experiment with over or under focusing, meaning, whatever your normal focus distance is from the lens to the wood, add or subtract distance. I've found that wood is pretty forgiving. If I need dark more than deep- cutting boards for instance- I'll set the focus at minus .1" from normal, sometimes a full 1/8", and the engraving looks great. Good on leather too.

FWIW I like to ADD distance rather than subtract distance when engraving wood, simply because if you're subtracting, the deeper you get into the wood, the more in focus the beam becomes. In some cases that might work better, so experiment!