Achromatic Microscope Objective, 10X Achromatic Objective Lens, 160/0.17 Biological Microscope Achromatic Objectives Lens, for Biological Microscope

I got this to try out on an Olympus CHA, 1976 vintage microscope. It worked fine and was as clear as the Olympus phase contrast objectives. However, as I expected, they are not parfocal with the original objectives. I want to have a set of brightfield objectives to play with creating darkfield patch "filters". The problem with it being shorter than the original 10x is the other objectives at 60x will run into the cover glass so the stage has to be lowered. I think the 40x didn't hit the cover glass. Need the other powers now - 20, 40 and 60 that would be parfocal with this 10x.