INTRODUCTION TO OPTICAL / LIGHT OR COMPOUND MICROSCOPE
The Optical microscope – commonly called as the Light microscope or Compound microscope is the most common type of microscope that is used in the diagnostic laboratories. The First optical microscope was invented in 1590 by Hans and Zacharias Janssen by placing two lenses in a tube. In the 18th century, Several technical innovations make microscopes better and easier to handle, which leads to microscopy becoming more and more popular among scientists.
PARTS OF A COMPOUND MICROSCOPE –
The parts of compound microscope are divided into three groups –
- Mechanical parts
- Magnifying parts
- Illuminating parts
Mechanical Parts of Compound Microscope – The mechanical parts consists of the following components –
⇒ Tube – the tube can be straight and fixed or bent and movable. It is hollow and holds the objectives at the lower end and the eyepiece at the upper end.
⇒ Body – the body gives support to the tube.
⇒ Coarse adjustment – it is controlled by a pair of large knobs one on each side of the body. On rotating this knob, the tube moves with lenses
⇒ Fine adjustment – The fine adjustment is used with high power (40X or 45X) and oil immersion (100X) objectives. This knob is present just below the coarse adjustment on either side of the body – gives clarity in observations.
⇒ Stage – The stage is a part of microscope where specimens to be observed is kept. This part is under the focus. It has a pair of clips, capable of moving the object horizontally as well as vertically.
⇒ Arm – The arm connects the body and the stage. It is used to hold the microscope while putting from one place to another.
⇒ Substage – The Substage is a part present below the stage. It holds the illuminating parts.
⇒ Foot – On the foot, other parts of the microscope are placed. It is horseshoe shaped.
Magnifying Parts of a Compound Microscope – the magnifying parts consist of objectives and eyepiece –
⇒ Objective lens –
- The lens that is present near to the object or specimen is called as the objective lens. It collects the light rays from the specimen and forms an inverted and magnified real image of the object. They are divided into 3 groups as follows –
- Low power objectives (4X, 10X) – magnifies the image 4 times or 10 times and provides maximum field of view.
- High power objective (40X, 45X) – magnifies the image 40 or 45 times.
- Oil immersion (100X) – magnifies the image 100 times and provides the minimum field of view.
⇒ Eyepiece –
- It is present at the top of the microscope tube or near to the eye. Eyepiece uses a magnified real image produced by the objective to produce a more magnified virtual image.
- The commonly used eyepiece has magnification 10X. it is also available in 5X, 15X and 20X.
- Some microscopes are available with only one eyepiece called monocular; and other is binocular, which has two eyepieces.
- The total magnification of the image of the object is the product of the magnifying power of eyepiece and that of the objective. For e.g. – when 10X eyepiece and 40X objective is used the magnification produced is – 10×40 = 400X & so on.
Illuminating Parts of a Compound Microscope – the illumination system provide proper illumination to the object. It comprises following parts –
⇒ Light source – modern microscopes are equipped with a built-in internal light source with an incandescent lamp, provides better control of illumination. The external light source can be an external lamp or from the sunlight.
⇒ Mirror – in case of external light source, the mirror is required to reflect the light beam from the source to the iris and condenser. It usually has two mirrors, mounted back to back. One side of the mirror is concave and the other is flat. The concave side is used without the condenser and the flat side is used the condenser.
⇒ Iris diaphragm – it is located below the stage between the mirror and the condenser. It regulates the amount of light. According to the necessity, the diaphragm can be closed for less light or opened for more light.
⇒ Condenser – the condenser is located at immediately under the stage. It is made up of a system of convex lenses, which focus light from the illuminating source on the plane of the object. The height of the condenser can be adjusted by rotating a knob, present on one side below the stage.