Fundamental of optics

Fundamental of microscope

Microscope – Microscope is an optical instrument which is used to see the object which are too small to be seen by naked ( unaided ) eye.

Microorganism – An organism that is too small to be seen clearly with t

he naked eye and is often unicellular or if multicellular does not exhibit a high degree of differentiation.

It is order to observe microorganism as well as to study then we required microscope.

  • Common unit of measurement
Unit Abbreviations Value
1 cm CM 10-2
1 mm NM 10-3
1 μm (micro) μM 10-6
1 nm (nano) NM 10-9
1 Å ( Angstrom ) Å 10-10

Microscope      micro     small

scope          view           Greek word

General principle of optics

  • Simple single microscope consists of a single lens or magnifying glass hold in a frame it is adjustable and provide with a stand to hold object (specimen slide)
  • Light is reflected by micron and image can be viewed

Compound microscope

  • Consists of two lens one is objective and another is eyepiece ocular
  • Body tube objective and eyepiece lens are mounted in a tube known as body tube

Fine adjustment

  • To attend accurate forecasting of a specimen the special screw is given known as fine adjustment
  • It gives greater magnification of a minute object then simple microscope
  • Magnification it is the degree to which some time can be magnified

Structure of light

  • All types of light moves in wave line pattern
  • In which wave pattern are high Points and low points the distance between two high points or two low points is called the wavelength
  • Light not only moves in wave it also moves with a flow of little particles called as photons
  • These packets contains energy that makes up the energy of the light
  • Light is transmitted from luminous bodies to the and other object by the vibrational movement is known as wave theory of light
  • Light wave travels at the rate of about 186 300 miles per second
  • Light behave as a wave and it is also categorised as electromagnetic wave because it is made up of both electric and magnetic field
Components of a basic wave
Components of a basic wave
  • Electromagnetic field are perpendicular to each other and hence they are known as transverse wave
  • When beam of white light is passed through a prism a spectrum of seven colour is obtained (i.e. deep red orange yellow green blue and violet)
  • Wavelength of each colour is different

Read = longest  wavelength

Violet  = shortest  wavelength

Wavelength of light


wavelength of light
wavelength of light

Wavelength – Distance from to crest of one wave to the crest of the next or distance from the trough of one wave to the trough of the next wave.

Deep water wave 2

Numerical apparatus resolving power

Objective lens is the most important on a microscope because it properties may make or mar (spoil) the final image

Main function of objective lens

  • To gather the light rays coming from any point of the object
  • To unite the light in a point of the image
  • To magnify the image

Numerical apparatus

Resolving power

It may be definite as the ability of objective lens to separate distinctly to a smaller element in the structure of an object which are short distance apart

Numerical apparatus

The major for the resolving power of an objective is known as numerical apparatus

Numerical apparatus is directly proportional to resolving power

  • Larger the numerical apparatus the greater the resolving power of the object and finer the detailed it can reveal
  • However object is smaller than the smallest wavelength of the visible light cannot be seen.

Egsmallest wavelength of visible light is 4000 Armstrong has the object is smaller than 400 nm in size cannot be seen

  • In order to observe such minute object it would be necessary to use microscope with shorter wavelength
  • When light passes through diaphragm will take the form of a bright disc surrounded by concentric dark and light rings. (Brightness of the central disc will be greater in centre and diminished towards the edge)
  • When there is an image object is present under the lens the image of light will form dark and light concentric rings known as antipoint.
  • If microscopic objects are equidistant from each other than each object produce separate concentric disc which are clearly visible.
  • Minimum distance between the image of two distinct objects decreases at the angle of light coming from the object increasing.