Microscopes are one of most popular optical instruments for the hospitals,
clinics, biology Labs, and pharmaceutical companies. Microscopes are available
in dozens of specifications and with a multitude of different features.
How to choose a microscope that best fit your needs? This buyer's guide
is intended to help our customers who need some basic information about
Quality of Microscopes
Quality is the most important "feature" of microscopes. In
many cases the brand name is a guide to quality. Companies like Celestron,
Konus, LW Scientific, Meade, Parks Optical, and Western Scientific Co.
have spent decades earning a reputation for high quality optical products,
and they are unlikely to produce a clearly inferior product.
A magnifying glass, an ordinary double convex lens having a short focal
length, is a simple microscope. The reading lens and hand lens are instruments
of this type. When an object is placed nearer such a lens than its principal
focus, i.e., within its focal length, an image is produced that is erect
and larger than the original object. The image is also virtual; i.e.,
it cannot be projected on a screen as can a real image.
Compound microscopes magnify the tiny detail and structure of plant cells,
bone marrow and blood cells, single-celled creatures like amoebas, and
much more. Almost every homeschool family or hobbyist will need a 400x
compound microscope to study cells and tiny organisms in biology and life
Stereo microscopes & dissecting microscopes are low-power microscopes
designed for observing whole objects like flower pollen and rock crystals
with a 3D view.
Optical microscopes, through their use of visible wavelengths of light,
are the simplest and hence most widely used type of biology and geology.
Optical microscopes use refractive lenses, typically of glass and occasionally
of plastic, to focus light into the eye or another light detector. Typical
magnification of a light microscope is up to 1500x with a theoretical
resolution of around 0.2 micrometres or 200 nanometers. Specialised techniques
(e.g., scanning confocal microscopy) may exceed this magnification but
the resolution is an insurmountable diffraction limit.
The electron microscope, which is not limited by the powers of optical
lenses and light, permits greater magnification and greater depth of focus
than the optical microscope and reveals more details of structure. Instead
of light rays it employs a stream of electrons controlled by electric
or magnetic fields. The image may be thrown on a fluorescent screen or
may be photographed. The scanning electron microscope gains even greater
resolution by reading the response of the subject material rather than
the direct reflection of its beam. Using a similar approach, optical scanning
microscopes achieve a resolution of 400 Angstroms, less than the wavelength
of the light being used. Finally, the scanning tunnelling microscope,
invented in 1982, uses not a beam but an electron wave field, which by
interacting with a nearby specimen is capable of imaging individual atoms;
its resolution is an astounding one Angstrom.
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