MICROSCOPE

Microscopes

-are instruments that are used in science laboratories to visualize very minute objects, such as cells and microorganisms, giving a contrasting image that is magnified.

• are made up of lenses for magnification, each with its own magnification powers. Depending on the type of lens, it will magnify the specimen according to its focal strength.
  -Their ability to function is because they have been constructed with special components that enable them to achieve high magnification levels. They can view very small specimens and distinguish their structural differences, for example, the view of animal and plant cells viewing microscopic bacterial cells.

light microscope
dark-field microscope,
phase contrast microscope,
electron microscope,
fluorescent microscope

TYPES OF MICROSCOPES:

head, arm, and base

There are three structural parts of the microscope i.e.

Head

The head is a cylindrical metallic tube that holds the eyepiece lens at one end and connects to the nose piece at other end. It is also called a body tube or eyepiece tube. It connects the eyepiece lens to the objective lens. The light coming from objectives will bend inside this tube. In binocular microscopes, they are adjustable so that the viewer can adjust the eyepiece for maximum visualization.

Arm

This is the part connecting the base to the head and the eyepiece tube to the base of the microscope. It supports the head of the microscope and is also used when carrying the microscope. Some high-quality microscopes have an articulated arm with more than one joint, allowing more movement of the microscopic head for better viewing.

Base

The base is the lowermost part of the microscope that supports the entire microscope structure. It provides stability for the microscope. Illuminators, light switches, and electrical wiring systems are fitted in the base.

1. Eyepiece

–The____ (ocular Lens) is closest to the viewer’s eye. They are located at the top of the microscope.
This part is used to look at the specimen. 
These lenses come in different magnification powers from 5X to 30X, but the most common ocular lenses are of 10X or 15X magnification.
They magnify the image for the second time.

2. Eyepiece tube

It’s the eyepiece holder. It carries the eyepiece just above the objective lens.
In some microscopes, such as the binoculars, the eyepiece tube is flexible and can be rotated for maximum visualization for variance in distance.
For monocular microscopes, they are none flexible.

3. Diopter Adjustment

– is a control knob present only in the binocular microscope that is used to change focus on one eyepiece.
It is used to correct any difference in vision and compensate for the differences in vision between the viewer’s two eyes.

4. Nose piece

– is a movable circular structure that houses all the objective lenses. It is also called the revolving turret.
It is connected to the body tube and lies just above the stage.
It can be rotated clockwise or counterclockwise to increase or decrease the magnification.
The change in magnification results due to a change in the objective lens.

5. Objective lenses

– T is the lens that is closest to the specimen. They are fitted on the nosepiece.
A standard microscope has 3 to 4 objective lenses of different magnifying powers: 4X, 10X, 40X, and 100X.
The objective lenses first receive the light transmitted from the specimen and magnify the image for the first time.

• are color-coded and are of different sizes. Size and color depend on the power of the lens.
  The smallest lens is of the lowest power, and gradually, the longest will be of the highest power.
  The high power lenses i.e. 40X and 100X, are retractable, i.e., their end can be pushed inward.
  In most optical microscopes, objective lenses with 100X or more magnification are of oil immersion type.

6. The Adjustment knobs

are the control knobs used to focus the microscope on the specimen.

a. Fine Adjustment Knob

Fine Adjustment Knob is used for fine adjustment.
It is a smaller knob and is used to move the stage up or down very slowly.
The stage covers a very small distance on each rotation of the fine adjustment knob. It is used to sharpen the image.
It is mostly used while viewing under high power.

b. Coarse Adjustment Knob

Coarse Adjustment Knob is used for focusing the image under low power magnification.
It is a larger knob and is used to move the stage up or down very rapidly.
The stage is raised or lowered rapidly with the help of a coarse adjustment knob.

7. Stage

– This is the section in which the specimen is placed for viewing. They have stage clips that hold the specimen slides in place.
The most common stage is the mechanical stage, which allows the control of the slides by moving the slides using the mechanical
knobs on the stage instead of moving them manually.

8. Stage Control Knobs

–  are the control knobs used to move the stage mechanically.
There are two knobs; one for moving left and right and the other for moving forward and backward.
This will move the slide in the field of vision.

9. Aperture

This is a hole in the microscope stage through which the transmitted light from the source reaches the stage.

