Thorlabs LC1439-A N-BK7 Plano-Concave Lens,

This is a Thorlabs LC1439-A – N-BK7 Plano-Concave Lens, �1/2″, f = -50.0 mm, ARC: 350-700 nm. As Thorlabs states: This Plano-Concave lens, which is fabricated from RoHS-compliant N-BK7 glass, is available A-Coated. N-BK7 is probably the most common optical glass used for high quality optical components. It is typically chosen whenever the additional benefits of UV fused silica (i.e., good transmission further into the UV and a lower coefficient of thermal expansion) are not necessary. However, for particularly harsh environments where the optic will be exposed to alkalis and acids, consider our N-SF11 plano-concave lenses.