WHAT IS FOCAL LENGTH

The lens is 20mm wide and a 50.6mm focal length (the one included). This lens will stand up to at least 30PSI air assist. The mirrors are 25mm wide mirrors. Focal length is the distance from the lens to the material for the laser converge into the best focal point. If a lens is listed as 2". You measure 2" from the lens to the material, this will be the tightest point the laser can go before it starts to re-expand again losing focus.