We cut a .500" square out of a piece of 1/8" Ply with an air assist and it measured .490" on one side and .485" on the other side. That's an average of .0125" kerf width. The beam's focal point is too large for any detailed photo engraving at that size regardless what power setting or feedrate we run at. The engraving just comes out blurred no matter. We are using the J-Tech single element lens which with the NDB7875 LD, we get just as small .005" focal point/burn line width as using a 3 element glass lens.
Look at the beam shape of a NDB7875 compared to a NDB7A75. http://imagizer.imageshack.us/v2/1024x7 ... 8/2b0j.jpg
Then, look at the beam shape of the NDB7A75 compared to the NUBM44. It's even longer.http://imagizer.imageshack.us/v2/800x60 ... gO5lB7.jpg
If you Invest in a more expensive lens/optics to get a smaller focal point, let us know how your tests go with image engraving using the 6W.