Adding a focal offset before engraving can help improve results depending on the application.
For the majority of jobs you will focus the laser to the surface of your material, this means where the laser hits the material the beam will be focussed down to its smallest point allowing you to achieve highly detailed engravings and fine clean cut lines.
Sometimes however we may want to use a slightly larger beam during engraving; a good example of this is when engraving acrylic – clear acrylic in particular – and you may notice lines in the engraved areas which are the path the beam has taken.
By putting the laser slightly out of focus you will increase the size of the beam creating more overlap with each engraving pass resulting in a smoother finished result. Just be careful you do not put it too far out of focus otherwise you may get blurry inconsistent results.