. Would anyone care to explain why?

I believe that the tracks on a CD are concentric rings,
which would make a CD something of a reflective Fresnel lens.

Andy
Received on Sun Dec 10 2000 - 21:31:58 GMT