Several types of microscopes are used to study the detailed structures of the organs. 
The Resolving Power of a microscope is a measure of the capacity of the 
microscope to separate clearly two points close together. 
The resolving power of the light microscope is about 0.2 micrometer. 
The resolving power of the Electron Microscope is 0.2 nanometer. 
The most important units of measurements used in Histology are: 
One centimeter (em)= 10 millimeters (mm). 
One millimeter (mm) = 1000 micrometers = I 000 microns (u). 
One micrometer (one micron)= 1000 nanometer (nm). 
One nanometer (nm) = 10 Angstrom= 10 A0
Types of Microscopes 
1. The Light Microscope (LIM) 
In this microscope, we use the day light or electric light as a source of illumination. 
The light is focused on the lens of the condenser by a mirror. 
The Optical System of The Light Microscope Consists of: 
a) The Eye Pieces which are near the eye. 
They are of different magnifying powers: 5, I 0 or 15 
This means that the eye piece magnifies the object either 5 times, 10 times, or 
15 times respectively.
b) The Objective lenses are near the object 
to be examined. 
Types of Objective Lenses: 
1. Low Power Objective (I 0). 
2. High Power Objective (45). 
3. Oil Immersion Objective (100). 
when used, should be immersed in a drop 
of cedar oil. This oil should be put on the 
covcrslide overlying the object to be 
How can we calculate the magnification of 
a histological section? 
We multiply the power of the used eyepiece 
(1 0 for example) by the power of tP.e 
used objective lens (45 for example). The Light Microscope 
So, the magnification of this examined histological section will be: 
I 0 x 45 = 450 times. 
2. The Transmission Electron tnicroscope (E/M) 
– In this microscope, a heam of electrons is used as a source of illumination. 
-The magniliL:d image is rcceicJ on a lluorcsccncc screen or on a 
phutugr.•phic plat~ . 
– The ElM g!ves a ve1) high magmfi~aLion. 
lt magni ries object. up tu 100.000 
3. The scanning Electron Microscope 
It is a special type of electron 
microscope by which we obtain a 3 
dimensional image for the examined parts as 
red hlood corpuscles and cilia of certain cells.
4. The Atomic Force Microscope 
It magnifies the examined fresh tissues up to 500.000 times. 
5. The Ultraviolet Microscope 
– In this microscope, the source of light is a beam of ultraviolet rays. The 
image is received on a fluorescence screeen. 
– The magnifying power of this microscope is up to 4000 times. 
6. The Fluorescence Microscope 
The source of light in this microscope is the ultraviolet rays which are harmful 
to the eye, so a filter should be inserted in its eyepiece. The fluorescent substances 
in the examined tissues will shine by giving off visible light. It is used to study the 
chemical components of the tissues. 
7. The phase • Contrast Microscope 
It is used to examine fresh tissues or living cells growing on a culture media.
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