Light transmission through lenses and imaging

An optical lens is a carefully ground (or moulded) piece of optical glass in which either or both of the lens s surfaces are curved. Lenses bend light rays so that they diverge or converge to form an image and they constitute essential components in, for example, telescopes and microscopes and many other instruments in everyday use that employ optical components. 

A large variety of types of lens exist, but they all can be classified into two general classes according to the effect they have on a parallel beam of light. These two 

The so-called lens equation expresses the quantitative relationship between the object distance a. 

In applications, in which high-powered lasers are used, the second method of beam expansion is the one of choice. This is because the tiny beam spot size created at the common focal point in a Keplerian beam expander results in energy densities that may be high enough to cause the air to break down or ionize. 

For either version of the two-lens beam expander/ collimator, the lateral magnification between the entrance and exit beams of diameters D and D2 respectively is related to the focal lengths of the two lenses,/i and/2, by 

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