Ok, I have seen reference to different focal length lenses, for example someone commented they have a "1-1/2in" lens. I am sure that refers to the focal length.
So, what is the advantage of having a different focal length from another? On the surface (no pun intended) it would seem that a longer focus length would be advantageous as it would keep the cone well out of the smoke zone and less likely to strike holddowns, weights or other protrusions from the cut item. Would having a longer focus length also be an advantage of having a longer more tapered cutting beam? Shorter wouldn't it have a fatter cone and thus affect straightness of edges in thicker material?