Digital microscope

A digital microscope is a variation of a traditional optical microscope that uses optics and a charge-coupled device (CCD) camera to output a digital image to a monitor, sometimes by means of software running on a computer. A digital microscope differs from an optical microscope in that there is no provision to observe the sample directly through an eyepiece. Since the optical image is projected directly on the CCD camera, the entire system is designed for the monitor image. The optics for the human eye are omitted.
Digital microscope is the term commonly used for low price commercial microscopes designed for use with a computer. Although some systems do not require a separate computer and can cost tens of thousands. These normally omit the optics for illumination (for example Köhler illumination and phase contrast illumination) and are more akin to webcams with a macro lens. For information about optical microscopes with a digital camera in research and development see optical microscope.

A primary difference between an optical microscope and a digital microscope is the magnification. With an optical microscope the magnification is found by multiplying the lens magnification by the eyepiece magnification. Since the digital microscope does not have an eyepiece, the magnification cannot be found using this method. Instead the magnification for a digital microscope is found by how many times larger the sample is reproduced on the monitor. Therefore the magnification will depend on the size of the monitor. The average digital microscope system has a 15" monitor, would result in an average difference in magnification between an optical microscope and a digital microscope of about 60%. Thus the magnification number of an optical microscope is usually 60% larger than the magnification number of a digital microscope.
Since the digital microscope has the image projected directly on to the CCD camera, it is possible to have higher quality recorded images than with an optical microscope. With the optical microscope, the lenses are made for the optics of the eye. Attaching a CCD camera to an optical microscope will result in a image that has compromises made for the eyepiece. Although the monitor image and recorded image may be of higher quality compared with the digital microscope, the application for the microscope may dictate which microscope is preferred.

http://en.wikipedia.org/wiki/Digital_microscope