Microscopes, All Types
Microscopes are instruments that are capable of producing a magnified image of a small object. They are used in many applications in the scientific and industrial arenas. Common applications include manufacturing inspection, high-technology quality control in areas such as semiconductor processing, medical imaging, cell research, and metallurgical analysis. Microscopes are supplied in one of three common configurations, student, benchtop and research.
There are many types of microscopes available including acoustic or ultrasonic, compound, fluorescent or ultraviolet, inverted, laser or confocal, polarizing, portable field, scanning electron microscope (SEM), scanning force or atomic probe microscope (SFM/AFM), stereoscopes and transmission electron microscopes.
Acoustic and ultrasonic microscopes use sound waves to create images of the sample.
Compound microscopes use a single light path. They can either have a single eyepiece (monocular) or a dual eyepiece (binocular). Compound microscopes have low depth perception but high resolution and magnification.
Fluorescent and UV microscopes use high-energy, short-wavelength light (usually ultraviolet) to excite electrons within certain molecules inside a specimen, causing those electrons to shift to higher orbits. When they fall back to their original energy levels, they emit lower-energy, longer-wavelength light (usually in the visible spectrum), which forms the image.
An inverted microscope has the illumination system above the stage and the lens system below the stage.
A confocal microscope or laser microscope uses a laser to light image one plane of a specimen at a time.
The polarized light microscope uses two polarizers, one on either side of the specimen, positioned perpendicular to each other so that only light that passes through the specimen reaches the eyepiece. Light is polarized in one plane as it passes through the first filter and reaches the specimen. Regularly spaced, patterned, or crystalline portions of the specimen rotate the light that passes through. Some of this rotated light passes through the second polarizing filter, so these regularly spaced areas show up bright against a black background.
A portable field microscope is designed for use outside of a laboratory setting. It may have a portable energy source, such as a battery, or it may use natural light for illumination.
An electron microscope in which the image is formed by a detector synchronized with a focused electron beam scanning the object. The intensity of the image-forming beam is proportional to the back scattered or secondary emission of the specimen where the probe strikes it. The magnification is controlled by the length or area scanned.
Scanning probe and atomic force (SPM / AFM) microscopes are used to study surface features by moving a sharp probe over the object’s surface (e.g., the scanning tunneling microscope). Atomic force microscopes enable the user to image the topography of a sample, and to monitor simultaneously ultrasonic surface vibrations in the MHz range. For detection of the distribution of the ultrasonic vibration amplitude, a part of the position-sensing light beam reflected from the cantilever is directed to an external knife-edge detector.
A stereomicroscope, or stereoscope, uses two different paths of light. This allows you to see a specimen in 3-D. Stereomicroscopes have high depth perception but low resolution and magnification. The best models have a built-in light source and zoom capabilities.
Transmission electron microscopes (TEM) pass image-forming rays through the specimen being observed. Contrast or diffracted beam images are used to analyze the sample.
Important parameters in specifying microscopes include total magnification and resolution. Microscopes can come in one of many types of eyepiece styles. These include monocular, binocular, trinocular or dual head. Important features in specifying microscopes include a digital display, mechanical stages, oil immersion lenses, fine focus, computer interfaces, and image analysis processing software.
