A focal length is the distance between the upper surface of substrate and the bottom of the lens, and the height will depend on what you're looking to do with your machine.
Normally, shorter focal length lenses, like the 1.5” and the 2”, are used for engraving.
The lower the focal length, the finer the point.
Longer focal length lenses, like the 4'', is better for cutting.
By Natalia Pereira
