[anc84]

That does not work at all and just confused me. The angles must change on the interrupted parts to follow the general curve of the lens' surface.

https://commons.wikimedia.org/wiki/File:Fresnel_lens.svg is a very good illustration.

[crottypeter]

As a counterpoint the GPs diagram was useful for me (perhaps because I have a background involving some study of optics).

Granted the parents picture is way better than the rough ASCIIart