OPTICAL LENS

WIPO Patent Application WO/2009/132538

A1

An optical lens for laser processing comprises a lens group and a diaphragm (1). The diaphragm is located in front of the lens group. The lens group comprises three lenses, being “negative-positive-positive”, i.e. a first lens (L1), a second lens (L2), and a third lens (L3) in order. The first lens is a meniscus negative lens, the second lens is a meniscus positive lens, the third lens is a meniscus positive lens, and all the concave surfaces of the first, the second, and the third lenses are toward the diaphragm. The focal distance of the whole optical system is f, the focal distances of the first, the second, and the third lenses are f1, f2 and f3, respectively, and the ratio of the focal distance of respective lens to the focal distance of the whole optical system satisfies the following relationships: -0.7