There are many Microscope Types and we can classify them based on several aspects.
We can classify them upon:
- what interacts with the sample to generate the image
- whether they analyse the sample via a scanning point
- their cost
- their versatility
- their area of application and performance
Most acceptable classification is based on how the image is generated. So, based on this classification there are:
1. Optical Microscopes
The first microscopes that were invented, belong to this group. They use light to magnify objects.
The Light microscope or Compound Microscope
The most used light microscope is the Compound Microscope. It contains two lenses to mignify the samples: objective and ocular.
Maximum magnification is 1000x. They are most often found in science and biology classrooms.
The image seen with this type of microscope is two dimensional. They cost from $150-$10,000.
Source of Radiation for Image Formation: visible light.
The compound light microscope is popular among:
- botanists for studying plant cells,
- in biology to view bacteria and parasites as well as a variety of human/animal cells.
- It is a useful microscope in forensic labs for identifying drug structures.
Types of Illumination in Microscopes
How light passes through a specimen changes the view of the specimen, making some parts more distinct. So, there are:
- Bright-field microscopy is the simplest of all the optical microscopy illumination techniques. The typical appearance of a bright-field microscopy image is a dark sample on a bright background, hence the name.
- Dark‐field microscope, which is used to observe live spirochetes, such as those that cause syphilis.
- Differential Interference Contrast microscopy
- Phase‐contrast microscope.
Fluorescent microscope (epi-fluorescent microscope) is a special type of a light microscope and uses ultraviolet light as its light source. When ultraviolet light hits an object, it excites the electrons of the object, and they give off light in various shades of color. Since ultraviolet light is used (visible light has a wavelength of about 550 nm, while ultraviolet light has a wavelength of about 400 nm or less), the resolution of the object increases. The resolution of a microscope increases as the wavelength decreases. A laboratory technique called the fluorescent‐antibody technique employs fluorescent dyes and antibodies to help identify unknown bacteria.
Microscope camera is a digital type of a video capturing device mounted on light microscopes and equipped with USB or AV cable. Then you can connect to a LCD or a computer monitor. In addition to, or instead of, directly viewing the object through the eyepieces, a type of sensor similar to those used in a digital camera is used to obtain an image. The trinocular type of digital microscopes have the possibility of mounting the camera, that would be an USB microscope.
The USB Computer Microscope
This is great for starting exploring micro world and for hobbyists and kids. Requires no preparation of the specimen.It is essentially a macro lens used to examine images on a computer screen plugged into its USB port. Magnification is restricted and is not comparable to your standard compound light microscope at only up to 200X. Price is usually under $200US.
The Pocket Microscope
This is a device which is a great gift for a child or your student. Magnification ranging from 25x to 100x. There are many different models available.
Dissection or Stereoscope
These microscopes magnify up to about maximum 100x and supply a 3-dimensional view of the specimen. They are useful for observing opaque objects.
A stereo microscope, also referred to as “dissecting microscope”, uses two objectives and two eyepieces which makes it possible to view a specimen under angles to the human eyes forming a stereo 3D optical vision.
The stereo microscope is an optical microscope which magnifies up to about maximum 100x and provides a 3-dimensional view of the specimen. Stereo microscopes are highly useful for observing opaque objects.
A dissection microscope is light illuminated. The image that appears is three dimensional. It is used for dissection to get a better look at the larger specimen. You cannot see individual cells because it has a low magnification. Price $100-$1500. Source of Radiation for Image Formation: visible light
Confocal Microscope (Confocal Laser scanning microscope)
This microscope uses a laser light. They are able to scan a sample also in depth with help of scanning mirrors. Then image is digitized and prepared for analyzing on computer. These Microscopes are expencive and used for research centers. Price is between $20,000-$100,000.
2. Electron microscopy
Here image is formatted with the help of beam of electrons. Electronic beam has short wavelength, so the resolution is high. Viruses and some large molecules can be seen with this instrument. Medium of electronic beam is vacuum, and image is created on computers. Magnification is up to 2 million times. They are most advanced and far more powerful in comparsion to light microscopes. Cost more then $50,000.
Transmission Electron Microscope (TEM)
There are 2 types mostly used electron microscopes. One of them is Transmission electron microscope. It gives two dimensional image. Slices of specimen are stains with gold or palladium. This coated parts deflect electron beam and this areas show up on the image.
Scanning Electron Microscope (SEM)
This are modern form of electron microscope. They gives lower magnification than TEM, but also gives 3 dimensional pictures. Electron beam is projected on the sample, so you can visualize the surface of the specimen.
Reflection Electron Microscope
Reflection electron microscopes(REM) are also designed on the principle of electron beams but they are characteristically different from TEM and SEM microscopes being that it is built to detect electrons that have been scattered elastically.
They uses scattered high-energy electrons falling on a surface at glancing angles to generate an image of the surface.
Scanning transmission electron microscope (STEM)
The STEM rasters a focused incident probe across a specimen that (as with the TEM) has been thinned to facilitate detection of electrons scattered through the specimen. The high resolution of the TEM is thus possible in STEM. The focusing action (and aberrations) occur before the electrons hit the specimen in the STEM, but afterward in the TEM. The STEMs use of SEM-like beam rastering simplifies annular dark-field imaging, and other analytical techniques, but also means that image data is acquired in serial rather than in parallel fashion. Often TEM can be equipped with the scanning option and then it can function both as TEM and STEM.
3. Scanning Probe Microscopes
They are used in physics, biology and chemistry in research and development sctors. Generated images has high resolution with highly magnification in 3 dimensions. With these instruments it can be observed specimens in real time.
First is anlyzied a single point in the sample and then scan the probe over a rectangular sample region to build up an image.
They helps visualize individual atoms.
4. Other Microscopes
As the name suggests, these microscopes use a beam of x-rays to create an image. Due to the small wavelength, the image resolution is higher than in optical microscopes.
The maximum useful magnification is therefore also higher and is between the optical microscopes and electron microscopes. One advantage of x-ray microscopes over electron microscopes is, that it is possible to observe living cells.
Scanning Helium Ion Microscope (SHIM or HeIM)
As the name suggests, these devices use a beam of Helium ions to generate an image. There are several advantages to electron microscopes, one being that the sample is left mostly intact and that it provides a high resolution. It is a relatively new technology and the first commercial systems were released in 2007.
Still under an experimental stage, Neutron microscope generates a high resolution image and may offer better contrast than other forms of microscopy. The new technology would use neutrons instead of beams of light or electrons to generate high resolution images.
Scanning acoustic microscope (SAM)
Scanning acoustic microscope uses focused sound waves to generate an image. An acoustic microscope has a wide range of applications in materials science to detect small cracks or tensions in materials. The scanning acoustic microscope is a powerful tool which can also be used in biology to study the physical properties of the biological structure and help uncover tensions, stress and elasticity inside the biological structure.
The Acoustic Microscope is less about resolution and more about finding faults, cracks or errors from samples during the manufacturing process.