( ( ( The image ) ( from ( ( the ( converging lens ) ) at ) ) ) ( ( serves ( as ( ( a ( virtual object ) ) ( for ( ( ( the ( concave lens ) ) , ) Lens ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN image)) (PP (IN from) (NP (NP (DT the) (JJ converging) (NN lens)) (ADVP (IN at))))) (VP (VBZ serves) (PP (IN as) (NP (NP (DT a) (JJ virtual) (NN object)) (PP (IN for) (NP (NP (DT the) (JJ concave) (NN lens)) (, ,) (NP (NNP Lens))))))) (. .)))
The image from the converging lens at serves as a virtual object for the concave lens, 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.