"Al Alkoloid" wrote

You can do the same thing with tiny spots on sunglasses Allow the sun to
reflect off of the spots while wearing them, and you'll see diffraction
patterns. I first noticed this only a couple of weeks ago and had the
same
thoughts you did about the perfect telescope. My eyes are 20/15 or
better,
so very good patterns.

I believe you can have "20/15" eyesight and still have tons of astigmatism.
Therefore, just because you have 20/15 doesn't mean the pattern of fresnel
rings will be good.