Note: This is an older page that describes the changes from the original 36x82mm lenses to the 40x84mm ones.
The viewer now has 40 mm dia by 84 mm FL achromats from American Science & Surplus ($15.50 each). They are anti-reflection coated and work well, though they have more pincushion distortion than the old lenses (36 x 82's from Edmund Scientific $32 each).
The white holders were made by Mark Robson on his lathe from PVC plumbing adapters.
He also made me holders for my old 36x82mm lenses. They are the forground ones (not attached to the viewer).
Notice that both holders have the same outside diameter, so Mark's design could be used for interchanging lenses in a viewer by removing and replacing holders.
Also notice that the viewer has the holders mounted from behind the panel, but that the foreground front panel has them mounted from the front. Either way works, depending on how much you want the lensholders to stick out.
This is my viewer (old lensholders) with the top removed in cross-eyed 3D.