A few vids of the c mount vs. a disposable camera back and vs. a ball point pen. This diode eats black plastic like nothing! Unfortunately my camera battery died during one of the vids so I had to stop, change batteries and continue. It literally does cut a pen in half in well under a minute though!!! I was also trying a new lens setup with a small 7mm coated lens within the focal range(closer to the diode than focus to infinity) plus one of my 15mm uncoated lenses after that. This seems to focus the output to an extremely small dot thus a higher power density.
RA_Pierce, as far as the focal length goes, with the way I have my setup I cannot get one of my lenses close enough to the diode to find the focal length exactly(restricted housing), but I know it's less than 1cm. If I use two lenses to focus, the output is a thin line at distance of 25ft, about 2.5cm long X 1/4cm thick. The thing is the slow axis requires special lenses depending on the diode's specs. What I have used for this is the viewfinder lens from a camera (the rectangle type) to squish the beam for long shots but it’s tricky. The lenses I have are not coated but they do work very well for burning, they have a high damage threshold and their cost effective!