The document discusses the different types of light microscopes including bright field, dark field, phase contrast, and fluorescence microscopes and explains their basic components, working principles, and applications. Bright field microscopy is described as the most basic technique that uses a condenser and objective lens to illuminate a specimen against a bright background for viewing. The various microscope types are used across fields like medicine, industry, and research to examine cells, tissues, and small objects.

1. Light
microscope
Presented by:
syeda jaweria
rehman

8. Components of a light
microscope

13. Working principle

15.  Followings are the basic types of light
microscope:
 Dark field microscope
 Bright field microscope
 Phase contrast microscope
 Flourescence microscope

16.  It is used to improve the contrast of unstained
and transparent speciman
 Light scattered by the specimen enters the
objective lens to produce a bright image against
the dark back ground
 It has low resolution
 Used in microbiology and many other fields
 Many variation are availeble for better results

20.  Brightfield microscopy is the most
elementary form of microscope illumination
techniques and is generally used with
compound microscopes.
 The name "brightfield" is derived from the fact
that the specimen is dark and contrasted by
the surrounding bright viewing field. Simple
light microscopes are sometimes referred to as
brightfield microscopes

21.  In brightfield microscopy a specimen is placed on the
stage of the microscope and incandescent light from the
microscope’s light source is aimed at a lens beneath the
specimen. This lens is called a condenser.
 The condenser usually contains an aperture diaphragm
to control and focus light on the specimen; light passes
through the specimen and then is collected by an objective
lens situated in a turret above the stage.
 The objective magnifies the light and transmits it to an
oracular lens or eyepiece and into the user’s eyes. Some of the
light is absorbed by stains, pigmentation, or dense areas of the
sample and this contrast allows you to see the specimen.
 For good results with this microscopic technique, the
microscope should have a light source that can provide
intense illumination necessary at high magnifications and
lower light levels for lower magnifications

22.  Brightfield microscopy is very simple to use
with fewer adjustments needed to be made to
view specimens.
 Some specimens can be viewed without
staining and the optics used in the brightfield
technique don’t alter the color of the specimen
 It is adaptable with new technology and
optional pieces of equipment can be
implemented with brightfield illumination to
give versatility in the tasks it can perform.

23.  The basic principle to making phase changes visible in phase-
contrast microscopy is to separate the illuminating
(background) light from the specimen-scattered light (which
makes up the foreground details) and to manipulate these
differently.
 The ring-shaped illuminating light (green) that passes
the condenser annulus is focused on the specimen by the
condenser. Some of the illuminating light is scattered by the
specimen (yellow). The remaining light is unaffected by the
specimen and forms the background light (red). When
observing an unstained biological specimen, the scattered
light is weak and typically phase-shifted by −90° (due to both
the typical thickness of specimens and the refractive index
difference between biological tissue and the surrounding
medium) relative to the background light. This leads to the
foreground (blue vector) and background (red vector) having
nearly the same intensity, resulting in low image contrast.

28.  The specimen is illuminated with light of a
specific wavelength (or wavelengths) which is
absorbed by the fluorophores, causing them to
emit light of longer wavelengths (i.e., of a different
color than the absorbed light). The illumination
light is separated from the much weaker emitted
fluorescence through the use of a spectral emission
filter.
 The filters and the dichroic beamsplitter are
chosen to match the spectral excitation and
emission characteristics of the fluorophore used to
label the specimen

30. Applications

31.  A 40x magnification image of cells in a
medical smear test taken through an optical
microscope using a wet mount technique, placing the
specimen on a glass slide and mixing with a salt
solution
 Optical microscopy is used extensively in
microelectronics, biotechnology, pharmaceutic
research, mineralogy and microbiology.[
 Optical microscopy is used for medical diagnosis, the
field being termed histopathology when dealing with
tissues, or in smear tests on free cells or tissue
fragments.

32.  In industrial use, binocular microscopes are
common. Aside from applications needing
true depth perception, the use of dual
eyepieces reduces eye strain associated with
long workdays at a microscopy station.
 Measuring microscopes are used for
precision measurement

33.  The principles and practice of light
microscopy
(cambridge university press)
 Classification of microscopes
( JR Blueford)