My machine came with a 150mmx150mm area lens. Options are 50mm, 70mm, and 100mm. I want to mainly do deep engraving on brass and steel. I understand that the wider the field, the less power density you will have at the spot. I have found a chart showing the spot sizes and power densities, but it doesn't mean much to me in real world terms. Can someone explain if going to a 50mmx50mm area lens will really allow me to engrave deeper faster with less repetitions?