The phase contrast microscope allows researchers to differentiate structures within the cell by viewing differences in thickness and refractice index. Retardation of the rays of light that pass through the object produces phase differences, allowing the viewer to compare cellular structures and the surroundings. 

Tulane University

Studying the morphology of bacteria requires using microscopes. The types of microscopes are:
- Optical microscope
- Phase contrast microscope
- Dark ground microscope
- Electron microscope

Microscopy

Al-mohanna, Moshtaq & H., quine. (2016). MORPHOLOGY AND CLASSIFICATION OF BACTERIA. 

Morphology and Classification of Bacteria

There are two types of optical or light microscopes:

- Simple Microscope: this microscope has one lens. Ex: hand lens
- Compound Microscope: this microscope has two or more lens in a series. The image from the first lens is magnified by the addition of another lens. Bacteria, living or fixed to the slide, may be viewed under the compound microscope. Observation of hanging drops indicates shape, motility, arrangement and size of the bacterial cells. Due to the absence of contrast, finer details cannot be examined. 

Optical Microscope

Phase Contrast Microscope

The dark field microscope improves the contrast as reflected light is substituted for transmitted light used in the optical microscope. The resulting contrast provides increased resolution; therefore, smaller organisms and structures, such as spirochetes, can be clearly observed. 

Dark Field/Dark Ground Microscope

Beams of electrons are used in electron microscopes; these electrons are dispersed after hitting the object, producing an image which can be viewed on a fluorescent viewing screen. 

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