( ( ( Concave Lens ) ( A ( concave lens ) ) ) ( ( is ( ( the opposite ) ( of ( a ( convex lens ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Concave) (NNP Lens)) (NP (DT A) (JJ concave) (NN lens))) (VP (VBZ is) (NP (NP (DT the) (NN opposite)) (PP (IN of) (NP (DT a) (NN convex) (NN lens))))) (. .)))
Concave Lens A concave lens is the opposite of a convex lens.
(ROOT (S (NP (DT A) (JJ concave) (NN lens)) (VP (VBZ is) (NP (NP (JJR thicker)) (PP (IN at) (NP (DT the) (NNS edges)))) (SBAR (IN than) (S (NP (PRP it)) (VP (VBZ is) (PP (IN in) (NP (DT the) (NN middle))))))) (. .)))
A concave lens is thicker at the edges than it is in the middle.