10 Dec
2000
10 Dec
'00
1:31 p.m.
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