Rest of parts of collection (unspecified) consisting of 24 glass and plastic ophthalmic lenses showing the various stages in the manufacture of trifocal lenses ophthalmic lens blanks showing the various stages in the manufacture of trifocal lenses
six stages in making fused tri-focal lenses (1) the segments are placed together, (2) segments fused together, and on to lens blank, (3) front surface of the compound lens is ground, (4) front surface of the compound lens polished, (5) lens cut to shape and bevelled, (6) plastic lenses mounted in spectacle frame. Supplied by Bateman, Frederick and Co (see note). six stages in making fused tri-focal lenses (1) the segments are placed together