So there is a DIC prism for sale labeled as "Olympus U-DPO40S Nomarski Prism for 40x APO Oil Objective Dry Top"
What is dry top?
Also I thought if the prism had an A in it like the U-DPA[O]## ones, that the A meant Apo.
https://bimedis.com/a-item/microscope-a ... 64-1420883