A microscope is an instrument used to magnify small objects that are too small to be seen by the naked eye. It works by using lenses to produce enlarged images of objects placed on its stage. The document discusses the basic parts and functions of microscopes, including the optical and illumination systems, as well as different types such as simple, compound, light, and electron microscopes. It also explains key microscope concepts like magnification, resolution, and oil immersion which are used to view specimens clearly.

1. Dr. Sarah Abdulsalam
Microscopes
1st STAGE / LEC2/ Lab
Instrumentation theory

2. WHAT IS A MICROSCOPE ?
 Origin of A microscope word came: (from the Ancient
Greek: mikron- "small“ and scopeos-"to look")
 Microscope: is an instrument used to see objects that
are too small for the naked eye.
 A microscope is an instrument that produces an
accurately enlarged image of small objects.
 Microscopy: The science of investigating small objects
using such an instrument is called microscopy.

3. Historical background :
 1590 - Hans Janssen and his son Zacharias Janssen,
developed first microscope.
 1609 - Galileo Galilei - occhiolino or compound
microscope.
 1674 – Anton van Leeuwenhoek built a simple
microscope with only one lens to examine blood, yeast,
insects and many other tiny objects. Leeuwenhoek was
the first person to describe bacteria.
 1931 – Ernst Ruska co-invented the electron
Microscope for which he won the Nobel Prize in Physics
in 1986.

4. Anton van
leeuwenhoek
Robert hooke

5.  The human eye can resolve objects down to about
0.2μm.
 The Microscope is used to magnify small objects,
those below the 0.2 μm range.
 Bacteria and cells are measured in mm or 1 x 10^-6
meters (0.4 micron).
 Viruses are even smaller, measured in nm or 1 x 10^-9
meters (0.02-0.25micron).

6. CLASSIFICATION OF MICROSCOPES
 Depending on lens system:
I. Simple
II. Compound
 Depending on optical technique:
A. LIGHT MICROSCOPE : use sunlight or artificial light.
 A. Bright field microscope.
 B. Dark field microscope.
 C. Phase contrast microscope.
 D. Fluorescence microscope.
B. ELECTRON MICROSCOPE : use of electron.
 1. Transmission electron microscope.
 2. Scanning electron microscope.

7. Principles of Light Microscopy
 Microscopes provide three important qualities:
1. Magnification: Degree of enlargement.
 No of times the length, breadth or diameter, of an object is multiplied.
 It depends upon –
I. Optical tube length
II. Focal length of objective
III. Magnifying power of eye piece
 Our microscope has four objective lens settings (scanning lens, 4X; low power
lens,10X; high dry
power lens, 100X oil immersion lens
 TOTAL MAGNIFICATION = magnification of the eyepiece X magnification
of the objective.
 Power of objective X Power of ocular =Total magnification
 10× low power objective × 10× = 100×
 40× high dry objective × 10× = 400×
 100× oil immersion objective × 10× = 1,000×
2. Resolution :Ability to reveal closely adjacent structural details as separate and
distinct.
3. Contrast: Differences in intensity between two objects, or between an object
and background.

8. Oil immersion:
 The white light used in a compound light microscope
has relatively long wave length and cannot resolve
structures smaller than about 0.2 μm.
 Oil immersion is placed between the glass and
objective lens.
 The oil immersion has the same refractive index as
glass of the microscope.
 The oil enhances the resolution by preventing light rays
from dispersing and changing wave length after passing
through the specimens.

10. SIMPLE MICROSCOPE
 Because of the limited ability of the eye's lens to change
its shape, objects brought very close to the eye cannot
have their images brought to focus on the retina.
 The "simple microscope" or magnifying glass reached
its highest state of perfection, in the 1600's, in the work
of Anton von Leeuwenhoek who was able to see single-
celled animals ("animalcules") and even some larger
bacteria.

11. LIGHT MICROSCOPY
THE COMPOUND MICROSCOPE
 In light microscopy, light typically passes through a
specimen and then through a series of magnifying
lenses.
 Oil immersion lens increases resolution.
 Have one or two ocular lenses.
 Light is transmitted and focussed by mirror and
condenser.
 The refracted light is collected by an objective where
primary image of the object is formed, it is real, inverted
enlarged image of the object.
 The eyepiece further magnifies this primary image into
virtual, erect enlarged image, this is the final image that

12. Brightfield Microscope (Compound Light
Microscope)
 Brightfield Microscope is also known as
the Compound Light Microscope. It is an optical
microscope that uses light rays to produce a dark image
against a bright background. It is the standard
microscope that is used in Biology, Cellular Biology, and
Microbiological Laboratory studies.
 This microscope is used to view fixed and live
specimens, that have been stained with basic stains
which gives a contrast between the image and the
image background. It is specially designed with
magnifying glasses known as lenses that modify the
specimen to produce an image seen through the

13.  The functioning of the microscope is based on its ability
to produce a high-resolution image from an adequately
provided light source, focused on the image, producing
a high-quality image.
 The specimen which is placed on a microscopic slide is
viewed under oil immersion or/and covered with a
coverslip.

14. Principle :
 The rays emitted from the light source pass through
the iris diaphragm and fall on the specimen.
 The rays passing through the specimen is gathered
by the objective and a magnified image is formed.
 This image is further magnified by the ocular lens to
produce the final magnified virtual image.

16. :
Part of a Microscope
A. SUPPORT SYSTEM:
 Base: It holds various part of microscope, such as the light
source, the fine and coarse adjustment knobs.
 Arm: the C-shaped upright structure.
B. FOCUSSING SYSTEM:
I. Course adjustment screw: Used to make relatively wide
focusing adjustments to the microscope.
II. Fine adjustment screw: used to focus the lenses by
moving the body tube, but by a much smaller magnitude.
C. THE STAGE:
I. Fixed Stage: the plate on which the specimens are
placed.
II. Mechanical stage: The arm bears a stage with stage clips
to hold the slides and the stage control knobs to move the

18. D. OPTICAL SYSTEM:
I. Body Tube: the hollow tube on which the objectives and
eyepiece lenses are mounted.
II. Nose piece : The upper part of a compound microscope that
holds the objective lens. Also called a revolving nosepiece.
III. Objective lenses: the lens closest to the specimen; The arm
also contains a revolving nose piece that bears three to five
objectives with lenses of differing magnifying power
(4X,10X,40X, and 100X).
IV. Eye piece or Ocular Lens: The arm contains an eye piece that
bears an ocular lens of 10X magnification power.
E. ILLUMINATION SYSTEM
I. Source of light: Light is an essential part of the system.
Sunlight, low voltage electric lamps,etc.
II. The mirror: is used to focus light up through the hole in
the microscope's stage, or slide platform.
III. The condenser: It is mounted beneath the stage which focuses
a cone of light on the slide.
IV. Iris diaphragm: it control the light pass through the condenser.