Different Types of MICROSCOPE

MICROSCOPE
Microbiology, the branch of science that has so vastly extended and expanded
our knowledge of the living world.
Leeuwenhoek, In 1673 introduced the world to the existence of microbial forms
of life.
Over the years, microscopes have evolved from the simple, single lens
instrument of Leeuwenhoek, with a magnification of 300x, to the present-day
electron microscopes capable of magnifications greater than 250,000x.

BRIGHT-FIELD MICROSCOPE

The compound brightfield microscope is the “WORKHORSE” This Is The Conventional
Microscope Which Is Most Widely Used In The Field.
It Magnifies Images Using Two Lens Systems. Initial Magnification Occurs In The Objective
Lens. The Final Magnification Occurs In Ocular Lens.
The specimen is illuminated by a beam of tungsten light focused on it by a substage lens
called a condenser; the result is a specimen that appears dark against a bright background.
Major limitation of this system is the absence of contrast between the specimen and the
surrounding medium, which makes it difficult to observe living cells. Therefore, most bright
field observations are performed on nonviable, stained preparations.
But It Provides Little Information About Internal Cell Structure.

DARK-FIELD MICROSCOPE:

The condenser system is modified so that the specimen is not illuminated directly.
The condenser directs the light obliquely so that the light is deflected or scattered from
the specimen, which then appears bright against a dark background.
Living specimens may be observed more readily with darkfield than with brightfield
microscopy.
Dark-field Microscopy is Useful In Observing Unstained Living Microorganisms,
Microorganisms That Are Difficult To Stain, And Spirochetes, Which Are Poorly Defined
By Bright-field Microscopy.

PHASE-CONTRAST MICROSCOPE (PCM):

Its optics include special objectives and a condenser that differ only slightly in their refractive
indexes.
As light is transmitted through a specimen with a refractive index different from that of the
surrounding medium, a portion of the light is refracted (bent) due to slight variations in density and
thickness of the cellular components.
The special optics convert the difference between transmitted light and refracted rays, resulting in
a significant variation in the intensity of light and thereby producing a discernible image of the
structure under study.
Developed by Frits Zernike in 1937
The image appears dark against a light background.