Study of Compound Microscope


1. To know the different parts and their functions.
2. To know about magnification and resolving power.
3. To know about focusing (handling) of microscope.
Microscopes are the instruments designed to magnigy as well as to resolve the image of an object seen through it. Light or optical microscope in which magnification is obtained by a system of optical lenses using light waves. eg compound microscope.
Magnification is the increase in size of optical image over the size of object being viewed. Magnification produced by
compound microscope is given in the magnification table.
Resolving power is the ability to distinguish two close points as two seperate points. The resolving power of compound
microscope is 0.25 micron when white light is used.

Different parts and their functions
Mechanical parts:
Foot or base: It is horse shoe shaped which helps to keep the microscope in plane.
Pillar: It connects the base with the arms of the microscope and supports the movable part.
Inclination joint: It joins the pillar with the lower parts of the arm and helps to tilt the microscope.
Arm of limb: It is the curved back rising from pillar that supports the different parts.
Mirror fork: It helps to hold the mirror.
Condenser knob: It helps to adjust the position of condenser.
Control lever: It helps to control the position of iris diaphragm.
Iris diaphragm: It helps to regulate the aperture, through which light rays are passed to the object.
Stage: It is the rectangular part with two stage clips and a stage aperture at the centre. It is a platform on which objects to be observed
are placed.
Coarse adjustment knob: It helps in the adjustment of body tube while focusing the object.
Fine adjustment knob: It is used to get sharp image of the focused object.
Body tube: It is the main body of microscope which carries the draw tube and a revolving nose piece below.
Draw tube: It is the hollow metallic tube that bears an eye piece at the top.
Nose piece: A revolving circular plate with about three objectives at the base of the body tube.

Optical parts
Mirror: A double faced plane concave mirror is fixed at the base of the limb. It reflects the light towards the hole of th stage through
the diaphragm . The plane face is used in strong light and the concave side in weak light.
Condenser: It is a system of two or more lenses under the stage, which converges the light rays received from a mirror.
Objective lens: At the lower end of the body tube, objective lens are screwed. It is usually three in number with a different magnifying
power ie. 4x, 10x, 40x and 1000x. It develops real, inverted and magnified image. By rotating the nose piece the particular objective is
Eye piece: It is licated at the top of the body. It is of various or occular magnifying powers such as 5x, 10x, 15x and 20x. It forms
virtual erect and magnified image.

Handling of microscope
- Iris diaphragm was opened fully and light was adjusted by turning the mirror towards the source of light.
- Low power objective was placed in place over the stage aperture.
- Prepared slide was placed on the stage in such a way that the object lies just beneath the objective lens.
- Looking through the eye piece the body tube was raised up from its lowest position until the object clearly focused with the help of
coarse adjustment knob.
- Fine adjustment knob was used for obtaining sharp focus.

Magnification table:

Mo/Me 5x 10x 20x
4x 20 40 80
10x 50100 200
40x 200 400 800

-The microscope should be carried in as upright position.
- The object should be observed with both eyes open.
- The lens and mirror should be cleaned before and after use.
- Only the adjustment knob should be used with high power objective.

View the Figure for this Practical