( ( ( Concave lens ) ( A ( concave lens ) ) ) ( ( ( ( ( is ( thinner ( in ( ( the middle ) than ) ) ) ) ( at ( its edges ) ) ) and ) ( ( causes ( light rays ) ) ( to ( diverge ( -LRB- ( ( spread apart ) -RRB- ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (JJ Concave) (NN lens)) (NP (DT A) (JJ concave) (NN lens))) (VP (VP (VBZ is) (ADJP (ADJP (JJR thinner)) (PP (IN in) (ADVP (NP (DT the) (NN middle)) (IN than)))) (PP (IN at) (NP (PRP$ its) (NNS edges)))) (CC and) (VP (VBZ causes) (NP (JJ light) (NNS rays)) (S (VP (TO to) (VP (VB diverge) (PRN (-LRB- -LRB-) (VP (VBN spread) (ADVP (RB apart))) (-RRB- -RRB-))))))) (. .)))
Concave lens A concave lens is thinner in the middle than at its edges and causes light rays to diverge (spread apart).
(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.