To use a simple usb webcam as a microscope, only a few modifications are needed.
In short, a small hack to the optics of a standard webcam with an adjustable focus-lens, allows to create video data, with a magnification of around 100 to 400x (depending on the model) at a working distance of a few mm. The highest magnifications can be achieved by inverting (putting upside down) the lens. Addition of good lighting by the use of leds allows to create images using a bright-field method (shine through the stuff) or dark field method (look at the reflections and scattering).
[[File:amoebae_dark.gif|frame|left|dark-field image sequence (4 sec) of an amoebae recorded on a modified webcam]] [[File:amoebae_bright.gif|frame|right|bright-field image sequence (4 sec) of an amoebae recorded on a modified webcam]]