The optical microscope, often referred to as the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were possibly designed in their present compound form in the 17th century. The image from an optical microscope can be captured by normal light-sensitive cameras to generate a micrograph.
A digital microscope is a microscope equipped with a digital camera allowing observation of a sample via a computer. Microscopes can also be partly or wholly computer-controlled with various levels of automation. Digital microscopy allows greater analysis of a microscope image, for example measurements of distances and areas and quantitaton of a fluorescent or histological stain.
Low-powered digital microscopes, USB microscopes, are also commercially available. These are essentially webcams with a high-powered macro lens and generally do not use transillumination. The camera attached directly to the USB port of a computer, so that the images are shown directly on the monitor. They offer modest magnifications (up to about 200×) without the need to use eyepieces, and at very low cost.
Images can be recorded and stored similar to a webcam on the computer. The camera is usually fitted with a light source, although extra sources (such as a fiber-optic light) can be used to highlight features of interest in the object. They generally offer a large depth of field at the cost of a smaller numerical aperture and so amount of light collected.
USB microscopes are most useful when examining flat objects such as coins, printed circuit boards, or documents such as banknotes. Their use is generally similar to that of stereo microscopes. USB microscopes offer the great advantage of being much less bulky than a conventional stereo microscope so can be used in the field, attached to a laptop computer.
1) Originally images were captured by photographic film but modern developments in CMOS and charge-coupled device (CCD) cameras allow the capture of digital images. Purely digital microscopesare now available which just use a CCD camera to examine a sample, and the image is shown directly on a computer screen without the need for eyepieces.
2) A primary difference between a stereo microscope and a digital microscope is the magnification. With an stereo 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 40%. Thus the magnification number of an stereo microscope is usually 40% less than the magnification number of a digital microscope.
3) 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 stereo microscope. With the stereo microscope, the lenses are made for the optics of the eye. Attaching a CCD
camera to an stereo 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 with the digital microscope, the application for the microscope may dictate which microscope is preferred.