For about 2 years I have been wrestling with two major "truths" about lenses and laser beams that do not stand up to practical tests. The first was focal length/spot size/energy density. It is well documented that you need more watts to use a 4" lens because its energy density is low due to its larger spot size. That implies that shorter focal lengths with smaller spot sizes cut better with the same power. It was when I discovered this "truth" to be incorrect, that I began my quest to understand how lenses work. At the same time I noted that lens theory takes us as far as the focal point and then dumps us without explaining how it is possible to get a parallel cut BELOW the focal point ( and for very long distances) . After the focal point the beam is diverging and losing it damage capability so how is such material damage possible? It seems to be something that is taken for granted and never been researched.
My search for a long compound lens may have ended in failure but some of the data I collected during that search has accidently unlocked the answer to both the questions above.

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