How a laser focusing lens works.
This Technical Library article discusses the purpose of the focus lens as well as guidelines for using lenses of different sizes for various projects.
What does a focus lens do?
A laser beam emanating from the laser tube is typically around one-quarter of an inch (240 thousandths) in diameter. This too large for practical engraving or cutting applications.
In order to achieve high-quality engraving and precise cutting with your laser system, the laser beam is directed through a series of mirrors and through the focus lens.
The focus lens narrows or “focuses” the laser beam to a very small, precise spot that will enable graphic images to be engraved or cut with extremely accurate results. As the laser beam leaves the focus lens, it takes on an “hourglass” shape, with the ideal focal distance within the center of the “hourglass.”
CO2 Lenses
The ideal focal distance is different with each lens. In general, the ideal focal distance is the same as the lens specification; i.e. a 1.5 inch focal length lens will have ideal focal distance at 1.5 inches from the lens.