10. Microscopic illuminator

is a light source.
In some compound microscopes, a mirror, which reflects the light from an external source to the sample, is used.
In other optical microscopes, different electric bulbs of low voltages are used as a constant light source.
Commonly used illuminators are tungsten-halogen lamps, 75-150W Xenon lamps, tin-halide lamps, mercury vapor lamps, etc.
The selection of types of bulbs is based on the requirement of intensity and wavelength for illumination.

11. Condenser

These are lenses that are used to collect and focus light from the illuminator into the specimen.
They are found under the stage next to the diaphragm of the microscope.
They play a major role in ensuring clear, sharp images are produced with a high magnification of 400X and above.
The higher the magnification of the condenser, the clearer the image.
More sophisticated microscopes come with an Abbe condenser that has a high magnification of about 1000X.

12. Diaphragm

It’s also known as the iris. It is found under the stage of the microscope, and its primary role is to control the
amount of light that reaches the specimen.
It’s an adjustable apparatus, hence controlling the light intensity and the size of the beam of light that gets to the specimen.
For high-quality microscopes, the diaphragm comes attached with an Abbe condenser, and combined,
they are able to control the light focus and light intensity that reaches the specimen.

13. Condenser focus knob

This is a knob that moves the condenser up or down, thus controlling the focus of light on the specimen.

14. The rack stop

It controls how far the stages should go, preventing the objective lens from getting too close to the specimen slide,
which may damage the specimen. It is responsible for preventing the specimen slide from coming too far up and hitting the objective lens.

15. Light Switch

is an electrical control device. Light switches are used to on and off the illuminator.

16. Brightness Adjustment

The brightness adjustment system controls the voltage supplied to the light bulb, controlling
the intensity (brightness) of the light bulb.

Scanning Objective Lens (4x)

Combined with the eyepiece lens, this lens will provide the lowest magnification power. For example, 10x eyepiece lens, multiplied by the 4x objective lens gives a total magnification of 40x.
This objective is often referred to as the scanning objective lens since the low power provides enough magnification to give the observer a good overview of the entire slide and sample.

Low Power Objective (10x)

This objective lens is the next lowest powered and is often the most helpful when it comes to analyzing glass slide samples. The total magnification for this lens is equal to 100x magnification (10x eyepiece lens x the 10x objective equals 100).
Since it still provides a good amount of magnification at a good distance from the slide, there is a limited risk of it breaking the glass and potentially ruining the sample. That’s why this objective lens is often preferred before going for a high powered lens.

High Power Objective Lens (40x)

This is referred to as the high powered objective lens since it is ideal for observing the small details within a specimen sample. The total magnification for this lens is equal to 400x magnification (10x eyepiece lens x the 40x objective equals 400).

Oil Immersion Objective (100x)

This objective lens will achieve the greatest magnification and has a total magnification of 1000x (10x eyepiece lens x the 100x objective equals 1000).
Because glass and air have different refractive indexes, light bends at different angles when it passes through each of them. When using the 4x, 10x, 40x objective lenses, the light refraction that occurs when looking through the lens to the specimen on the glass slide is not very noticeable. However, when using the higher power objective lenses, for example the 100x, the light refraction is much more obvious. 
A drop of special oil which has a similar refractive index to glass, is placed on the cover slip over the specimen.  The oil immersion objective lens is immersed in the oil, rather than air, enabling a clear image of the specimen.

1. Turning the lamp on.
2. Placing the specimen/Prepared slide on the stage.
3. Adjusting the focus.
4. Adjusting the interpupillary distance.
5. Adjusting the diopter.
6. Adjusting the condenser position and aperture iris diaphragm.
7. Switching the objectives.
8. Placing oil if necessary especially in OIO.

Observation Procedure:

1. When carrying the microscope, use both hands. One holding its arm and the other is supporting base with the cord in secure position.
2. Clean all glass components by wiping gently with lens paper. In the absence of such, use tissue paper moistened with a mixture of ether 70% and alcohol 30% to remove fingerprints and oil smudges.
3. Don't disassemble any part of the microscope as this could result in malfunction or reduced performance.
4. Store microscopes in a cabinet with cover to avoid subjecting it to direct sunlight, high temperature, humidity, dust or vibrations.

SOME HANDLING and STORAGE PRECAUTIONS