Resolution and Depth of Field

The advantages of the scanning microscope as compared with conventional optical microscopes include superior resolution and depth of field. Resolution of 200 A is obtained with a depth of field several hundred times dial of a conventional optical microscope. The scanning microscope also makes possible the display of other kinds of data obtained from the specimen. notably cathodoluminescent photons emitted by fluorescing samples. 

The resolution and depth of field of the image are established by the electron beam intensity, energy, interaction volume, and the final spot size, which are attuned with one or more condenser lenses and... 

C. Cremer, T. Cremer, Considerations on a laser-scanning-microscope with high resolution and depth of field. Microscopica Acta 81(1), 31-44 (1978)... 

Figure 25. Electron micrographs showing three typical views of a water4n-oil emulsion by direct observation. The resolution and depth of field are significantly better than can be achieved via optical microscopy.

Compare resolution and depth of field of light microscopes and electron microscopes. The wavelength of electrons is 0.0037 nm (100 kV) and the angle a of an electron microscope is 0.1 radians. 

Of course, the optical microscope was not so well suited for paint research because of inherent resolution and depth-of-field limitations. For example, pigment particles are often well below lum in size therefore, the most interesting features of their surfaces are below the resolving power attainable. Optical scientists have continually pushed for greater resolution through... 

Scanning electron microscope (SEM) Electron beam instrument used to observe surface features of materials at great resolution and depth of field, usually used in eonjunction with X-ray spectrometers to obtain chemical analytical information from the specimen. 

Much more detailed information regarding the mechanism of fractnre is available from microscopic examination, normally using scanning electron microscopy. Studies of this type are termed fractographic. The scanning electron microscope is preferred for fractographic examinations because it has a much better resolution and depth of field than does the optical microscope these characteristics are necessary to reveal the topographical features of fracture surfaces. 

Table 7.4. Examples of Working Distance Resolution and Depth of Field as a Function of Objective Numerical Aperture...

The principles of resolution and depth of field discussed in Section 20.3 hold for electron microscopes, but the wavelength of the radiation used in electron microscopes is much less than the wavelength of light. The wavelength of an electron is given by... 

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