Labelled Diagram of Compound Microscope

The below mentioned article provides a labelled diagram of compound microscope.

Part # 1. The Stand:

The stand is made up of a heavy foot which carries a curved inclinable limb or arm bearing the body tube. The foot is generally horse shoe-shaped structure (Fig. 2) which rests on table top or any other surface on which the microscope in kept. The foot is generally heavy in order to increase the centre of gravity of the whole instrument.

Just above the foot, near its joint with curved limb of body is present an inclination joint on which the curved limb or whole of the microscope could easily be tilted according to whether the observer is in sitting position or in standing posture.

Usually, the curved limb or body should not be tilted unless unavoidable because, in doing so the centre of gravity of the apparatus is disturbed and there are enough chances of it’s falling down.

Part # 2. The Body Tube:

The body tube is a hollow cylindrical metallic tube attached to the upper end of curved inclinable limb through a rack and pinion mechanism. The body tube, in almost all types of compound microscopes, is about 160 mm. in length. It can be moved up or down on the curved limb through a knob the coarse adjustment knob.

The movement of the body tube is required for purpose of focusing. A little below the coarse adjustment is present another comparatively smaller knob-the fine adjustment knob, either on the upper or lower end of curved inclinable limb.

This knob is used for more accurate focusing while using the instrument for high magnifications. The clockwise movement of coarse adjustment knob brings the body tube downwards and its anticlockwise movement takes the body tube upwards.

Part # 3. The Eye Piece:

With the upper end of body tube is attached a narrow and smaller tube which houses the eye piece. It is a compound lens made up of a lower convex lens and an upper plain lens. The most commonly usable eye pieces are of the magnifications 5×; 10× and 15× (Fig. 3).

Part # 4. The Nose Piece and Objective:

The nose piece is a concavo-convex circular disc attached to the lower end of body tube. The nose piece or nose plate is attached with the body in such a way that it can easily rotate on its axis or point of attachment.

On the lower convex side of nose plate are present 2, 3, or 4 rounded holes tor attachment of objectives of different powers. By rotating the nose plate the desired objective could be brought in line of light rays. The objective is a small tube containing a combination of lenses.

It is formed either by putting a convex lens at its lower end or, in better makes, by putting a convex and concave lens together in the same position. Usually, the most common usable objectives are of the focal length 2/3 inch (16 mm), 1/6 inch (4 mm) and 1/12 inch (2 mm).

The first objective gives minimum magnification and the last the maximum. The last one is usually known as oil immertion lens. As an approximate guide it may be remembered that an objective of 2/3 inch magnifies about 10 times; the 1/6 inch objective about 40 times and the 1/12 inch objective magnifies about 90 times. Fig. 4.

Part # 5. The Stage:

The stage is a squarish or rectangular piece of bakelite or metal attached to the lower end of the curved inclinable limb. It has a small rounded hole in the middle on which the material to be observed is put on a rectangular glass slide. To keep the slide and the material in position a pair of spring clips may be fitted on this stage.

At times, for detail observation of the different parts of the material under high power, a mechanical stage may also be attached on this stage, which helps in moving the slide forward, backward and on either side. The stage generally measures about 4 × 4; 4 × 5 or 5 × 5 inches.

Part # 6. The Condenser and Sub-Stage:

Below the stage, attached either to it’s under surface or to the lower part of curved inclinable limb, is present a metallic rim, which is called the sub-stage. In the former case the sub-stage is fixed but in the latter case it could be moved up and down through a sub-stage adjusting knob.

The sub-stage is situated around the central hole of the stage and holds a complicated structure, the condenser (Fig. 5). The condenser is a conical metallic structure having a convex lens at the top and an adjustable iris diaphragm (Fig. 6) or a movable circular disc with holes of different sizes below it.

The purpose of diaphragm or disc is to control, at will, the amount of light passing through the material to be observed. Below the diaphragm, in some better makes, there is also present a thin metallic rim to hold the ground glass or coloured or tinted filters which are used to control the intensity or shade of light passing through the condenser (fig. 5, 6).

 Part # 7. The Mirror:

The last component is a Plano-­concave mirror (Fig. 1) which is fixed in metallic frame and is attached to the lower end of curved inclinable limb below the sub-stage. The mirror can be moved in desired direction in order to focus light rays on the material through sub-stage condenser. The concave surface is used without condenser and plain surface with condenser.

(I) Magnification:

To determine the magnification following formula is used:

m = l/f × e

Here m = magnification

l = length of body tube = 160 mm

e = magnification of eye piece.

f = magnification of objective.

In simple words final magnification of image may also be determined by multiplying the magnification of objective with magnification of eye piece.

(II) Focusing:

Put the slide on the stage in such a way that the material to be observed remains directly above the central hole in the stage. Now, move the nose plate (piece) and bring the low power objective immediately above the material.

Put your eye directly above the eye­piece and by moving the slide bring material directly below the objective in such a way that you are able to see it through the eye piece. Now, moving the coarse adjustment knob slowly and slowly focus the material clearly However, fine and accurate focusing, could only be done with the help of fine adjustment knob.

For using the high power, first of all the material should be focused under low power as above. Then swing the nose plate (piece) and bring the high power objective above the material already placed on the slide covered by coverslip. Never use the coarse adjustment knob while observing under high power objective. A slight turn of fine adjustment knob will bring the object in sharp and accurate focus.

(III) Care of the Microscope:

(1) Always lift the instrument by its arm.

(2) Never allow any liquid to get in touch of the lens. Clean the out side of lenses with a piece of clean and soft muslin cloth, chamois leather or tissue paper.

(3) Do not touch the lens with wet fingers and keep them away from dust because it is the worst enemy of microscope. Usually, dust can not be wiped off with cloth. Therefore always use a piece of clean and soft cloth dipped in alcohol.

(4) Never use the high power objective unless the material is perfectly covered with a coverslip.

(5) Use microscope with both eyes open.

(6) Always keep the instrument covered with a plastic or cellophane cover, when not in use.