Technical Library: Choosing the Correct Size Focus Lens

What does a focus lens do?
A laser beam emanating from the laser tube is typically around ¼ inch (240 thousandths) in diameter – too large for any practical engraving or cutting. 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 small, precise spot that will enable graphic images to be resolved with resulting good engraving or cutting. 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."


	1)	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.

	2)	Which focus lens do you need for which projects? Laser systems are typically equipped with one particular focal lens - one that is generally good for most engraving and cutting applications. Epilog provides a 2.0 inch focal length lens on all systems we manufacture; however, we offer additional lenses that can help to improve specific applications. 1.5 inch, 2.0 inch, 2.5 inch or 4.0 inch lenses are all commonly used lenses with laser systems (no optional lens is available for the Epilog Mini 18x12 and 24x12 ). Which lenses are right for which applications? 2.0 Inch Lens Standard lens on most laser systems. Multipurpose for both engraving and cutting applications. Recommended for raster engraving from 300 DPI to 600 DPI resolutions. Produces spot size of 0.004 to 0.007 inches in diameter. 1.5 Inch Lens Optional lens for “High Resolution” engraving. Recommended for raster engraving above 600 DPI resolutions. Recommended for small font or fine detail engraving. Produces spot size of 0.003 to 0.0065 inches in diameter. Good cutting lens for thin (<=1/16 inch) material. 2.5 Inch Lens Optional lens for “Low Resolution” engraving. Recommended for raster engraving at or below 300 DPI resolutions. Recommended for large-area engraving (produces larger laser beam spot size thus removes wider path of material resulting in smoother engraved area). Produces spot size of 0.008 to 0.01 inches in diameter. Good cutting lens for thicker (1/16 inch or greater) material. 4.0 Inch Lens Produces focused beam over longer vertical distance. Specialty lens typically used for engraving within recessed area (bowl or plate). Used for cutting thick materials. While the above serves as a general guideline for industry standards, there may be exceptions. We find many of our customers using different lenses for different applications and generating exceptional results. If you have an application where you think a different lens will produce a different result, give it a try – you will probably be surprised with the results!

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