Magnification | Magnification
Key Words: N.A., Resolution, field-of-view, immunocytochemistry, immunohistochemistry
Definition:The degree to which the specimen is enlarged on the microscope
The final magnification of the specimen under the microscope is determined by both the magnification power of the objective and the magnification of the eye-piece (and any other magnifying modules in the light path). For example, a 40X objective and a 10X eyepiece (with no intermediate modules) provides a total magnification of 400X.
The range of 'useful magnification' for an objective/eyepiece combination is determined by the N.A of the microscope optical system. As the N.A. increases across a series of objectives of the same magnification, light gathering capability and resolution increase. There is a minimum magnification necessary for the detail present in an image to be resolved, and this is usually defined as 500 times the N.A. The maximum useful magnification of an image is usually set at 1000 times the N.A. Magnification beyond this value will yield no further useful information and is termed 'empty magnification'.
The magnification of a compound light microscope is limited to about 2000X. This enables visualization of eukaryotic cells, bacteria, algae, and protozoa. Direct visualization of viruses and molecules is beyond the capabilities of light microscopy. These may, however, be observed by indirect methods such as immunohistochemistry, immunocytochemisty, and other amplification techniques.
The range of magnifications required on the microscope will depend on the subject being imaged. Most applications require the use of a low power objective to obtain a large field-of-view for initial assessment and selection of regions for further high power observation (magnification is inversely proportional to the field-of-view - i.e. the greater the magnification the smaller the field-of-view). The use of high power objectives may be improved through the use of immersion media (water, glycerin or oil) to improve resolution.
Magnification requirements are dependent on the application. However, to maintain parcentricity and parfocality when switching objectives, it is important to use a matched set of objectives.
Please consult your local Nikon representative for advice relevant to your applications.