A microscope outfit acquired can sometimes have a phase objective but not a phase condenser. The 40X NA0.65 objective in a Cooke M2000 outfit acquired was for phase but the condenser was the Cooke achromatic.
Various methods have been published to make phase plates. The inner and outer dimensions of the phase rings increase with magnification and for 40X and above may be large enough for a simple card crafting approach to be used.
Sizing the rings requires a ruler of some sort to be placed at the filter tray plane and inspected down the tube. It can be a homemade ruler but in this case a micrometer slide with 0.1 / 1 mm graduations was handheld against the tray and found that the inner and outer ring required was 6 and 7 mm respectively. Sets of hollow hole punches typically include these dimensions so was a simple procedure to make the phase plate card as shown and stuck onto a clear acetate disc. Outlying card tabs allow it to be centred by inspecting the back focal plane of the objective while in place.
The outer and inner ring sizes used in a filter tray are quite a lot smaller than those in the Cooke phase condenser (an example outfit was accessible to compare) for 40X presumably because of the differing optical array.
Fortuitously the phase ring also gives inky black darkfield for the Cooke 10X NA0.28.
Back focal plane of the 40X objective.
Stauroneis phoenicenteron diatom, Klaus Kemp 8 form test plate.
Epithelial cheek cells in water.
Klaus Kemp 8 form test plate using the Cooke 10/0.28 objective and 40X card phase plate.
Comments to the author David Walker are welcomed.