Light Microscopy

Light microscopy is based on the interaction of light and tissue components and can be used to study tissue features.
Upon completion of this lecture, the student should be able to:
1- Explain the basic principles of each type of light microscopes.
2- Explain the additional materials required for the examination with each microscope.
3- Define: total magnification, resolving power, quality of the image, optical section.
4- Choose the appropriate microscope type according to the specimen type and aim of the examination.

Bright-Field Microscopy
With the bright-field microscope (e.g. Compound Microscope), widely used by students of histology, stained preparations are examined by means of ordinary light that passes through the specimen. The microscope is composed of optical and parts mechanical (Figure 1–3). The optical components consist of three systems of lenses. The condenser collects and focuses light, producing a cone of light that illuminates the object to be observed. The objective lenses enlarge and project the illuminated image of the object in the direction of the eyepiece. The eyepiece or ocular lens further magnifies this image and projects it onto the viewer s retina, photographic film, or (to obtain a digital image) a detector such as a charge-coupled device (CCD) camera. The total magnification is obtained by multiplying the magnifying power of the objective and ocular lenses.
The critical factor in obtaining a detailed image with a light microscope is its resolving power, defined as the smallest distance between two particles at which they can be seen as separate objects. The maximal resolving power of the light microscope is approximately 0.2um; this power permits good images magnified 1000–1500 times.