All microscopes serve to enlarge the size of an object and allow people to view smaller regions within the sample. Microscopes form optical images and although instruments like the SEM have extremely high magnifications, the physics of the image formation are very basic. The simplest magnification lens can be seen in Figure 1. The formula for magnification is shown in Equation 1, where M is magnification, *f* is focal length, *u* is the distance between object and lens, and* v* is distance from lens to the image.

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size 12{M= { {f} over {u - f} } = { {v - f} over {f} } } {}

(1)Multistage microscopes can amplify the magnification of the original object even more as shown in Figure 2. Where magnification is now calculated from Equation 2, where *f**1**, f**2 *are focal distances with respect to the first and second lens and *v**1**, v**2*are the distances from the lens to the magnified image of first and second lens, respectively.

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size 12{M= { { \( v rSub { size 8{1} } - f rSub { size 8{1} } \) \( v rSub { size 8{2} } - f rSub { size 8{2} } \) } over {f rSub { size 8{1} } f rSub { size 8{2} } } } } {}

(2)In reality, the objects we wish to magnify need to be illuminated. Whether or not the sample is thin enough to transmit light divides the microscope into two arenas. SEM is used for samples that do not transmit light, whereas the TEM (transmission electron microscope) requires transparent samples. Due to the many frequencies of light from the introduced source, a condenser system is added to control the brightness and narrow the range of viewing to reduce aberrations, which distort the magnified image.