Illumination systems optical microscopy

The ability to discern fine details within a magnified image is referred to as the resolution of a microscope. Since light is used as the illumination source in optical microscopy, the resolution is expressed in the same units as the wavelength of light (nm). The theoretical resolution, R, of any optical system may be calculated using Abbe s equation (Eq. 1) ... 

One of the most critical aspects of observation using any optical microscope is the specimen illumination. Two illumination systems are commonly used in optical microscopy transmitted light and reflected light (Fig. 2). Transmitted, also called diascopic illumination, requires the specimen to be transparent. It is used primarily to examine thin sections of biological or material samples. Reflected light, or episcopic illumination (epi-illumination), is most commonly used for fluorescence microscopy, where fluorphores inside the specimen are excited to produce fluorescent light. The fluorescence is then emitted, or reflected back to the objective and collected by the detector (eyes, or camera). The reflected light is also used to study the surfaces of opaque specimens, which is the focus of this session. 

For single-capillary systems, a conventional PMT is used for detection. Light is routed to that PMT either with fiber optics, a collecting mirror, epi-illumination microscopy, or a microscope objective. For multiplecapillary systems, the system must be scanned [6] or the light imaged onto a CCD camera. 

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