Digital video microscopes are essentially small cameras with built-in manual focus or zoom lenses. These range from hand-held USB models through to those with stands and integral displays. Most models use color image sensors but monochrome units for visible and near infrared use are also available. Some hand-held models have optional stands.
Magnification in these microscopes is the ratio of the size of the display to the camera field of view. Typically, the quoted numbers assume a 17" display with the same aspect ratio as the camera. For example, a 100X setting with a 17" monitor means that the diagonal field of view of the camera will be 0.17 inches or 4.3 mm. if the microscope is going to be used at high magnification, it is recommended that a stand be used. Holding a camera still by hand is very difficult with the small field of view.
Currently, we are offenring a line of 0.3 to 2 MP hand-held USB 2.0 microscopes from ToupTek, shown here: