Here's a very interesting piece, an Asahi Pentax 100m x 1200mm doublet oil-spaced lens cell. I am unsure of whether this is an achromatic or apochromatic doublet, but there is some good discussion of the subject here:
Would love for this to end up with someone who is either restoring a Pentax refractor or with someone who intends to build themselves a Pentax-grade huge 4" refractor. Happy to answer questions if I can, but most of what I know is in that discussion link above.
Filed under: Eyepieces & Accessories