A digital microscope is a traditional optical microscope with a built-in charge-coupled device (CCD) camera, and is used for the magnified viewing of samples and specimens. These microscopes can usually be connected to a computer so that the images they produce can be saved onto a hard drive for later inspection, or displayed on a monitor so that several people can see a specimen at the same time. By using a combination of technologies, digital microscopes play a crucial role in research and education.
How They Work
Most digital microscopes are built on the same foundation as other optical or light microscopes. A sample is placed beneath an objective lens; an attached light source is usually used to make the sample easier to see. The objective lens magnifies the sample, and it is brought into focus within the tube of the microscope. In a stereo microscope, the eyepiece, also called the ocular lens, then magnifies the image again, making it visible for the observer. A digital microscope may not include an eyepiece, but use a digital camera to focus the image instead.
Types
The original digital microscopes required the use of a computer to view the images. A box at the top of the microscope included a cord so that it could be connected to the computer, and software interpreted the image and displayed it on a monitor. Microscopes of this type are still available, with most including USB cords.
Other digital microscopes do not require a computer. Instead, a small monitor, usually at the top of the microscope where the eyepiece would traditionally be, displays an image of the sample. Some include a separate LCD monitor, which may allow for larger images. All-in-one models like this usually include a hard drive so that images can be stored and transferred.
Portable digital models are also available. Magnification levels with these small devices is usually limited, and they must typically be attached to a computer to see the image. The hand-held nature of these microscopes can be a big advantage, however, as the sample does not usually need to be moved or altered in any way. The camera may also be able to be put into small spaces and at unusual angles that the human eye could not achieve.
Combination stereo and digital microscopes include eyepieces so that they can be used like traditional microscopes, but have a built-in camera that allows images to be transmitted and saved. In most cases, the magnification of the eyepiece determines the magnification level of the final image. Camera kits are also available that attach to a separate stereo microscope, making it into a digital one.
Digital Magnification
Both stereo and digital microscopes are dependent on the optics of the objective lens for much of their magnification. While stereo microscopes rely on the optics of the eyepiece to make the image visible, the resolution of the camera and the monitor size determine how much magnification is possible with a digital microscope. This type of microscope does not necessarily include an eyepiece, it may be possible to capture images with far greater optical magnification. In addition, the image may be further magnified digitally, especially with a high resolution camera.
Digital magnification — or zoom — manipulates the image to make it larger. When the image size is increased, the tiny points of color that make up the image, called pixels, are increased in size. Since this can make the image look blocky, special algorithms are used to add new pixels and interpolate their value. While this can in theory reduce the image quality, most digital microscopes have high resolution cameras, so the images they produce can be as good or better than stereo optical microscopes.
Although it may be possible to magnify a digital image more than one seen through an eyepiece, that magnification is restricted by how large the sample can be reproduced on a monitor. Most all-in-one microscopes have relatively small view screens, sometimes as small as 3.5 inches (8.89 cm) or less. Even larger units often include a 15 inch (38.1 cm) monitor, which still limits the size of the image. In most cases, this means that digital microscopes supply a little more than half of the magnification of comparable stereo microscopes.
Stereo vs. Digital
Both stereo and digital microscopes come in a range of magnifications and quality, and each has its pros and cons. Despite the disadvantages related to image magnification, digital models do have the added advantage of being able to capture and display images. Images of specimens can often be printed easily, and some digital microscopes provide resolutions as high as 54 megapixels. For people who must use the microscope regularly, being able to see the image on a screen may create less eye strain as well.
Compared to stereo microscopes, basic computer-connected digital microscopes are also often more affordable and can be used for more purposes. The ability to manipulate the image digitally means that more can be done than simple display and printing; some scientific models feature high dynamic range, which provides more contrast in images, and 3-D rotation and display functions. Some models also provide overhead LED illumination similar to that in tissue culture microscopes.