The document describes the components and working of a compound microscope. It discusses: 1. The key parts of a compound microscope including the base, pillar, arm, stage, body tube, coarse and fine adjustment screws, draw tube, nosepiece, objectives, and eyepiece. 2. The optical principles of transmission, absorption, diffraction, and refraction that allow light microscopes to work. 3. How light from the illuminator passes through the specimen and objective lens to form a real, inverted intermediate image, which is then magnified by the eyepiece to form a final virtual image visible to the user. 4. Specialized lenses like the oil immersion objective that provide higher

1. COMPOUND MICROSCOPE
Dr. P. Nithiya
Assistant Professor,
Department of Botany,
Seethalakshmi
Ramaswami College,
Tiruchirappalli

2. MICROSCOPY
Microscopy is a technique for making very
small things visible to the unaided eye.
An instrument used to make the small
things visible to naked eye is called a
Microscope

3. LIGHT MICROSCOPE
Light or optical microscope uses visible
light as a source of illumination.
Light travel through the specimen, this
instrument can also be called a
Transmission light microscope

4. WORKING PRINCIPLE OF LIGHT
MICROSCOPE
Light microscope creates a magnified
image of specimen which is based on
the principle transmission,
absorption, diffraction and refraction
of light waves.

5. TRANSMISSION
Transmission of light is the moving of
electromagnetic waves (whether
visible light, radio waves, ultraviolet,
etc.) through a material.

6. ABSORPTION
Light absorption is a process by which light is
absorbed and converted into energy.
Absorption depends on the electromagnetic
frequency of the light and object’s nature of
atoms.
Absorption of light is therefore directly
proportional to the frequency.
If they are complementary, light is absorbed.

7. DIFFRACTION
Diffraction: Diffraction is the slight
bending of light as it passes around
the edge of an object.
The amount of bending depends on
the relative size of the wavelength of
light to the size of the opening.

8. REFRACTION
Refraction is the bending of a wave when it
enters a medium where its speed is different.
The refraction of light when it passes from a
fast medium to a slow medium bends the light
ray toward the normal to the boundary between
the two media.
The amount of bending depends on the indices
of refraction of the two media and is described
quantitatively by Snell's Law.

9. TRANSMISSION AND ABSORPTION

10. COMPOUND MICROSCOPE
The simplest form of light microscope
consists of a single lens, a magnifying
glass.
Microscope made up of more than one
glass lens, in combination is termed
compound microscope
A compound microscope is an optical
microscope with multiple lenses

11. LIGHT MICROSCOPE

12. MECHANICAL PARTS
a. Base
b. Pillar
c. Arm
d. Stage
e. Body tube
f. Coarse and fine adjustment screw
g. Draw tube

13. MECHANICAL PARTS
A. Base:
It is a supporting stand resting on the table.
It bears weight of the microscope.
B. Pillar: it stand vertically on base.
C. Arm:
It is curved, solid piece.
It can be adjusted with the base at the
inclination joint.

14. MECHANICAL PARTS
D. Stage:
(i) It is a rectangular platform.
(ii) It has a circular hole at the centre with two
clips.
E. Body tube:
It is a metal tube.
It has revolving nosepiece with objective lens.

15. MECHANICAL PARTS
F. Coarse and fine adjustment screw:
The coarse adjustment screw moved the tube
vertically very fast.
The fine adjustment screw moves it slowly.
G. Draw tube:
The upper part of the body tube is called draw
tube.
Its length can be adjusted.

16. OPTICAL PARTS
Nose piece: A metal disc with 2 or 3 holes.
Objectives:
The lens system nearer to the specimen is
called objectives
It magnifies the specimen for several times.
There are three objectives namely low power
(10X), high power (100X) and oil lens (100X).

17. OPTICAL PARTS
Eye piece:
The lens system nearer to the eye is called eye piece.
It magnifies the real image of the object.
There are 3 types of eye piece- a) Huygenian eye piece b)
Compensating eye piece c) hyper plane eye piece.

18. EYE PIECE
Huygenian eye piece was invented by Christian Huygens and first
compound eye piece.
It consists of two Plano- convex lenses separated by an air gap and
used to correct chromatic aberrations
Ramsden eyepiece
An eyepiece consisting of two plano
convex glass lenses of equal focal length, placed with the
convex sides facing each other and with a separation between the lens
es of about two-thirds of the focal length of each. It was discovered by
Jesse Ramsden in 1782.

19. OPTICAL PARTS
D. Condenser:
Condenser & iris diaphragm and fitted below the stage.
It consists of two or more lenses.
It condenses light rays from mirror and converges and focuses the
light into the specimen.
E. Mirror:
A Plano concave round mirror and fitted below the stage.

