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Microscope operation
The practical is divided into a number of sections.
You will need your Practical Manual.
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Familiarisation of the parts and use of the light microscope
The structure and use of the light microscope.
Parts of the microscope:1. Refer to the Practical Manual Introduction Section C.2. Using this as a guide, get out the microscope and
place it on the desk in front of you. Identify the parts of the instrument, noting the functions of each. When you feel conversant with this proceed to the next step.
3. Use the following presentation for microscopes with an inbuilt light source.
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Getting a microscope The microscopes
are stored in boxes on trolleys
Each box has a number, as does the microscope
The numbers on the microscope, the box and its marked position on the trolley MUST all agree
Key and lock
Box and microscope number
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Opening the box Please remember
the position and number of the microscope so that you can ensure that it is returned to the correct box and position on the trolley
Open the box with the key attached to the box
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Picking up the microscope You are to ALWAYS
use two hands when carrying a microscope
Place one hand around the PILLAR of the microscope and the other under the BASE
Do not carry the box to your desk as there is insufficient room
Base
Pillar
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Turning the eyepiece Place the
microscope squarely on the table in front you, with the pillar away from you
Undo EYE PIECE TURRET lock and then rotate the turret towards you
Lock into position, finger tight
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Eyepiece to back
Eyepiece
turret
Eyepiece
Locking
knob
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Eyepiece in correct position
Eyepiece
Locking knob
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Eyepiece and eyepiece tube
Please be careful carrying microscopes as the eyepiece is easily removed from the eyepiece tube
This is a 10x eyepiece
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Positioning the microscope Move the
microscope until it is in a comfortable position for you
The front side of the microscope should be facing you
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Turning on the lamp The microscope has a built in lamp, so
locate the on/off switch on the left-hand side and turn it on
Locate the brightness adjustment on the left-hand side High Low
On/Off switch Brightness adjustment
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Comparison of light intensities
Low intensity brightness of lamp
High intensity brightness of lamp
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Right sideEyepiece
Eyepiece tube
Rotating turretObjectives
Mechanical stageCondenser
Slide holder
Light
Base
Stage movement knobs
Coarse focusing knobFine focusing knob
Cord
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Left side
On/Off switchBrightness adjustment
Condenser knob
Coarse focusing knob
Fine focusing knob
Eyepiece
Light
Eyepiece tube
Rotating turret for objectivesObjectives
Eyepiece turret
Slide holder
Mechanical stage
4x
10x
40x
20x
Iris diaphragm
Base
Pillar
StopCondenser
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Front
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The iris diaphragm Locate the iris
diaphragm which is in the lower section of the condenser
Locate the flat silver lever on the right hand side of condenser which is used to open and close the iris
Do not touch.This is the centring
lock for the condenser
Iris diaphrag
m
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The iris diaphragm
Stage
Condenser
Iris diaphragm
Filter slot
Condenser knobLight
Stage knobs
Slide holder
Iris lever
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The iris diaphragm
Position backwards towards pillar = fully closed
Lever in back positio
nIris
almost closed
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The iris diaphragm
Position towards you = fully open
Open the iris diaphragm of the condenser fully
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Adjusting the condenser Locate the
condenser and its adjustment knob on the left-hand side
Set the condenser, using its focusing adjustment knob, so that the top of the lens of the condenser is about 2 mm below the upper surface of the stage
Condenser
Adjustment knob
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Position of condenser
Top of the lens of the
condenser
Stage openin
g
About 2 mm
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Focus adjustment knobs Locate the fine and
coarse focus adjustment knobs on both sides
Lower the microscope STAGE with the coarse focus adjustment knob so that the objectives on the rotating nosepiece will NOT hit the stage when rotated into position
Fine Coarse
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Of interest NOTE that the
stage and condenser move together
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Focusing using low power
For most microscopes this isOBJECTIVE 4xEYEPIECE 10x
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Rotating objective lenses Swing the low
power (4x) objective into position above the stage
Practice clicking the objectives into place, noting that the objectives SHOULD be changed in one direction only from LOW 4x to 10x to HIGH 40x
4x
10x
40x
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N.B. Always focus the
microscope with the low power (4x) objective first
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Objective characteristics
4x = low power objective Red ring, shortest in length widest field of view, brightest image
10x = Mid range objective Yellow ring, mid length Reduced field of view, image duller
40x = High power objective End sprung loaded, blue ring, longest Very limited field of view, image very
dull
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10x objective
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40x objective
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Slide holder on movable stage
Make sure that slide holder is positioned to back of the stage and that the two knurled knobs are finger tightSlide holder
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Slide into slide holder To place the slide in
position on stage
press lever at A and slide holder arm will swing to side
A
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Slide to stage (do not remove)
Place the slide against the left side and top of the slide holder
Press on A Lever swings
outwards Insert slide
Slowly release the movable section to hold the slide
Spring-loaded lever
A
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Movable stage The stage is moved
by two knobs on the right-hand side
The larger top knob moves the stage towards and away from you
The smaller lower knob moves the stage from left to right
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Horizontal and vertical stage scales
2 scales on the stage One at the back
which shows the amount that the microscope is moved from side to side
One on right-hand side for forward and backward movement Coordinates can also
be recorded of particular points of interest on slide
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Positioning the slide Use these knobs to
position the slide so that the OBJECT you wish to view is placed in the centre of the condenser lens
N.B. Scales for both movements (one on right for away and towards, and one at back for right to left) measure how much the slide is moved
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To start focusing Looking from the
side, using the coarse focus knob, lower the low power objective until it is about 6 mm above the glass cover strip of the slide
6 mm
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N.B.
