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Unit 17 AB-Luke JonesMicroscopes
A light microscope is a microscope that allows visible light to pass through the specimen
accompanied by a series of magnification lenses to produce a magnified image. The lenses
that are used on a light microscope are known as the
low-power objective lens (x4), medium-power objective
lens (x10) and high-power objective lens (x40). All the
lens’s magnifications become enhanced by the
eyepiece, which is usually x10. They are easy to use,
cheap and portable. When viewing the specimen, the
natural colour is maintained which allows you to easily
identify the components that make up the specimen.
The samples that are required for the light microscopes
can either be living or dead, and must be divided into
thin sections, which means that they can be prepared
easily, and the distortion of the specimen is minimal.
The maximum magnification that the light microscope can handle is around the x1500 mark,
which limits the microscope to resolve points of a specimen that are 200nm apart.
A stereo microscope is a microscope that is designed for low
magnifications when observing a sample by using light that reflects off
the surface of the specimen, instead of passing through it. The
microscope uses two different optical paths, with two eyepieces,
which provide different viewing angles of the specimen for each eye.
Due to its low magnification, the stereo microscope gives the user the
ability to perform small dissections on the specimen, which can either
be alive or dead. By the light reflecting off the specimen, a 3D image is
created.
Oil immersion microscopy is a technique used to increase the resolving power of a
microscope. Its high magnification is achieved by putting drops of oil onto the objective lens
and the specimen and uses light that has been transmitted through the sample. It can be
used to view samples at magnifications between x40 and x1000.
Phase contrast microscopy is a technique used by light microscopes
that transfers variations that are in phase into their corresponding
changes in amplitude, which can then be displayed as differences in
the contrasts of the image. This technique can be used to examine
living cells, without the need to kill, harm or stain the specimen. It
grants the visualisation of cells and their components as without
using the phase contrasts technique, it would be difficult to see what
the cell holds using a basic light microscope.
, A transmission electron microscope (TEM) is a microscope that utilises beams of electrons
that pass through the chosen specimen, they are focused using
electromagnets to visualise what the specimen looks like, and projects
it onto a photographic film. The microscopes are extremely difficult to
run and maintain due to the cost being so high. When preparing the
specimen, they must be stained using heavy metal compounds, as the
metals absorb some of the electrons that would be projected onto the
microscope’s lens. The samples that the TEM can make use of need to
be divided into very thin sections, (20-100nm), which can take great
skill and could potentially produce artefacts (errors). The specimen’s
need to be dead in order to be viewed under the microscope, which
requires a vacuum to prevent electrical discharge. The maximum
magnification that the transmission electron microscope can manage is
anything up to x500,000, which gives a 2D image when viewing. The
wavelength of the electrons is 0.004nm, so points of 0.2nm can be resolved.
A scanning electron microscope (SEM) is a microscope that makes use of beams of
electrons, that bounce off the surface of the gold-coated sample. The
SEM is quite like the TEM, regarding their maintenance and the
preparation of the samples. SEM are extremely difficult to run and
maintain due to the cost being so high. When preparing the specimen,
they must be stained using heavy metal compounds, as the metals
absorb some of the electrons that would be projected onto the
microscope’s lens. Again, very thin sections (20-100nm) are necessary,
which requires preparation and skill to be performed. If care isn’t taken
during the sample preparation, artefacts can be produced. Only
deceased specimens can be viewed using the SEM, which is why a
vacuum is required to prevent electrical discharge. The maximum
magnification that the scanning electron microscope can operate is
anything up to x100,000, however it forms a 3D image with a resolution of 5-20nm.
Every microscope relies heavily on magnification and resolution, as they are the source of
the image and it’s details. Magnification is how many times larger an image can be
perceived, compared to its actual size. This is achieved by using various different
instruments, such as the eyepiece lens and the objective lenses. The objective lens
magnifies the sample and forms a virtual image. The eyepiece lens then magnifies the virtual
image further, which creates a real image. Resolution is the ability of a microscope to
produce an image with great detail, that can also be perceived clearly without distractions.
Light microscopes are mainly used to study living or deceased cells that
require a relatively low magnification and resolution. Electron
microscopes are only used to investigate the structure of deceased
specimens in intense detail, which requires an extremely high
magnification and resolution. Both of the microscopes use radiation to
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