Phase contrast is one of more popular contrast techniques developed in the 1930's by Frits Zernike. This technique helps make unstained objects such as bacteria, protozoans, blood cells, sperm, etc, visible. Phase contrast is a method where a portion of the light is treated differently from the rest, and caused to interfere with the rest in a way to product a visible image from an otherwise transparent specimen.
Phase contrast requires three components:
Phase Contrast Objective
2. Phase Contrast Condenser: The condenser will contain what is called the annulus. The annulus is the second component to complete the optical aspect of phase contrast. The annulus must match with the phase plate (ring) inside of the phase contrast objective. Each annulus will be marked just as the objective with Ph followed by a number - 1, 2, or 3. In order to achieve phase your condenser must be centered and your phase annulus must be aligned. Once this is done in order to achieve phase contrast simply match the objective to the corresponding annulus. For example if your objective reads Ph1 you should engage the phase annulus which reads Ph1.
Phase Contrast Slider: If your microscope has a slot in the condenser then you can use a phase contrast slider which contains the phase annulus. The slider will have a brightfield position and positions with the phase annulus. This method is a more economical method than the alternative phase turret condenser. It typically has a limitation of only being able to carry two phase annulus. The advantage of a phase slider is that they usually come per-centered and aligned.
Phase Contrast Turret Condenser Phase Contrast Slider
Phase Contrast Telescope
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