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Parts of the compound microscope (Fig. 278) may be grouped into two major categories, viz., mechanical parts and optical parts.
(a) Mechanical Parts:
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These include base or foot, pillar, arm, inclination joint, stage, clips, diaphragm, body tube, nose piece, coarse adjustment knob and fine adjustment knob.
(b) Optical Parts:
These include eye piece lens, objective lenses and mirror.
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All these parts are briefly described below:
1. Foot or Base:
It is the basal, horse shoe-shaped structure. It provides support to all the remaining parts of the microscope.
2. Pillar:
A small, strong vertical projection developing from the foot or base is called pillar.
3. Arm:
It is a curved and strong structure used for handling the entire instrument.
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4. Inclination Joint:
A joint at which the arm is attached to the pillar of the microscope is called inclination joint. It is used for tilting the microscope.
5. Stage:
It is a flat rectangular plate attached to the lower end of the arm. Slide or object is placed on the stage and studied. A hole is present in the centre of the stage. Light rays pass through this hole.
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6. Clips:
Two clips are attached on the upper part of the stage. These are used for holding the slide in position.
7. Diaphragm:
It is attached beneath the stage. It regulates the intensity or amount of light entering into the microscope. It may be of two types viz., iris diaphragm and disc diaphragm.
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8. Condenser:
It is a lens situated beneath the stage. It controls the size of the light beam. It gathers light from the mirror (Fig. 279) and directs it to objective lens. Condenser may be lowered or raised by a knob present on one side beneath the stage.
9. Body Tube:
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It is the tubular, hollow part attached to the upper part of the arm of microscope. It can be moved up and down with the help of adjustment knobs.
10. Nose Piece:
It is a circular and revolving metalic part attached to the lower end of the body tube. It has three holes in which objective lenses can be fitted.
11. Coarse Adjustment Knob:
It is a large-sized knob used to move the body tube up and down for bringing the object into focus.
12. Fine Adjustment Knob:
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It is a small-sized knob. It is used for fine and sharp focussing of the object. Exact focussing is done by this knob.
13. Eyepiece or Ocular:
It is a lens fitted at the top of the body tube. It is always marked with a number (5X, 10X, 15X) on its rim. This number shows its magnification power. Magnified image of the object is seen with the eyepiece.
14. Objective Lenses:
Three objective lenses are attached to the revolving nose piece at the bottom of the body tube. These are low power objective (10X), high power objective (45X) and oil immersion objective (100X).
15. Mirror:
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It is either attached to the lower end of the arm or to the pillar. It contains a plane mirror on one side and a concave mirror on the other side. Mirror is used to reflect light rays into the microscope.
Working of the Compound Microscope:
1. First of all, see through the eyepiece and adjust the mirror in such a way so that sufficient light is seen entering into the microscope.
2. Now make sure that there is no dust on the stage, mirror, lenses and slide.
3. Put the slide in the centre of the stage.
4. Fix the clips on two corners of the slide so that it does not move.
5. Now turn the nose piece and bring the low power objective in line with the object to be seen in the slide.
6. Now move the coarse adjustment knob up or down so that the slide comes well in focus.
7. Move the fine adjustment knob up or down so that the image becomes as much sharp and clear as possible. (Observe all details of the material under low power and draw the diagram.)
8. Now turn the nose piece and bring the high power objective in line with the object. Again use the fine adjustment knob to make the image of the object as sharp and clear as possible. Observe the details of the material under high power and draw the diagram. Do not use coarse adjustment knob while studying under high power. It may break the slide.
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Calculation of Magnification:
Magnification is calculated by multiplying the power of eyepiece and objective. An object, when viewed with a 5X eyepiece and 10X objective is magnified 5 × 10=50 times. When you are using the eyepiece of 10X and objective of 45X, the magnification is 10 × 45=450 times.
Precautions:
1. Clean the eyepiece and objective lenses with lens paper or clean silken paper before use.
2. Do not tilt the microscope while working with it.
3. Always study the material first under low power and then only under high power of microscope.
4. After completing all observations, leave the low power objective in place.
5. Never allow an objective lens to strike either the slide or the stage while focusing.
6. While studying with high power objective, use only the fine adjustment knob.
7. All wet-mount preparations should be covered by a coverslip before making any observation under microscope.
8. Avoid habit to remove the parts of the microscope.
9. Always hold the microscope with both the hands while carrying it.
10. Keep the microscope back into its box after using it.
11. In dim light use only the concave side of the mirror.
12. Never use oil immersion lens without oil.
