A very long focal length, ideal for cutting thicker suitable materials or engraving on slightly curved or uneven surfaces.
These are double sided anti-reflection coated focusing lenses for 10.6uM laser engravers and cutters. The material is Zinc Selenide ZnSe and the lens is positive meniscus, they have a focal length of 101.6mm or 4 inches which is generally the standard focal length on most Chinese larger laser cutters from 60W to 120W.
The extended focal area of the beam trades off depth cutting for power concentration. i.e. it can not increase power over the focus area.
They differ from more expensive lenses in that they are unbranded and made in China.
Packed in a hard case and include a lens cleaning cloth.