Back Button







Shown here are phase telescopes made by Leitz, Wild and Olympus. They all have an outer tube that drops into the microscope where an ordinary eyepiece would be and they all have standard society diameter of 22-23 mm. They all have an inner tube which goes in and out for focusing. In use they are designed to focus on the top (rear) plane of the objective. The Leitz and Olympus focus is a coarse sprial thread, but the Wild simply slides up and down. The Leitz version has a collar which can be used to adjust how far the telescope fits inside the tube, whereas the Wild and Olympus versions are designed to fit only to one depth. All have a diaphragm to eliminate stray light from entering the optical path. The diaphragm in the Leitz version is inside, above the distal optical element. In the others the distal outer lens is set into the diaphragm. These telescopes are all of different lengths with the Olympus being the shortest and the Leitz the longest. The Olympus is about 74 mm long when maximally open and about 51 mm closed. The Wild range is about 50 to 104 mm and the Leitz 79 to 89 mm.


The Phase contrast phenomenon was discovered by the Dutchman Frits Zernicke about 1930. He built his first phase contrast microscope about 1938. It was confiscated by the Nazis. Phase contrast microscopes started to come into commercial production immediately following the end of World War II. Phase telescopes therefore have been made since about 1945-50, and continue in production today. The Leitz version likely dates to the 1950's the Wild and Olympus versions to the 1970s-80s.

All phase contrast microscopes utilize a phase plate in the condenser and a phase ring at the back or top focal plane of the objective. When using a phase contrast microscope, one has to align the phase ring in the back or top focal plane of the objective, with the phase plate ring in the phase contrast condenser. Although this can be accomplished reasonably well for a 10X objective with the eyepiece removed and just the naked eye, a magnified view is needed for the higher power objectives. This is where the phase telescope comes into use. Another way to view the back focal plane of the objective is to use a Bertrand lens. Instead of removing the eyepiece, this lens is inserted between the eyepiece and the objective and the eyepiece and Bertrand lens together form another version of 'telescope'. Bertrand lenses are much more common on petrographic polarizing microscopes, but a similar form of optical device was produced by Olympus as an accessory to be inserted into the optical path below the binocular tube, and a control would allow one to turn it in or out of the optical path, and focus it. The Bertrand lens is somewhat more sophisticated than a simple phase telescope, and acts as a relay lens, transferring an image of the objective focal plane to the microscope intermediate image plane located in the eyepiece aperture diaphragm.

If you would like to know more about phase contrast systems please consult the Nikon Web Site Phase Contrast Web Page for more information.