20. OIL IMMERSION OBJECTIVE
Objective lens used for oil immersion to get the maximum
resolution of specimen under a compound microscope is called
oil immersion objectives.
A drop of cedar wood oil is placed on a specimen and gives
maximum resolution.
Disadvantage of oil immersion : it absorbs blue and ultraviolet
light, damage objectives with repeated use, and Cedar oil must
be removed from the objective immediately after use.
While removing , hardened cedar oil can damage the lens. In
modern microscopy synthetic oil is used

21. OIL IMMERSION LENS
In the case of an oil-immersion objective of x100,
the magnification of the primary image at the plane of the eyepiece
diaphragm is x100, and the intensity of the magnified image is
therefore one ten thousandth of the illumination intensity at the plane
of the specimen.
The primary image is further magnified by the eyepiece, which
projects it (with or without a focus achromat) an appropriate distance
to fill the film gate of the camera in use.
Since this distance is also subject to the inverse square relationship
between projection distance and image intensity, it is not surprising
that it takes a much longer time to expose a 10" x 8"
photomicrographic plate than a frame of 16mm film.

22. https://www.youtube.com/watch?v=baFTRZN_fQU

24. OIL IMMERSION OBJECTIVE

25. WORKING PROCEDURE
Compound microscope has two sets of lenses, the objective and the
eyepiece. The basic principle –
1. When the beam of light passes through the specimen and then
convex lens of objective lens, it forms a real inverted.
2. The enlarged image of the object in the focal plane of eyepiece.
This image now acts as object for the eyepiece.
3. Eyepiece lens finally forms a further enlarged virtual image of the
object.
4. Magnifying power of a compound microscope = M0×Me). (M0-
magnification of objective lens, Me- magnification of eye piece.)

26. MAGNIFICATION
M=M0×Me
M0- magnification of objective lens
A’B’/ABMe- magnification of eye piece.
A”B”/A’B’

27. Magnification of Objective lens = size of an real image
A’B’ / size of a specimen AB
AB= 1mm
A’B’=5mm
Magnification of Objective lens =A’B’/AB= 5/1=5X
Magnification of Ocular lens = size of an second
image / size of a real image
A’B’=5mm
A”B”=50mm
Magnification of Ocular lens =A’B’/AB= 50/5=10X

28. WORKING PROCEDURE
 A compound microscope consists of two
convex lenses: an objective lens O of small
aperture and an eye piece E of large aperture.
 The lens which is placed towards the object is
called objective lens, while the lens which is
towards our eye is called eye piece.
 These two convex lenses i.e. the objective and
the eye piece have short focal length and are
fitted at the free ends of two sliding tubes at a
suitable distance from each other.

29.  Although the focal length of both the
objective lens and eye piece is short, but
the focal length of the objective lens O is a
little shorter than that of the eye piece E.
 The reason for using the eye piece of large
focal length and large aperture in a
compound microscope is, so that it may
receive more light rays from the object to
be magnified and form a bright image.

30. FOCAL LENGTH AND FOCAL POINT
Focal length (shown in red) is the distance between
the center of a convex lens or a concave mirror and
the focal point of the lens or mirror — the point where
parallel rays of light meet, or converge.

31. FORMATION OF IMAGE IN
COMPUND MICROSCOPE
The ray diagram to show the working of
compound microscope is shown in figure.
A tiny object AB to be magnified is placed in
front of the objective lens just beyond its
principal focus fo’.
In this case, the objective lens O of the
compound microscope forms a real, inverted
and enlarged image A’B’ of the object.

32. FORMATION OF IMAGE IN
COMPUND MICROSCOPE

33. Now A’B’ acts as an object for the eye piece E,
whose position is adjusted so that A’B’ lies
between optical centre C2 and the focus fe’ of
eye piece.
Now the eye piece forms a final virtual, inverted
and highly magnified image A”B”.
This final image A”B” is seen by our eye hold
close to eye piece, after adjusting the final
image A”B” at the least distance of distinct
vision of 25 cm from the eye.
This image is called ‘Ramsden’s disc’ .
The lens of the eye casts an image of Ramsdens
disc over the whole surface of retina now fills

35. RAMSDEN DISC
The circular spot of light formed at that
distance above the eyepiece
The small disk of light visible in the back focal
plane of an eyepiece.
An eyepiece consisting of two plano-convex
crown-glass lenses of equal focal length,
placed with the convex sides facing each other
and with a separation between the lenses of
about two-thirds of the focal length of each.

37. RAMSDEN DISC
The diagram shows the concept of the Ramsden
circle, and is a key to understanding the problems
of film exposure in light micrography.
The Ramsden circle, also called the exit-pupil of
the microscope, is a circular area through which
pass all the image-forming rays leaving the
microscope.
It is itself an image of the back-lens of the
microscope objective, demagnified in proportion to
the power of the eyepiece, and is usually located a
few millimetres above the eye lens of the eyepiece.

38. THANK YOU