Correspondence regarding optical design, including Redman's correspondence with W.A. Goodsell, S.C.B. Gascoigne and D.S. Brown, including his notes of 5 January on the position of Cassegrain focus; correspondence between J.D. Pope and Brown on changing the radii of three convex mirrors, including reference to the optical diagram, drawing No. 006, issue 6; a copy of a letter to Gascoigne from W.H. Steel, National Standards Laboratory, 21 October 1970, with Gascoigne's letter of 23 December concerning checks for astigmatism in the primary mirror; and correspondence on changes and extra costs.