Bright field microscopy

  Bright field microscopy is the simplest of all the optical microscopy illumination techniques. Sample illumination is transmitted via white light, ie. illuminated from below and observed from above. The most common use of the microscope involves the use of an organism mounted to a glass microscope slide.

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Common components

• Base - Supporting structure that usually contains an electrical light source or illuminator.
• Objective lens(es)- Magnify the image.
• Oculars - Magnify the image from the objective lens. A microscope with one ocular lens is often called a monocular, a microscope with two oculars is called a binocular.
• Arm - The support structure that connects the lens systems to the base.
• Body tube - Sends light to the ocular lens.
• Condenser lens - Directs light to pass through the specimen.
• Stage - Platform that allows mechanical movement of a microscope slide.
• Adjustment knobs - Course and fine focus adjustment.

The magnification of an optical microscope is only limited by the magnifying power of the lens system. However, the limit of magnification for most light microscopes is 1000x which is set by an intrinsic property of lenses called resolving power.

Advantages

• Simplicity of setup with only basic equipment required.
• No sample preparation required, allowing viewing of live cells.

Limitations

• Very low contrast of most biological samples.
• Low apparent optical resolution due the blur of out of focus material.
• lamp

Enhancements

• Reducing or increasing the amount of the light source via the iris diaphragm.
• Use of an oil immersion objective lens and a special immersion oil placed on a glass cover over the specimen. Immersion oil has the same refraction as glass and improves the resolution of the observed specimen.
• Use of sample staining methods for use in microbiology, such as simple stains (Methylene blue, Safranin, Crystal violet) and differential stains (Negative stains, flagellar stains, endospore stains).
• Use of a colored (usually blue) or polarizing filter on the light source to highlight features not visible under white light. The use of filters is especially useful with mineral samples.

References

1. Advanced Light Microscopy vol. 1 Principles and Basic Properties by Maksymilian Pluta, Elsevier (1988)
2. Advanced Light Microscopy vol. 2 Specialised Methods by Maksymilian Pluta, Elsevier (1989)
3. Introduction to Light Microscopy by S. Bradbury, B. Bracegirdle, BIOS Scientific Publishers (1998)
4. Microbiology: Principles and Explorations by Jacquelyn G. Black, John Wiley & Sons, Inc. (2005)
5. Microscopy and Imaging Literature