( ( As ( ( in ( the grindings ) ) ( ( this polisher ) ( is ( fastened ( to ( the pedestal ) ) ) ) ) ) ) ( , ( ( the ( concave lens ) ) ( ( ( ( rubbed over ) it ) ( until ( there ( ( is ( enough OshineO ) ) ( to ( perform ( a ( knife-edge ( and ( Ronchi test ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (PP (IN in) (NP (DT the) (NNS grindings))) (NP (DT this) (NN polisher)) (VP (VBZ is) (VP (VBN fastened) (PP (TO to) (NP (DT the) (NN pedestal))))))) (, ,) (NP (DT the) (JJ concave) (NN lens)) (VP (VBD rubbed) (PRT (RP over)) (NP (PRP it)) (SBAR (IN until) (S (NP (EX there)) (VP (VBZ is) (ADJP (RB enough) (JJ OshineO)) (S (VP (TO to) (VP (VB perform) (NP (DT a) (JJ knife-edge) (CC and) (NNP Ronchi) (NN test))))))))) (. .)))
As in the grindings this polisher is fastened to the pedestal, the concave lens rubbed over it until there is enough OshineO to perform a knife-edge and Ronchi test.
(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.