( ( ( ( ( He ( knew ( ( a ( flat lens ) ) ( ( would n't ) ( have ( any effect ) ) ) ) ) ) , ) so ) ( he ( decided ( that ( ( ( a combination ) ( of ( a ( convex ( and ( concave lens ) ) ) ) ) ) ( must ( be ( ( the answer ) ( -LRB- ( ( although ( Kepler ( subsequently ( showed ( how ( ( a telescope ) ( could ( be ( made ( with ( two ( convex lenses ) ) ) ) ) ) ) ) ) ) ) ) -RRB- ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (PRP He)) (VP (VBD knew) (SBAR (S (NP (DT a) (JJ flat) (NN lens)) (VP (MD would) (RB n't) (VP (VB have) (NP (DT any) (NN effect)))))))) (, ,) (IN so) (S (NP (PRP he)) (VP (VBD decided) (SBAR (IN that) (S (NP (NP (DT a) (NN combination)) (PP (IN of) (NP (DT a) (NN convex) (CC and) (NN concave) (NN lens)))) (VP (MD must) (VP (VB be) (NP (NP (DT the) (NN answer)) (PRN (-LRB- -LRB-) (SBAR (IN although) (S (NP (NNP Kepler)) (ADVP (RB subsequently)) (VP (VBD showed) (SBAR (WHADVP (WRB how)) (S (NP (DT a) (NN telescope)) (VP (MD could) (VP (VB be) (VP (VBN made) (PP (IN with) (NP (CD two) (NN convex) (NNS lenses))))))))))) (-RRB- -RRB-))))))))) (. .)))
He knew a flat lens wouldn't have any effect, so he decided that a combination of a convex and concave lens must be the answer (although Kepler subsequently showed how a telescope could be made with two convex lenses).
(ROOT (S (NP (DT The) (ADJP (RBS most) (JJ common)) (JJ two-lens) (NN telescope)) (, ,) (PP (IN like) (NP (DT the) (JJ simple) (NN microscope))) (, ,) (VP (VBZ uses) (NP (NN convex) (NNS lenses))) (. .)))