[Laser] Re: Fresnel lenses and dispersal angle

[Chris L]

Sorry, but it isn't!

The effect you're referring to is CHROMATIC aberration.

SPHERICAL  aberration is the effect produced by the curved lens surface 
approximating a spherical contour.

Later fresnels had their annulus cuts corrected to approximate a near-ideal 
aspheric surface.

With a spherical surface, such as a simple glass plano-convex lens, 
different radiii of the lens focus to slightly different focal lengths. THAT 
is SPHERICAL aberration.

OK?

Chris Long, Melbourne, Australia.