Seems like you merely focused the output of the laser diode with a bigger lens, didn't have it focused to what is considered infinity. At infinity, if you held a PCX or plano-convex lens out in front of the raw output of a laser diode the spot would be a larger diameter and be more difficult to burn anything, if at all. If your stock lens wasn't flat on one side, you were just focusing it with a bigger lens, that's all.
You can make a beam expander with a convex lens(es), there are some diagrams showing how to make them at this link as a downloadable PDF doc:
Yes it's just focused At a certain distance .
I need to adjust the focus each time I move far away by moving the lens toward the raw Beam.
I tried at 10m and it still burns but the dot is a little bit bigger (2x2mm).
Then I tried outside from my roof , I focused it the more far away I could see with a binoculars , it easily goes far beyond a miles but I doubt it will burn anything .
You are right , at the output of the lens the beam is about 2cm wide which is the lens size.
Just saw the beam expander schematic , it's not really like that, the beam is only bigger near the lens but goes narrower with distance until â Small spot then diverges again . I will try with a 50mm lens it should be more precise and infinity focus should be better ?