Microscope
FOCUSING OF AN OBJECT
A. Under Low Power :-
1. Place the slide to be focused the stage and fit
it into the mechanical stage. By means of the screw of the mechanical stage
bring the object on the central aperture in the stage.
2. Using the light source and by adjusting the
plane mirror, focus the light on the object. Partially close the iris diaphragm
and lower the objective (10x) with coarse adjustment near the slide.
3. The position of the slide is so adjusted that
the aperture of the objective lens is just above the point to be focused on the
slide.
4. Now look into the eye – piece ; the optical tube
is moved upwards (again using coarse adjustment ) slowly and confidently, till
the object comes under view. Once this is achieved , the coarse adjustment
should Not be used.
5. Lower the condenser from the top position till
the object is properly illuminated. The condenser usually occupies a low position.
6. Next , using the fine adjustment only, the slide
can be brought to a sharp focus.
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B. Under
High Power :-
1.
For focusing under high power (40x) , simply
rotate the nose – piece so that the high power objective lens may come to lie
above the slide to a sharp focus.
2.
The iris diaphragm is fully opened and
concave mirror is used to condense the light on the object.
3.
The condenser is kept in the beginning at
the top and is then gradually lowered till the object is properly illuminated.
The condenser usually occupies a higher
position than that for focusing under the low power.
4.
With the fine adjustment screw, attempt the
final focusing.
HIGH
POWER LENS
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C. Under
Oil Immersion Lens :-
1. For
focusing under oil immersion lens (100x), a drop of cedar – wood oil is placed
on the slide. Then turn the nose piece further so that the oil immersion lens
may be in use. It will automatically dip into the drop of oil.
2. As
the slide is moved, the drop of oil will also get moved on its own. Thus any
part of the slide can be observed.
3.
The iris diaphragm is kept fully opened and the
condenser is kept in the top position. Use only the fine adjustment to focus
the necessary area.
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Important Note:-
While putting the stained slide, care should be taken so that the
stained smear may be facing the
objective.
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Important Points to Remember
1.
Position of Condenser :- The Desired position of
the condenser is as follows :-
Objective Lens Power
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Condenser Position
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(i) Low Power (10x)
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(i)
Lowest
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(ii) High Power (40x)
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(i) Higher (in between i and iii)
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(i) Oil Immersion (100x)
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(i) Highest
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1.
Type of Mirror to be used
(i) The Plane side of the Mirror is used when:-
(a) A condenser is used ;
(b) The source of light is diffuse such a
daylight.
(ii) Concave mirror is used when source of light
is from a point source such as bulb, as
used in labs.
2.
The Higher the Magnification, the smaller the
area that can be examined at a time. Therefore, to start with, irrespective of
what is being examined, it is always advisable to focus a slide under low power
(10x) first. Obtain a general view of the object and choose the field you would
like to examine in detail. Bring this field in the central position. Then
switch over to the next high power. Now use only the fine adjustment for
focusing. If necessary, select the field further and bring it in the centre
again.
Most Important Part of Microscopy
PRECAUTIONS
1. A
clear image can never be seen through dirty lenses. Make sure that the eye
piece as well as all the objectives is clean.
While cleaning microscope
lenses, do not rub them with dry cotton or rough cloth which might leave
permanent scratch marks on the lenses. Apply xylene to the lenses (to
dissolve the grease) and then wipe dry gently with a piece of silk cloth or
softest material available.
Most
Important
NOTE :- Always clean the Microscope lenses BEFORE and
AFTER the use.
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2. Do
not clean the objective with alcohol, as it may dissolve the cement which
unites the component lenses.
3. Never
lower the optical tube while you are looking through the eye piece.
4. Make
minimal and careful use of ONLY the fine adjustment while using the high power
and oil immersion.
5.
If the microscope has to be moved, it should be
held upright by the limb keeping a hand below its foot.
