A microscope is an instrument that uses lenses to magnify objects too small for the naked eye. A good microscope has good resolution, contrast, and magnification. Resolution is the ability to distinguish closely placed objects, contrast is improved through staining, and magnification comes from objective and ocular lenses. Common microscope types include brightfield, darkfield, phase contrast, fluorescence, and electron microscopes. A brightfield microscope uses light to form a dark image against a bright background. It has mechanical, magnifying, and illuminating parts and works by emitting light through the specimen which is then magnified by the objective and ocular lenses.

1. MICROSCOPE
Microscopy
MBBS June 2023

2. What is microscope?
Amicroscope is an instrument used to see objects
that are too small for the naked eye.

3. Properties of a microscope
A good microscope should have at least three
properties:
• Good Resolution
• Good Contrast
• Good Magnification

4. Good Resolution :-
Resolution power refers to the ability to produce
separate images of closely placed objects.
• So that they can be distinguished as two separate
entities.

5. Good Contrast:
• Contrast is improved by staining the specimen.
When the stain bind to the cells, the contrast is
increased.

6. Good Magnification:
• Ocular lens with a magnification power of
10X.
• Objective lens-
• Scanning (4X)
• Low power (10X)
• High power (40X)
• Oil immersion (100X)

7. Total magnification of a field is the product of
the magnification of objective and ocular lens:
• Scanning field (40X)
• Low power field (100X)
• High power field (400X)
• Oil immersion field (1000X)

8. TYPES OF MICROSCOPE
The following types of microscopes are in use
now-
• Bright field or light microscope
• Dark field microscope
• Phase contrast microscope
• Fluorescence microscope
• Electron microscope

9. Bright field or light microscope
Light microscope forms a dark image against a
brighter background, hence the name bright
field.
Structure:
• The parts of light microscope is divided into
three groups-
• Mechanical part
• Magnifying part
• Illuminating part

10. viewing.
Mechanical part:
Base: It holds various part of microscope, such as
the light source, the fine and coarse adjustment
knobs.
C- shaped arm: It hold the microscope, and it
connects the ocular lens to the objective lens.
Mechanical stage: The arm bears a stage with
stage clips to hold the slides and the stage control
knobs to move the slide.
It has an aperture at the center that
permit light to reach the object from
the bottom.

11. Magnifying part:
Ocular lens: The arm contains an eye piece that
bears an ocular lens of 10X magnification power.
• Microscope with two eye pieces are called
binocular microscopes.
Objective lens: 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).

12. They
Illuminating parts:
Condenser: It is mounted beneath the stage
which focuses a cone of light on the slide.
Iris diaphragm: it control the light pass
through the condenser.
• Light source: it may be a mirror or an electric
bulb.
• Fine and coarse adjustment knob:
sharpen the image.

13. MICROSCOPE

14. virtual
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
image.

15. Compound microscope Dark-field microscope

16. How to Use a Compound Microscope.
1.Turn the revolving nose piece so that the lowest power objective lens (eg. 4x) is clicked into
position.
2.Place the microscope slide on the stage and fasten it with the stage clips.
3.Look at the objective lens and the stage from the side and turn the focus knob so the stage
moves upward. Move it up as far as it will go without letting the objective touch the coverslip.
4.Look through the eyepiece and move the focus knob until the image comes into focus.
5.Adjust the condenser and light intensity for the greatest amount of light.
6.Move the microscope slide around until the sample is in the Centre of the field of view (what you
see).
7.Use the focus knob to place the sample into focus and readjust the condenser and light intensity
for the clearest image (with low power objectives you might need to reduce the light intensity or
shut the condenser).
8.When you have a clear image of your sample with the lowest power objective, you can change to
the next objective lenses.
9.You might need to readjust the sample into focus and/or readjust the condenser and light
intensity.
10.If you cannot focus on your specimen, repeat steps 3 through 5 with the higher power objective
lens in place.
11.Do not let the objective lens touch the slide!(when using x4, x10 and x40).
12.For stained films allow the objective lens to torch the immersion oil.
13.When finished, lower the stage, click the low power lens into position and remove the slide.

17. • Always carry with 2 hands
• Only use lens paper for cleaning
• Do not force knobs
• Always store covered
• Be careful of the cords
Rules of using a microscope