Black Lens

Black Lenses are items dropped by Demon Eyes with a 1% (1 in 100) chance. They are used to craft Sunglasses and Optic Staff and cannot be used to make the Suspicious Looking Eye. Blood Moons are useful for collecting these, as Demon Eyes spawn more frequently. A common strategy is to make a tunnel underneath one block of any material and then cover those blocks in enough lava to kill the Demon Eyes, but not enough to burn the drops. (A copper coin can be used to test for the proper depth.)

History
Lentille noire Черная линза