A microscope is used to visualize objects or the details of objects that are too small to be seen without assistance. Microscopes are the foundation of microscopy, the science of investigating such small objects and structures. The criteria for microscopic study are varied, so many types of microscopes are available to address specific needs.
Compound microscopes are used to view images of small objects on glass slides. Magnification can range from 40x to 1000x and is achieved by multiple convex lenses in the eyepieces and in magnifying objectives.
In upright microscopes, the objective lens is closest to the object, and the eyepiece further enlarges the image. A light source illuminates the object to produce a two-dimensional image.
Compound microscopes may also be inverted. Inverted microscopes’ light sources and condensers are above the object, with the objective lens pointing up toward the object to be viewed. They are commonly used to observe cells growing on the bottom surface of a culture flask and can also be used for micromanipulations or metallurgical applications.
A stereo microscope (also called a dissecting microscope) offers lower magnifications and reflects light from an object’s surface. Separate right and left light paths provide slightly different viewing angles, which create a three-dimensional sample view. Stereo microscopes are used to examine the surfaces of solid specimens or for dissection or microsurgery. In addition, they are used in manufacturing for inspection and quality control.
(See Stereo Microscopes)
Digital microscopes create digital or electronic images and may be any type of microscope (compound, inverted, stereo, etc.). Before digital imaging was available, users attached cameras to the microscope itself to capture documentation images. Many digital microscopes also have a separate screen to preview the images.
USB Computer Microscopes
USB computer microscopes, also called computer or computer-connected microscopes, plug into a USB port on a computer or television. Instead of looking using an eyepiece, the viewer examines the specimen via the computer monitor or TV screen, like a webcam with a lens. Most of these microscopes are handheld and can save images as files or videos. However, most have only low-level magnification, and adequate illumination can be a problem.
Pocket microscopes are handheld, durable, and useful for field work. Sizes vary, and some are the size of an ink pen. Most use natural light or are battery-powered, with 25x to 100x magnification. Portable microscopes may also be digital.