Here’s an experiment I did with 1/2" acrylic from Inventables. This was done in Oct 2017, before the software allowed .500" focus.
This is the inverse of the experiment I mentioned in the post above. Here, I am moving the focus from .300" below the surface of the material to .077" below.
But, the difference in .100" of focus change is very definitive, nonetheless.
What is difficult to see in this picture, but is there if you look closely, is the change in kerf. Look at the top cuts verse the bottom cuts.
I still have these pieces somewhere. I’ll see if I can get some better pictures of the changes to the kerf.
An interesting side note is that you can clearly see the over-burn at the start and stop of each cut when the laser is at full power before the head begins to move.