Transparent living organisms can be more easily seen with dark field microscope This method is particularly useful when one is attempting to identify spirochaetes in exudate To achieve the dark effect it is necessary to alter the light rays that approach the objective in such away only oblique rays strike the objects being viewed The obliquity of the must be extreme that if no object are in the field the background is completely light free objects in the field become brightly illuminated however by the rays that are reflected up through the lens system of microscope Darkfield production star diaphragm dark field condenser Phase contrast microscope first developed by Frederick Zernike referred as Frederic microscope instrument. To study living transparent cell Various configurations o f diaphragms and materials that can be used to retard or advance the direct light ray it differs from bright field different type of diaphragm phase plate the diaphragm consists of annular top allow only hollow cone of light to pass rays through the condenser to the object on the slide the phase plate is a special optical disk located at rear focal plate of objective it has a phase ring on it that advance or retard the direct light ray ¼ wave full course https://www.udemy.com/course/practical-bacteriology-from-scratch/?referralCode=D8BE0B0A84BFDA0E94FD