These microscopes have STOPS on the left side of the stage mechanism to prevent damage to slides so DO NOT FORCE the KNOB past these
When you feel resistance to the free turning of the knob STOP because this point should allow all the objectives to be swung into place without them touching the slide
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Microscope stop – left side
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Field of view illumination The field of view of
the microscope should now be fairly evenly illuminated. Close the iris diaphragm until the light is about half its maximum intensity.
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N.B. N.B. A common cause of poor
definition of a specimen is over-illumination. Best definition is often obtained by cutting down light, not by increasing it.
Also remember that the light intensity can be reduced:
by changing the light intensity slide on the sideOR by reducing the diameter of the iris diaphragmOR by lowering the condenser
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Focusing on low power Keeping both eyes
open, look through the eyepiece and LOWER the STAGE by means of the coarse focus adjustment until the specimen comes into focus. Use the fine focus adjustment knob for critical focus
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N.B.
Never focus by moving the stage with the slide towards the objective lens. When you are looking down the eye piece you are unaware of where the objective lens is in relation to the slide, and it is easy to crush the cover slip and possibly the slide itself.
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Focusing using high power
These microscopes have two higher power objectives:
10x and 40x (100x oil immersion)
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Centring to point of interest
After finding the object with the 4x, move the slide until the object of interest lies in the exact centre of the field of view using the stage moving knobs
At this point you will find out whether your microscope is parafocal
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Parafocal
Parafocal means that once the microscope has been focused in one power, it is approximately in focus in the other magnifications
These microscopes should be parafocal
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Using the 10x objective Swing in the 10x
objective, watching to see that it does not touch the slide. The lower end of the objective will come close to it
A partial revolution of the fine adjustment focusing knob should bring the object into focus, if it is in the field of view
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Using the 40x objective Swing in the 40x
objective, watching to see that it does not touch the slide
Open the iris diaphragm slightly
Using the fine focus adjustment ONLY, bring the object into focus
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Problems If the object is not
in the field, or the slide has moved accidentally, swing in the 4x objective, then centre the object and proceed as before
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N.B.
Always return to low power before removing the slide from the stage.
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General precautions (1) Always be sure that the objectives will
not contact the stage or slide when moving them into a new position
ALWAYS FOCUS STAGE DOWN, never up, while looking through the microscope. This will avoid breaking the cover slip, crushing your specimen, damaging a prepared slide or even damaging the objective lens or condenser lens
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General precautions (2)
KEEP BOTH EYES OPEN ALL OF THE TIME, and alternate the viewing eye, to avoid eye strain and fatigue. This will seem very difficult at first, but practice will overcome the difficulty
Cover slips MUST always cover objects under examination, to protect the lens and the specimen
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General precautions (3) NEVER TOUCH ANY OF THE GLASS
PARTS OF THE MICROSCOPE WITH YOUR FINGERS
If a lens system is dirty or you have any trouble with the microscope, report it to your teacher. DO NOT ATTEMPT TO CLEAN a lens system with a handkerchief, tie, or anything else. Certain cloths will scratch the soft glass of the lens system
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Putting the microscope away
ENSURE that the following steps are carried out:
Swing the 4x objective into operational position
Unlock the turret and rotate to back, and lock here. Finger tight ONLY
Remove the slide from the stage. Allow stage clip to return to position on the stage
Carefully return the microscope to the trolley and place in the appropriate box.