Give+a+brief+description+about+Ray+Diagrams

__These schematics show the ray traces for two probe-forming lens focusing conditions: small working distance (left) and large working distance (right). Both conditions have the same condenser lens strength and aperture size. However, as the sample is moved further from the lens, the following occurs:__

· __the working distance__ //S// __is increased__ · __the demagnification decreases__ · __the spot size increases__ · __the divergence angle__ //alpha// __is decreased__ __The decrease in demagnification is obtained when the lens current is decreased, which in turn increases the focal length__ //f// __of the lens. The resolution of the specimen is decreased with an increased working distance, because the spot size is increased. Conversely, the depth of field is increased with an increased working distance, because the divergence angle is smaller. http://mse.iastate.edu/microscopy/ray_diagrams.html__